Hello Michael,
Am 14.07.2012 21:23, schrieb Michael Karcher:
This filter has a quite flat passband in the interesting range for DAB (-768kHz..+768kHz) but by far not enough attenuation at 1280kHz (which will alias to 768kHz at a sampling rate of 2048kHz) to get satisfactory adjacent channel rejection. The experimentally observed alias rejection is good enough, which lead to the conclusion that there is another low-pass filter, which might be part of the resampling unit.
I've got a passband of nearly 2MHz with the original coefficients. Did I miss a factor 2 somewhere? I tried to construct a narrower filter using the gnuradio function.
Here is a python script to construct the FIR register and plot the frequency response. Maybe the script is also helpful to you.
Regards, Stefan