RAK811 tx power

Hi guys,

Quick question, I want to configure the transmission power of my RAK811v1.2.
I just want to know how to configure it? I know using the the AT command at+set_config=lora:tx_power:0. What does the zero value represents? Is it zero dbm max power? If i want to use the max EIRP of 16dbm for EU868. What AT command should i use?


You can refer to this document https://lora-alliance.org/sites/default/files/2018-04/lorawantm_regional_parameters_v1.1rb_-_final.pdf
And this is what the digits (0 to 15) means in AT command.


Thank you for the reply @velev.

So with the given values, does it means the command at+set_config=lora:tx_power:0 corresponds to a 16dB power (max for EU868)? And at+set_config=lora:tx_power:7 corresponding to 2dB power?

Is this right?

The max EIRP is what comes after the antenna. When you set a value you have to add the antenna gain. For example:
at+set_config=lora:tx_power:0 will result in 16dB at the antenna port. If you have a 3dBi antenna this will leave you with a total EIRP of 19 (if you are assuming the connector is perfect, you have no antenna line attenuation, etc.)

So basically yes. But keep in mind the antenna gain.

Noted @velev.

Basically we can say that at+set_config=lora:tx_power:0 is the highest setting for tx power while at+set_config=lora:tx_power:7 would yield the lowest tx power setting? Since 8-15 is reserved future usage. Is this right?

Yes, basically right. :slight_smile:

Noted and Thanks @velev.

Do you know what is the maximum payload bytes can be sent per transmission?

It is not so simple. You should check this document https://lora-alliance.org/sites/default/files/2018-04/lorawantm_regional_parameters_v1.1rb_-_final.pdf
It is the main book of LoRaWAN :slight_smile: In page 18 you will find the max payload with different conditions. But as a rule for me is to keep the payload under 12 bytes.


Does that mean that if I use RAK811 breakout module (Take Advantage of LoRa® Features with RAK811 LPWAN Breakout Modules – RAKwireless Store) with the antenna that comes with it (probably with gain 2 dBi), do I have to set at+set_config=lora:tx_power:1 ,in order to comply with EU868 regulations ?

For example, with tx_power =1 that means MaxEIRP- 2dB, so (16 - 2) dBi at antenna port + 2dBi antenna gain = 16 dBi after the antenna, is that correct ?
Or does the MaxEIRP implies a 2 dBi antenna ( such as 14 dBi + 2 dBi antenna gain = 16 dBi final output after the antenna, with tx_power:0 ) ? I got a bit confused

Hi peter,

The 1st one is correct. If you set tx_power=1, then 14dB is going out from the module excluding your antenna gain.

But you also have to consider losses on the cable, connector, etc. (if there are any).

Ok, thanks @carlrowan

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