Jim, N2EY wrote: I'm highly skeptical of *any* simple wire antenna that claims multiband performance without a tuner or tuner-like device.
---------------------------- And so am I. In this case it's rather like the trick of feeding a 40 meter dipole on 15 meters where it's 3/2 waves long. The SWR is adequately low for use with little or no correction from a tuner. The antenna mentioned sounds like the one developed by Bill Wright, G0FAH who says he came up with a combination of radiator and open wire feed line that will have low reactance (be self resonant) on 40, 20, 15 and 10 meters. However, the impedance at the feed point will be close to 200 ohms on 40, 20 and 10 meters and about 50 ohms on 15 meters. So Bill used a switchable balun that selects 4:1 on 40, 20 and 10 meters and 1:1 at 15 meters. There are three advantages:: 1) The balun is operating at a low SWR to avoid excessive losses and it should behave predictably, 2) No tuner is required for most rigs, and 3) The low SWR on the coax means any length within reason can be used with low losses The dimensions of the antenna are critical! As the original poster said, he changed the length of the open wire line section. That means he simply has an off-center-fed wire. Any advantage provided by Bill's design to provide a low SWR at the balun and on the coax is lost. The dimensions Bill gives for the antenna are as follows: Short leg of the radiator is 23 feet and the long leg is 46 feet. Using 450 ohm ladder line, he recommends either 55 or 111 feet. This dimension is very important as the line acts as an impedance transformer. The balun goes at the end of the ladder line and the coax feeding the balun can be any convenient length as the SWR is (supposed to be) very low on those bands if the balun is switched for a 1:1 impedance transformation on 15 and a 4:1 transformation on 40, 20 and 10 meters. Of course, on 30 meters (or any other band) the antenna simply becomes an off-center-fed doublet in which the whole system, including the balun and coax will see high SWRs and the attendant losses. I believe this antenna first appeared on the "Yankee side of the pond" at least in QST for February 1996 Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
