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Wire and Wireless Communication Applications Chap. 8
where the true azimuth, as measured clockwise from the north, is given by either A or 360° -A, as
appropriate, since a calculator gives a value between 0 and 180° for cos -1 (x). Using these formulas
for the Washington, D.C., TVRO site, † we get l = 134 - 77 = 57° and
b = cos -1 [ cos(38.8) cos(57)] = 64.9°
(8–51)
The slant range is
d = 3(26,205) 2 + (3963) 2 - 2(3963)(26,205) cos 64.9)
= 24,784 miles
(8–52)
The elevation angle of the TVRO antenna is
E = tan -1 1
c
tan (64.9)
The azimuth angle of the TVRO antenna is
-
3963
(26,205) sin (64.9) d = 16.88
(8–53)
A = cos -1 -tan (38.8)
c
tan (64.9) d = 247.9°
(8–54)
Thus, the look angles of the TVRO antenna at Washington, D.C., to the satellite are E = 16.8°
and A = 247.9°.
A block diagram describing the receiving system is shown in Fig. 8–26. Using (8–43), the
CNR at the detector input of the receiver is
a C N b dB
= (P EIRP ) dBw - (L FS ) dB + a G AR
- k
T dB - B dB
syst
bdB
(8–55)
The corresponding path loss for d = 24,784 mi at a frequency of 4 GHz is
(L FS ) dB = 20 log a 4pd b = 196.5 dB
l
5 meter
antenna
Transmission
feedline
G a =0.98
LNA
G a =50 dB
T e =120 K
FM
receiver
T e =2610 K
B IF =30 MHz
Composite
video out
m c (t)
Figure 8–26
TVRO terminal.
† Here for convenience and for ease in interpretation of answers, the calculator is set to evaluate all trigonometric
functions in degrees (not radians).