Page 298 - Satellite Communications, Fourth Edition

278 Chapter Nine

From Eq. (9.16):
2
777.8 35
G P ° ¢ > 26.36
3.1 108

From Eq. (9.15):

c S d c C d 10 logG P [P] [W]
N N
25 14.21 4 2.5
45.7 dB

9.6.8 Signal-to-noise ratio for TV/FM
Television performance is measured in terms of the postdetector video
signal-to-noise ratio, defined as (CCITT Recommendation 567-2, 1986)

a S b peak-to-peak video voltage (9.21)
N V rms noise voltage

Because peak-to-peak video voltage is used, 2ΔF replaces ΔF in Eq. (9.8).
Also, since power is proportional to voltage squared,

2 B (2 F) 2
a S b 1.5 C N (9.22)
N v N W 3

where W is the highest video frequency. With the deviation ratio D
F/W, and the processing gain for TV denoted as G ,
PV
sS/Nd 2 V

G PV
C/N
2
12D sD 1d (9.23)
Some workers include an implementation margin to allow for nonideal
performance of filters and demodulators (Bischof et al., 1981).
With the implementation margin in decibels denoted by [IMP], Eq. (9.15)
becomes

2
ca S b d c C d [G ] [P] [W] [IMP] (9.24)
PV
N V N
Recall that the square brackets denote decibels, that is, [X] 10 log X .
10
This is illustrated in the following example.