00:02
When a radio or tv station sends out an electromagnetic signal through their antenna system, transmission system, the signal actually is riding on what's called a carrier frequency.
00:19
The carrier frequency is typically a fairly high frequency, still in the radio band, but a high frequency.
00:28
So, for example, if you have heard of am radio, the am stands for amplitude modulation, which we will get into.
00:38
But the carrier frequency for am is in the range of 525 to 1606 .6 .5 megahertz.
00:55
Yeah, let me say that right.
00:57
Mega -meaning 10 to the 6th or a million.
01:01
So a fairly high frequency.
01:04
The actual voices that come over the radio, the music, etc., are embedded in the signal with modulation.
01:14
What modulation means is changing the...
01:21
When you talk about modulating your voice, you're talking about changing its strength in a very controlled manner.
01:29
In amplitude modulation, what you're actually doing is using sound and turning the sound into a voltage level and using those voltage differences to change the carrier amplitude.
01:46
Now, sound has frequencies in the range of about 100 hertz, we'll say, to 8 kilohertz.
01:56
It depends how good of a sound you want.
02:00
So kilo is 10 to the 3.
02:03
So a much slower change on top of the carrier.
02:10
And the way the modulation works is i'll try to draw a signal.
02:14
Let's say this looks like the electric field amplitude in time at a single point.
02:23
So what will happen is if there's no modulation, the signal will just simply look like an oscillating sine wave.
02:34
I'm not drawing this very perfect, but you get the idea...