Dear CASPERites, I am a graduate student at the University of Toronto (working with Marten van Kerkwijk) and I have some raw baseband data collected using PUPPI (Arecibo) - and I am on a quest to invert the polyphase filter bank. I have 32 channels of complex-baseband that I would very much like to combine into a single 100 MHz bandwidth stream.
To do this, I would need to understand some of the specifics of the filter bank pipeline (so that I can successfully invert each step). This is my current understanding of what happened to the data I have: 1. Real-valued data sampled at 200 MS/s arrives at the Casper BEE2 board. 2. This goes through a real-input PFB implementation such as `pfb_fir_real` and using a 12-tap, 64-branch polyphase filter (I have the filter coefficients that were used here). This step outputs 64 streams of real-valued data. 3. Then, for the DFT step of the filterbank, the 64 real-valued streams are passed through the `fft_wideband_real` block to get 32 channels of complex-valued data. 4. This is then saved to disk. (I hope someone familiar with PUPPI can correct me here if I am wrong about any of the above) Step 3 is the step I am confused about. `fft_wideband_real` does not appear to be a conventional real-input N-point FFT implementation (Else I would have N/2 + 1 channels instead of just N/2). Some documentation on this block says that it "computes the real-sampled Fast Fourier Transform using the standard Hermitian conjugation trick". What is this standard Hermitian conjugation trick? I am totally unfamiliar with this. Would I be wrong in guessing it uses some sort of trick to convert 64 real numbers to 32 complex numbers and then applies a regular ol' complex-valued FFT on them? Thank you so much! I appreciate any and all guidance this mailing list can provide. Cheers, Nikhil Mahajan -- You received this message because you are subscribed to the Google Groups "[email protected]" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAA39X0%2B3z051d%2B%2BAB0D%3D1LHNHdOSDJp6JEYzzRXatj-ij11_qA%40mail.gmail.com.
