Communication is an important part of police work. Officers rely on radios to respond to emergencies and coordinate units. In some cases, a situation requires a high level of privacy. Scrambled police radios can help prevent eavesdroppers from hearing sensitive police information. These types of radios use circuitry to encode outgoing signals and ensure that only authorized listeners can hear the message.
A traditional, non-scrambled radio's messages can be easily intercepted by nearby listeners with inexpensive police scanners. Many people listen to emergency communications as a hobby, and there are many radio receivers specifically designed for this purpose. Some police messages are not intended for the public, however. A scrambled radio can help emergency service workers keep personal information private, or use radios to coordinate a surprise operation.
A scrambled radio uses a special electronic circuit that modifies the audio signal. The user speaks into the radio normally, but the audio is changed within the radio before it transmits. Other police radios are equipped with similar circuitry, and reverse the audio changes to unscramble the message. If an eavesdropper does not have the correct radio, he hears a garbled message or unintelligible white noise.
Some radios have a scramble option installed at the factory, while other radios can be modified with an add-on circuit. This allows police departments to scramble their communications without purchasing entirely new radios.
There are several different types of scrambled police radios, and each works in a somewhat different way. One of the most common types of scrambling is called "simple inversion." As the term implies, this method of scrambling inverts the high and low audio frequencies. The result is a radio transmission that is difficult to understand. While inversion is a common method of scrambling, however, it can be reversed by listeners with basic equipment.
A more secure type of scrambled police radio uses digital encryption. This method converts audio into a digital format, and applies a complex encoding algorithm. The digital voice signal is impossible to interpret without the correct encryption key. Authorized police units have the key programmed into their radios, while unauthorized listeners cannot break the coded message.
Scrambled police radios come with some limitations. One problem is compatibility. Traditional radios can transmit and receive with any nearby unit that is tuned to the same frequency, but the nature of a scrambled radio makes it more difficult to communicate with radios of differing types. If police departments from two different cities need to work together, for instance, a scrambled message might not be properly heard by all of the units.
Cost is another drawback of scrambled police radios. A 2011 report by the "San Diego Union-Tribune" indicates that scrambling circuits cost around $50 per radio. This cost can be significant for police departments with hundreds of officers.
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