Jim, I did a little chatting with Guy K2AV when he was starting to work on that project (W0UCE lives only a few miles from me), and I recall that changing the height above ground changed the behavior. So if you do not have the lowest wire 8 feet above the ground, it will not be tuned properly. Maybe Guy will comment, he frequently posts on this reflector.
73, Don W3FPR On 2/28/2012 5:22 PM, Jim Bennett wrote: > I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters is > my biggest hurdle. I put up an 80 meter Inverted L several months ago - prior > to getting the KPA500. The vertical part of the antenna is 40 feet in length. > I had been using two radials, about 14 inches above ground - small lot, > CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the internal > tuner. I had done some pruning of the radials to get it resonant on 3.550. > The K3 tuner took care of the rest. Well, along came the KPA500 and as yet, > no KAT500. So I started looking at the antenna to see what I could do. I > opted to replace the two single radial wires with a K2AV Folded CounterPoise > (FCP). Not sure if this was a mistake or not. Everything I've read said that > the FCP approach on 80 / 160 meter Inverted L antennas would result in a > greatly improved signal. What has happened is that I cannot for the life of > me get this thing resonant around 3.520. And yes, I did build the isolation tr an > sformer, per the instructions. > > Here is what is happening and I am certainly perplexed. I'm using an MFJ-259B > meter, at the shack end, to take my readings. I get TWO SWR nulls. Yes, two. > One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null is at > 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at 3.520 > or so, I started adjusting the length of the antenna. Adding wire to it makes > the two "nulls" go down in frequency, as I would expect. If I instead shorten > the antenna wire, the "resonant frequencies" both go up. However, there comes > a point with both approaches where the change of frequency stops, but the SWR > goes up. > > As you can guess, I am NOT an antenna expert. Why do I get two different > resonant frequencies, separated by only 200 KHz? > > I've spent the better part of two days futzing around with this thing and am > about at my wit's end. I don't necessarily want to toss the entire FCP > assembly in the trash, and go back to the two radials, but this is not going > as I'd hoped! If someone on this list who has a good handle on wire antenna > tuning can give me some pointers and/or hints, off the list, I'd certainly > appreciate it. :-) > ______________________________________________________________ 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
