[KevMan10]

Hi-

Im starting electrical engineering school in the fall and I've been studying up on circuits, designs and radio technology and have come up with many questions!

My current question is this. How is it possible to tune an FM radio to a station if the broadcast frequency is constantly changing to match the dynamics of the audio stream? I understand that AM radio is broadcast on a single frequency and the amplitude of the wave determines the audio signals dynamics, but how is it possible to tune to a radio station if the broadcast frequency is constantly changing?

Thanks!

[InfoJunkie4Life]

What do you know about frequency filters or isolaters?

Basically what happens is the carrier frequency is modulated to change with the audio it needs to carry. You now have a high frequency usually several million hertz that is in flux. The cool part is that it still remains a high frequency. The audio carried within from its lowest variation to its highest variation only changes the overall frequency a fraction of a percent.

Just a math example.

Say you are sending a tone of 20hz (bottom of the hearing range) over a 5mhz signal, the tone then jumps to 12khz (the top of the hearing range) you see a flux of 11980 hz. Lets see this as a percentage.



Now, consider filters, they are designed to accept a range of frequencies centered around a tuned frequency. A filter that is tuned to accept 5mhz +/- 2% is capable of listening to a range much wider than the human hearing range. When it is demodulated, the original audio is then reproduced with the same range it was modulated from.

I hope this makes sense to you.