Goonhilly WEB-SDR is not on Frequency ?!

  • Hi,


    after change of the bandplan the UK WEB-Sdr is -80Hz off frequency.


    By the way, it is not very smart to set the center frequency of the Sdr to the beacon frequency because of the zero point at the middle, what is shown as a black bar.


    It will be nice if somebody can inform the responsible old man :-)


    73, Mike

  • Hallo Mike DK1ML


    Which bar do you mean ? The left or right one ? The left bar sits on 10489750.00 and the right one on 10489750.16 kHz. In between it's on 10489750.08. The left bar is constant modulated and the right bar is wider and can be PSK-modulated. So I think the beacon QRG is correct adjusted. On your screenshot I can see the same result as in my browser.


    Any other opinions ?


  • Hi Thomas,


    I am talking about the center beacon at 10.489.750,00 as shown on the picture.



    This is the center frequency of the SDR range at 0 (zero) hertz.

    All SDR receivers have this "blind" frequency in the middle of the reception range, sometimes with a phantom signal if the balance is not accurate or if there is some 50hz hum.


    I have set the range of my online WEB SDR 5khz left of an important signal.


    But more important to me is that you confirmed the same frequency error at 10489750.08


    73, Mike

  • But more important to me is that you confirmed the same frequency error at 10489750.08

    No, this is the frequency between the two bars, your "phantom error" frequency. The center bar/beacon is on 10489750.00. Where is the problem ?


    EDIT/Nachtrag:


    Now I see the problem. We are talking of both bar's, look at http://websdr.is0grb.it:8901/ , zoom in and we will see the error of 80 Hz at Goonhilly. You are right. Btw. http://appr.org.br:8902/ is also misadjusted.

    Or is this a wrong interpretation of the PSK-signal by me ?

  • Hi all,


    Half a year later, the issue remains unchanged. The Goonhilly WebSDR now seems to be off by around 130Hz. Apart from the offset, there is a visible jitter of quite a few Hz.


    The screenshot below shows the same audio signal as received simultaneously by the Brazil WebSDR (trace at the left side), the Goonhilly WebSDR (trace at the right side) and by my own receiver (trace at 762Hz).


    The Brazil WebSDR (http://appr.org.br:8902/) is shown just for comparison as Thomas mentioned it above and I guess it uses a simple TCXO as a reference. Both offset and drift are heavily dependent on the time of day.


    73 Jean DJ0VL


  • 130Hz in 10 GHz? Shocking. Don't think anyone said it was a standard frequency reference, but don't forget to account for Doppler and relativity.

  • 130Hz in 10 GHz? Shocking. Don't think anyone said it was a standard frequency reference, but don't forget to account for Doppler and relativity.

    Not shocking, just wondering as it apparently uses a GPSDO reference that states an Allan Deviation of 5E-11 @Tau=1s.


    73 Jean DJ0VL

  • Allan deviation is stability.. 130Hz in 10 GHz is accuracy. Check here for a good explanation of the subject.

    That said, there are numerous explanations for this offset including hw failures. Maybe telling the WebSDR team directly?

  • Allan deviation is stability.. 130Hz in 10 GHz is accuracy. Check here for a good explanation of the subject.

    That said, there are numerous explanations for this offset including hw failures. Maybe telling the WebSDR team directly?

    Thanks for the link and of course you are right. I'm familiar with the difference between stability and accuracy, my comment referred to the noticeable jitter. Sorry for the unclear wording.


    73 Jean


    PS: I would like to tell the team directly, but finding a contact address on the webpage is not easy.

  • Hi @ll,


    it is not a question of the stability, there is an offset of 100 Hz which is caused in a faulty setup by the operator.


    It is know, that QO-100 will drift +/- 30 Hz over the day.


    73, Mike

  • I am sure he knows. I will ask next time. The reasons for these errors are probably interesting and subtle.


    See http://g4jnt.com/QO100_Stab.pdf

    Thank you for this highly interesting paper. Figure 4 confirms my observations regarding the short term stability. I commented on this as the observed stability may be normal behaviour for the type of GPDSO used, however it seems somewhat higher than the stated and measured stability data for this GPSDO.


    I'm fully aware that we are discussing deviations on a very high level, nevertheless I'm interested in knowing the reason for the errors. We do not know whether its all due to the stability of the GPSDO, but imho a decent GPSDO has a significantly higher stability.