Does anyone know of an output gated 16 bit integer complex to real FFT code? That would substantially reduce the amount of space required to do TDR on the stock nanoVNA.
While the FFT is fundamentally just reordering operations so that the additions are done before the multiplications, they do get fairly complicated. I'd prefer not to write one from scratch if I can avoid it. And there are a lot of FFT codes out there. And lots of tutorials any of which may or may not discuss gating the output. So it's a serious time sink to search for one.
Without output gating, a 1 microsecond TDR trace will require 8 KB of RAM for 500 ps resolution. I don't see a way to get below needing 3.6 KB for the frequency domain magnitude and phase. The sample spacing in frequency is what governs the maximum time of the TDR trace whether you gate the output or not.
Reg
