2012/7/15 Michael Karcher <osmosdr@mkarcher.dialup.fu-berlin.de>:
Good point, but actually, I am sure it is not an effect of the tuner output filter. My USB stick contains a fc0012 tuner, which is always set to 6MHz bandwidth. The bandwidth of the suspected anti-alias filter changes clearly when I change the sample rate, though, on the other hand, if I manipulate the FIR coefficients to contain sharp dips in the range of hundred kHz, the dip position does not change when I change the sample rate. This makes me cofident that the suspected anti-alias filter has to be located in or after the resampling unit. The only thing I can think of now is the raised cosine filter used in digital modulation receivers, but IMHO that should be implemented in the FIR filter.
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