Loggings > North American Shortwave Pirate
Northern Relay Service, 6930.48 AM
Zoidberg:
--- Quote from: DavidB on November 10, 2011, 0323 UTC ---Gradually becoming one with the (obscenely high S-7, gotta love SWLing in the city :-[) noise floor as of 0323 UTC.
--- End quote ---
Yup, know wut ya mean. If I hadn't switch to a homebrewed indoor magnetic loop I'd probably have given up on SWL by now.
If I'm recalling correctly, the only flaw with that Doty antenna design was the TV "balun" being a less than ideal match for HF. But I'm using a typical cannister type TV balun for my magloop and it works ok, even if it's not ideal.
Take a peek at the KR1ST loop design. Several folks have reported good results with that as a compromise indoor antenna for dealing with typical manmade RFI.
My loop is somewhat similar but made from coaxial cable rather than copper tubing. It's based on a Joe Carr design I already had in one of his books from the 1990s. Same principle though. I used it as a passive untuned loop for a couple of years and it worked well for certain bands, especially 6600-7500 kHz and the MW AM band, but was pretty much deaf above 10 MHz. But by early this year when propagation tanked it wasn't quite enough so I added an amplified tuner. The original design tended to overload with the amplifier so I adjusted the pickup loop to a much smaller diameter (around 8"-10") and it works just fine. Not as convenient as the untuned loop for bandscanning though.
The other alternative is to just tote a portable on my walks. I often get much better reception in certain low noise zones in my suburban neighborhood.
DavidB:
--- Quote from: Lex on November 11, 2011, 0043 UTC ---Yup, know wut ya mean. If I hadn't switch to a homebrewed indoor magnetic loop I'd probably have given up on SWL by now.
If I'm recalling correctly, the only flaw with that Doty antenna design was the TV "balun" being a less than ideal match for HF. But I'm using a typical cannister type TV balun for my magloop and it works ok, even if it's not ideal.
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Thanks, but I don't really have room for an HF loop in my very cramped quarters, or I wouldn't have put mine into storage. I find the Doty design works very well, all things considered. I've heard things with it I haven't heard for decades in the city. Plus, I can use my computer when the radio is on and have it not affected at all. It's just that no antenna can do miracles; there's ultimately no substitute for getting far away from the city. It's time to go camping with my radio again sometime soon.
Regarding the TV matching transformer, actually Doty's design does not use one. It uses the toroid from one and has you wind a 9:1 impedence matching transformer (3:1 turns ratio) with that. The TV transformer I took apart had a ridiculously small toroid, so I ordered a ferrite toroid (Core F-50, Ferrite Mix 61) from Palomar Engineers and used that.
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