Motorola GM300

For local traffic a Motorola GM300 (VHF) has its place in the shack. The set is placed on a ‘base stand’: the original Motorola desk stand with internal speaker, together with the desk microphone. Also available is the original Motorola power supply, which is perfectly silent as it doesn’t have any blowers. So I can have the VHF radio on without having the heavy main power supply on as it also brings noise in the background.

Although the radio is already about twenty years old is it apart from some dust in new condition. This is one of three GM300 in my stock. The set has the advantage of a front speaker, which provides good audio quality so there is no need for hassle with external speakers. After mounting the set it only requires an antenna and power connections and you’re ready to go. With that reason I’ve bought my first GM300 more than 10 years ago.

Motorola GM300 met base stand
Motorola GM300 met base stand

Out of band programming

Very easy with this radio:

  • first ‘read’ the set with the correct Motorola RSS. Carefully store the codeplug so you can always return to a functional configuration;
  • then go to the screen where you can change the ‘personalities’. ‘Personality’ is M-language for ‘channel’;
  • when entering frequencies you should only use the numeric keys on top of the keyboard. Don’t use the numeric keypad at the right side of your keyboard;
  • nevertheless the RSS will nag when you enter a frequency lower than 146 MHz (in case of the VHF version);
  • to solve this: keep the ‘shift’ key pressed when entering the digits of the QRG. Only release the ‘shift’ key when typing the decimal separator. Also be aware to type the frequency including the last digit. So in stead of  ‘145.50000’ you type ‘!$%.%))))’;
  • on tabbing out to the next field the strange characters ‘!$%.%))))’ correctly change into ‘145.50000’;
  • when saving and writing the radio the software will also nag a bit with a warning you’re programming out of band so probably the set needs alignment. Just ignore it: the GM300 works perfectly well in the HAM band.


This happend to a GM300 which had been stored for years. On first glance nothing was wrong with the radio, except it didn’t receive anymore. TX was fine, RS not. And it wasn’t just ‘deaf’, because also with a handheld next to the radio nothing was received. I started thinking about faulty capacitors. In that case the GM300 wasn’t as indestructible as supposed to…

Some research on the internet revealed an issue with a crystal in the RX stage, which could affect the GM300 after years. A 44.645 MHz crystal (VHF version) is somewhere hidden, deep in the radio. But as a Motorola radio is easy to disassemble the radio had been repaired within 30 minutes: opening, replacing the crystal and assembling the radio again. After powering it up the radio was working great again. Just as expected. Radio amateur happy, case closed!

I had to purchase a set of 5 crystals, which means I have some spares left. Don’t hesitate to contact me in case you have a GM300 with the same issue.

40 instead of 16 channels

On the internet there is a modification available to expand the number of channels to 40. The modification isn’t really difficult, but it requires some concentration (and experience with a hex editor). I successfully did this modification with one of my GM300. With the remark that the set will only scan the first 16 channels.

As always: I’ve successfully completed this modification. But it’s always on own risk. The modification can be found on the ‘’ website in the GM300 section in the paragraph ‘Add channels by modifying the .MDF file