GPS functionality test

The %XRFTEST AT command with the GPS SNR ON parameters starts a Global Positioning System (GPS) Signal-to-Noise Ratio (SNR) test. The test expects the Carrier Wave (CW) in the signal generator to be at 1575.750 MHz, which means a 330 kHz offset from the GPS center frequency of 1575.42 MHz. The duration of the measurement is 1 ms.

The test is automatically disabled when it is finished. The %XRFTEST AT command with the GPS SNR OFF parameters is not needed.

The recommended signal level for GPS testing is -90 dBm. The expected SNR with this signal level is normally more than 12 dB.

Note: The reported SNR is very sensitive to external RF disturbance that may be present in the test environment. An RF shielded chamber is recommended as a stable test environment. A known device, such as a golden unit, can be used as a reference to confirm the validity of the test result.

The following command example executes a GPS SNR test:

%XRFTEST=2,1,0
%XRFTEST: 514, -27392	// Result: SNR 514/16 = 32.125dB, RSSI -27392/256 = -107dBm
OK

The GPS functionality test has one input parameter that is described in the following table:

Table 1. Input parameter of GPS functionality test
Parameter name	Parameter description	Range	Value description
<param0>	Signal level at antenna	-127 to -25	Signal generator level at antenna [dBm]

nRF9160 responds to the GPS SNR ON parameters of the %XRFTEST AT command with the measured GPS SNR and RSSI values. The SNR is given in the q4 (dB) format. Dividing the result by 2⁴ = 16 gives the dB value of the antenna power.

The RSSI signal level at the antenna is given in the q8 (dBm) format. Dividing the result by 2⁸ =256 gives the dBm value of the RSSI.

Note: The GPS signal level parameter in the %XRFTEST command refers to the signal level at the nRF9160 GPS antenna input pin. Consider external Low-Noise Amplifier (LNA) gain with this setting.

For more information on GPS testing with the %XRFTEST AT command, see GPS SNR testing in nRF91 AT Commands Reference Guide.