Rnode tx power > 17dBm

[TomF8COD]

Hi Mark and all,
I'm planning to use a T-beam in tnc mode to make a linbpq node, Lora packet radio would be a fun use. I've seen that rndeconf doesn't allow more than 17dBm ; is there a way to set the power higher for the devices that support it?

[faragher]

Hey, saw you on BlueSky, glad to see you here. To the best of my knowledge, the power limits are baked into the firmware, and you should be able to go to that cap using TNC mode. I don't use TNC, but every time I use serial commands it works as expected. That being said, the SX series chips can be misleading. Some are rated to 20 dBm for very short duty cycles (which are never defined) with 17 dBm being the highest continuous power mode, thus the RNode cap. I don't know what the failure mode is, it could be thermal, it could be reflected power, or it could be something I don't expect! The firmwares are generally set to use the maximum safe power as the cap, and they should be field-programmable to that limit. If you want to push them hotter, knowing the risks, the firmware can be modified and recompiled with a higher maximum power. If you require any assistance with that, knowing the risks, we're happy to help. That being said, the stock antennas are absolute trash so the first step should always be getting something nicer. Low Power Labs used to have dirt cheap PCB dipoles that were pretty well tuned, but they've gone up quite a bit last I checked. Let us know what you're looking for.

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On Thu, Feb 20, 2025, 1:45 AM TomF8COD ***@***.***> wrote: Hi Mark and all, I'm planning to use a T-beam in tnc mode to make a linbpq node, Lora packet radio would be a fun use. I've seen that rndeconf doesn't allow more than 17dBm ; is there a way to set the power higher for the devices that support it? — Reply to this email directly, view it on GitHub <#725>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ALIZNI5XEDNHEU4QVAHRUKL2QWB3FAVCNFSM6AAAAABXQB5ODOVHI2DSMVQWIX3LMV43ERDJONRXK43TNFXW4OZXHE4TGMBWGQ> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[TomF8COD]

Hi and thanks a lot for these infos !
I've seen where the limitation is in the code sx127x.cpp line 349, I'll disable it and recompile to make some test, keeping what you said in mind ie: it may be a destructive test. I would bet on thermal failure, due the total garbage of an antenna provided with it I suppose the finals can handle a pretty high SWR. As I'm doing test with a packet radio application, I always replace the stock antenna with a homebrew quarter wave antenna and for applications like this one I have a dedicated vhf/uhf antenna on the roof.
To recompile, all I have to do is :
make prep-esp32 then
make firmware-tbeam and finaly
make upload-tbeam
Right ?

[markqvist]

Correct, if the device already has a valid EEPROM configuration loaded. That would be the case if you've already flashed it with rnodeconf or similar. Otherwise you can do that first, and then just upload your custom firmware afterwards.

[TomF8COD]

Hi Mark :-) Thank you, yes it has been installed with the --autoinstall method to start from a safe base.

[TomF8COD]

Well, sorry to bother you with that but I'm stuck with something that is probably silly.
I've commented out the line 349 in sx127x.cpp (// else if (level > 17) { level = 17; } )
I made a 'make clean', 'make prep', 'make firmware-tbeam', 'make upload-tbeam'
Then I typed 'rnodeconf -T /dev/ttyUSB0' to switch to TNC mode and specified a txpower of 20dBm and... I'm limited at 17dBm again. Is there another place I should look in the code ?
I've tried the same with the CE firmware to see if I've missed something, the limitation is at line 1332 of Radio.cpp and there it worked, I was able to set the tx power above 17dBm.
So, I bet it's something totally silly that sits in front of my eyes, but I can't find it though. Do you have any idea ?

[TomF8COD]

I new I was missing something obvious... Th limitation is in 3 files, not just one.

So I commented it line 349 in sx127x.cpp

348     if (level < 2) { level = 2; }
349 //    else if (level > 17) { level = 17; }                                                                                             
350 

`Then in line 145 in 'Python Module/Rnode.py'

145         #if (self.txpower < 0 or self.txpower > 17):                                                                                   
146         #    self.log("Invalid TX power configured for "+str(self), RNodeInterface.LOG_ERROR)
147         #    self.validcfg = False
148 

And finally line 845 in RNode_Firmware.ino

845         //#else                                                                                                                       
846         //  if (txp > 17) txp = 17;
847         #endif

Now I can set more than 17dBm.