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Very High Fequency Systems | Up
Information Systems Technician Training Series, Module 4 - Communications Hardware | Next
Super High Frequency Systems |
VHF transmit and receive system using a transceiver.
Although a transceiver is used in this system, the
transmit and receive systems are described separately.
Refer to figure 1-4 as we follow the signal path on the
transmit side of the system.
On the transmit side of the system, the operator, at a
remote location:
1.
2.
3.
4.
5.
Talks into the handset.
The handset is connected to the C-1138 Radio
Set Control.
The output of the radio set control is sent to the
transmitter transfer switchboard.
The output of the switchboard is sent to the
transmit side of the transceiver.
The transceiver converts the input signal to an
RF signal for radiation by the antenna.
Continue to refer to figure 1-4 as we follow the path of
the incoming signal.
1.
2.
3.
4.
5.
The incoming signal in figure 1-4 is received by
the antenna.
This signal is sent to the receive side of the
transceiver.
The output of the transceiver is sent to the
receiver transfer switchboard.
From the receiver transfer switchboard, the
output is sent to either the C-1138 Radio Set
Control or to a speaker amplifier, or both,
depending on the preference of the user.
The output of the radio set control is sent to a
handset.
6. A speaker receives the output of the speaker
amplifier.
ULTRA-HIGH-FREQUENCY SYSTEMS
The ultra-high-frequency (UHF) band (300-MHz
to 3-GHz) is used for line-of-sight (short-range)
communications. The term “line of sight,” as used in
communications, means that both transmitting and
receiving antennas must be within sight of each other
and unaffected by the curvature of the Earth for proper
communications operation.
The UHF band is also used for satellite
communications. Although satellite communications
are line of sight, the distance the signal travels is much
greater than that of UHF surface communications,
because the antennas remain in sight of each other.
As in the VHF section, the transmit and receive
systems will be described separately. Figure 1-5 shows
a basic block diagram of a UHF transmit system, which
uses a transceiver.
1.
2.
3.
4.
On the transmit side of the nonsecure voice
system, the operator at a remote location talks
into the handset. The handset is connected to the
C-1138 Radio Set Control.
The C-1138 is connected to the transmitter
transfer switchboard, where it is patched to the
transmitter.
The operator at a remote location talks into the
secure voice remote phone unit (RPU).
The RPU is connected to the secure voice
matrix. This is the tie point for connecting more
than one RPU. The output of the matrix is
Figure 1-5.—Ultra-high-frequency transmit system.
1-5
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