[TowerTalk] Receive Verticals

Roger Parsons ve3zi at yahoo.com
Wed Sep 10 15:11:24 EDT 2008

I think I can answer my own question now, and the answer is faulty measurement technique...

I am only using an MFJ259 to measure both impedance and resonant frequency, but my instrument cannot differentiate between real and imaginary parts of an impedance. When I measure the antenna resonances without the added series resistor, they are all very close together, but the series resistor changes the apparent resonance by different amounts on each one. But of course, the frequency at which the MFJ shows minimum SWR is _not_ the resonant frequency - it is just the frequency at which the impedance is closest to 50 Ohms. 

I am pretty sure that the antenna with its feet in the swamp does have a better ground than the other three and although the feed impedance is very similar in each case, that only has general implications for the resonant frequency.

As I don't have any better instrumentation easily available, I will adjust the verticals to have the same 'resonant frequency' without any added resistance and then put that in later.

73 Roger


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