MFJ 1788 Loop Antenna Fixed (#65)

After several videos and disappointments, the MFJ-1788 Hi-Q Loop Antenna didn’t work on 40 m. Now it does! I took it apart to discover that the big capacitor was not fully meshing because of a mis-set limit switch. See how it works!

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2 Responses to MFJ 1788 Loop Antenna Fixed (#65)

  1. David Casler says:

    Hi Gerhard, you’re beyond my experience with antennas. Please let me know how it works out—I’m curious!

  2. Gerhard Spangenberg says:

    Hi Dave
    Just found your site. Love it.
    Please give me an explanation to my observations on the MFJ RX&TX loop antenna.
    I constructed a current (toroid) and voltage (voltage divider) sampler and mounted it right after the transmitter before the loop tuner.
    As I varied the transmitter frequency (about 10 w) around the previously center tuned loop frequency, the resultant lissajou figure did move, but it never went through the typical 45 degree angle as seen on resonant circuits. nor was the typical +-90 degree phase shift observed.
    Using time differences at zero crossover between the current and voltage waveforms in nanoseconds, it indicated a phase shift that went from a maximum to a minimum (at resonance) back to maximum, but never reversed direction.
    Examination of the coupling revealed an air coil inductor of many turns and a fixed capacitor on the input circuit before the single 16 ga loop, both of which I saw also in your “Unpacking” video.
    What is going on with the voltage to current relationship ?? why is the classical phase angle reversal not observed with this L/C antenna design????
    KF4GGK (General)

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