Noise in Modulation SystemsNoise in DSB systems
The required bandwidth of the predetection filter is 2W. The output of the predetection filter is
where
Carrier to Noise Ratio (CNR)
The carrier power C is
The noise power is
The CNR = C/N and is given by
SNR: Coherent Demodulation
The band limited noise
Thus
In both cases, the signal power is
The noise power at the detector output is
The signal to noise ratio SNR =
SNR: Envelope DetectionIn this case, the output of the predetection filter is expressed as
where
The output of the envelope detector is
when
and
Noise in FM Systems
The receiver using the ideal discriminator with a band-pass limiter is
illustrated in Figure
Noise in FM Systems
The receiver using the ideal discriminator with a band-pass limiter is
illustrated in Figure
|
is an arbitrary phase angle induced by the channel and
at the output of
the predetection filter may be expanded into quadrature components about 
so that
and is given by
(i.e. the CNR is high). Thus the signal and noise powers are
