406 Electronic Communication and Data Systems
The signal transmitted by the satellite is picked up
on earth by a receiving dish or parabolic antenna. The
dish focuses the received signals into a small area called
the focal point. The feedhorn, which acts as a receiver, is
located here, Figure 23-30. Located near the feedhorn is
a low noise amplifier (LNA) that amplifies the received
signal. The signal is then fed through a piece of electrical
coaxial cable to the TV receiver. A coaxial cable has a
conductor inside another conductor. The two conductors
are insulated from each other.
Figure 23-31 shows four dish designs. Motors are
often used to move dishes. This way, signal from more
than one communication satellite can be received or the
dish can be lined up with a particular satellite.
A satellite receiver is shown in Figure 23-32. This
receiver can be programmed with infrared remote control.
Complex circuitry allows the user to store satellite posi-
tions, polarity, frequencies, and tuning voltages into
memory. The programmed information can then be
recalled from the unit’s front panel or the remote control
unit. Other remote control functions include volume con-
trol with mute, direct or scan channel selection, and video
fine tuning.
Coaxial cable
The signal that is supplied by the local cable televi-
sion company or through a satellite dish system typically
connects to the initial receiver in the home from a single
coaxial cable. Coaxial cable is designed to carry high fre-
quency signals. The coaxial cable is designed to limit the
radio waves generated from the center core conductor to
the area between the core conductor and the shield. The
shield will absorb the radio signal emanating from the
core conductor when the high frequency passes through.
See Figure 23-33. The shield also protects the inner core
Transmitting
antenna
Homes, industries, and
offices receiving signals
Equator
Earth
Earth transmitter
to satellite
Receiving
antenna
Satellite
From studio to
satellite (antenna)
From satellite
to receiver dish
Feedhorn
Cable to
receiver
Low noise amplifier
Transmitted signals
Dish reflects
transmitted signals
into small
focal point
area
Satellite
Transmitted signals
22,300 miles
Figure 23-29. Study the operation of a satellite.
Figure 23-30. A parabolic, or dish, antenna. Study the parts.