There are many bands and hundreds of TV antenna model available. However, choosing the right one is relatively easy if you are aware of the few basic reception and TV antenna characteristics.

First, “good reception,” or production of a snow-free color TV picture, requires a signal level of about 1000 microvolts. To deliver this signal level to the receiver, the antenna requires a certain antenna gain. The amount of gain required is dependent on the distance between the station’s transmitting antenna and the receiving antenna. The required type of antenna therefore depends on the channels to be received and the distance and direction of the customer’s home from the transmitting antennas. These facts are readily available for any area, but be sure your information is accurate and complete. Call a local TV station if you have questions. Most television stations are willing to help TV antenna installers because they also benefit from the improved reception to the station’s viewers.

Be sure to discuss with your customers the number and types of channels that are receivable. This may sound basic, but your customers may not understand the difference between VHF/FM and UHF. They also may not be aware that with the right equipment they may be able to receive out-of-town channels, some of which may carry sports programs that are locally blacked out. The most important points to remember when selecting an antenna are its gain, sensitivity classification, directivity, and front-to-back ratio.

GAIN
The gain of an antenna indicates the relative strength of signal it can deliver to a receiver. Most manufacturers list gain in their antennas in decibels (dB). The higher the antenna gain, the stronger the signal at the antenna output terminals. In most cases, the larger the antenna, the higher the gain.

If you are in doubt about the amount of gain required, select an antenna that is slightly larger than you think is actually needed. The performance of all components deteriorates slightly during the years they are exposed to rain, sun, wind, and corrosion. Consequently, to ensure quality reception for a longer period, choose an antenna with a little more gain than is necessary. (Note:Excessive gain may cause overloading. Therefore, choosing the antenna with the highest gain might create more reception problems than it cures.)

Sensitivity classifications are used to indicate the type of reception area for which the antenna is designed. Certain ranges of gain are best suited for certain types of areas. The appropriate range of gain for a specific area is what a manufacturer is indicating when labeling an antenna, i.e., Outer Suburban or Near Fringe. The table below is a chart of typical sensitivity classifications. It indicates, in miles, how close an antenna must be to the transmitter to produce the best signal level. The classifications are somewhat general because reception conditions at various sites within a particular type of area may be different.

DIRECTIVITY
Directivity is the ability of an antenna to intercept signals from only one direction and reject those from other directions. Directivity indicates the antenna’s ability to intercept signals arriving at its front and reject signals coming from the sides and rear. Generally, the more highly directive an antenna, the better it can reject signals from the sides and rear.

The front-to-back ratio of an antenna can be helpful when attempting to determine its directivity. Front-to-back ratio is expressed in decibels (dB).This ratio indicates an antenna’s ability to reject signals coming from the rear (rear rejection). For example, an antenna with a front-to-back ratio of 25 dB will receive about 18 times more signal strength from the front than from the back.

In most cases, comparing its specified front-to-back ratio with the relative sensitivity classifications listed in Typical Sensitivity Classifications table can make an acceptably accurate estimate of an antenna’s directivity.

The sensitivity classifications in the table to the right are intended only as general guidelines for evaluating directivity. Other factors, such as the antenna’s beamwidth, can affect its directivity.

Beamwidth is related to an antenna’s overall gain and indicates how wide or narrow the reception area of the antenna is. For example, if two antennas have the same front-to-back ratio, the one with the highest overall gain will have the narrowest beamwidth and consequently, will be the most directive.

An antenna with a relatively narrow beamwidth generally is best suited for areas where interference from sides is a problem. An antenna with a broad beamwidth is best suited for areas where a broad beam is needed to capture the signals from widely separated stations, and where interference is minimal. Beamwidth information, if included by the manufacturer, is usually displayed by use of polar plots as in the example at right.

Selecting the most suitable antenna becomes easy with experience, but selecting quality materials should be the first decision to make before starting any installation. High-performance reception usually requires highly sensitive equipment. In the end, it pays to use the finest equipment available, from the antenna down to the receiver including the transmission line. The slight additional cost should be considered an investment in longer system life and optimum performance.