Ken wrote:
How can I use it to test a 40M double zepp with 300 ohm twinlead
feedline? I am at this point interested in finding the frequencies in
160M band at which this antenna and particular-length feedline will
propagate.

A 40m double Zepp is 1/2WL on 80m. You didn't say how long the
feedline is. You can get a ballpark idea of the impedance by
downloading the free demo version of EZNEC from www.eznec.com.

Assuming the dipole is 130 ft. long, EZNEC says the antenna
system can be resonated by a feedline length of 96 ft. using
300 ohm line with a VF = 0.9. The impedance seen looking into
the feedline is 0.7 ohms. EZNEC says the antenna has a feedpoint
impedance of 9.3-j1060 on 1.9 MHz with a sky high SWR on the
300 ohm line. This antenna will perform poorly on 160m.

A better solution for 160m would be to short the parallel
feedline together at the tuner and feed the whole thing against
ground, aka Marconi style, with the 40m double Zepp acting as
a top hat.
--
73, Cecil http://www.qsl.net/w5dxp

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