10. Near Vertical Incidence Sky-Wave (NVIS).
The disadvantage of HF communication is that at times it is
unreliable as compared to FM communication. What one forgets is that
even though HF transmitters are often high powered, their most
effective frequency range (2 to 5 MHz) works against them. If we try
to use a whip, most of the RF power is used up by the loading coils
trying to match the antenna to transmitter.
In some cases, the FM
set has more effective radiating power than the HF set. What to do?
To maximize the sky wave, when forced to use a whip, add additional
sections (3-116 for frequencies, 2-12 for AN/GRC-142) so that the
length will nearly equal a quarter wave. Bend the antenna down until
it is at a 45 degree angle.
Do not use the extended whip in a
vertical position unless our stations are within ground wave range
(consult ground wave book), because the radiation takeoff angle is
too low to be effective for short distance sky-wave communication (0
to 100 miles).
To be effective, our radiation pattern needs to be
straight up.
The slant or sloping wire antenna will also offer a
good compromise short distance sky wave communication. A doublet, 10
to 30 feet high, is the best antenna. Orientation of the antenna is
immaterial.
a. During a nuclear war, your equipment could be destroyed
without your even knowing about it. You and your equipment could be
hundreds of miles away from the blast area. After a nuclear blast,
an electric charge is sent out many times stronger than a lightning
bolt. The charge travels through space and is attracted to antennas
and power lines.
A lightning bolt may have 50,000 volts while a
nuclear EMP charge might have 1,000,000 volts.
The bolt follows a
path to ground. When we upgraded our equipment from tubes to solid
state, we made our equipment susceptible to EMP. We have known about
this problem since the early sixties, but we have not known about
what to do from a practical point of view.
b. There is no simple and inexpensive solution to the problem.
The Russians on the other hand have decided to take a step backward
as a solution to the problem.
When a MIG-25 pilot defected to the
west it was noted that the air frame was made of steel, not a
lightweight metal.
Also, some of the electronics were not solid
state, but of vacuum tube design.
c. During a nuclear test in the sixties, circuit breakers tripped
causing a power blackout 800 miles away in Hawaii at the exact
instance of the blast. Several years went by before the two events
were put together as one related incident.
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