A primary service area is the geographic region served by a radio station.

A tropospheric wave is a radio wave that is propagated by reflection from a place of abrupt change in the dielectric constant, or its gradient, in the troposphere.

An electric current that reverses direction in a circuit at regular intervals.

Amateur radio, commonly called "ham radio", is a hobby enjoyed by many people throughout the world (as of 2004 about 3 million worldwide, 70,000 in Germany, 5,000 in Norway, 57,000 in Canada, and 700,000 in the USA). A holder of an Amateur Radio licence has studied and passed required tests in his or her country and been issued a call sign by its government. This call sign is unique to the operator and is often a source of pride. The holder of a call sign uses it on the air to legally identify all voice and data communications. Amateur Radio should not be confused with CB radio, General Mobile Radio Service or Family Radio Service which are limited to voice operation, allowed lower power limits, fewer frequency allocations, and are unlicensed in most countries.

Ambient noise level is the level of acoustic noise existing at a given location, such as in a room, in a compartment, or at a place out of doors.

A unit of electric current in the meter-kilogram-second system. It is the steady current that when flowing in straight parallel wires of infinite length and negligible cross section, separated by a distance of one meter in free space, produces a force between the wires of 2 ? 10-7 newtons per meter of length.

1. The encoding of a carrier wave by variation of its amplitude in accordance with an input signal.
2. A broadcast system that uses amplitude modulation.

Of a periodic signal, pertaining to transmission in which the time interval separating any two corresponding transitions is not necessarily related to the time interval separating any other two transitions.

A metallic apparatus for sending or receiving electromagnetic waves.

Antenna noise temperature is the temperature of a hypothetical resistor at the input of an ideal noise-free receiver that would generate the same output noise power per unit bandwidth as that at the antenna output at a specified frequency.

Arbitron is a radio audience research company in the United States. It collects data on radio audiences similar to the data collected by Nielsen Media Research on television audiences.

The transmission of data in which each character is a self-contained unit with its own start and stop bits. Intervals between characters may be uneven. It is the common method of transmission between a computer and a modem, although the modem may switch to synchronous transmission to communicate with the other modem. Also called "start/stop transmission."

AGC is an electronic system found in many types of devices. Its purpose is to control the gain of a system in order to maintain some measure of performance over a changing range of real world conditions.

Radio wave propagation in which the direction of the incident and scattered waves, resolved along a reference direction (usually horizontal) are oppositely directed. A signal received by backscattering is often referred to as "backscatter."

Extraneous noise contaminating sound measurements that cannot be separated from the desired signal.

Refers to a cable design that uses the same wire types for the signal and ground. Twisted pair cable is a balanced line.

A specific range of wavelengths or frequencies of electromagnetic radiatio.

1. The numerical difference between the upper and lower frequencies of a band of electromagnetic radiation, especially an assigned range of radio frequencies.
2. The amount of data that can be passed along a communications channel in a given period of time.

The transmission of two or more messages from one station to another without intervening responses from the receiving station.

In bit-stream transmission, the bits usually occur at fixed time intervals, start and stop signals are not used, and the bit patterns follow each other in sequence without interruption.

Transmission that combines a very high data signaling rate with very short transmission times - i.e. the message is compressed. This is popular with the military and spies, who wish to minimise the chance of their radio transmissions being detected.

In satellite communications, the ratio of the received carrier power to the receiver noise power density.

In satellite communications, the ratio of the received carrier power to the receiver noise power density.

The ratio of the channel noise at any point in a transmission system to an arbitrary level chosen as a reference.

At any point in a transmission system, the ratio of the circuit noise at that point to an arbitrary level chosen as a reference.

A radio-frequency band officially allocated for private radio communications.

A cable consisting of a conducting outer metal tube enclosing and insulated from a central conducting core, used for high-frequency transmission of telephone, telegraph, and television signals. Also called coaxial line.

The establishment of the Federal Communications Commission (FCC) in 1934, the regulatory body for interstate and foreign telecommunications. Its mission is to provide high-quality services at reasonable cost to everyone in the U.S. on a nondiscriminatory basis.

A composite cable is a communications cable having both optical and metallic signal-carrying components.

Emitting or capable of emitting continuously; not pulsed: a continuous wave laser; continuous wave radar.

Radio-frequency radiation originating outside Earth's atmosphere, such as that originating from sunspots.

In radio propagation by way of the ionosphere, the limiting frequency at or below which a wave component is reflected by, and above which it penetrates through, an ionospheric layer.

The free-space wavelength that corresponds to the critical frequency.
Note: The critical wavelength is equal, in meters, to the speed of light (3 ? 108 m/s) divided by the critical frequency in hertz.

A unit used to express relative difference in power or intensity, usually between two acoustic or electric signals, equal to ten times the common logarithm of the ratio of the two levels.

An effect--lasting from several minutes to several hours--that causes electromagnetic sky wave signals to disappear rapidly as a result of greatly increased ionization in the ionosphere caused by increased noise from solar storms.

The reduction or elimination of government power within a particular industry. Deregulation is usually enacted to create more competition within an industry.

One that detects, especially a mechanical, electrical, or chemical device that automatically identifies and records or registers a stimulus, such as an environmental change in pressure or temperature, an electric signal, or radiation from a radioactive material.

A digital transmission group is a group of digitized voice or data channels or both with bit streams that are combined into a single digital bit stream for transmission over communications media.

An antenna, usually fed from the center, consisting of two equal rods extending outward in a straight line.

An electrical current that travels in one direction and used within the computer's electronic circuits.

A directional coupler is a transmission coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line.

A directional coupler is a transmission coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line.

Diurnal phase shift is the phase shift of electromagnetic signals associated with daily changes in the ionosphere.

Transmission in which (a) the frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier and (b) the carrier level is reduced for transmission at a fixed level below that which is provided to the modulator.

In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or in a room, by the walls. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound.

In telecommunications, effective input noise temperature is the source noise temperature in a two-port network or amplifier that will result in the same output noise power, when connected to a noise-free network or amplifier, as that of the actual network or amplifier connected to a noise-free source.

Of a transmission medium, its length expressed as a multiple or submultiple of the wavelength of a periodic electromagnetic or electrical signal propagating within the medium.

The path traversed by electromagnetic waves that is not subject to reflection or refraction by the atmosphere.

An equivalent noise resistance is a quantitative representation in resistance units of the spectral density of a noise-voltage generator

In telecommunication, equivalent pulse code modulation noise (PCM) is the amount of thermal noise power on a frequency-division multiplexed (FDM) or wire channel necessary to approximate the same judgment of speech quality created by quantizing noise in a PCM channel.

The Federal Communications Commission (fcc.gov) is the U.S. government agency that regulates interstate and international communications including wire, cable, radio, TV and satellite.

A filled cable is a cable that has a nonhygroscopic material, usually a gel, inside the jacket or sheath.

In a noise-measuring set, a noise weighting based on an amplitude-frequency characteristic that is flat over a frequency range that must be stated.

The FM improvement factor is the quotient obtained by dividing the signal-to-noise ratio (SNR) at the output of an FM receiver by the carrier-to-noise ratio (CNR) at the input of the receiver.

The FM improvement threshold is the point in an FM (frequency modulation) receiver at which the peaks in the RF signal equal the peaks of the thermal noise generated in the receiver.

Frequency modulation (FM) is a method of impressing data onto an alternating-current (AC) wave by varying the instantaneous frequency of the wave.

Pronounced "fraynel zone." The pattern of electromagnetic radiation that is created by a transmitting station from its antenna to receiving antennas. It is in the shape of an ellipsoid, or 3D ellipse, which looks like an elongated football.

A measure of the thermal noise generated in the first stage of a receiver.

Having the ability to originate, produce, or procreate.

A radio wave that travels along the surface of the earth.

The group velocity of a wave is the velocity with which the overall shape of the wave's amplitude (known as the envelope of the wave) propagates through space.

see Amateur Radio

A radio frequency in the range between 3 and 30 megahertz.

Noise that is present in a communications channel when no signals are applied.

A region of the earth's atmosphere where ionization caused by incoming solar radiation affects the transmission of radio waves. It extends from a height of 70 kilometers (43 miles) to 400 kilometers (250 miles) above the surface.

Isochronous burst transmission is a method of data transmission. In a data network where the information-bearer channel rate is higher than the input data signaling rate, transmission is performed by interrupting, at controlled intervals, the data stream being transmitted.

In electromagnetic wave propagation, the knife-edge effect is a redirection by diffraction of a portion of the incident radiation that strikes a well-defined obstacle such as a mountain range or the edge of a building.

A communications cable, as one used to transmit telephone or telegraph signals.

An unobstructed path between sending and receiving antennas.

In telephone systems nomenclature a long line is a transmission line in a long-distance communications network such as carrier systems, microwave radio links, geosynchronous satellite links, underground cables, aerial cables and open wire, and submarine cables.

Hardware or software device which feeds the incoming signal or data back to the sender.

A radio frequency in the range from 30 to 300 kilohertz.

Low-power broadcasting is the at very low power and low cost, to a small community area. These stations tend to serve small towns in rural areas in the United States, and neighborhoods in cities. In the U.S., the FCC re-legalized LPFM licenses in 1999, after the NAB, CPB, and NPR convinced them to stop issuing the FM class D license in 1978, which forced many stations off the air. The Prometheus Radio Project is an advocacy group for LPFM and continues to lobby the FCC to extend the low-power FCC program to cities.

A disturbance or fluctuation in the earth's magnetic field, associated with solar flares.

Maximum usable frequency (MUF) describes, in radio transmission, using reflection from the regular ionized layers of the ionosphere, the upper frequency limit that can be used for transmission between two points at a specified time. This index is especially useful in regards to shortwave transmissions.

In communications, medium is an intervening substance through which a message or information is transmitted or carried on. In art, medium is a specific kind of artistic technique or means of expression or the materials used in a specific artistic technique.

A radio frequency or radio-frequency band in the range 300 to 3,000 kilohertz.

Micropower radio, or microcasting, is a term for low-power broadcasting. Instead of covering a wide area by broadcasting, trasnmitters cover a smaller area such as a neighborhood or town by microcasting. In the US, the FCC requires licensed AM/FM radio and TV stations to transmit with at least 6000 watts of power, making the cost of setting up a radio station prohibitive for individuals and small communities. That changed in 1999 with a low-power FM program that allowed a few hundred micropowered radio stations in rural communities. A movement is currently trying to pressure the FCC to allow low-power FM microcasts in more urban communities.

In an optical communications link, phase jitter of the signal caused by the combined effects of mode hopping in the optical source and intramodal distortion in the fiber.

Refers to a radio signal that winds up taking two or more paths because the signal is reflected off buildings or other obstructions. Although multipath is a problem with all kinds of radio transmission, ghosts on a TV channel are an example of multipath that you can see with your own eyes.

In the study of diffraction and antenna design, the near field is that part of the radiated field that is within a small number of wavelengths of the diffracting edge or antenna. The part of the radiated field that is beyond this is known as the far field.

New media usually refers to a group of relatively recent mass media based on new information technology. Most frequently the label would be understood to include the Internet and World Wide Web, video games and interactive media, CD-ROM and other forms of multimedia popular from the 1990s on.

In general usage, noise can be considered data without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. Noise is still considered information, in the sense of Information Theory.

A flexible optically transparent fiber, usually made of glass or plastic, through which light can be transmitted by successive internal reflections.

An electronic circuit used to generate high-frequency pulses.

Transmitting one or more bytes at a time using a cable with multiple lines dedicated to data.

A path profile is a graphic representation of the physical features of a propagation path in the vertical plane containing both endpoints of the path, showing the surface of the Earth and including trees, buildings, and other features that may obstruct the radio signal.

Rapid, short-term, random fluctuations in the phase of a wave, caused by time domain instabilities.

In a spread spectrum system, the process gain (or 'processing gain') is the ratio of the spread bandwidth to the unspread bandwidth. It is usually expressed in decibels (dB).

A man-made or natural physical feature that lies near enough to a radio path to cause a measurable effect on path loss, exclusive of reflection effects.

The wireless transmission through space of electromagnetic waves in the approximate frequency range from 10 kilohertz to 300,000 megahertz.

The August 13, 1912 was an "Act to regulate radio communication." This was the first act in the United States to require radio stations to be licenced--the earlier ship acts only required that certain ships to have radio equipment installed.

The Radio Act of 1927 (signed into law February 23, 1927) made almost no mention of the radio networks that were in the process of dominating radio. The only mention of radio networks was vague: The Commission {the Federal Radio Commission} shall "Have the authority to make special regulations applicable to stations engaged in chain broadcasting." Advertising was mentioned in the act with only slightly more authority than networking; merely requiring advertisers to identify themselves: "All matter broadcast by any radio station for which service, money, or any other valuable consideration is directly paid, or promised to, or charged to, or accepted by, the station so broadcasting, from any person, firm, company, or corporation, shall at the time the same is so broadcast, be announced as paid for or furnished as the case may be, by such person, firm, company, or corporation."

The calculated or measured noise power, within the bandwidth being used, at the receive end of a circuit, channel, link, or system.

A device, such as a part of a radio, television set, or telephone, that receives incoming radio signals and converts them to perceptible forms, such as sound or light.

Reference noise is the magnitude of circuit noise chosen as a reference for measurement.

The turning or bending of any wave, such as a light or sound wave, when it passes from one medium into another of different optical density.

A principle, rule, or law designed to control or govern conduct.

In telecommunication, relative transmission level is the ratio of the signal power, at a given point in a transmission system, to a reference signal power.

In telecommunication, return loss is the ratio, at the junction of a transmission line and a terminating impedance or other discontinuity, of the amplitude of the reflected wave to the amplitude of the incident wave.

Broadcasting radio programs in digital format via satellites. XM Satellite Radio (www.xmradio.com) and Sirius Satellite Radio (www.siriusradio.com) are the two major players in this arena with their own satellites. Satellite radio offers 120 channels of digital audio (music, news, sports, etc.), and unlike terrestrial digital radio (DAB), the signal stays tuned no matter where you travel within the U.S.

A receiver that continuously broadcasts signals it detects from specified radio frequencies.

The dispersal of a beam of particles or of radiation into a range of directions as a result of physical interactions.

Transmitting data one bit at a time.

The attenuation caused to a radio signal by obstructions in the propagation path.

Either of the two bands of frequencies, one just above and one just below a carrier frequency, that result from modulation of a carrier wave.

The ratio of the power or volume (amplitude) of a signal to the amount of unwanted interference (the noise) that has mixed in with it. Measured in decibels, signal-to-noise ratio (SNR or S/N) measures the clarity of the signal in a circuit or a wired or wireless transmission channel.

Single-sideband transmission (SSB) is a method of transmitting audio based on amplitude modulation in which only one sideband is transmitted. Essentially, the carrier and one sideband of an AM signal are removed, leaving only the other sideband. Assuming both sidebands are symmetric, no information is lost in the process. The required signal bandwidth is reduced and, since the final RF amplification is concentrated in a single sideband, effective power output is greater than normal AM. The carrier and redundant sideband account for well over half of the power output of an AM transmitter.

A skip zone is an annular region within the transmission range of an antenna, within which signals from the transmitter are not received.

A radio wave that travels upward.

The white specks on a television screen resulting from weak reception.

The range of electromagnetic radiation (electromagnetic waves) in our known universe, which includes visible light. The radio spectrum, which includes both licensed and unlicensed frequencies up to 300GHz has been defined worldwide in three regions: Europe and Northern Asia (Region 1); North and South America (Region 2), and Southern Asia and Australia (Region 3). Some frequency bands are used for the same purpose in all three regions while others differ. Frequencies above 40GHz have not been licensed, but are expected to be made available in the future as the technology is developed to transmit at these smaller wavelengths (higher frequencies). The spectrum can be viewed in meticulous detail from the Federal Communications Commission (FCC) and National Telecommunications and Information Administration (NTIA) by visiting www.fcc.gov/oet/spectrum and www.ntia.doc.gov/osmhome/osmhome.html.

Airwave regulations debated by politicians are called 'spectrum policy' as the regulations set policy for all electromagnetic radiation.

An undesired signal occurring in the main channel from modulation of the stereophonic channel or that occurring in the stereophonic channel from modulation of the main channel.

Any component of a communication cable, metallic or optical, the function of which is to protect the transport medium, i.e., conductor or fiber, from excessive tensile and bending stresses during installation and while in service.

Any of the relatively cool dark spots appearing periodically in groups on the surface of the sun that are associated with strong magnetic fields.

In physics, a surface wave is a wave that is guided along the interface between two different media for a mechanical wave, or by a refractive index gradient for an electromagnetic wave. An example is the waves at the surface of water, ocean surface waves.

A balanced transmission line, in a multipair cable, having equal conductor resistances per unit length, equal impedances from each conductor to earth, and equal impedances to other lines

The transmission of data in which both stations are synchronized. Codes are sent from the transmitting station to the receiving station to establish the synchronization, and data is then transmitted in continuous streams.

Telecommunications legislation passed by the U.S. Congress in 1996. Although it covers many aspects of the field, the most controversial has been the deregulation of local phone service, allowing competition in this arena for the first time. Long-distance carriers (IXCs) and cable TV companies can get into the local phone business, while local telcos (the LECs) can get into long distance. Some of the major provisions follow.

A transmitter and receiver housed together in a single unit and having some circuits in common, often for portable or mobile use.

A small electronic device containing a semiconductor and having at least three electrical contacts, used in a circuit as an amplifier, detector, or switch.

The act or process of transmitting. The propagation of a signal, message, or other form of information by any means, such as by telegraph, telephone, radio, television, or facsimile via any medium, such as wire, coaxial cable, microwave, optical fiber, or radio frequency.

Conducting line used to transmit signal energy between two points.

An electronic device that generates and amplifies a carrier wave, modulates it with a meaningful signal derived from speech or other sources, and radiates the resulting signal from an antenna.

Tropospheric scatter (or troposcatter) is the scattering of distant TV and FM radio stations by the troposphere so that they travel farther than the line of sight. This effect sometimes allows reception of stations up to a hundred miles away.

TV DX and FM DX are two terms, customarily grouped together, that mean "distant reception" of TV and FM radio stations, respectively. These terms refer to the search for faraway radio or television stations that can be received during unusual tropospheric conditions, or E-skip. An FM or TV tuner or receiver must be used to pick up stations.

A band of radio frequencies from 300 to 3,000 megahertz.

The range of electromagnetic frequencies from 30MHz to 300MHz.

The range of electromagnetic frequencies from 3 kHz to 30 kHz

An International System unit of power equal to one joule per second.

A system of material boundaries in the form of a solid dielectric rod or dielectric-filled tubular conductor capable of guiding high-frequency electromagnetic waves.

The distance between one peak or crest of a wave of light, heat, or other energy and the next corresponding peak or crest.

Acoustical or electrical noise of which the intensity is the same at all frequencies within a given band.

A set of standards that set forth the specifications for transmitting data over a wireless network.

Of or relating to radio or communication by radiotelegraphy or radiotelephony.

That hour of the year during which the median noise over any radio path is at a maximum. (188) Note: This hour is considered to coincide with the hour during which the greatest transmission loss occurs.