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Posted by Bruce WA1HGJ on March 13, 2024 at 16:41:47.
In Reply to: Re: Receive Transformer Build posted by Ed Holland on March 11, 2024 at 02:56:15.
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Hi Ed, wanted to respond here before your messages got too far down the board. Thanks for sharing the details and pics of your transformer windings. Sounds like a great set-up. I have several mix 31 split ferrite cores laying around from DX Engineering for RFI use, so will keep this in mind next time I need to wind a transformer. Great idea! And speaking of feed lines and RX noise/performance, I have a conceptually similar LW receive situation to yours, at least for about 160 kHz and above (below 160 kHz I get better performance with an LF Engineering remote active antenna with up-converter to 4.000-4.160 MHz). Above 160 kHz I get better LW RX results using my ham end-fed Zepp antenna but bypassing the tuner circuitry. The antenna is 67' end-fed (1/2 wavelength on 40 meters), up about 25' and fed with the same length of 450 ohm ladder line, passing through a couple knife switches and 2 levels of lightening protection. When bypassing the tuner circuitry for LW RX, the tuner balun toroid is still used, with the balun's ground connection midway between the 2 windings from the ladder line down leads. One lead goes up the ladder line and is connected to the 67' antenna, the other lead dead ends at the end of the feed line (classic end-fed Zepp set-up). What's remarkable to me--and what your post got me thinking about--is that both legs of the feed line are required for good RX performance. If I disconnect either leg, signals go down and noise goes up. Only with both leads do I get (fairly) quiet RX performance, and switching them doesn't make a difference. My interpretation is that any noise picked up in the feed line (which comes into the house after lightening protection and is thus closer to AC household wiring) is common mode on both legs so it cancels itself out in the balun. Only signals that originate from the Zepp antenna itself come down one side of the feed line asymmetrically and thus are not canceled at the balun but are transferred on to the receiver via coax. Anyway, your post triggered some thinking about my own set-up so wanted to respond and thank you. GL LW DX! Bruce WA1HGJ
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