Hi all,

I’ve seen several post mentioning the need to compute the FFT on the LimeSDR’s FPGA but no post for this sole purpose:

Has anyone tried to do it or put some thoughts in it?

@mzs mentioned about the size that such IP would take on the FPGA:

I personally would be interested in FFTs of size 1024 to 2048. If possible the LimeSDR would return both IQ and FFT, so that we can still do whatever processing on the IQ if necessary, but wouldn’t need to compute the FFT on the CPU. Could it be added to the LimeSDR USB and/or PCIe? It would be great to have the possibility to have 2 gatewares, one with the FFT and one without, for those who want to use the FPGA for other uses.

For the hydrogen line in particular, the “useful range” for galactic hydrogen is only about +/- 1.5MHz or so.

Doing high-resolution FFTs at those kinds of bandwidths is an EASY job for a general purpose CPU, and there’s little justification for doing them on the FPGA.

The FPGA route becomes interesting when you go into the 10s-of-Msps, but I’m going to guess that doing 2048-bin FFTs on the FPGA on the Lime is a non-starter.

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