teletypewriter communications.
A
greater
separation
is
required for voice communications.
Type of modulation (AN or FM).
Tactical FM radio equipment
requires a 50-KC band for each channel (older sets require
100-KC channels); AM equipment requires a 10-KC band for each
channel.
Ensure that the separation between adjacent FM
channels is proportionately greater than the separation
between adjacent AM channels.
Frequency stability and accuracy of transmitter.
The
calibration of most field radio transmitters is not accurate.
Also, the frequency generated by the oscillator in the
transmitter often has a tendency to change or drift.
To
reduce inefficiency caused by an off-frequency operation,
ensure that most field radio stations maintain an accuracy of
0.01 percent of the assigned frequency.
For example, an
assignment of 4,000 KC (4,000,000 cycles), with a tolerance of
0.01 percent, permits the transmitter frequency to vary 400
cycles above or below the assigned frequency.
This factor
obviously affects the amount of separation between adjacent
operating channels.
Power output of transmitter.
The transmission distance and
the interference capability of a transmitter are directly
related to its rated power output. A high-powered transmitter
can block local radio receivers completely if you provide a
sufficient separation in operating frequencies.
For this
reason, the use of minimum power output consistent with
satisfactory communication is often stipulated in the SOP.
Distance separation between different nets.
A radio signal,
when received at a distant station, may occupy only a few KCs
on the receiver dial. When received on a nearby receiver, the
same signal will normally occupy a much broader band of
frequencies. Since adjacent channel interference occurs more
readily when stations are located close together, provide a
relatively large separation between operating frequencies
assigned to different net stations located at the same command
post.
The various factors listed above indicate that the amount of
separation between operating frequencies can vary.
To conserve the
usable
frequency
spectrum,
it
is
important
to
use
minimum
separations.
You can make satisfactory radio frequency assignments
by referring to the short distance ground and sky-wave prediction
charts, which are published every three months in the command SOI.
The army signal officer can provide you with these charts.
38
TR1009
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