Terk : Glossary of Terms

Glossary Of Terms

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Amplifier or amplification is a way to enhance signal gain and increase performance. Amplifier are either built in or can be a separate device that installs in-line between the antenna and TV. An amplifier that installs on an outdoor antenna or mast is often called a preamplifier or "preamp." Most experts recommend only using an amplifier if you need to. The potential drawbacks of amplifiers are that they amplify noise along with the signal, and they can be overdriven by strong signals, which can make reception worse.

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.

Antenna Power Gain
The ratio of the antenna's maximum radiation intensity in a stated direction to the maximum radiation intensity of a reference antenna (dipole, isotropic antenna) with identical power applied to both.

The loss in power of electromagnetic signals between transmission and reception points.

Horizontal direction expressed as the angular distance between the direction of a fixed point (as the observer's heading) and the direction of the object.

A range of consecutive frequencies comprised of a band (i.e. the US cellular bandwidth is 72 MHz wide between the frequencies of 824 MHz - 894 MHz) over which an antenna shall perform without the need of any adjustment. The width of a band of frequencies used for a particular purpose. A range of frequencies, usually +/-3 dB of the amplitude of a reference frequency.

The angle of signal coverage provided by an antenna. Beamwidth typically decreases as antenna gain increases.

Cable Loss
A numeric value describing the amount or signal loss from one point on a length of cable to another. This is measured in decibels (dB).

Center Fed
Transmission line connection at the electrical center of an antenna radiator.

Coaxial Cable
Cable consisting of a single copper conductor in the center surrounded by a plastic layer for insulation and a braided metal outer shield. Coax is used to transfer radio frequency energy from the transmitter to the antenna.

Collinear Array
A system of two or more antenna radiators arranged in a line and connected end-to-end to generate a directed field pattern (serial linear topology).

A system of two or more antenna radiators arranged in a line and connected end-to-end to generate a directed field pattern (serial linear topology).

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Abbreviation for decibels adjusted. Weighted absolute noise power, calculated in dB referenced to 3.16 picowatts (-85 dBm), which is 0 dBa. A one-milliwatt, 1000-Hz tone will read +85 dBa, but the same power as white noise, randomly distributed over a 3-kHz band (nominally 300 to 3300 Hz), will read +82 dBa, due to the frequency weighting. Synonym dBrn adjusted.

Quantification of the gain for an antenna in comparison with the gain of a dipole.

The dB power relative to an isotropic source.

A measure of power based upon the decibel scale, but referenced to the milliWatt: i.e. 1dBm = .001 Watt. dBm is often used to describe absolute power level where the point of reference is 1 milliWatt. In high power applications the dBW is often used with a reference of 1 Watt.

The ratio of the power to one Watt expressed in decibels.

DC Ground
An antenna which is a dead short to a DC current, and has a shunt fed design. To RF it is not seen as a short.

Also called dB. The standard unit used to express transmission gain or loss and relative power levels.

An antenna ‐ usually a half wavelength long ‐ split at the exact center for connection to a feed line.

Directional Antenna
Directional antennas are able to pull in signals from greater distances, and because they "see" in only one direction they are resistant to noise and "multipath distortion" (a problem created when an antenna receives reflections of the desired signal). An antenna having the property of radiating or receiving electromagnetic waves more effectively in some directions than others.

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The ratio of useful output to input power, determined in antenna systems by losses in the system including losses in nearby objects.

Field Strength
An absolute measure in one direction of the electromagnetic wave field generated by an antenna at some distance away from the antenna.

FM Antenna
An antenna designed to receive signals in the FM band, ranging between 88.5MHz to 108MHz [FM Radio].

The number of cycles per second of a wave. The rate at which a process repeats itself. In radio communications, frequency is expressed in Hz

Front-To-Back Ratio
The ratio of radiated power off the front to the back of a directive antenna. A dipole would have a ratio of 1, for example.

The relative strength of the signal an antenna can deliver to a tuner is referred to as "gain" and is measured in decibels (dB). The higher the dB rating, the greater the gain.

Gigahertz (GHz)
One billion cycles per second.

Global Positional Satellite or Global Positioning System.

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Hertz (Hz)
A unit of frequency equal to one cycle per second.

The Ohmic value of an antenna feed point, matching section or transmission line at a radio frequency. An Impedance may contain a reactance as well as a resistance component.

A degradation of a received signal caused by another transmitter, a noise source, or the desired signal propagation over two or more different routes.

Lightning Protector
A device designed to divert large surges of current such as a lightning strike from reaching the RF equipment. There are many types of lightning protectors including Quarter Wave Stub and Gas Discharge Tubes.

Megahertz (MHz)
1 million cycles per second. Also called MHz

A mount is the apparatus onto which an antenna attaches.

Multi Directional
"Multi-directional" or "omni-directional" antennas are able to receive signals from all directions. Because multi-directional antennas "see" in many directions they are more likely to pick up noise, interference, and multipath distortion.

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Random pulses of electromagnetic energy generated by lightning or electrical equipment. Any unwanted and un-modulated energy that is always present to some extent within any signal.

Multi-directional or "omni-directional" antennas are able to receive signals from all directions. Because multi-directional antennas "see" in many directions they are more likely to pick up noise, interference, and multipath distortion.

Parabolic Antenna
An antenna consisting of a parabolic reflector and a radiating or receiving element at or near its focus. Parabolic antennas are very directive and includes a preliminary source and a parabolic reflector to focus the energy.

Planar Array
An antenna in which all of the elements, both active and parasitic, are in one plane.

A communications channel running from one point to several other points.

A communications channel running from one point to another.

The sense of the wave radiated by an antenna. This can be horizontal, vertical, elliptical or circular (left or right hand circularity) depending on the design and application.

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Relative Antenna Power Gain
The ratio of the average radiation intensity of the test antenna to the average radiation of a reference antenna with all other conditions remaining equal.

Transmission Line
The connecting link allowing the radio frequency energy generated by the radio to be delivered to the antenna. (Coaxial cable, microstrip or coplanar lines in our industry.)

An electronic device consisting of oscillator, modulator and other circuits which produce a radio electromagnetic wave signal for radiation into the atmosphere by an antenna.

Ultra-High Frequency - The tremendous growth in television broadcasting following World War II made it obvious that 12 channels were not enough. So in 1952, the FCC allocated 70 additional channels above the VHF television band and called them "ultra high frequency" or UHF band. The channels are 14 through 83. UHF signals, however, due to the physics of radio frequency transmission, are inherently less efficient in the conversion of radio waves to the electrical signals used by the television receiver, and are subject to more losses from some environmental conditions then VHF. Good UHF reception, therefore, requires more attention to antenna installation and set tuning than does VHF reception. On the other hand some VHF channels are subject to certain types of interference to which UHF channels are generally immune.

Uni directional
Antennas described as "uni-directional" or sometimes just "directional" are designed to receive signals from one direction.

Very-High Frequency - The Federal Communications Commission originally allocated twelve channels for television broadcasting. These channels, numbers 2 through 13, are in the "very high frequency" or VHF band. (Originally Channel 1 was also included, but was soon reassigned to other purposes.)

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