Martin, Perhaps the title of your article should have been "Most Popular Radio Ever?". That may have been closer to the truth and avoided the apparent debate that has surfaced.
I've dealt with two of these radios, in the past. The first, I fixed up for a family member. The following Christmas, I gifted the "Royalty of Radios" book to him, as well.
The second Trans-Oceanic was given to me and sat on a shelf for several years, until I passed it along to a collector friend of mine. He, in turn, totally refurbished the radio and added it to his impressive collection. He also documented the entire restoration and shared the restoration with the local ham radio club. It was good to see that radio finally go to someone who would properly appreciate it (my friend also has a fully restored set of the Collins "Gold Dust Twins", along with an impressive collection of Drake and SBE equipment). One of these days, I've got to go back and photograph his collection. Just the smell of old radios, at his house, takes me wayyy back.
https://hdradio.com/stations lists stations that they claim broadcast in HD. They list three AM stations in the Boston area, two of which are strong in my location, WBZ 1030 and WNNW 800. I receive WBZ 1030 broadcasting in HD in the daytime (and I hear its data as hash noise on analog radios around 1020 and 1040). I receive WNNW 800 broadcasting not in HD (and no data noise around 790 and 810). Interestingly, WBZ is talk and WNNW is music.
But that's little bit circular logic. AM is primarily talk radio because the audio quality is so abysmal. Plus, even just voice sounds a whole lot better when sybillants sound as they should. Voice limited to (in practice) 4 KHz or even less, sounds muffled and bad.
When I still had my HD Radio tuner connected to my stereo system, it was a simple job to do A/B testing in the AM band. There is simply no comparison, even with voice. The difference is striking. As to inteference, absolutely. In hybrid mode only, that is. In order to support a digital signal, in hybrid mode, the sidebands in the AM band have to go out to +/- 15 KHz. In all digital mode, in the AM band, there would be no night time problem at all with the HD Radio/IBOC scheme. Day and night, the signal would remain in its 10 KHz channel.
If AM finally stopped be so primitive and went to all digital, I would expect that at night, at most, some stations would have to reduce power. But this can never happen as long as digital radios are being strictly kept away from the market.
AM radio north of Boston is mostly talk radio, which has no need for enhanced audio quality. AM HD digital signals are turned off at night because they interfere with adjacent-channel AM stations that are heard when the AM band opens up at night. I like that AM is the same as it was a century ago.
With respect to AM stereo, the new(ish) Ibiquity HD Radio standard easily beats any old analog AM stereo design, for transmission in the AM band. But without FCC mandate of any kind, even this digital radio standard could languish and disappear. It's almost impossible to find HD Radio tuners on store shelves, a system that has existed for a good 15 years by now.
I did own a stereo tuner with HD Radio, and audio quality in the AM band was astonishingly good. And unlike any good quality analog AM tuner you can find, extremely few and far between, digital in the AM band can provide excellent stereo audio while staying strictly inside a 10 KHz channel, in all-digital mode. In hybrid mode, the digital sidebands are restricted to a significant 35 dB below analog AM power. So of course, you need a pretty good signal for the tuner to decode digital AM, in hybrid mode. And at night, lights out. When in hybrid mode, digital in the AM band isn't permitted (I'm assuming nothing has changed in that regard, in the past couple of years).
If radio could go all digital, the improvement would be substantial, in the AM band certainly, and also in the FM band. Way higher power in both bands, than what is permitted in hybrid mode, and in FM, at least twice the program capacity, in each channel, compared with digital in the FM band now. (There is also the German DRM digital standard, which operates in the AM, FM, and shortwave bands, which could be an equivalent option nowadays. DRM has expanded its repertoire over the years. Used to be only for the AM and SW bands, and did not have a hybrid mode originally.)
That tuner, from Sangean, the only manufacturer to offer a stereo component HD Radio tuner that I found, was discontinued years ago. Best bet, these days, is to buy their WiFi radio tuner.
The big mystery, in my view, is why HD Radio tuners are still so rare. They have even been combined, in single chips, with analog AM/FM tuners. For years now. I'd like to know why they aren't available everywhere, even in the cheapest of clock radios. The much less attractive DAB system, for Europe, which doesn't even use the AM and FM radio bands (not much in demand for anything else), is far more available. Why? Beats me. Almost seems like the manufacturers are on the take, to not market digital radio.
We had one of the later models Zenith Trans-Oceanic transistor radios, which my dad bought when we moved to West Africa. It's a portable radio, with the front folding down, and the handle housed the telescoping antenna. Fundamentally, a very, very straightforward multiband radio, no single sideband reception, and its greatest weakness, in my view, was that it had single conversion IF. As I said, a very straightforward, text book design. Think in terms of, the simplest AM radio, which also happens to mechanically tune in the shortwave bands. That's pretty much the extent of it.
The radio even came with a schematic diagram, a rarity these days, to confirm just how basic and textbook it was!
The days of interesting shortwave DXing are gone, or at least, for me they are, because now you can do so much of that over the Internet, at way higher quality levels. Important shortwave broadcasters, such as the BBC, have discontinued their broadcasts for North America many years ago. I'm sure it's more than a decade ago, by now. But no problem listening to the BBC, with excellent audio quality, no fading, no intermod racket, over the Internet!
Anyway, I'd say that lack of SSB and lack of a dual-conversion IF were the greatest shortcomings of the Zenith Trans-Oceanic, making it completely vulnerable to intermodulation squealing and unable to listen in on those SSB conversations. We later got a Grundig portable multiband radio, with dual conversion IF, that was far better for shortwave reception.
My last radio of this type was a Sangean, with SSB and drift-free digital tuning, but then the SW bands started becoming unpopulated of what I consider to be interesting content. Don't know whether the digital DRM system has found any success in these SW bands. That could make SW fun again, although it goes counter to the idea that SW remains primarily as a means for getting news to emerging countries, in which simple and basic is the best choice.
The problem with the Best Ever Fill In the Blank is it doesn't last long. Around 20 years ago I purchased a Denon TU-680 NAB (National Association of Broadcasters) tuner. In addition to excellent specs for FM it had extended AM and the fabulous Motorola C-QUAM AM Stereo. Last time I checked there was one radio station in my state broadcasting in AM stereo. And it's not nearly as impressive as my father's Atwater Kent with Model E Speaker. Then there was the GE Super Radio. So where are these units today? In my closet. Next to my great, high quality film cameras and VCRs. I only listen to satellite and internet radio and use digital cameras. The only thing I have no nostalgia for are my CRT monitors and TVs and they are in the trash.
Over the next three years, the U.S. broadcast television stations are being repacked to fit into RF channels 2 through 36 (channel 37 is reserved for radio astronomy), so channels 38 and up can be used for cellphones.
http://www.nab.org/repacking/clearinghouse.asp is a searchable clearing house of which RF channel is moving where, and when. I believe that stations with no listing, are going off the air.