Re: [Discuss-gnuradio] Pulse on FSK Preamble

[Adrian Musceac]

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 <address@hidden> 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
>