Hello to all,
With the topic of "rig choice", and the recent discussions comparing various new rigs (and some confusion over some of these rigs' architecture), I thought maybe some clarifying info and a bit of history would be helpful?
Frank, Zak, Jim, Ed, et al,
1) Rig choice for experienced radio ops is rather easy....and, except for those looking for a serious CW contest rig (particularly for 160m CW contesting), the ranking on the list is rather moot.
This is not only my opinion and of many, many other experienced ops....but, surprisingly to some, is also Rob Sherwood's opinion! (read what he writes and listen to what he says, don't just look at a list)
But, these days, (in my opinion), it seems that many newer / less experienced hams (or those new to HF / less experienced in HF comms), seem drawn to the simplicity of "a list", rather than understanding the nitty-gritty of what is needed / what works best in various environs and applications....so...
So, here we are....with this discussion.
So....
1)
While I'm known here-abouts for concentrating on "the other half of our transceivers", you know ---- the transmitters! I've seen a bit of confusion and/or misused terms in reference to our modern HF receivers.
And, while I've written here in this thread...in some detail:
https://www.eham.net/community/smf/index.php/topic,128776.msg1194749.html#msg1194749
https://www.eham.net/community/smf/index.php/topic,128776.msg1195427.html#msg1195427https://www.eham.net/community/smf/index.php/topic,128776.msg1221132.html#msg1221132https://www.eham.net/community/smf/index.php/topic,128776.msg1224671.html#msg1224671https://www.eham.net/community/smf/index.php/topic,128776.msg1227431.html#msg1227431https://www.eham.net/community/smf/index.php/topic,128776.msg1227433.html#msg1227433....written in some detail, and included quotes from Rob Sherwood, etc., regarding various criteria for transceiver choices, as well as many specific receiver specs/numbers and their meanings/relevance, etc.
But, I still see some of my fellow hams (
AND the marketing teams of some radio manufacturers!) that are mixing various terms and/or misunderstanding some things...SDR, DSP, super-het, phase-noise, "roofing filters", etc., etc...
So, I thought maybe a brief bit of history and a quick look at our HF receiver progressions over the past 50 some years, might be helpful to some of my fellow hams? (or, it might not? heck, some cynics might even wonder "why is he bothering?"....but in any case, I'll try to be brief and just talk in generalizations so as to not tick-off anyone...)
2) So, here ya' go...
The unfortunate facts are that today's local RFI environs (and today's transmit IMD / splatter of our SSB transmitters on the phone bands) eliminate most hams' ability to even come close to using all the capabilities of most of our receivers (whether good old venerable classics, or modern 21st Century rigs)...
But, many still desire to "buy the best" or at least "buy what works best for them, at the price they can afford".....and, unfortunately many are still looking at "the list", thinking this is what will determine "the best", rather than
actually reading what Rob Sherwood (and others) actually say/recommend, let alone learn about these criteria and make their own decisions....so...here's some history / info that might provide some additional clarity...
A case-in-point....modern Direct-sampling SDR's might be great, but they ain't perfect....i.e. super-hets, properly designed, still rule! 
Have a look down the tunnel of history with me for a moment....(don't worry, I'm only going back to the late 60's, 'cuz this is as far back as I have personal experience with / knowledge of...and, forgive me if, for ease of explaining and clarity, I generalize some things here!)
Of course, there are some "outliers" such as some TenTec Omni's still being "down-conversion" radios, when most of the rest of the market having moved to VHF-first-IF's (i.e. "up-conversion" radios), here is a general outline of our HF receivers' progression over the past 50 some years...
a ---- Back in the days I started in radio comms (late 60's / early 70's), we went from single-conversion super-hets to double-conversions super-hets (and some triple-conv super-hets) .....these all had HF first IF's, with some of the early ones having simple LC first-IF filters and/or just "pre-selectors", the good ones (and later ones) had decent first-IF selectivity (or were modified to have decent first-IF selectivity), with first-IF crystal filters (what many hams, oddly even Rob himself, now call "roofing" filters?), or had options to add first-IF filters....and, some even had provisions for crystal filters in both first and second IF's...
These are what we now refer to as "down-conversion radios"...
{there were no "phase-noise" issues, as these were not PLL- synthesized radios}b ---- Then, in order to provide "general coverage receivers", into our HF rigs, and/or even incorporate many HF transmit bands, across the 1.5mhz - 30mhz range, without gaps nor image-rejection issues, then we got "up-conversion" radios....those with VHF IF frequencies....originally these had low-VHF IF's in the 40mhz - 48mhz range...[the Drake TR-7 was the first of this design....and, still to this day holds-its-own, even in competition with modern 21st Century rigs, 45 years newer in design.]
These are what we call "up-conversion" radios....but, they were still conventional super-hets....and, later "up-conversion" radios had first IF's in the 64mhz to 75mhz range...
{most of these radios used PLL-synthesizers / VCO's...and while some were quite good....a few were very bad --- like the old Yaesu FT-ONE, and lest we forget the Collins KWM-380 is one of the worst in this regard....it's really got to burn those "Collins guys" when they find out their '380's RMDR is beat by 20 - 25db by the likes of a bone-stock IC-735, or the older TS-830, etc.}c ---- Then, we got DSP....Digital Signal Processing....which at first was done at AF / Audio stage of the radio....and, some worked "okay" but providing minimal "improvement" in our receivers....(and some weren't even worth turning on)....most were simply additions into existing designs...and, as many more up-conversion radios were made, some of the receiver functions (noise blankers, etc.) were migrated to DSP-implementation...
d ---- Shortly followed by IF-DSP's....which at first were done at a very low final IF freq (some at an IF freq of 12khz, or so), and while this was supposed to be an improvement over Audio-DSP (and some were), some allowing the AGC loop to be run thru this low-IF / DSP, but in some rigs the overall implementation wasn't great (not trying to be overly-critical here, it's just that the technology wasn't quite there yet, at amateur-radio price-points)....but, some did function well and provide some rather steep-skirt IF filtering, without serious ringing, etc...
As time went on the DSP algorithms improved....as did the hardware (the DSP processors, etc.)...so, we had higher-frequency DSP-IF's and better AGC controls, etc., as well as better DSP implementation over all...and, things were getting better....well, sort-of...
We also had noise blanking being done in DSP in many radios now, which if done correctly could've been a good thing ---- but that didn't happen....as, the DSP just wasn't good enough yet, and about this time we also the first narrow VHF First-IF filters appear (and, they took on a new moniker: "roofing filters"), and some were pretty crappy, which made noise blanking difficult (as the poor narrow first-IF filters significantly changed the noise shape, thereby making blanking of impulse noise pretty difficult to do.....note that this still holds true today, and it's only through better noise-blanking algorithms that any modern radio with a narrow first-IF filter has a functioning noise blanker at all.)
Please take note here, excellent noise blanking and narrow, step-skirt, first-IF filters are counter-intuitive....perfecting the latter, all but eliminates the perfection of the other! Hence, the 9khz wide, smooth 4-pole crystal filter in the 48mhz first-IF of the TR-7 is one of the reasons its optional noise blanker works so well....(fyi, the 7-NB noise blanker for the TR-7, was a ~ $75 option in 1977 dollars = ~ $370 in today's dollars....for just the noise blanker!) Still 45 years later, one of the best noise blankers in any HF radio, ever! Sorry about the digression...So, now we had manufacturers putting narrow first-IF filters into their rigs, some were crap --- some were good....but we still had some noisy VCO's (poor phase noise / poor RMDR)...
{together with DSP tech, we had radios now sporting "band scopes" which quickly became not just a toy, but a useful tool for contesters....}e ---- At this point (10 - 12 years ago), concurrent with the advancements in DSP tech.....Rob Sherwood, et al, had been concerned about the poor oscillator noise (poor phase noise) from many of our radios' VCO's, for quite a while at this point....and, with these many squeaky-wheels pointing this out, many of the manufacturers (all the while working behind-the-scenes on designs of amateur-priced direct-sampling systems) simply changed from old-tech, bargain-basement VCO's to lower-noise oscillators (not super-perfect, but pretty good....although the TS-590S and SG were in 2010-2014 almost as good as today's state-of-the-art rigs)....and, we got some pretty decent "up-conversion" IF-DSP radios!
{and again, band-scopes, etc., had become an almost mandatory feature....and, at some point "waterfall" displays also started to show up....}f ---- And, again, at about the same time and just after (8 - 12 years ago)....although we had Flex SDR's around for a while at that point, they were "niche" radios and not really a mature technology at amateur-radio price points....but, we had other manufacturers working behind the scenes on Direct-Sampling-SDR type radios.....and, Icom beat 'em all with a reliable, mature-tech, amateur-priced direct-sampling-SDR, the IC-7300!
And, it had "everything" that "everyone" needed....bandscope, waterfall, touchscreen, etc...but, it was also a great little radio, with excellent transmit audio, and in comparison to most modern 21st Century amateur radios a pretty clean transmitter (although, still not as clean as I'd like / not as good as we had 40+ years ago) BUT...
But, as many found out....direct-sampling-SDR's needed good operators to use 'em, especially in crowded bands / with lots of strong signals....AND...
And, as we also saw the TS-590SG (which is both an "up-conversion" and "down-conversion" super-het) actually worked better in contest environs, crowded bands, noisy locales, etc...
{BTW, around 5 years ago we had the roll-out of FT-8.....which by happenstance was a solution to the many hew hams / those new to HF, that had been suffering with significant receive RFI for the past few years (due to the rise in so much "made-in-China" consumer electronics / switch-mode power supplies / LED-light regulators / etc. / etc....that surrounds so many urban/suburban ham locations)...and, since the radio becomes less of an important factor in FT-8 operations, and since the '7300, in addition to it being a great little radio over all, was also an excellent FT-8 rig with its 100% duty-cycle ability, etc...so, is it any wonder that the '7300 (and direct-sampling SDR's in general) garnered quite a following....}g ---- And, then we have manufacturers that answered the call of "one-up'ing" the competition (in regards to HF receiver performance AND features!), and it was clear that the "best-of-both-worlds" was a "down-conversion" super-het with IF-DSP (particularly one with low-noise VCO's, and excellent first-IF [roofing] filters, etc.)......along with a direct-sampling-SDR receiver built-in (so, they'd have their band-scopes, waterfalls, etc.), and that brings us to the current (2022) state in amateur HF receiver design / marketing
(a "down-conversion" super-het with IF-DSP, with low-noise VCO's, and excellent/narrow first-IF [roofing] filters....hmmm, what's that old saying, "everything old is new again!"....sort makes me smile that we're coming full-circle now!
just adding some new-tech abilities to old-tech designs/architecture!
)
3) So, when you're looking at different radios (whether a more conventional "super-het" like the '590SG; or a full Direct-sampling-SDR like the '7300/7610's; or a "super-het" with an SDR handling the bandscope, etc., like the '101d/101MP...or
especially if you're looking for a bargain and buying an older radio!) and trying to figure them out, and trying to figure out why/how/which receiver is best for your application, now you'll be able to figure out what all these various names / abbreviations / acronyms actually mean, and how they work....all on your own!

I do hope this helps?
73,
John, KA4WJA
P.S. Once again, I know some may quibble with the details / dates, etc....but, I'm just using generalities here for ease-of-explaining / clarity....and, with a few quick exceptions to make a specific point, I'm not mentioning specific radios, so that nobody feels offended nor put-upon to respond / defend something.

So, for my fellow old timers or purists, please just take a breath before being overly critical.....thanks!