WILLIS COOKE wrote: >I have a 1973 and a 1977 Handbook and I don't see it in either. What >matching method did they use?
Sorry my error, I should have said the 13th (1974) edition of the ARRL *Antenna* Handbook - page 219. They used an airwound transformer at the centre of the driven element, 19 turns of B&W 3025 stock connected between the two halves of the helical driven element with a 12 turn tightly coupled link primary. Looking into the link the impedance at antenna resonance was approximately 12 ohms. They used a broadband 1 : 4 balun to raise the impedance to 48 ohms. To reduce antenna Q, short lengths of aluminum welding rod were attached to the free ends of the helical elements. The antenna was a yagi, driven element and director spaced 15ft 8 inches. >I don't think that EZNEC can model a helix very well. EZNEC can only handle >straight wires and inductances can be entered either by inductance value or >impedance. The closest representation >would be short lengths of wire with >several loading coils. I agree, and I am not certain either that an EZNEC model consisting of several loading coils would provide useful answers because the helix could be viewed as a slow wave structure rather than a classic loaded wire. 73, Geoff GM4ESD _______________________________________________ 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
