Spectrum Analyzer

The spectrum analyzer request detects frequency spurs.

It scans a set of GPS or GLONASS frequencies and looking for spurs.

It is desirable to use a high baud rate for this feature (1 Mbps or more).

The initial and the ending frequency are relative to the center frequency of GPS or GLONASS.

The RBW is fixed at 1000Hz.

The VBW can be directly specified via VideoBandwidthHz="10". The permissible range is 1Hz to 100Hz. If not specified, the VBW is 100Hz.

The default InitL1OffsetHz and EndL1OffsetHz are -8000000Hz and 8000000Hz.

Default Spectrum Analyzer Job

This job is tuned for finding most problems with a single test and sets the stage for subsequent analysis if a spur is detected or suspected.

There are four tasks within this job:

  • overall - the entire +/- 8MHz span.
  • gps - a closer look at GPS with tighter VBW.
  • glonass - a closer look at GLONASS.
  • spur - a 1MHz span showing a how to look for a small spur. The span chosen is a likely place for LTE interference with GLONASS.

    <job id="spa">
        <task id="overall-"> <req_freq_scan/> </task>

        <task id="glonass-"> <req_freq_scan
                Band              = "GL_FACT_TEST_BAND_GLONASS"
                InitL1OffsetHz    ="-4000000"
                EndL1OffsetHz     =" 4000000"       /> </task>

        <task id="spur-">
            <req_freq_scan
                Band              =  "GL_FACT_TEST_BAND_GLONASS"
                VideoBandwidthHz  =        "5"
                InitL1OffsetHz    = "-2500000"
                EndL1OffsetHz     = "-1500000"
                SmallSpur         =     "true"      /> </task>
    </job>

When using a function generator to create a CW tone to test this feature, set the signal strength to be in the range -115 to -120 dBm. Set the frequency to be any value with in the respective span range relative to respective center frequency. Please refer to Factory test page for GLONASS frequency range : Factory Test .

The output of the Spectrum Analysis is provided through the pglor_spa_v1 NMEA message for 47511 or pglor_spa_v2 for 4752

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