I made a small transmitting loop a couple of years ago as an experiment with a material I wanted to try. One of the materials was not appropriate, but I made it work for the sake of the experiment. I plan to make another loop at some point from a different material so it's not an issue, but that was only the *support* material for the loop. I wanted a loop I could fold or roll up into a small package to take it to parks and such, that wouldn't require stakes or lofting things into trees, in case the local authorities don't like that.
The support material was some plastic perforated strap for supporting pipes, conduits, and BX cables in basements and attics. The holes are an inch apart on centers, and the stuff is VERY strong. It's also flexible...but TOO flexible. It had no supportive strength whatsoever, which was a problem for this project. I wound up making supports for it out of thin wood, which worked, but it wasn't what I originally had in mind. But it's not the support material I'm writing this to mention. I'm talking about the conductor. I used 1/2 inch wide adhesive copper foil. The adhesive is also conductive. It's not very strong, but it's VERY conductive, and it's lack of thickness isn't an issue because it has a lot of surface area, where the RF is actually conducted, so it should have great bandwidth. I had a decent variable air-gap capacitor, with a 10X vernier control on it, and used a small wooden base, like a miniature pallet, as a platform for the entire thing. I priced thin wooden furring strips for the rest of the supports, but they were more expensive than I liked. So I bought a dozen wooden meter-sticks for about half what the furring strips would have cost. They work very well for situations where you need a thin but strong piece of wood. I ran the copper foil tape the length of a piece of the plastic strap to give me a loop I calculated for 40m-10m. The copper foil takes solder very nicely, so it was simple to work with. The wooden supports I made were a six-pointed star, the bottom being flattened for the connections at each end of the loop and the capacitor. I made a coupling loop out of a similar piece of plastic strap and the same foil tape, and connected it to the coax, about 15 feet of RG-174. I used this loop indoors, on a wire rack next to my workbench, and used it with FT8 at various output power levels. I used a laser thermometer to check the temperature of the conductor in multiple places, and it only showed a tiny increase in temperature above room temp when I tried it with 100W. (KX3 + KXPA100) It was easily tuned on the bands I expected to use it with, and with the internal tuner of the amp I managed to tune it on 80m, but didn't expect any significant efficiency, and was right not to expect it. But on 40m through 10m it was very serviceable. I'm in the Philly area, and managed to have FT8 contacts as far as Fargo, ND and a couple in Cuba. The bandwidth was fairly wide as I expected. I haven't used it to try and make CW or SSB contacts, but I see no reason why I couldn't, though it is firmly in the "compromise antenna" category for those emission types. It's a proof-of-concept, mostly, but a functional one. I've attached pictures, so you can see what it looks like. -=-=-=-=-=-=-=-=- 73, Gwen, NG3P On Wed, Jan 20, 2021 at 10:50 AM Raymond Sills via Elecraft < elecraft@mailman.qth.net> wrote: > Hi Group: > OK... here's my mag loop story: > I have two AlexLoops.... and one is the original version that uses copper > tubing for the main loop. I used that loop to make an RTTY QSO with a > station in Moldova. I had set the loop up indoors (in my sunroom, which > has a lot of windows) and worked that station on 40 meters... running 3 or > 4 watts. > OK, it was during a contest... the contact was quick, but acknowledged > both ways... so a Q is a Q.And, that was my best DX with that antenna. The > fact that it was 40 meters, the loop's least efficient band, is amazing to > me. I suspect that the other guy was using a much better antenna, and > likely more power. > 73 de Ray K2ULR KX3 #211 > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to ard...@gmail.com
______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
