I agree that loops are fun and interesting but my best success was with attic doublets while being an apartment dweller some years ago. Not loaded dipoles but non-resonant center fed wires.
My approach was to get into the attic space and, based on where the rig was located below me, figure out how I could best run the two halves of the doublet as far as possible without having bends greater than 90 degrees and with the center "feed point" over the rig. I fed it with open wire. Not the big, clunky stuff but homebrew line made up of two small gauge wires spaced about 2 inches. My installations were in various apartments where I rented on the 2nd (top) floor. The walls and ceilings were painted apartment white so I used small gauge white wires. An ice pick made two tiny holes in the ceiling drywall right next to the wall where the rig was sitting on my desk below. Snaked the two "feed" wires through the holes and stapled them to the dry wall. Put my balanced tuner above the rig on that wall and connected the feeder to it. With about 40 feet or so of wire in the attic perhaps 25 feet above ground I easily found contacts on 40 and 20 meters CW running between 5 and 15 watts output along with interesting DX when the higher frequency bands were open. When visitors sat at the operating position, I had to point out the feed line in front of them before they noticed it. When it was time to move on, the whole affair could be removed and the holes plugged in a matter of minutes, especially if I didn't bother to remove the part in the crawl space above the ceiling. LS makes a good point about the impact of wiring, etc. That's why I worked to get my wire up above that and directly under the roofing material. But even that can backfire, as it did once. After considerable success in three previous locations I found one where I could not get out worth a darn. One day I noticed a bit of broken roofing tile on the ground, left by someone making repairs. The tiles were of colored lightweight concrete. I took it inside and put it in my microwave with a glass of water and ran it on high for a minute or so. The bit of tile was "smoking hot" meaning it was absorbing the RF energy. No wonder I couldn't get out, especially on the higher frequencies. Fortunately the next QTH was a house I owned. IF it is an "Isotron" you are looking at, they are a very poor excuse for an antenna and proof that even a dummy load will make contacts when conditions are right. Just about anything else will work better. 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Bruce Nourish Sent: Wednesday, April 6, 2016 1:06 PM To: David Guernsey; Elecraft Reflector Subject: Re: [Elecraft] [k3] Isotropic Antenna Hi David, I'm a little puzzled by your question, and I suspect others are too. The isotropic antenna is a theoretical construct which is sometimes used as a baseline for the comparison of other antennas; it is not possible to build one. The most primitive antenna that can actually be built is a dipole (but don't take primitive to mean ineffective!). Having recently taken up ham radio again, in an urban QTH, I would very much *not* recommend a dipole for your use case. I wasted a lot of time trying to get a loaded dipole to work well in my attic. Then I started reading about small magnetic loop antennas, built one for myself, and never looked back. I now mercilessly evangelize them to anyone who will listen. Some reading on mag loops here: http://www.g4ilo.com/stealth.html http://www.ahars.com.au/wp-content/uploads/2014/05/The-Underestimated-Magnet ic-Loop-HF-Antenna-version-1.1.pdf The quickest way to get started with mag loops is probably to pick up one of these MFJ units: http://www.mfjenterprises.com/Product.php?productid=MFJ-9232 (QRP) http://www.mfjenterprises.com/Product.php?productid=MFJ-933 (QRO) The QRP model includes wire, the QRO doesn't. Bruce ______________________________________________________________ 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
