Hi,

in the main window of the AD9361 Filter Wizard the Magnitude Response of the programmable FIR is shown. What I don't understand is the frequency axis. If I want the FIR to interpolate by 2 or 4, shouldn't the frequency axis go from 0 to 2*Fs/2 or 4*Fs/2. With Fs I mean the Data rate, that is entered by the user in the UIControl on the left.

An interpolating filter first upsamples the signal and then filters. So at the input of the filter the signal has a higher sampling rate, in our case double of quadruple.

Shouldn't the frequency axis, and thus the bandwidth of the filter then conform to the higher sampling rate?

I attached an image indicating what I mean.

With best regards,

Andrei

The FIR filters in the part are polyphase therefore they filter then interpolate on the TX, and decimate then filter on the RX. Therefore, the bandwidth will always be with respect to the data rate for the wizard. The filters are also component independent (no cross multiplies), so their frequency response will always be symmetrical.

-Travis