
DIY Programming cable for a Motorola GM 300 series two-way radio
To make a DIY programming cable for a Motorola GM300, you will need the following materials:
- A USB-TTL adapter
- An RJ45 Ethernet connector
- A standard silicon signal diode, such as the 1N4148
- An Ethernet cable.
Once you have gathered your materials, follow these steps to create your programming cable:
- Strip the insulation off of the ends of the Ethernet cable.
- Solder the ground wire from the USB-TTL adapter to the blue-white wire in the Ethernet cable.
- Solder the signal wire from the USB-TTL adapter to the orange wire in the Ethernet cable.
- Do Solder the anode of the signal diode to the TX pin on the USB-TTL adapter.
- Solder the cathode of the signal diode to the RX pin on the USB-TTL adapter.
- Insert the RJ45 Ethernet connector into the end of the Ethernet cable.
Your DIY programming cable is now complete! You can use it to program your Motorola GM300 radio using any programming software that supports the radio.

Additional tips
Here are some additional tips for making a DIY programming cable for a Motorola GM300:
- Make sure that you use a USB-TTL adapter that is compatible with your computer.
- Use a high-quality Ethernet cable to ensure that the signal is transmitted properly.
- Be careful when soldering the wires to the connectors.
- Test the cable before using it to program your radio.
Here are some of the programming options that you can change on a Motorola GM300 radio:
- Channel settings: This can change the radio’s channel frequencies, CTCSS/DCS codes, and scan lists.
- Zone settings: It can create zones that group together channels.
- Talkgroup settings: It can create talkgroups that allow you to communicate with specific groups of users.
- Privacy settings: This can set the radio to use CTCSS or DCS codes to block unauthorized users from listening to your transmissions.
- Other settings: Using this option can also change the radio’s display language, backlight brightness, and other settings.
With a little bit of time and effort, you can easily make your own DIY programming cable for a Motorola GM300 radio. This will save you money and give you the freedom to program your radio whenever you need to.
Supported USB-TTL modules
- CP2102 USB 2.0 to TTL UART Serial convertor Module – (*This module should work with almost all Motorola radios except GM300*)

- FT232RL USB to TTL 3.3V 5.5V Serial Adapter Module – (*Only suitable module for programming GM300*)

The same cable supported to
All Maxtrac Mobile radios, MOTOROLA Radios with crystal plug.
PM400, GR400, GR500, GM300, GM338, GM950, GTX Mobile.
M1225, M10, M100, M120, M130, M200, M1225.
Sport base Mobiles, M400, Radius Mobile.
GR300, GR1225, R1225, LCS2000, Maratrac, SM50, SM120 and Desktrac GM3188, GM368, GM300.
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