W8EMV - Whiskey Eight Echo Mike Victor

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.

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!

New gear: MMDVM hotspot from Radioddity

New radio! This one is an MMDVM hotspot assembled for and sold by Radioddity. The part I got is clearly labelled "Made in China", but it was shipped promptly from the Radioddity depot in Las Vegas, Nevada. It arrived in a small cardboard box with a single page of tutorial instructions and a few extra screws.

The tutorial text is "Geek Teches THE MMDVM DMR TUTORIAL". I'm certain that it reads better in whatever language it was originally written in, and frankly the text is confusing at best. Fortunately the software and hardware is an ordinary MMDVM and Pi-Star configuration, and there's plenty of good tutorials for that.

Some useful tutorials include:

• Playing with Pi-Star, Amateur Radio Notes, Toshen KE0FHS
• Pi-Star Digital Voice Software, Pi-Star. Official docs
• Pi-Star integration with Brandmeister API, Brandmeister wiki

Nick W8XM was very helpful - I happened to catch him on the ARROW 2m FM repeater while I was putting things together, and I related the problem I had originally where people could hear me but I could not hear their return. It seems that the hardware in this kit is subject to frequency drift, and you need to tune the "RX Offset" with some trial and error (using Parrot) to get an accceptably low BER. At zero offset I had 1.3% error rate; after tuning to -200 my BER was down to 0.2%. Ailunce has a good description of what you need to get to.

I had one glitch on setup - typing in the wrong wifi SSID for our home network! - and had to manually add a new wpa_supplicant.conf file to the SD card to make it work. Fortunately, this tutorial from KE0FHS made that quick work.

The Brandmeister network does not like hear lots of short transmissions in sequence from a single station, so if you are testing things out vigorously and punching a lot of buttons in short sequence you might get a user blocked voice message from the network. This corrected itself for me by waiting an hour.

With all of that set up, I'm back on the air with DMR. There's a weekly Michigan net via Michigan One DMR, and the Brandmeister Feditalk talkgroup is one I hope to make more contacts on.

73 de Ed W8EMV