ICOM R-75 opinions
I am interested in hearing opinions, pro or con, regarding the performance of the ICOM R-75 in the longwave spectrum. Most receiver reviews focus on shortwave performance, but you folks are the gurus of below 500 KHz.
Re: ICOM R-75 opinions
Posted by Warren K2ORS/WD2XGJ/WD2XSH/23 on May 03, 2007 at 06:47:06.
In reply to ICOM R-75 opinions posted by D. Williams on May 03, 2007
D.,
The Icom R75 is one of the most popular LW receivers. You will need to figure in the cost of narrow i.f. filters which are not included if you want to dx NDBs or Lowfers.
There are a number of good LW receivers, but the R75 is perhaps the best value since most others are considerably more expensive. If you live near strong AM BC stations you will probably need to use a low pass filter or a tuned loop so that the R75 doesn't overload on longwave.
Hope this helps.
73 Warren K2ORS
WD2XGJ (137 kHz)
WD2XSH/23 (505 kHz)
Re: ICOM R-75 opinions
Posted by John Andrews, W1TAG on May 03, 2007 at 08:41:55.
In reply to ICOM R-75 opinions posted by D. Williams on May 03, 2007
Doug,
I agree completely with Warren's comments. I currently own two R-75's, and use them for all of my LF listening, including NDB's, broadcast, CW, and the various low data-rate amateur/experimental modes. The latter require serious tuning accuracy and stability, and the R75 has performed well.
Your need for plug-in filters will depend on what you plan to do with the receiver. Mine have a 500 Hz crystal filter in the 1st IF, and a 250 Hz mechanical filter in the second IF. Those have been sufficient for all work to date. Note that the slow speed data modes using a computer for DSP do not really require narrow filters in the receiver. The DSP routines establish very narrow audio bandwidths, and IF filtering would only be needed if there was a very strong interfering signal in the passband. That's common at HF, but much rarer at LF. The receiver filters can be a great help for aural listening, though a really serious NDB chaser might want to use a narrow external audio filter in addition.
I am in close proximity to a number of AM broadcast stations, and have had few problems with 2nd-order mixing products. As Warren notes, the use of tuned LF antennas helps to prevent out-of-band interference.
In case the receiver is not sensitive enough for your antenna setup, good preamp circuits are readily available. Most of my LF listening is done with a 14-turn square loop (6 feet on a side), and a 20 dB preamp. That arrangement has worked well for some pretty weak-signal receptions.
R75 prices on the various auction sites have been attractive, and the receiver has been popular enough to provide plenty of choices. Have fun!
John Andrews, W1TAG/WD2XES Re: ICOM R-75 opinions
Posted by D. Williams on May 03, 2007 at 12:43:16.
In reply to ICOM R-75 opinions posted by D. Williams on May 03, 2007
Warren & John,
Thank you for your comments. Sounds like the R-75 is a darn good "bang for your buck". From what I have read, the R-75 has a passive 3db AM broadcast band attenuator inline with the antenna, but I couldn't find out if it is a MW only attenuator or a low pass filter that would also affect frequencies below 500 KHz. Re: ICOM R-75 opinions
Posted by John Andrews on May 03, 2007 at 18:28:35.
In reply to Re: ICOM R-75 opinions posted by D. Williams on May 03, 2007
Doug,
I believe the 3 dB pad will be in-line for LF operation. That's hardly an issue, though, and certainly not worth a modification. Bulletproof gain is easy to come by at these frequencies. Looking back at some notes I made about 5 years ago, the receiver had an MDS of -137 dBm in a 500 Hz BW at LF. Operation with the R75's Preamp 1 on and my external 50 ohm, 20 dB preamp gave an MDS around -145 dBm. That's based on a rather antique signal generator, but the figures probably aren't far off. You'll be much more limited by atmospheric and man-made noise than by the receiver, assuming a halfway decent antenna.
I also have an Icom 746PRO, and the R75 is a much nicer LF receiver. The 746 is deafer, and the frequency stability isn't as good. But I have definitely done some decent weak signal work with the 746 and a preamp, so I don't agree with the "remove the pad" philosophy.
John Andrews, W1TAG/WD2XES Re: ICOM R-75 opinions
Posted by D. Williams on May 04, 2007 at 04:42:47.
In reply to Re: ICOM R-75 opinions posted by John Andrews on May 03, 2007
Thanks, John. That is exactly the response I was hoping for. Sounds like the R-75 is an excellent choice for LF work.
You have mentioned that the R-75 has good frequency stability. May I ask if you are talking about a stock unit, or have you installed the CR-282 high stability oscillator?
Re: ICOM R-75 opinions
Posted by John Andrews on May 04, 2007 at 18:45:00.
In reply to Re: ICOM R-75 opinions posted by D. Williams on May 04, 2007
Doug,
I have the high stab option in one of the R75's. It does warm up more quickly, and seems to be a little less sensitive to room temperature. But we're talking shifts in the milliHertz range (I'm not kidding). Both receivers have been fine for modes like WOLF, QRSS60, etc.
John Andrews, W1TAG Re: ICOM R-75 opinions
Posted by D. Williams on May 05, 2007 at 16:23:57.
In reply to Re: ICOM R-75 opinions posted by John Andrews on May 04, 2007
You sold me. I'll have to break into my piggy bank and buy one soon. Thanks for all your help.
Medfers EH and HI Heard
Posted by Warren K2ORS/WD2XGJ/WD2XSH/23 on May 06, 2007 at 18:22:33.
Copied EH and HI while driving through CT today. I copied EH as far north as the rest area on I-91 in Meridan. I copied both EH and Hi as far west as mile 14 of the Merritt Parkway. Good job guys!
Setup: LF Engineering L-400B E-probe antenna, Icom 706 MKIIG w/500Hz i.f. filter.
73 Warren K2ORS/WD2XGJ/WD2XSH/23
LF Dead Zone
Posted by Peter Barick on May 07, 2007 at 12:09:43.
Fellows,
Activity around 185 seems down or missing these days. However EAR on 188 has been a regular at this location in N IL using Argo, a Grounded Vert into an R-8 rx. But the past few days there has been noticable QRN heard and no signals, not even "noise traces" on Argo. Might this be due to the limiting action of the rx AGC affecting what Argo can display? Or an Argo quirk?
EAR is again visible today and the QRN is gone. Re: Medfers EH and HI Heard
Posted by Sal DeFrancesco on May 07, 2007 at 16:57:12.
In reply to Medfers EH and HI Heard posted by Warren K2ORS/WD2XGJ/WD2XSH/23 on May 06, 2007
Hi Warren,
How do you like my antenna, the L-400B that is.
I designed it back in 1985. I still have the prototype
on my roof.Happy to hear you copied our signals. I hear
your part 5, wa2xsh/23 FB at my QTH using various
antennas including a new 2' loop design that I will market
soon (LF Engineering Co.), I'm still in business, we do alot of government/military/commercial work now.
73s Sal K1RGO
Re: Medfers EH and HI Heard
Posted by Warren K2ORS on May 08, 2007 at 07:36:24.
In reply to Re: Medfers EH and HI Heard posted by Sal DeFrancesco on May 07, 2007
Hi Sal,
I really like your e-probe (L-400B)antenna, works very well. When I'm asked for antennas/preamps etc I recommend your company.
Very good on the 2' loop, sounds like you will be giving Wellbrook a run for their money!
73 Warren K2ORS/WD2XGJ/WD2XSH/23/WE2XEB/2
Re: LF Dead Zone
Posted by John Davis on May 08, 2007 at 18:03:10.
In reply to LF Dead Zone posted by Peter Barick on May 07, 2007
I doubt that it is limiting action, in the sense of hard limiting, but the problem is with the signal from the antenna more than it is the receiver or Argo.
The AGC is reducing the gain of the receiver, as indeed it should, to keep it from being overloaded by the noise. The noise level at the input of the receiver is up, but the signal level is not. This is the definition of reduced S/N ratio. FFT algorithms are pretty amazing, but there is no free lunch. As the QRN increases, the signal component of the receiver output will eventually drop so far below the noise level that any practical integration time is still not enough to sort it out from the noise.
One technique that has been used to work around this effect is the Dicke Limiter (which is, in fact, a hard limiter) in lieu of AGC. LWCA member Rick Wright wrote an article on the subject several years ago, using a couple of Motorola 1590 ICs in a sort of TRF front end for a more or less conventional receiver. By clipping noise impulses to a specific level without simultaneously cranking down the signal, one can improve the odds of signal detection.
Adjustment was critical, at least when copying CW by ear. Rick's work was before the era of Argo and similar software, so I couldn't say whether a computer waterfall display would make the gain adjustments any less critical.
John
Re: LF Dead Zone
Posted by Peter Barick on May 09, 2007 at 07:12:25.
In reply to Re: LF Dead Zone posted by John Davis on May 08, 2007
Okay, John, that sounds reasonable about the S/N vs. signal detection. Heard similar before, only now it's crucial as the only part-15 signal I had to watch is sinking in the abyss ;-) An unknown factor is the "black box" of Argo. One has to accept its display devoid of other senses. Example: Some marginal, close-by NDBs can be heard through the same level of QRN, can be ID'd after a few clobbered IDs. Communication is made. The "non-existant" signals of all part-15s here are inaudible. (Only once heard LEK, RB always) So all I have now is EAR, a day/night caller during the good times. This morning w/ light QRN, EAR is sketchy on a 30Sec screen. I've tried fast and slow AGC and manual w/ no display improvement. Ah, maybe May is truely time for the off-LF season break. Thanks
Re: LF Dead Zone
Posted by Peter B on May 09, 2007 at 09:45:02.
In reply to Re: LF Dead Zone posted by John Davis on May 08, 2007
On going testing...
Had some success. I checked over the Vert loading coil. Chgd the tap conns from 9t to say 5t. Signal was worse. Next I shorted the series cap (meas 3,700pF) to the coax lead-in. That brought the Argo display up showing EAR nicely. So this is an improvement. Usual noise seems the same. Will try rx at 185.3 tonight. Also notice a BC birdie that was at 181kHz now missing. Another blessing!
TIS/HAR on 1710 kHz?
Posted by Robert KB7AQD on May 09, 2007 at 11:15:33.
Are there currently any Travellers Information Stations on 1710 kHz?
Thank you,
Robert H.
Phoenix, AZ
Re: TIS/HAR on 1710 kHz?
Posted by John Davis on May 09, 2007 at 12:21:14.
In reply to TIS/HAR on 1710 kHz? posted by Robert KB7AQD on May 09, 2007
Even though digitally tuned car radios have had 1710 kHz for a long time, the FCC Media Bureau no longer speaks of that frequency as being available for TIS.
There's a handy TIS search-by-frequency engine on this FCC page, which includes 1710 but shows no current authorizations there.
John
Re: TIS/HAR on 1710 kHz?
Posted by John Andrews on May 09, 2007 at 12:30:28.
In reply to TIS/HAR on 1710 kHz? posted by Robert KB7AQD on May 09, 2007
Robert,
According to the FCC rules, (section 90.242), TIS is only authorized from 530 to 1700 kHz. There are any number of web sites claiming that the TIS/HAR band goes to 1710, but the FCC doesn't seem to agree. Dunno!
The FCC regs may be seen here.
John Andrews, W1TAG Re: LF Dead Zone
Posted by Alan G3NYK on May 12, 2007 at 03:21:49.
In reply to Re: LF Dead Zone posted by Peter Barick on May 09, 2007
Hi Peter, It is not always possible with modern receiver, but I find it always useful to use ARGO or Spectran with the AGC switched off. I may mean you have to reduce the level from the RX to the sound card (below the level you can hear signals on the PC speakers), but these programs are capable of diplaying a 90dB range even at audio. Hopefully then what happens is the static crashes saturate in the receiver and are clipped. If you use AGC you can very much reduce your capability of seeing weak stations, because the crashes set the gain level for the receiver. Even so "you can't get ought for nowt"
I had a problem early on, of logging (ADC) signal levels (CHF Halifax) for a plot, and found I was recording the peak crashes. The plot was about 20dB wide. Then I took 6 samples at 10 sec intervals and plotted only the lowest one of the six, which gave a very good clean noise free plot. I used a 3 sec time constant on the wide-band voltmeter on the 455kHz output of the RX. You can get some of this kind of effect on Spectran by using "averaging". The rate your crashes occur may swamp the receiver, they are rarely so bad in the UK.
Cheers de Alan G3NYK
Would this make a VLF/LF Receiver? (and HF for that matter)
Posted by Clive S Carver on May 12, 2007 at 11:33:01.
I came across this web page whilst looking for something entirely different!
http://www.rfspace.com/sdriq.html
A Software Defined Receiver with 500Hz to 30MHz in 1Hz steps sounds interesting. And circa $500 does not seem too bad for the cased version.
Has anyone come across this device before? Any comments?
Re: Would this make a VLF/LF Receiver? (and HF for that matter)
Posted by Warren K2ORS/WD2XGJ/WD2XSH/23/WE2XEB/2 on May 14, 2007 at 10:45:49.
In reply to Would this make a VLF/LF Receiver? (and HF for that matter) posted by Clive S Carver on May 12, 2007
Clive,
I have no direct experience with this but there are several guys on the LWCA mail list with it and they are very happy:
http://mailman.qth.net/pipermail/lowfer/2007-March/016350.html
73 Warren EAR summer operations
Posted by J.B. Weazle McCreath on May 16, 2007 at 17:24:14.
Lowfer beacon EAR on 188.830 kHz. will be operational 24/7 thru the summer months except during times of local electrical storms. Signal reports and captures would be appreciated.
73, J.B., VE3EAR/VE3WZL
NDB 'LA' Freq. Change?
Posted by Dave Childs on May 18, 2007 at 22:02:19.
I haven't heard LA, Lansing, MI, on its original freq. of 206 KHz. for some time. This AM I heard LA for the first time on 393 KHz. stronger than I'd heard it in over a decade & from the same direction as it did on 206 KHz. I presume it's the Lansing NDB although I can't find any directories that show this change; anyone know if LA changed frequency? Thanks. Re: NDB 'LA' Freq. Change?
Posted by Michael on May 19, 2007 at 03:38:37.
In reply to NDB 'LA' Freq. Change? posted by Dave Childs on May 18, 2007
Hi Dave,
Just checked the NOTAMs for the airport and found the following: 04/181 - 28L ARTDA NDB/ILS LO 393 VICE 206 WIE UNTIL UFN
So the frequency change is confirmed.
vy 73 + gd DX,
Michael
Re: Would this make a VLF/LF Receiver? (and HF for that matter)
Posted by Mark KU7Z on May 19, 2007 at 08:11:08.
In reply to Would this make a VLF/LF Receiver? (and HF for that matter) posted by Clive S Carver on May 12, 2007
Clive, I would say yes. I had a loaner for a week and used it mostly on VLF. Worked Great! A new way of looking at the band, literally! The only thing I would do differently would be getting the audio out of the soundcard to any Audio filter or headphones that gets you what you want to hear with your ears that makes you happy. I look forward to picking one of them up once they become available myself.
73, Mark, Ku7z
DN41af, Northern Utah (NUT)
Re: LF Dead Zone
Posted by PAUL DAULTON on May 19, 2007 at 21:52:49.
In reply to Re: LF Dead Zone posted by Peter Barick on May 09, 2007
LAST YEAR I COPIED MO AND WEB UP TILL FIRST OF APRIL. NO
COPY AGAIN UNTIL OCTOBER.
MO I BELIEVE IS OFF BECAUSE OF INTERFERENCE WITH 500KC GRABBER. I GOT AN EMAIL FROM BILL BOWERS WHO OPERATES
WEB AND HE IS DOWN FOR REPAIRS, BUT CHECK WITH HIM FOR
CURRENT STATUS. I WAS COPYING WEB UNTIL END OF APRIL.
DAVE W0CH AND I RAN SOME TRIALS IN APRIL WITH NO LUCK,MY
COPYOING HIM OR HE COPYING ME( WMS AT 187.5KHZ.
I GOT MYBEACON ON IN FEB FARTHEST COPY THUS FAR IS 42 MILES.
2006/2007 SEASON WAS NOT AS GOOD AS 2005/2006.
YOU CAN RUN MULTIPLE COPIES OF ARGO AND SPECTRAN. I "BRACKET" MY SETTINGS ON WEB TO FIND THE BEST RECEPTION
I CALL UP ARGO AND SET CAPTURE, ASSIGNING A DESK TOP FOLDER
THEN FOR THE NEXT SCREEN I SET ANOTHER FOLDER FOR CAPTURES
ie WEB1,WEB2 AND WEB3 AND SET THE SENSITIVITY AT 5, 7 AND 9.
ONE CAN RUN ARGO AND SPECTRAN AT THE SAME TIME ALSO BY THE SAME METHOD. AND MULTIPLE SPECTRAN. I PUT THE CURSOR ON THE
EDGE AND STAGGER THE SCREENS SO I CAN GO THROUGH AND CHECK
EACH ONE. THIS TECHNIQUE MAY NOT BE WELL KNOWN. I USE A
700MHZ MACHINE AND HAVE NO TROUBLE WITH THREE SIMULTANIOUS COPIES. I ALSO HAVE SET ONE FOR MO AT 189.500 AND ONE FOR
189.95O(MO AND WEB) HOPE THIS HELPS
PAUL DAULTON Re: NDB 'LA' Freq. Change?
Posted by DaveC on May 19, 2007 at 23:28:51.
In reply to Re: NDB 'LA' Freq. Change? posted by Michael on May 19, 2007
Thanks, Michael, I was 99% sure that was the same station.
73s,
Dave Re: New Detica VLF Receivers for British Navy
Posted by Paul G8GJA on May 24, 2007 at 03:59:24.
In reply to New Detica VLF Receivers for British Navy posted by Todd WD4NGG on March 08, 2007
Don't believe all you hear in press releases. The new receivers are not significantly different in size, both are about 4U high. They are shorter but this does not impact the fit. They ARE lighter but this is only important when lugging them around - once they are in they're in. Weight is pretty immaterial in naval usage, the previous rx (Redifon R800, using 56K dsp) was seriously inconvenient to move and its predecessor (CJD) was a definite 2 man job, especially when bolted to the psu. Both used die-cast ali chassis which seemed to be 'de rigeur' for naval tx/rx use for years. Both of these are excellent for lf work if you have the space......... Testing on 6776.8 Khz using PSK31
The bit about 'enabling submarines to remain underwater....' is nothing to do with the rxs, being just a function of the frequency used. There is an existing interference cancelling unit available externally and, surely, there should not be any 'internal interference'?
Posted by Bill deCarle on May 28, 2007 at 05:23:07.
I'm running some tests today on 6776.8 Khz using standard PSK31 encoding at 31.25 bits per second. Power output is about 4 milliwatts. If anyone is able to copy I'd sure appreciate a report. Thanks, Bill
Hifer RY back on air
Posted by John Andrews, W1TAG on May 28, 2007 at 11:33:18.
Hifer station RY is back on the air for the summer season, on 13555.39 kHz with DFCW3. A temporary antenna is currently in use, and a more permanent one will be installed in mid-June. RY is in Raymond, ME (FN43sv). Reports are welcome.
John Andrews, W1TAG
potrzebie