1.
Jamming Concepts.
Jamming is the deliberate radiation or
reradiation of energy to prevent or degrade the reception of
information by a receiver. The jamming function is tied directly to
the information provided by the EW support measures (ESM) component
of the EW program.
The tactics for using jamming vary with the
tactical situation and the commander's plan of action. Conceptually,
the jamming transmitter is placed between the signal transmitter and
the receiver to which the transmission is directed.
However, the
ability to place the jammer between the transmitter and the receiver
is seldom possible.
Thus, many jammers have enough power to
compensate
for
the
additional
range
needed
to
jam
signals
effectively.
a. Three methods of communications jamming are commonly used on
the battlefield.
Each is used to attack a different signal or
signals.
(1) Spot jamming is directed against a single or specific
frequency, while allowing adjacent frequencies to remain free of the
effects of the jamming.
It applies the full radiated power of the
jamming transmitter against enemy signals, one frequency at a time.
(2) Barrage jamming targets multiple frequencies.
It may be
used over a large portion of the frequency spectrum or the entire
amplitude modulation or frequency modulation band.
Barrage jamming
needs high power to operate. It cannot distinguish between enemy and
friendly frequencies.
(3) Sweep jamming is
used to block several preselected
sequential frequencies.
It
moves from one frequency to another,
remaining on each frequency
for a predetermined period.
It can
affect both friendly and enemy
frequencies.
b. Various types of signal modulation can be used during jamming.
These modulation types are selected based on their effectiveness
against the transmission being attacked. In some cases, the jammer's
signal generator can produce only a limited number of signals.
In
other cases, the generator can produce a large number of signals or
sounds.
Some of the most commonly used modulation types are
discussed below.
(1) The stepped tone signal is a series
of
varying
tones
normally sent in an ascending or descending order.
(2) The
bagpipe
signal
is
like
the
sounds
produced
by
a
bagpipe.
(3) The
gulls
signal
is
similar
to
the
sounds
made
by
sea
gulls.
SS0134
3-2
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