hackrf-spectrum-analyzer VS portapack-havoc

This may be close to what you want: https://github.com/pavsa/hackrf-spectrum-analyzer I used it before to look at the output of a satellite TV LNB to see if the weaker transponders that the STB wasn't able to detect are really there or if they're disabled. They were there, just not strong enough for the STB.

hackrf_sweep may be what you're looking for: https://github.com/pavsa/hackrf-spectrum-analyzer

Isn't that equation what a spectrum analyzer does, continuously? I'm planning to use a SDR as a GNU Radio software oscilloscope for looking at the pulses generated by the transmitting SDR, and it can also be used as a spectrum analyzer. It would be interesting to see a malformed pulse's wideband noise, if I could even get the transmitting SDR to pulse that fast.

I really like its ability to sweep frequencies quickly. Check this out.

I think I used GNURadio to convert files, it was not very complicated. https://github.com/furrtek/portapack-havoc/wiki/Capture (Not directly related to your problem but maybe it helps)

https://github.com/furrtek/portapack-havoc/issues/157#issuecomment-367577577 talks about changing the sampling frequency through a text file for the Havoc Firmware. Issue is dated 2018, so it's not certain that this hasn't been made more configurable in recent releases.