[TowerTalk] Topband: Estimating RF Choke impedance

[DAVID CUTHBERT]

Picture 5 shows the generator connected to the coax inner conductors It
should be connected to the coax shields.

   Dave WX7G

On Thu, Jul 29, 2010 at 1:04 AM, Tod -MN <tod at k0to.us> wrote:

>
> 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
> www.k0to.us/HAM/Balun/Estimation%20of%20RF%20choke%20impedance.pdf
>
>
> Tod, K0TO
>
>
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