>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...

Reply by Kappa●July 5, 20082008-07-05

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.