I am transmitting a QPSK signal via GRC and when I look at it on the spectrum analyzer, the signal is shifted away from my center frequency. This shift increases the higher the center frequency (i.e. 1 MHz = almost no shift, 10 MHz = 1kHz shift, 50 kHz = 2.3kHz shift, 900 MHz = 43.5 kHz shift). Why does this shift occur? I have attached my flowgraph screenshot below. enter image description here

  • 1
    $\begingroup$ The most likely cause is that the USRP and the SA don't completely agree on what "one second" is. $\endgroup$
    – MBaz
    Mar 10 at 19:48
  • $\begingroup$ also, PSK Mod is deprecated. Don't use it. It's mostly broken. $\endgroup$ Mar 10 at 21:31
  • $\begingroup$ @MarcusMüller Is there another option to use? $\endgroup$
    – lceans
    Mar 11 at 14:02
  • $\begingroup$ Since you're starting a new thing here, definitely use GNU Radio 3.8 or 3.9 instead of 3.7. The digital blocks are undergoing changes, and I really don't think it pays to support the 3.7 way of doing things, now that nobody's going to use that. $\endgroup$ Mar 11 at 14:04
  • $\begingroup$ In 3.8 and later, there's nice examples in the examples/digital subfolder. Orient on these. $\endgroup$ Mar 11 at 14:05

Well, there are answers in the comments, but I am just going to put it down here.
Most probably the Local Oscilators (LOs) of your USRP and the Analyzer are not tuned/synchronized.
You could try to provide a common, external clock signal source to both of these devices.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.