What the Gain of an Antenna Can Tell You - and What it Can't
Gain, usually expressed in decibels, indicates how well the antenna focuses energy from a particular direction, in comparison with a standard reference antenna (an antenna with known performance, used to calibrate other or developing antenna technologies). The gain number specified on an antenna is the value in the direction of maximum reception intensity. What this means is that the distance measured for an antenna's reception capacity is based on the hypothetical instance where the broadcast transmitters you're trying to receive signals from all line up like points on a single straight line. Also, it is relevant to note that "gain" in this usage doesn't take into account possible dips in reception from what is called "impedance mismatch". In practice, the antenna's performance can be faulty if its impedance is different from that of the cable connected to it.
When shopping for an antenna, consider the gain if it’s available, and all of its other characteristics as well. Buying an antenna based on gain and price alone would be like going shopping for an automobile and only considering power and price. While high values of gain - in the 7 to 12-decibel range - are usually better than low gain values, you would be better off not focusing on the gain, but instead purchasing an antenna that provides good overall performance, as long as it meets your reception and installation requirements.
We can attempt to illustrate using the following two examples:
A family in rural Nebraska would need a long-range, multi-directional antenna, a tower of about 60 feet -which is highly uncommon- and a preamplifier, in order to pick up stations from their broadcast towers, which would more than likely be located somewhere over the visual horizon.
This complex setup would be excessive for a person living in Salt Lake City, where most of the broadcast towers are on a mountain ridge just above the city, within line-of-sight for most viewers. If you live close to Salt Lake City, you will get decent reception, even with a short-range, indoor antenna.
Usually, claims of excessively high gain are for marketing purposes. Some manufacturers label small, indoor antennas with high gain numbers between 30 and 55 dBi. This style of antenna is probably paired with an amplifier and the gain value stated on the package is really the gain of the amplifier plus the gain of the antenna. While it is possible to improve reception by using a low-noise amplifier, most of the inexpensive antenna designs actually have low-quality amplifiers with too much gain. Low-quality amplifiers with too much gain could overload the TV's tuner or set-top receiver, causing signal distortion that can degrade or, most likely, eliminate TV reception entirely. A well-designed, non-amplified unit, also known as a passive antenna, would be the better choice. If television reception requires an amplifier, the best choice is a high-quality, low-noise model, connected as close as possible to the TV antenna.
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