Disclaimer: This is a VERY basic tutorial. I have been critiqued on this attempt as simplifying the theories too much. For these people I will issue the following disclaimers:

The human voice is a very complex waveform. To assume that a nice clean sign wave is produced is not true. For the purposes of the illustrations let us assume that the wave being produced is from an AF frequency generator and is producing a nice clean sine wave. This is a basic article whose purpose is supposed to lay the foundation for an understanding in radio theory. It is not to get you ready to go home and build your own radio transmitter.

That being said; here is a very basic simplified explanation of the radio theories:

Basic RF Theory

This is a basic sine wave. This is what energy looks like as it travels. Sound waves, radio waves, even light travels in sine waves. This is how we graph a sine wave:

You'll notice that in the first picture there are vertical and horizontal lines through the center. We put those there to help us graph the sine wave on paper to better understand it. The horizontal line through the center is 0, any portion of the wave above the line is graphed as a positive number, everything below the line is a negative number.

Energy waves move through space. Some sign waves move faster than others; this is why one sees the smoke of a gun before he hears the shot because "sound waves travel slower than light waves".

Let us use sound waves for now because we are all familiar with sound.

Lets say a singer sings a pitch of C1. A second singer sings C2 one octave higher, which is exactly twice as high as the first note but both singers are singing the same volume.

The Blue sign wave is the base note, the red is exactly double.

The horizontal line through the middle signifies 0. As the wave travels follow the red line each time it passes the 0 mark. Every other time the red wave passes 0 it collides with the blue wave. This means that the red wave moves up and down twice as much as the blue wave. One might say that the red wave vibrates with more "frequency" than the blue wave. This is what frequency is. It measures the frequency (how many times) the sine wave completes one full cycle in one second.

Cycles Per Second

A Cycle is one full wave on the graph. The wave must pass from positive to negative. One cycle is when the wave goes positive, goes negative and just before it starts to go positive again.

This is one cycle because as you follow the wave's path it starts from 0, goes positive, swings to negative, and starts back up to positive.

The Frequency is how many cycles are completed in one second. Frequency is measured in hertz (Hz). One cycle in one second is refereed to as 1 hertz. Three Cycles in one second is 3 hertz and so on.

Note: Because 1 cycle per second is equal to 1 hertz the terms "Cycles-Per-Second" and "Hertz" are often used interchangeably.

Amplitude

Now that you understand frequency, let us talk about the other portion of a sign wave. Lets say the two singers are singing the exact same note but singer A has a loud voice and is singing louder than singer B. This is what it would look like:

As you can see both waves cross 0 at the exact same places so they occur at the equal frequency but one is exactly twice as high. This means that the pitch is the same but one is louder.

Amplitude vs. Frequency

Please note that the amplitude of a wave has nothing to do with the frequency and visa versa. Once a wave is generated the frequency will not change as it passes through space. There are things like doppler shift that will cause the perceived frequency to change but that is advanced and beyond the scope of this article. For these basic purposes let us state that once the wave is generated the frequency does not change. In the vacuum of space with nothing to impact the wave there is 0 resistance and the amplitude will not change either. Theoretically a radio wave that makes it past the atmosphere goes on forever until it hits something. Here on earth it is a different story.

We know that the wavelength is measured in Hz and represents its frequency. Amplitude is the strength of the wave. As the wave passes through the air there are many forces that cause resistance. As time goes on and the wave travels it encounters resistance and slowly dissipates until the amplitude gets to 0 at which time the wave no longer exists. Think of a singer on an outdoor stage. As he sings you walk away from him. As he sings a note and you walk away the pitch wont change but the loudness will. Even though the frequency never changes and the amplitude (strength) of the sound does not change at the stage the amplitude (strength) decreases as you walk away until you cannot hear it anymore.

Waves with a higher amplitude will carry farther because there is more energy behind it. This is why one cannot yell to someone a mile away but a gun shot will carry for a mile or more. The gun shot has a much higher amplitude and will carry farther than a yell. The gunshot will carry until the amplitude reaches 0 and then the shot will not be audible.