GPS SNR testing

The command executes a Global Positioning System (GPS) Signal-to-Noise Ratio (SNR) test.

GPS L1 frequency is 1575.42 MHz and this test expects the Carrier Wave (CW) in signal generator to be 1575.750 MHz, i.e. the offset is 330 kHz. The measurement duration is 1 ms.

The command parameters and their defined values are the following:

1 – ON
Note: "OFF" is not needed due to automatic stop.

GPS SNR ON has three parameters:

RX signal power at the System in Package (SiP) GPS port in dBm.
Valid range from −127 to −25 or 0 = default gain −105 dBm.
AFC correction.
1 – Enable AFC correction in measurement
0 – Disable AFC correction in measurement
Frequency. Manually give RF frequency for nRF9160 in the 100 kHz format. Accepted value is +/- 10 MHz from the default GPS frequency of 1575.42 MHz. Set the signal generator to f = <param2> + 330 kHz.
Note: If <param2> is not given, nRF9160 uses the default GPS L1 frequency 1575.42 MHz.
Note: It is recommended to set the signal level defined in the GPS SNR ON parameters to the expected signal level at the GPS antenna port of the nRF9160 SiP.

Response syntax when <operation> is ON:

%XRFTEST: <snr>,<antenna_power>

The response value is the following:

The result of the SNR measurement in q4 dB. q4 means that dividing the result by 24 = 16 gives dB.
Measured signal power at the SiP GPS port in q8 dBm. q8 means that dividing the result by 28 = 256 gives dBm.

The following command example executes a GPS SNR test, AFC disabled:

%XRFTEST: 514,-19968 
Note: 514/16 = 32.125 dB and −19968/256 = −78 dBm.

The following command example executes an GPS SNR test for -80 dBm. AFC correction is enabled and uses the result of the previous AFC measurement or AFC set. Instead of the default, the receiver frequency is set to 1575.0 MHz:

%XRFTEST: 312,-20480
Note: 312/16 = 19.5 dB and -20480/256 = -80 dBm.