Radioddity RD-5R "RX Group List" - or, why can you hear me and I can't hear you?

A programming quirk of the Radioddity RD-5R.

If you want to add a DMR talkgroup to talk on, there are really four things you need to do:

1. Add a digital contact, listing call ID and name.
2. Add a channel, listing that contact along with frequencies.
3. Add that channel to a zone, allowing you to select it on the radio.
4. Add the channel to the "Rx Group List" so that you can listen to it.

If you miss step 4, you get the following: people can hear you on a channel, but you can't hear them.

Debugging this was tricky. I had added a few extra talkgroups to my hotspot configuration, so I thought I had checked everything - and it turns out I had everything correct for transmitting. What could be different about the Feditalk group? Well, it's UK based, so I tried connecting to the UK Brandmeister server and listening to some other UK talkgroups, and that didn't work.

The AHA moment was of course an RTFM situation. Section 3 of the Radioddity DMR Quick Start Guide referenced a screen I hadn't seen before, the "RX Group List". Adding the channels to that list (and noticing that they weren't there already) fixed the problem.

Thanks to the following for helping me through this bit of troubleshooting:

• Nick W8XM for the ARROW RD-5R codeplug and some timely consulting on RX offset programming
• Patrick KC3OWU for encouragement and debug help and a first successful QSO on Feditalk, TG 23514
• Christopher M0YNG for running mastodon.radio and prompting this exercise in the first place

Having figured all this out, I'm now intrigued by OpenGD77 which is open source firmware for this RD-5R radio and for other DMR radios. Perhaps a next project!