>I have built a QPSK modulator, but I have some doubts about the Baseband 
>Shaping Filter. The Baseband Filter is a "SRRC Digital Filter" with
cutoff 
>at Nyquist / 2 with selectable roll-off. In my project roll-off is 0.35.
>
>Example (SAT):
>
>27500 Msymb/s ---> Nyquist Frequency is 55000 Mhz (for I and Q) --->
cutoff 
>Frequency 27500 Mhz.
>
>May need to interpolate at least 2 ? Is right ? It is necessary to 
>interpolate in all ways ?
>
>How many taps used for filtering ?
>
>What window of approximation it up for the calculation of taps filter ?
>
>Thanks in advance.
>
>Kappa.
>
>
>
>
%%%%%

In ur case fs=55000 and B=27500

so u need to insert fs/B-1 zeros between symbols, which means 1 zeros
between symbols.

in ur case the taps should be 2 but ideally the data should be oversampled
i.e. fs=N*B where N could be any interger greater than 2, i am using 12.

there are plenty of shaping filter formulas availble in standard books...

I have built a QPSK modulator, but I have some doubts about the Baseband 
Shaping Filter. The Baseband Filter is a "SRRC Digital Filter" with cutoff 
at Nyquist / 2 with selectable roll-off. In my project roll-off is 0.35.

Example (SAT):

27500 Msymb/s ---> Nyquist Frequency is 55000 Mhz (for I and Q) ---> cutoff 
Frequency 27500 Mhz.

May need to interpolate at least 2 ? Is right ? It is necessary to 
interpolate in all ways ?

How many taps used for filtering ?

What window of approximation it up for the calculation of taps filter ?

Thanks in advance.

Kappa.