23cm Repeater

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The basics

Perth has not had a 23cm FM voice repeater. Most other capital cities in Australia do have one or more 23cm repeaters. Some amateurs decades ago purchased 23cm FM equipment assuming one day soon there would be a 23cm repeater in Perth. Well it did not happen. No one volunteered to build such a repeater. Strangely it was easier to build such a repeater 20 or more years ago than it is today, and this is because today 23cm amateur equipment is no longer manufactured as just a 23cm FM mobile or base. This is the easiest way to build a 23cm repeater, from existing mobile or base transceivers. I have obtained 3 Yaesu FT-2311r mobile transceivers. One has been in operation as the 23cm port of the Cross Band Repeater. This has allowed me to find out about 23cm operation using the FT-2311r and work out how to build a complete 23cm FM repeater. Two FT-2311r's are needed to make a repeater. One is used as the receiver and one as the Transmitter, as shown below, in simple form. The input and output to the transceivers is via the microphone socket. As it would happen audio and mute logic are available from the 8 pin microphone socket. This means no connections have to me made to the transceivers other than via the microphone socket.

Construction

The two FT2311r's will be mounted in the same rack mounting box, along with the NHRC-4 controller and any other circuitry that may be required. One import issue is heat sinking, as the FT-2311r would not have been designed for 100% duty cycle, as is required with a repeater. Also at 23cm the efficiency of the driver and PA stages is poor, and even though the transmitter is only 10 watts, heat dissipation is important. Fans In order to dissipate the heat of the transmitter radio, 3 fans will be used. Two small ones directly attached to the heat sink, and a larger one blowing air over the entire transmit radio. Should any of the fans fail, then there will always be backup. The fans of course only come on when the transmitter is transmitting.

3 fans for transmitter cooling


12 volt wiring rear of  housing