I just found one of those old switch boxes a few days ago. The boxes where the antenna and the Atari plugged in, and then you switched it to whichever input you wanted.
In the Netherlands we've always had coaxial connections as long as I can remember. A quick google search tells me this has been so since the introduction of TV in the 1940's.
They're still a thing, kind of. TV Antennas are still inherently wired this way, and need the part in the picture (a balun) to convert the signal from the "balanced" 300 ohm twin antenna wire to "unbalanced" 75 Ohm coax cable.
Most TVs used to have the twin screw connections to hook directly to a roof antenna. But at some point (I'm guessing the 90s), more people got their TV directly from cable providers, delivered over Coax, so it made more sense for manufacturers to provide a direct coax input for the antenna.
So now, if you do have a roof antenna it probably has the balun integrated right into it, so you can take the coax (hopefully through some lightning protection) directly inside.
This was an adapter for old RF tvs that were mostly in use in the 80s and earlier. They were meant for use with an antenna. By the 90s coax and later RCA (composite) was the standard on most cheaper TVs. You'd probably see S-video or component video on higher end TVs. SCART, on the other hand, was completely unknown in the US.
Kinda weird that having not thought about SCART for years it's come up three times in conversation today. My first taste of 1080p was over SCART. Good times.
I used to do home integration and security and I found one of these installed at a client's house by the last installer...you'll never guess how they were using it.
The prongs were soldered to a transformer and the other end was on a coax that went outside...but to where?
Turns out it was the old cable run from Comcast that they repurposed...to power the path lights in the backyard.
I still have it in my toner kit bag. They're great for tracing coax!
Oh no, it was 100% stupid and not to code. The client didn't pay for jank - we're talking about a $5m home! It was shorted and we thought the switch had just died before realizing.
The other end didn't have any adapter, it was just stripped back and twisted onto the light wire...smashed between the grass and stone path. No solder. The second "wire" in a coax is the braided sheath so you can imagine the quality of that "splice"