Television Antenna Terms/Definitions

Anodizing:

A Chromate Conversion process, for Aluminum used to provide corrosion protection, which prevents degradation and intermodulation of raw Aluminum.

Antenna Efficiency:

Fraction of the radiated power to the power put into antenna. Ideal perfectly matched lossless antenna has efficiency of 1 (or 100%).

Antenna Gain

Measured in (plus/gain) Decebils. Antenna gain is a measure of directivity properties and the efficiency of the antenna. It is defined as the ratio of the radiation intensity in the peak intensity direction to the intensity that would be obtained if the power accepted by the antenna were radiated isotropically. The difference between the antenna gain and the directivity is that the antenna efficiency is taken into account in the former parameter. Antenna gain is measured in dBi, i.e. decibels relative to isotropic antenna.

Antenna Impedance

Ratio of voltage to current at antenna input.

Antenna polarization

Polarization is the orientation of the electric field vector component of the electromagnetic field. In line-of-sight communications it is important that transmitting and receiving antennas have the same polarization (either horizontal, vertical or circular). In non-line-of-sight the received signal undergoes multiple reflections which change the wave polarization randomly.

Amplified antenna

Antenna equipped with a Radio Frequency Amplifier installed in series with the Coaxial Cable, to improve antenna sensitivity to weak signals.

Bandwidth

Antenna bandwidth is the frequency range within which the antenna performance meet specifications.

Beam Width

Measured in Degrees (°). Directional antennas have a radiation intensity peak in the particular direction. Beam width is the angular distance between the points on two opposite sides of the peak direction where the radiation intensity drops to the half of the peak intensity. The beam diameter or beam width of an electromagnetic beam is the elliptical cross section diameter along any specified line that is perpendicular to the beam axis and intersects it. Beams typically do not have sharp edges. Profiles of Beams called Propagation Graphs, frequently look like ragged circles, orbs (main lobe), orb type projections with reliefs similar to a profile of a Leaf from a Tree.

Beam Width at Half Power Points

Measured in Degrees (°). In the radio regime, of an antenna pattern, the angle between the half-power (-3 dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe. Beamwidth is expressed for the horizontal plane, but may also be expressed for the vertical plane.

dB or dBi

An expression of Physical Quantity, usually Power.

db Gain over Rererence Dipole

Measured in (plus/gain) Decebils. Decibels relative to an isotropic antenna. Units of antenna gain.

Directional antenna

Antennas having a preference for a particular direction and radiating (receiving) a signal more efficiently in (from) this direction than in other directions. Directional Antennas beam width at the half power point, have a limit of 30° or less.

Directivity

Directivity is a measure of how strongly the antenna favors the particular direction of its maximum transmission (reception) sensitivity, comparing to other directions. More specifically, it is defined as the ratio of the radiation intensity in the peak intensity direction to the averaged radiation intensity in all other directions.

Front-to-back (F/B) ratio

Measured in negative (rejected) Decebils (dB). A parameter measuring antenna directivity defined as the ratio of the peak radiation intensity in the "front" direction to the radiation intensity at 180 degrees behind the point ("back" direction).

Intermodulation

A change in electrical characteristics.

Isotropic antenna

Antenna transmitting (receiving) equal radiation in (from) all directions. Isotropic antenna is a hypothetical idealized device that does not exist in reality. It is usually taken as a reference when measuring directivity of actual realizable antennas.

Multidirectional antenna

An Antenna receiving radiation in (from) a range of horizontal directions of more than 30°, but less than 360°.

Noise figure

Signal-to-noise ratio degradation in antenna amplifier. Amplifier noise figure should be as low as possible.

Omnidirectional antenna

An Antenna transmitting (receiving) equal radiation in (from) all horizontal directions. A typical example is a whip antenna. Whip antenna’s radiation power is distributed equally in all directions in a plane perpendicular to the whip. In TV Antennas, a small “Blind Spot” is always present, limiting the actual reception to about 360°.

Polar Pattern

A shape/pattern usually represented in graph form, of the Band Width/reception strength area of an Antenna. (see Beam Width)

Propagation Graph

A shape/pattern usually represented in graph form, of the Band Width transmition/strength area of a Transmitter.

Range (reception)

Getting reliable UHF DTV reception beyond the curvature of the earth (approximately 70 miles) is difficult. Terrain has a major impact on reception. Going over water is about the best it gets, since water is generally flat and has positive impacts on temperature for sending the signal along. Still, beyond 70 miles, unless you can get direct line-of-sight to the transmitters, the number of things that could impact reception negatively are numerous.

Terminator: (a Cap)

Terminates open “F” connector terminals, usually 75 ohm.

Transformer: (a Balun or Matching Transformer)

A Pigtail, matching (usually) from 300 ohm down to correct impedance (75/56 ohm)

Transmitter Locator Calculator:

Locates any/all TV Transmitter whose signal is receivable at your location.

You enter your location, and the Calculator locates Television Transmitters which you can receive, and gives you a rating in Minus Decibels (-db) of their Signal Strength.

Turning Radius:

Measured from the center of the Mast, to the (fartherest) end of the Antenna. Measurement applies to circular free area, which the Antenna would need, when used with a Rotator.

UHF

Ultra High Frequency (UHF) band. TV channels 14 to 69 are transmitted in UHF band in frequency range 470-806 Mhz.

VHF

Very High Frequency (VHF) band. TV channels 2 to 13 are transmitted in VHF band in frequency range 54-72 Mhz, 76-88 Mhz, 174-216 Mhz.

VSWR (or SWR)

Voltage Standing Wave Ratio is the ratio of the maximum to minimum voltage on the antenna feeding line. Standing wave pattern is created on the feeding line when the impedance match is not perfect and a fraction of the power put into antenna is reflected back and not radiated. For perfectly impedance matched antenna the VSWR is 1:1.

Yagi (Antenna)