Think of the AT1846S as the engine of a radio.
The UV-5R has this engine bolted to a very rudimentary chassis, no gearbox or suspension to speak of and a really cheap set of tyres. As a result, the performance of this combination is ho-hum.
A bit of a step up is the GD-77. A better chassis, perhaps a better set of tyres.
Going whole hog is the D868UV. It's got a great chassis, a gearbox and suspension and some really good rubber.
The GD-77 uses a better pair of low noise receive pre-amps than the ubiquitous UV-5R, and a better design bandpass filter.
The D868 pulls out all the tricks: better bandpass filters, in addition to a four stage varactor track tuned front end each for VHF & UHF, as well as evidence of some audio DSP'ing going on. Curiously though, they use a 20 year old 2SC3356 mid-gain class preamp design. There's much better devices available these days, so wonder why they went that way? Perhaps the 3356 has better compression margins? Whatever the reason, it's a really good receiver for a direct conversion design, as good as it gets.
