Re: [Discuss-gnuradio] FIR filter in fsk_tx.py

[Sachi]

Let me make my question more clear.
If I understand the code correctly, after
"bytes_to_syms", the signal should be a float sequence
of +1 or -1.  I am very confused about what the signal
will look like after "interp".  I think it's no longer
+-1 sequence any more.  So does it have any special
function here?

Here are several problems invloved.

For the FIR interpolation filter, why we choose
1.2*data_rate/2 as the cutoff frequency and
0.4*data_rate/2 as the transition band?

Second, why k = 2 * math.pi * max_deviation / self.fs?


Hope anyone of you could help me get out of the
confusion.

Thanks for your time

Sachi

--- Sachi <address@hidden> wrote:

> Hi, Eric
> 
> I've got a question on the interpolation FIR filter
> in
> the fsk_tx.py.  Here is the filter uesd:
> 
> interp_taps =  gr.firdes.low_pass (self.sw_interp,  
>  
>  # gain
>                                               
> self.fs,             # sampling rate
>                                               
> data_rate / 2 * 1.2, # cutoff
>                                               
> data_rate/2 * 0.4,   # trans width
>                                               
> gr.firdes.WIN_HANN)
> 
> I am a little confused. Why do you use sw_interp as
> the gain? And how do you select the cutoff freq. and
> transition bandwidth?
> 
> Thanks in advance
> 
> Sachi
> 
> 
>               
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