Depending on the bandwidth of your signal, that could be a lot of offset, and you might need a PLL to do frequency correction. That's 130 ppm, which is a little more than you should see between two HackRFs.
On Wed, Jun 24, 2020 at 5:13 PM Artur Nogueira <[email protected]> wrote: > Thanks a lot. > I'll read the block specifications. > And yes, the offset is small (120 kHz). > > Em qua., 24 de jun. de 2020 às 17:53, Jeff Long <[email protected]> > escreveu: > >> Assuming the difference is small enough, this is a normal RX problem that >> a GMSK demod should be able to handle. The labels on your frequency plot do >> not say what the offset is, but hint that it is small. Take a look at >> gmsk.py >> <https://github.com/gnuradio/gnuradio/blob/b76e8788687b4feef610e501c0c7d167c4f04a98/gr-digital/python/digital/gmsk.py#L165> >> to >> see how it's handled in the built-in demod. >> >> On Wed, Jun 24, 2020 at 4:10 PM Artur Nogueira <[email protected]> >> wrote: >> >>> Hi Jeff, >>> >>> Thanks for the feedback. >>> I'm using GNU Radio Version 3.7.13.5 and two Great Scott Gadgets HackRF >>> units for the transmission/reception. >>> My workflow looks like this: >>> >>> [image: image.png] >>> >>> Do you usually use any artifact to compensate for this frequency shift? >>> I'm afraid this could affect demodulation and therefore the BER. >>> >>> Best regards, >>> Artur >>> >>> >>> Em qua., 24 de jun. de 2020 às 16:31, Jeff Long <[email protected]> >>> escreveu: >>> >>>> Artur, >>>> >>>> You haven't mentioned what software you are using, how you have it >>>> configured, or what your flowgraph looks like. >>>> >>>> If you are using two SDRs and the frequency difference is a few kHz, >>>> then that is just oscillator differences. >>>> >>>> On Wed, Jun 24, 2020 at 3:12 PM Artur Nogueira <[email protected]> >>>> wrote: >>>> >>>>> Hi everyone, >>>>> >>>>> I'm comparing the spectra of a pair of transmitted/received GMSK >>>>> signals (carrier frequency = 923 MHz). >>>>> As expected, there is a certain channel attenuation. >>>>> Nevertheless, there is this frequency deviation at the Osmocom Source >>>>> output: >>>>> [image: image.png] >>>>> >>>>> I suppose this is something related to the receiver hardware. >>>>> Do you have a suggestion on how to compensate for this effect at a >>>>> software level? >>>>> >>>>> Best regards, >>>>> Artur >>>>> >>>>>
