Radioddity GD-77 VFO DMR transmit audio bug

posted in: DMR, Ham radio | 8

Tony VK3CAT recently alerted me to a bug he found when using the GD-77 in VFO mode on DMR


The bug manifests itself if you change the frequency band that the VFO is using. The bug does not seem to happen absolutely all the time, but seems to be fairly easy to reproduce.


To see the bug, you just have to change the “band” that the VFO is using.

e.g.  if you have the VFO set to 439.200 and it was working OK, for both Tx and Rx, and then you enter the frequency of 144.800….

The GD-77 seems to stop transmitting audio.

The green LED on my receiving radio was illuminated when there is an incoming signal, and the display shows the DMR ID number and TG of the transmission, but there is no audio whatsoever.

Enabling the monitor mode does not seem to make any difference, nor does manually changing the Timeslot or the Color Code using the Set->Radio config menu


Tony reported if he power cycled the GD-77, that the problem was resolved, but this didn’t seem to fix it for me.

The only thing that seemed to work for me, was to go into the Radio Config menu, and set the channel type to FM, and then set it back to DMR.



I initially thought this was a Rx bug, but Jason VK7ZJA has done some testing and confirmed it a Tx audio bug, where the audio part of the data transmission appears to be empty.


Jason reported a workaround for the problem is to switch to memory mode and then back to VFO mode, but I’ve not confirmed whether it makes any difference if the memory is on the same band as the VFO.



8 Responses

  1. B. D. S.

    I love almost everything about the GD-77 but bug after bug after bug is making me think it may be time to move on to another dual band FM/DMR radio… I really hope Radioddity gets these bugs resolved but I’m not holding my breath. Thankfully you provide a site like this so there’s a compilation of data and info for all us users….

  2. Roger Clark

    I agree

    Unfortunately. Radioddity have never been very good at fixing bugs. I don’t think TYT are any better. The only reason the MD-380 is a good radio is because the firmware was cracked and modified to add a load of useful features.

    Possibly the Anytone radios may end up being the best to go for, as the firmware is unencrypted, but they are considerably more expensive than the GD-77 and I don’t know if anyone is currently working on custom versions of firmware, as its quite a difficult job.

  3. ken

    thank you

  4. Anthony Metzidis

    Hi there Roger I ran into your blog while investigating a GD-77 bug — I was going over a hexdump and saw the MD-780, which led me to your site. Great info I can tell you’re very experienced in reverse engineering!

    I have a question for you if you have a minute about a bug I’m troubleshooting. I thought you might be able to guide me in decoding the codeplug hex format.

    The bug I’m experiencing goes like this . 1. choose channel #4. 2. hear nothing. 3. scan=on 4. hear traffic on channel #4 . 5. scan=off, 6 . hear nothing again on channel 4 (RX list and mon=on have both been tested).

    Despite the channel having the right TG RX list set, and also being in monitor mode — it’s common that at step #6 I will hear nothing.

    This is a severe bug that I noticed from day one, because it means the radio does not receive on the talk groups it’s configured to.

    Given your earlier post about issues with receiving, I thought this issue sounded similar.

    Now my question for you is: do you have any info on the hex format for channel settings. I’ve been trying to compare channels, but i don’t have enough positive and negative results to form a control test.

    tl;dr — any info on the GD-77 codeplug hex format can help me continue troubleshooting.

  5. John Tetreault

    Sorry to go off topic, but i couldn’t find another way to contact. Question… Do you know if the community CPS does, or can support the Radioddity RD-5R (which is basically the GD-77 in a uv-5r case, with some minor codeplug variations as I understand it). Also what are the chances of getting community CPS compiled for Linux? I don’t have a Windows PC at all.

  6. Roger Clark

    Although the RD-5R is basically the same radio, they codeplug format is different and t would not be possible to easily modify the GD-77 CPS to work with the RD-5R

    I know some other people asked the same question, and I even went as far as decompiling the RD-5R CPS and sending the source code to someone (I can’t remember who).
    But whoever it was, does not seem to have managed to rebuild the CPS for the RD-5R let alone incorporate the “community” additions.
    (Its probably because its not a simple process to recompile from the decompiled sources, as the decompilation causes thousands of errors in the code, all of which need to be manually fixed before the CPS can be rebuilt.
    It took me several weeks to do this, and I doubt anyone else could be bothered.

    Re: Linux version
    The CPS is written in C# and in theory there are ways to compile it for Linux, however in practice I don’t think it would be that easy to convert it.

    I know a few people have tried running it under Wine, but it doesn’t work, because there is an error in Wine caused by the HTML viewer, used to display the Help at the bottom of the screen.

    Potentially if the CPS was modified to remove the HTML Help, it may run under Wine, but I don’t have any spare time even to try that.

  7. Roger Clark

    Unfortunately the GD-77 has a lot of bugs but Radioddity don’t seem to think it makes financial sense for them to allocate resources to fix them.

    I don’t use the scanning function, so have not experienced the bug you found.

    Re : Hex format for the codeplug.
    I did some analysis on the codeplug before I found it was easier to just decompile the CPS C# and modify it at C# level.

    I think some other people also have tried to document the format, but you’d need to Google for that to see if they ever posted it online.

  8. Anonymous

    thanks roger for pointing me in the right direction

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