GNSS functionality test

The %XRFTEST GNSS SNR test starts Global Navigation Satellite System (GNSS) Signal-to-Noise Ratio (SNR) measurement. By default, 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 GNSS center frequency of 1575.42 MHz. The duration of the measurement is 1 ms.

The test is automatically disabled when it is finished. OFF <operation> is not needed due to automatic stop.

The recommended signal level for GNSS testing is -90 dBm. The expected SNR with this signal level is normally more than 16 dB. For details on setting the correct signal level parameter for the %XRFTEST command, see GNSS mode.

AFC correction can be performed to increase the accuracy of the SNR measurement. This can compensate the frequency error between nRF9151 and the test equipment used. AFC measurement and setting is supported by modem firmware v2.0.x and later.

Note: The reported SNR is very sensitive to external RF disturbance 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 GNSS SNR test with AFC correction disabled, default receiver frequency, and external Low-Noise Amplifier (LNA) gain of 16 dB.

%XRFTEST=2,1,-80,0
%XRFTEST: 364,-20506,455,-16
OK

Note: 364/16=22.75dB. –20506/256=–80.1dBm. 455/16 = 28.4dB.

The GNSS functionality test input parameters are described in the following table.

Table 1. Input parameters of GNSS functionality test
Parameter name	Parameter description	Range	Value description
<param0>	Signal level at antenna	–127 to –25	Signal level at the nRF9151 GNSS input port (dBm)
<param1>	AFC correction	0–1	AFC correction control in measurement
<param2>	Frequency	1565.42–1585.42	Manual setting of RF frequency

nRF9151 responds to the %XRFTEST GNSS SNR test with the measured GNSS 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 SNR.

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 GNSS signal level parameter in the %XRFTEST command refers to the signal level at the nRF9151 GNSS input port. Consider external LNA gain with this setting.

For more information on GNSS testing with the %XRFTEST AT command, see GNSS SNR test %XRFTEST in nRF91x1 Production Test AT Commands Reference Guide.