Why getting two or more radio stations on the same frequency?

Answer 1

Take the United States for example . . .

-- In the USA, there are exactly 100 frequencies for FM stations, 118 frequencies

for AM stations, and 68 channels for TV stations.

-- For each of those types of service, there are probably more stations than that

just within, say for example, 100 miles from downtown Los Angeles.

-- So each radio frequency or TV channel must be shared by several stations

around the country.

That's a part of the job of the Federal Communications Commission (FCC) ...

keeping order among all of the companies that want to put a radio station on

the air in order to broadcast commercial announcements and make money from

advertisers (the main purpose of almost all radio broadcasting); regulating the

requests for frequencies, and managing the grants, in such a way that applicants

all have the same access to audiences, and they all operate in a 'clean' environment

where listeners can hear them without interference.

It's done by maintaining enough distance between users of the same frequency

so that listeners to any one of them will not be bothered by interference from

another one.

To give you an idea of what's involved, I picked some frequency numbers at

random, and then looked them up in the FCC's on-line licensing system. Here's

what I found:

-- AM radio, 1340 on the dial . . . 172 licensed stations, all on 1340 KHz.

-- FM radio, 97.5 on the dial . . . . . 82 licensed stations, all on 97.5 MHz.

-- Television, Channel 11 . .. . . . . . 55 licensed digital stations, all on Channel 11.

Every time you tune your radio to the station you want to hear, there are

actually all of those others on the same frequency ... hopefully located far

enough away from the one you want so that the interference won't be

objectionable. But technically, it's there.

There's one more issue also involved that must be mentioned: A typical "consumer-grade"

radio generally can not completely ignore stations that it may be receiving on the frequencies

next to the one you're trying to hear, either above or below it. When you get far enough away

from the transmitter you're trying to hear, like across the city, or in the next town, there's a

very good chance that your radio will also present you with sounds from those "adjacent channel"

stations, even though they may be much farther away.