GM340 & MMDVM Pi Hat

A few people have asked me for info on the MMDVM Pi Hat and Motorola GM340 setup as used here for MB6ILC (works with most Motorola radios with facilities socket)

 

 

 

 

 

 

 

 

The wire up is straight forward just use the labels on the MMDVM board and connect to the relevant pin.

One thing to note at some point in time Motorola changed from a 16pin socket to a 20pin socket I have added another pic lower down.

However the main problem with these types of MMDVM boards are the pots. They rearly needed to have been multi turn pots of a higher value to give more range. I found once testing the RX af levels with the scope that they were still way to high with the pot set to max resistance. So I found a 10k pot from the junk box and connected like so

Between the ground and the RX pin then wire on the top of to the radio.

Set the pot at mid point and start again from there. If I remember correct you are looking for around 1v peak-to-peak using the two pots now this can easily be achieved. I have tested this on both VHF & UHF gm340’s and also VHF CM140 and works perfect.

Only other thing to mention is the radio config. Make sure the audio is set to flat here is a screen shot of the cps setting thanks to EI4JR

Pin out is the same its like you ignore the extra pins (does catch some people out)

MMDVM settings below

Do not forget to run mmdvmcal and find the correct levels but these should normally get you in the ball park

73 Chris G0WUS