On 8/2/2014 9:55 PM, Lostgallifreyan wrote:
Rob wrote in :

Deviation is something different than bandwidth. To receive an FM signal,
as a rule of thumb you require a receiver with a bandwith of about
twice the deviation plus twice the maximal audio frequency. So to receive
a signal with 15kHz audio and 75kHz deviation, you require a bandwitdh
of about 180kHz.

This is not "to make things less critical". It is a requirement because
of the characteristics of FM modulation, where sideband frequencies are
determined by a Bessel function.

The ratio between deviation and maximal audio frequency, the modulation
index, determines the signal/noise ratio after demodulation for a strong
signal.

That's useful. It ties in with things I have read about phase modulation
synthesis. At risk of opening a wild (but fun) bit of off-topic, I wonder if
given a reference carrier at precise fixed frequency, a phase modulation
technique might allow advantages to signal transmission that FM lacks.


Not really. All phase modulation does is integrate the modulating
signal and use that to shift the phase of the carrier (which also
requires a frequency change to effect the phase change). The resulting
signal is exactly the same as if the carrier were directly frequency
modulated. The only difference is how you got there.

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