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[TowerTalk] Estimating RF Choke impedance

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Subject: [TowerTalk] Estimating RF Choke impedance
From: "Tod -MN" <>
Date: Thu, 29 Jul 2010 02:04:27 -0500
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This is a follow up to Jim Brown's note on my measurements of choke
impedance using a power meter. As Jim pointed out, the circuit he used on
page 31 of his tutorial allows one to measure the impedance of a choke made
by winding coax around one or more combined cores. Jim's circuit used a
signal generator and an RF Voltmeter [in his case a spectrum analyzer]. By
making measurements at several frequencies one can get an idea about
performance of a choke over a band of frequencies.

Since I happen to have an HP spectrum analyzer and tracking generator I
decided to see if I could generate and photograph curves of the impedance of
a choke over a frequency range. Jim's "Choke Cookbook" suggests that one use
seven turns of coax through five combined toroidal cores of type 31 material
to make a choke for 160m and 80m. Since I had a combination of six such
cores on hand I decided to make a seven turn, six core choke which I would
then measure across the 160 and 80 meter band
In addition to the measurement of the choke I decided to measure some small
resistors in the same circuit. The curves for the various resistances would
allow one to visually estimate the impedance of the choke when the choke
curve was compared with the resistor curves.
The result of this simple experiment has been posted on my web site. If you
have an interest in this you can click on the link below to see the pictures
and commentary.

Estimating RF Choke impedance

Tod, K0TO


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