b. Suppose that symbol A is assigned to a station S. Then, on a
heavy traffic system, that station, one hop away from S, could be
assigned A1 on a lighter traffic system the station one hop away from
S could be assigned B or M.
c. The series, of symbols with prime and non-prime letters (A,
A1, B, B1, M, M1) need not be used for heavy traffic systems only.
However, the single ABM series or the single A1, B1, M1, series is
better for the lighter traffic systems because it permits a greater
number of interconnections between sites.
d. A system can be made up partly of one series of symbols and
partly of another, such as A1, A, B1, M1.
Symbols shifts of this
kind help in making interconnections.
50. XY Plan.
The XY plan is used when planning a very heavy traffic network.
This plan is not as flexible as the ABM and double ABM.
For
flexibility,
it
relies
on
the
interconnection
with
them.
Interconnection between the XY plan and the ABM or double ABM plan
can be worked out by the communications-electronics planning officer.
a. The XY plan (figure 27 uses the same six frequency blocks as
the ABM and double ABM plans.
Station labeled X and Y can
communicate with each other (without mutual interference) by using
very high frequency or ultra high frequency channels in four
frequency blocks (two in each direction).
Figure 27.
XY plan.
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