perhaps that could work. A delta loop or sky loop in a horizontal configuration is supposed to help with all that and be a great performer otherwise. 73 Colin, V A6BKX ----- Original Message ----- From: "Martin McCormick" <[log in to unmask]> To: <[log in to unmask]> Sent: Friday, February 25, 2011 5:26 AM Subject: Re: magnetic loop antennas? > There is an article in the December "QST" about how all signals > that arrive via sky-wave propagation get converted in to > elliptically-polarized signals such that the best antennas for > receiving and transmitting should be circularly polarized. > > The author tells us how to build two crossed dipoles > with a 90-degree phasing difference between the two to get > circular polarization. His experimental designs are for > reception of WWV at 10 MHZ, but the principles are the same for > any band. > > In other words, you needn't worry so much about your > polarization except when making local contacts where it does > matter. A loop should be circularly polarized so, except for the > issue of narrow bandwidth, it should be a very good antenna. > > I am thinking about going to some sort of loop for my > HF, here, but haven't done anything yet. I have terrible power > line QRM most of the time and a loop might help separate all the > garbage from the signals. > colin McDonald writes: >> the author of the website I posted has a magnetic loop for 80M that is 12 >> feet square, made from 2 inch aluminum tubing and is vertically mounted >> with >> the bottom 6 inches off the ground. >> he says on the website that it works equally as well as an 80M dipole. >> What I like about the magnetic loops is that their performance seems to >> equal something similar to a dipole, but you can set one up in your >> living >> room or on your balcony very easily. Especially for the higher bands...a >> magnetic loop for 10M would only be 2 feet square or less...around 85 to >> 90 >> percent of the quarter wave of the band you wish to work the most on. >> A guy could easily have several loops for 6M 10M 12M 15, 17 and 20M all >> set >> up on the balcony. >> In this article he uses a coaxial stub as a capacitor, but you can also >> get >> a gennings variable cap rated for 10KV that you can motorize and remotely >> tune the antenna for allot of different bands and frequencies. >> You get polarization if the loop is vertically polarized as well...you >> get >> lobes off the sides in a figure 8 pattern with a nul at the center of the >> square...so you can use it as a directional antenna or to null out QRM or >> QRN. >> Of course, with 100W into the antenna, the capacitor has something like >> 3KV >> on it, so that piece has to be well above or beyond human contact. >> Definitely an interesting project to think about. >> These antennas are pretty hard to tune up with out an antenna analyzer as >> you have to tune the feed point, then tune the capacitor...difficult to >> do >> as oftent he antenna's feed point resonance will be way way out of the >> ham >> band...after tuning the feedpoint, you tune the stub or cap to bring it >> up >> to resonance on the band you wish to use. >> Essentially, you use an antenna analyzer after hooking up the feedline by >> the method recommended...then, where ever you see a dip in the SWR, you >> move >> the center conducter up or down the side until you achieve a flat match >> regardless of the frequency. >> Then, you start cutting your coaxial stub until your very close to the >> frequency you want, and have a flat match still. With a coaxial stub, >> it's >> something like 1 inch of coax for every 200KHZ or so. >> In his example, he starts out with 3FT of coax, and a feedpoint match >> frequency of 10MHZ...he cuts the coax down until he's at about 14.00MHZ. >> Then he just slides the outer brade of the coax back another half inch to >> get into the phone portion of 20M. >> It doesn't seem to matter what the feedpoint resonant frequency is, as >> long >> as you can get it down to 1 to 1 somewhere in the HF spectrum. >> apparently as long as that point is lower in frequency to the frequency >> you >> wish the antenna to perform on, then your ok. >> I don't yet completely understand the theory behind this style of >> antenna, >> but I certainly understand what needs to be done to make them work >> properly...even if that is a bit counter intuative to other kinds of >> antenna >> theory. >> >> 73 >> Colin, V A6BKX >> ----- Original Message ----- >> From: "Lou Kolb" <[log in to unmask]> >> To: <[log in to unmask]> >> Sent: Thursday, February 24, 2011 4:40 PM >> Subject: Re: magnetic loop antennas? >> >> >> > Colin, >> > >> > I've never used one but worked a guy using one a couple months ago on >> > 40 >> > meters. I'm in PA and he was somewhere in New England but he was 20 >> over >> > S9 >> > and I was amazed when he told me what he was running. He had not only >> > a >> > competitive signal, but an outstanding one. As you say, he couldn't >> > really >> > move from that frequency without readjusting, but the thing worked >> > remarkably well. As you might imagine, we spent most of the QSO >> > discussing >> > the merrits and drawbacks of that antenna. Sounds like a fun and >> > worthwhile >> > project. 73, Lou WA3MIX >> > ----- Original Message ----- >> > From: "colin McDonald" <[log in to unmask]> >> > To: <[log in to unmask]> >> > Sent: Thursday, February 24, 2011 6:11 PM >> > Subject: magnetic loop antennas? >> > >> > >> >>I have a couple questions for the list regarding magnetic loop >> >>antennas. >> >> Firstly, has anyone used them on HF? I'm speaking of the small >> >> transmitting loops that are made in a square and use a capacitor on >> >> one >> >> side >> >> to tune to resonance. >> >> And, if so, what sort of results has anyone found with them? >> >> Also, has anyone on list built one using a coaxial stub capacitor? >> >> Check out this website: >> >> HTTP://www.standpipe.com/w2bri/ >> >> >> >> he's got a very straight forward, step by step description of how to >> >> build >> >> a >> >> magnetic loop antenna from copper plumming supplies, and using a piece >> of >> >> coax as a capacitive stub. >> >> The antenna looks exceedingly easy to build, and his claims, as well >> >> as >> >> others, say the 3.5 foot square loop will perform as well as a half >> wave >> >> dipole on whatever band you tune it for...of course, as long as the >> >> loop's >> >> circumphrence is something less than a quarter wave on that band...for >> >> instance, this loop is 14 feet all around and therefore is less than a >> >> quarter wave on 20M. I've heard allot of great things about the >> magnetic >> >> loop type antenna...of course it's only draw back is that it has an >> >> extremely narrow band width...something like 20 to 30KHZ. >> >> >> >> anyway, check out that website and tell me what you guys think. >> >> >> >> 73 >> >> Colin, V A6BKX >> > >> >>