Programming Adapter For Philips PRM80 Series Radios

I recently needed to program frequencies into a couple of newly acquired Philips PRM8025 radios for 70cm. Programming is done by means of a TTL-level serial connection to the radio’s RJ45 microphone socket and software that was written for DOS and requiring an RS232 port on the PC.

My first attempt was to run the software in an emulator such as DOSBox and use an USB to RS232 adapter but that failed due to, as I later found out, the software requiring the RS232 DTR/DSR, and RTS/CTS lines to be connected. Unfortunately, most adapters don’t provide for this.

Matt, VK3SMB has solved this problem by soldering the lines together on the adapter chip and has instructions on how to do it on his website here. I, on the other hand, don’t have the ability to solder such small pins and so had to settle for building an RS323 adapter. It seems that finding a PC with a serial port is not easy these days, but luckily an obliging neighbour had one on their pile during the last council junk collection.

Circuit

The circuit is straightforward, it uses a pre made MAX3232 board for level conversion. The 78L05 regulates the 9v coming from the radio to the 5v required by the MAX3232.

Construction

The circuit just fits inside a DB-9 to RJ45 adapter. The coloured wires come from the RJ45 and the pins inserted in the appropiate hole in the DB-9. The
wire colours didn’t correspond to the normal ethernet colours, so testing with a multimeter determined which was which. Also, the TX and RX pads on the
MAX3232 board were only connected on one side, so short wires were soldered to the pads on each side.

At bottom right you can see the blue ethernet cable connected to the radio’s microphone/programming socket.

The power supply components were soldered togther dead-bug style and the coloured wires were cut with just enough length extending from the case so they could be soldered. The cut ends with the pins were then inserted into the DB-9 plug.

After initial testing, all the exposed connections were insulated with hot-melt glue and stuffed into the adapter case.

Success! The unit in action programming the radio. I am now on air on 70cm and very happy with my neat looking little programming adapter.