d. There are three categories of electronmagnetic jamming:
Radiation.
Reradiation.
Jammers, which are too far away from a target or are putting out a weak signal,
will have only marginal success. The primary reasons for this target distance
and jamming-to-signal ratio.
(1) Radiation Jamming
Radiation jamming involves those equipments and devices that
radiate
electromagnetic energy. It employs one of the following techniques.
Barrage Jamming.
Barrage jamming is the simultaneous jamming of a
number of adjacent channels or a range or band of frequencies.
The barrage
jammer transmits electromagnetic energy over a broad band of frequencies to
mask a large portion of the electromagnetic spectrum.
It is capable of
simultaneously jamming all receivers within the bandwidth of the jamming
signal.
The effectiveness of the barrage jammer in masking a strong
electromagnetic signal is limited because of the power spread over the range of
frequencies involved.
Effective barrage jamming requires a high-powered
emitter. This type of jamming should not be used in frequency bands used by
friendly forces, except when previously coordinated to eliminate interference
with friendly force communications.
Spot Jamming.
Spot jamming is the jamming of a specific channel or
frequency. This is the most common type of jamming because it causes minimum
interference with friendly emitters and permits maximum use of available power.
Sweep Jammers. Sweep jammers transmit a narrow band jamming signal in
which the carrier frequency is continuously varied within a given bandwidth.
Sweep jammers can be tuned over a broad frequency range and combined with the
high-power capabilities of the basic spot jammers, or with the broad bandwidth
coverage of barrage jammers. They are effective against noncommunications and
certain communications receivers. The sweep rate may be adjusted for specific
applications. It can sweep a different rates with two or more sweep jammers to
increase effectiveness. The sweep jammer is more complex than the basic spot
jammer. Its usefulness is limited in situations in which the frequency bands
covered include frequencies required for use by friendly forces.
Sweep Lock-on Jammers.
Sweep lock-on jammers employ a sweeping
receiver.
When it detects a signal, the receiver stops the sweep and locks
onto the victim signal. The jamming transmitter is then activated to perform
as a spot jammer on that frequency. This jammer has the advantage of covering
a broad band of frequencies on which there is enemy activity. It may also be
equipped with a means for identifying or discriminating among emitters by
modulation type, direction of intercepted signal, signal strength, or frequency
to assure that only victim receivers are jammed. A look-through capability is
provided, which permits the transmitter to automatically stop jamming and
permit the receiver to resume sweeping when the victim signal on that
IS3007
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