[CluelessAboutScience (OP)]

Specifically, I'm trying to understand whether an rf transmitter actually "creates" radio frequency or whether it simply "channels" radio frequency that already exists in nature.  If it simply "channels" radio frequency that already exists in nature then my question would be what determines the limits of the frequency it can channel.  Can any rf transmitter channel any frequency or do you have to choose a transmitter specific to a range of frequencies? 

[lyner]

A 'transmitter' is basically an amplifier that takes a small RF signal and amplifies it in just the same way as an audio amplifier produces a large signal from a low level device like a CD player in order to drive a loudspeaker.
The low power RF signal is produced by a drive unit which may also put the modulation (the programme) on it.
Your actual question is not too clear but the 'frequencies' you refer to are just numbers. The electrical oscillations in the circuit are produced using the resonance of components in it.
A transmitted RF signal is usually required to be band limited in order to reduce interference. Many transmitters are narrow band, achieving some degree of usefulll filtering. These tend to be more efficient, too. You can get broadband transmitters which can amplify several signals at once.
But, basically, when you buy a transmitter, it will have been designed to operate within a certain frequency range - MF, HF, UHF, X Band. Etc.

[CluelessAboutScience (OP)]

My apologies for not being real clear with the question.  I kept doing google searches using various search terms, all of which included the phrase "radio frequency" and I kept getting nowhere.  Then, I just used the word "radio" and Bingo! started to get information about how radio works which, of course, includes radio frequency.  Unfortunately, I had already posted my question before I started getting better search results.  Nevertheless, you've done a wonderful job at answering my question! 

Just to be clear, I'd like to make sure I understand something, here.  After having done some reading, I've learned that "radio frequency" is basically a sine wave, right?  So, now, if I'm getting the "transmitter" stuff right, a circuit designed to transmit radio frequency would first of all create a sine wave and then after creating the sine wave, it would amplify it.  Is this correct? 

And, wow!  Now I know what broadband really means!  That's really cool.  Thanks.

[lyner]

A continuous, pure wave of one frequency is a sinewave. As soon as you start to add information (modulate it) the wave is no longer a simple sinewave. Remember - the term 'sinewave' only refers to the graph of the way the fields vary. Nothing actually 'wiggles' around!

[techmind]

Well, the electrons in the transmitting and receiving antenna (aerials) will oscillate (or "wiggle") up and down.   []

I built a little 3-transistor audio transmitter way back when. One transistor amplified the signal from the microphone, one formed part of an oscillator (in conjunction with a coil/capacitor resonant circuit) -and also did the modulation- and the third transistor amplified the RF signal. Connect a wire aerial to that, and there you go.