So-called “border-blasters” are stations that are physically located in Mexico that broadcast into the US. Since they’re not subject to American broadcast licensing conventions, they’re free to pretty much ignore power limitations that would affect stations in the US. They are, of course, licensed in Mexico, so they must follow Mexican broadcast regulation, which includes playing the Mexican National Hour and the Mexican national anthem at specified times. (From the Wikipedia article.) In the past, their audience was English-speaking Americans, but now much of their programming is aimed at Spanish speakers.
As for Europe, I can’t really say. I’m fairly sure there are stations along the borders that broadcast into both countries, but what with the EU, I don’t know how those are regulated.
Back in the late 60’s to early 70’s, I was big into DXing on the AM band. I used a Heathkit multi-band receiver that I had built and had more fun on AM than on shortwave. Gave that radio away to a friend 25 years ago and he still lstens to it.
Being in Central Texas, XELO came in better than the local stations at night. The studio was in Del Rio, but the 150,000 watt transmitter was in Mexico. They carried standard Top 40 music at the time, and all the “DJs” were named after animals. I got a DSL card from them at the time that had drawings of all the DJs like Fred Lion and Joe Eagle, or something along those lines.
I used to easily get a Shreveport station and WLS out of Chicago. Seems to me there was a station in Alabama that came in fairly regular.
If you received a strong station out of San Antonio, it was probably WOAI at 1200. It was 50,000 watts and had a vitually clear channel to itself. Only a few very low powered or daytime only stations were on that frequency, so I think it was heard up into Canada fairly easily.
I had a lot of fun trying to pick up far away stations late at night and into early morning. Many was the time that I listened for a long time for a station to identify itself, only to have the signal fade away and disappear before I could identify it.
The FM band is normally line-of sight, like TV, so your mountaintop would be a good place for DX (distance reception). And abnormal atmospheric conditions can cause FM to bounce.
I don’t know if smog can act like the atmospheric layers that do reflect, but my WAG is it would attenuate (reduce) a signal rather than reflect it. LA smog as I know it (and I lived in it for 30 years) is spread over a large area both horizontally and vertically, and begins at ground level, unlike distinct atmospheric layers miles high.
I regard the term “ridiculous supercharged” hype because the station is, in fact, in an established class. There are two or three dozen American stations licenced to operate on clear channels at 50,000 watts. Granted, an AM with that much power kicks butt compared to most stations, but KNBR is not unique. (It’s like Cox Cable describing its Internet service as “crazy fast” - cute, but not particularly informative.)
Visible smog is often due to the presence of a temperature inversion that disrupts normal convection, and traps it near the surface. The same temperature inversion can result in refraction of EM radiation, expanding coverage. The refraction is due to a slight temperature dependance of the speed of light in air…which also gives rise to visible “heat waves” and mirages. So there is a corrilation between visible pollution and EM propigation, but the cause of both is a third factor.
When such inversions occur over salt water, the signals are bent downward by the inversion, then reflected back upward by the seawater, wash-rinse-repeat. This is known as “Tropospheric ducting” or just “Tropo” and can result in spectacularly long range for VHF signals. Transatlantic hops are not unknown.
You misunderstood me. The question of whether any AM station might be licenced for more than the 50kW AM maximum made me think of an FM station that I knew had once been (and may still be) licenced for more than the FM maximum of 100kW e.r.p. (Heck, in the mid-80s I had some contact with KANU’s chief engineer. I’ve forgotten his name, but he was a bit famous in engineering circles at the time for coming up with a method for multiplexing a stereo signal on a single wideband RPU channel.) I wasn’t trying to compare them. It’s just that one made me think of the other.
[FM stations are rated in terms of effective radiated power, which is transmitter output power times the gain of the antenna. You are giving the power measurement method for AM broadcast transmitters. You do have a point about the efficency of the feed-line/antenna system having an effect on the the actual signal strength produced at the antenna, but this effect is modest. And for what it’s worth, the 50kW plate input power is for an unmodulated signal. At 100% modulation, the actual power is rather more than 50kW. I’ve forgotten how much.]
I see from a link in one of Musicat’s other posts that I’ve misguesstimated the number of 50kW AM’s by a factor of three. Sorry about that.