The double ABM plan uses the same six frequency blocks as the ABM
plan.
In addition to the symbols A, B, and M, the double ABM plan
uses A , B1, and M1. Figure 2-20 shows the block chart for the double
1
ABM plan.
Figure 2-20.
Double ABM plan
NOTE: Stations labeled A can communicate with stations labeled A1.
Four of the six frequencies can be used. This allows for heavy
traffic using A and A1. Stations B and B1, and stations M and
M1 can be used similarly.
d. XY Plan. You employ the XY plan for extremely heavy traffic
routes.
The XY plan generally interconnects with an ABM or double
ABM system.
The XY plan uses the same six frequency blocks as the
ABM plan. Stations X and Y communicate with each other by using the
frequencies in four of these blocks (two in each direction) as
indicated in figure 2-21. Interconnection with an ABM system can be
made by either the X or Y station.
2-29
SS0016
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