How Radio Scanners Work

Scanner Features

Radio scanners can be either portable, with rechargeable battery packs, or desktop, like a regular radio. Scanners are gaining popularity with consumers. With the huge popularity of NASCAR racing, many people now use scanners at auto racing events to eavesdrop on the crew-driver communications at races. At a typical race, there are hundreds of frequencies in use. Each team has two or three frequencies, while race control, the sanctioning organization, the medical, fire and track crews and many others each have assigned frequencies during the race.

Some of the recently released scanners are capable of tracking municipalities and police frequencies in the 800-megahertz (MHz) range. This is known as trunk tracking of computer-controlled trunked radio networks.

Higher-end scanners can be controlled by the serial port of a personal computer using special software. This helps the user with the logging of stations as well as with duplicating the scanner controls within the software application.

Many models receive the NOAA weather radio broadcasts. This can be a very useful feature during pending tornadoes or hurricanes.

The controls on a radio scanner can vary, but practically all of them have:

  • Volume
  • Squelch - This is an adjustable control that keeps the speaker muted (quiet and free from static) when a station is not transmitting. It works whether the radio is scanning, searching or manually stepping through stored frequencies. CB radios also have this control.
  • WX button - This is common on some newer models. This button typically does a mini-scan of some factory-written frequencies that receive the nationwide NOAA weather broadcast reports.
  • Numeric keypad - This is used for entering frequencies or in combination with the "Limit" button, used for entering upper and lower ranges of a search between two frequencies. The keypad also lets you enter frequencies found during a search. More expensive models automatically store frequencies found during a search. Buy a copy of "Police Call" (you can get a used one for next to nothing at or the CD-ROM version at Radio Shack) to get some frequencies for your area. See these Frequently Asked Frequencies, too. Useful Book Scanners & Secret Frequencies by Henry L. Eisenson and Bill Cheek Thanks to frequency synthesizers, most scanners can receive frequency bands in the 29-MHz to 512-MHz range. If you enter a frequency outside that range, you typically see an error indication on the display. More expensive models often have a higher range and often include military aircraft frequencies. (Earlier scanners did not have numeric keypads and required the owner to purchase individual crystals manufactured for a given frequency. Most early scanners only held six or 10 crystals. The cost of filling up a scanner with individual channel crystals often approached the cost of the scanner, much like buying ink cartridges for today‚Äôs low-priced color inkjet printers.)
  • Search button - This starts the scanner on a continuous loop between two frequency limits, finding unknown frequencies within a given range. The searches typically are in the same automatic increments that the Federal Communications Commission (FCC) assigns for the given frequency band being searched. U.S. scanners cannot search the frequency bands assigned for analog cellular telephone calls. If you were at a car race, for example, you could do a search from 460 to 470 MHz and note when the scanner stops (or look in the race program for assigned frequencies). You could make a note of the displayed frequency or store it at that time, and then continue the search. The instruction manual that comes with a scanner typically shows what frequency bands are for government, business, aviation, and other users.
  • Manual button - This lets the user manually step through a range of frequencies stored in the scanner. Modern scanners have 100 to 300 channels for storing frequencies in the built-in memory. More expensive models have even more.
  • Scan button - This starts the scanner on a continuous loop through all of the frequency banks (containing stored frequencies). The scanner stops when it detects a radio signal on a stored frequency; it moves to the next stored frequency when the radio signal ends. The user can typically enable or disable certain banks of frequencies for scanning. Each bank can hold 10 to 30 frequencies, depending on the brand and model of the radio scanner. Often, banks contain frequencies according to the type of radio service. Types include emergency, police, fire, aviation, marine and business.
  • Delay button - This makes the scanner stall for a short duration on a frequency before moving to the next one. This delay helps the user hear the other part of the radio conversation on that frequency.
  • Lockout button - This temporarily disables the radio scanner from stopping on a stored frequency. For example, you might want to lockout the frequency of a busy airport tower at peak travel time during the day when you're really trying to hear the traffic helicopters in your area.

Radio scanners usually come with small whip antennas as well as an external antenna connector. An outside antenna or attic antenna enables you to hear more transmissions at a greater distance.

Scanners cannot hear everything. The typical consumer-grade scanner cannot listen in on 900-MHz cordless phones that use digital spread spectrum (DSS) technology. Analog cell phone frequencies are also blocked by law on all scanners.

Some law enforcement agencies also use audio inversion and other scrambling technologies to prevent the reception of sensitive communications. You will not be able to decipher these conversations.

Even so, there is an unbelievable number of radio services that use frequencies most scanners can hear.

Until you buy your own scanner, you can try out scanning frequencies on Web-controlled receivers.