Through a fellow ham i got hold of 2 Motorola MTR2000 repeaters with the plan to convert them to DMR using the MMDVM board made by G4KLX. Here are my notes
Special thanks go out to Graziano IZ5IGB for building the first MMDVM MTR2000 and helping me get started.
You can find my working codeplug here
Settings in the configuration file:
Possibly it would be required to change some settings in the RSS to make it work with your repeater
Ajust the external audio input diviation
Wire the System connector
Install and configure MMDVM and MMDVMHost (i will not cover this, there is plenty of info around)
Modem config in MMDVM.ini
[Modem] Port=/dev/ttyACM0 TXInvert=1 RXInvert=1 PTTInvert=0 TXDelay=100 DMRDelay=162 RXLevel=50 TXLevel=50 # CWIdTXLevel=50 # D-StarTXLevel=50 # DMRTXLevel=50 # YSFTXLevel=50 # P25TXLevel=50 OscOffset=0 RSSIMultiplier=1 RSSIOffset=10 Debug=0
The main difference of the Modem block is in the DMRDelay this feature is there to compensate delay in the repeater of around 7 msec best setting should be somewhere between 162 and 168
IZ5IGB found that there is a phase shift of 2 signals createing about 7 msec delay.
Adjust the MMDVM board untill the point you can tx/rx over the repeater i suggest starting with the tx side of the repeater. Depending on the MMDVM board this could take a while calibrating the pots on the mmdvm board took me about 30 min with just 1 dmr radio the repeater preforms well