Modulation ?

You need to give us a lot more information before we can tell what you're asking for. Where did you hear about "modulation"? Is it in reference to "amplitude modulation" or "frequency modulation", both of which describe ways information is encoded in radio waves?

 

Let's say the signal we want to transmit is [tex]s(t)[/tex]. AM modulation is the following:

[tex]s(t) A \sin(\omega t)[/tex]

Here [tex]\sin(\omega t)[/tex] is the carrier signal, [tex]\omega[/tex] is its angular frequency, [tex]A[/tex] is a constant, and [tex]t[/tex] is time.

FM modulation is the following:

[tex]A \sin(B s(t) t)[/tex]

[tex]B[/tex] is a constant, and the other variables are the same as they were above.

I don't know the specifics of how these are used in radio.