Antijamming Techniques

TM 11-5820-509-12

(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

NOTE

pitch. The effect is similar to the sound produced by

Many forms of jamming are used depending

Scottish bagpipes.

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.

Some

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

interference.

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.

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