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Choke Self-Resonance


Choke Self-Resonance

In troubleshooting the matching network for my 43′ vertical antenna, I discovered that somewhere along the way, the RF-blocking choke in the matching network had overheated and melted all of its insulation off, shorting all of the turns together.  I suspect that this was caused by the wiring errors I discovered earlier, but I did find references (here) on the internet saying that the 100 uh chokes from Radio Shack have some series self-resonance that cause them to leak RF through at certain frequencies.

I read elsewhere (don’t remember where) that removing the top layer of the coil can improve things a bit.  So I re-wound the coil with just one layer of windings, resulting in a 50 uh coil, rather than 100 uh.  The following experiment shows that the new coil does not appear to have any significant self-resonance between 1.5 and 30 mhz.  However, I’m not sure the 50 uh is going to give enough inductance at 160 meters to me usable.

Anyway, here are some videos of my experiment…

Migrated Comments:

5 Responses to “Choke Self-Resonance”

  1. Don Rudolph Says:

    I see you got the matching network working.
    How do you like it?
    I have rebuilt mine with 4 vacuum relays so now it works on 160 meters at 900 watts.

    Don W9BHI

  2. Randy WB0SMX Says:

    Very pleased with the matching network and antenna, once I got the wiring errors straightened out. It allows me to work 160 meters, which I could not do very well before. On 80 – 20 meters, the 43 foot antenna outperforms my 135′ doublet (only 30 feet high). On the higher bands, the doublet does better.
    But reading about the 43′ vertical, that does not surprise me. It’s doing just what it is supposed to do.
    Thanks for your comments & 73… Randy wb0smx

  3. 43′ Vertical Antenna Construction – Pt 2 Says:

    […] Choke Self-Resonance […]

  4. Dan Schaaf Says:

    So, in the end, what inductance worked for you? 50 uH or 100 uH ? If 50, how many turns on 1/4″ original form ? I have no way to do the measurements that you did so I must depend on advice.
    I built a vertical that was 65 ft tall with a 30 meter trap and I designed a base matching unit using Toroid cores ( 3 inch OD ) and a vacuum relay. Worked very well and snagged 200 countries with it on 160. But, now I am limited to a 43 ft vertical and I want to get back on 160. I am concerned about RF getting into the DC supply and back into the AC Mains.

    Dan K3ZXL

  5. wb0smx Says:

    Hi Dan. Well, in the end, I never went back to refine the Bias-T. The next time I used the vertical, I modified my bias supply to send the voltages out through a separate RG-6 cable to the matching enclosure, and connected it separately from the RF path. I know… not optimal, but it got me on the air easily. Sorry that I can’t help more with this right now. I may revisit it some time in the future.
    73… Randy wb0smx


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