Re: [Discuss-gnuradio] Pulse on FSK Preamble

[Andy Walls]

> Date: Tue, 22 Jan 2019 10:42:19 +0100
> From: samuel verdon 
>
> hello Everybody,
> 
> I am trying to recover my fsk signal with the Muller&muller block.
> Here is my configuraiton:
> Sample rate of USRP = 240K
> bitrate of signal = 9600bps
> 
> receiving the signal from the USRP,
>  apply a low pass filter -> quadrature demod ->rational resampler ->
> m&m
> sync block
> 
> 
> My signal contain a preamble of 100ms of 1010 (0x55). after my
> Muller&Muller block, I can see the recovering working for my signal
> but not
> for my Preamble. I have pulse on the preamble which sometime are
> visible on
> the data part as well.
> https://ibb.co/hfLt62K  <https://ibb.co/hfLt62K>
> https://ibb.co/xqRkRP7

The M&M Timing Error Detector (TED) gain collapses to 0 when operating
on "clock patterns" of 1010101, so the M&M TED works horribly on trying
to acquire such a preamble.

>  I have tried also with Polyhpase clock sync block but this one took
> to
> much time to be syncronised with my preamble.
> 
> Can someone help me by explaining this pulse? I porbably do not use
> correctly the sync block ( I have left the default value except for
> the
> omega=sps ). Can someone redirect me to a documentation to use it
> correctly?
> let me know if I have to give more information.

Switch to using the Symbol Synchronizer Block.

You should read this brief:

https://www.gnuradio.org/wp-content/uploads/2017/12/Andy-Walls-Samples-to-Digital-Symbols.pdf

And read my recent comments in this GNURadio Issue:

https://github.com/gnuradio/gnuradio/issues/2134#issuecomment-456238039

Regards,
Andy

> Thank you in advance for your help
>