Specifications

CONSTRUCTION
S.C. DWIVEDI
BUILD YOUR OWN C-BAND
SATELLITE TV RECEIVER
S
atellite TV reception has gained
much popularity in India over
the last three decades, specially af-
ter the live telecasting of the Gulf
war by CNN. Both the S-band and C-band
satellite signals are available to India.
C-band signals are beamed from various
satellites like Asiasat, Aralisat, and
Insat 2B.
In India, the C-band reception is much
more popular compared to the S-band.
The popular satellite programmes which
can be received on C-band include Star
TV, Zee TV, PTV2, CNN, ATN, Sun TV,
and Doordarshan. Besides, programmes
from Russia, China, France, and Saudi
Arabia are also available on C-band chan-
nels, although their language is a bar-
rier.
Fundamentals of C-band reception
You are aware that to receive any satel-
lite signals, a dish antenna is required.
The mechanical aspects and the dish-ori-
entation principles to receive satellite sig-
nals in S-band and C-band remain basi-
cally the same. The C-band downlink fre-
quencies range from 3.7 GHz to 4.2 GHz
The direct reception system comprises:
(i) Dish antenna
(ii) LNB (low-noise block converter)
and feed horn assembly.
(iii) Satellite receiver.
Dish antenna: There are different
types of dish antennae (e.g. fibre and
mesh) available in various sizes ranging
from 1.8 metres to 4.8 metres. The size of
the dish is dependent on the size of the
distribution network and the strength of
the signal.
The area where the signal is weak
requires a large dish, and vice-versa. The
strength of the signal can also be
recognised from the footprints of differ-
ent satellites. As an example, the foot-
print (i.e the geographic area on ground
covered by a satellite downlink antenna)
measured in terms of effective isotropic
radiated
power
(EIRP) in
dBW (deci-
bels w.r.t.
one watt) of
Asiasat sat-
ellite (transmitting Star TV programmes)
over India is given in Fig.1. Star TV rec-
ommends the following sizes of dish an-
tennae for various regions:
In order to maintain optimum carrier-
to-noise ratio (C/N ratio), a larger size of
dish is required for the larger cable dis-
tribution network. A dish consists of the
following parts:
(a) The stand or the base structure
which supports the entire dish.
(b) The parabolic reflector.
(c) The electromechanical arrange-
ment to move the dish in the horizontal
and vertical planes to track the satellite.
(This arrangement is generally used in a
dish of 3.7 metre and above sizes.)
(d) LNB mounting arrangement.
Base structure should be strong
enough to withstand the entire load of
the dish. To withstand the wind load dur-
ing heavy wind or storms, the base struc-
ture should be firmly grounded in con-
crete.
The parabolic reflector. It is the most
important part of the dish. The reflector
TABLE II
Specification of the DBS tuner
with FM demodulator
Receiving frequency 950 MHz to 1750 MHz
Input impedance 75-ohm
IF 479-5 MHz
Channel select (SY) By electronic tuning
ODU supply in-and-out 18-25V DC
Tuning voltage 0.6V to 20V DC
IF bandwidth 27 MHz (3 dB down)
Output impedance 75-ohm
Demodulation (SY) PLL
TABLE I
Relationship between F/d and X
F/d X (mm)
0.42 0
0.40 5
0.38 10
0.36 15
0.34 20
S. DAS GUPTA
Fig. 1: Footprint of Star TV (Southern)
Personal Cable distribution
receiving system
system
Delhi 1.8 mtr 3.0 mtr
Mumbai 2.0 mtr 3.0 mtr
Calcutta 3.0 mtr 4.8 mtr
Chennai 3.7 mtr 6.0 mtr
Fig. 2: Feed horn
103