Extending the frequency range of the GD-77

posted in: Ham radio | 45

Update 22nd March 2018

This article has been superseded by the replacement version of the Radioddity GD-77 CPS (aka Community Edition), which I have created

Please see my posts about this new CPS




Following on from my initial post about the Radioddity GD-77 DMR transceiver, I’ve now found all the places in the CPS software, where it stores the frequency limits imposed on the “Basic information” screen

Normally the limits are

VHF 136Mhz to 174Mhz and UHF 400Mhz to 470Mhz, however these limits don’t seem to be the practical limits of the transceiver under normal domestic conditions, and by changing the PC CPS program  DMR.exe the actual hardware limits can be extended (or reduced if required).



If you change these values in your DMR.exe and update your codeplug etc with frequencies outside the normal operational range, you do so at your own risk.

Also. The transceiver will probably not be FCC (or CE etc) compliant outside the original limits


In version 2.0.5 of the CPS, the limit values are held at the following locations.


UHF lower frequency is held in bytes 3e6d2 and 3e6d3 , with values  0x90 0x01 = 0x0190 = 400Mhz

UHF lower frequency is held in bytes 3e6ef and 3e6f0 , with values  0xD6 0x01 = 0x01D6 = 470Mhz

VHF lower frequency is held in bytes 3e6da and 3e6db, with values 0x88 0x00 = 0x0088 = 136Mhz

VHF upper frequency is held in bytes 3e6f7 and 3e6f8, with values 0xae 0x00 = 0x00ae = 174Mhz


Once DMR.exe has been modified with new values, in these locations, the “Basic Information” screen will check for these new value (limits), and if the frequency range is extended e.g. the upper UHF values changed to 0x08 0x02, the Basic Information panel will allow a frequency limit of 520Mhz to be entered,



Looking at the available data on the GD-77; it uses the AT1846S, Single Chip Transceiver. The PDF datasheet AT1846S shows the frequency range as






I have done some basic tests, and my GD-77 seems to be able to transmit on Australian UHF CB band (into a dummy load) on 476Mhz , and can receive on these frequencies

I’ve tested the reception below the frequencies specified for the AT1846S and I’m pretty sure it will receive on 132Mhz as I appears to be able to hear some local Air Traffic Control signals on 132Mhz, but it did not detect the weather broadcast from the local airfield on 120Mhz or any FM broadcast radio stations e.g. on 107Mhz.



Looking in more detail at the AT1846S, there seems to very little data on the internet about this device, but it seems virtually identical to the RDA1846, for which there is Programming Guide document RDA-1846_programming_guide


Reading the Programming guide, the 200 – 260Mhz band would not be accessible, because the AT1846S has distinct bands on which it operates, and which are delectable via its MCU interface, so I’m not sure whether the GD-77 would simply be able to use this band, without a major hack to the firmware.
I will need to look in more detail at the codeplug data in a hex viewer to see if the band value is encoded into the data or whether the firmware reads the frequency range and sets the band values in the AT1846 accordingly.


Update. 19th Jan 2018

Jason VK7ZJA, has let me know that the 200 – 260Mhz band does indeed work on the GD-77, by changing the UHF lower frequency to 200 or the VHF upper frequency to 260Mhz, However the GD-77 the receive sensitivity is not that good, as the receiver has band pass amplifiers for UHF and VHF and this falls half way between both filters.

The interesting thing about this, is that the firmware must be setting the appropriate “band” value into the AT1846S chip, and this must be independent of the codeplug and the CPS.

I’ve tested setting the VHF and UHF frequency ranges to (130 – 520) the same values and it everything seems to work fine.
Frequency Range 1 to 130 – 520
Frequency Range 2 to 130 – 520


This confirms that the values in the CPS are probably there to prevent people entering values outside of defined ranges, into the channels, and I think possibly some versions of the CPS have the Basic Information screen locked so that these values can’t be changed at all, let alone outside of the range by making changes to the EXE.
But as the software quality of the CPS is quite low, its really hard to know quite what the author was intending.


For those that feel like doing more hacking, there is an Arduino library for this device on GitHub https://github.com/phishman/RDA1846


Generally I think the best option is just to extend these values to the documented range of the AT1846S, which does give a useful addition to places which have UHF CB on 470 – 520Mhz (see https://en.wikipedia.org/wiki/UHF_CB  – dependent on the specific licensing in each country)


However if you specifically wanted to receive on the 200 – 260 Mhz band, then just change the values so that both VHF and UHF contain the max range 136 – 520, and just be careful when programing the channel information or using the VFO, so you don’t end up transmitting on a frequency you are not licensed to transmit on.

For those who do not want to edit their own files, I’ve zipped up the DMR.exe and Default.dat that I’m using, and the need to replace your existing versions (in whichever folder they are installed)


45 Responses

  1. EvO

    Hi Roger,
    This one is really terrific!
    I used your modified CPS and it works like a charm.
    The only thing I had to change is the lower limit because mine GD-77 doesn’t allow 130MHz, it is happy with 136MHz though!
    Really awesome!!!
    Thanks to you now I can use my GD-77 as wide band receiver, thank you Roger!
    I believe that as you rightly observed it is need to pay attention where to transmit because there is a risk of damaging the transceiver, especially with the provided antenna that for sure is not resonant on the whole frequency range.
    It’s really miraculous what you can get by changing a handful of bytes, of course for those who are able to do it!
    Please go on like this!
    Many thanks Roger.

  2. Roger Clark

    No worries.

    I’ll double check the setting in the DMR.exe file, when I get time… I initially did a version which left the lower limit as 136Mhz, after discussion with VK7ZJA and looking in the data sheets the transceiver ID can go down to 130Mhz, so I thought I’d updated the hex vales in the exe to allow this.

    However, perhaps I didnt upload the latest version back to the blog.

  3. EvO

    Thank you Roger.
    That isn’t a problem.
    You explained well what is need in order to make changes, so actually people can do that by them self or at least try.
    Thank you very much Roger!

  4. Roger Clark

    No worries…

    Unfortunately, I’ll need to do it all again when they release a new version of the CPS (which they seem to do every time they release new firmware), but hopefully next time it should be easier to find these limit values, inside the EXE

    BTW. I did try to decompile the EXE, as its written in .NET and there are tools to decompile back t source code.
    However the exe has been deliberately modified so it breaks the decompiler tools. (using a another tool specifically for protecting from decompiling)

    I still think it would be possible to decompile the CPS if anyone has the time and experience to do it, as I’ve seen several YouTube videos on what you have to modify in the exe so that its OK.
    I just don’t have time to do it at the moment.

  5. giovanni marletta

    ciao, on my system with win 7 64 bit the dmr.exe won’t start, it crash quickly without explaination, what I wrong ?

  6. Roger Clark

    Thats the same system as I’m running.

    You need to put it in the same folder where your exist DMR.exe is located. (make a backup copy of your original version first).
    It won’t work if you put it somewhere else, as there are loads of other DLL’s which are in the installation folder, which I needs

    You could try making a copy of your DMR.exe and change the bytes in it, as I describe the post.

    I used Hxd to do this, but any hex editor should work.

  7. giovanni marletta

    ok! I will test it soon, just now I’m working for a toy, get a look here, [FACEBOOK_LINK_BLOCKED]

  8. Roger Clark


    Unfortunately facebook links which can’t be access unless you are logged into facebook get blocked as a security measure, as their content can’t be verified.

  9. Manu López

    Hola buenos días. Os escribo desde España. Yo tengo un G77 ya actualizado a la versión V3.00.06 / HRC 6000 V1.2
    Esta versión va muy bien mejorada y incluso si al walkie le cambias la antena por otra mejor ya es la máquina.
    Mi pregunta es?
    Si el CPS se podría modificar para el rx en la frecuencia de 66MHZ hasta 88MHZ sólo en FM para recibir NO emisoras de radio locales. Rx en FM normal.
    Gracias y muy buen aporte del equipo.
    Un saludo

    —————————- Google Translate into English ———————————–

    Hello good day. I am writing from Spain. I have a G77 already updated to version V3.00.06 / HRC 6000 V1.2
    This version is very well improved and even if you change the antenna on the walkie for another, it is the machine.
    My question is?
    If the CPS could be modified for the rx in the frequency of 66MHZ up to 88MHZ only in FM to receive NO local radio stations. Rx in normal FM.
    Thanks and very good contribution from the team.
    a greeting

  10. Roger Clark

    The transceiver IC in the GD77 is the AT1846S. This only operates on 3 bands,
    134MHz – 174MHz
    200MHz – 260MHz
    400MHz – 520MHz



    I tried selecting 100MHz but that did not work.

    I think 130MHz may work, but not much below that

  11. Ivan

    Hi Roger,

    how to raise the sensitivity on 255 MHz ???

  12. Roger Clark

    AFIK. The GD77 has 2 different RF pre-amp sections. One for 144 and one for 430Mhz

    But as its not desiged to work on 255Mhz, neither pre-amp is tuned to the correct frequency

    I don’t know which pre-amp gets selected when you use 255Mhz, however the only way to make it work better on 255Mhz would be to change the pre-amp circuit values it uses for that band.

    But this would make one of the other bands less sensitive

  13. Hai Nguyen Ly

    Hi Roger:
    Radioddity has come out with a standard or simple version of the GD-77 called the GD-77S. Basically, this variant of the radio excludes the front programming panel and adds a channel selector dial. I’m wondering if you might be able to take a look at the CPS to determine how much of a difference there is between the radios with regard to programming code plugs and whether it would be possible to increase the RX/TX range using a similar method as detailed in your original post?
    The CPS for the GD-77S is available here.
    Radioddity Download: https://www.radioddity.com/radioddity_download/
    Thanks in advance.

    Hai, KC1BLT

  14. Roger Clark

    I don’t know anyone with a GD-77S, but I think VK4JWT has ordered one, so I’ll contact him and find out whether he can try my CPS with his GD-77S it arrives

  15. Sean

    I tried to download the extended file and it appears to be not working, I getting a error message. although Im not really sure what Im doing.

  16. Roger Clark

    This post has been generally superseded by the ones about my improved CPS for the GD77. I’d recommend you try that as it includes extended frequency range

  17. Rick Swenton

    Hi Roger. I tried this and had the same experience. The lower limit needs to be 136. At 130 the change totally messed up transmit. Looking at my signal on the SDR it was warbling all over the place. The fix I chose that worked was to factory reset. Flash FW 2.6.6, flash FW 3.0.6 and then load the code plug with 136 set. The factory reset was required and I did 2.6.6 first just in case. Two radios now on 220. The receiver does appear to be a little less sensitive on 220 but the radios work well. Thanks,

  18. Roger Clark


    We’ve still not worked out why some codeplugs seem to work down as low as 130 and some dont

    If you load the default / blank codeplug in the latest version of the community cps, it will work on 130, so there is something else in existing codeplugs that the GD77 has a problem with which causes the factory settings to be applied, which kills the PA power

    BTW. VK7ZJA is investigating the PA power issue and we hope to have a fix which does not require reloading the firmware, but its early days with this, as we have no documentation on how the GD77 stores the values which control this.

  19. Anonymous

    Thank you for reaching back out to my post. I’m still having zero luck getting the Radio to read 520 MHz

  20. Roger Clark

    Try my latest CPS and upload the blank codeplug, it should allow the VFO to be set up to 520Mhz

  21. Anonymous

    whats the link?

  22. Tracy c goodlett

    Thanks for putting this out there. It worked a treat. I’ve found the new locations for software version 3.1.1:

    UHF lower frequency is held in bytes 56136 and 56137 , with values 0x90 0x01 = 0x0190 = 400Mhz

    UHF lower frequency is held in bytes 56153 and 56154 , with values 0xD6 0x01 = 0x01D6 = 470Mhz

    VHF lower frequency is held in bytes 5613E and 5613F, with values 0x88 0x00 = 0x0088 = 136Mhz

    VHF upper frequency is held in bytes 5615B and 5615C, with values 0xae 0x00 = 0x00ae = 174Mhz

  23. Roger Clark

    AFIK the locations have not changed in 3.1.1
    The only difference between 3.0.6 and 3.1.x is the Rx Group list data and the addition of the Scan Time setting

    However, there should be no need to manually change this, as you can use the new version of the Community CPS which allows those settings to be changed using the Basic Settings screen.

    Note. Some people have reported that their GD-77 does a factory reset if they set the lower VHF frequency below 136Mhz. (as it can be set as low as 130Mhz)

    Also FYI. The maximum frequency can be set as high as 520Mhz and it is also possible to access a band from 220 Mhz (I cant remember the exact details, but I’m sure its listed in one of my posts), but the transceiver is not designed to operate on the 220Mhz band, and doesnt have an RF section tuned for this, so reception sensitivity is reduced.

  24. Flavio VE2ZFP

    Could you please tell me what version of the GD-77 programming software you are using?
    I’ve tried to do it here but both versions GD-77S 1.1.7 and 1.1.8 crash when I try to read from the radio. It works fine with the original dmr.exe and default.dat.
    When it crashes it gives me the following warning: Unhandled exception has occurred in your app. If you click continue, the app will ignore this error and continue. Value cannot be null. Parameter name:url

    I appreciate any help

    Thank you

    Flavio VE2ZFP

  25. Roger Clark

    GD-77S is different from the GD-77 it uses a different format of codeplug, based on a much older version of GD-77 codeplug

    The GD-77 will not work with any GD-77 CPS, either my community CPS or official Radioddity CPS.

    You can modify the codeplug file using something like HxD to edit the hex bytes, like can be done on the GD77 codeplug, buy I don’t know if the bytes you need to change are in the same place in the codeplug file. What to change has been documented by many people including me

    Also if you open the Basic settings in the CPS it will overwrite the settings and will reset the frequencies on all channels outside the normally allowable range

    But its your best option at the moment.

  26. Flavio VE2ZFP

    Hi Roger!
    I don’t have a GD-77S, mine is GD-77. I didn’t even know that there was a S version without display.
    Maybe I’ve been using the wrong CPS, the one for the ”S” version.
    Therefore in that case can I use your community CPS?
    Thank you for answering.


  27. Roger Clark

    Hi Flavio


    Latest (Beta) versions of the Community CPS is this one for version 3.1.x https://github.com/rogerclarkmelbourne/radioddity_gd-77_cps2.0.5/raw/development/installer/RadioddityGD77CPS31XCommunityEditionInstaller.exe

    and this one for the previous firmware (3.0.6) https://github.com/rogerclarkmelbourne/radioddity_gd-77_cps2.0.5/raw/development/installer/RadioddityGD77CPS306CommunityEditionInstaller.exe

    Its too difficult to support the older firmware(s) e.g. 2.6.6 as the codeplug format is different both 3.0.6 (CPS 2.0.5) and 3.1.0/3.1.1/3.1.2 (aka 3.1.x)

  28. Flavio

    I’m still in the stone age I have version 2.06.03. Should I upgrade to the newest firmware? which one would you recomend? Doing it means losing my old codeplug and it can’t be retrieved later on?

    Thank you for your pacience.

    73 Flavio

  29. Roger Clark

    Firmware version 3.1.1 (the latest non-Beta version) seems to be the most stable.

    However I don’t know any way to update such and old codeplug.

    Colin G4EML has tools that allow conversion by exporting to spreadsheets, for versions 2.6.6 and 2.6.8 and 3.0.6, but I don’t know if the your version (2.6.3) is the same as 2.6.6 or not.

    Sorry. I can’t find a link to where you download the tools.

  30. Flavio

    Hi Roger!

    I’ve managed to upgrade the firmware to ver
    3.1.1 and your CPS worked just fine.
    The only thing I’m missing is the testmode=0 service menu like the TYT MD-380 that allows you to reduce both HI and low power levels.
    Low power seting on the GD-77 is way too high.
    Is it possible to do that with the Gd-77?

    Thank you

  31. Roger Clark

    Hi Flavio

    We are working on a feature to adjust the power setting for High and Low.
    We can’t more settings eg. High Medium Low is not possible.

    However Radioddity does not have the Test mode in their official CPS, so we have to write this from the beginning without any help from Radioddity, about how this is possible.

    Jason VK7ZJA has disassembled a GD-77 and has connected it to some test equipment to try to determine how power and other settings can be adjusted.
    But it takes many hours of work to find each memory location used for each setting

  32. Flavio VE2ZFP

    Hi Roger

    That would be great. Low and High is just fine.
    I was wondering about this. I have done a modification to the Boafeng UV-3R, although the power output is much lower than VHF and UHF the RX sensibility is good as my native 220 MHZ HT. I have noticed that 220 RX on the GD-77 is not so good( not deaf) maybe because its using the 70 cm filters and not the 144 one. I’ve programmed my GD-77 as 136-520 on top and 136-520 below. What if we do it 136 to 400 and 400 to 520 instead? not the same thing on both? do you think that the 220 would pick a less worse filter? I think the 144 MHZ filter would attenuate less than the UHF one.

    Let me know what you think



  33. Roger Clark


    The default codeplug we now use has the lower band from 136 – 400 and the upper band from 400 to 520 as this seems to work best

    However we think the GD-77 has some internal parameters it uses to select which band is used for the hardware like the PA and input tuning.

    Also, the firmware does not correctly support cross band operation, as it seems to use the PA power frequencies associated with the Rx frequencies, for the Tx.

    Actually, I don’t know if anyone has tried cross band on DMR, it may not work at all, but I think Analog works OK.


    please firmware 3.1.5 …… my problen is offset frecuency…thanks

  35. Mark Girard

    could not get the extender program to run on win 10

  36. Mark Girard

    I got it working, I failed to read the instructions

  37. MistaM

    If i read this correct, It will NOT RX on air band? 123mhz range?

  38. Roger Clark

    The chipset it uses will not go that low. Also Airband uses AM, this transceiver is FM and DMR only

  39. David

    Roger, will these hacks work on USA versions of the GD-77 ? Sorry if i posted this twice. Got something flaky going on..

  40. Roger Clark

    AFIK all GD-77 are the same hardware and run the same firmware. (the only hardware difference is between the model which has the inverse video screen).

    So the tricks to extend the frequency range should work on all GD-77

    Note. The method explained in this post has been superseded by the Community version of the CPS (see the other posts)

  41. stephan

    What about crossbanding on a single channel? I cannot get the software v3.1.1 to allow me to have TX 440 Mhzand a RX 144 Mhz?
    is this a bug in the CPS? All my other radios allow me to do this.

  42. Roger Clark

    The official CPS does not allow crossband operation at all.

    The GD-77 itself capable of limited operation on FM (Analogue) crossband, but not DMR.

    On FM there is problems with Tx power because of a bug in the firmware, where it uses the wrong calibration values for the PA.
    Strangely, the power output on crossband FM seems always to be lower, where as in theory, it should be higher if TX was on 2M and Rx was on 70cm, than the other way around, because the Tx power drive levels, held in the calibration are higher on 70cm than on 2m, (for obvious reasons).

    So if you are using the official CPS you wont be able to use cross band.

  43. Stuart Cumming VK6MK

    Thanks for the hints on extending the frequency. I have edited as per instructions and all works and now get the UHF CB frequencies in addition to the Amateur repeaters. I am unable to get “Scan” function to work with the extended frequency edits to 490 mhz. I have tried the Community Code Plug from your site plus the first one listed and one of the Radioditty 3.1.1 site and have the same issue with both. I have Firmware 3.01.03. If I put the original default.dat and a saved codeplug back and the scan works but without the extended frequency range.
    Any suggestions? Something else may control the scan function and resetting the freq limits may need to be complemented with editing the scan settings, just not sure if this is the case and where to find them.



  44. Roger Clark


    The default codeplug in the Community CPS should have extended frequencies enabled already. You can check by opening a New codeplug from the File menu.

    I’m not sure about scanning extended frequencies, as hardly ever use the scan feature, but no one else has reported a problem

    The only other thing I can think of, is that somehow the codeplug gets corrupted (probably by the CPS or by reading back from the GD-77) and then strange things can happen.

    Did you try just adding 2 UHF CB frequencies to the blank / default codeplug and seeing if the scan works ?


    Firmware 3.01.03 is probably fine. I think I’m using 3.01.06 on my GD-77’s as I had some problems with the call name display when using my hotspot with the latest firmware.
    And Radioddity have not really changed a whole lot between 3.01.03 and the latest version.

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