I’m building a slightly crappier and less ambitious 0-200MHz one at the moment for HF use. Basically a step attenuator, LPF, a pair of NE602 for first and second LO+mix, an old Toko helical filter for first IF and hand built crystal filter (12MHz) for second IF resolution filter and then an AD8307. First LO is a VCO with varactor control driven from an opamp ramp generator. Doesn’t work yet as the Toko filter is broken and I can’t find a suitable replacement and can’t be bothered to make a helical filter.

The things look like rocket science but they are basically superhet receivers with a log converter instead of speakers and a much larger tuning range.