How can I read RSSI value in radio_test Example without SoftDevice?

[Pietro Beraldini]

Hi,

I need to read RSSI value without implementing the SoftDevice. Now I'm producing modulated and unmodulated carrier starting from the radio_test example.
How can I read the RSSI and selecting the rx frequency?
I'm using nRF52840 with SDK 15.2.0.

Thanks

[cbd]

RSSI - Received Signal Strength Indicator.

This is essentially a comparison of the measured signal strength of a received signal against what the transmitting device states the transmitted signal strength was at transmission. Obviously the Soft Device provides this for you, I'm not sure whether you can achieve this without it.

Are you actually wanting to measure this without using the Soft Device or do you wish to set the signal strength of your unmodulated/modulated carrier so that it can be tested by some external equipment?

For direct testing of unmodulated signals you're into using the Direct Test Mode functionality. Transmission power can be set using dtm_tx_power command.

For frequency selection you'll need to select channel and calculate it from there see dtm_cmd in the Direct Test Mode documentation. The two frequency extremes are channel 0 and channel 39 with channel 19 & 20 being close to the mid point.

Edit

I've now had a quick look at the Radio Test example and you can't measure the RSSI with it as it is really for testing transmission.

You can set the frequency by selecting the start_channel  to the channel closest to the frequency  that you're after (see dtm_cmd for frequency & channel relationship) and then using start_tx_carrier or start_tx_modulated_carrier for a plain carrier wave or modulated signal at that frequency.