Mastr II VHF/UHF Mobile Full Duplex Mods

Notes from the Northwest Repeater Association

PO Box 230788
Portland, OR 97281
1 June 93

  1. Obtain a pair of GE ICOMs on a commercial frequency in the range the radio was originally operating. Follow the tune-up procedures in the GE manual (see above) and check to see if the radio meets specs before attemptimg any modifications.

  2. If your radio is an "E" model (thick case):
    Check to see what is located below the main radio chassis. Remove the second exciter or receiver front end and take out all extra wiring, splitters, etc. These are not needed to make a basic repeater. Again, check to see if the radio is still operating properly before proceeding.

  3. On the bottom of the control board, cut the trace between H95 and H96. This will disable the RX audio mute circuit.

  4. On the top of the control board, cut the trace going into pin 7 of J904 (the Rcvr/Audio Squelch board). This will disable the PL RX mute circuit (if desired).

  5. Put a jumper between J903-11 and J903-12. This puts 10V on the receiver to keep it on all the time.

  6. If you are using the GE factory PL deck, several modifications are necessary to keep the RX decoder from being disabled when the radio goes into transmit. First, cut the top lead of CR1009 which is mounted vertically on the PL deck. Next, cut the trace on the bottom of the board that goes from PTT to pin 7 of U1001.

  7. Install a small fan on the top of the radio directly over the PA compartment to pull air out of the radio. Fan cooling on the rear heatsinks may also be required if you are running the radio close to its rated power.

  8. The factory control head can be used but you are probably going to want to shorten the cable. If you build you own control box, the cable can be used to bring out all of the connections. CAS is used for the COR line and if you are using the factory PL deck, RX mute will give a decoded PL signal. Pullup resistors may be required depending on the controller you are trying to interface to.

Good luck!