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Thread: Astro Spectra - CR3903 RX Switch Pin diode Zapped..... again

  1. #1
    tim No Longer Registered

    Default Astro Spectra - CR3903 RX Switch Pin diode Zapped..... again

    Yesterday I replaced one of the TX/RX switching diodes on my high power VHF Astro Spectra. It was shorted, and the receive sensitivity was about 5uV.

    This afternoon I couldn't key up a distant repeater & put the analyzer on the radio, and same thing.

    Configuration: The top of my Yukon has 3 antennas. 5/8wave VHF in front, 1/4 wave VHF in Middle, and low band base loaded in the back. The front and back antennas are separated by about 4 feet.

    I had moved the antennas around, as I thought that the Spectra's antenna may have touched the lowband antenna while I was talking on 6 meters, zapping the diode.

    Today, I didn't talk on 6, I only keyed up the radio about 10 times, checking coverage in a bad area.

    Sooooo, are the Spectras prone to this diode going <poof> in the presence of high RF? (I had the same problem in my car (Impala with VHF/LB antenna on the back deck). I changed the VHF to a 1/4wave, and haven't had any other problems.

    Ideas?

    Thanks,

    Tim


  2. #2
    GS4 No Longer Registered

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    I have heard of this a few times from hams with high power low band radios and VHF Spectras.

  3. #3
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    Your problem is you have no circulators on a mobile since the Micor radios (the "Pork-Chop" module). This dumps return RF to a dummy load and acts like a one way RF diode, sort of. It will keep high SWR RF from coming back into the radio and blowing the RF diodes. I have a crapload of Range 1 UHF PA pullouts that are fine, but are in Q bandsplit, so if you need replacement diodes, we can talk...

    I have also heard rumors that with the lowband and VHF radios that TX'ing in a viaduct (under a bridge) canl reflect the RF back into the radio and cause the problem mentioned. It may be possible that proximity to the tunnel might detune the antenna or reflect some RF but that sounds like it might be an urban legend.

    You might at least want to double check the antenna SWR reading at the radio to make sure your antenna or feedline isn't the culprit.