On Thu, 03 Jan 2008 18:45:46 -0800, candy rosa wrote:
Could someone try to explain to me -- very succintly -- what exactly
an oscillator does in a radio??

An oscillator generates a pure, steady single-frequency signal.

Most of the time, this is used to change the frequency of a received
signal to some other frequency. For example:

1105kHz (oscillator) - 650kHz (signal) = 455kHz
1435kHz (oscillator) - 980kHz (signal) = 455kHz
1965kHz (oscillator) -1510kHz (signal) = 455kHz

By tuning the oscillator from 1105 to 1435 to 1965, you can convert the
signals of three different stations, on 650, 980, and 1510kHz, all to a
constant 455kHz. You can then amplify the 455kHz signal, remove the
program audio, and send it to the speaker. You don't have to change the
frequency of the amplifier - it's always 455kHz.

Oscillators can be used for other things in a radio. For example, to make
it easier to copy a Morse Code station. (on a regular radio, a Morse Code
station would sound like a regular station going on and off the air really
fast. Which really is precisely what it is. By mixing an oscillator on
456kHz with the Morse signal on 455, you get a 1kHz audible tone when the
Morse station is transmitting - and nothing when it isn't.)

They are also used to allow computer circuitry to "keep time" - so it can
count the frequency of another oscillator, telling you what frequency
you're tuned to. Or so that, when you program your radio to turn itself
on at 3:45pm, the radio knows when 3:45pm is. Or to generate high voltage
to run the frequency displays in some radios.