Specifications

CONSTRUCTION
Another important
parameter of the LNB is
its noise temperature.
The noise equivalent tem-
perature of most of the
good-quality LNBs ranges
from 26
o
K to 40
o
K (K
stands for kelvin). The
picture on a 26
o
K LNB
will show less noise com-
pared to that of a 40
o
K
LNB, especially when the
received signal is weak.
Theoretically, the noise
power is related to the
temperature as follows:
Noise power = KTB
watts
where K is the
Boltsman’s constant =
1.381 x 10
-23
T is tempera-
ture in
o
K; and B is the
system bandwidth in Hz.
A coaxial cable con-
nected between the LNB
and receiver serves two
purposes: (i) it feeds +18V
DC to the LNB, to power
the amplifier and con-
verter circuits inside
LNB, and (ii) the con-
verted frequency (950
MHz to 1,450 MHz) is fed
from LNB to ‘C-band’ re-
ceiver.
C-band receiver.
The main function of the
receiver is to select a par-
ticular channel from the
converted block of fre-
quencies (between 950
and 1450 MHz) and re-
trieve the audio and video
signal information. The
audio and video output
signals are finally fed to
the TV monitor’s audio-
and video-input termi-
nals, respectively. If the
TV does not have sepa-
rate audio and video in-
put points, then feed the
audio and video output
signals from receiver to
an RF modulator which
modulates the RF and
provides a modulated
VHF RF output (corre-
sponding to anyone of the
channels in the VHF
Fig: 4: Circuit diagram of C-band satellite receiver
105