I'm not sure exactly what you're asking.
It could be
==> Why do radio stations use different frequencies from TV stations ?
or it could be
==> Why don't all radio stations, or all TV stations, use the same frequency ?
Radio and TV can't coexist among each other in the same "band"
of frequencies, because they use different amounts of "space" on
the dial. One analog TV channel uses enough dial space for about
600 AM radio stations, or 30 FM radio stations ! That's one click on
the TV channel knob !
So if they were all jumbled up together on the same dial and you
wanted to tune your radio from one AM station to another, you
might have to crank through enough space for 600 radio stations ...
or even 1200 or 1800 of them ... to go to the AM signal you want.
And maybe even worse than that ! I'm sure you've never heard what
a TV signal SOUNDS like on a radio. It is horrendous, and it is loud !
It sounds like a thousand cats shrieking at each other, and it never stops.
That's another good reason to move the TV transmissions to frequencies
where radios will never hear them. If radios just randomly tuned in to a
TV picture signal every now and then, a lot of people would be shocked
out of their socks. They would stop listening to radio, and thousands of
advertisers would not like that.
For the second question ...
OK, so we don't mix radio and TV in the same band of frequencies.
But why does each station need its own frequency ? Why not just
put every radio station on one frequency, and every TV station on
a single frequency that's different from the radio frequency ?
The answer is: It's because people don't want to listen to two radio
stations at the same time, or watch two TV movies at the same time.
We like to make our choice, and then watch them or listen to them
one at a time. And FREQUENCY is the only way our radios and TVs
know how to pick out ONE and ignore all the others.
If there are two, or 5 or 10 stations all on the same frequency within
10 or 20 miles from you, then when you tune your radio to that frequency,
you HEAR two, or 5 or 10, songs, church services, newscasts, political
speeches, or commercials, all at the same time.
So if all radio stations were on the same frequency, or all TV stations
were all on the same frequency, then any time you turned on your
radio or TV, you'd see or hear all of them together. Radio and TV
would completely lose their entertainment value, everybody would
give up watching and listening, and once again ... thousands of
advertisers would not like that.
After all, advertising is the main reason why we have so much radio and TV at all.
The advertiser buys, the broadcaster sells, and YOUR eyes and ears are the product.
