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Michael Karcher osmosdr at mkarcher.dialup.fu-berlin.deAm Sonntag, den 15.07.2012, 01:22 +0200 schrieb Francesco Gugliuzza: > 2012/7/14 Michael Karcher <osmosdr at mkarcher.dialup.fu-berlin.de>: > > I furthermore found out that this is not the only filtering going on in > > the RTL2832 chip in SDR mode. There seems to be a second anti-aliasing > > filter before the DAC, making signals disappear that are at frequencies > > above 0.7 times the sample rate (in the baseband), even if the > > programmable FIR filter lets them pass. > That's probably an effect of the E4000 output filter. You can see the > filter bandwidth being set in the tuner initalization code. 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. Regards, Michael Karcher