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Topband: 259B, CIA-HF and Cablemate?

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Subject: Topband: 259B, CIA-HF and Cablemate?
From: W8JI@contesting.com (Tom Rauch)
Date: Mon, 23 Sep 2002 15:05:47 -0400
> 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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