Re: FM "deviation"
Maximum deviation for FM broadcast is 75kHz as you say. But if the programme material is quiet, (low audio amplitude), then the carrier frequency gets deviated a lot less than 75kHz.
Pre-emphasis and de-emphasis is just about treble boost of the audio before it gets to the modulator in the transmitter, and treble cut after the discriminator in the receiver. This improves the signal-to-noise ratio, because the treble cut also cuts down the background hiss.
|