Should I remove the MVP TX - RX antenna relay?

Concept:  Once the radio is duplexed, there is no need for the T/R relay since both the receiver and transmitter have their own antenna connections on the back of the radio set.  The power for the T/R relay is supplied by the 3 pin connector directly between the harmonic filter box and the side of the radio directly in front of the original antenna connector.  This connector is referred to as P951 and mates with J1 on the filter board.  Originally, power (A+) is constantly applied to the relay on pin 1 which is the one closest to the front of the radio.  Pin 1 and 2 (front & center) are tied together.  Pin 3 is the one closest the back (original antenna connector) and is the negative connection (ground) which is switched by the PTT signal to actuate the relay.

There are three things that can be done, as the transmitters RF signal will still pass through the relay if it is not removed.  The new receiver connection that has been added to the back of the radio will bypass the relay, so, as for the receiver -  the relay is of no concern.

Procedure:  Here are the 3 options:

  1. You can choose to do nothing with the relay.

  2. You can leave the T/R relay alone, clicking in every time the transmitter is keyed. The problem with leaving the relay alone is that the relay can fail, or make a bad connection.
  3. You can jumper power to the relay coil so it stays in the transmit position.

  4. Applying power the relay coil at all times will keep the relay pulled in. This eliminates the clicking, but the relay can still fail.  To jumper the relay into the transmit position cut the wire leading directly from P951 pin 3 and ground this wire.  This option separates the PTT signal from getting to the relay and provides a constant ground for the relay.
  5. Remove the Relay.
    One PC board comprises the harmonic filter and the T/R relay.  Remove the screws hold the SO-239 antenna connector to the chassis.  Heat the center connection and carefully remove the antenna connector.  Remove the screws that hold the harmonic filter / T/R relay assembly, then unsolder the jumpers that couples the power from the filter board to the PA.  Remove the filter board, but leave the PA coax connected unless you want to unsolder it too.  Remove the relay (this is a bit of work!) and jumper the harmonic filter output into the antenna jack on the PC board.   I typically use a piece of short coax for this jumper. Verify that you have not shorted out the PA's output, and reassemble the filter board back onto the radio set and resolder all wires.



Note:  If you are uncomfortable with modifying the board, it may be best to do nothing.  Some things are better left alone...  In most cases I do nothing with the relay as they seem to last even in repeater duty.

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