Frequency calibration with GPSDO?

SDRPlay Independent Community Forum Forums SDRUno Frequency calibration with GPSDO?

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  • #260
    BillyTampa
    Participant

    I purchased a GPSDO (Leobodnar MINI Precision) and connected it to my RSP2 Pro. The GPSDO is set to 24 MHz at 16ma and all seems to be working well. If I tune the RSP2 to 24 MHz and set the mode for SAM and DSB the frequency offset indicates +.5 Hertz.

    With an antenna connected this value varies either side of zero, but with the Hi Z port terminated with a 1000 ohm resistor the value is steady at +.5 Hertz. My question is this:

    Should I use the built in frequency calibration feature to further calibrate the software to the reference 24 MHz frequency? Or should I ignore the +.5 Hertz offset shown while using the external GPSDO reference input?

    Thanks

    #299
    Roger
    Participant

    I assume you have the offset in the calibration section set to 0.

    It is not surprising that the SAM DSB indicates a +/- .5 Hz. offset. You may be down to the frequency resolution limit of the SAM algorithm.

    #1891
    Cosmic Ray
    Participant

    I am using the Leo Bodnar Precision GPS Reference Clock as the external clock for my RSP2 and using the SDRPlay ExtIO interface with Spectrum Lab (no SDRuno). I measure a consistent +0.5 Hz offset of the measured WWV carrier frequency with respect to the expected value from 5 through 20 MHz (even with large FFTs and bin widths less than 0.1 Hz). I am not using any of the calibration coefficients that are stored in SDRuno (at least as far as I know). Are there any other places where a frequency offset could lurk, either in the RSP2 or in the ExtIO interface? If so, how can I adjust them? Any advice would be gratefully received, thanks.

    #1894
    Cosmic Ray
    Participant

    BillyTampa: Did you ever get to the bottom of this? I also observe an offset of about +0.5 Hz on all WWV frequencies that I can hear (using my Bodnar GPSDO). SDRPlay tech support thinks this might be due to the accuracy of the fractional-N synthesizer in the receiver chip (something like it can’t get closer than 0.5 Hz to a required frequency). This seems like a reasonable suggestion, but then, how can it be tested, and more importantly, how does it change with other settings of the receiver? Presumably one could find a combination of LO and other settings that would cause the synthesizer to use an “integer” frequency that would not have this problem, but I have not yet been able to figure out how to do that. So, I wonder if you made any progress on this issue. Thanks!

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