Well here's the scoop on the GM300's, M120's and M10's. The sheet says there is a difference between the 8 and 16 channel units. We'll try to describe both.
8 Channel units Pin 1 = int spkr megative (not gnd) Pin 2 = mic audio, 80mv for 60%dev Pin 3 = mic PTT Pin 4 = not used Pin 5 = flat tx audio, 150mv for 60%dev Pin 6 = not used Pin 7 = GND Pin 8 = COR active low RUIndicator follows tone if used. Pin 9 = not used Pin 10 = IGN control Pin 11 = Disc audio, 600mv controlled by JU551 Pin 12 = not used Pin 13 = Sw A+ 1/2 amp max! Pin 14 = remote hook sw Pin 15 = int spkr pos Pin 16 = ext spkr pos
16 Channel units same as above except: Pin 4 = programmable output defaults to external alarm. Pins 6,8,9,12,14 = programmable I/O (the options can be viewed with the RSS)
I know you can get all the right ins and outs but as you can see, they must be set up.
The plug that goes into the radio is as follows.
Looking from the rear of the radio (or plug), Pin 1 is upper right with pin 2 below, pin 16 being lower left. Top row is odd numbers, bottom row is even.
Based on the above information this is how the CROSS-CONNECTION between the radios should go!
Radio1 Radio2 PIN 3 PTT ___________________ PIN 8 COR PIN 8 COR ___________________ PIN 3 PTT PIN 5 TX Audio ___________________ PIN 11 Disc Audio PIN 11 Disc Audio ___________________ PIN 5 TX Audio PIN 7 Gnd ___________________ PIN 7 Gnd
**** CAUTION **** Check to see the programable outputs of the 16 pin connector prior to hooking up. Also, the 5 pin radios will not do this because you can't get COS and PTT outputs.
You might want to cut the jumper for the local spkrs - PIN 15/PIN 16
If you want to use DPL or CTCSS you will need to use shorting plugs or Gnd. the remote hook switch on the microphone.