Excellent post on clarifying different implementations of SDR.
One comment though, the Baofeng UV-5R & family actually have a reasonable amount of filtering on both receive and transmit; it can even be seen in the teardown link you yourself linked.
By “reasonable” I mean it’s close to the legal requirements even if a large part of the units don’t actually meet them by a few microWatts. Those filters are designed to be first of all cost effective (generic capacitors, etc) and they certainly could use improvement, but they’re far from “no filtering”. Strongest harmonic is -49dBc.
The FT-4X is a slightly better implementation of the RDA1846, more attention has been paid to frontend filtering (on both radios filtering is largely shared between RX and TX) and it surpasses emissions requirements easily. RX is a bit less sensitive to adjacent channel intermod but it’s still in the same class as the Baofeng for all SOTA intents and purposes due to the weak RDA1846 radio. Strongest harmonic -65dBc.
For reference, here is how the harmonics of a “no filtering” radio look. This radio is popular and has been out there for a few years already, yet no one complained so far. I won’t say what it is yet as it’s a review sample and I’m still waiting to hear back from the manufacturer. Strongest harmonic -29dBc.
