Page 295 - Satellite Communications, Fourth Edition
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Analog Signals 275
Figure 9.13 (a and b) Effect of preemphasis on the modulating signal frequency
response at the transmitter. (c and d) Effect of deemphasis on the modulating
signal and noise at the receiver output. The deemphasis cancels out the pre-
emphasis for the signal while attenuating the noise at the receiver.
Weighting curves have been established for various telephone hand-
sets in use by different telephone administrations. One of these, the
CCIR curve, is referred to as the psophometric weighting curve.When
this is applied to the flat-noise density spectrum, the noise power is
reduced by 2.5 dB for a 3.1-kHz bandwidth (300–3400 Hz) compared
with flat noise over the same bandwidth. The weighting improvement
factor is denoted by [W], and hence for the CCIR curve [W] 2.5 dB.
(Do not confuse the symbol W used here with that used for bandwidth
earlier.) For a bandwidth of b kHz, a simple adjustment gives
b
[W] 2.5 10 log
3.1 (9.14)
2.41 [b]
