Icom IC-751A external RX antenna overload

Discussion in 'General Technical Questions and Answers' started by W0BTU, Oct 4, 2010.

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  1. K7ZRZ

    K7ZRZ Ham Member QRZ Page

    From that line above... what the heck is a "fuse lamp" and what does a "diode 3v limiter" look like (specific part numbers and/or diagram).

    The rest before that was good, but the practical part of it all got lost on me.

    Thanks again.
  2. W8JI

    W8JI Ham Member QRZ Page

    For a fuse lamp, use a 50-100mA low voltage incandescent lamp. The limiter would have to be zener regulated bias into a diode clamp, to hold the signal diodes off until around 3 volts peak is reached. With small antennas or narrow band antennas, you could use less voltage. The AM BCB is most of my voltage problem at night, when the band opens.
  3. W0BTU

    W0BTU Ham Member QRZ Page


    You see anything wrong with this?:
    RX ANT===RELAY====FUSE LAMP===RX INPUT ... And then a pair of back-to-back 1N4148'a from that point to ground?
  4. AA7NM

    AA7NM Ham Member QRZ Page

    Icom 751/751a RX antenna overload

    I use an Icom 751 with a dedicated RX antenna (loop) and a 160 meter dipole. I can confirm this is a problem with an amplifier. While I haven't seen any signs of rig damage, the problem was enough to trigger a feedback loop into the amplifier, which nearly damaged that. My answer was to build a switching relay into an Altoids tin that actuates in line with the amplifier's TX control. It shunts the RX loop to ground during transmit. It's working fine ever since.
  5. K3STX

    K3STX Ham Member QRZ Page

    I have a Kenwood TS-850S that has been modified to have a "receive antenna port" ala the N6TR mod for this radio. I have been told that what this mod does, and how most RX antenna ports work in modern rigs, is to DISCONNECT the RX antenna during transmit, and NOT to ground it.

    It was recommended to me to buy an ICE model 196 RF limiter. (I think Array Solutions sells them now.) So huge RF signals can NOT get through the RF antenna port. Works for me, and all it took was a phone call, a VISA card, and the desire to spend $40.

  6. W5HTW

    W5HTW Ham Member QRZ Page

    This is the system the FT101E series used, installed by the factory. A small lamp in the antenna line. I had seen that lamp light up rather brightly one day when I was using my amplifier. A clue that the receiving antenna was too close to the transmitting one.

  7. KB0TT

    KB0TT Ham Member QRZ Page

    Hooked Up


    You did hook up to the correct wagon this time . :D

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