Tip on using the RPC-M300 "3 in 1" programming cable:

I was inspired to create this page because I got a programming interface for a GM300 which came with no documentation. I ordered the interface off of eBay and it came with no documentation and I would later learn that the interface requires a 9 volt input to work.

I started out with a GM300 radio, it came to me with no documetation about the radio and how to use it and no documentation on how it was currently programmed. I only knew that it was programmed for the HAM bands. I used a frequency counter and guessed based upon the standard repeater offset what the receive frequencies were. However this did not give me any information on what if any CTCSS tone programming had been done on thoe frequencies.

I joined the Radio Doctor Yahoo Group and downloaded the Radio Doctor software from the files section of the Yahoo Group. I also ordered from eBay a "3 IN 1 Programming Cable" which is an RPC-M300 or a clone of that unit (see photos below to find a similar unit) which had the RJ-45 Crystal plug or whatever Motorola calls their RJ45 connector on the GM300 radio.

The "3 IN 1 Programming Cable" shipped from China and arrived within a few days of the estimate in the eBay listing. The Interface came with no documentation at all. I contacted the seller with specific questions about how to connect the interface and whether the red and black wire-pigtail on the adapter also required power and if so how much power. They replied with a semi-coherent reply which essentially told me that it was radio and the PC. They did not in anyway answer my question.

I bit of digging and I found on this web site an answer; these "3 in 1 programming cable" units require a nominal 9 volts DC to the red and black pigtail. Once I applied power to the pigtail the Radio Doctor software worked as it should and I was able to retrieve the radio's configuration and figure out which repeaters were still current and which ones were not.

With the power applied to the red & black pigtail the Radio Doctor software worked just fine.

Be aware that the Motorola pin numbering convention on the RJ45 connector is the reverse sequence from the standard pin numbering convention. So if you make your own cable make sure to use the Motorola pin numbering convention.

Very helpful GM300 web sites:

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