Changing Main frequency of HM-TRP 3DR Radio for Telemetry using AT Commands

I spent some time reading inHM-TRP Series 100mW Transceiver data sheet as well as SiK source code I wanted to know that if the 433MHz and 913 MHz is something fixed in the chip, that is why modules are sold either 433 or 913 or it is something you can change EASILY :)

Luckly I found that frequency is something not fixed, however in the source code of SiK, it is stored in board_frequency as input preset parameter when building the code, and it is passed to the firmware part in main.c where it is used for initialization.

Well I decided to make minor change,  I added a new variable -the 16th variable- called Main_Freq 

it can be given the following values


FREQ_433 = 0x43,

FREQ_470 = 0x47,    

FREQ_868 = 0x86,

FREQ_915 = 0x91,

These values are defined in board_info.h file 

Typical steps to change frequency are:

  1. +++ to enter AT commands mode.
  2. ATS16=67 to change to 433 MHz
  3. AT&W to save settings
  4. ATZ to reboot (Mandatory)

Another interesting thing is that the chip originally support frequencies as low as 240 MHz, however the firmware does support the above four frequencies only.

Now if you need to change frequency using only Firmware without the need to update the Bootloader you can use my changes...I hope you find this useful. 

Please note that you should use proper antenna for each frequency

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as Marcin Krawczyk  said ... the chip is the same ... the output LC is different, so u still can change frequency using chip , but will not be able to practically use it for any useful range.

Ahh ok :) i really enjoy fiddling with these things! 

beside all the discussion about circuitry and frequencies - I flashed my (use in Europe is a bad Idea) 915Mhz Kits - my mistake in ordering - to a legal 868 Version.

next week I'll do some range test.

@ MHefny you made my day!

Anybody got any updates to this post .. i wanted to take a RFM23B  433 to 466?

Based on replies the antenna circuitry will affect the range, but I guess for two adjacent frequencies it might work ok.

you need to try and remember all firmware could be reversed back. 

Almost worked for me!! Have a connection problem no one seems to be able to solve!!

Hello to All. I have question for You Guys. I need to change freq from 915 to 433 in ma oryginal SIK  can i do it without special dongles ? I have never do that all i have  is my pixhawk with which i see i can upload firmware to my radios and maybe some usb rs232 converters. Can i do it with that on some windows machine ??

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