I recently picked up a few old Motorola GM300 radios on eBay. These radios are very stable and work well for unattended operations or in repeaters. They are very affordable and carefree. But they are also hard to program, at least if you don’t have the information how it works on modern computer. So I was looking for a solution. Many people suggest to just use an old MS-DOS computer, but these are hard to get these days and there must be a better solution than this.
After some digging into this topic, I came across this wonderful article by NotPike where he was building a POSAC Unipager setup with one of these radios. It pretty much tells it all. But for anyone who is to lazy to cherry pick the article for information, here is a short summary:
All you need is an old CAT5/6/7 network cable, a 1N4148 diode and a few wires. Cut the cable in half and solder it together with the other components as pictured above. As Interface make sure to get a FTDI of the type FS232RL. This is very important, there are many many FTDI and FTDI like adapters on the market but only a FT232RL based adapter will work with Motorola GM300 radios. You can get them cheap from China for about 1 EUR a piece.
Using RSS in Dosbox
Once you build the cable, use this guide by KK6JYT to setup the programming software in Dosbox.
Make sure you have the cycles settings correctly. 191 is not exactly needed but below 250 is required for a stable connection. A second modification I did towards the original guide was setting the cputype to 386. This is not needed but made me a bit more comfortable with the settings.
Programming worked very well that way. I programmed multiple GM300 on a Elitebook G6 with Windows 10 like this. If you have any further questions feel free to leave me a comment. Happy hacking!