Re: [Discuss-gnuradio] Pulse on FSK Preamble

Hi Samuel,

Is there any reason why you do the quadrature demodulation before the
resampler? Usually the CPU limitations require to decimate the signal
as soon as possible to a manageable rate for the quadrature demod
block. Also, if the FSK symbols are not RC filtered and represent a
square wave, I remember reading that the M&M clock recovery algorithm
does not deal well with a square wave. Perhaps your resampler deals
with that?

Hope this helps,
Adrian


On 1/22/19, samuel verdon <sam.verdon@gmail.com> wrote:
> 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
>
> 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.
>
> Thank you in advance for your help
>
> --
> Samuel Verdon
>

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