Television Antenna


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television antenna

[′tel·ə‚vizh·ən an‚ten·ə]
(electromagnetism)
An antenna suitable for transmitting or receiving television broadcasts; since television transmissions in the United States are horizontally polarized, the most basic type of receiving antenna is a horizontally mounted half-wave dipole.

Television Antenna

 

an antenna for transmitting or receiving the video and audio signals of television broadcasts. Television antennas are classified as transmitting or receiving antennas for the very-high-frequency (VHF) or ultrahigh-frequency (UHF) band.

Transmitting television antennas are usually constructed as a system of horizontal, symmetrical dipoles; the feed arrangements and circuitry for the dipoles determine the shape of the polarization pattern and the antenna gain. The radiation pattern of transmitting antennas is usually circular in the horizontal plane; in the vertical plane it is lobe-shaped and directed along the earth’s surface. If the cross-sectional dimensions of the antenna mounting are relatively small and only a few units of antenna gain are needed, a turnstile antenna may be used in the VHF band. In other cases, it is preferable to use an antenna composed of separate panels, each consisting of dipoles and several auxiliary elements. Depending on the radiation pattern desired, the panels may be arranged symmetrically or nonsymmetrically with respect to the cross-sectional configuration of the mounting, and the radio waves radiated may either be in phase or have specific phase shifts.

Other antenna configurations are also used. For example, the VHF antennas at the All-Union Television Technical Center in Moscow on the Ostankino tower are constructed in the form of radial rods that are disposed uniformly around the periphery of the tower’s cross section and perpendicular to its surface; the rods are grouped in tiers, with eight rods in each tier. Television transmitting antennas for the VHF band have gains ranging from several units to 12–15; in the UHF band they reach several tens of units.

Receiving antennas may feed a single receiver or several receivers; the former type may be located outdoors or indoors, while the latter is always outdoors. Receiving antennas may be single-channel or multichannel designs; they operate in the frequency band of one or several television channels, respectively. Broadband designs are also used. Master antennas—those that feed several receivers—are usually unidirectional wave guides. Antenna gain is several units in the VHF band and several tens of units in the UHF band. In areas with good VHF reception, outdoor antennas for feeding individual receivers are simple, single-channel dipoles, with a straight-line or loop configuration and a figure-eight polarization pattern. In areas where VHF reception is poorer because of greater distance from the television station, outdoor antennas are unidirectional wave guides of varying complexity. Such antennas are also used for all UHF reception. The TAI-12 and ITA-12 multichannel VHF antennas have simple structural and circuit designs and have become fairly common.

Indoor antennas are used only where reception is good. For the VHF band they are usually a straight-line or loop dipole with arms that can be continuously varied to tune the antenna; telescoping whip antennas and curved loops are the most common designs. Indoor UHF antennas are usually wave guides. Nontunable indoor antennas with built-in transistor amplifiers have also come into use. They combine a short symmetrical dipole for VHF reception and a wave guide for UHF reception. (See alsoRADIATION AND RECEPTION OF RADIO WAVES.)

REFERENCES

Kapchinskii, L. M. Televizionnye antenny. Moscow, 1970.
Kuzinets, L. M., E. V. Metuzalem, and E. A. Rymanov. Televizionnye priemniki i antenny: Spravochnik. Moscow, 1974. (Contains bibliography.)

V. K. PARAMONOV

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