OpenGD77 Tx power display and controls

posted in: DMR, GD-77, Ham radio | 48

I’ve added a more user friendly power display and control system to the OpenGD77 firmware

Power display showing 750mW

Initially the only way to control the Tx power was to set the raw PA drive level number in the Options screen.

Although this was OK for the developers and testers, its was never intended to be the final solution, so today I have implemented a new feature which makes the power control more user friendly.

The power can be set to 250mW, 500mW, 750mW, 1W, 2W, 3W, 4W or 5W.

The power is displayed in the middle of the top of the display.

To change power level.

Press Function + Right to increase power
Press Function + Left to decrease power

The output power will only be accurate if you calibrate your own radio, because the factory calibration for Tx power hardly ever seems to be accurate.

I checked one of my GD-77’s today and the “Low” power calibration point which is supposed to produce 1W was only producing 0.35W on UHF, and the “High” power calibration point was only producing 3.5W

This is despite the battery being fully charged.

I used the calibration editor in the Community CPS to enter new values for the Low (1W) and High (5W) calibration points, and after I did that, the power output was correct to plus or minus 0.1W according to my power meter.

For those interested in the technical details…

The calibration data stores the Tx Power calibration points for multiple 5Mhz wide frequency bands, for both the High and Low power settings available in the official firmware.

The value stored is 1/16 of the DAC value used to generate the voltage that is fed into an OpAmp, and finally drives the PA FET’s.

For power levels of 1W and 5W I use the values from the calibration table (multiplied by 16).
For 2W, 3W and 4W I assume a linear relationship between PA drive level and output power, and this is reasonably accurate to about plus or minus 0.1W.

If people give me enough data points so that I know that the relationship needs to be slightly modified, I can make minor adjustments to this straight line calculation.

Below 1W, the power curve becomes increasingly exponential, so I’m using my own data points as a offset below the 1W calibration data point.

I doubt that the power output below 1W can be made totally accurate for everyone, but its probably good enough…

This change and the FM DTMF change are in the latest Tier2 file

I also made one more small change.

When a DMR call is received, if the call does not contain Talker Alias information which needs to be displayed on the bottom line of the display, either the Channel name or the Rx frequency is now displayed near the bottom of the screen using a small text size.

I initially displayed the Channel name in the same text font size as the Callsign + name, however this looked confusing, so I use the small text font size which is used for the zone name on the Channel screen.

Channel mode receiving a DMR signal from VK4NGA on Channel name “VK3RTE DMR”
VFO mode receiving a DMR signal from VK4NGA on Channel name 438.9125

48 Responses

  1. Matt Fairbairn (M6SEU)

    Like it Roger.
    Great Work Sir.

  2. Petr

    Hi Roger,

    it’s fantastic progress and really thanks for your time spent on the project.

    My question is if current version still contain HotSpot mode or i need to use older one. I still hope for improving hotspot mode support since HotSpot mode is unreliable and mostly ends like “Waiting for pistar” message during MMDVMHost start.

    73 de Petr, OK2ZAR.

  3. IU4LEG

    Very good. Thank you Roger. Have a nice day
    Good work

  4. ken, M1DYP

    Hi Roger, great update, dtmf certainly great addition and the power output display also, many thanks

  5. luc83

    Good job and good ideas, as habitually. It seems to work like a charm at the moment

  6. Roger Clark

    I will look at re-integrating Hotspot mode during the weekend

  7. luc83

    Oups I have a bug with this last version of the firmware:
    After playing a while with the keyboard (probably to change the power), I transmit on Private Call instead of TG…
    Nothing on the screen changes. I have to swith off then on the GD-77 to reset this

  8. Roger Clark

    The bug was probably already in a previous version.

    So. If you manually enter another TG, e.g. TG 9

    Is it still in Private call mode, even though the display displays TG 9?

  9. luc83

    I have had this bug three times before writing my precedent comment and of course now I can’t have it any longer …
    I never had it before today

  10. Roger Clark

    The cause of the bug is probably not what you think it is πŸ˜‰

  11. Ron Sparrow N7RDE

    Thanks – Worked great this evening for a qso through BM on 31088 with G8HCB

  12. RiKu Bister

    Heya, alot new features going on! Good work.
    Any eta for the power save function? πŸ™‚

    opengd77 facebook group has already almost 500 users!
    OH1E, riku

  13. Roger Clark

    I’m blocked from accessing Facebook, because if I try to login, I get blocked because FB say that I am impersonating Roger Clark.

    But even if I was able to login, I would not have time to participate as developing the firmware and the CPS and doing my other projects already takes 110% of my available time.

  14. luc83

    I have not be able to reproduce the bug I’ve had yesterday… The TG are still TG and dont become private call any longer…
    I didn’t say yet, but I love the display as it is now

  15. RiKu Bister

    it is ok Roger, I mean how much fans there is already. they are all saying only good for this project. πŸ™‚
    I tried new firmware, it is improving every time better, maybe dtmf sound is way too loud on loudspeaker, no need right away repair but on future maybe take a look into it, to lower volume.
    And other thing, the right key thing is almost gone, it does now very rare. it still does, but it is more usable atm than before.
    Best 73 OH1E

  16. Jason Turning

    I’m suffering from the chip crash, audio does a digital sound repeat before picking back up. Though I love the direction of where you’re going with the Tier II firmware. But that crash makes me put the Tier I firmware back in as the audio bug repeats every few seconds. I just bought my HT when I learned of your firmware project, so just wondering if people experiencing the issue have purchased radios recently? I know you said your radios don’t do it, and you were yet to get hands on with one.

  17. Roger Clark

    A few people reported this problem.

    It seems to be a calibration problem, where the Tx and Rx frequency do not quite match.

    Try disabling the Calibration in the Options menu

  18. Roger Clark

    There is a problem with the deviation of the DTMF and Tone burst at the moment.
    Too much deviation

    I will investigate at the weekend.

    I will also see if there is a way to reduce the audio output from the AT1846S chip when it’s producing the tones

  19. Roger Clark


  20. Roger Clark

    Re: Power save

    I will add it to the Issues list, however it will be low priority.

    The radio will run for at least 12 hours on standby with now signal.

    The power save only effects standby operation, and I think they disable the Rx for 100mS then enable, sample the RSSI and if there is no signal, they disable the Rx again

  21. Jason Turning

    I tried turning off the calibration, and the audio would drop out every few seconds without the digital defect sound repeating. But then eventually it started to make the digital defect sound as well. I must say I used the new version of the CPS to load the firmware and that was nice. You’ve really made that easy to use for playing with the OpenGD77 firmware.

  22. Roger Clark


    For some reason the calibration needs to be more accurate with the OpenGD77 to the official firmware, but I don’t know what.

    Possibly there is a calibration setting which is not being read from the calibration table and applied to the RF hardware, but it looks more likely that the master oscillator frequency in the radio is not quite right.

  23. Alen Ruvic

    Hi Dear, please info, i just instaled latest firmware, all perfect, thank you for your great work.

    1. I need info. I cant find where is scanning??no info in user manual. Exsample, I need scan into one of the programmed zones.
    2. Where can i increase rx audio on DMR?

    73 and all the best de E71AR

  24. Alen Ruvic

    Hi What is about scann

  25. Alen Ruvic

    Hi Dear,

    please i cant find
    1.where is scan? exs.. scaning into one of the zones?
    2. keypad lock
    3. selfpass tx tone

    73 de e71ar

  26. Alen Ruvic

    Thank you very much, if i understand good in this moment Memory.channels scanning and tx selfpass tones no able yet?

    73 de E71AR

  27. Roger Clark

    Whats a tx selfpass tone

  28. Alen Ruvic

    Hi again.

    Problem with CTCSS on analog

    NONE CTCSS on latest firmware registered as 0.00 Hz . But squelch not opened on 0.00 hz. Only with option OFF(None)

    I must manualy enter channel setting and replace 0,00Hz with NONE(Off).

    I think you must replace delete option 0.00hz

    73 de E71AR

  29. Alen Ruvic

    Selfpass tone is tone when press Ptt key(like motorola Mototrbo tone).

    On DMR when repeater is out of range when you press PTT button NO SELFPASS TONE.
    When you with your radio in range of repeater when you press PTT you hear sound like Mototrbo

    73 E71AR

  30. Roger Clark

    Thats for commercial users.

    This firmware just keeps trying to access the repeater while you press PTT, so you can adjust your antenna rotator etc until the Tx goes to permanent RED and the countdown timer starts to count.

    This allows access to repeaters even when the coverage is margin

  31. Alen Ruvic

    Yes i saw, thank you.

    73 E71AR

  32. Anonymous

    I mis VFO and Memory scanning

    73 S53TS

  33. Radio klub Zenica


    battery heat(warm) in hand on transmitting 250mW.

    On factory firmwarr no heating. Maybe some bug


  34. Roger Clark


    The radio does not operate in power saving mode.

    Last time I checked the current during Rx it was around 75mA and some warming of the radio occurred all the time.

    I’ll run some more tests

  35. Roger Clark

    Did you test how much power is being produced when you set to 250mW ?

    Possibly there is a bug if the calibration data in the radio is incorrect and the power setting of 250mW may be producing more power.

  36. Radio klub Zenica

    Hi, yes i checked on power meter, all calibration is good.

  37. Roger Clark


    Did you calibrate your power settings for Low = 1W and High = 5W , using the CPS ?

    What power do you get for 1W, 5W and 250mW, 500mW and 750mW ??

  38. Radio klub Zenica

    when is on radio display 250mW on my power meter is also 250mW all is good

  39. Roger Clark


    Below 1W the power curve is very non-linear, so the values I used are based on my radio, with reference to the value required to produce 1W

  40. Radio klub Zenica

    One more problem. After use Community CPS and upload dmr contacts i cant work trought hotspot. After press TX exsapmle TG91 i recieve RX Private call with anouchment “user blocked”.

    I tried turn back on firmware 3.0.6. but problem i same. please help.

    How total factory resset all memory?

  41. Anonymous

    Hi Dear,

    definitly had same problem with baterry heating with last firmware opengd77.

    I checked again, rf power calibration is good. But on smallest rf power 250mW baterry is same heat as on 5W.

    I tried again with lastest factory firmware, with no power save mode and no any heating.

    Please can you check whats can be problem?

    Thank you friend


  42. Roger Clark

    If this is a problem, reload the official firmware.

  43. Anonymous

    I just tried to inform you for fix in the future

  44. Anonymous

    Thank you.

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