(3) Stepped tones or "bagpipes". This type of
unusual or peculiar forms of modulation. Several forms
jamming signal is very distinctive and consists of
of electronic jamming are described below to familiarize
several separate tones transmitted first in an order of
the operator with the peculiar characteristics of each.
increasing pitch, and then in an order of decreasing
pitch. The effect is similar to the sound produced by
Many forms of jamming are used depending
upon the tactical value and proximity of the
(4) Random noise. Jamming by the use of random
legitimate station. The operator must be
noise modulation produces a rather broad jamming
aware of the legitimate use of the channel to
spectrum. This type of modulation is characterized by a
which he is tuned in order not to confuse
sound similar to the output of a receiver when it is not
legitimate signals with enemy jamming.
tuned to an incoming signal.
a. Continuous-Wave Jamming. Cw jamming is
(5) Gulls. This type of jamming signal is
transmitted as a steady carrier that often beats with the
characterized by a fast rise and a slow decrease in a
desired incoming signal to produce unintelligible
variable audio range. The sound produced in the
transmissions. Random on-off keying of this jamming
receiver is one that simulates the cry of a sea gull.
signal at, or near, the transmission rate of the desired
(6) Tone. This form of jamming employs a single
signal may also be employed.
audio tone or one that varies only slightly around a
b. Modulated Jamming. Modulated jamming signals
signal frequency. The resulting signal is one that
may consist of laughter, singing, music, various tones,
produces a howl.
or noise pulses. Often, more than one of these forms of
modulation may be used simultaneously.
3-20. Antijamming Techniques
variations of modulated jamming are listed below.
When it has been determined that the incoming signal is
(1) Spark. This form is perhaps the simplest, most
being jammed, the operator should notify his immediate
efficient, and most readily produced jamming signal. It
supervisor and continue to monitor the incoming signal
is characterized by a rough, raspy, and somewhat
to the best of his ability. A response to the transmitting
regular form of interference that has no musical
station indicating that his signal is being interfered with
properties. The sound is similar to the interference
may result in a different channel selection. Several
produced by a rotating electric motor with excessive
techniques may be employed by the operator to partially
brush spark. This signal is extremely broad and may
overcome the effects of jamming provided the jamming
occupy considerable portions of the spectrum.
signal is not too strong.
(2) Sweepthrough. This type of signal is the result
a. Slightly detune the receiver to either side of the
of varying an interfering carrier across a band of
operating frequency to separate the desired signal from
frequencies at a more or less continuous rate. The
the jamming signal if possible.
sweep rate may vary from quite slow to extremely rapid
b. Vary the VOLUME control slightly. This may
and is characterized by the generation of many and
reduce the intensity of the jamming signal sufficiently to
varied beat notes that sound like a low-flying airplane
permit reception of the desired signal through the
passing overhead. This type of jamming is effective
over a broad range of frequencies and, when the sweep
c. Cw telegraphy is the most efficient mode of
rate is rapid, it has an excellent jamming efficiency
transmission in the presence of high-interference levels.
against voice signals.
A transfer of operations to this mode may be helpful.