1. In the wiring harness going from the receiver IF and crystal oscillator boards, cut the white wire. This wire applies 10 volts to the receiver oscillator during receive only. During transmit this 10 volts is removed, killing the receiver. Connect this white wire the 10 volt supply to provide power to the receiver at all times. The red wire in the same harness is full-time 10 volts.
2. On the system audio squelch (SAS) board, cut the collector of transistor Q905. This transistor is located toward the end of the board with three large transistors. Q905 is located just to the right of the large capacitor on the front edge of the board. This is the receiver audio mute transistor. Cutting the collector will prevent the receiver audio from being cut off during transmit.
3. Install a separate receiver antenna connector. You can use the existing coax between the receiver helical and antenna relay.
4. The radio is now ready for the addition of a controller.
5. The receiver audio is pre-emphasized and must be rolled off at typically 6db per octave.
6. COS active high can be located at TP901 (7.9 volts un squelched and 0 volts squelched).
7. PTT (pull to ground for transmit) is at P908 pin 6.
73, Ron N9EE/R
Micro Computer Concepts