RADIO LINK CABLE – The TYT-TH9000D UHF radio, used for this project, did not have a repeater link cable included. The unit did have the link connector on the radio main PCB, and the radio heat sink had a hole for a DE-9S connector. A short cable was installed and sealed with RTV, where it went through the radio heat sink.
RADIO FAN BRACKET AND MOUNTING – These are 40W radios that will probably be run at around 15 – 20 watts. Since the duty cycle of a repeater is very high, a medium CFM fan was required. The optimum position thermal position was on the radio heat sink, directly above where the audio and RF power amps were located. Two aluminum “L” brackets were machined to provide holes for mounting screws, and a cutout for the fan.
RADIO TEMPERATUE SENSOR THERMISTOR – To reduce power consumption and fan wear, a thermistor was affixed to the radio heat sink. It was located at the hottest part of the radio heat sink.
RADIO FINAL ASSEMBLY – The radio, fan, fan brackets, power cord, and fan/thermistor cable was assembled into a stand alone radio assembly.
TEMERATURE CONTROLLER ASSEMBLY – Since the cooling fan is only on when the thermistor temperature is above an adjustable level, a thermal fan controller was needed. A controller with a 5 degree C hysteresis setting was designed to avoid rapid cycling. RF filtering of the input and output lines, and a slow op amp comparator circuit was selected to prevent transient fan transitions. Note: This is a dual controller, which will monitor both radios on a repeater.
