Hello Radio Friends, I wonder why I don't observe a fixed phase difference between a demodulated 500Hz doppler FM-signal and a fixed GNR 500Hz sine source. The setup is a USB-RTLv3 in a RaspberryPi. The RTL-oscillator is divided by a (hardware!) synthesizer chip and drives the antenna rotation which results in a 500Hz audio-tone. Due to the fact that the rotation of the antenna is based on the SDR-clock I expected that both 500Hz signals would have a fixed phase difference. I think however I make a fundamental mistake and the 500Hz GNR sine-source is not related to the sample rate of the incoming IQ-stream originating from the SDR...
Question: What is your opinion on this and can you provide guidance how to sync the 500Hz GNR sine-source to the incoming IQ-stream? Background information: - The GNRsetup is running on the RaspberryPi4: In the flowgraph the received 500Hz audio signal from the NB-FM receiver is displayed in a Time Sink together with a second fixed 500Hz source. video: https://youtu.be/OxQMvt5ILUY (grc-code and GNR-status messages in the shared folder) - Validation of the doppler effect occurring: The pseudo doppler effect is validated and demonstrated with a SDR++ recording (below the video of the test and the related base band IQ recording) In this recording the RPi runs RTL_FM. An ethernet connected Windows computer runs SDR++ and processes and records the IQ-stream. video: https://youtu.be/kwGM5PabdAA (recorded IQ-stream is in the shared folder) Shared folder with recorded IQ-stream, GRC-code and high-resolution videos: https://tinyurl.com/34zv37x4 Thanks for your guidance! Robert ps. As a rookie (still in the steep gnr learning curve) I did read the tutorial pages.
