nRF51822 carrier-only test mode

[florentb]

I am testing the DTM mode on the nRF51822_QFAA, and I use the carrier-only test with the following command :

dtm_init();    
dtm_cmd(LE_TRANSMITTER_TEST, 39, CARRIER_TEST, DTM_PKT_VENDORSPECIFIC);
while(1);

The result, with a spectrum analyzer (radiated test), looks like this:

While this seems within spec, is it normal to have the two additionnal peaks, 165kHz apart from the carrier?

Or is it caused by a PCB / design issue?

I am sure these are not coming from my spectrum analyzer, as I reproduced it with several analyzers and also with several nRF devices with different antennas.

[bjorn-spockeli]

I assume this is a custom board? No, you're not supposed to see two additional peaks 165kHz from the center frequency. I am pretty sure that this is noise that is modulated onto the carrier. How are you powering the board? It could be noise from the boards power supply, I suggest using a battery or an external power supply and then redo the measurement