Re: [Discuss-gnuradio] GMSK at 768kb/sec and other good stuff

[Robert McGwier]

Dawei:

You have understood it.  Can you suggest a less expensive way than a 
single pole iir filter (integrator) to compute the running average of 
the data so we can subtract that mean?  That was the only thought. We 
needed a very low frequency cut off and this is computationally cheap.

Bob


Dawei Shen wrote:

> Hi Eric and other dudes
>
> I am studying the GMSK2 code now. The code is very clean and obviously 
> designed sophisticatedly. I feel excited to read the code. Could you 
> please help explain the following code to me?
>
>     alpha = 0.0002   # FIXME, maybe 0.0008/spb
>     self.freq_offset = gr.single_pole_iir_filter_ff(alpha)
>     self.sub = gr.sub_ff()
>
>     fg.connect(self.fmdemod, (self.sub, 0))
>     fg.connect(self.fmdemod, self.freq_offset, (self.sub, 1))
>
> This part is following the FM demodulator.  My guess is you are going 
> to remove the DC offset, is that right? But why do you use an IIR filter?
>
> I plan to add comments to the codes and put them on my website once I 
> finish studying them.
>
> Thanks for your time
>
> Dawei
>
>
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