Yup, I know the HackRF. Being too old to write Santa a letter I'm already saving money for that gift:).

Anyway my point was that those cheapo DVR boards are just asking to be repurposed for other tasks, SDR is just one of them, that chipset specs are interesting. https://www.burglaryalarmsystem.com/pdf/Hi3520.pdf

Here are some firmware files for a few models, hopefully compatible with that one. Binwalk-ing them shows they're normal ARM Linux images.

https://domar.com/support/softwares-firmwares/ip-firmware-up...