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Re: [TowerTalk] Resistor Across a Choke Balun

To: <>
Subject: Re: [TowerTalk] Resistor Across a Choke Balun
From: "Paul Christensen" <>
Date: Thu, 30 Jun 2022 21:36:10 -0400
List-post: <>
>" what is the best way to drain static off a vertical with either a
resistor or choke?" 

I'll throw this out for others to comment on, but this is the general rule
of thumb I've used when calculating the value of a static choke across a
typical base-fed vertical radiator:

Assuming a typical 1/4-wave vertical with an adequate radial field, the base
impedance is approximately Z=36+j0.  Find a value of L where the reactance
is at least 10x the base impedance so that the base Z is not appreciably
affected by the parallel inductance of the choke.  For 160m, Xc=2pi*fL and
L=Xc/(2Pi*f).  L computes to about 33 uH.  

As a practical matter, I use a J.W. Miller #5250-RC 100 uH choke on a 160m
Marconi "T."  Prior to adding the choke, the SWR bridge diodes in my
Elecraft K3 would blow open with every wind storm.  Be mindful of the
self-resonant frequency when selecting from a datasheet.

Paul, W9AC


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