If you crack open a real spectrum analyzer (not some hacked together SDR toy) you’ll still find plenty of distributed and analog circuitry. That’s what it takes to get spur-free performance.
Speaking of hacked together RF toys, I picked up an IM-Me toy a few years ago just so I could play around with Michael Ossmann's "$16 spectrum analyzer". I was able to see (poorly) the transmissions from my wireless weather station with it.
There is also a five part series on Youtube talking about what else you can do with the IM-Me. It is pretty amazing and well worth watching if you have some time.
SDRs are total spur-fests, yes, but at 0% the cost of a real SA (rounded) the economics sometimes work out :-)
That said, at the high end of the SDR range, the new AD937x chips ($325 in qty 1k!) make impressive claims wrt automagic spur suppression. They still don't beat high-IF or YIG preselected SAs, but now they claim to be in the ballpark under non-overload conditions. Has anyone here dug deep enough to comment?
The pre-selection is a big deal. The AD936x needs good front end filtering to reject n*LO. For instance 5x146 MHz = 730 MHz, which translates that 730 MHz nation-wide LTE signal smack-dab into the 2m amateur band. Unless they have a new front-end architecture in the AD937x, all the I/Q calibration won't help them.
Of course as you said, for $325 it's not a consumer chip, so some $ will be spent on external passives.
