Duplex MMDVM PiStar HAT (with Retevis RT3)
I decided to get in to DMR radio, this I thought was a good idea at the time and due to the local repeater being out of comission, I bought a DMR hotspot on Ebay. You have to realise I knew nothing about DMR at the time apart from the theory of operation.Simplex and Duplex DMR MMDVM hats..
I selected the Duplex version of the MMDVM as what is better than simplex! That where things went awry. I later on bought a simplex radio just for comparisons (but that is now fitted with Nextion display)
Conclusion.. (read down for more of the detail)
The Retevis RT3 handheld radio using stock firmware and the Pistar MMDVM Duplex hat do not play nicely together. I ended up configuring the duplex radio as a SIMPLEX and disconnected antenna 2.The Saga..
Challenge 1:
On the packet, there was a crystal offset of -474. Using that number in PiStar, the radio would connect but the bit error rate was high. Pulling out the SDR and running pistart-mmdvmcal application to output a carrier, the actual error is -400. Voila!, BER was below 1%Challenge 2:
Using the pistar mmdvm upgrade application, it failed to initiatlise the hardware completely!
The board would not flash the new firmware. To fix, a solder-blob needed to be placed to allow upgrades to happen. (Red Circle!)
Challenge 3:
I Failed! Using the Duplex radio with a Retevis RT3 radio, keying up and talking work a treat - but after a few minutes audio stops working. I really dont know how to make it work properly with this radio as all calibrations I tried failed.Notes
If you know how to get it to work in Duplex mode and still have audio after an hour, I would love to hear from you! Two handheld radios below.. one linked to a Simplex Hotspot, the other a duplex. Both are on the same TG91 Talkgroup. After a few minutes, the duplex handheld goes silent. To resotore audio, PTT needs to be keyed.
