Police scanners

Radio scanners are radio receivers which are capable of scanning through a lot of programmed channels or frequencies. Radio scanners can also be user programmed to scan or search between two given frequencies in predetermined steps.
Scanning radios are available at different price levels offering different features and capabilities. Higher priced scanners can cover a much wider range of frequencies, have more memory channels and are capable of scanning through the channels a lot quicker than the lower priced models.
A Radio scanner must be pre-programmed with frequencies into some or all of its memory channels. The Scanner is then set to "scan memory" mode. It will then listen momentarily to the frequency in each of its programmed memory channels. The scanners memory channels are numbered and the scanner will run through them in ascending order.
Radio scanners have a squelch control which is a circuit, usually controlled by a knob that can be set to suppress the audio output of the receiver and cause the scanner to skip or ignore a channel when the received signal is not strong enough. This feature is set to tune out or attenuate any natural or man made background radio noise.
A scanner will run through its programmed frequencies and it will stop on a channel which has a signal strong enough to break the squelch, that is a signal higher than the minimum squelch setting. There is also a delay feature available on most scanners which can be set so that the scanner will stay on a channel until the transmission ends or it can be programmed to stay on the frequency for a predetermined amount of time, say 10 seconds or so before it resumes scanning.
Before the scanning radios were developed, to achieve the similar results as a 50 Channel radio scanner you would have to have 50 radios, each one tuned to a different frequency, then each of these radios would have to be turned on and, if nothing was heard off-again. The next radio in line would then have to turned on then off again and so on down the line of radios until a signal was received on one of the radios. Each of these radios would have to be turned on and off again sequentially in under two seconds.
Quite a few of the modern scanning radio receivers radio scanners have a very wide frequency range Some manufacturers offer wideband scanners which can tune from 152 kHz to 1310 MHz.
The typical household analog transistor FM radio receiver usually has a frequency range from about 85 MHz to 105 MHz and the tuning display or dial is under three inches long. If the tuning range of the typical household transistor radio was the same as a wideband scanner and it displayed the tuning frequency in the same way it would have to have a display or dial well over 25 feet long.
Radio scanners can receive most analog FM and AM radio transmissions and are usually used to listen to voice radio communications. Most two-way radio utilizes narrow FM. Most FM broadcast stations utilize wide FM. Some of the higher end scanners are able to receive both narrow and wide FM signals and can also be used to listen to broadcast stations. On a scanner that receives only narrow FM, broadcast stations will sound a little pinched or tinny. Some high-end scanners are even capable of receiving digital radio transmissions.
Radio scanners are used mainly used by radio enthusiasts to listen in on the two-way radio traffic from police departments, fire departments, ambulances, marine and ship to shore radio, the Coast Guard, aircraft communications from the tower to the aircraft or from one aircraft to another, CB radio, amateur radio, business radio, which might include towing companies, railroads, taxis etc, family radio walkie-talkies and even race car drivers talking to their pit crews during a race.
Radio scanners can also be used to listen in on telephone conversations on some of the older wireless or cordless phones.
The more modern cordless phones now use spread Spectrum technology to prevent telephone conversations from being overheard using radio scanners.
Legislation was introduced in the USA making it illegal to sell scanners which are capable of or easily modifiable to receive the frequencies that are used by the cell phone companies. For the most part the cell phone companies have also adopted spread Spectrum technology and encryption to prevent any eavesdropping and keep cell calls private.
Most radio scanner hobbyists use their scanners to monitor the radio communications of their local fire, police and ambulance departments.
Because all radio transmitters in the U.S.A. have to be registered with the FCC, all the information about the transmitters, their transmit frequency and their location is readily available to the public. in the United States it is very easy to look up all the frequencies in your city or your and your surrounding townships for the services that interest you and program these frequencies into your radio scanner.
When a radio scanner owner hears a siren in their neighborhood then can switch on their scanner and usually within a few seconds they will be listening to the radio traffic between the responders and the dispatchers and find out exactly what the emergency is and which departments are responding to it.
Radio scanners are available as a base models for home use or hand-held units. A basic entry level scanner will cost around $75 Higher end scanners with all of the bells and whistles will cost several hundred dollars.
Even the low-cost entry-level Radio scanners provide hours of very informative entertainment but a mid range scanner costing a couple of hundred dollars is still a very good value and a really good investment.

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