Waveform alignment / frequency calibration

SDRPlay Independent Community Forum Forums SDRUno Waveform alignment / frequency calibration

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  • #2133
    3Icomman
    Participant

      Greetings from a new SDRPlay DX owner.

      I’m a stickler for details. I have spent hours experimenting with the SDRuno’s built in frequency calibration window using 25Mhz WWV signal.
      When I open up the manual calibration window I see that the system crystal factor is -0.864ppm
      This results in a frequency offset of 0.5 to 0.7 hz. Based on previous discussions, this appears to be acceptable. Also, I have toggled back and forth from USB to LSB while listening to the WWV, and the tonal qualities are equal. So it appears that the calibration is good.
      However, the FFT waveform peak is not centered on the frequency marker. I believe it should be? Am I incorrect?
      If I do a manual calibration on the 25mHz WWV signal and set the crystal frequency value to 0ppm, I find that the frequency marker centered on the maximum spectral peak indicates a 25hz offset….
      Can someone please explain all of this??..
      My belief is that the autocalibration should align the SDRPlay internal oscillator with the the known reference value (in this case, WWV at 25mhz), AND the FFT spectral peak would also line up with the calibrated frequency.

      Mike
      KG5EJB

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      #2174
      NoelC
      Participant

        Hi Mike,

        Do you mean that when you zoom your MAIN SP or AUX SP window in all the way you’re seeing a big offset between the center of the power peak and the tuned frequency?

        I hadn’t tried zooming the MAIN SP window all the way in before, and when I do that even though SAM mode shows me almost perfectly tuned, I am seeing the power peak somewhat to the right of the red line. Probably only a couple of Hz, though. The signal in the AUX SP window, zoomed in, however, is dead on center.

        At typical zoom levels (i.e., all the way out) I’m seeing maybe a single pixel of misalignment in the other direction. Pixel perfection across multiple systems with different GPUs is actually more difficult than you might think.

        FWIW, I’m using LIF, not ZIF.

        Screen grab image attached. EDIT: It wouldn’t take my first screen grab; trying to overcompress it to get under the 512 KB size limit…

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