Continuous Wave for nRF9160

[jlienau03]

Is there any test firmware available (or reference code) for doing total radiated power measurements?  I have the nRF9160 designed onto a PCB and we'd like to do some antenna measurements. Ideally I'd be able to put the nRF9160 into a continuous wave mode.

Thanks!

Johnny

[Håkon Alseth]

Hi,

 

There's a test AT command specified in the AT Command pdf at chapter 4.19, "%XRFTEST".

You can input this command by using the example at_client, in combination with nRF connect application "LTE Link Monitor".

 

Kind regards,

Håkon

[jlienau03]

Thank you.  Some follow-up questions: 

I know I can send AT commands via the LTE Link Monitor program, but could I instead use a terminal program like Putty and tap into the UART pins to the nRF9160 on the development kit? 

Looking at the schematic for the development kit, P0.26 through P0.29 appear to be the UART comms for the AT commands.  Where on the development kit would I connect to those UART lines? Is it TPs7-10? Or is it D19 - D22?

What I'm hoping I can do is load the at_client example onto my prototype PCB with a few modifications and send the AT commands over UART.  But I wanted to try it first on the development kit.

Thanks again for the help!

Johnny

[jlienau03]

I connected the DK directly to my spectrum analyzer so I could measure the conducted power directly.  I am actually seeing correlation between the %XRFTEST: some number response and what I am measuring on the spectrum analyzer.  I set the output power to 0 dBm and the response was -795.  -795/16 = about -49dBm.  This is approximately what I see when I measure it.  So, my question above now changes slightly: why is the power delivered to the antenna so low when I am requesting 0 dBm?  I am plugging directly into the connector that is on the DK.

[Håkon Alseth]

Hi Johnny,

 

Yes, you're right regarding the XRFTEST vs RFTEST in the AT commands pdf. I'll report this as a bug internally.

Have you tried running the command without using a spectrum analyzer, just to see if the response is as expected then? Could the problem be the cable?

I get a reported 22.69 dBm when running this command:

***** Booting Zephyr OS v1.13.99-ncs1-4741-g1d6219ffec *****
The AT host sample started
AT%XRFTEST=1,0
OK
AT%XRFTEST=1,1,13,7777,23,1,4
%XRFTEST: 363
OK

Kind regards,

Håkon

[jlienau03]

I originally tried it without a spectrum analyzer.  I later used the analyzer to verify that the RF output was actually matching what the terminal program was telling me.

I have two development boards here and they are both showing similar behavior.  I tried your same command (AT%RFTEST=1,1,13,7777,23,1,4).  One DK board gives me about -411 and the other gives me about -330.  

I assuming it must be something with the software, I think it's unlikely I have two bad development kits.  Unless there's something I need to do to the DK prior to using the RF test commands?

[Håkon Alseth]

Hi,

 

That is strange. Do you have the latest modem firmware flashed onto your boards?

You can download the latest modem fw here:

https://www.nordicsemi.com/Products/Low-power-cellular-IoT/nRF9160/Download#infotabs

Kind regards,

Håkon

[jlienau03]

That solved it! I updated the firmware on both modems and now I'm getting the correct output power.