And by the virtue of shortwave propagation, it could be heard across the world. For the past month and a half (from when the news of its impending shutdown was revealed) I was regularly picking it up in Australia right up until the bitter end.

Radio stations are usually measured by the last of those: Effective radiated power.

You can have a radio station with a 50,000 watt ERP, but running only a 2,500 watt transmitter.

For FM radio stations, it's all about the height of the transmitter above average terrain. For AM, it's about the ground conductivity and frequency.

I once worked at a 1,000-watt AM station that had a signal much larger and clearer signal than the 5,000-watt AM station a few miles away.

I'm not a radio engineer, but I'm sure there are plenty on HN who can correct and clarify what I've written.

In the USA there have never been commercial longwave stations, though various WWV time signals are broadcast in that band.

https://en.wikipedia.org/wiki/Atlantic_252

"Although the transmitter was in Ireland, the signal's reach meant that it was often looked upon as a "UK national station". Reception reports were received from such locations as Berlin, Finland, Ibiza and Moscow."

Vacuum tubes also aren't vulnerable to nuclear weapon electro-magnetic pulses.

However, other than ham radio enthusiasts I guess no one listens to analogue radio anymore.