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FM 24-18: Tactical Single-Channel Radio Communications Techniques



AC alternating current

ADM atomic demolition munitions

AF Audio frequency(ies)

AH ampere-hour

ALTHQ alternate headquarters

AM amplitude modulation(ed)

ARTEP Army Training and Evaluation Program

ASC area signal center

ASCII American Standard Code for Information Interchange

ASI additional skill identifier

aux auxiliary

BCS burst communications system

BFO beat frequency oscillator

bn battalion

BPS bits per second

BPSK biphase shift keying

CB common battery

CEP circular error probable

co company

COMINT communications intelligence

COMSEC communications security

CP command post

CRT cathode ray tube

CW continuous wave

dB decibel

dBm decibels above or below 1 milliwatt

DC direct current

DF direction finding

DISCOM division support command

DIVARTY division artillery

DMDG digital message device group

DOD Department of Defense

DS direct support

DSB double sideband

DTMF dual-tone, multifrequency

DX duplex

ECCM electronic counter-countermeasures

ECM electronic countermeasures

EEFI essential elements of friendly information

EHF extremely high frequency

ELF extremely low frequency

EMCON emission control

EMP electromagnetic pulse

ESM electronic warfare support measures

EW electronic warfare

F Fahrenheit

FDX full duplex

FID foreign internal defense

FLOT forward line of own troops

FM frequency modulation(ed)

FOB forward operational base

FSK frequency-shift keying

ft feet

GHz gigahertz

gnd ground

GS general support

HF high frequency

HOB height (depth) of burst

Hz hertz

IC integrated circuit

IED imitative electronic deception

IHFR improved high frequency radio

IMC international Morse code

JEWC Joint Electronic Warfare Center

kHz kilohertz

km kilometer

kW kilowatt

LB local battery

LED light emitting diode

LF low frequency

LOS line of sight

LPI/LPD lower probability of intercept/lower probability of detection

LRRP long-range reconnaissance patrol

LSB lower sideband

LUF lowest usable frequency

m meter

MAC maintenance allocation chart

MCW modulated continuous wave

MED manipulative electronic deception

MF medium frequency

MFP moisture and fungusproofing paint

MHz megahertz

MIJI meaconing, intrusion, jamming and interference

mi mile

MOPP mission oriented protection posture

MUF maximum usable frequency

MWO modification work order

NATO North Atlantic Treaty Organization

NBC nuclear, biological, chemical

NCS net control station

NESTOR a communications security device

NRI net radio interface (replaces RWI)

NSK narrow shift keying

NVIS near vertical incidence sky wave

OJT on-the-job training

OPORD operation order

OP Operator

OWR one-way reversible

PEP peak envelope power

PMCS preventive maintenance checks and services

PROSIGN procedure sign

PROWORD procedure word

PTT push-to-talk

RATT radio teletypewriter

rcvr receiver

RDF radio direction finding

REC radio electronic combat

RF radio frequency

RT Receiver/transmitter

RWI radio-wire integration (replaced by NRI)

SAT satellite

SED simulative-electronic deception

SF special forces

SFOB special forces operational base

SHF super high frequency

SID sudden ionospheric disturbance

SIGSEC signal security

SINCGARS single-channel ground and airborne radio subsystem

SO special operations

SOI signal operation instructions

SOP standing operating procedures

spt support

SSB single sideband

STANAG Standardization Agreement

sub subscriber

swbd switchboard

SWR standing wave ratio

tel telephone

TM technical manual

TMDE test, measurement, and diagnostic equipment

TRANSEC transmission security

TTY teletypewriter

USAREUR United States Army, Europe

UHF ultra high frequency

USB upper sideband

UW unconventional warfare

VHF very high frequency

VLF very low frequency

VSWR voltage standing-wave ratio

WPM words per minute

xmtr transmitter


Absorption. Removal of energy from a radiated field by objects which retain the energy or conduct it to ground. Loss by absorption reduces the strength of a radiated signal.

Addressee. The activity or individual to whom a message is to be delivered.

Agency of Signal Communication. A facility which has necessary personnel and equipment to provide signal communication.

Alternating Current (AC). Current that is continually changing in magnitude and periodically in direction from a zero reference level.

Amplification. The process of increasing the strength (current, voltage, or power) of a signal.

Amplifier. A device using an electron tube, transistor, magnetic unit, or other amplifying component that increases the strength of the input signal.

Amplitude. The level of an audio or other signal in voltage or current. The magnitude of variation in a changing quantity from its zero value.

Amplitude Modulation (AM). Modulation in which the amplitude of the carrier wave is varied above and below its normal value in accordance with the intelligence of the signal being transmitted.

Angle of Incidence. The acute angle (smaller angle) at which a wave of energy strikes an object or penetrates a layer of the atmosphere or ionosphere.

Antenna. A device used to radiate or receive electromagnetic energy (generally RF).

ANTIJAMMING. A device, method, or system used to reduce or eliminate the effects of jamming.

Audible. Capable of being heard.

Array (antenna). An arrangement of antenna elements, usually dipoles, used to control the direction in which most of the antenna's power is radiated.

Audio Frequency (AF). A frequency that can be heard as a sound by the human ear. The range is roughly from 15 to 20,000 Hz.

Authentication. A security measure designed to protect a communication system against fraudulent messages.

Automatic Frequency Control (AFC). A circuit used to maintain the frequency of an oscillator within specified limits.

Automatic Gain Control (AGC). A control circuit that automatically maintains a constant output of some amplitude despite variations in strength of the input signal.

Axis of Communication. The line or route on which lie the starting position and probable future locations of the command post of a unit during a troop movement. The main route along which messages are relayed or sent to combat units in the field.

Auzimuth. An angle measured in a horizontal plane from a known reference point.

Band. A range of frequencies between two definite limits.

Bandwidth. The width of a band of frequencies used for a particular purpose.

Beat Frequency. The resultant frequency obtained when signals of two different frequencies are combined in a circuit.

Beat Frequency Oscillator (BFO). An oscillator which produces a signal which mixes with another signal to provide sum and difference frequencies. Generally used to provide an audible signal for reception of CW transmissions.

Calibrate. A process in which an instrument or device is compared with and adjusted to an accurate standard.

Carrier Frequency. The frequency used by a communication channel to transmit intelligence between two or more distant locations.

Carrier Wave. The RF component of a transmitted wave upon which an audio signal, code signal, or other form of intelligence can be impressed.

Channel. An assigned band of frequencies for a radio or television over which transmissions can be made from one station to another.

Circuit. An arrangement of one or more complete paths for current flow.

Coaxial Cable. A transmission line consisting of two conductors, one inside the other, and separated by insulating material. The inner conductor may be a small copper tube or wire; the outer conductor may be metallic tubing or braid. Radiation loss from this type of line is very little.

Command Post (CP). The headquarters of a unit or subunit where the commander and staff perform their functions.

Communications Center. A communications agency charged with the responsibility for receipt, transmission, and delivery of messages. It normally includes a message center, a cryptocenter, transmitting facilities, and receiving facilities.

Communication Security. The protection resulting from all measures designed to deny to unauthorized persons information of value which might be derived from a study of communications.

Conductor (electrical). A wire, cable, or other object capable of carrying electric current. Good conductors are made of metals such as silver, copper, and aluminum.

Continuous Waves (CW). Radio waves having a constant amplitude and a constant frequency. An unmodulated RF signal from a radio transmitter. When properly keyed on and off, CW is used to transmit messages by international Morse code (IMC).

Counterpoise. A conductor or system of conductors used as a substitute for ground in an antenna system.

Coupling. The association of two or more circuits that permit energy transfer from one to the other.

Critical Frequency. The highest frequency at which a given wave at any given time will, if transmitted vertically, be refracted to earth by a layer of the ionosphere.

Cross Modulation. A type of crosstalk in which the carrier frequency being received is interfered with by an adjacent carrier, so that the modulated signals of both are heard at the same time.

Cryptocenter. An establishment maintained for the encrypting and decrypting of messages.

Crystal. A natural substance, such as quartz or tourmaline, that is used to control the frequency of radio transmitters.

Date-Time Group (DTG). The date and time, expressed in digits and zone suffix, when a message is prepared for transmission. The DTG is expressed as six digits followed by a zone suffix--the first pair of digits denotes the date, the second pair the hours, and the third pair the minutes.

Decibel (dB). The standard unit used to express transmission gain or loss and relative power levels. Also a unit used to measure and compare signal levels on a logarithmic scale.

Decibels Above or Below 1 Milliwatt (dBm). The unit used to describe the ratio of the power at any point in a transmission system to a reference level of l milliwatt.

Deflection. The displacement of an electron beam from its straight-line path.

Detection. The process of recovering the audio component (audible signal) from a modulated RF carrier wave.

Dielectric. An insulator. A term applied to the insulating material between the plates of a capacitor.

Dipole Antenna. An antenna having an electrical length equal to a half wavelength at the frequency for which it is designated. It may be a single conductor (rarely); but it generally consists of two elements, whose total length is one-half wavelength, separated by an insulator or an air space at the point of connection to the transmission line from the transmitter.

Direct Current (DC). An electrical current that flows in one direction.

Directional Antenna. An antenna designed to transmit and receive RF energy in a specific direction(s).

Discriminator. A circuit that has an output voltage which varies in amplitude and polarity in accordance with the frequency of the applied signal. It is used primarily as a detector in an FM receiver.

Distortion. The amount by which the output waveform differs from the input waveform. Distortion may exist in amplitude, frequency, or phase.

Diversity System. A system of radio communications in which a single received signal is derived from a combination of, or selected from, a plurality of transmission channels or paths. The system employed may include space diversity, polarization diversity, or frequency diversity. The diversity principle takes advantage of the fact that fading characteristics of a given signal generally vary widely, at any given instant, at different receiving antenna locations and with different frequencies.

Doppler Effect. The change in frequency due to a relative motion difference between source and observer.

Double Sideband Transmission. That method of communications in which the frequencies produced by the process of modulation are symmetrically spaced, both above and below the carrier frequency, and are all transmitted.

Dummy Antenna. An impedance device used in place of a regular antenna to prevent unwanted radiation or reception during testing or adjustment.

Dummy Load. A dissipative nonradiating device.

Duplex Operation. Duplex (or full duplex) operation refers to communications between two points, in both directions simultaneously.

Electromagnetic Field. The field of force that an electrical current produces around the conductor through which it flows.

Electromagnetic Wave. A wave propagating as a periodic disturbance of the electromagnetic field and having a frequency in the electromagnetic spectrum.

Facsimile. A system of radio or wire communications by which still pictures, illustrations, maps, or printed pages are transmitted and received. Type-A facsimile is a system in which images are built up of lines or dots of constant intensity. Type-B facsimile is a system in which images are built up of lines or dots of varying intensity.

Feedback. Returning a portion of the output of a circuit to its input. Negative (out-of-phase) feedback reduces gain and distortion. Positive (in-phase) feedback increases gain and can produce oscillation, both acoustical and electrical.

Fading. Variations in the strength of a radio signal at the point of reception.

Frequency. The number of complete cycles repeated in a given period, usually per second.

Frequency Band. A continuous range of frequencies extending between two limiting frequencies.

Frequency Distortion. Distortion caused by the unequal attenuation or gain of the frequencies present in a waveform.

Frequency Drift. The gradual change in frequency of an oscillator or transmitter.

Frequency, Lowest Useful High (LUF). The lowest high frequency effective at a specified time for ionospheric propagation of radio waves between two specified points.

Frequency, Maximum Usable (MUF). The upper limit of the frequencies that can be used at a specified time for radio transmission between two points and involving propagation by reflection from the regular ionized layers of the ionosphere.

Frequency Meter. A device that is calibrated to indicate the frequency of the radio wave to which it is tuned.

Frequency Modulation (FM). The process of varying the frequency of a carrier wave, usually with an audio frequency, in order to convey intelligence.

Frequency Spectrum Designation. VLF (very low frequency): below 30 kHz (0.03 MHz). LF (low frequency): 30 - 300 kHz (0.03 -0.3 MHz). MF (medium frequency): 300 - 3000 kHz (0.3 - 3 MHz). HF (high frequency): 3 - 30 MHz. VHF (very high frequency): 30 - 300 MHz. UHF (ultra high frequency): 300 - 3000 MHz. SHF (super high frequency): 3000 - 30,000 MHz (3 - 30 GHz). EHF (extremely high frequency): 30 - 300 GHz.

Full-Duplex Operation. Telegraph or signaling circuits arranged for transmission in both directions at the same time.

Fundamental Frequency. The lowest frequency of a complex wave.

Gain. The increase in signal strength that is produced by an amplifier.

Ground. A metallic connection with the earth to establish ground (or earth) potential.

Ground Wave. A radio wave that travels along the Earth's surface rather than through the upper atmosphere.

Half-Wave Antenna. An antenna whose electrical length is half the wavelength of the transmitted or received frequency.

Harmonic. A whole-number multiple of a fundamental frequency.

Hertz (Hz). The standard term used to state frequency. One hertz is the same as one cycle per second.

Hertz Antenna. A half-wave antenna which does not depend upon earth ground or ground plane to operate properly.

Heterodyne. To beat or mix two signals of different frequencies to produce two additional frequencies which are the sum and the difference of the two original signals.

Histogram. A graphical representation of a frequency distribution by a series of rectangles having for one dimension a distance proportional to a definite range of frequencies, and for the other dimension a distance proportional to the number of frequencies appearing within the range.

Horizontal Polarization. Transmission of radio waves in such a way that the electric lines of force are horizontal, parallel to the Earth's surface.

Image Frequency. An unwanted signal combining or beating with the local oscillator signal to form the intermediate frequency (IF). It is twice the frequency of the IF away from the desired signal on the opposite side of the local oscillator signal.

Impedance. The total opposition offered by a circuit or component to the flow of alternating current.

Impulse. Any force acting over a comparatively short period of time.

Indirect Wave. A wave received after being reflected from the layers of the ionosphere or from another reflective surface.

Induction. Process of inducing a current into a conductor by moving the conductor or the magnetic field.

Inductor - Coil. A device for introducing inductance into a circuit.

In Phase. The condition existing when two or more signals of the same frequency pass through their maximum and minimum values of like polarity at the same instant.

Insulator. A device or material that has a high electrical resistance.

Intensity. The strength of value of a current. The symbol I, for current, comes from this word.

Interference. Any undesired signal that tends to interfere with the desired signal.

Intermediate Frequency (IF). The fixed frequency to which the principal amplifier of a superheterodyne receiver is tuned. The intermediate frequency is produced by beating the received RF against the output of a variable frequency oscillator to produce a constant beat frequency. In some receivers, the IF is tunable over a limited range.

Ion. An atom that has more or less electrons than normal.

Ionosphere. Highly ionized layers of atmosphereexisting between the altitudes of approximately 48 to 402 kilometers (30 to 250 miles).

Jamming. Deliberate interference intended to prevent reception of signals in a specific frequency band.

Keying. The breaking or interrupting of a radio carrier wave (either manually or automatically).

Kilometer (km). One thousand meters, which is approximately equal to 3,280 feet. To convert kilometers to miles, multiply kilometers by 0.6214. To convert miles to kilometers, multiply miles by 1.6093.

Limiter. A circuit that limits the output amplitude to some predetermined value.

Load. A device that consumes electrical power.

Local Oscillator. An oscillator that is part of the receiver and is used to generate an RF output which is combined with the incoming RF signal to produce an intermediate frequency.

Loop Antenna. An antenna consisting of one or more complete turns (loops) of wire. It is designed for directional transmission or reception.

Marconi Antenna. An antenna system in which the ground is an essential part.

Means of Signal Communication. A medium by which a message is conveyed from one person or place to another.

Message. Any thought or idea expressed in brief form or in plain or secret language and prepared in a form suitable for transmission by any means of communication.

Micro. A prefix representing one-millionth (abbreviated u).

Milli. A prefix representing one-thousandth (abbreviated m).

Modem. Acronym for MOdulator-DEModulator. Modems are primarily used for converting digital signals into analog signals for transmission and reception and for reconverting the analog signals into digital signals for processing.

Modulate. To mix two or more signals to produce another signal; to vary or change the amplitude, frequency, or phase of the signals to be modulated.

Network. A system consisting of a number of designated stations connected with one another by any means of communication.

Null. The absence of a signal, information, indication, or deflection.

Ohm. The basic unit of electrical resistance.

Originator. The command by whose authority a message is sent. The responsibility of the originator includes the responsibility for the functions of the drafter and releasing officer.

Out of Phase. Two alternating quantities are out of phase when they do not pass through corresponding values at the same time. For example, if the current in a circuit reaches its maximum value before or after the applied voltage does, the current is out of phase with the voltage.

Phase. The difference in time or electrical degrees measured from the beginning of a cycle to any point on the same cycle. A full cycle is considered as having 360 electrical degrees.

Power. The rate of doing work or the rate of expending energy. Unit of electrical measurement is the watt.

Propagation. The travel of electromagnetic waves through space or along a transmission line.

Quarter-Wave Antenna. An antenna with an electrical length that is equal to one-quarter wavelength of the signal being transmitted or received.

Radiate. To transmit RF energy.

Radio Channel. A band of adjacent frequencies having sufficient width to permit its use for radio communication.

Radio Frequency (RF). Any frequency of electrical energy capable of propagation into space. Usually above 20 kHz.

Radio Wave. Electromagnetic waves at a frequency lower than 3000 GHz and propagated through space without an artificial guide.

Rear Echelon. That part of a headquarters which is principally concerned with administrative and logistical matters.

Reflection. The turning back of a radio wave from an object or the surface of the Earth.

Refraction. The bending, or change in direction, of a radio wave passing into a layer of atmosphere or the ionosphere.

Relay. A transmission forwarded through an intermediate station.

Rig. A term (jargon) used by communicators to designate their communications or other equipment. Example: "What rig are you using for NRI?"

Saturation. The condition of a circuit when an increase of the input causes no further increase in the output.

Selectivity. The characteristic that determines the ability of a radio receiver to discriminate between signals of different carrier frequencies.

Sensitivity. The degree, or amount of response, that a circuit has to signals to which it is tuned (related to signal strength).

Sideband. A band of frequencies created by the modulation process located on each side of the carrier frequency.

Sideband Power. The power contained in the sidebands. It is this power to which a receiver responds (not to the carrier power) when receiving a modulated wave.

Single Sideband. A system of radio communications in which the carrier and either the upper or lower sideband is removed from AM transmission to reduce the channel width and improve the signal-to-noise ratio.

Skip Distance. The distances on the Earth's surface between the points where a radio sky wave leaves the antenna and is successfully reflected and/or refracted back to Earth from the ionosphere.

Skip Zone. The space or region within the transmission range where signals from a transmitter are not received. It is between the end of the ground wave and the point where the refracted wave returns.

Standing-Wave Ratio (SWR). The ratio of the maximum to minimum amplitudes of voltage, or current, along a waveguide or transmission line.

Static. Sharp, short bursts of noise on a radio receiver caused by electrical disturbances in the atmosphere or by electrical machinery.

Tone Modulation. A type of transmission obtained by causing the RF carrier amplitude to vary at a fixed AF rate. When the type of transmission is keyed, it becomes modulated continuous wave (MCW).

Transceiver. A combined radio transmitter and receiver made as a single unit, generally used for portable or mobile applications. Some or all of the stages and components are used for both transmitting and receiving. Switches are used to change from transmit to receive or from receive to transmit.

Transmission Line. Any conductor or system of conductors used to carry electrical energy from its source to its load.

Transmitter. A radio transmitter is a piece of equipment that generates and amplifies a radio frequency signal, adds intelligence to this signal, and then sends it out into the air as a radio frequency wave.

Tuning. The process of adjusting a radio circuit so that it resonates at the desired frequency.

Unidirectional. In one direction only.

Vernier. Any device used to make a fine adjustment.

Voltage. A term used to designate electrical pressure that exists between two points.

Voltage Standing-Wave Ratio (VSWR). The ratio of the amplitude of the electric field or voltage at a voltage maximum to that at an adjacent voltage minimum.

Wavelength. The distance a wave travels during one complete cycle. It is equal to the velocity divided by the frequency.

Wave Propagation. The transmission of RF energy through space.

Zero Beat. The point of complete silence reached when two frequencies being mixed are exactly the same.

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