Tuning capacitor limits

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  • #3533
    bobarry
    Member

    1. Hint for the instructions. The tuning cap must be turned with a feather touch. If you hit the ends the knob keeps turning.

    2. Design mod idea. Drill a finger hole (with rubber plug) so you can fully mesh the cap and align the knob.

    3. Question. Should the cap be fully meshed when the finger hole or the white dot is on the calibrate line?

    The instructions worked great initially until I turned the knob way past the end.
    Goal was to use it on the porch, but that’s not possible with a SWR bridge alone. Bringing it indoor until I have it mastered.
    Very well made, great design effort.
    73 Bo W4GHV since ’54

    #3840
    AniaDeely
    Member

    Hi…It’s hard enough finding the right tuning capacitor for the AM BC band. The AM band goes from 550 to 1710 kHz, a ratio of just over 3:1. The capacitor needs to have a range of 9:1 as the capacitance varies as the square of the frequency, so the common value of 50 to 450pF just doesn’t quite cut it. It gets worse as you go down to the longer wavelengths and adding fixed capacitance reduces the tuning range even more.

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