MMDVM modem hat

by on under hamradio
2 minute read

MMDVM Modem Hat

I am using a Icom IC-E208 and a “MMDVM_pog” hat to make a GMSK DStar gateway.

mmdvm-modem-overview

My fiend 2E0EOL has written a article on a similar setup: daybologic GMSK Gateway

Software installing

Requires Pi-Star beta image for Raspberry Pi 3B+ at time of writing.

UPDATE 07/04/2020: “Raspberry Pi 3B+ out of beta”.

Pinouts

For some reason my PI wont boot with the hat on. I haven’t figured out why yet. See: wojciechk8/MMDVM_pog/issues/4

I connected the modem pins “GND”, “TX”, “RX” and “PTT” accordingly to my radio. You need a radio with a “DATA IN” jack accepting 9600 bps GMSK.

The “SQL” pin of rig doesn’t seem to be needed for basic setup.

The “RSSI” pin of modem doesn’t seem to be needed for basic setup.

Icom IC-E208

mmdvm-modem-hat mmdvm-modem-breadboard

Software configuration

Pi-Star web UI page configuration/expert/mmdvmhost you will find the following fields.

txoffset is worth playing with try -100 or 100 or 200.

txinvert was default 1, for some radios like mine you may need to change it to 0 however in my case I later found my radio was off frequency and upon correcting it (see: IC-E208 Calibration) I had to put txinvert back to original value.

Ensure suffix of call sign for gateway is not just a space but its last char of input string.

I had some issues changing the gateways call sign without re-flashing.

Thread: facebook.com/groups/pistarusergroup/414855285738167

Hardware calibration

There is a couple trim pots on the board which allow you to adjust the mic gain. Use the ACL meter on the radio to gauge this.

Also see the DVAP page on my website: ham-radio/dvap

Useful documentation

My friend Rob (2E0RPT) took pictures of the document he received with his board. I didn’t receive any such documentation with mine.

mmdvm-modem-settings-guide

MMDVM_pog, MMDVM, D-Star, GMSK
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