OpenGD77 DMR mic gain

posted in: DMR, GD-77, Ham radio | 19

By popular demand, I’ve now added a DMR mic gain control into the OpenGD77 firmware

The gain control only works for DMR as the signal path is different for DMR and FM. In FM the mic is connected directly into the input of the AT1846S RF chip, however in DMR mode the mic is connected to the analogue input of the HR-C6000 DMR DSP chip, which digitises the audio.

The HR-C6000 has an input gain control on the analogue input in 3dB steps, with the default value actually being 33db (or 11 as a direct value). In the OpenGD77 firmware the default value is displayed as 0dB, and adjustments can be made to increase or decrease from this value in 3dB steps, e.g. +3dB, +6dB, -3dB, -9dB etc

Additionally I’ve added a mic level monitor bar graph during Tx, which is displayed in the same position as the Rx signal meter bar graph.

This is only intended as a general guide to the mic level, which I created by sampling the mic audio for 100mS and recording the peak waveform level over that period.
I then take the square root of that peak level, and scale the value to match the width of the screen in pixels.

I think technically, the ideal method to monitor the level is to take the sum of the square of every sample than divide that by the number of samples and then take the square root of that value; however that would be a huge and unnecessary load on the CPU, and my more simplistic approach seems to give usable results.

This feature is available in the Tier2 Latest version of the firmware.

19 Responses

  1. Anonymous

    Hi Rodger,

    I much appriciate your work it is really awesome.
    One thing on my wishlist would be sanning option for channels.
    Like the original firmware had.

    Tnx and 73

  2. Ken, M1DYP

    nice ty

  3. Anonymous

    Hello Roger,

    After a long time, in which I have not reported, I would like to thank for the further development of the OPENGD77 firmware heartily.
    The new microphone level function does not work on my GD77. I have loaded the last firmware (2019-11-04). I did not find a more recent version on GitHub.
    On my wish list are currently two points: A scan function and a way to adjust the audio volume for DMR and FM separately. In DMR, the maximum preset volume is too low.
    I wish you continued success! It is a great firmware / CPS.
    VY 73 from Germany, DL8BBK (Axel) (Google translation)

  4. Anonymous

    I don’t have DMR mic in my menu ? using file:

  5. Leif OH0KCE

    Hi! I don’t have DMR mic in my menu using file:

  6. Angel

    Good Roger great job the one you do. The last version that appears is from November 4 and the mic dmr does not work in the utilities you could check it. thanks and 73.

  7. Anonymous

    Scan would be great. Thanks Roger

  8. Cesar Silva

    hello Roger!! I try to upload this feature in my radio,but i did not see any changes!!last firmware (04/11/2019) in the options menu i don’t see the DMR Mic options!!

  9. Roger Clark

    I had to remove both again because of a code plug incompatibility.

    I will fix and rerelease the firmware

  10. Roger Clark

    It’s on the To Do list

  11. Cesar

    Roger eres muy grande, trabajo genial seras recordado por esto por mucho tiempo en la comunidad de la radioaficion.

  12. Roger Clark

    Some other people have asked for louder volume on DMR.
    I don’t know if the GD-77 has the CPU power to increase the volume of the audio by processing the wav sample data.

    I will need to do some experiments to see if this is possible.

  13. Roger Clark

    BTW. I think I need to do some tests and see how fast the AT1846S RF chip can sample the RSSI data

  14. Angel

    Tnx great Clark good work!!

  15. Anonymous

    thank you for information can i use this also for my baofeng dm1801 (dm 840)

  16. Roger Clark


    The radio hardware is not identical, even though the radio looks similar to the GD-77 on the outside

  17. Anonymous

    Any ideas or any source for DM1801 mic gain (also very low)? thank you in advance

  18. Roger Clark

    This post is about the OpenGD77 firmware of the Radioddity GD-77. Not the Baofeng or any other radio.

  19. Anonymous

    ok thank you

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