Testing out the air-wound choke

Yesterday I managed to get out to a home renovation store to purchase a three foot length of 4″ diameter ABS sewer pipe for my mobile installation. I cut a 6″ section from the pipe, drilled some tie-down holes and then made 23 windings of RG-8/U (solid dielectric).

Common mode choke

Common mode choke (aka. ugly balun)

This morning, I took a drive to warm up the FJ (it is -20°C outside) and to find a nice quiet spot to test the installation out. After installing the ATAS-120A on the end of the coax, I fired up the FT-857D and hit “tune”. The radio was tuned to 14.070 and even before matching the antenna, I could hear signals booming in.

Success! After the initial 30s tuning procedure, the antenna lengthened until it was resonant with an SWR of nearly 1:1.1on 20m. I was quite pleased. I then tried 30m and had no luck. Tuning down to 40m also gave me no joy – perhaps a few more turns (therefore feet) in my current choke might help me out!

In any event, all bands from 20m to 10m tuned up very nicely. With an excellent SWR on 20m I will be more or less set for the road-trip. To finish up my frigid testing session, I managed to make a PSK31 contact to Scotland (while parked) and had a quick QSO with Rick (MM3UOR) at 16:53UTC who was approx 4900km away.

More to follow …

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2 Responses to Testing out the air-wound choke

  1. James says:

    Hi Bob,

    Thanks for the input! Yes, having an out-standing ground is a requirement and since my install was rather hastily completed (ie. less than ideal grounding), I suspect that is where my problem lies. It is my intention to properly ground the antenna to the vehicle chassis – the only trick is doing it from the factory roof-rack. I’ve got some ideas in store – lets see how well they turn out.

    I will definitely give the TPN a shot while on the road – I’ve jotted the details down in my notebook so I don’t forget.

    With any luck I might catch you on 40m!


  2. Bob VA3QV says:

    hi James,

    Although I have never owned a ATAS 120 I seem to remember something about making sure your ground was excellent to get it to tune up on the lower frequencies (30 and 40m).

    Just a suggestion…


    when you are in transit don’t forget that 40m is getting a little more active with the band conditons slightly improving… The Trans Provincal Net is on 7.055 lsb between 7am and 5pm so you might have someone to talk to …

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