Here are instructions for building either uni- or bi-directional repeaters with CDM type radios like the CDM750.
There are no external component used other than some wires and connectors as shown. Two Motorola part number
HLN9457A accessory terminal kits should be all you need. These kits contain the connector shells and some
pre-assembled jumpers and connector pins.
Turn down the power on the TX radios to about 5 Watt and hopefully the transmitter won’t overheat.
The repeat audio gain is adjusted by setting the accessory mic input gain to about 3 dB using the programming software.
The default is 28.5 dB and is definitely way too high. Also make sure the timeout timer on the transmitting radios
is set to something around 30 seconds.
Since CDM radios use a push on push off type power circuit for turning the radio on and off, the ignition control line
is used to let the radio power up in the on state after a power failure etc. The easiest way to do this is a by getting the
needed 12 V for the Ignition control pin (pin 10) from the Alarm pin (pin4). Pin 4 is always at 12 V when programmed
for Alarm and active low.
It is important that both radios use the same solid ground. Do not let the ground of the transmitting radio float above
the ground of the receiving radio.
A pdf file showing details is available through the link below. Take note of the audio settings. The repeater uses filtered
(squelched) de-emphasized audio on RX and pre-emphasized audio for TX. Flat audio is not used to keep things simple.
http://domtoren.com/990/Bi-_or_Uni-dire ... radios.pdf
Or for some older stuff look here:
http://domtoren.com/990/rptr.pdf
http://domtoren.com/990/PassiveRepeater.xls
Nand.
