Understanding AM Clear Channel

I was out prototyping my “Zombie radio station detector” today in South Charlotte NC – going station by station looking for AM stations that should be there – but aren’t. The FCC rarely gets complaints that stations are off the air completely or running at low power because their transmitter is broken or the station can’t afford their electric bill. Radio stations are not permitted to turn the transmitter off or run at less than 90% power unless they notify the FCC and get temporary permission.

My test was not finding anything unexpected until I reached WAGL-AM (1560 kHz) which is licensed to serve Lancaster SC. It is a Daytime only AM station – but licensed for 50,000 watts during the day – yet in far South Charlotte, 20 miles from the transmitter, there wasn’t the slightest hint of a signal. It was more than an hour before sunset.

Now, because it is protecting a station in Winston Salem on the next frequency over, this station has a directional antenna during the day, requiring 4 towers. Let’s look at the predicted coverage area.

Predicted Coverage

While it is directional and I was outside the local coverage area, I should have still heard the station fairly clearly.

While that might be interesting, it isn’t the point. Why does this station have to turn off the transmitter and go home at 5:30 PM in January?

The answer goes back all the way to 1928 when the Commerce Department under President Hoover approved a scheme designed to protect the pioneer radio stations (almost all in major cities) from interference from small town unimportant radio stations. While phonograph records existed, magnetic tape didn’t – meaning most programming was live, either produced locally or relayed from one of the radio networks like NBC.

Class “A” stations would be able to continue at 50,000 watts in all directions all night and have exclusive protection of their signals for a 750 mile radius. Let’s look at 1560 kHz and see who is protected and why stations still have to go dark at sunset 75 years after the agreement.

1560 kHz stations centered on WAGL-AM

Scan down the list and you’ll see that almost all the stations on this list are daytime only. When you get to 585 miles, we find the answer – WQEW-AM in New York City is just too important in South Carolina to allow local stations to be on the air at night – remember these rules were created before FM Radio and TV when that made sense.

WQEW was in the news this week – they have been running Radio Disney and the sale to Family Radio was just finalized.

It’s worth explaining the exceptions – in 1986, the FCC decided it would issue no new daytime only licenses and require new AM stations to stay on the air until at least 10 PM. In order to not bounce the signal off the ionosphere and protect my right to hear Radio Disney from New York in Charlotte [Radio Disney has a station in Charlotte with identical programming!], the station in Gallatin TN is limited to 3 watts at night. Stations with higher power (like in Texas) are more than 750 miles from New York City.

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