Mike, KK5F wrote: Moxon's "HF Antennas For All Locations" book, pages 47 to 49, has some interesting and convincing observations on the Zepp which conclude that it should NOT work either theoretically or practically as it is typically depicted, were it not for the effect of stray capacitances to ground and between conductors in the matching section.
------------------------------ Moxon makes a number of odd statements about what people believe is true that can be confusing. Reading his book carefully, I came to the conclusion they are the result of his not distinguishing between "Ham lore" and engineering data. For example, when speaking of an HF antenna he says that "antenna current used to be regarded as a good indication of antenna efficiency..." He uses that to indicate the confusion over how a 1/4 wave section of transmission line works, as on the classic Zeppelin antenna. More current means more efficiency was correct when antennas were worked against ground and were less than 1/4 wave long, such as when all Ham operations were around 200 meters, but I've never heard anyone knowledgeable say that more current meant greater efficiency at the frequencies where the Zeppelin antenna was used. It can be true under certain very specific conditions, but that text is the first time I ever saw someone claim that it might be generally true at HF. Perhaps Moxon is speaking to some misconceptions that British hams held that never made it across the Atlantic <G>. He never explains who thought that antenna current was regarded as an indication of efficiency. The Zeppelin feeder arrangement is simply a 1/4 wave transmission line, such as is used in a great many antenna designs. The J-pole is a good example as you point out, although that also includes a matching stub to work with 50 ohm coax. The degree of balance in the Zeppelin antenna is not perfect, but it's good. There is leakage at the insulator at the un-connected end of the feeder that allows some current to flow and, of course, the impedance at the end of the 1/2 wave wire is not infinite, so some current flows there too. The exact amounts and their phase relationship is not perfect, but perfect balance is never achieved. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] 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
