> I am trying to use a 259B to measure the impedance of a short vertical
> for a receiving array.
You have to load the vertical, and swamp it with a series resistor if
you want any reliable performance. You could use a source follower
FET buffer. A J310 biased at about 50mA has about 75 ohms source
impedance but unfortunately overloads easily. I've had to use power
FET's at nearly 500mA of standing current to operate in crowded RF
environments, and low-noise 25-watt 28 volt power FET's cost about
$40 or more each.
So I just settled on using L and R loading, as described on my web
page at W8JI.com
I have an FM station about 1 mile away that
> I'm pretty sure is giving me erroneous readings, I've had this trouble
> before on 40 and 80 meters. I've tried the MFJ filter but it's notch
> is for the AM band and it doesn't seem to help much.
I'd just build an FM trap, and/or a 50 MHz lowpass. That would have
minimal effect on 160 impedances, since it would look like a fairly
short transmission line rather than appear like one dozens or
hundreds of feet long like a low-band lowpass would appear.
73, Tom W8JI
W8JI@contesting.com
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