When Cale, K4CDN, wanted to put up a new repeater, we thought this would make for a great build project. The goals were to set up a repeater that would have great performance and reliability and come in at a reasonable cost. We also wanted to have the option to expand the system by linking over the internet or RF in the future.
We settled on a pair of used Motorola CDM1550 mobile radios, Sierra Radio Systems repeater controller, Sinclair mobile duplexer and accessories all mounted in a 12U open frame wall mount equipment rack.
Top view showing the transmitter and cooling fan on the left and the receiver on the right. The blue PCB is a Sierra Radio interface board.
The interface board is essentially a breakout board that makes it easy to interface two radios, fan and other accessories to the single control cable that runs to the control system.
Basic board features as seen in the picture
– Single PowerPole connector for 13.8 volt power input
– Input fuse and fuse for each radio and terminal block connections to power the radios
– Splitter that routes the 9 signals on the control system cable to the terminal blocks that go to each radio
– Fan speed control pot and control relay
– LEDs to indicate COR, PL Decode, PTT and fan control
Additional functions can be populated later which include…
– Microcontroller and 2.4 GHz data radio to communicate to the optional linux CommServer in the repeater controller.
– Remote control DC latching power relay
– Remote monitoring of DC power voltage and current
– Remote monitoring of RF wattage with external directional coupler
– Remote monitoring of temperature (external probe), and receiver signal strength (RSSI)
– Remote control of user programmable digital outputs which can be used to change radio modes (frequency, PL, power, etc)