d. Another effect of EMP is a radio blackout lasting from a few
seconds to several hours, depending on the frequency. After a blast,
the ionosphere becomes superionized and absorbs all frequencies. The
upper frequencies will come back first, with HF and the lower bands
coming back last.
e. What can you as an operator do to lessen the effect of EMP?
Very little.
Some progress has been made toward hardening
communication equipment - extra shielding around cables, air vents,
etc.
Some basic precautions are: equipment not needed should be
turned off. Antennas should not be installed until needed. Bury all
Equipment not used should be left unplugged when not
in use.
Never use commercial power.
Always ground your equipment.
Rethinking of our use of communication equipment is in order.
Some
of our net radios as well as our multichannel links should be turned
off. Have only one net up at a time to lessen the effect of EMP.
12. FM Squelch Capture Effect.
a. We are familiar with the obvious methods of jamming, but not
of subtle jamming.
We have a characteristic in our FM radios that
make them highly susceptible to this type of jamming.
b. When we listen to our FM radios we don't want to be bothered
with noise when no one is transmitting.
We have a squelch circuit
that eliminates that noise.
To overcome the squelch, a friendly
radio transmitter, as part of his signal, transmits a 150 hertz cycle
tone (NEW SQUELCH POSITION) that deactivates the squelch enabling
another station to communicate with him. To let him know a call is
coming in, the CALL LIGHT lights.
A jamming station on the other
hand, will not transmit a 150 hertz tone.
The CALL LIGHT will not
light. Therefore, you will not know if someone is calling you or not
because the jamming signal will be many times stronger.
c. What can you do? Things you can do violate signal security,
such as commo checks. Radio checks are unnecessary on an established
radio circuit.
By contacting other stations, you compromise your
location. Valuable signal intelligence can be gained even though the
net is encrypted.
An electronic signature identifies all units and
their locations.
One thing you can do that doesn't violate signal
security is to put the squelch switch to OFF. If you hear noise, you
know you are not being jammed.
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