Voice Radio-The Most Important Law Enforcement Tool

By Chu, Jim | Law & Order, August 2002 | Go to article overview

Voice Radio-The Most Important Law Enforcement Tool


Chu, Jim, Law & Order


A mobile voice radio is the most important piece of equipment a law enforcement officer will use. Having a functional voice radio system must be the highest information technology priority for a law enforcement agency. To back up this assertion, one only has to look at the media headlines and officer anger generated when radios do not work.

Basic Concepts

The term "radio" refers to the radiation and propagation of signals through space to convey information. Initiating an electromagnetic disturbance will cause waves to spread from the source to another point some distance away-- very similar to a pebble causing ripples in a pond. These waves travel at about the speed of light (186,000 mph). Other variable characteristics are amplitude (the magnitude of the disturbance of a wave), frequency (the number of complete waves propagated past a fixed point in one second- cycles per second or hertz) and wavelength (the distance between one wave and the preceding or succeeding wave, measured in meters.)

There is an inverse relationship between a frequency and a wavelength. The higher the frequency of a wave, the shorter its wavelength will be. As the distance from the source increases, the intensity of the radio signal decreases.

For a radio to work, four processes need to occur. First, a transmitter receives some inputs and produces an electromagnetic disturbance. Second, an antenna radiates the disturbances through space as electromagnetic waves. Third, the waves enter a receiving antenna and produce electric currents in a receiving circuit. Fourth, the receiving circuit changes the electric currents into a form comprehendible by an operator.

Radio waves generally travel in straight lines, like light waves, but certain characteristics of the atmosphere cause certain frequencies to behave in ways that can expand their use. Very low frequency waves tend to follow a path close to the earth's curvature. These are known as ground waves and have frequencies below 30 KHz. They can be received thousands of miles away but their information carrying capacity is limited.

Higher frequency waves, which travel in straight lines, are known as direct waves. They are used in line-- of-sight transmissions and very tall antennas, or a series of relay antennas that can see each other are required. Because their transmission distance is limited, these tend to be used for local transmissions and the frequencies can be reused in other geographical regions without interference. Because of the inverse relationship between frequency and range, larger systems (such as for a rural area) use VHF or low UHF frequencies since the coverage footprint can be achieved with less infrastructure (fewer towers and repeaters), thus saving costs.

Public Safety Frequency Allocations

To control the use of frequencies, every country has a regulatory body (FCC in the United States, Industry Canada in Canada) to manage spectrum usage. As a scarce and nonrenewable natural resource, it has a high economic value. Additional spectrum cannot be created or discovered, and the FCC has raised billions of dollars in spectrum auctions. Industry Canada is a more recent entrant to the auction process. Radio license (spectrum usage) regulations are stringent and transmitting equipment cannot be moved, even in emergencies, without government agency approval.

The term bandwidth in modern data communications has been used to describe the throughput of a given network connection. In spectrum allocation, bandwidth refers to the range of frequencies that are assigned to a single channel. The bandwidth allocated to public safety radio frequencies ranges from 12.5-30 kHz. As a comparison, FM radio stations are spread 200 kHz apart. To conserve spectrum, regulatory bodies are loath to license new radio installations that are broadband (25 kHz).

In the late 1990s, Industry Canada and the FCC undertook redeployment or refarming of the bands from 100-500 MHz. …

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