Sachi wrote: > 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?
Interpolation by N inserts N-1 zeros between each incoming sample, and then filters the sequence. The resulting signal will now contain values other than -1,0, and 1. > 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? The 1.2 and 0.4 are somewhat arbitrary. What you need is to have the cutoff frequency be above the first image in the interpolation and below the second. The transition band should also end before the second image. > Second, why k = 2 * math.pi * max_deviation / self.fs? This is how we set the deviation in radians per sample. max_deviation is a frequency in cycles per second. Multiplying by 2*PI gives us radians per second. Dividing by the sample rate gives us radians per sample. >>I am a little confused. Why do you use sw_interp as >>the gain? The interpolation ratio is used as the filter gain. The reason for this is that performing an interpolation by N will reduce the amplitude in the signal by a factor of N. By using N as the gain, this effect is canceled out. Matt _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
