To obtain greater range from your system, you must plan your site
setup carefully.
Lesson 2 discusses system planning in detail.
Avoid locations where hills, buildings, woods, or other obstructions
block the transmission path. Transmissions from elevated sites, over
open paths, provide optimum results.
Any obstructions, such as
bridges, power lines, or generating equipment block or weaken the
signal.
Figure 1-18 is a block diagram of a basic multichannel radio system.
Several voice frequency (VF) channels multiplex into one wideband
signal at the east site.
This wideband signal is commonly referred
to as the baseband signal. The radio set then modulates this input
signal with a radio frequency (RF) carrier (F1) for transmission. If
the west site were in range of the east site, the receiver of the
west site would capture this transmission signal.
Figure 1-18.
Basic multichannel radio system
Our example uses a relay site to extend the range of the system.
Here, the receiver of the relay site receives the transmitted signal
F1, demodulates it back to the baseband, and cables it to the relay
transmitter.
The relay site transmitter modulates the baseband
again, but on a new RF carrier frequency F2.
The RF signal F2
reaches the west receiver, where it again demodulates, and cables to
the multiplexer.
The baseband signal demultiplexes back to the
original VF channels, and completes the transmission.
The same
operation takes place in the west-to-east direction.
Figure 1-19 shows a block diagram of a multichannel radio system
using a cable link.
This system operates much like the system in
figure 1-18 except that a cable link separates the relay site
transmitter and receiver.
For example, you may want to locate the
receiver on one side of a hill and the transmitter on the other side.
A cable link joins the two units to relay the transmission. Due to
characteristics of the radio, cable, and signal, such a configuration
requires an interface unit to couple the radio sets to the cable
link.
The interface unit amplifies, equalizes, and regulates the
signal for transfer to the cable or radio set.
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SS0016
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