the appropriate method for each item of multichannel equipment in its
applicable technical manual.
The purpose of a frequency plan is to minimize the effects of
In duplex systems, the transmitter power greatly
exceeds the receiver signal.
The receiver must reject the
transmitter signal, and accept the weaker signal of its tuned
frequency.
Therefore, you must separate the receiver from the
transmitter by distance or frequency.
Two common methods of frequency selection are the ABM method and the
two-block method. You typically use the two-block method for simple,
isolated routes.
The ABM method is typically for more complex
systems.
For heavy traffic systems, you may need to employ the
double ABM or the XY method for frequency assignment. The following
paragraphs describe these frequency assignment methods.
a. Two-Block Frequency Assignment Plan.
You use the two-block
plan for simple isolated systems.
For example, the system may
consist of two terminals and three repeater stations such as shown in
figure 2-11. These radio sets operate between 200-300 MHz .
Figure 2-11.
Simple isolated radio system
(1) Arrange the frequencies in a numerical sequence and divide
the frequencies equally into two lists (blocks) as in figure 2-12.
To determine the amount of frequency separation required, refer to
the TM for the type of radio set you are using.
(2) Assign transmitter frequencies beginning at terminal A (see
figure 2-13). Alternate selecting a frequency from block I and from
block II.
Assign frequencies in the same manner for transmitting
from terminal B.
(3) Make certain you maintain receiver-to-receiver separation
when two or more receivers are at the same site.
For this reason,
you may not always assign consecutive frequencies from a specific
block.
2-23
SS0016
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