GNSS SNR testing

[Arthur M]

Hello,

We are currently developing with the nRF9151 and would like to request more information regarding GNSS SNR testing.

We have reviewed the documented GNSS functionality test procedure (GNSS functionality test), which utilizes the AT%XRFTEST (Set command) from the PTI modem. (Set command)

We are wondering how does the "<param0> RX signal power" parameters plays in the calculation of the results returned.
Would it be possible to run the same command (power) with a different signal in input? (more attenuated signal)?
I am not sure why the command output "antenna_power" level changes depending on the "expected power level", shouldn't it be a raw value?
Also I understand that the parameters is the expected power level at the module port, but why is it mentioned as GAIN? Is it because the GAIN applied on the signal is directly linked to the value given?
Would it be possible to have a "raw" level received?

Also, If we are confirming our RF path viability during production, is it recommended to use AFC on or off?

Thanks for you answers,

Arthur M

[Øyvind]

Hello Arthur, my apologies for the late reply. Here is the answer I got from our team:

Same procedure should apply to 9151, yes.

<param0> is used to set the receiver gain. During normal operation the gain is automatically adjusted (automatic gain control) but such thing is not feasible in SNR testing. Theoretically increasing gain should increase RSSI but have no impact of SNR since both signal and noise get amplified. I believe this answers also the following question: “I am not sure why the command output "antenna_power" level changes depending on the "expected power level", shouldn't it be a raw value?“

Different input signal levels can certainly be used for testing. This will obviously results in lower SNR measurement. Note that <param0> should be adjusted accordingly.

It is recommended to have AFC ON to eliminate possible test equipment frequency error as well as any uncalibrated TCXO offset in nRF9151. During normal GNSS operation TCXO offset will anyway be resolved very accurately so there is no reason not the compensate it away during RF testing.

Kind regards,
Øyvind