In a message dated 2/21/07 4:59:24 PM Eastern Standard Time, [EMAIL PROTECTED] writes:
> > our club W5KA uses 80 M Inverted Double Extended Zepp > element wire doublets. If my math is right, that works out to about 330-340 feet of wire, center-fed! > > We have had up to 250 feet of two types of window line, and with the large > Dentron tuner, we have a low loss match, and it works every signal we hear. > That is on multiple bands where we use the above antenna between 80 and 15 > meters. (10 having been dead for last several field days down here). > Good job! > No problems matching with the popular nominal 300 and 450 ladder lines of > poly insulation. A number of Cebik's models are done without assumption of > big ceramic insulators, or home made 600 ohm line. > > If a particular lenght of feeder presents a matching problem on a given band > > you add or subtract a few feet of line. Keeping 5 and 10 foot adder > sections is not hard and wire nuts make a quick splice of the added section > into the feeder to move the optimum impedance position to suit the tuner. > > I have matched such antennas as 5/8 leg Zepps on 20m with the smaller B&W > tuner, also without a problem with random feed line length. > One key point to remember is that the feedpoint Z of those antennas is neither very high nor very low on any band. Nor is it likely to be highly reactive. The end result is that the ladder line is probably operating at an SWR of less than 10:1, and maybe even less than 5:1. Which is a good recipe for low loss. See Ron's (AC7AC) commentary on the situation where the feedpoint Z is very high or low. > Such antennas have less weight and wind load than Windom, (OCF) types that > require a balun at the feed point. > True - but one could also use open line, and a balun near the ground. All depends on the situation. In a domestic contest like Field Day, a lot depends on things like where you are. Hams in the middle of the country face different antenna challenges than those on the coasts and the corners. For example, somebody in NE or KS is within 1500 miles or so of every ham in CONUS. Someone in WWA, SDG, SFL or ME may be twice that distance from a sizable number of CONUS hams. OTOH, a stations in the corners don't have to deal with the fact that the rest of CONUS is all around them. 73 de Jim, N2EY ************************************** AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com. _______________________________________________ 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
