#4 - Range and Coverage

FACTORS AFFECTING RANGE AND COVERAGE

The factors that have the greatest impact on range and coverage include. The frequency band of the radio system The power output of the radio transmitter The type of antenna being used The height and location of the antenna The terrain the system will be operating in The amount of electromagnetic noise in the general area of operation Each of these are prime factors in determining how far we are able to communicate and to where we can communicate.

ANTENNA HEIGHT AND LOCATION

Antennas radiate energy in all directions, much like a light bulb radiates light.  A mobile radio moving further away from the transmitting antenna receives less and less radio frequency energy.  The distance from the antenna to the furthest point of communications can take place is known as a radio system's range. As a radio moves away from the base antenna, at some point it receives too little radio signal for reception, or it is unable to generate enough energy from it's own antenna to talk back to the base station.  When this occurs, that radio has reached the limit of it's range. If you think of range as the radius of a circle, the circle itself will be the coverage area. In a radio system, this circle drawn on a map indicates the usable area of the radio system.  The range of a radio system is affected by many different factors. The most critical coverage factor is base station antenna height and location. This is because the range of a radio system is theoretically limited to the radio horizon as seen by the radio antenna.  Thus, the range of a radio system, for the most part, depends upon the base station antenna.  Basically the higher up in the air that antenna can be installed, the greater an area will be covered.

TERRAIN

Because the radio waves follow a line-of-sight path, terrain variations can also cause difficulties in communications.  Hills and valleys create shadows in a coverage area.  These shadow areas are often called communication holes. Tall buildings can also have the same effect on coverage. In such cases, if we raise the antenna height, we can eliminate most of the holes.  Thus, antenna height, to a large extent, also cures terrain problems.

NOISE

Another factor affecting range and coverage is noise.  By noise we mean electrical interference of any and all types.  Some causes of electrical noise are power lines, neon signs, electric motors, and other radio systems.  As a radio moves away from the base station antenna it eventually receives too little energy for effective communications reception.  Noise problems at these limits of the coverage area, called fringe areas, can be severe.  The radio signal is simply too weak compared to the noise signal.  In the fringe areas, increasing transmitter power can increase the energy level at the receiving radios antenna, and will help to overcome the noise. Another way to overcome this problem is through the use of gain antennas. Recall that gain represents an antenna's ability to increase it's effective related power.  This is done by channeling the antenna's normal radiation pattern in a particular direction and thus extending the distance it will cover.  The use of a high gain antenna ensures better reception in the fringe areas of a system.