W8EMV - Whiskey Eight Echo Mike Victor

Tuning an MMDVM hotspot to minimize BER for multiple radios

My RD-5R gives about 0.4% BER when talking to my MMDVM hotspot, but my GD-77 with the same configuration gives nearly 1.0% BER. Audio quality is still good, but of course it's worthwhile to tune things to minimum error rates regardless.

Some notes on tuning the TX level on the radio:

• N6AMD, How to tune your MMDVM repeater with an SDR for low BER. Focuses on getting your audio levels correct; "If the raw audio is either too quiet or too loud, subscriber radios will not decode the digital signal properly." Uses pistar-mmdvmcal and an SDR to calibrate audio levels (TXlevel).

• F5UII, Install MMDVMHost on Raspberry Pi and tuning MMDVM for DMR digital mode . N6AMD's article is derived from this one, which uses both SDR and oscilloscopes for tuning. "The goal is simply that the audio levels are not too strong and do not saturate the analog input of the arduino".

Some notes on tuning the RX offset on the hotspot

• Ailunce, How to set RX TX offset. "Also every DMR radios may get a different BER when using the same hotspot. If you can't find a good balance for the BER between the different modes, it may be better to use different hotspots for each different mode."

Thanks to Christopher M0YNG on Feditalk to help me with some tuning ideas.

New radio notes: Radioddity GD-77

I got two new Radioddity GD-77 radios the other day - one for new ham KE8PFB, and one for myself.

Programming the radio from the keypad is awkward but not impossible, and we got one analog channel up and running to reach the ARROW repeater. That was plenty to confirm that it was working.

We'll tackle DMR next. I have a DMR hotspot, so it should be possible to share it.

The included instructions were in German and in English, and the "how to get a DMR ID" instructions were for Europe. This led to a support ticket - the USA instructions are at RadioID.net.

The GD-77 is supported by dmrconfig, and I was able to convert my RD-5R configuration to it without too much trouble. The GD-77 only has two squelch settings, so the RD-5R's configuration needs to be edited - other than that, surprisingly easy.

The GD-77 user interface is nearly identical to the RD-5R. A few of the key bindings are a little different, but it's otherwise effectively the same radio as far as capabilities and controls. I guess that's OK, but I sort of wanted to get a completely different rig from what I already had. The tradeoff of course is that it was completely familiar.