HFU HF Underground
Technical Topics => Equipment => Topic started by: Treehouse SWL on September 21, 2022, 0536 UTC
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Question from an antenna novice: My long-wire antenna previously was simply connected through a feedline wire that my dog chewed through. So, now, as I resurrect my use of that antenna, I'm using coaxial cable (out of the dog's reach) and proper connectors.
One question: What's the best coaxial type to use for an antenna feed line: plain-old RG6 or something else?
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Any coax will work. I use RG-6 because it's easy to work with, I use compression fittings.
If you are presently just connecting the antenna wire directly to the coax center connector, you may want to consider a transformer at the feedpoint instead. Take a look at this post for some ideas: https://www.hfunderground.com/board/index.php/topic,74042.0.html
The basic idea for a long wire, the grounding block near the shack end is optional but can help:
(https://i.imgur.com/puXPv9O.png)
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Yup, I've successfully used RG-6, mostly old TV cable salvaged from my apartment complex dumpster. It was good quality cable, still in great shape, but after the landlord discontinued offering free basic cable around 12 years ago, few tenants were transitioning to paid premium cable. Our complex had a weird deal with the local cable TV provider that amounted to an all-or-none group discount, because this place had mostly elderly and/or disabled retirees. But hardly anyone wanted premium service. And soon afterward streaming services made cable obsolete.
So every time an apartment was vacated, the maintenance crew tore out the old cable during make-ready for a new tenant. I salvaged the undamaged cable from the dumpsters to use for my shortwave receiving antennas.
My landlord didn't like my radio hobby, so the maintenance crew tore down my outdoor stealth antennas whenever they found 'em. She got a complaint from a grumpy old tenant, a former Coast Guard radioman, who claimed my receive-only antennas were interfering with his TV reception. He was full of beans and knew better, but was a diehard trouble-maker for everyone. Rather than argue with him they just tore down my reception antennas.
So I switched to the cheapest materials available: discarded cable TV coax, magnet wire and cheap TV impedance transformers, to build my homebrewed loops. I hid those in the wooden fence outside my window. The magnet wire was nearly invisible, and I located the TV balun near the bottom corner to make it less noticeable. The only tricky part was hiding the coax feedline. I'd jam it into the dirt between the yard and building. There was still a telltale feedline going up about two feet from the ground to my window. But usually I could keep an antenna going for a few months at a time before the crew would spot it and tear it down.
Anyway, my cheapo primitive fence loop worked great for two or three years. I aimed the null at the noisiest outdoor lights that kicked up the worst RFI. Gain was very low, but so was noise, so it was pretty effective and not unpleasant to listen to for hours as harsh RFI static was practically nil.
I think my last such loop was torn down around 2017 when the apartment complex was sold to new owners. I got busy with life and family stuff at the time, didn't have time to rebuild it and the radios sat in the closet for years until recently when I dug 'em out to listen again. I may put up another stealth fence loop soon, since I still have most of the materials. I think all I need is one of those cheap TV baluns, which shouldn't work -- wrong ferrite core for HF -- but do pretty well on shortwave anyway.
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I think my last such loop was torn down around 2017 when the apartment complex was sold to new owners. I got busy with life and family stuff at the time, didn't have time to rebuild it and the radios sat in the closet for years until recently when I dug 'em out to listen again. I may put up another stealth fence loop soon, since I still have most of the materials. I think all I need is one of those cheap TV baluns, which shouldn't work -- wrong ferrite core for HF -- but do pretty well on shortwave anyway.
The Loop On Ground guys often use TV baluns on HF as well. I've actually got a TV splitter on my sky loop, so it can feed both the online KiwiSDR and netSDR. Works fine down through the MW band. It may not be optimal, but for receiving that's rarely an issue. Signal (and noise) levels are almost always way way above the receiver noise floor, so you're not losing anything important. 5 or 10 dB of loss? You'll never notice.
Quite different than transmitting where you try to eliminate every dB of loss.
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Actually, RG-6 coax wouldn´t be a bad choice for MW and HF RX´ing, especially with with today´s noise levels being what they are. In fact, this Fall, I was planning to redo my W.O.G., (Windom On Ground.), to get it further away from the house. RG-6 isn´t just nice & cheap, but also 100% shielded with outer braid and foil. That said, there is one caveat with double shielded coax. The aluminum foil and steel braid are dissimilar metals, and will corrode with time. When you strip it years later, you´ll have that fine AL dust coming out. Water and air tighten the ends as well as possible. The least amount of O2, the least amount of corroding. So, Chris has used TV Baluns with success on RX´ing HF and MW? Well, they make those cheap enough that it shouldn´t surprise me, and good to know.
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The answers here are way to complicated and techniques not necessary.
I feed a standard 347 foot horizontal endfed wire antenna with standard ohm coax via a 9:1 coaxial balun.
My LDG tuner or FT-dx101MP does the rest with only one band at 2:1 SWR, and the rest 1:3 to 1:0 (of course, there is no perfect match, just a figure of merit).