SCA.1
If this station were a plain old-fashioned monaural FM station, all it
would have to do is feed in the audio signal -- voice, music or funny
sound effects -- which you want the listeners out there in Radio-Land
to hear.

The signal would modulate the carrier, be amplified, fed to the antenna
and radiated.  It would come swooping down into your ordinary, Monaural
FM receiver.  The receiver would say, hmm...  The frequency is F + K*M
I therefore have to subtract F and divide by K to give my loyal owner
the instantaneous value of the signal waveform, which is M.  Voila!  Out
of the FM demodulator comes M in livid high fidelity.

(I don't think the following information is needed for present purposes,
but I include it so somebody won't say I am oversimplifying things!!
Now, even in simple monaural FM there is one trick that we haven't
mentioned.  This is called pre-emphasis and de-emphasis.  Very early in
the game, it was noticed that in FM systems if you fed in no modulation
at all and listened to the receiver's reconstructed value of M (after it
did the arithmetic noted above), there was a NOISE output from the
receiver, even at fairly strong signal levels.  The noise was
particularly noticeable because its amplitude increased with frequency.
Thus a quite noticeable high-frequency hiss was present on even fairly
good signals.  Somebody then had the bright idea that they should
effectively "turn down the treble control" at the receiver.  A fixed
frequency compensating network called a "de-emphasis" network was
designed and standardized to do that.  But then the music had its highs
"de-emphasized", so an "inverse" network called a pre-emphasis network
was added at the transmitter.
CONTINUED IN FILE SCA.2