[Discuss-gnuradio] problem with clock_recovery_mm on low data rates

[Niaz Ahmed]

Hi all,

I am implementing a fsk receiver and using clock_recovery_mm for synchronization. The block was working fine till I lowered my data rate to 50bps. I do not know what goes wrong for low data rates.

I am using 48k sampling rate and while working with 100bps I was having 480 samples per symbol (As i am implementing binary FSK so symbol rate= bit rate ). When dealing with 50bps I changed the symbol rate => omega =  960 but the block was not giving the right output.

I dig into the block and found some strange things. I found that the clock recovery goes wrong when consecutive sequence (either 1 or 0) is input to it. The problem that i figured out by using the scope sink (in grc) 

was with both the 100bps as well as 50 bps. But the 100 bps it was still decoded by the binary slicer, however in case of 50 bps it was becoming weird. Screen shots of for 100 bps ad 50 bps are attached. According to our understanding the highlighted portion is not correctly decoded.

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Best Regards

Niaz Ahmed

NUCES-FAST, Islamabad Campus

EXT-369

Engineers motto: cheap, good, fast: choose any two (copied)

50bpsM$M.png
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100bpsM$M.png
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