On Wed, Jun 24, 2020 at 5:21 PM Jeff Long <willcode4@gmail.com> wrote:
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 <artur.nogsj@gmail.com> 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 <willcode4@gmail.com> 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 to see how it's handled in the built-in demod.On Wed, Jun 24, 2020 at 4:10 PM Artur Nogueira <artur.nogsj@gmail.com> 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: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,ArturEm qua., 24 de jun. de 2020 às 16:31, Jeff Long <willcode4@gmail.com> 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 <artur.nogsj@gmail.com> 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: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
