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I'm brand new to DSP and I'm experimenting with GFSK modulation to eventually output the signal using ultrasound. Could someone please explain why this set up doesn't work.

I'm receiving a serialized protocol buffer on the ZMQ Pull source and I'm expecting that if I just modulate then demodulate the signal I will get the same protobuf sent, back in the process that sent it (ZMQ push source sending it back). But that ends up not being the case and the byte pattern received after demodulating is off. Could someone explain why my set up doesn't work, Thank you again.

Flowgraph of GFSK mod/demod

MGB
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You can either use pack instead of repack or you can use repack, but change the endianness from LSB to MSB.

This demo shows both approaches: enter image description here

Mark H
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  • Thank you, I now have this flowgraph "almost" working with my custom source. After demodulation and repacking my application is always missing the last byte of the message, could that come from how they're being repacked after demod? – MGB Mar 14 '21 at 23:06
  • Have you seen this? https://github.com/gnuradio/gnuradio/issues/2530 (specifically in Options, changing to No GUI and then Run To Completion) – Mark H Mar 14 '21 at 23:31
  • If I change QT GUI Time Sink to show 1024 points (same as Random Source), I see them all in the plot. BTW, my yrange for QT GUI Time Sink is [-1,256] – Mark H Mar 14 '21 at 23:34
  • Exactly what I needed, runs now. – MGB Mar 15 '21 at 02:03
  • Awesome! You can accept the answer to close the question, if you'd like. – Mark H Mar 16 '21 at 18:39