Page 296 - Satellite Communications, Fourth Edition

276 Chapter Nine

Here, b is the numerical value of kHz (a dimensionless number). A
noise weighting factor also can be applied to TV viewing. The CCIR
weighting factors are 11.7 dB for 525-line TV and 11.2 dB for 625-line
TV. Taking weighting into account, Eq. (9.13) becomes

c S d c C d [G ] [P] [W] (9.15)
P
N N

9.6.7 S/N and bandwidth
for FDM/FM telephony
In the case of FDM/FM, the receiver processing gain, excluding empha-
sis and noise weighting, is given by (Miya, 1981, and Halliwell, 1974)

2
B IF F rms
5 ° ¢ (9.16)
G P
b f m
Here, f is a specified baseband frequency in the channel of interest, at
m
which G is to be evaluated. For example, f may be the center frequency
m
P
of a given channel, or it may be the top frequency of the baseband signal.
The channel bandwidth is b (usually 3.1 kHz), and ΔF rms is the root-mean-
square deviation per channel of the signal. The rms deviation is determined
under specified test tone conditions, details of which will be found in CCIR
Recommendation 404-2 (1982). Some values are shown in Table 9.1.
Because ΔF rms is determined for a test tone modulation, the peak devi-
ation for the FDM waveform has to take into account the waveform
shape through a factor g. This is a voltage ratio that is usually
expressed in decibels. For a small number of channels, g may be as high
as 18.6 dB (Ffthenakis, 1984), and typical values range from 10 to 13 dB.
For the number of channels n greater than 24, the value of 10 dB is often

TABLE 9.1 FDM/FM RMS Deviations
Maximum number RMS deviations per
of channels channel (kHz)

12 35
24 35
60 50, 100, 200
120 50, 100, 200
300 200
600 200
960 200
1260 140, 200
1800 140
2700 140