RE: Frequency width and Modulation/Non-modulation

roger.k — Wed, 07 Sep 2016 01:34:24 GMT

Thank you very much. Very helpful.

RE: Frequency width and Modulation/Non-modulation

Einar Thorsrud — Tue, 06 Sep 2016 11:35:39 GMT

I think I may have been a bit unclear in this answer. The only available modulation type is GFSK, in four variants (different bit rates and modulation index). However, you can output an unmodulated carrier signal by setting the CONSTCARRIER field of the TEST register.

As far as I can see, you are configuring the radio to output an unmodulated carrier with the following line from your code:

NRF_RADIO->TEST       = (RADIO_TEST_CONSTCARRIER_Enabled << RADIO_TEST_CONSTCARRIER_Pos) \
                        | (RADIO_TEST_PLLLOCK_Enabled << RADIO_TEST_PLLLOCK_Pos);

The spectrum plot you have uploaded seems to be in line with what you would expect with the radio configured for an unmodulated carrier output. If you do not enable constant carrier, but instead output some data, you would see that the signal would require more bandwidth (be wider). The easiest way to test this is to use the radio test example or simply copy what you need from there. The radio_modulated_tx_carrier() will generate and output a random packet on a specified channel, with a specified modulation mode and output power.