TV Antenna Terms Glossary - G to P

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Overload

Signal amplifiers are supposed to be linear. That is, the output is a magnified but otherwise unaltered version of the input. But too much signal can make an amplifier non-linear, usually clipping off the tops and bottoms of the sine waves. When this happens, all channels are affected, not just the one that is too strong. In fact, the too strong signal is usually not a TV station. A close FM station or police station is more likely.

If you add a good amplifier to your antenna system and your results get worse instead of better then you have overload, and you need to reconsider more carefully what you are doing.

Overload never causes any equipment damage.

An attenuator is a resistor network that can be used to reduce the gain of an amplifier.. If an antenna system needs two amplifiers, where the output of one amp feeds into the other amp, too much gain (overload) can result and an attenuator is usually the simplest solution. If you don’t have two amplifiers, it is unlikely that you will ever need an attenuator.

If you are close to an FM station, there might be a narrow range between too much and too little amplifier gain. You can make that range larger by using an amplifier with an FM trap or by using a more directional antenna. VHF preamplifiers usually include FM traps that can optionally be disabled. Freestanding FM traps are also available. FM traps can either cover the entire FM band or can be single frequency traps that you tune to the offending station. The former are less effective and tend to attenuate channel 6. If the FM station is close enough you might need more than one FM trap.

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Plug

A plug is a male connector.

Polarization

AM radio antennas are always some sort of vertical wire. This is because AM radio waves have vertical polarization. Other directions are possible. Most TV signals have horizontal polarization and thus require antennas with horizontal elements.
If you hold an antenna perpendicular to the polarization of the signal, you will receive no signal. The received signal strength varies with the cosine of the angle of the antenna relative to the signal polarization. (Reflections off nearby objects commonly make this experiment imperfect.)

If a transmitter uses two antennas, one vertical and one horizontal, the result is most likely diagonal polarization, which the station could also produce with a diagonal antenna. Vertical, horizontal, and diagonal polarizations are examples of linear polarization. But if this station introduces a quarter-cycle delay into one of these two antennas, the result is circular polarization (or elliptical polarization if the two components are not equal).

Circular polarization can be visualized as a signal that spins as it moves through space. But it is equally valid to think of circular polarization as just two independent overlapping signals that have linear polarizations that are perpendicular and have a quarter-phase shift.

Circular polarization can be right circular or left circular. DBS satellites use circular polarization, with adjacent channels using opposite spin. A right circular antenna will ignore a left circular signal, and visa versa. DBS satellites alternate the polarization to make it easier for the receiver electronics to separate the channels.

A linear antenna can be used to receive a circularly polarized signal, but half of the transmitted power will be invisible to it. A circularly polarized antenna can be used to receive a linearly polarized signal, but half of the received signal will be retransmitted with the opposite linear polarization. Because of these problems, circular polarization has not become popular for terrestrial radio services other than FM broadcasting.

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