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GM300/M120 - BatLabs
http://batlabs.com/gm300.html
9600 Baud Packet Modifications. The GM300 Series are 9600 baud packet capable. They do need a minor modification though. For RX, its no big deal, just take RX audio from PIN 11 of the Accessory Connector and swing JU551 to the (A) position (Flat RX Unmuted).. For TX audio, you will have to run a jumper to the junction of R223, C228, R222 on the RF board to inject the data …
GM300 Information Page - Repeater Builder
https://www.repeater-builder.com/motorola/maxtrac/gm300-info.html
The audio power amplifier is one single IC rather than discrete transistors. The heat-sink is considerably different and mounts only to the bottom of the chassis - no more T8 flat-head screws through the side of the chassis. There are far fewer components on the board too. All GM300 logic boards have a 16-pin accessory connector.
Motorola GM300 Information Page
https://qrzcq.com/pub/RADIO_MANUALS/MOTOROLA/MOTOROLA--GM-300%20Information%20Page.pdf
The GM300 logic board is significantly different from the MaxTrac logic board. It can control the RF board's local/DX circuit. The audio power amplifier is one single IC rather than discrete transistors. The heat-sink is considerably different and mounts only to the bottom of the chassis - no more T8 flat-head screws through the side of the ...
Maxtrac/GM300 Digital audio | RadioReference.com Forums
https://forums.radioreference.com/threads/maxtrac-gm300-digital-audio.230443/
Pin 5 is flat TX audio input. Pin 11 is RX audio output, type programmed by CPS. Pin outs are available at batlabs or repeater builder. In fact, all the answers to the questions you've been asking are already there for the reading.
Motorola MaxTrac / Radius / GM300 Index Page
https://www.repeater-builder.com/motorola/maxtrac/maxtrac-index.html
Adding a Flat TX Audio Input to a 5-pin MaxTrac or Radius By Robert Meister WA1MIK Only the radios with 16-pin logic boards have a flat TX audio input. Three extra components give you the same functionality on 5-pin logic boards. Getting Discriminator Audio from a 5-pin MaxTrac radio by Scott Withrow, KC9LQV
eHam.net
https://www.eham.net/reviews/detail/1756
I use the GM300's as link radios and as repeaters. They work great. The have great transmitt audio and receive audio. The 16 pin plug in the back is ideal for tapping into COR, squelch, mic audio and speaker audio as well as "flat" audio and discriminator audio and a host of other features and be able to connect that to a repeater controller.
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