|From:||Wilson, Ryan N.|
|Subject:||[Discuss-gnuradio] Burst FSK Receiver Clock Synchronization Problems|
|Date:||Mon, 7 Dec 2015 18:31:57 +0000|
I am currently attempting to get a bit stream from a captured RF signal that I know is from a burst FSK transmitter( 433.92 MHz carrier, 10kHz deviation, Manchester).
Using GNU Radio 3.7.8.
I have isolated the signal and would say I have successfully demodulated the signal. I am not sure of the bit rate but approximated it from the preamble
and then ran the signal through a matched low-pass filter (I approximated the bit rate of 20k) giving me this output below:
It is with the clock recovery/binary slicer that things are not going my way. I have been digging a lot and see people have questions about the
M&M clock recovery. I have found some paper and blogs that I have followed which seem to be working with signals very similar to mine:
I have also read many threads from the gnuradio mailing list and it seems like the M&M clock recovery works the best with around 2-4sps (I have not
adjusted any of the other values from this block at this time). The amplitude of my signal is between +/- 1 going into the clock recovery .So I have
decimated to give me a sampling rate of 100k and 5sps and ran my demodulated signal into the M&M clock recovery block:
I am not sure why it looks so bad. So then I found others recommending the polyphase sync block instead of the M&M clock recovery block. I have tried
loop bandwidth between 2pi/100 to 2pi/200, 5 sps, and low-pass filter taps with 20khz cut-off with similar results:
I do not know much about the polyphase sync block and I could have not configured it correctly. And now
that is why I am worried that I may have something else misconfigured. Here is my flowgraph:
I just ran into the work that was done for better support burst modems (which is what my transmitter is):
So I will be attempting to get my flow graph running with this FSK burst modem and report back with results. But any other input or
recommendations would be greatly appreciated.
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