Past Longwave Messages - April 2001

Addresses and URLs contained herein may gradually become outdated.

Re: K0LR 160m beacon in QRSS mode
Posted by Robert Bicking on April 01, 2001 at 11:51:43

Saw the message last nite 4-1-01 and listened about 230Z, nothing. Checked again before bed at 435Z and heard K0LR 569 with some amplitude changes noticable, especially on the long dashes. No trouble copying by ear. 73, W9RB.

Latest Survey Says...
Posted by webmaster on April 02, 2001 at 01:47:55

Our late-March opinion poll about new features for the LW Message Board didn't receive as heavy, rapid, or unanimous a response as the one at the beginning of the month, but there were a few clear signals.

1. Most of the respondents favored a different type face for messages, although a few felt there was less ambiguity between certain characters with the conventional Times New Roman/Times Roman face.

Effective with this post, we are implementing the different type face. To try to accomodate both points of view, however, Verdana will be the default type face...at least, for readers who use recent versions of Windows. Verdana is a quasi-sans-serif style, optimized for readability on rasterized displays. It uses a limited amount of serifs so as to be as unambiguous as possible between certain characters, such as the lower-case letter "l" and the numeral "1," for instance. (Users of other operating systems will see Arial, Helvetica, or a generic true sans-serif.)

2. The other topic of the recent survey was inclusion of HTML code and images in posts. Some of you have already taken advantage of our ability to do this manually through the e-mail method. While the idea was generally looked upon favorably, some respondents even felt it should be implemented as an "open" feature of the board.

Unfortunately, that doesn't appear to be a practical approach. Past examples of unwanted advertising on this board demonstrate that there are those out there who lurk about for opportunities to spread their points of view in any forum, no matter how inappropriate, even with our current limitations. Therefore, I'm not inclined to make it any easier for them. Also, there have been attempts to hack this site which you have not seen--fortunately. It would not be prudent to open such a wide hole in our security blanket with unrestricted use of HTML and scripting.

What we will do is make it possible for you to register a username and password to gain access to a posting form that does not remove HTML coding.

Only the posting form is new...there will still just be one message list, and it will remain accessible to everybody just as it is now. The only difference is, trusted users will have an additional way of posting enhanced messages to it.

As a trusted user, you will be able to include live links in your messages, and format the body of your message with HTML tags. (Eventually, you will be able to upload graphics files as well. I will have to master the necessary software first, though.) Be watching for details at a later time.

Thanks for your feedback. It always helps.

John

winding
Posted by Donald R Moler on April 02, 2001 at 01:59:30

We just finshed winding my loading coil in my driveway Sunday with copper strap. Before I wound the copper strap on the coil form I painted the fiberglass with white paint and as we were winding the coil, we were painting the copper strap with a polyurethane coating as it was coming off the spool. This turned out to be a messy job and it started to rain when we were half through. We took pictures of this three man operation and will post them here in a few days. The copper has that new look and with a white background should bring out the copper look in the pictures. Does anyone know what the dielectric loss of polyurethane is?. After we finish the loading coil we took it into the basement and started to measure the tunning range of the coil ( This coil inductance is varied by motor) then we took a crude measurement of it's Q. Don Moler N8BKR Girard, Ohio vonj@cboss.com

Re: winding
Posted by Les Rayburn, N1LF on April 02, 2001 at 11:48:27

Donald,

I'm very interested in your experiments. Please keep us all informed about your progress. What kind of rough measurement did you obtain for the "Q"
of that coil.

The state of the art lowfer coils appear to be those constructed by Bill Bowers. Their measured "Q"
in some cases is over 700! These are air core,
basket weave designs.

I also know that Dexter, (NC) has had much success with his large diameter coils.

Can't wait to copy your beacon...do you plan to run in WOLF mode?

Wellbrook ALA-1530
Posted by Al Scanandoah on April 02, 2001 at 14:25:42

Hello

I'm considering ordering one. Does anyone have any experience with this antenna?

Thanks - Al

Re: winding
Posted by Tim Brannon on April 02, 2001 at 23:20:40

Donald,
I couldn't find anything specific on the dielectric loss of polyurethane. You might try the trick that Les mentioned from the RSGB reflector about trying it in a microwave oven. Take some of your polyurethane and "paint" a piece of scrap glass with it, and then put it in the microwave with a cup of water (as a load for the oven). The hotter the painted glass sample gets in the microwave, the more dielectric loss it has. You could use a known good performer as a control sample, like a piece of polystyrene, Plexiglas, or Lexan from Home Depot.
I'm actually a little more worried about this white paint on the form--you might do the same test with it.
BTW, why paint the coil and form? I would imagine the fiberglas will deteriorate with UV exposure so I can understand that. And if the copper strap oxidizes and gets wet that could be a problem. But why not just put the whole coil inside a protective covering (upside-down plastic trash can?) to keep it shaded and dry? The wind loading of a coil this big is gonna be sizeable even without a cover, so your tower will have to be pretty sturdy anyway. If it's dry, would the copper oxide on the strap be more lossy than the polyurethane???
(I don't have any of these answers!)

Re: Wellbrook ALA-1530
Posted by Jacques d'Avignon on April 03, 2001 at 07:11:09

I have one and it is a superb antenna. I reviewed it last year in Monitoring Times and I have no complaints about its performance. Matter of fact it is the only antenna that I am presently using for receiving.

I also have other equipment sold by Wellbrook, and find that the quality is above average. The receiving antenna amplifier/splitter is one of the best I have used.

Re: VLF circuits
Posted by Joe T. Penrod on April 03, 2001 at 22:21:38

I designed a 1750M (160 -- 190KHz) receiver that shouldn't be difficult to construct. Even though this is an analog design, it would be ideal for the LW novice. Will send details to those interested.

Re: Wellbrook ALA-1530
Posted by Keith Ballinger on April 04, 2001 at 19:12:48

Jacques - I have been considering the Wellbrook loop too but I live near a couple of MW tx's (south Ottawa) as well as CHU. Have you any experience with using the loop in this kind of environment? I tried an MFJ active antenna but it just folded up under intermod and desensing.

73 - Keith VA3QF

help id and ndb
Posted by George Hardesty on April 07, 2001 at 06:55:06

hello the group,
i have found a ndb on 380 that id`s in morse as "mw" . frequency 380 khz
i hear this beacon day and night, on an 160 meter dipole.. loop is in my near future plans, but as of now i dont have any way to get a bearing on it... the internet site, i use to look up these beacons list one mw and at a different frequency,, (408)
also the list for this (408 mw) has it in washington state, which while i dont have the experience at listening to this band to back it up , would seem unreasonable to me from my qth in southern illinois..
any info ......??
thanks George em57

Litz Wire Soldering
Posted by Mitch VE3OT on April 07, 2001 at 11:09:37

Hello all:
I searched through some old e-mails and found the following that should help with the different litz wire showing up. I have 100 meters of the "Crawley" Decca 143 with the outer polythene - rather "tough" stuff.

Here are several contributions by others from several months ago.

Good luck Mitch VE3OT

--------------------
From G3GRO
Fortunately along with the wire, we aquired a solder pot to go with it and found it very easy to tin the ends of the Litz wire when adjusting the number of turns. We wound one or two extra over the erstimated number and then adjusted it one or two turns at a time.

-----------------------------

To All from PA0SE

May I inject an item on a low-tech subject into the stream of high-tech stuff that has been coming to us via the reflector?

I know that soldering litz wire has been discussed extensively lately but by chance I came across an article on the subject written by a professional that may interest you. It relates to litz wire with strands covered by enamel.
Modern litz has a coating that dissolves in molten solder and soldering is no problem.

I found the article in the 1949 edition of ELECTRONICS MANUAL FOR RADIO ENGINEERS (McGraw-Hill).

I wish you and yours a happy and healthy New Year with extreme DX!

73, Dick, PA0SE JO22GD

Soldering Litz Ends

By EMERICK TOTH

The writer had occasion to design a receiver for aircraft using coils of litzendraht wire. These coils ranged in diameter from 12 inches, wound with litz of about 180 strands of number 38 wire, to little fellows of 1/2 inch ID using 7/41 litz. Over 150 coils were involved, a total of more than 300 coil ends, thousands of individual strands that must be properly tinned and soldered. Careful tests were made of the following three methods:
(1) Cautious removal of the silk and enamel from the coils end by abrasion against a relatively soft high-speed rotary wirebrush.
(2) Heating of the coils end in an alcohol or Bunsen-burner flame and subsequent plunging of the hot coil end into alcohol.
(3) Application of a small quantity of a paste of zinc chloride and water to the coil end and heating with a soldering iron, immediately followed by tinning with rosin-core solder while the resulting zinc chloride and enamel mixture was still boiling. The silk insulation was burned and stripped off by a very short exposure to a flame, and subsequent wiping with a rag prior application of the zinc chloride.
Method (1) was found to damage individual strands excessively, and did not clean all strands in sizes of litz with many strands, such as 70/38 and 180/38.
Method (2) was difficult to control. Insufficient exposure to the flame resulted in the enamel not cracking off when the hot coil end was plunged into cold alcohol. Overheating caused individual strands to burn off. Even when satisfactory cleaning was obtained, the copper was left so brittle that soldered coil end would break easily.
Method (3) provides easy and effective tinning. The appearance of the tinned end was neat and clean after the residue of zinc chloride, enamel, rosin, and solder had been wiped off while still hot with a damp rag. The ease of tinning even 180/38 litz suggested that inside strands were not properly coated. Several samples were cut in cross-section but all strands appeared to be clean of enamel and tinned.
Samples were placed in a salt-spray chamber and subjected to the Navy's standard salt-spray test for two hours.
It was found that except for a light accumulation of powdery salt the samples were in no way affected by the test and all 300 coil ends were processed as outlined in method
(3) above.
Eighteen months after delivery, one equipment was examined which had been in service in Panama for a year. No trace of corrosion or any other damage was found.
Zinc chloride is very hygroscopic and should be kept in a suitable well-stoppered glass bottle, with only as much paste prepared at one time as is needed for a few hours use.

----------------------------

Hello Dick and all Lowfers
Interesting article abt soldering litz-wire Dick .
But If You don't like the professional way . Then do the following .
1 Put an ASPIRIN ( nothing ells ) on the table .
2 Lay the litz-wire on top .
3 Push with the solderiron on the wire , and solder .
I uses this method for mny years with success .
Don't hang to close with our nose over it because it picks .
Happy new year to all . Werner ON6ND

----------------------------------------------------------------------------

As David G0MRF has indicated , the radio club here in Crawley have a quantity of unused spare Litz wire "rescued" from the old Decca Navigator stations when they were recently closed down. The type which most people find most suitable for LF antenna loading coils has 143 individual strands of copper with a diameter of approx 1.8mm. It then has an outer insulating jacket of polythene with an OD of 2.75mm. giving a good voltage breakdown rating between turns for LF antenna coils.

The litz is on offer at Ł10 UK or $15 US per 100metres as a donation to club funds plus shipping cost.
The weight per 100m is about 2 kilos. I will enquire and let you know what the shipping cost will be but I guess from experience in sending wire to Finland and Sweden recently, that it will be in the region of $25. Payment in $US would probably be the most convenient.

de Derek Atter, G3GRO

Re: help id and ndb
Posted by chirs steele on April 07, 2001 at 14:34:04

Hey George,
I checked Rock's longwave beacon log and found yuor UNID It seems to Marion, IL.
Hope this helps...Chris in Ft. worth

Argo beta 1 build 127, with logging features
Posted by Alberto di Bene, I2PHD on April 08, 2001 at 08:43:09

Hi all,
I have just uploaded Argo beta 1 build 127 to the weaksignals Web site : http://www.weaksignals.com

>From the Readme file :

Beta 1, build 127 (Apr. 8th 2001)
- Added the 20s dot mode, upon request.

- Right-clicking with the mouse on the spectrogram toggles between full band
view and the current dot mode, without changing the center frequency.

- The Visual Gain can now be set to : AGC, Low, High

- The length of the ticks is selectable between short (as before) and
long (full stroke across the spectrogram).

- The peak frequency is now computed with a quadratic interpolation between
three consecutive bins.

- An indicator of the relative signal magnitude has been added, both near
the field showing the mouse cursor frequency, and as a floating text that
follows the cursor. The 0 dB reference level can be selected between the
magnitude of a monochromatic signal that would just saturate the ADC of the
sound card, or the magnitude of a signal arbitrarily selected with the mouse.
The relative magnitude displayed near the peak frequency is however always
referred to the ADC full scale.
The dB display has a lower limit of -80 dB (computers still have to learn the
concept of negative infinity...)

- A couple of logging features have been added :

- Serial Log : The frequencies of the ten strongest frequency components are
output to COM1 or COM2 (selectable), sorted in decreasing magnitude order.
This can be used for FDK experiments, or for DFCW outboard decoding.
Thanks to Steve Olney, VK2ZTO for the idea and the serial output routine.

- File Log : the magnitudes of all the bins displayed in the current running
mode are logged to a file, with a comma-delimited format, useful to be
imported in, let's say, Excel or Access. The file name and the logging
interval are selectable, and each snapshot is time-stamped.

For both forms of logging, see the Readme for the exact format.

- Some code adjustment, tuning (should require less memory) and error correction.

As usual, please send to me bug reports, and any feedback you may have on the program. TNX

73 Alberto I2PHD

Summer Loop Project
Posted by Steve McDonald on April 08, 2001 at 17:31:52

Initially I had planned to re-build my 8' single-turn shielded loop and Burhan's preamp combination but after investigating it seems that current thinking favors the hi-Q multi-turn tuned air core style (perhaps it always did!) so...change of plans for now. I plan to remote tune the loop with NTE618s and I am wondering...with a 5'- 8' diameter loop...if I use a low impedance single turn coupling loop inside the main loop, can I get by without a preamp? It seems to me that an aperture of this size should hear fairly well on its own or am I wrong. At one time I used a 5' loop with the same arrangement and it seemed very sensitive all by itself (but this was in a suburban location).
I have a local NDB (AP-378) just down the beach from me and my thinking is that if I can keep the loop passive, my possible intermod effects will be minimized.

Any thoughts on preamp vs no preamp at this size?

Steve / VE7SL

Stupid mistake in Argo build 127
Posted by Alberto di Bene on April 09, 2001 at 18:07:34

I made a very stupid mistake in build 127 of Argo.
The signal strength indicator is wrong by a factor of two.
So please download build 128, in the hope that there are no other errors stupid as this one (this must not be construed as to imply that sophisticated errors are acceptable :-)

Thanks to Bob, ZL2CA for pointing it out.

73 Alberto I2PHD

Re: Summer Loop Project
Posted by John Andrews on April 09, 2001 at 21:52:41

Steve,

You may be able to skip the preamp. It would certainly be worth trying without it. And since there may not be a big advantage to having the preamp outside, you could tinker with a 50 ohm preamp right in the shack. You certainly should try using a 1:1 transformer in the line before the receiver or inside-the-shack preamp. The "antenna" side of that transformer should not put a ground on the coax shield.

Give it a shot. My preamp does improve the minimum discernable signal from my receiver, and manages to do so without any big dynamic range problems. And that preamp is in the shack. I'm tuning my antenna differently than you will be, but the end result should be identical.

John

Know what'd be nice to see in the LOWDOWN?
Posted by Lee Reynolds on April 10, 2001 at 13:10:27

Given the proliferation of digital modes in use (remember when COHERENT was amongst the very few?) in the last six months or so, it'd be very useful for the beginning listener to have a series of articles on the "How-Tos" of WOLF, QRSS, etc.

I, for example, ain't no dummy - but I know it's going to take a lot of time searching on the 'net and sieving out the few tdibits in print in order to get a halfway sane checklist together for getting started.....

Lee

Re: Know what'd be nice to see in the LOWDOWN?
Posted by Chris Catotti on April 10, 2001 at 15:35:32

I agree! I have just rejoined LWCA. I recall coherent as having been arouund and BPSK just starting to be experimented with. I looked around and was at first totally puzzled with WOLF (1. mammal 2. a rank in Cub Scouts 3. eat fast 4. what's it got to do with radio?). I am looking around the garage for my old copies of the LOWDOWN and Ken Cornell's scrapbooks. Meanwhile I ordered one copy of Cornell's scrapbook in case I can't find mine.

Beacon WA continues QRSS transmission
Posted by Bill Ashlock on April 10, 2001 at 23:41:26

Hello All,

Beacon WA at 185.301 is sending QRSS(60) during the night time hours and will continue in this mode into the summer months or until further notice. Mitch Powell in London Ontario (533mi) reports regular reception so it appears the season is still on-going - at least at this distance, limited only by local thunderstorm activity.

All signal reports are greatly appreciated.

Bill WA Andover MA

Re: Know what'd be nice to see in the LOWDOWN?
Posted by Tim Brannon on April 10, 2001 at 23:41:45

In either the February or March issue of the LOWDOWN, there was a great "how to" article on QRSS by Les Rayburn. Check it out!

Re: Know what'd be nice to see in the LOWDOWN?
Posted by John Davis on April 10, 2001 at 23:43:09

Les Rayburn's article "Getting Started in QRSS" appeared in the February issue of The LOWDOWN. It contained step-by-step instructions on using the Argo software with a Windows-based computer and soundcard to receive QRSS. It discussed keying QRSS by several means, including software and hardware designs available from Lyle Koehler's Web site.

Both Lyle's and Les' sites contain info on WOLF, and I hope we'll be able to put together a compendium of currently available information on this mode during the summer months when everything else settles down a bit.

It has been an extraordinarily successful year on LF, thanks largely to these two modes becoming available to everyday experimenters.

73,
John

Mods or Hints?
Posted by Chris Catotti on April 10, 2001 at 23:51:44

Since logging NDB's many years ago on my Radio Shack Realisrtic DX-300 (which got fried in a lightning storm in 1989), I am interested in logging NDB's on my Realistic DX-394. Are there any useful modifications or tips for using on low frequency?

Yesterday I was in Sanford FL and stopped by the airport to see the SFB 408 kHz NDB. The maintenance crew gladly drove me out around the runways the the NDB on property. It uses a horizontal dipole, centerfed and perghaps 40 feet above ground. When I develop the pictures I'll put them on the web for a short time.

Chris

Getting Started in QRSS (Lowdown Article Reprint)
Posted by Les Rayburn, N1LF on April 11, 2001 at 09:32:01

Getting Started in QRSS (Slow Speed CW)

By Les Rayburn, N1LF

The QRSS Revolution

Slow Speed CW is often called QRSS, which comes from the code QRS, which means “send more slowly”. Another “S” was added to this to identify CW transmissions that are made at very slow rates, often much slower than 1 word per minute.

In a nutshell, the mode involves sending standard Morse code at very slow speeds. 0.4WPM has become the de-facto standard for Lowfer ID’s…this translates out to 3 second long “dits” and 9 second long “dashes”.

The purpose for sending such slow CW is that it allows for reception that is well below the noise floor, using personal computers and specialized software. In this regard, the mode is similar to BPSK, another weak signal technique developed by Lowfers.

Tests by Lyle Koheler, K0LR indicate that QRSS mode may actually perform better than BPSK (at least at the MS100 ET1 settings that most Lowfers have used for several years). At any rate, it is clear that QRSS performs at least as well as BPSK and this mode is VERY SIMPLE to get into. Let’s get started…

Receiving QRSS Signals

To get started on this mode, you’ll need a personal computer running Windows 95, 98, ME, or Windows 2000. Most of the software that we will mention here is not capable of being run under DOS. You’ll also need a decent 16 bit soundcard, though most any card you can buy will work fine. Horsepower of the processor is not critical, but it is helpful. I’d suggest at least a 200mhz or faster system.

Connecting the soundcard to your receiver is a snap. Simply take an audio output from the receiver and connect it via a cable to your soundcard’s input. In my case, I ran a shielded cable from my Icom 746’s earphone jack to the “MIC” input of my soundcard.

Adjust your soundcard’s mixer settings so that the incoming audio from the receiver is not too loud. The steps are easy:

1. Select “Start” on your Windows toolbar at the bottom of your screen.
2. Select “Programs”.
3. Select “Accessories”.
4. Select “Entertainment”
5. Select “Volume Control”.

This open a “mixer” control panel under Windows. As a default it enables you to adjust the “output” levels of various devices. We’re interested in the “input” levels, so we’ll have to add a couple of more steps:

1. In your Volume Control program, select “Options”.
2. Select “Properties”. The “Properties” control panel should open.
3. Now Select “Adjust Volume for Recording”. This is a check box setting.
4. Be sure to put a check in next to the device you want to control, usually this will be either the microphone or line setting.
5. Click OK. The “Properties” box will close.

Now you’re looking at the Volume Control box for your incoming audio sources. In my example, I then adjust the slider control for the MIC input so that the audio is at a good level.

If you can hear receiver audio coming out of the computer speakers, then you’d done with the connections! That’s about as easy as connecting a rig to a computer gets to be…

Now you need to download some software. There are several free programs out there in use for QRSS reception. They are all simply audio spectrum analyzers that allow you to visually look at the audio signals your receiver picking up.

One recent addition is a program called “Argo” which was designed just for QRSS work. It is by far the easiest one to get started with, and we’ll use it as an example here. Below is an example of what a strong Lowfer QRSS signal will look like on the screen:

You can download a free copy of Argo at the following web site:
http://www.weaksignals.com

The software has very few controls and is easy to use. For best results you will need to know the exact output frequency of your BFO. The easiest way to determine this is to tune your receiver to WWV at 5mhz, or 10mhz and place the receiver in CW mode. Using ARGO, look for a sharp peak. This will be the BFO frequency. Mine is adjusted for exactly 800hz, as this is what I need for BPSK reception as well.

With this information, I can tune to a given Lowfer frequency, and then look at the 800hz line on Argo to search for my station. If I am receiving the station, then I will begin to see a series of “dots and dashes” similar to the ones in the photo above.

Another nice feature of Argo is that it allows you to do automated “screen captures” overnight. In this way, you can set your receiver to the desired station, start Argo and tell it to take photos of it’s own display every 5 minutes during the night. In the morning, you simply review these photos to see if you have received the beacon! Very handy for those of us who like to sleep.
Recommended settings are:

AGC “OFF”
Sensitivity: 4th Notch Contrast: 3th Notch Audio Level: (Green Bar on the side) Lower 1/3.

Just as when trying to copy weak CW signals, it is best to use some filtering at the IF level (250hz or more). DSP filters in the receiver can be helpful as well, but require some experimenting with the display to avoid “smearing” the QRSS signals. Reduce your RF gain so that you’re not just amplifying noise.

On the 1750 Meter band, false signals can be a problem. Power line carriers (PLC’s) can look remarkably like Lowfer signals! If there is any doubt, your best bet is to capture the image and save it as an image file. This can then be e-mailed to the beacon operator for confirmation.

The other common problem with reception is the noise generated by the computer itself. Depending on your individual computer and monitor this can range from virtually no noise at all, to a problem that would totally prevent LF monitoring when the computer is on.

There are several fixes for this as well. A rule of thumb for reducing interference from the computer is:

1. Distance. The further away the computer can be from the receiver and antenna, the better.
2. Shielding. Make sure that the computer case is grounded. It is even possible to add foil shielding inside the monitor case, but be careful of the high voltages present in any CRT.

I’ve also found it helpful to use shielded microphone cable for the connections from the receiver to the PC. Further, I’ve added clamp on ferrite beads on every cable that is attached to the computer. At this point, I have no problems with radiated noise from my PC.

Argo is a popular choice for QRSS reception, but some find other programs can sometimes pull out weak signals better. A complete list of QRSS software is available at my web site:

http://www.highnoonfilm.com/xmgr/qrss.htm

I’ll also be happy to send out floppy discs with Argo, Spectran, and etc. for those who lack Internet access. Simply mail a blank cassette and return postage to:

Les Rayburn, N1LF
4919 Cox Cove Helena, AL 35080

Transmitting Your Own QRSS Signal

Using QRSS vs. conventional CW could literally double the range of your beacon. Hard to believe, but true. And transmitting in this mode is a very simple task indeed.

There are many software programs available that allow you to transmit in QRSS mode, including one developed by Lyle Koehler, K0LR. Links to these can be found at my web site address. All of them require you to build a simple interface between the computer and your transmitter, but construction is easy.

You may also be able to program your own keyer to send code at these speeds. Before obtaining one of Lyle’s “All in One” transmitters, which use a programmable ROM for keying, I used an old AEA Morse-Matic keyer.

It was simple and easy to program the keyer to send CW at speeds all the way down to .20WPM. This keyer cost me $15 bucks at a hamfest last year. Divider circuits are another easy “fix” for nearly any programmable ID keyer.

You may want to consider changing your callsign to something shorter for QRSS. It takes a very long time to transmit each character, and propagation can cause a long ID to fade out before being completed.

For example, Lowfer beacon TEXAS, uses an ID of “TX” when in QRSS mode.

The only real “con” to operating in QRSS mode is that you might miss out on local listeners who would be able to easily copy a CW ID at normal speeds, but would likely pass by a QRSS signal without even knowing what it was.

Some beacon operators use software that allows them to send a QRSS ID followed by one or more ID’s at standard speeds. This allows for the best of all worlds.

Earlier this year, we even sent out the traditional Lowfer holiday messages in QRSS. Lyle Koehler was able to copy my New Year’s greeting at over 967 Miles!
The message was simply:

HPY Y2K1 XM

(Happy Year 2001 This is XM!)

See, told you this weak signal stuff was fun!

What Does The Future Hold?

Credit for this season’s success must go in part to this remarkable mode. By next season, I hope that everyone who has a beacon will consider running at least part time in QRSS mode.

Most of the software continues to undergo improvement and development, for instance the latest version of Spectran incorporates software DSP filters, which could further push the edge of weak signal recovery.

Get started today!

Sanford? SFB? DX-300? Those sound familiar:)
Posted by Mike Thompson (KG4JYA) on April 11, 2001 at 09:58:37

Hello Chris,

Speaking as someone who has received the SFB NDB on 408 Khz with a DX-300, I can say that the best reception came from using an 8 turn loop, with about a 20 foot circumference. 1 Inch spacing between the turns.

This loop roughly tuned to around 460Khz without the aid of any capacitor.

Coming from the loop I used twin lead shielded cable going into a couple Capacitor Decade boxes I picked up at SkyCraft, down off of Fairbanks Ave. in Winter Park. BTW the boxes were in parallel with the loop. A few hundred pico farads and the loop tuned very sharp at 408Khz.
I can easily pick up this NBD indoors, with the loop hanging from my ceiling in the middle of a bunch of operating test equipment.

I'll admit my attempts at weak signal work are pretty pathetic, but seeing as I live in an apt. I'll take what ever reception I can get.

There are also some other NDB's that come in pretty strong. One from Kissemee, and I think one from Lake County.

These loops are easy to build and barely even touch your wallet as far as cost if you use pvc and some cheap wire. I used some speaker wire.

Anyways hope this helps, and its nice to know there are other Lowfers in Central Florida.

Mike T.

Solar Activity
Posted by John Davis on April 11, 2001 at 23:23:14

If you have been visiting the Spaceweather.com link on the LW Home Page, you know that an extraordinary solar wind (the shockwave from one of the recent CME's) hit the Earth's vicinity today, and that a polar absorption event occured today and a satellite proton event continued.

Just as an illustration of how much force a few particles per cubic centimeter can exert when moving at several hundred km/hr, Telstar 4 was knocked out of its assigned orbital slot for about 2-1/2 hours tonight. Loral Space Systems managed to regain control of the bird and restored service to a number of statewide public television networks, paging and data services, and so on. The satellite's predecessor, T401, disappeared entirely a few years ago after some rough space weather.

Aurorae may be visible as far south as 45 degrees north magnetic latitude tonight. (Since the magnetic pole is south of the real pole on the North American side, southern Tennessee and north Georgia are approximately 45 degrees.) HF propagation was very disturbed today, and there may have been an SID at LF when the flare from AR9415 occured earlier. Experimenters monitoring for geomagnetic effects should have had fun today!

John

TEXAS Off-The-Air during storm season
Posted by Bill Cantrell on April 12, 2001 at 01:09:57

Hello All,

TEXAS will be off-the-air April and May, during our annual thunderstorm season . This year, it looks like the weather is going to be particularly active, with lots `o lightning. I would rather not risk damage to the equipment. Be back up in June!

Regards,
Bill
"TEXAS" & WD5CVG

Re: Litz Wire Soldering
Posted by Robert Bicking, W9RB on April 12, 2001 at 15:56:56

A product (available in the USA, don't know about overseas) called Strypeeze and intended for paint removal works well. It can be found in building supply stores.

LowFER RB off for Storm Season
Posted by Robert Bicking, W9RB on April 12, 2001 at 16:05:51

Due to frequent storms and planned improvements; RB, 186.92 kHz will be off the air for the next few months. Will let you know when it is back on.
P. S., being an optomist, I'm building a 400W LF transmitter in the belief that the FCC will eventually join the rest of the world in granting a Ham allocation at LF. I want to be ready. I'm covering my bets by making it work at both 137 and 180 kHz! P. P. S., Also am busy finishing my 1922 Harley-Davidson restoration project. Old time metal rather than old time radio. 73, Rob, W9RB

antenna testing
Posted by Donald R. Moler on April 13, 2001 at 23:02:00

I built a platform about 7 foot high in my front yard and placed a 3 foot by 3.5 foot loading coil on top. I then put together the top hat that is 40 foot in diameter and had a friend come over and help put it on top of the loading coil. The platform is large enough so that I can walk around the loading coil seven foot off the ground and make adjustments and run test on the antenna. I built a insulated temperature controled box for the electronics under the platform. I am now on the air with about one tenth of a watt. As soon as I get the antenna working properly at this height I will take measurements. I will then double the height and take my measurements again. This will tell me a lot about the antenna. I would like to do this at four different heights and find out where the losses are and what percentage of the input power is lost in the coil then in the ground and see what I can do to eliminate them. The zonning people have not shown up yet. I think they are afraid of me ever since I cleared the branches around my 80 meter dipole with my shotgun. (Boy !does that work nice.) Don Moler N8BKR Girard, Ohio Vonj@cboss.com

SF NDB sick?
Posted by Matt W on April 13, 2001 at 23:24:47

Hi folks

just trying out my new VLF upconverter and while I can't get much at the house (too noisy and no loop yet)
I was able to pick up SFO airport's OMB/NDB "SF" All the guides point this beacon as sitting on 379 khz. But I was picking it up as low as 377. The pitch of the morse and the pitch of the carrier seem to be wavering up and down. I was going to blame the upconverter but I don't hear this fluctuation when tuning Loran or the baseline upconverter frequency in SSB mode.

Anyone in the SF bay area (or elsewhere) hearing this?
-matt

Re: SF NDB sick?
Posted by Mick Reed on April 14, 2001 at 08:49:23

It sounds like you haven't listened to beacons before? I have noticed that I can hear beacons on several frequencies near the reported frequency. I think these are what are sometimes called spurs. I think they are related to some kind of distortion by the transmitter.

Some of the hams could stop me if I'm wrong.
Mick Reed

Re: SF NDB sick?
Posted by Donald R. Moler on April 14, 2001 at 12:35:59

Sounds like the transmitting station is having a problem. If you want to check it out yourself just zero beat a signal generator against the station and measure the frequency of the signal generator with a frequency counter. This will eliminate the problem being in your receiver. There are a lof of image problems with receivers especially when a converter is added to the front end but in your case I think it is the transmitting station. Don Moler N8BKR Girard, Ohio Vonj@cboss.com

Re: SF NDB sick?
Posted by Tim Brannon on April 14, 2001 at 13:09:17

Matt,
Which up-converter are you using?

metal roof antenna
Posted by Donald R Moler on April 14, 2001 at 13:21:16

The idea of putting an antenna on 1750 meters that is mounted on a metal roof and a full 15 meters is probably not legal. The top of this antenna will see the ground around it and there will be return current flowing back to the metal roof from the ground and this will add to the radiation therefor will extend the heigth of the antenna, making it more than 15 meters. I am open to argument on this one but with all the work I have done with antennas iam almost certain I am correct on this one. Therefore I claim that Lyle Kohler's antenna is illegal.
Don Moler 2623 Morris lane Girard, Ohio 44420 vonj@cboss.com

Re: SF NDB sick?
Posted by Matt W on April 14, 2001 at 13:57:31

ack! sorry, gentlemen, but it was an artifact of my trying to use the sync detector of my Sony 2010. I also heard the same fluctuation on another NDB. The reason I was doing that was that I was trying to zero in on the exact frequency. So is your typical NDB carrier modulated? It certainly doesn't sound like SSB.

Tim--I'm using the Palomar Engineers converter. I am planning a trip to a more remote area soon to give it a real workout

Re: metal roof antenna
Posted by John Andrews, W1TAG on April 14, 2001 at 16:53:22

Should we skip the trial and go right to the televised execution?

Don... it's a hobby. Relax.

John Andrews, W1TAG

Re: metal roof antenna
Posted by Chris Curtis on April 14, 2001 at 17:34:46

I would beg to differ with your opinion of Lyles antenna. I also think it would be safe to say that the FCC wrote an exceedingly broad definition for part 15 antennas. Which could give some opportunity for educated adults to have differing opinions on the interruption of the rules.

Then there is the other issue weather the FCC actually has the manpower to check to see if someone’s one watt lowfer station has a 49.1’ antenna or a 50’ one. The job of the FCC is to assist with organizational aspects of managing this peoples RF resources. But any look at the FCC today, and one sees that it is an arm of broadcast special interests groups, making rules to assist the corporate few at a great cost to the masses. Take a look at what the FCC did to the LPFM people who wanted to bring extremely low power publicly owned radio to communities. Apparently their non interfering stations would “harm” the big boys. The broadcast and public radio interest groups lobbied to fake the legislation down. It's now written to fail. It's now doubtful that anything good will come out of the effort to bring truly public radio to the people. Same thing happened to the Cable industry. Don’t you remember the early cable days, promises of publicly available airtime were given by the financiers to get limited regulation. Where are all the public resources today.

Nobody asked me, but I don’t consider the FCC to be a part of the government that works for the people. Anyone in my neighborhood wishing to start a LPFM station or hang a little extra wire on 1750 meters has my support.

Chris Curtis

sorry
Posted by Donald R. Moler on April 14, 2001 at 20:52:31

Let me start off by saying that I am the biggest rebel you guys ever met. I said about metal roofs and lowfer antennas only to start a technical debate off with a bang. I and KT8D built very short vertical antennas for 160 meters and they had above ground radials. We built one that was only four foot high above the radials and it worked too good so we came to the conclusion that the wires going up to the antenna were radiating and adding to the signal after some testing we found that to be true. So John and Chris and others.....I am not for big government and when I was a youngster I built pipe bombs, launched weather balloons with railroad flares attached, ran a 500 watt pirate AM station on the broadcast band for a year,rode freight trans all over Ohio and a lot more I won't mention here. ....as long as it didn't hurt others I did it. I am a firm believer thay we are headed toward a one world government and we should do everything we can to slow down the trend. Do you know NAFTA and GATT are treaties and overrides our constitution and now we can't get rid of them. But getting back to antenns; I do expect to get the DX record on 1750 with my super big loading coil and my 40 foot top hat. I am the new kid on the block and this low frequency stuff has gotten me really excited. I can't wait to learn how to operate WOLF and try some of this below the noise signal searching. Thank goodness for this web site where we can all get together. And this summer if any of you are going by Youngstown on I 80 stop by and take a look at my antenna and I will buy lunch. I still say antenns that are 15 meters and are on metal roofs are illegal. Now lets debate that ... I could be wrong.
Don Moler Girard, Ohio N8BKR Vonj@cboss.com

Easy to build, cheap LW antenna?
Posted by Jason on April 14, 2001 at 22:17:16

I have a Sony ICF-SW7600G and live in coastal New Jersey. I want to be able to hear Europe's LW stations.

Can someone give me advice on the simplest antenna to build (and how to) that would give me a good shot at it?

Or is there a LW antenna availible on the market that works and is affordable?

(money, and size are major factors)

I mean, could I simply get some cheap wire and make a 5ft. loop? Or do I have to build something very complex?

FWD: Re: WOLF bandwidth suggestions
Posted by John Davis on April 15, 2001 at 09:48:59

Subj: LF: Re: WOLF bandwidth suggestions Date: 4/14/01 7:20:40 PM Eastern Daylight Time From: sn@scgroup.com (Stewart Nelson)
To: rsgb_lf_group@blacksheep.org

Hi Markus and all,

Thanks for your post. I've fixed some of the minor problems, and have comments on the major ones. WOLF new version is 0.53, which can be downloaded at http://www.scgroup.com/ham/wolf.html
: 1. WOLF is using cosine-shaped zero-crossings with a risetime of only 5 ms, : which causes a few extra sidebands on each side of the spectrum. I'd prefer : to extend the cosine-envelope to the full symbol duration (like in PSK31), : then ideally only the 10 Hz wide main spectral lobe would persist.

The 't' (transition) option has been added for transmit. You specify a transition time, relative to the symbol duration. Values from 0 to 1 are valid. The web page shows spectra for 0, 0.1, and 1. The improvement, when 't 1' is specified, is dramatic. Many thanks for your suggestion.

> At a given > PEP level and with 50% phase transitions, on average we'd lose only 0.8 dB > SNR while saving 24% transmitted energy.

Unfortunately, the receiver is still matched to "rude" BPSK, so about 1.3 dB is lost, relative to the old (and default) setting.

> 2. I wonder whether it would be possible to use fewer bits for the > pseudo-random reference stream, as this is known in advance and could be > averaged over longer times than the actual data. With only 1 out of 4 bits > donated, data rate could be increased by 50%.

At present, most failures to decode are failures to sync up. Some are directly caused by shortcomings in the program (poor search and tracking), and some are caused by incorrect settings, e.g. sample rate, which are indirectly caused by the lack of good status and diagnostic outputs. After I get a chance to improve both of those areas, I'll reconsider how much sync information is really needed.

> 3. QPSK at half symbol rate would reduce the BW down to 5 Hz. With 3 dB less > signal per channel and 3 dB less noise, SNR would remain unaffected. If only > one reference stream were needed for both I and Q, the net data rate could be > increased further.

QPSK works well for e.g. DBS satellite downlinks, where, although the signal is very noisy, it's possible to average many thousands of bit transitions to get an accurate carrier phase reference. You can't do that in a weak signal ham situation, because the packets are short, and path / equipment instabilities limit the time constants for phase recovery. If the reference for a BPSK signal is 45 degrees in error, you have an additional 3 dB loss, and it will take twice as long to recover the message. But in the QPSK case, you have total garbage, because the detector sees the "right" bit and a "wrong" bit with equal amplitudes.

PSK31 has an error correcting QPSK mode, which is rarely used, because most of the coding gain is eaten up by the loss described above, and the small remaining gain does not justify the added delay. IMO, the error correcting mode would have been far more successful, if it simply ran in BPSK at half speed. Most hams can't type that fast.

> 4. We might then turn to OQPSK, ie. offset the I and Q streams by 50ms to > avoid the zero crossings. While we'd still want to use a linear amplifier, > the difficulties of Class-D envelope restoration schemes due to the undefined > phase at zero amplitude would be much alleviated.

The good news is that OQPSK with proper filters has an essentially constant envelope, and is used on some satellite links so that the transponder can be run saturated for maximum output. The bad news is that it is essentially equivalent to MSK with a recoded input stream, and IMO weak signal FSK should use every other bin, to minimize interference resulting from reference errors, even if one must use a higher rate code to maintain the same bandwidth. Going from, say, a rate 1/6 code to a 1/3 costs only about 0.44 dB, see graph at http://scitec.uwichill.edu.bb/cmp/online/p31q/Lecture14/lect14.htm

I believe that a coherent m-ary FSK system would be technically superior to WOLF, but have not attempted to implement one, because there are very few hams (you being one of them) who have the means to generate such a signal at LF. But that would be the best way, IMO, to build a system that would occupy about 1 Hz of bandwidth, but would still permit a transatlantic LF QSO to be completed within one hour.

> 5. In the current implementation, the transmit file apparently uses only half > of the DAC range.

The 'a' option can now be used to specify transmit attenuation, relative to full scale.

> Also, I wonder if one could possibly use Spectrogram's > RX-files taken at 5512 sps without resampling.

WOLF will now accept .wav files recorded at any sampling rate, and will display a warning if the rate is not 8000 Hz. If -r is not given, the internal sampling rate is set to that of the input file.

> After cheating by overwriting > the sampling rate in the wav header, I could decode using -r 5512, but > somehow WOLF didn't terminate at the end.

I wrote several files with Spectrogram 6.0.8, but could not reproduce the trouble. If you use the undocumented -v (verbose) option, WOLF will display (among other things), the amount of data it thinks is in the input file. You can compare that to the file length or other software's notion of the size. It's also possible that there is a bug where certain data or settings causes the program to hang or loop, having nothing to do with the input file format. If you can see a failure on a relatively small file, email it to me, along with the console output, and I'll try to find the bug.

Everyone, please let me know of any problems with the new code.

73,

Stewart KK7KA

DCH off
Posted by Dave Holland on April 15, 2001 at 10:46:03

DCH is off for the season. The antenna and xmiter made it through the winter, with all the high winds. In the off season I adjust the antenna's length for a 1/4 wave on 40 meters, with a small fixed top hat.

Dave

Re: metal roof antenna
Posted by Jonathan W2MXW on April 15, 2001 at 16:57:32

For that matter, if we're gonna nitpick, and I know this is gonna ruffle a few feathers (apologies in advance) but technically loading coils are illegal if the length of wire used to wind them added to the sum of the antenna/feedline/ground lead lengths exceeds 49.2 feet (15m). I have this directly from an FCC engineer responsible for the Part 15 rules, so there can be no argument from anyone about whether this is the case or not. The antenna "length" and not "height" is specified in the rules (despite popular interpretation of the latter) purposely to prevent increasing the electrical, as well as physical, length of the radiator. So despite the wire in a loading coil being coiled, it's length *if it were stretched out* is what counts.
Physical height of the antenna structure however, is not relevant to legality, and a 49' antenna on a rooftop, metal or otherwise, is legal as long as it conforms to the rules (but zoning issues may be another factor altogether).
BTW I do know a way of legally using an inductor to tune the antenna to resonance without using a loading coil per se and I *could* tell ya' but then I'd have to kill ya :-) But you should be able to figure this one out...
Then again, it is as John said, just a hobby, and I think the FCC has more pressing issues to concern itself with.

Jonathan W2MXW

remove "spam.this.and.die." in email to reply

Sound Utility-Wolf
Posted by Lloyd Chastant on April 15, 2001 at 17:16:38

Been using the Cool Edit sound utility for the initial checkout of the Wolf mode,but that has a 30 day trial period.Was just wondering what others have used and are there other freeware/shareware that may be OK or is maybe the Cool Edit 2000 Lite Ok for one to go with???
Was sure exciting and interesting to be investigating the Wolf mode-even though I only was on the receiving end.Look forward to next season..Thanks de Lloyd W3NF

Re: Easy to build, cheap LW antenna?
Posted by Thomas A. Schopp on April 15, 2001 at 18:10:09

LF Engineering (http://lfengineering.com)has LF, VLF, ELF (down to 300Hz) for modest (?) costs. There are also some excellent designs in Joseph J. Carr:RadioScience Observing Vol I, Chapter 12 (p.195), describing low cost VLF (ferrite loop) antennas. There are ferrite cores available (will have to look these up) for construction of ferrite loop antennas. (By the way, the Palomar Engineering loop antenna w/antenna tuner is no longer available, having been out of production for some time.) Let me know if you need additional assistance.

Re: VLF circuits
Posted by Thomas A. Schopp on April 15, 2001 at 18:24:11

Have you tried Joseph J. Carr:RadioScience Observing, Vol.I, Chapter 10? LF Engineering (http://www/lfeingeering.com) has a converter and active antenna system (his L-111) which covers 3kHz-530kHz. Palomar Engineering (available at Universal Radio (http://www.universla-radio.com)), both designed to for general coverage communications receivers.

Re: Loop Antennas for Receiving
Posted by Thomas A. Schopp on April 15, 2001 at 19:12:16

The large loop antenna responds to the electronic component (electric field) of the RF signal, but the smaller loop antenna are magnetic component sensitive, which is less affected by electrical field interference. See Joseph J. Carr: RadioScience Observing, Chapter 12. The L-400B, a vertical LF/VLF Active Antenna available from LF Engineering (http://www.lfengineering.com) also responds to the magnetic field component, according to converations I have had recently with LF Engineering. Antennas designed to act on the magnetic component are less affected by electrical field interference and therefore are more "quiet". Find a diagram of the RF signal which shows the grid and the polizaration of the 2 (electronic and magnetic) RF field components.

Re: Easy to build, cheap LW antenna?
Posted by Jonathan Smick W2MXW on April 15, 2001 at 19:25:05

Hi fellow Jerseyan :-)

Check out Lyle Koehler, K0LR's page at www.computerpro.com/~lyle He has a design for a universal preamp, very simple to build and can use many different antenna types of your choice. You can use it with an air-core box loop, longwire, E-field whip, ferrite bar, etc. I made one with a large (6") ferrite bar antenna, and the thing works great. It's almost pocket-size but really pulls 'em in. I use it with an older Realistic DX-390 (or Sangean ATS-818, same thing) mostly for NDB DXing. Another option, from someone who uses your exact same RX, is at: http://members.tripod.lycos.nl/Aren/id31.htm He goes into some detail about his LF reception problems and how he solved them.
The Icelandic LF broadcast station is the most often heard on the East coast, also there is the BBC, the ones in Allouis, France, Germany, and Atlantic 252 in Ireland (mostly club/dance/pop format), their site is www.atlantic252.com but watch the P.I.A. Macromedia Flash crapola. There are many other LF BC stations too but less often heard.

73, Jonathan

you know the drill if you want to reply by email...
nix the "nix.spam."

Re: Sound Utility-Wolf
Posted by Mitch on April 16, 2001 at 17:05:25

Hi Lloyd:
Could never get Soundedit to work - hi !
Have been using RECALL - very simple, and records well. I have been able to record a WOLF station and get successful results . It is at http://www.sagebrush.co

Good luck Mitch VE3OT

Re: Sound Utility-Wolf - correction
Posted by Mitch on April 16, 2001 at 17:06:57

Lloyd:
address should be http://www.sagebrush.com

73 Mitch

Re: metal roof antenna
Posted by John Davis on April 16, 2001 at 19:32:46

Just goes to show even FCC engineers are susceptible to some pretty silly interpretations of fairly simple rules.

It happens all the time. A couple of decades ago, the TV broadcast rules required a daily log entry of visual and aural carrier frequency measurements made with the station's frequency monitor...a rule devised back when one such reading a day was quite a technological feat. Well, by the late Sixties, we were logging them every half hour, along with all our other readings. And guess what? We got cited for not having a SINGLE daily entry! Shame on us for complying with the rule every 30 minutes instead of just once in 24 hours!

Our Washington attorney is presently having to "guide" the FCC's antenna structure database people through the idea that a tower registration may need to be amended because the data in it is simply wrong, and that new construction is not the only valid reason why an entry might need to be modified. And while the relevant officials in D.C. agree with us, the ones in Gettysburg keep rejecting the application. The right hand and the left hand, and never the twain shall meet, etc....

In short, one FCC employee does not a Commission make.

Common sense is still a valid guide for us mere mortals, provided "sense" is the operative word.

The rules talk about total length of antenna, transmission line, and ground connection. Period.

I submit that, as worded, the rule is a simple linear measurement. The simplest practical definition is to stretch a tape measure between the transmitter output and the farthest point of the antenna, and you've got the antenna and transmission line part.

There's nothing in the rules that says any reactive components included in the antenna itself have to be treated as something separate and unique. A loading coil is a significant reactive component only when it is coiled, after all. When it _is_ coiled and performing its natural function, it has a linear dimension from the start of the winding to the end that the simple tape measure test accounts for quite nicely. A loading coil that is part of the end-to-end run of the antenna can't be excluded from the definition, any more than a top hat can but it doesn't have to be disassembled and measured separately, either.

(If one still wishes to fret over the issue, the solution is to put the coil in a big box with the rest of the amplifier circuitry and call it part of the transmitter, not the antenna. If one is really obsessive, but still wants to stretch the point of the rules, there is no limit on TRANSMITTER height, now, is there?:)

Moving on, from the ground connector to the ground system is the other part of the total length. Note that there is no evident obligation to account for the hardware that makes up the ground system. A water pipe is a ground system; an 8-foot rod is a ground system; a copper screen and radials is a ground system. In real-world practice, any array which makes effective RF contact with the earth --or alternately, any array which functionally _replaces_ contact with the real earth-- is a ground system. Our conflict of conscience should arise when we combine these two concepts.

Elevated counterpoises with no earth contact are widely acknowledged as ground systems in their own right. This can include metal roofs or radials atop a regular roof, if they're not connected to earth. (That's a dangerous way of operating; I certainly don't recommend it for one's home!) But alas, any conductors from the roof down to ground are in series with the rest of the radiating element and are part of the connection to the _real_ ground, against which the antenna is also working.

The FCC has ruled against broadcast-band devices that were sold under the pretense of being "Part 15" compliant, when in fact the metal poles on which they were mounted were part of the connection to earth, and contributed far more to the radiation than the 3-meter structures atop the transmitters themselves.

I apply the TARS principle here (This Ain't Rocket Science) and conclude that we needn't be sea lawyers when interpreting the rules. As has been so widely pointed out, the FCC may never pay any attention to you--if you're not calling attention to yourself, that is. But if you want the good feeling of being able to say you achieved your victories openly and above-board, the conscience factor needs to come into play too.

That's why the traditional LowFER rule of thumb makes a lot of sense. If you use the ground-connection-to-farthest-point-of-antenna test (where one is measuring from the actual ground the antenna is working against) you're in compliance with the simplest practical reading of the rules and are justified in having warm feelings about whatever you manage to accomplish with the setup.

73,
John

Re: Sound Utility-Wolf - correction
Posted by Lloyd on April 16, 2001 at 22:53:27

Thanks Mitch-I downloaded Recall and it seems to work just fine.Thanks for info

73 Lloyd

Re: metal roof antenna
Posted by Jonathan W2MXW on April 16, 2001 at 23:49:36

"In short, one FCC employee does not a Commission make."

True, however, I'm going by what one of the people who writes the Part 15 rules, according to their own interpretation, intended them to mean (and I therefore would tend to agree with them since it is the "spirit" of the rules that they intended); of course while I realize that the letter of the law and the interpretation thereof often differ, and may not always even make sense, I personally prefer to err on the side of conservatism in my own Part 15 ventures, so I can sleep well at night knowing I'm in as total compliance as possible with the ideology of the Rules that was intended. But, to each his own.

Of course, another point is that this interpretation comes from an official source whereas the "Lowfer rule-of-thumb" does not...

I am well aware that different divisions within the FCC don't agree on their own rules interpretations, at times this has led to infighting even among different offices within the Commission. "The right hand and the left hand, and never the twain shall meet", indeed.
The enforcement guys in our local Field Office however are aware of the "no loading coil" interpretation and will ask that it be removed should someone be using one. If there were a case of disagreement between the Enforcement and OET Division then certainly the opinion of the OET, being the law drafters, should be the outstanding one, but on this point there is no disagreement, at least in our case here (your mileage may vary).

"(If one still wishes to fret over the issue, the solution is to put the coil in a big box with the rest of the amplifier circuitry and call it part of the transmitter, not the antenna. If one is really obsessive, but still wants to stretch the point of the rules, there is no limit on TRANSMITTER height, now, is there?:)"

That's exactly what I meant by the alternative method I referred to. The secret's out! :-) Put the transmitter at the top of the pole, capacity hat above, less-than-15 meter mast below, coil inside xmtr. box and thus call it a "final tank coil" and you're good to go. Current flows up the mast, and everybody's happy. This is what I refer to as the "inverse-fed antenna" and it is very efficient (about as good as using a top loading coil). Totally compliant with both the letter and the strictest interpretation possible of Part 15 Lowfer rules, even if it is indeed as any engineer can see, on a taxonomic technicality (and mechanically inconvenient).
Of course, the xmtr. with it's *built-in* coil can also go at the base of a non-loaded 15 m mast but what we have then is a tall capacitive E-field probe (not as efficient) but much easier to adjust and maintain. But still 100% legal.
But, a separate loading coil in series with your antenna, whether at base, middle or top could get you in trouble here (unless you have length to spare from using a shorter-than-legal antenna, say, 20 or 30 feet, and use that remaining length for the loading coil winding). Then it's legal but you need a ferrite core (lossy) for any reasonable inductance with so little wire.

"The FCC has ruled against broadcast-band devices that were sold under the pretense of being "Part 15" compliant, when in fact the metal poles on which they were mounted were part of the connection to earth, and contributed far more to the radiation than the 3-meter structures atop the transmitters themselves."

The part about the mast doing most of the radiating is true, (and using the "inverse feed" scheme that's the whole point) but funnily enough, it's done all the time on the BCB (and the FCC knows it) for low power AM broadcasting and no one complains, nor am I aware of any official "ruling" against it. Why apply a double standard aginst BC operations v. Lowfer/Medfer? Since as you pointed out there is no *height* limit on the transmitter, we can use a nice, tall support structure which just happens to be metal and grounded :-) We can avoid a direct connection from transmitter ground to mast if there is objection to such connection but RF capacitance takes care of that anyway. (There is the lightning safety/compliance with National Electrical Code standards, potential for forfeiture of homeowner's insurance, etc. issue which needs to be addressed if no direct DC ground connection is made, and violation of said standard can result from a "letter of the law" compliance with the Part 15 rules concerning ground leads. So which law does one choose to comply strictly with?) As hinted at by John that is a dangerous way to operate. I personally think the Rules should be amended to account for this. But that's going off on a bit of a tangent...
Since the installer of the system is considered the "engineer" they are therefore responsible for their own determination of what constitutes "ground" (not necessarily "earth" ground).
An acquaintance of mine who also manufactures compliant, Certified Part 15 AM transmitters approved for low power broadcasting (yes, they are *truly* compliant) and is also well-connected with numerous FCC personnel uses this philosophy of "ground" determination and no one has ever had a problem with this. Someone I know was inspected by Enforcement 3 times and declared legal. They use a tall metal mast with xmtr. (and it's 3 meter whip ant.) at the top.
If not using a direct ground connection between xmtr. and mast, whether the mast is grounded or not is immaterial to legality even on the BCB since there is no "ground lead" at all (again it's a capacitive connection). We are calling the transmitter ground lead the "ground lead" in this case and there's little room for contention over whether that is the correct application of terminology. And the rules do not limit height of transmitter, nor height or type of its support structure.
And our F.O. personnel here don't have a problem even with a direct DC gnd. on the xmtr. as long as it's tied off somewhere to the mast, but others may encounter different opinions. However, I am not personally aware of anyone who has been told to modify their system on the basis of this point.
Then too, taking the opposing viewpoint, technically using the most literal interpretation of "ground lead length" you could forget about having radials (despite whether they are tied off at "earth ground" or not). However, Enforcement here doesn't mind radials, - as long as they are tied off at a common earth ground (driven rod, etc.) For my own use again in my conservative way of thinking, I personally would be careful (perhaps a tad "obsessive") about stretching the ground lead interpretation as cited above, as well as the loading coil one. But I do sleep well at night!

73, Jon

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Metal roofs
Posted by Mick Reed on April 17, 2001 at 02:47:38

I read the earlier thread, and couldn't quite understand everything being said about the ground system. I agree with Moler where a 'mast' that is grounded and is radiating a significant amount of power, that's not fair.

The point where I'm not sure is the metal roof. Like Jonathan said, a 'ground lead' has to end somewhere. If you included the ground lead, in this sense, how could you put it into the earth? Would you have to include the earth in the calculation? Should we use a battery to power our tx so it 'floats' and put it directly at the base of the antenna?

I believe that if the roof is grounded, as it should be, calling it a ground lead is not much different than calling a salt marsh or wet onion field a ground lead.

This is a good thread - not all of us have accessed our local FCC office. Personally, I am afraid to, as I figure I might be treated as an idiot anyway. I'm half suspecting I would have unmarked white vans on my block if I said the wrong thing.

Mick

Re: Easy to build, cheap LW antenna?
Posted by Mick Reed on April 17, 2001 at 02:54:48

Hey, I really recommend the Lyle Balanced Preamp. It did so much for my rx you wouldn't believe it. I used to struggle to hear stations 40 miles away. Now I have heard Hawaii from Oregon (2547mi) and I have to attenuate almost anything in Oregon. I made a 8' diagonal square loop with 14 turns, grounded at the 7th turn. It's really not hard. I use some NTE618 varactors (4) and a couple of fixed caps to tune to resonance. Easy.

Mick

Re: metal roof antenna
Posted by John Davis on April 17, 2001 at 09:43:33

::True, however, I'm going by what one of the people who writes the Part 15 rules, according to their own interpretation, intended them to mean (and I therefore would tend to agree with them since it is the "spirit" of the rules that they intended); ::

Source, please? Over the years, I've seen two FCC clarifications to the Part 15 R&R. The simple linear-measure rule of thumb is consistent with what's in both, but I have not found reference to loading coils in either.

:: The part about the mast doing most of the radiating is true, (and using the "inverse feed" scheme that's the whole point) but funnily enough, it's done all the time on the BCB (and the FCC knows it) for low power AM broadcasting and no one complains, nor am I aware of any official "ruling" against it. Why apply a double standard aginst BC operations v. Lowfer/Medfer? ::

In point of fact, there _have_ been complaints about this form of unlicensed "broadcasting." A few weeks back, the lowfer@qth.net reflector quoted a response from an FCC official, printed in RADIO WORLD, in connection with these mast-mounted devices. A search of their digests should turn that item up.

The very name "inverse feed" denotes deliberate use of the ground connection as a radiating surface. On the face of it, a mast and antenna length in excess of 3m total therefore very clearly exceeds what is permitted by the Rules.

It's very puzzling that a field office would turn a blind eye to that, yet glare at a loading/tuning coil or anything else that's not even mentioned in the rules. Perhaps it's just not safe at all to operate Part 15 in that office's jurisdiction...

:: Since as you pointed out there is no *height* limit on the transmitter, we can use a nice, tall support structure which just happens to be metal and grounded :-) ::

I was referring to the H dimension of the transmitter enclosure, not how it is mounted; and, of course, it was tongue-in-cheek. But that might not be enough to prevent someone from building their transmitter into a 7 foot equipment rack, alas.

73,
John

Re: metal roof antenna
Posted by Jonathan W2MXW on April 17, 2001 at 16:24:27

I'll email you personally for more detail, John. I don't think I should be "naming names" and such in public forum.

A search of both turned up nothing. I've been on the Lowfer list for quite awhile, and I never saw such a post. Could you possibly send it to me via email if you have it? I'd appreciate it very much.

I coined the term "inverse feed" and it is meant as a descriptive term because of the behavior of a system where anything (wire, pole, mast, etc.) connected (physically, or capacitively, by proximity) to the low side of the transmitter's final tank ("ground" side) carries current and thus radiates, therefore acting like an antenna fed from the top instead of the bottom. It isn't violating anything if there isn't a direct connection from transmitter RF common ground proper to physical earth ground though.
(Although said physical connection would naturally be okay in a Lowfer setup if one had length to spare in the antenna system - in other words, we can choose to have all "ground lead" and no "antenna" as long as the sum of these lengths is still within the legal limit). RF capacitance makes a "virtual" connection but is unavoidable, as anything conductive in the vicinity of the transmitter has capacitance to it.
Since there is no part of the rule specifically limiting the type of support structure or height thereof, we can use a metal pole of any size to mount the transmitter - the fact that capacitance exists between the two is a given, but *not* specifically ruled against as long as there is no physical ground wire connection between the transmitter ground proper (RF circuitry common ground bus) and the mast, so why not take deliberate advantage of the phenomenon since it exists and is inevitable?
The only physical grounding lead of any sort that there is in the type of AM transmitter I referred to is a lightning protection ground and this is separate and distinct from the transmitter ground (it goes thru a gas discharge-tube arrestor). This can't be considered a "ground lead" according to any reasonable interpretation of the rules because it is not connected to the RF circuitry ground bus nor is it intended to carry RF (And is necessary for safety).
The definition of what constitutes the "ground" and thus "ground lead" is open to interpretation by the system engineer as mentioned in my previous post (and I am awaiting a copy of this from an FCC source via a colleague who has this in writing).

On the contrary it's perfectly safe, as long as one doesn't use a big honkin' loading coil in the antenna proper (any inductance has to be in the form of a final tuning coil in the xmtr. box). The F.O. here isn't turning a blind eye at all to the grounding issue because they realize that any ground we do use is (a) a lightning protection ground which we have heard from other FCC sources is specifically encouraged and (b) that merely mounting an xmtr. atop a grounded mast does not a violation make, in accordance with what I said above.
Grounding the transmitter's common RF ground bus to such an earth-grounded support however, would probably be a problem but at least in the case of the xmtrs. we are familiar with, the only ground provided is for the gas-tube arrestor and is separate and not internally connected to the RF common ground bus.
Yet there is still capacitive coupling between mast and xmtr., thus the "inverse feed phenomenon" still works despite the lack of a physical RF ground connection, and it is arguably still legal.
*None* of the Certified AM transmitters available (ones which are *truly* compliant - and this again from a colleague well-connected to FCC engineers in charge of Type Acceptance approval, being a manufacturer of these units)
have a loading coil in the antenna proper and a unit would never be approved for Certification/Type Acceptance if it did.
Therefore, that is further evidence that loading coils in series with the antenna structure itself are frowned upon by FCC, whether it is written in the rules or not.

That actually would be funny, but beside the point. Imagine a 100 mW transmitter in a huge rack! Can you say "Golden Coccoon Award"?? :-)
What I meant (and thought you meant) was how high above ground or the roof of a building, etc. the transmitter is mounted. There is no limit on that, nor on the type of support structure (metal or otherwise). Numerous AM broadcast operations across the country which have been inspected and approved by F.O. personnel from many different F.O.'s are mounted on such things as metal billboards, poles, and in one case a 70 foot tower (construction of which was advised by and approved of by their relevant FCC Field office).

73 de Jon

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Re: metal roof antenna
Posted by Jonathan W2MXW on April 17, 2001 at 16:43:33

Now that I look at it, I realize there might've been some confusion because of my choice of words, when I said "DC ground" in the first post I meant "lightning protection" not "RF" ground. It was late at night, I was getting a tad punchy...

I apologize.

73 de Jon W2MXW

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Re: metal roof antenna
Posted by John Davis on April 17, 2001 at 18:59:21

I'm forwarding a redacted version of my reply to your personal e-mail below, then have a comment on the radiating mast.

******Subj: Re: Part 15 interpretations

Thanks, Jonathan. However, Mr. (omitted)'s reply appears more ambiguous than the rule itself. I notice he says "length of the coiled wiring," which is not necessarily the same as saying the length of the wire which makes up the coil.

I can't find any engineering text which defines the "electrical length" of a coil, so that part doesn't help a lot either. I could therefore just as easily argue that the electrical length of a coil is from end of winding to end of winding, as that's the dimension of the coil which radiates, not the individual turns.

Obviously they don't care about a tuning coil inside the transmitter improving system efficiency, so why would it matter if that same physical element is outside, so long as the total linear measure is within the rules?

73,
John *******

As you said in your e-mail, the point of the rule is to limit radiating efficiency. Why, then, would a mast be exempt? If it's grounded at the base, then the pole is a connection to the ground system and would need to be accounted for. If it's not grounded, then it's the other half of an asymmetrical dipole, and would need to be included in antenna length. Either way, it's a deliberate radiating element.

Anyone recall this discussion in the qth.net reflector last year?

73,
John

Re: metal roof antenna
Posted by John Davis on April 17, 2001 at 20:40:54

Re: " ...merely mounting an xmtr. atop a grounded mast does not a violation make, in accordance with what I said above."

The complaint I mentioned about the commercial devices using this technique, and the response published in RADIO WORLD thereto, were cited in an August 3, 2000, post in the qth.net list by John Andrews. I quote John's text in its entirety:

* * * * * Quoted Text * * * * *

In the August 2, 2000 edition of Radio World magazine, there was an interesting response from the FCC to a letter questioning the legality of some equipment being sold that supposedly conforms to the 100 mw/3 meter requirements of Part 15 for unlicensed operation in the AM broadcast band.
It may be of interest to the LF community. The original letter was from Robert Ladd, of WNRR(FM) in Bellevue, Ohio. Here is the response:
------------------------------------------------------------
Mr. Ladd:

Your inquiry was referred to me for reply. Before responding, I ran your question by our lab people who are responsible for issuing the required grant of certification on the AM transmitters before they can be marketed or used.

Under Section 15.219 of our rules, the maximum power is limited to 100 mW input to the final RF stage and the total length of the antenna plus the connecting lead plus the ground lead may not exceed three meters.

The antenna is part of the package that is certified. If a loading coil is used in the antenna design, we count the electrical length of the coil toward the three meters. In other words, this rule is designed to keep the practical transmission range no greater than about 250 feet.

If the installer/user places the transmitter atop a metal pole or other conducting structure and grounds the transmitter to that structure, the height of that structure also is counted toward the three meters maximum length.

You did not mention the FCC ID number on the transmitter, so I am not able to identify the responsible party. If you can supply that number to us, I would be happy to provide it to our laboratory staff. If no FCC ID number exists, the equipment may not be legally imported, sold or used.

Let me know if you need additional information on this issue.

John A. Reed, Senior Engineer, Technical Rules Branch FCC Office of Engineering and Technology, Washington.
------------------------------------------------------------

John Andrews, W1TAG

* * * * * End Quote * * * * *

Re: metal roof antenna
Posted by Jonathan W2MXW on April 17, 2001 at 22:11:31

"...If a loading coil is used in the antenna design, we count the electrical length of the coil toward the three meters."

I rest my case. It is obvious that "electrical length" was intended to mean the apparent length in electrical degrees of the coil, i.e., 90 for one which makes a 3 meter or 15 meter antenna respectively look like their full-sized counterparts.

"If the installer/user places the transmitter atop a metal pole or other conducting structure and grounds the transmitter to that structure, the height of that structure also is counted toward the three meters maximum length."

I submit that taking note of the statement "...and grounds the transmitter to that structure" in accordance with my previous posts that my statement "merely mounting an xmtr. atop a grounded mast does not a violation make" still holds true. The *mast* might be grounded but the transmitter is *not* grounded to said mast (not directly through a wire having dc continuity). Neither I nor any other engineer worth their salt could call a ground through a lightning arrester a "grounding of the transmitter" since there is no DC continuity, and we know "grounding of the transmitter" means via its "RF common ground bus".
Further neither the rules nor the quoted party specify what their definition of "ground" is; DC, RF, earth, at what point does "ground" become "ground". Again, it has been stated by FCC officials within the very same division that the "installer/user" is the "engineer" and thus responsible for their own determination of what constitutes "ground".
Nor could the mutual capacitive coupling which exists between the transmitter and mast be called a "ground lead or ground connection".
Yet this would still result (given sufficient capacitance) in the same results as far as RF is concerned. But since there is no direct grounding of the transmitter to the mast I submit that this is still a legal situation in perfect accordance with the above official interpretation.

73, Jonathan

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Re: metal roof antenna
Posted by Jonathan W2MXW on April 17, 2001 at 22:25:59

"As you said in your e-mail, the point of the rule is to limit radiating efficiency."

*I* didn't say it, it was quoted from one of the emails from the FCC person. Of course anyway it is the point of the rules but we knew that already.

I didn't say that masts are exempt and coils not, but this is what I mean by playing favorites: conversely why should masts be purposefully pinpointed for inclusion and not coils?
They both can increase efficiency. But if you don't use a mast, (or pole, or bracket, or whatever you wanna call it), how can you mount the thing on say, a rooftop (assuming you don't want it sitting directly on the roof). I dunno 'bout over your way but we haven't gotten a shipment of those anti-gravitation transmitter levitators here yet. :-)
If you use a mast, it's usually gonna be metal. Ergo, capacitively coupled to the transmitter mounted upon it. Now, for home insurance and safety of life-and-property and NEC compliance reasons we must ground the mast. So it becomes a radiating element. So what? So does everything else conductive in the vicinity including things like powerlines. Again, radials and ground screens also improve efficiency, how come no one here is complaining about those? (And actually I know that in the past the same FCC person has, while others in Enforcement have no problem with them).
A coil *somewhere* in the final circuit is not just for improving system efficiency, it is necessary for the thing to work *at all* (as much as the power supply!)- they have to allow you to use one. Otherwise, it'd be like having a rule which says "you can have a transmitter but you can't use any power source to power it". But they can tell you where you can and can't put that coil, so as it's position changes so does its taxonomy.
They want it in the box, it goes in the box. They say mast okay, mast okay. If the rules change, we get out the ol' magnifying glass and look for new loopholes. And argue about them ad infinitum or at least until the next rules change and so forth...

73 de Jonathan

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Re: Metal roofs
Posted by Jonathan W2MXW on April 17, 2001 at 22:32:04

Can they say "Well, your building has a metal roof and since that would enhance your signal, we can't permit you to mount your transmitter there..."?
So okay what if you set it up in a junkyard full of old metal car chassis, as you said, a salt marsh, etc.? Or near a powerline (which we find by incidental carrier-current coupling in the induction field also enhances the signal significantly). Where could you find a place that's not near any powerline? (And if you know of one I'd like to make it my permanent whistler listening post! :-)

Well, gotta go salt my lawn (just kidding!!)

73, Jonathan W2MXW

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Re: metal roof antenna- electrical length of coil
Posted by Mick Reed on April 18, 2001 at 00:14:07

So for electrical length, we have Period * 3e8 * vp or 116 meters, right? I'd like to see one of these transmitters that are being sold. I have a feeling that they DONT have loading coils - someone let me know. I know it is different, but say on a FM wireless mike, they would have a tank circuit with a cheap section of wire soldered to it. The wire just hangs out and 'spills' rf out.

Am I wrong? Or do the commercial products have loading coils?

If we use the electrical length of the coils, like Jonathan says, they would be illegal, at least in some jurisdictions of the local FCC offices...

Re: metal roof antenna
Posted by John Davis on April 18, 2001 at 00:22:11

"It is obvious that 'electrical length' was intended to mean the apparent length in electrical degrees of the coil, i.e., 90 for one which makes a 3 meter or 15 meter antenna respectively look like their full-sized counterparts."

There's nothing obvious about that at all. And in point of fact, a loading coil does no such thing.

In no way does a 3 or 15 meter whip/wire/pole/tower, no matter how loaded, look electrically like a quarter-wave radiator at the frequencies of interest to us. Not in current distribution, not in radiation resistance, and certainly not in field strength.

Conversely, there seems little point in splitting hairs over the meaning of grounding. The FCC regulates RF. They don't regulate audio, they don't regulate AC power, and they don't regulate DC. Ergo, if they say "ground," one is safe in presuming they mean RF grounding, whether achieved by direct contact or intentional capacitive coupling to a radiating surface.

I don't see a need to muddy the waters by introducing powerlines, either, to which the capacitive coupling (of a sensible installation) is going to be a fraction of a picofarad. There's no comparison with those alleged Part 15 devices, whose power and audio leads are going to provide several pF per foot of coupling to the radiating structure, in addition to what the mounting arrangement provides. And quite intentionally, because otherwise they would be only a 3m radiator working against the transmitter enclosure for a ground return, and wouldn't impress many customers that way.

Straining at a gnat but swallowing a camel doesn't seem a practical way of interpreting rules...even ambiguous ones.

73,
John

The illegality of antennas
Posted by Mick Reed on April 18, 2001 at 00:35:34

I have heard the heavyweights in the part 15 crowd (in lowfer@qth.net, lwca board)talking about possible allocation for amateur use. Am I wrong by saying that even the possiblilty of a ham allocation makes some of the arguments moot? If we think that amateurs might operate in Lowfer modes in a few years, why worry about so many strict legalities of coils, etc.?

Sure, if it is illegal today, it doesn't matter if it is legal tomorrow or next year. But if the current rule of thumb is 'illegal' but we are not actually causing interference or harm, why should we change it? I can't imagine that we are causing harm if we have so many 'possibly legal' setups around the country.

Don't you think that we will still have the current lowfer rule of thumb when/if the band is allocated for amateur use? I bet we all agree that the fun is in the challenge of efficiency and DXing. Even if we are breaking the rules a bit now, I know I would not have any fun if I could just crank the power to 1500 watts or build a 300 foot tower.

Sure, I would feel better if I was strictly inside the law. However, I take the most comfort in knowing that I have a clean signal that isn't beating up people's AM,TV,etc reception. Again, the amateur allocation argument.

Please comment Mick Reed

Re: The illegality of antennas
Posted by Jonathan W2MXW on April 18, 2001 at 01:39:13

The problems with an amateur allocation, at least at 160-190 kHz:

No more unattended beacons (very likely).
ARRL/FCC telling us what modulation modes we can/can't use (even more likely).
More, not less, rules and regulations.
People wishing to operate QRP will be run off the band by the high-power boys.
Those wishing to break into LF operating will have to get an amateur license, no more unlicensed operation (the assumption being that there will be no more Part 15).
Even if there is still Part 15 after such an allocation, one whimper of "interference", whether or not substantiated, from a DX-crazed appliance operator and said Part 15 operator goes bye-bye.
No more opportunity to conduct the amazing experiments now being done with the current limitations.
All for an amateur LF allocation, just not @ 160-190 kHz.
'Nuff said.

73 de W2MXW

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Re: metal roof antenna
Posted by Jonathan W2MXW on April 18, 2001 at 02:17:24

There's nothing obvious about that at all. And in point of fact, a loading coil does no such thing.

How else do you define "electrical length"?

Then, using your logic, *no* transmitter is legal; you might as well pull the plug and call it a day.
It is incorrect to assume they mean RF ground via a capacitance since the words "lead" and "connection" are used; it may seem like splitting hairs to you but it is a big difference to me. It implies a physically continuous connection (this is normally what is meant by "ground lead", now who's splitting hairs?) C'mon, you're an engineer, you telling me you've called capacitive coupling a "ground connection or lead" in the past?
As I said I am awaiting a response from several contacts on this but I believe it will be in our favor.
Otherwise, the manufacturers would all be put out of business (like LPB, which happens to be friendly with that FCC official you and I discussed earlier), and my contacts which have a long and close relationship with that very same, and other FCC officials in the OET and Enforcement and make and sell these units which we have picked apart in the minutia of detail with Type acceptance people as 100% legal and compliant. Oh, and don't forget the hundreds of people around the country using these transmitters who would have to shut down too.
If you don't believe me about powerlines I invite you to try it with a rigged-up transmitter and your fave receiver and see for yourself.
I mean overhead distribution lines, not power supply leads to the transmitter. As long as they are in the lambda/2pi induction field you get coupling. Of course you'd get it to the power/audio leads to the xmtr. too but for the fact that we use chokes on the audio/power leads to the transmitter to prevent radiation from them in accordance with conducted emissions standards (subpart B). It is necessary for full compliance. So radiation from audio/power leads is a non-issue.

Straining at a gnat but swallowing a camel doesn't seem a practical way of interpreting rules...even ambiguous ones.

Seems like your "gnat" is my "camel", and vice-versa!

73, Jonathan

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Re: metal roof antenna- electrical length of coil
Posted by Jonathan W2MXW on April 18, 2001 at 02:59:49

I don't think anyone can argue on the meaning of "electrical length". As you point out, Mick, it would be far in excess of the legal limit if used as a criterion for compliance by a given jurisdiction.
The whole point here is, how do you define what is a "loading" coil versus a "tuning" coil.
The commercial rigs I mention do have coils, they are in the box, not the antenna. So they're called tank coils. My colleague who manufactures these units, and others I know as well have been specifically told that a transmitter would never even be considered for Certification if it had a coil in the antenna proper whose electrical length exceeded 3 meters. Only transmitters for operation under Part 15.221 paragraph (b), Campus Free-Radiate are sold with loading coils in the antenna (but they don't have length limits electrical or otherwise to comply with).
To my knowledge there is no unit claiming to be compliant with Part 15.219 on the market with a loading coil in the antenna (and if it had it's Cert. would be rescinded).
Also to my knowledge, each and every single unit on the market has a coil, but always in the box.
But the coil when in the box is not considered a loading coil according to their terminology.
Even though it is of a different ilk, what's the "tank coil" in the FM mic you mention? See what I mean?
The transmitter has to have an inductor somewhere to work at all, it just depends on where you put it and what you call it.
Strange, but true.
And these commercial units are Type accepted (and no, no funny business, it is 100% valid, I'll send the cert. number to anyone doubting this so you can check on it yourself). The mfr. is very close with FCC people in the OET.
Seems this whole thing which started out as what was intended to be a casual mention of a rule interpretation I found interesting got blown WAY out of proportion...

73, Jonathan

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Re: The illegality of antennas
Posted by Donald R. Moler on April 18, 2001 at 03:11:41

I like the 1750 meter band the way it is...one watt..15 meter vert. And we should all follow the rules and compete on an even basis. All the DX contacts made with a station operating outside the rules should be thrown out and not be published in the Lowdown or any where else. I am going to try to get the Dx record on this band operating within the rules. I think I can do it because of my past experence with antenna design. When I read about the Alantic crossing that takes a week with 100 watts input and 350 mw ERP.....This makes me sick...If these guys can't build an antenna with a better efficency they don't deserve any kind of acknowledgment. Hell! if one puts a wet string on a rock he would do better then they did...
I just put up my three foot loading coil with my 40 foot top hat on a 7 foot test stand in my front yard. I put this monster up on this stand so I could work out the bugs before I put it up in the back yard on a 30 foot tower. We have been having bad weather and I have not been able to get much done on it. The weather is going to break this week so I will be on the air with 100 mw and this ten foot vertical. I will offer my advise to all of you " build big loading coils for this band" The "Q" goes up with size untill you reach about 2.5 feet diameter for this freq.( broad statment) Skin depth is about 6 mils at 180 kc (that is off the top of my head but close and I don't want to look it up) I use copper strap one half inch wide 20 mills thick it is light and I have lots of it. If this loading coil doesn't do it ...I will go to half inch diameter copper tubing as it is made nearby and I can get 500 feet of it. Antenna are not hard to design....think about it ...you want the antenna to radiate all the power you put into it. Where does the input power get wasted....guess what ....mainly in only two places ...the loading coil ....and the radial system....some gets lost in nearby objects so put the antenna in the clear. Go to Dayton and buy a big spool of fine wire and make your own litz wire - is one way to do it. I cover the ground with fence and put radials on top of it. I will post pictures on this antenna as soon as I get the bugs out and know the exact number of turns on the main coil and on the rotating inside coil that the motor tunes it across the band. I will try to post some construction pictures in the next few days.
Don Moler N8BKR Girard, Ohio Vonj@cboss.com

Re: The illegality of antennas
Posted by Mick Reed on April 18, 2001 at 10:39:08

I totally agree with

..All the DX contacts made with a station operating outside the rules should be thrown out and not be published ..

And I hope you do make a new record with your LF setup.
Then we have to figure that your LF setup is _inside_the_rules_, right? From what I have seen, I am honestly jealous of your antenna system, I do want to see the latest pictures and know how well it gets out.

However, I think that the concensus ia that loading coils are probably not legal. You stated that the metal roof is probably not legal. What is the difference between a metal roof, or a 40' tophat, or covering the ground with fence? Also, about your tophat. Is it 40 feet in diameter, or radius? is the tophat a single strand, or are there several pieces that come out from the center? I think as a group we are still uncertain about what 'inside the rules' means.

I figure it's about time to move this thread somewhere else. I think we are cluttering up the message board. Am I right?

Thanks,
Mick

Sun spot detection use phase comparator
Posted by Richard Arndt on April 18, 2001 at 11:15:37

I have found a surplus TrueTime 60TF WWVB receiver which has the capability to charting phase changes between a local 10mhz standard and WWVB. I understand that one is able to detect sun spots with this set up. So, I am looking for information on how to do this and what to look for.

Thank you,
Rich - WB4TLM

Re: metal roof antenna
Posted by Mick Reed on April 18, 2001 at 11:57:54

Hey, Jonathan: could you point to where you have 'electrical length' from? I'm not trying to doubt you, but I can't find this in my copies of Part 15. Or did this come directly from some FCC people? Remember I'm not an engineer yet, maybe I should know this already..

Thanks.
Mick Reed

P.S. I wonder how many replies until they spill off the end of this web page?

Re: FWD: Re: WOLF bandwidth suggestions
Posted by Mick Reed on April 18, 2001 at 12:29:26

If the reference stream was averaged over a longer time, would that mean that the actual message would need to remain the same during the period? I don't know if that's what you meant, but if so, I suggest against it. That method wouldn't save us any time since we would have to transmit the message for a longer time anyway.

I see that in the future, we will want a more 'real-time' WOLF where we may be able to send single 'packets' for QSOs of greatly reduced time. For example, we see the band opening up early in the morning for 15 minutes. If WOLF could read a wav file that is being continuously captured in real time, we could see results (messages) in real time, every 90 some seconds. Using the serial port perhaps, we could then type a reply, which WOLF encodes and sends out on the TX.

Re: metal roof antenna
Posted by John Davis on April 18, 2001 at 15:19:13

I wrote:
There's nothing obvious about that at all. And in point of fact, a loading coil does no such thing.

Jonathan wrote:
How else do you define "electrical length"?

Better ask Mr. Reed. I've never seen a definition of that term in connection with an inductor in any textbook I've encountered.

73,
John

Re: metal roof antenna
Posted by Lyle Koehler on April 19, 2001 at 10:55:06

John Davis wrote:

Yes, the rule "clarification" regarding MedFER transmitters that appeared in RADIO WORLD was posted to the Lowfer reflector on March 3, 2000 by John Andrews under the subject "Interesting Letter".

The discussion of what constitutes a legal LowFER antenna re-surfaces about twice a year on this message board and/or the Lowfer reflector. The FCC letter regarding MedFER antennas was the first *published* FCC opinion I had seen on the subject. If this rule interpretation applies to the 160-190 kHz band, there are not many "legal" LowFER beacons on the air. Nothing is said in the MedFER interpretation about the dimensions of top hats, the length of ground radials, whether it makes a difference if the radials are elevated, on the surface, or buried, etc., etc. If anyone asked, I would not be surprised if the official FCC position would be that extended ground systems are also illegal.

The kicker in the rule interpretation is the statement that "In other words, this rule is designed to keep the practical transmission range no greater than about 250 feet". Nearly all Part 15 devices are intended only for very short-range applications, and it would be surprising if the FCC ever intended to make exceptions for devices operating in the 160-190 kHz and 510-1705 kHz ranges. We have operated for many years under a "don't ask, don't tell" policy, and have been permitted to exist because even the most blatantly illegal operators have not put out a big enough signal to bother anybody :-)

Re: metal roof antenna
Posted by Mick Reed on April 19, 2001 at 12:29:03

Okay now, nobody thought I was defining electrical length of an inductor, I was asking about it to make sure what was being talked about. Electrical length is applied to transmission lines and antennas, however, which we are discussing all at the same time.

I was at the FCC ASD checking out the expanded AM band and saw the reference to an AM broadcast tower being 90 electical degrees tall.
(http://www.fcc.gov/mmb/asd/decdoc/letter/1997--04--18--attachC.html) (question 9)

Re: metal roof antenna
Posted by Mick Reed on April 19, 2001 at 12:42:11

Let's look at that 250 foot 'rule' as it applies only to MEDFERs. We would have to use 'practical transmission range' to mean 'receivable by a good consumer grade AM receiver' or something similar.

Could someone tell me whether our current MEDFERs would follow this interpretation? I honestly have no experience there.

Also, there is the question of how this would apply to Lowfers. Surely even if we followed the most strict interpretation of 15, someone could still pick up the Lowfer station on an amateur radio at 251 feet. Otherwise, what other consumer equipment would notice the Lowfer signal? 'practical transmission range' IMO means receivable by consumer appliances.

I find it difficult to beleive that computer monitors or switching power supplies or TVs or radios would be thumping with morse code. I only base this on experience with my own setup, which has put out some evil harmonics at certain times in its construction. I have to admit that during some testing, I put more than 1 watt into the final for brief periods. I don't have cable, so any garbage I was putting out with LEA had free reign to jump into all my appliances.

Re: Parts Sources
Posted by Nick van Vonno on April 19, 2001 at 13:05:34

Anyone know of a source for a 4.5MHz ceramic resonator to control a NE602?

Thanks in advance,

nvv

Re: metal roof antenna
Posted by Mick Reed on April 19, 2001 at 13:14:20

I agree - 'length of coiled wire' is ambiguous.

If an inductor is 'coiled wire' then building any transmitter would be hard.

On the other hand, they might want to call a solenoid 'coiled wire' as it does have external flux. (this is why we want them off the ground, right? TX loops are solenoidal..)

Then we could make our Lowfer coils into toroids, even if they are air-core! The toroid has much less external flux. It could still be a loading coil without being an antenna, transmission line, or wire..

What is the length of my car (including ground system)?
Posted by Bill Ashlock on April 19, 2001 at 14:01:44

After scanning through another round of arguments over what is the meant by the FCC's "total length" limitation I have decided to re-define the length of my automobile as 1 mile rather than the 9ft or so that I used to think it was. I have to, according to some, add in all the copper wire in the electrical system, including the many relays, motors, coils in the radio, and all the 100s of feet of connecting wires.

Doesn't this sound supid? Well, that's what I think about some of the arguments on this site over the last few days on this issue. Why can't we think of the antenna "length" as the geometric length or height of the highest point of the total antenna? It makes a lot of sense to me from a technical standpoint because this puts a limitation on the far field radiation controlled by the parameters that count - the power and the actual radiating member.

After a review of many pages of text and after making hundreds of far field measures on different Lowfer antenna configurations I am convinced that the height of the vertical member and current distribution on this member, are the only factors that effect radiation. I am sure that all Lowfer antennas 15M in height with near-constant current distribution (IE: reasonably large top hat) have approximately the same radiation when the loading coil and local ground loss are factured in. This amounts to ~150uv/M, for 1w input, at 2 miles for a good job of loading coil construction and ground connection (not much more for a perfect loading coil or a perfect ground).

I believe the FCC was wise not to detail all the acceptable antenna configurations (requiring pages of requirements) but to, instead, identify the one all-encompassing parameter limiting radiation at a given frequency - the geometric length.

Bill Ashlock

Class E power amplifiers - Simulation
Posted by Mick Reed on April 19, 2001 at 14:08:04

I have simulated using SPICE two 'class E' topologies. The first, by Bill C. can be found at:

http://www.qsl.net/k3pgp/Notebook/Wd5cvg/Classetx/classetx.htm

The other is found by:

http://www.ussc.com/~turner/mpm_class_e.html

Something I found about both designs is that upon startup of the circuit, the output doesn't slowly ramp to a steady state as you see in the graphs on either website.

Instead, it ramps up to some value which it oscillates about at some random, noisy rate, which is almost steady, perhaps.

I have tried two methods on either circuit: 1) Apply a square wave to the Mosfet I'm using in my circuit 2) Make a voltage controlled switch where the Mosfet belongs. I have tried to get the duty cycle exactly 50% in both designs, but there is some room for discussion there.

A secondary issue is that for the Bill C design, I must use a substantially smaller Cshunt to make the Cshunt voltage land softly. Something like 10% of the suggested value. I tried to recreate the analysis directly from the IEEE version of the article. It behaves pretty well, except for the noisy oscillation I mentioned.

Any help would be greatly appreciated. I had used the Class E with good success on my Lowfer LEA for a while, and I had to use a really small Cshunt there, too. The reason I am simulating them is that I feel better when the simulation matches the math which matches the circuit. Also, the better efficiency is worth the trouble.

Thanks Mick

Re: What is the length of my car (including ground system)?
Posted by Mick Reed on April 19, 2001 at 14:21:00

I agree - Even if they went into minute specification of what's what, people would find ways to get around the rules. We aren't dealing with a case of high treason here. As said by some on this msg board, even different local offices of the FCC would probably differ in opinion on the rule. Maybe it's best _not_ to ask.

I figure we might like to have our own specific definition that could be agreed upon by those interested in friendly Lowfer/Medfer competition. However, if we got one directly from the FCC we probably wouldn't like it. So we will have to go without a written specification and use the 'don't ask, dont tell' setup.

We all agree with the 'no interference' part, and I believe that is every Lowfer/Medfer's main concern. All the other arguments should be secondary, even though they are important too.

Re: What is the length of my car (including ground system)?
Posted by Mick Reed on April 19, 2001 at 14:31:10

P.S.: If the length of your car is 1 mile, you won't be able to get speeding tickets in it anymore :)

Re: metal roof antenna
Posted by Jonathan W2MXW on April 19, 2001 at 15:31:08

I wouldn't worry about the 250 foot thing. I could start a whole new thread on this one but it's been done to death already. Bottomline: There is NO range limit under Part 15 (other than that naturally imposed by compliance with the rules). And I have this IN WRITING from our FCC friend.
End o' story. :-)

73 de Jon

remove "diespamdie." to reply

Re: SF NDB sick?
Posted by Mike KB6WFC on April 19, 2001 at 16:21:07

Matt & Group,
We have had quite a few geomagnetic disturbances of late, so I don't know if that was the cause of your experience. NDB typically emit an AM signal. NDBs are listed by their AM carrier frequency. The ID is usually send in Morse is above and/or below the carrier frequency by 900 to 1020Hz. I live 14 miles from the SF NDB and have seen, using Spectran, just the lower or upper sideband disappear during these geomagnetic disturbances. Sometimes both sidebands disappear and the signal strength of the carrier diminishes. If you own a computer, try feeding the audio into your soundcard and give it a look with Spectrogram, Spectran, or other S/W pkg.
73 & GL,
Mike KB6WFC

Re: What is the length of my car (including ground system)?
Posted by Donald R. Moler on April 19, 2001 at 19:01:33

These antenna length arguments are not stupid....I think you misunderstood what I was trying to say and that was probably my falt for not explaining it more clearly. Let me try again. A 15 meter high ground mounted antenna with a good set of radials that are laid out on flat ground is legal. If you now raise that antenna and have the radials tilted down, the radials start to radiate. On 1750 meters the wavelength is so long if the radials were tilted down at 45 degrees (like a roof) and were 100 feet long, the effective length of the antenna would have been increased by .707 times the length of the radials or 70 feet. (it would be a little less because the radials are not a point source.) and if you went to the extrem and put the radials stright down you would have an antenna that was 15 meters high on top of 100 foot radails and we know that is not legal. We should learn to have technical discussions with out getting upset. I have my ten foot antenna on the air but the "Q" of my large loading coil is very bad. when I tested it in the basement I thought it had a low Q because it being on the floor. It could be the wood absorbed water or the fiber glass coating is bad. I will check it out to see where the problem is. At the same time I am working on a one half inch thin wall copper tubing loading coil wound on a plexiglass form. The 40 foot top hat when made with eight spokes and webbed ith aluminum wire has much more capacity than I figured, so I am tapped way down on the loading coil
Don Moler N8BKR Girard, Ohio Vonj@cboss.com

Re: What is the length of my car (including ground system)?
Posted by Lyle Koehler on April 19, 2001 at 19:57:58

Most of us agree that mounting a LowFER antenna on a metal roof, or on a hilltop with the ground radials sloping downward, will increase the radiation efficiency over the same antenna above a flat ground plane. I think we also agree that a top hat improves the radiation efficiency, that a short vertical won't work worth a darn without a loading coil, and that the position of the loading coil can make a difference. And you also need a very good ground system to minimize the series loss resistance. So it could be argued that the FCC doesn't want us to incorporate *any* of these things, because they all make the antenna work much better than a straight 15 meter hunk of wire attached to an isolated, battery-powered transmitter box. However, here is what the rules actually say:

Section 15.217 Operation in the band 160 - 190 kHz.
(a) The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed one watt.
(b) The total length of the transmission line, antenna, and ground lead (if used) shall not exceed 15 meters.

The rules don't say "height", they say "length"; and they don't say "electrical length". There is no mention of top hats, ground radials, buildings, hills or loading coils. The dictionary defines "lead", when used in the electrical sense, as a wire or cable that is used to carry an electrical current. If the rules had specified something like "ground current path" rather than "ground lead", I might interpret that to include my metal garage roof. But my roof doesn't look anything like a wire or cable. We all look at those rules and interpret them in a way that our own consciences can accept. If I wanted to accuse somebody else of "cheating", there are any number of things that I could read into the rules besides what is printed in the simple sentence that makes up 15.217 (b). However, I worry only about my own antenna; not about how much wire is in Bill Ashlock's loop or where Don Moler sticks his loading coil. If the FCC issues a formal interpretation of the rules for operation in the 160-190 kHz band that parallels the statements they made last year regarding MedFER devices, I'll consider myself to be in violation on at least two counts, and will shut 'er down immediately. The rest of you guys can do whatever you want to.

Re: What is the length of my car (including ground system)?
Posted by Donald R. Moler on April 20, 2001 at 12:10:36

Lyle, The point I am trying make is that the radial system can be made into a radiating element by sloping them down or by mounting the antenna on a roof this then adds to the length of the vertical and becomes part of the antennas radiating system. At some distant point the radial system looks like a single wire because of it's size compared to a wavelength. It is really not important except for a technical discussion and I thought I would bring it up as most lowfers did not know that one could get the radials to radiate by sloping them down. A 15 meter vertical is aprox 3.5 degrees, does anyone know what the radiation resistance is at this length? I have been trying to find the formula but no luck yet. Most of the charts I looked up don't go that low. At about 16 degrees on the chart I can see that it is about one ohm. It is not linear so I would expect it to be in the order of a tenth of an ohm at 3.5 degrees. If this is true then if one has a loading coil plus ground loss that equals a tenth of an ohm there would be a 3 db loss of signal. The other question I have is has anyone measured the field strength of their antenna and converted that to antenna efficency? I would like to know what is a well built lowfer antenna running in efficency. Don Moler N8BKR Girard Ohio vonj@cboss.com

new kid on the block
Posted by Bill in RTP on April 20, 2001 at 13:21:02

This really looks like fun. I am Bill, AB4OB in Morrisville, NC. I am going to AES tomorrow to look for a VLF receiver (What-me impulsive?). Maybe I can set up a sked if someone likes. Guess we are allowed 1 watt, I suppose this is looking into 50 ohms. We must not be radiating very much with such a teeny wire relative to the wavelength. The guy in the next office has a phD in antennas and he says I should maximize the current on the wire. I am sure that is the basic idea of the humongous loading coil discussed later down the forum. I know of some op amp circuits which can simulate inductors; perhaps these could be used instead of loading coils at these small currents. It would be fun to launch a VLF transmitter on a balloon. I bet it would have quite a range. Since I live next to RDU airport, I better not try it. 8-) I had a QSO back in the late 80's using a TTL gate into a 12 foot piece of wire over a DX of about 6 miles. That was really fun. I tried to subscribe to your mag but the link doesnt work.

73's AB4OB

Re: What is the length of my car (including ground system)?
Posted by John Andrews on April 20, 2001 at 13:37:50

Don,

I believe the old expression for the radiation resistance of a short vertical wire is:

R = 10 * G^2

Where G is the electrical length in radians.

That should give about 0.03 ohms for a 15 meter wire at 180 kHz, assuming my math is correct.

John Andrews, W1TAG

Noise and loops and K9AY
Posted by Mitch on April 20, 2001 at 16:28:04

Hello all:
While observing the AMRAD beacon ( usual daily check and routine) I started comparing my new K9AY (KAZ ) antenna with the K0LR/KI0LE open wire loop. The results were verrrrrrrry interesting - as I was able to see a complete signal with one antenna - and lots of noise and questionable signal with the other antenna. For a few dollars and a tree limb, this K9AY is really performing. I have placed pictures of the capturedsignal on http://technology.fanshawec.on.ca/eltn225 and hope they help some of those with noise problems such as I have.

73 Mitch VE3OT

Re: What is the length of my car (including ground system)?
Posted by Lyle Koehler on April 20, 2001 at 16:33:48

Yes, I agree that the sloping roof (and the rest of the building, in the case of my antenna installation) looks like an extension of the antenna, and contributes to the radiation. That was one reason for suspending the LEK antenna above the garage roof, although the primary reason was simply convenience and laziness -- I didn't have to bury a bunch of radials and don't have to mow around the antenna.

The radiation resistance of a short, straight vertical antenna above a flat ground plane is 400 times the square of the height divided by the square of the wavelength. For example, a thin 15 meter vertical operating at 185 kHz (wavelength approximately 1622 meters) has a radiation resistance of 0.034 ohms. When a top hat is added, there isn't any simple formula that I know of, but the radiation resistance can be calculated fairly accurately with NEC or MININEC based modeling software. A description of the modeling process and several antenna examples are given on my web page at www.computerpro.com/~lyle.

Not many LowFERs have actually made accurate measurements of the field strengths from their antennas. Bill Ashlock may have some numbers for his loop setup, but otherwise I don't know of any. A good estimate of efficiency can be obtained by using measurements of antenna impedance to give the system losses, combined with computer modeling predictions of radiation resistance. Bill Cantrell's TEXAS beacon is probably the best "legal" LowFER vertical installation in operation today. It has a 10-foot top hat radius at a height of approximately 40 feet, a loading coil Q in excess of 750, and an extensive ground system. The radiation resistance of his antenna, as predicted by a MININEC model, is about 0.045 ohms, the ground and wire losses are around 5 ohms, and the series resistance of the loading coil is about 4 ohms. (The ground and coil losses are from an article by Bill in the March 1999 LOWDOWN, and I don't think there have been any significant changes to TEXAS since then). The efficiency of the TEXAS antenna is therefore about 0.5 per cent. Sounds awfully low, but it is very tough to beat because of "ground" losses, which include the effect of trees and other lossy objects in the induction field of the antenna. My losses are in excess of 20 ohms, so LEK is not as efficient as TEXAS even with the increase in effective height from mounting above the metal building.

According to my modeling results, your (Don Moler's) planned antenna system with a 40 foot diameter top hat at 30 feet should have a radiation resistance of .04 ohms. The top hat improves the current distribution, but reducing the overall height to 30 feet eats up some of the gain in radiation resistance. However, the big top hat also reduces the reactance to about 2000 ohms, as opposed to almost 6000 ohms for a 1.5 inch diameter, 15 meter high straight vertical, so the loading coil losses will be correspondingly reduced. The trick is to get rid of those darned ground losses!

Re: What is the length of my car (including ground system)?
Posted by Donald R. Moler on April 20, 2001 at 16:55:41

John, Thanks for the formula. The formula I found gave the field strength of the E field in millivolts per meter for a given current in a given size vert. If it is as you figured out (.03 ohms) then my idea of a large size high Q loading coil has some merit and I think I will go to the onehalf inch copper tubing for the coil instead of this half inch copper strap that I am using. All I can say is WOW!...If my total antenna resistance is .3 ohms then I am throwing away about 90 percent of my power. ( Am I reinventing the wheel?) I do like the idea of putting the antenna on top of my barn and putting the radials down to the ground and getting them to radiate as this will add to the effective height of my antenna increasing the radiation resistance and therefore the efficency of the antenna. Lyle is right the rules did not define the antenna very well. My barn is about 25 feet high and I did have an antenna on 160 meters mounted there. It rained here today and my coil got wet and my power dropped by 10 db. I have to put a cover on my loading coil.
Don Moler N8BKR Girard, Ohio vonj@cboss.com

cw reception
Posted by Edgar Heinen on April 20, 2001 at 18:26:30

Does anyone know if a cw signal can be copied as per the theory shown in the classical literature abounding in the libraries? Like at an Eb/No of 1 or 2 does it mean copy?
Dr Richard Blahut in his book (and others) say that the Ber at an Eb/No of 2 under rayliegh fading is 0.250000 out of 0.5000000 or 50%. This would assume some kind of copy, however poor. Here we are missing half of our characters, for NONCOHERENT CW reception.
Regardes,Edgar Heinen.

Re: What is the length of my car (including ground system)?
Posted by Clint Turner, KA7OEI on April 20, 2001 at 19:17:18

Back in the late 1980's, Mark Mallory (MPM) put up what was probably the most efficient LowFER beacon (efficiency-wise) at the time. It was rather elaborate, taking (admittedly) somewhat liberal interpretations of the part 15 rules. The closest present-day beacon is probably one of the Texas beacons.

This beacon was atop the metal roof of an office building. Atop a 35 foot Rohn-25 tower, he mounted the beacon transmitter, and atop this was a 15 foot aluminum pipe (total of 15 meters - as the "grounded" tower was clearly radiating - a center-loaded vertical, if you will,) topped with a 15-20 foot radius "guyed" tophat.

This beacon used his own Class-E transmitter, now described at:

http://www.ussc.com/~turner/mpm_class_e.html

He also used an auto-tuning variometer that kept the system resonant under rain/snow/dry conditions using a stepper moter on the variometer coil. This also had the effect of maintaining a precise 1 watt input power level.

Having access to quite a barrage of high-end test gear, he was able to actually measure the field strength directly (using known-calibrated field-strength meters) as well as predicting radiated efficiency using measured antenna and coil parameters - using a NEC-type program that he himself had written especially for his LowFER antenna. Surprisingly (to him) both sets of numbers were nearly equal.

The *measured* efficiency of his system was approximately 1 percent - corresponding to an EIRP of about 10 milliwatts.

Getting this efficiency was a rather hard-fought effort: The loading coil was a basket-wound type (using the optimum height-width proportions) using heavy-gauge litz wire (using #40 strands, I believe) as well as the "auto antenna tuner" keeping the system at optimal resonance.

The result was well worth the effort: It could apparently be copied during daylight hours in California (approximately 600 miles.) and was frequently copied in Oregon. (These sort of details were reported in the Western Update in the late 1980's.)

My approach to interpretation of the part 15 rules is similar to his - somewhat liberal. The 15 meters of the antenna is the vertical radiating part, and the tophat and loading coil are part of the matching network. The ground (that "reflective" part that, ideally, would be an infinitely-large conductive sheet underneath the antenna) is *not* included in the antenna height calculation - the fact that the antenna wasn't planted on a silver-plated hilltop is irrelevant. (Anyway, it would be silly to assume that a significant portion of the radiation occurred in the vertical steel structural members of the building considering the antenna configuration anyway and that the height of the building was a part of the 15 meter height: That would be like saying that putting a beacon (and ground plane) on a mountaintop was illegal because of the height of the mountain being greater that 15 meters HAAT...)

From what I remember him telling me (and what I've read about other LF/VLF antenna systems) extending the diameter of ground system much past 2-3 times the antenna height (the tophat diameter being less than the antenna height) puts you well up on that theoretical asymptotic curve showing the difference between no ground and an infinitely-large perfectly conducting one. Since the roof of the building the antenna system was on was quite a bit larger than the diameter of the tophat, it was, for all practical purposes, "infinetely" large. (That is, were it bigger, it would have had no significant effect on the radiating efficiency. This does not take into account the propagation of the wave to its ultimate far-field destination and the commensurate losses over imperfect ground... That's a different matter altogether.)

While the validity of such an approach to interpreting part 15 rules (for LowFER and MedFER) could be argued, doing so would be simple reiteration (so I'll be brief) except to say that I'm confident that the *real* intent of the FCC rules is to prevent effective unlicensed broadcasting (i.e. Playing "D.J.") as well as preventing harm to licenced stations: In MedFER and LowFER service, these two points are precisely in line with the our sole purpose for putting up a MedFER/LowFER beacon: We have no interest in broadcasting and it is in our best interest to avoid QRMing any licensed entity, as that would reduce the liklihood of our being heard. From my experience, even a fairly efficient MedFER station (such as mine) while radiating far more than the FCC probably intended (owing to deliberately efficient grounding and matching) doesn't have more than several hundred yards of "useful" range when using consumer-grade receivers in typical (noisy) household environments - hardly competition to broadcasters.

Clint KA7OEI

Re: new kid on the block
Posted by Robert Bicking on April 20, 2001 at 19:45:14

I have built and used active filters using capacitors and op amps in lieu of inductors in many applications but doubt that they would exhibit the Q of a good Litz wire air core coil. The problem in LF is that due to the requirement for a 15 meter max antenna length, the radiation resistance is only a fraction of an ohm, whereas the coil resistance and ground resistance can easily be 10 ohms each or more. Your friend is exactly right, the power radiated is I^2Rr, so by minimizing ground and coil resistance, the current and radiated power can be maximized. I think the problem with a balloon antenna would be that you wouldn't have a ground plane and thus, the radiation would be close to nil. There is a reason that everyone uses verticals with big top hats, excellend loading coils and big ground planes. You might take a look at my website which is listed under links on the LWCA page and also at www.qsl.net/w9rb/ for a description of a LowFER antenna.

Re: What is the length of my car (including ground system)?
Posted by Donald R Moler on April 20, 2001 at 21:26:30

Clint, On Mark Mallory's set up. I think one has to think of the wavelength of 1750 meters. The roof and the building were very small compaired to the wavelength and currents were flowing up and down the buildings steel structure and adding to the radiation of the antenna ( these currents may be small) so I am sure the FCC would consider this part of the antenna if they looked into it in fact I am going to write the FCC and get a better definition of the antenna height. I would really like to put my 40 foot top hat on top of a 15 meter tower so I will ask them about that. I would also like to know if I could put up a 100 foot tower and put my loading coil and top hat on top of it with radials coming down from the 50 foot level at a 45 degree angle. This would raise my radiation resistance by a factor of four or so and give me an advantage. Even though the radials are radiating they won't be part of the antenna cause they are called radials. In fact I think a 200 foot tower with radials coming down from the 150 foot level will work better. But getting serious for a minute I do think we have to get a better definition of antenna height from the FCC. I am quite sure they will say anything that radiates will be considered part of the antenna. I do have a variometer coil in my big loading coil and I think it is a must on this band since I am xtal controled. As soon as I find a scanner I will post some pictures. Don Moler N8BKR Girard, Ohio vonj@cboss.com

Re: What is the length of my car (including ground system)?
Posted by Bill Ashlock on April 21, 2001 at 00:22:49

Lyle,

Again, what we need is a reasonably accurate measuring stick to determine the truth in our mathematics, modeling, and construction techniques. Hope to help out here in the near future with a PCB blank and plans for constructing a portable SVM and an E-probe antenna including a uv/M calibration procedure using simple test equipment.

Bill Ashlock

Re: metal roof antenna...and something new!
Posted by John Davis on April 21, 2001 at 01:21:09

:: I wouldn't worry about the 250 foot thing. I could start a whole new thread on this one but it's been done to death already. Bottomline: There is NO range limit under Part 15 (other than that naturally imposed by compliance with the rules). And I have this IN WRITING from our FCC friend. ::

I have to agree 100% on this. Let's remember that the input power/antenna length limits are an ALTERNATIVE provision; specifically, they were an alternative to the rest of the Rules which _do_ specify range in terms of measured signal strength. As an alternative provision, there is NOTHING shady or underhanded about achieving long range with Part 15 operation provided the limitations are being observed to the letter.

Jonathan and I may disagree on what some of the letters of the rule mean. To me, an RF ground is an RF ground, and an inductor is an inductor, not a long piece of wire. However, we both agree that traditional Part 15 operation is a legitimate activity, and is explicitly provided for in the law.

As for statements of intent from OET, these are guidelines, not final "decisions." The anticipated effective range of 250 feet is not itself a criterion of legality and was never intended to be, so one need not nitpick over it. It was just a guess as to what an ordinary experimenter might achieve with casual, everday receiving apparatus.

OET's opinions can be (but don't always seem to be) the basis on which inspectors enforce existing Rules. But they do not actually have the weight of law behind them unless or until they are formulated as Rules and voted upon by the Commission, or unless the Commission makes them a footnote to the Rules through a Majority Opinion or a Report and Order.

Also bear in mind, the people in OET now are not the same ones there when the alternative provisions were first codified decades ago. Current interpretations may differ from earlier statements, and there have even been instances of outright historical revisionism too.

Now for something completely different--sort of. Wonder what part of whose rules "Cadillac Radio" in Las Vegas is operating under on 1710 kHz, carrying full-time advertising for Cadillac cars??????? Seems to be all over town, or at least the parts I've been through today, with the same low fidelity as TIS/HAR.

73,
John

Re: What is the length of my car (including ground system)?
Posted by Lyle Koehler on April 21, 2001 at 10:17:26

A calibrated E-field probe would be a very useful project. I also like Dick Rollema's magnetic probe design at http://www.lwca.org/library/articles/pa0se/fsm.htm A magnetic probe is not influenced by nearby objects and height above ground to the same extent as an E-field probe, which would make it easier to calibrate and use.

Re: metal roof antenna...and something new!
Posted by Jonathan W2MXW on April 21, 2001 at 11:44:13

"Cadillac Radio"...totally illegal, no ifs, ands or buts. That's why they aren't listed on my Part 15 site.
The FCC, both Enforcement and OET, are in agreement; and have clarified this point numerous times to colleagues who've asked: operation at 1710 kHz is NOT permitted.
But, apparently if you have enough $$$$ and clout and connections and so forth, *anything* is legal in this country (especially in 'Vegas...c'mon, hookers, excuse me, "women of the night", know what I mean? :-)

73 de Jonathan

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Re: cw reception
Posted by Robert Bicking on April 21, 2001 at 20:43:47

From practical experience, I know that cw can be copied at much lower S/N ratios than SSB. There is a reason that most DX on 160M is via CW and if you multiply the wave length by 10x, the noise increases and the propagation decreases (LowFER band at 180 kHz).I know what my ears tell me! As a practical example, how come reception of LF broadcast stations from Europe is relatively rare in the USA, excepting from the east coast, when they run several megawatts input to some pretty impressive antennas.

Re: What is the length of my car (including ground system)?
Posted by Tim Brannon on April 21, 2001 at 22:29:13

"...in fact I am going to write the FCC and get a better definition of the antenna height."

Gentlemen,
My favorite saying:
Its always easier to get forgiveness than permission.

If you ask them this, they will say No, if you get an answer back at all. While there are commercial interests who have a stake in the interpretation of 15.219, we are the only ones who have any interest in 15.217. If they authorize one persons variation of the interpretation of the antenna rule, they would have to do it for everyone, or else re-write the rule extensively. Why would they want to expend resources to do that when the Amateur Radio Service already exists to support this type of operation?
Certainly the author of 15.217 never intended for it to fascilitate 1700 mile DX contacts on 185 kHz. But I'm sure that person would be (or is) fascinated that this is possible under a reasonable interpretation of his rule!!! While Part 15.219 remains useful for the purposes already discussed, the original objective of 15.217 became obsolete many years ago. If I were the engineer in charge and I realized that staff time was being eaten up answering letters like this, I'd simply recommend that this rule be deleted. Need I say more?
Let sleeping dogs lie.

Re: What is the length of my car (including ground system)?
Posted by Mick Reed on April 22, 2001 at 01:37:10

"...in fact I am going to write the FCC and get a better definition of the antenna height."

I have to agree that writing them is scary at best. I was going to suggest against contacting them also.

Sure, we'd all like to have certain questions answered, but it's hard to beleive that we could get any info that would be really official.

I saw an news report on television about a recent Californial law regarding assault rifles. A gun owner living in a different state wrote to the ATF asking if a gun he owned was defined as an assault rifle. He got a response, the gun was not defined as an assault rifle.

He then contacted some agency in California to make sure that they agreed, since he was going to move there. He received another response, this time from California that the gun was allowed.

After moving to California, many months later he was contacted and the gun was confiscated. He was charged with a crime (I think a felony) even with all the okays he had received about the gun earlier.

I don't know how the whole thing was resolved, or exactly how true it was. At the same time a police officer was also being charged with some crime regarding a similar rifle.

You can see the parallel. I suspect that unless the response to a letter to the FCC was a new Part 15 chapter or revised Part, published nationwide, it wouldn't matter what someone at some office said in a letter. It could always be reversed by someone else, in another area of the country.

If 160-190 was important to them at all, they would use it for something else! It isn't worth their time to bother with it, otherwise they would have written a very specific rule.

TEXAS Beacon
Posted by chris steele KG4LQZ on April 22, 2001 at 10:50:26

I am looking to make contact with the operator of the TEXAS longwave beacon. I am active in longwave dxing and live real cllose to the TEXAS beacon location so if you get this message Mr. Cantrell drop me a line, I wiould really like to look at your setp up close...Chris Ft. Worth---Western Center Blvd and 35 W

Re: What is the length of my car (including ground system)?
Posted by Bill Ashlock on April 23, 2001 at 18:30:18

Lyle,

Yes the magnetic probe (H-probe or loop antenna) is also a good tool for the reasons you mentioned and can be calibrated and connected to my SVM. However, I frequently find that holding the loop and tuning the receiver at the same time to be a bit cumbersome. If certain rules are followed, such as going for accurate measurements only when dense tree coverage is > 200 ft from the antenna, the E-probe measurements come out to be reasonably accurate and easy to make. If an E-probe is mounted to a car and the system is re-calibrated all you have to do is drive around and make measurements with the engine off. The major problem for both approaches is powerline interference and it turns out shopping center parking lots (during the day), school playgrounds, and cemeteries have low interference levels.

BTW, attenuation factors due to terrain and soil conditions that are common to the AM braodcast band as described to me by John Andrews (long time Engineer for WTAG) are much less pronounced at 1750 meters. My measurements even indicate mountain valleys have about the same distant signal levels as mountain tops.

Bill WA

Re: Noise and loops and K9AY
Posted by Keith Ballinger VA3QF on April 24, 2001 at 09:42:43

I had been looking at the K9AY for LW and MW reception, but had been discouraged by comments from Wellbrook that the horizontal elements had to be kept at least 1 foot above the snow - a bit difficult to maintain this in Eastern Ontario! Have you found this to be an issue - or do you dig the elements out of the snow?

back issues of Lowdown
Posted by Bill in RTP on April 24, 2001 at 06:27:26

Is there any way to obtain back issues of Lowdown Magazine?

tnx es 73's

Bill AB4OB

Re: back issues of Lowdown
Posted by John Davis on April 24, 2001 at 10:39:31

For the past few years' issues, the publisher can supply copies. Contact him directly at the address on the back of the publication.

Farther back than that, you would need to find a member who might let you make copies of his back issues...at least for now. We are attempting to release back issues on CD-ROM some time this year.

73,
John

Re: back issues of Lowdown
Posted by Bill in RTP on April 24, 2001 at 12:58:37

Many thanks John. The articles and archives on this website are invaluable resources too. Nice job.

Bill in RTP NC AB4OB

Re: Noise and loops and K9AY
Posted by Mitch on April 24, 2001 at 21:46:44

Hi Keith:
I have been using home-brew K9AYs and now the "squashed K9AY" or KAZ over the past winter. Had between two and three feet of snow in the back-yard this winter, covering the bottom elements, and the ground counterpoise. I could notice no difference. I certainly would not let this "requirement" stop me from using this excellent antenna. I have added further files and reference links on the web page listed in my original post, and these may interest you in your experiments. I just threw a rock/fishing line over a low (20 ft ) branch... tied it to a piece of wooden dowel, and raised the antenna. The antenna is actually draped through branches and certainly is not a perfect delta shape !! The whole exercise took less than an hour - but, as I note on the web site - you really need the preamp on LF ( not on broadcast and HF ).

Hope this helps.

73 Mitch VE3OT

Part 15 Antenna Discussions
Posted by Mike KB6WFC on April 25, 2001 at 16:14:14

Hi,

Would a legal length vertical antenna mounted on a hill with drooping radials running down the hill be interpreted as legal?

Would a legal length vertical antenna with a vertical parasitic element .2 wavelength or so away from driven element be legal? What if the existence of the vertical parasitic element existed in this proximity by coincidence because one couldn't get the bandwidth from a single antenna for recieve?

All regulations are vague, and the word of the regualtion is never adequately defined until some legal recourse forces intrepretation under the particular circumstances in question.

Best 73,
Mike KB6WFC

Re: Part 15 Antenna Discussions
Posted by Donald R Moler on April 25, 2001 at 19:03:58

I think logic tells us how the FCC would rule on a 15 meter vertical antenna mounted on a hill with long radials slooping down at a steep angle and transmitting on the 1750 meter band. The radials would radiate electro magnetic energy very efficiently and therefore be considered as part of the antenna and if we could find the right hill and place radials down one side ...We could call it a hill-side-radial-assisted antenna and patent it. On my monster antenna I increased my power to one watt at 180 kc an as I keep adding radials this baby is starting to sing. It is hard to keep the antenna tuned to the transmitter frequency as I don't have the internal coil hooked up yet and the 40 foot top hat is too close to the ground (ten feet) giving me an antenna Q that is too high so I ruff tune it by moving a coil tap and then moving an aluminum ladder that is laid against the antenna stand. I can see that I am going to need a servo system installed to tune the coil. I have the beacon on when I am not working on it. If anyone hears this ten footer let me know.
Don Moler N8BKR Girard, Ohio Vonj@cboss.com

Re: Part 15 Antenna Discussions
Posted by Mike KB6WFC on April 25, 2001 at 20:15:10

Hi Don,

Been reading the mail on your antenna development. Hope it works, but I have to admitt I have my reservations. Have you seen this article: http://www.cebik.com/gp2.html ? It shows that much gain is to be lost by having a top hat larger than the vertical. Perhaps it is a computer modeling anomily, but it may be worth a look-see.

What mode is your beacon emission?

Best 73,
Mike KB6WFC

Re: Part 15 Antenna Discussions
Posted by Donald R Moler on April 25, 2001 at 21:12:12

Mike, The top hat on this antenna is forty feet and I am going to mount it on top of a fifty foot tower in the back field. Right now the antenna is mounted in the front yard and is on a test stand that is seven feet high and the loading coil is about three feet high equaling ten feet total. Donald Moler N8BKR Girard, Ohio

Re: 74HC4059's DATA
Posted by Arif Deshmukh on April 26, 2001 at 10:12:46

I am intrested in application notes on CD 4059.

Re: Part 15 Antenna Discussions
Posted by Donald R. Moler on April 26, 2001 at 19:08:43

Mike, At the moment my mode of operation on the beacon is cw at about ten wpm. I am going to try syncronous detection when I get this antenna at the fifty foot level. Thanks for telling me about Cebik. I looked up the web site and wrote him a E-Mail. Lyle and someone else came up with the figure of an Ra of .034 ohms for the radiation resistance of a 50 foot vertical at 180 khz. Off the top of my head I thought it would be much higher. So It means that I will go with a larger loading coil. Right now I am debating between a one half inch diameter copper tubing and three quarters tubing for the windings on the loading coil. The differance in cost is quite a bit and I am wondering if the radial system will dominate the resistance in the circuit making the differance between onehalf inch and three quarters not worth the larger size.........Can someone help me here and do some computer modeling.....at least offer some suggestions as I hate to go off on another tangent.
Don Moler N8BKR Girard, Ohio vonj@cboss.com

Re: The illegality of antennas
Posted by Tim Pauly on April 26, 2001 at 19:08:52

I backed out of all these arguments last year when I was heavily criticized by some folks for a two-day experiment I wanted to do. Oh well. But in any case, I'll throw my $.02 in now...

I agree. Keep 1750 the way it is. As it is now, it's a real challenge and turning it into another ham band will make it so easy it won't be fun anymore. If I want a two way QSO I'll get on my Yaesu on 80 meters and my 250 foot longwire and have at it.

As far as the legality of antennae with loading coils, using fences & roofs for gorund planes, etc: Well, use common sense. I haven't heard of anyone getting in trouble for adding a loading coil to their 50 foot vertical.

If we were all honest, I think we'd agree that this hobby wouldn't be a hobby at all without such things, because there'd be no signal whatsoever. I can testify to that. I have experimented with several antennae, including (oh my!) a 500 foot longwire that didn't radiate more than a mile!
Don't bother to criticize that one. I put it on the air for about an hour or so to see if it would actually radiate better than my vertical. Guess what? It didn't. But I'm sure there are some strict do-gooders out there who would love to send the Feds my way because my experimenting might "jeopordize the possibility of turning the 1750 meter band into a ham band", as was told to me regarding my kite experiment (that never happened because I got disgusted with the criticism) last summer.

This hobby isn't about high power, tall towers, or anything like that. It's about having fun. Why do it if you don't enjoy it? There's a fine line there. Too little efficiency, no signal, no one hears you at all, no fun. Too much efficiency (or power), no challenge, no fun.

My $.02, and you people who have nothing better to do, don't bother sending me any critical e-mails about kites and 500 foot longwires, because they'll go in the trash bin anyway.

Tim Pauly Beacon MV

Beacon MV off the air, probably moving south.
Posted by Tim Pauly on April 26, 2001 at 19:27:01

Beacon MV is off the air, and hopefully will return this fall, but God knows where it will be.

I have been on a job search for a few months now, and it looks like we'll be moving to a warmer climate soon. I'll disclose the details this fall when we are in our new location and the beacon is once again on the air. It will probably have a new callsign since MV is associated with an area of New York. (Maybe GBH, for "goodbye Hellary") .

Tim Pauly Beacon MV
187.600 kHz.

Re: Part 15 Antenna Discussions
Posted by Mike KB6WFC on April 26, 2001 at 20:25:17

Don,

I'm not sure why your planning on using so much copper for a 1W top loaded TX antenna, but if winding 1/2" is more cost effective than winding 3/4" then why not just double up on the 1/2"? You could wind the first and second concentrically or both may share the same diameter, then just strap and/or tack them along the coil length thereby doubling capacity. With as much copper as your putting up, it should make one nice RX antenna; lots of capture area! :o)

73,
Mike KB6WFC

Re: Part 15 Antenna Discussions
Posted by Lyle Koehler on April 26, 2001 at 22:05:36

The radiation resistance of 0.034 ohms was for a straight 15 meter vertical, with no top hat. It will be considerably higher with that 40 foot hat; AO modeling results indicate that it could be slightly over 0.1 ohms. Even so, you still need to minimize losses wherever possible. Most LowFERs find that the "ground" losses dominate. For example, in my system the loading coil losses are around 5 or 6 ohms, but the total system losses (including loading coil) are over 20 ohms. It wouldn't make sense for me to spend a lot of time or money on a better loading coil. My general recommendation would be to start with a modest loading coil (Q of 500 or better, which isn't too hard to achieve) and find out what the system losses are. If they're under 10 ohms, an exotic coil might make a noticeable difference. In many installations, the copper might be better used to improve the ground plane. However, if you have trees within 50 feet of the antenna, the ground plane won't solve all the problems either, and you may have to use Bill Ashlock's loop idea.

Re: Homemade NDB receiver and matching active antenna
Posted by Aren van Waarde on April 27, 2001 at 16:59:15

Hallo Charlie,

Although I would like to post the schematic, I cannot do so since both the antenna and the receiver design are copyrighted by Elektor Electronics. However, if you send me an e-mail with your address I can send you photocopies for your private use by snail mail.

Sorry for this,

Aren van Waarde

hat capacity
Posted by Donald R Moler on April 28, 2001 at 04:14:54

The forty foot top hat seems to have much more capacity to ground than I calculated so I resonated it with a different coil and used a standard variable capacitor as a subsitute for the top hat. A ruff measurment of the distributed capacity of the big loading coil shows a little less then 100 pf. That seems to be to high so I will take another more accurate measument tomorrow. On the big coil I am using only 48 turns to resonate antenna at 180 khz with the top hat at ten feet. I would like someone on here to calculate the top hat capacity for ten feet above ground and In the next few days I will measure it to see how close you come. I now have eight spokes with wire around the outside. I will need to know the capacity of the top hat so that when I put it up at fify feet I will have the right tap on the coil and the rotating coil on the inside will cover the band. I don't think I will be able to climb the tower and make adjestments to the coil once it is up.

Again, This seems to be the way to go....Large coil and large top hat as this keeps the current at Max over the whole fifty feet. I don't think Litz wire will make much difference over the copper strap or tubing for the coil. With a large top hat I don't need much copper on the coil and I am near Ra with the total resistance which means the antenna efficency should be near 25% The real questions are what is the optimum size of the coil for the copper strap or the onehalf inch diameter tubing (this changes with the top hat size) and how close to the top hat does one place the loading coil and how does one design the antenna so the loading coil does not set up eddy currents in the tower or the top hat. I think when I finish this antenna I will try one with a 60 foot top hat since I already have the aluminum tubing here. My next coil will be onehalf inch copper tubing. Can someone tell me what size litz wire it takes to match this strap or tubing. I don't see what the fuss is over litz wire when I can approch Ra with strap or tubing. Don Moler N8BKR Girard, Ohio vonj@cboss.com

Re: hat capacity
Posted by Lyle Koehler on April 28, 2001 at 11:21:40

Here are some AO modeling results for a top hat with eight 20-foot radials, each 1.25 inches in diameter, and a number 8 skirt wire connecting the ends of the radials. The feed point and loading coil are two feet below the top hat, and the modeling frequency was 185 khz. A segmentation density of 800 segments/halfwave was used for the computations. I assumed that the effective diameter of the tower was 10 inches, and that a #10 wire was used between the top of the loading coil and the top hat. The model assumes that the loading coil has zero diameter and height, so coil capacity effects are not taken into account. Actual measured results will not agree exactly with the model (what else is new?), but they should be fairly close.

With a top hat height of 50 feet, the calculated reactance is 2276 ohms (378 pF) and the radiation resistance is 0.109 ohms. Lowering the top hat to 10 feet, the reactance is 1781 ohms (483 pF) and the radiation resistance is 0.005 ohms.

My web article at http://www.computerpro.com/~lyle/models/lftxant.htm provides information on how to model LowFER antennas, and includes a link to a site where a free version of the modeling software can be downloaded. I've also added a zip file containing two models for Don Moler's proposed antenna at http://www.computerpro.com/~lyle/models/moler.zip Anybody who wants to tweak the dimensions and see what happens can do so -- the tools are readily available, free, and not especially difficult to use.

The first model in the MOLER.ZIP file is called MOLER.ANT. It has zero losses and is used to determine the radiation resistance. Wire, loading coil and ground losses are included in the second model, MOLER1.ANT. The modeling software does not predict ground losses -- first of all the low-cost (or free) versions of the software can't do it, and even with the expensive software there are so many unknowns that it would take an extensive study to determine what parameters to enter into the model. However, you can enter an estimate of ground losses as another "load" resistance, and the model will take this into account in the efficiency calculation. I normally use 5 ohms for ground losses, because this is about the best that any LowFER installation has achieved in the past. With a ground loss of 5 ohms and a coil Q of 1000, Don's antenna would have an efficiency of about 1.7 per cent. This is more than three times the efficiency of TEXAS, but it's not an apples to apples comparison. TEXAS uses the "conservative" LowFER interpretation of the Part 15 rules; that the top hat radius is included in the antenna length. No, I don't want to open that pail of worms again; I'm just stating the main reason for the efficiency difference. Don's original proposal was for a 30 foot antenna with a 20 foot top hat radius, and would have an efficiency of 0.66 per cent if it had a coil Q of 1000 and ground losses of 5 ohms.

As mentioned earlier, the modeling software does not predict the effects of coil proximity to the top hat, tower, ground, etc. These effects increase as the coil dimensions are increased, and probably set a limit on the effective coil Q that can be obtained in a practical installation. Don's experiments at the 10-foot height should help to nail down some of these unknowns.

measurements
Posted by Donald R. Moler on April 28, 2001 at 14:27:40

The big loading coil has a lot of capacity to ground it is larger than a 50 gal drum and capacity couples to everything so I found a small eight inch diameter coil in the basement and used it to also measure the top hat capacity. This way I may find something I missed when I calculate the top hat capacity using the large and then the small coil and also find out what the distributed capacity of the large coil is. I put the small coil on top of the platform and hooked up the ground wire to the bottom of the coil and resonated the coil (link coupled) with a signal generator with different capacity values across the coil. 50 pf............470 khz
150 pf...........339 khz small coil with large 250 pf............275 khz coil disconnected at
400 pf............225 khz top and bottom.

I then removed the standard capacitor and hooked up the top hat then resonated the coil with the top hat connected and it resonated at 205 khz I then went back and substuted the standard capacitor to re resonate it at 205 khz which turned out to be 498 pf. from the above I should be able to calculate the distributed capacity of the small loading coil and subtract it from 498 pf, giving me the top hat capacity to ground. I measured the average height of thd top hat and it is 9 foot ten inches. I then counted the turns that I am using on the large coil and it is 49 turns. ( the total turns is 60) I then calculated the inductance that I am using of the large loading coil it is 1.475 mh and this inductance resonates at 180 khz with the 40 foot top hat. ( the extra capacity of the turns that I am not using at the top of the coil may be screwing things up) I just now thought ...why not put them at the bottom.. The top hat sees the bottom of the loading coil and short circuts the apparent currnt thereby reducing the efficency. This loading coil is not the one I started out with, it is smaller in order to fit out my basement door. I will raise the loading coil and the top hat and take another reading.....am I forgeting anything? Don Moler N8BKR Girard, Ohio Vonj@cboss.com

Re: measurements
Posted by Lyle Koehler on April 28, 2001 at 16:10:51

The measured capacitance of the top hat appears to be very close to the value predicted by the computer modeling program (498 pF measured versus 483 pF predicted) That's a disagreement of about 3 per cent, which is probably pushing the accuracy limits of the model or the measurements!

If you haven't already tried it, it might be interesting to put the loading coil out in the open, with nothing connected to either end, and find the frequency where it is self resonant. That frequency, along with an inductance measurement made at a much lower frequency like 10 kHz, should let you calculate the self-capacitance of the coil.

distributed capacity
Posted by Donald R Moler on April 28, 2001 at 19:02:11

Lyle, The easy way to measure distributed capacity is to measure the resonant frequency of the coil at two or three different frequency's by changing a known capacitor across the coil and ploting it ( remember electronics 101 ?) The Y=c and X = frequency. where x intersects c is the distributed capacity. Nonlinnear of course. The 498 pf is the capacity of the top and the distributed capacity of the coil. Don Moler N8BKR Girard Ohio

Re: distributed capacity
Posted by Lyle Koehler on April 28, 2001 at 19:38:34

Yep, I know about the slope-intercept stuff. I was giving the easy version that eliminates most of the arithmetic. As one smart-assed friend of mine used to say back in engineering school, "If you know so much about it, why'd you ask?"

TLTX down untill Jun
Posted by Tony Levstik on April 29, 2001 at 12:52:44

I will be taking beacon TLTX (184.283khz)down untill Jun.
Due to bad weather and needed repairs.
Regards Tony Levstik

adding five feet
Posted by Donald R. Moler on April 29, 2001 at 17:04:36

I just improved my signal by ten DB by improving the match and adding more radails. Now I am making a wooden ladder so I can remove the top hat and add another wire near the ends of the spokes so as to increase the capacity. I want to get the top hat capacity as high as I can as that takes turns off of the coil. This week I will raise the coil and the top hat another five feet take some measurements and then move the antenna to the back field and put it up on a fifty foot tower. I made a new friend and his call is KB8PDU, Bob Hartman,and I have introduced him the the Lowband and helped him build a receiving loop for 1750 meters. He is helping me with the big antenna on 1750 meters. Don Moler N8BKR Girard, Ohio

Re: hat capacity
Posted by bill in rtp on April 30, 2001 at 08:22:34

Great site Lyle, many thanks...

73, AB4OB

New loading coil
Posted by Donald R Moler on April 30, 2001 at 16:13:04

I just ordered 500 feet of one half inch copper tubing for my next loading coil. I will design this next coil a little differently to eliminate some of the losses. I think a longer fiberglass coil form with the coil wound in the middle so the top hat and the tower is not in the field of the coil. ( large coil, large field). According to Lyle about the best ground losses in any lowfer system Is about 5 ohms so I think I will put in two radial systems one meager system on the ground and another suspended about two feet above ground with such a system I think I can get below 5 ohms. Ground losses seem to be less at the low end of the band. I may put my beacon on 161 Khz. I am going to look into this to see if there is an advantage in operating at one end of the band or the other. I sent in some pictures of this antenna to QST and asked if they would give a plug for these web sites. Jim W7KBF in Lolo Montana has his receiving loop working very well so If any one of you want to contact him, he is willing to look for your beacon on 1750 meters. Don Moler 2623 Morris Lane Girard, Ohio N8BKR

Re: New loading coil
Posted by Lyle Koehler on April 30, 2001 at 19:48:45

Most LowFERs operate close to the top end of the band, in order to take advantage of the higher radiation resistance. At 190 kHz, the Rr for a given antenna will be about 40 per cent higher than it is 160 kHz. It also takes about 40 per cent less loading coil inductance at the high end of the band as compared to the low end. Atmospheric noise increases at lower frequencies, and in my part of the country the Loran-C interference starts to come up above the noise floor at frequencies below 170 kHz.

Having said all that, I should add one other fact. LowFER Z2 was operating on 165.7 kHz when its CW signal made the trip from California to Hawaii, establishing a DX record that still hasn't been broken by the new digital modes. Was this just a freak propagation occurrence, or are there other factors that the calculator doesn't take into account? Wish I knew!

www.lwca.org

potrzebie