Glossary

A

Active Antenna Describes a high gain antenna that is short in length. These are useful where space is at a premium and commonly used on shortwave frequencies below 30 MHz

ADC Analog to Digital Converter.

AGC Automatic gain control.

AM, Amplitude Modulation Varying, by modulation, the transmitter power output in line with the modulating audio signal variation.

Amplification The process by which the strength of a signal is increased. Both radio and audio signals can be amplified.

Attenuator Circuit that reduces receiver sensitivity in fixed steps. These fixed steps are measured in decibels.

Attenuation Blocking radio waves.

Attenuation Coefficient The amount of power absorbed by a dielectric. A low attenuation coefficient will allow radio waves to easily pass through the material.

B

Band Pass Filter Filter that allows a specified ranges of frequencies through, while rejecting those that are not within the specified range. Usually constructed by combining a high pass and low pass filter.

Bandwidth The frequency space which is occupied by a radio signal.

Bank A scanner bank is a way to organize channels. They allow for grouping a set of channels into logical banks.

Baud Measured in bits per second, the rate data is transmitted.

Beam Antenna Antenna, used outdoors, that receives best from a certain direction.

Beat Frequency Oscillator, BFO Circuit in a receiver that enables reception of SSB signals by generating a replacement carrier.

BCB See Broadcast Band.

Birdie Birdies are spurious radio signals created by the internal electronics in a scanner. These signals have no sound or static however will stop the scanner in its search mode. The average scanner will have four or five birdies.

BNC Common antenna connector which locks in place by being twisted.

Broadcast Band, BCB Also known as AM, BCB is the frequency range between 540 and 1700 kHz. This is the AM band on your car radio.

C

Carrier A radio transmitter’s unmodulated output.

Center Frequency In an FM transmitter, the unmodulated carrier frequency.

Channel Frequency where radio transmission occurs. May also describe the input and output frequencies of a repeater or the location where a frequency is stored in a scanner’s memory.

Coaxial cable, Coax An electrical cable specifically designed to transmit RF energy. In a coax cable the inner conductor surrounded by a flexible insulating layer which is then surrounded by a tubular conducting shield. Invented in 1880.

Cochannel Interference When frequencies adjacent to the signal cause undesired interference.

Act of 1934 The Communications Act of 1934 combined and organized federal regulation of telephone, telegraph, and radio communications. The Act created the Federal Communications Commission (FCC) to oversee and regulate these industries. As new communications technologies have been created, such as broadcast, cable, and satellite television, new provisions governing these communications have been added to the Act.

Conductor Matter that transfers electrical and radio waves.

Coordinated Universal Time Previously known as Greenwich Mean time.

Counter See Frequency Counter.

Critical Angle The angle at which radio signals refract in the Earth’s ionosphere. Measured in reference to the Earth’s surface. Lower angles allow for greater distance of travel by way of ionospheric refraction.

CTCSS Continuous Tone-Coded Squelch System (CTCSS) also known as tone squelch, is designed to allow users on a shared frequency to hear only users in their user group. Each group is assigned its own squelch tone, and the radio only plays to the audio when the squelch tone is transmitted. The transmitter adds a unique sub-audible code to the transmission

Cutoff Frequency The frequency where a filter will reject signals.

D

D-layer Approximately 25-50 miles above Earth’s surface, the D-Layer is the lowest region of the Ionosphere. The D-Layer absorbs signals passing through it. The D-Layer disappears soon after sunset, and on short days may not form.

DAC Digital to Analog Convertor

dB, decibel A measurement of sound defined by a logarithmic scale between power levels. 3 decibel increase is equivalent to double the power, while 20 dB increase is 100 times the power.

DCS Digital Coded Squelch. Digital version of CTCSS.

Dead Zone Area where radio reception of a signal is not possible due to difficulties in propagation.

DECT Digital Enhanced Cordless Telecommunications is a digital communications standard used by cordless telephones.

Delay The length of time for which a scanner pauses after a transmission ends before moving on to the next channel.

Dielectric Matter that insulates radio waves. Generally nonmetallic matter.

Dipole Antenna made up of two wires connected in a straight line. One wire connects to the radio and other wire connects to group. Usually made to operate best on a specific frequency. Commonly used as a base antenna.

Discone An omnidirectional, vertically polarized antenna with a disc shape. Discone antennas are broadband antennas (able to receive a wide range of frequencies) that are generally base-mounted.

Output Provides access to the unfiltered audio signal from a radio. This is often required to decode data signals over 1200 Baud.

Communication Communication between stations without using a repeater.

Direct Wave Radio signal propagated by line of sight.

Drift Gradual frequency change in a transmitter or receiver. Commonly occurs when the temperature of a radio changes.

Duplex Transmission and reception occur on separate frequencies, functions like a telephone, allowing simultaneous talk on both ends.

Dynamic Range A description of a receiver’s ability to receive strong signals without being overloaded.

E

E-Layer 50 to 90 miles above the Earth, the E-Layer is a part of the Ionosphere. The E layer absorbs energy from signals that pass through it. Several hours after the sun sets, the E-Layer disappears. This is why AM broadcast stations must lower transmission power at night.

Effective Radiated Power, ERP Output of a transmitter multiplied by the gain of the attached antenna.

F

F-layer Responsible for most long distance propagation below 30 MHz, the Ionosphere is the region of the Earth’s atmosphere approximately 90 to 400 miles above the surface. Solar heating can cause the F-Layer to split into the F1 and F2 Layers.

Feedline Cable that connects the radio to the antenna.

Filter Allows certain frequencies to pass and rejects other frequencies. May be a device or a circuit.

Flutter Commonly caused by variations in propagations, flutter is the rapid variation in a station’s signal strength.

Frequency Modulation, FM Modulation which varies the carrier frequency of the transmitter according to strength variations in the modulating signal.

Frequency When used in the context of radio, is the number of times that a wave occurs in a set amount of time. Measured in hertz.

Frequency Counter A device used for measuring the frequency of a radio wave. Can be used to identify the frequency used by a transmitter.

Frequency Step The intervals of frequency that the tuner changes when adjusted.

G

Gain When an antenna appears to increase the signal transmitted or received., gigahertz: Unit of measurement for radio frequency waves equal 1000 megahertz or 1,00,000 kilohertz or 1,000,000,000 Hertz

Ground A wired connection, usually to the Earth, to a zero voltage point.

Ground wave A radio wave which propagates along the Earth’s surface.

H

Harmonic Frequencies that are multiple of a lower frequency.

HF, High Frequencies 3 to 30 MHz. Note: HF is commonly used to refer to 1.7-30 MHz

High Pass Filter A high pass filter allows frequencies above a specified point through, and rejects those below that point. See also Low Pass Filter.

Polarization Antenna that receives or transmits best radio waves with an electrical field parallel to Earth’s surface.

Hz, Hertz Frequency is measured in Hertz. Hertz denotes the number of cycles per second in radio frequency, with one Hertz denoting one cycle passing per second.

I

Image False signal when produced by circuitry within the receiver.

Indirect FM See phase modulation.

Input Frequency When used in the context of repeaters, describes the frequency the repeater listens to and retransmits signals received on this frequency.

Intermodulation, Intermod Spurious or false signals. Occur when multiple signals mix in a receiver or repeater.

Ionosphere The region approximately 40 to 400 miles above the Earth’s surface. This electrically charged region refracts radio signals.

K

Key Up Slang term for pressing the push to talk (PTT) switch on the radio so items said into the microphone will be transmitted.

kHz, Kilohertz 1000 Hertz

L

Law of Inverse Squares The signal strength of a radio wave is inversely proportional to the square of the distance from the source. Because of signal strength does no grow in a linear fashion the closer you get to a transmitter. Instead signal strength will dramatically increase the closer you get to a transmitter.

Line of Sight As the name implies, communication between two stations that are within sight of each other.

Lockout A scanner feature that allows for the exclusion of specified channels from the scanning sequence. Can also be applied to the search feature on a scanner to exclude specific frequencies from the search sequence.

Low Pass Filter Filter of circuit that allows frequencies below a defined point through, and rejects frequencies higher than the defined point. See also High Pass Filter.

LSB, Lower Sideband Lower frequency sideband that transmitter carrier. See Single Sideband Modulation.

Low Threshold How weak a signal the radio is able to pick up. Used to determine the sensitivity of a radio.

Lowest Usable Frequency, LUF The lowest frequency that propagate between two points.

LTR Logic Trunked Radio, or LTR, systems use a transmission protocol developed by the E.F. Johnson company. LTR is used primarily in single site applications.

M

Maximum Usable Frequency, MUF The highest frequency that can propagate between points.

Medium Wave Often used to describe any AM signal (540 hHz to 1700 kHz) Medium wave is technically signals between 300 to 3000 kHz.

MHz, Megahertz 1,000,000 hertz, 1000 kilohertz.

Modulation Altering the output carrier of a transmitter to encode information into a radio wave. Frequency Modulation (FM) is the most popular types of analog modulation used over 30 MHz.

Monoband Antenna Antenna designed to operate on only one frequency band.

Multiband Antenna Antenna designed to operate on multiple frequency bands.

Multihop Describes a signal that is refracted multiple times between transmission and reception.

Multipath occurs when the signal from a transmitter is bounced around enough that it arrives at the receiver at different times; the signals arrive at different points in the phase. Also known as Ghosting.

N

Notch Filter Combines high and low pass filters and only allows a small section of the spectrum through.

O

Omnidirectional Antenna Describes an antenna can transmit and receive in all directions equally.

Output Frequency In the context of repeaters, the frequency on which the repeater will retransmit received signals on.

Overloading Interference causing false signals. Caused by strong signals within the frequency range.

P

Passband Tuning A receiver feature which allows the user to adjust bandpass to get the best reception based on interference.

Path Route a signal takes from the transmitter to the receiver.

Phase Locked Loop (PLL) Circuit which generates a large range of frequencies in discreet intervals.

Phase Modulation (PM) Much like FM, PM varies transmission carrier frequency in proportion to strength and frequency of the modulating signal.

Phonetic Alphabet Words used to represent letters of the alphabet to prevent confusion/misunderstanding.

Polarization Describes whether an antenna transmits or receives best in a vertical or horizontal plane.

POTS Plain Old Telephone Service. Voice grade telephone service.

Preamplifier, Preamp Receiving circuit, which can amplify weak signal. Note that a preamp will often create background noise and may cause signal distortion.

Priority Channel In scanners, the priority channel is a user defined channel to which the scanner will check for activity more frequently or immediately switch if a signal is present.

Propagation Describes the process of a radio signal traveling from transmitter to receiver.

Q

Quad A type of directional antenna made up of two wire squares, each one wavelength, a quarter wavelength apart.

R

Repeater a device that receives a signal and retransmits it, usually at a higher strength, helping radios cover a larger geographical area.

Resonance when an electric signal can travel from one end of a wire and back in the period of one cycle of the RF frequency

Resonant Frequency The frequency where an antenna best receives or radiates.

RF Gain Control that continuously varies receiver sensitivity.

Rubber Duck (Rubber Ducky) A type of antenna, the rubber duck is an electrically short monopole antenna which is sealed in a rubber housing. There is debate as to where the name rubber duck originated.

S

S-Meter A graph that shows the relative strength of a signal at reception.

Scanner a radio receiver that switches between multiple channels or frequencies, stopping when there is activity on the channel or frequency.

Scatter When a signal scatters directly from the ionosphere.

Search A feature of scanners and some other receivers that scans a frequency at set intervals and stops when a signal is present. Useful for finding transmitters in a set frequency range.

Selectivity the ability of the unit to pull a signal out of a noisy environment, or in other words, the ability to select between two signals that are close together on the spectrum. Selectivity depends primarily on the phase noise of the synthesizer and associated circuitry

Sensitivity Describes how well a receiver can pick up weak signals, measured in microvolts.

Shortwave Commonly used to describe frequencies between 1.7 to 30 MHz, shortwave is technically 3 to 30 MHz.

Single Sideband Modulation, SSB An analog modulation types popular below 30 MHz. When an AM signal is generate it has twice the bandwidth of the input (baseband) signals. SSB cuts this AM signal in half by removing one of the side bands and transmits only one side of the signal, because of the way AM signals are generated the entire signal can be reproduced with only one side band. Depending on the side band transmitted it can either be an USB (Upper Sideband) and LSB (Lower Sideband).

Simulcast In a multi-site trunked system all traffic is repeated across all sites in a trunked system regardless of which talk groups are using the site at the time.

Simplex Transmission and reception occur on the same frequency.

Skip Describes sky wave propagation that occurs by Ionospheric refraction. See Sky Wave.

Sky Wave Describes when radio waves are refracted by the ionosphere. This is what allows AM stations to be heard far away.

SMA A type of standard antenna connector used for coaxial connections.

SmartZone In a multi-site trunked system traffic to specific talk groups are only broadcast by site where that talk group is present.

Spectrum, Radio Electromagnetic spectrum from about 3 kilohertz to about 300,000 megahertz

Spectrum Analyzer A device that analyzes the frequency response, distortion and noise of radio frequencies.

Spread Spectrum Modulation types that incorporate methods that spread a signal over a chunk of the spectrum to make better use of the bandwidth and avoid interference.

Spurious False signals that occur by over amplifying a signal, overloading part of the radio or are generated by the internal circuits of the radio. Birdies are examples of spurious signals generated by the internal circuits in a radio.

Squelch A feature in scanners and other radios that silences the receiver until received signal strength exceeds a predetermined threshold.

SSB Single Side Band Modulation.

Super High Frequencies, SHF Frequency range over 3000 MHz.

Surface Wave See Ground Wave.

T

Terminal Node Controller, TNC TNC converts digital signals from a computer into analog signals for radio transmission, and vice versa.

Tone Access Activation of a repeater with a predetermined tone or tone sequence. The tone must be received before the repeater relays any transmissions.

Trap Dipole A type of dipole antenna which has multiple coils, also known as traps, that allow the antenna to be effective on multiple bands.

Troposheric Ducting occurs when cold and warm air streams meet about 2 kilometers, or approximately 1.25 miles above the Earth. This phenomenon, which is often see during the summer and usually lasts about an hour at a time, creates a “pipe” that allows signals to travel great distances.

Trunking Radio system using several channels or frequencies, and allows those channels to be shared by a large number of users, in multiple talkgroups, without their conversations interfering with each other. Trunked systems use a control channel, called the trunk, which transmits data packets which allow a talkgroup to carry on a conversation by telling members of a talk group which frequency to communicate on when they key up.

Tuner Part of a receiver where the signal from the antenna is selected at a specific frequency from other radio wave.

U

UHF Ultra High Frequency. UHF is the frequency range from 300 MHz and 3 GHz (3,000 MHz)

UHF Low 450-470 MHz

UHF-T 470-512 MHz

Unity Gain Antenna with effective radiated power equal to the transmitter power. Does not have gain or loss

USB, Upper sideband Higher frequency sideband that transmitter carrier. See Single Sideband Modulation.

UTC, Universal Coordinated Time See Zulu Time.

V

Vertical Polarization Antenna that best receives radio waves with an electric field that is perpendicular to the Earth’s surface.

VHF Very High Frequency. VHF is the frequency range from 30-300 MHz.

VHF High band The range of VHF from 150 to 175 MHz.

VHF low band The range of VHF from 30 to 50 MHz.

VOX A VOX circuit powers a transmitter on and off automatically when it detects someone speaking into it.

W

Wavelength The wavelength of a frequency is the distance over which the shape repeats.

Y

Yagi A Yagi antenna, short for Yagi-Uda, is type of directional antenna.

Z

ZigBee A low-power consumption protocol for wireless control and monitoring of devices such as light switches and HVAC. ZigBee is becoming more prevalent, especially in green buildings.

Zulu Time Zulu, which is Z in the phonetic alphabet, is used to describe Coordinated Universal Time, or UTC.