APPENDIX. DEFINITIONS-continued

TM 11-490-5

frequencies which are the sum and difference of the

the use of electromagnetic energy to determine, exploit,

two original frequencies.

reduce, or prevent hostile use of the electromagnetic

Image frequency--The frequency which differs from the

spectrum, and action which retains friendly use of the

electromagnetic spectrum. There are three divisions

tuned frequency of a receiver by an amount equal to

within EW:

twice the inermediate frequency (the first

Electronic Warfare Support Measures (ESM): That

intermediate frequency of a dual conversion

receiver) of the receiver. The image frequency can

division of EW involving actions taken to search for,

be above or below the receive tuned frequency

intercept, locate, and immediately identify radiated

depending on whether the local oscillator is set

electromagnetic energy for the purpose of immediate

above or below the receiver tuned frequency. An

threat recognition.

unwanted signal at the image frequency may

Electronic Countermeasures (ECM): That division of

become an interfering signal.

EW involving actions taken to prevent or reduce an

Inductive coupling--The type of coupling in which the

enemy's effective use of the electromagnetic spectrum.

mechanism is mutual inductance between the

ECM includes:

interference source and the signal system; that is,

1. Jamming. The deliberate radiation, radiation, or

the interference is induced in the signal system by a

reflection of electromagnetic energy with one object of

magnetic field produced by the interference source.

impairing the use of electronic devices, equipment, or

Intermodulation--The production of frequencies in the

systems being used by an enemy.

output of a nonlinear device equal to the sums and

2. Deception. The deliberate radiation, radiation,

differences of the frequencies present at the input of

alteration, absorption, or reflection of electromagnetic

the device, plus the sumsand differences of

energy in a manner intended to mislead an enemy in the

harmonics of the input frequencies. For example, if f

interpretation or use of information received by his

a and f b are the frequencies of the two input signals,

electronic systems. There are two categories of

the output signal could contain signals at frequencies

deception:

of fa , fb , 2fa , 3fa , 4fa. . . . , 2fb, 3fb, 4fb. . . . , fa fb, fa

a. Manipulative. The alteration or simulation

2fb , fa 3fb. . . . , fb 2fa , fb 3fa , fb 4fb , and so

of friendly electromagnetic radiations to accomplish

forth; in general; nfa mfb , where either n or m could

deception.

be 0, 1, 2, 3 and so forth. The signal components

b. Imitative.

Introducing radiations into

thus

generated

are

sometimes

called

enemy channels which imitate his own emissions.

"Intermodulation products" The "order" of the product

Electronic Counter-Countermeasures (ECCM): That

is n + m; for example, fa + 2fb is a third order

division of electronic warfare (EW) involving actions

Intermodulation product.

taken to insure friendly effective use of the

Ionization--The process which results in the formation of

electromagnetic spectrum despite the enemy's use of

an atom, or molecularly bound group of atoms, in

EW.

which one or more electrons have been gained or

Emission spectrum--The power versus frequency

lost, resulting in an ion or ions, each having a net

distribution of an emitted signal, including the

negative or positive charge.

fundamental frequency, associated sidebands, and

Jamming--See Electronic Warfare Local oscillator-An

all spurious emissions.

oscillator, incorporated within the equipment, whose

Frequency division multiplex (FDM)--A means by which

output is mixed with another frequency waveform for

two or more channels of information are transmitted

frequency conversion.

and received simultaneously without mutual

Magnetic field coupling--Identical with Inductive

interference by virtue of assigning each channel a

Coupling.

separate frequency within the total available

Nonlinear Element--An element in which the

frequency band.

relationships between the output and input are not

Group loop--In an electrical system, a potentially

linear; that is, the element alters the input (voltage

detrimental

circuit

path

formed

the

and/or current) waveform and produces an altered or

interconnection. of two or more points that are

distorted version of the input waveform. Some

nonimally at ground potential.

elements or devices are designed to be non-linear

Harmonic frequency--An integral multiple of the

(such as mixers, detectors, and clippers) while some

fundamental frequency; that is, the frequencies of 2,

are linear under some conditions and nonlinear under

3, 4, 5, ... times the fundamental frequency.

other conditions (for example, a linear amplifier

Heterodyne-The combining (beating) together in an

operating under designed conditions versus

electrical circuit of two frequencies to produce new

overdriven conditions resulting in waveform

distortion). Distortion causes harmonics

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