Radio Frequency Scanners

Radio Frequency Scanners: Police, Fire Services Live Audio

Radio scanners are used by civilians to listen in on police, fire fighter, ambulance, NOAA weather, ham radio, FRS (walkie-talkie), CB (Citizens’ Band), air traffic control, NASCAR drivers and crew, taxi, railroad, marine and other radio communications. Large concerts and sporting events have multiple crews working to make everything work smoothly. A scanner provides an interesting behind-the-scenes look at a world hidden from most people.

Radio Frequency Scanners

They can be used for:

  • Entertainment (they are good gifts for retirees, anyone with time on their hands).
  • Keeping track of family members who are pilots or who work in emergency services.
  • Situational awareness during disasters or smaller emergencies. Find out what is really going on, as it happens.
  • Spotting airplanes, ships or trains.

The main types are:

  • Handheld (these look like walkie-talkies). Good for disaster situations, when it might be necessary to run off batteries or evacuate the area.
  • Base or console models. These are usually the most advanced scanners. There’s space to display more information, and for more buttons (easier to use).
  • Clock radios. Good for casual use.

Scanner brands include AOR, GRE, Icom, Radioshack (PRO) and Uniden (Bearcat). Prices range from under $100 for basic analog models, to over $500 for trunking and digital models.

Some of the information in this article is based on user reviews of radio scanners on the website, and on the Uniden BCD396T Owner’s Manual (this model was chosen at random to represent a typical scanner). Reading through this or other user manuals is a good way to learn about scanners.

How Radio Scanners Work (Basic Scanner Terminology)

Radio scanners are basically radio receivers with advanced tuning capabilities. Two-way radio communications are intermittent, and there are many frequencies in use. A scanner helps automate the search for active transmissions over different frequencies.

There are two main operating modes: searching and scanning.

When searching, the radio searches a range (band) of frequencies (say, 25 to 225 MHz). If a transmission is detected, the radio will stop at that frequency to allow the user to listen to it. After the transmission stops, the radio continues to search the other frequencies. An optional delay of a few seconds, makes the radio wait at the same frequency for the other party to reply, before moving on.

Searching is an easy way to get started, for beginners or when in an unfamiliar area. Some radios come with pre-programmed search ranges. They allow users to search only services that interest them: public safety, railroad, marine, aircraft etc. A custom search feature allows the user to set his own search range. A chain search feature allows multiple ranges to be searched.

Scanning is like searching, but the radio only listens in on a user-defined list of frequencies. Each frequency is called a channel. A 100 channel scanner can store 100 frequencies in its memory for scanning. Scanners can have over 1,000 channels, depending on the model.

The advantage of scanning is that less time is wasted testing empty or uninteresting frequencies. Scanners can scan about 100 channels per second.

Scanner Programming

Storing a frequency into memory, creates a channel. This is called programming the scanner. There are different ways to program a scanner:

  • Saving searched frequencies. In search mode, the user saves the current frequency into memory, if he hears something interesting. This is the only programming method on simpler scanners.
  • Keypad entry. A numeric keypad allows frequencies to be directly entered. The frequencies (also called codes), can be found from websites such as The main disadvantage is that the sequence of keys to press can be complicated.
  • PC control. This is the fastest method (useful when programming hundreds of channels), but some computer knowledge is required. The PC is connected using a serial or USB cable. Custom software from the manufacturer is required (often sold separately). Third-party software such as FreeScan, ProScan and Butel, are often preferred over the manufacturer’s own software. Frequencies and related information (trunking, party line, channel bank number) are entered into the software (like a spreadsheet), then downloaded into the scanner. Different software is needed for each scanner model, even with scanners from the same manufacturer.

Whatever the method used, the scanner should not allow duplicate frequencies to be entered.

Radio Scanners and the Law

US federal law makes it illegal to listen in to any telephone conversation, including cellphones and even home cordless phones. Encrypted communications are also off limits. Some local laws prohibit the use of scanners in moving vehicles, or require permits. Users should familiarize themselves with applicable laws before buying and using a scanner.

There’s more information on radio scanner legal issues on the website

Types of Radio Scanners: Analog, Digital, Trunking

Basic scanners aren’t very different from scanners from twenty or thirty years ago. They can still pick up transmissions from many services. However they are not compatible with the new analog trunking and digital systems used by emergency services in large cities.

  • The most basic scanners will cover frequencies below 800 MHz. This includes almost everything except police systems.
  • The next step up are police scanners that also monitor 800 MHz (actually about 806-956 MHz) frequencies, commonly used by police departments.
  • A party line or sub-band feature allows monitoring of CTCSS and DCS transmissions.
  • More advanced are radio trunking (trunk tracking) scanners that can scan trunked systems. Trunked systems are used by police and other municipal services in large cities. They allow more users to share the same frequencies, saving on precious bandwidth. There are different types of analog trunked systems (Motorola, LTR, EDACS). The scanner needs to understand all of them.
  • The most advanced scanners are able to monitor digital broadcasts. The main digital broadcast system of interest, is the APCO-25 or P25. It is used by police and emergency services in large cities.

Websites such as have lists of frequencies and trunking systems used by public service agencies, broken down by city or county. Before buying a scanner, users should check that the scanner is compatible with the systems used in their area.

How to Choose a Scanner: Features

Aside from the basics of frequencies, party lines, trunking and analog/digital; additional features provided by a scanner can greatly affect its usability:

  • Grouping of channels into banks (groups), allowing scanning of selected banks only. Basic scanners have only one bank of channels.
  • “Control channel only” mode to identify talk groups in a monitored trunk system.
  • Setting of names (alpha tag) for each channel. No need to memorize what each frequency is for.
  • Channel lock-out to temporarily disable some channels.
  • Listening to local transmissions only (Uniden Close Call, Radio Shack Signal Stalker).
  • Support for SAME (Specific Alert Message Encoding) NOAA weather alerts, to filter out alerts for other areas.
  • Monitoring trunk and conventional frequencies at the same time. Some scanners can only monitor one type at a time.
  • Priority channels. These are checked every few seconds for transmissions, instead of waiting their turn. Some scanners disable this feature when trunk channels are being monitored.
  • Fire tone-out support, to identify calls for individual fire stations.

Useful hardware features are:

  • Audio jack for headphones and external speakers.
  • Socket for external antenna, for better reception.
  • Signal strength meter.
  • Lots of buttons. Scanners with fewer buttons, assign more than one function to a button (with a shift or function key), making it harder to operate the scanner.
  • 12 volts DC cigarette lighter power adapter, for use in cars.

The Best Radio Frequency Scanner

Users need to decide what kinds of transmissions they want to listen to, and check what their local services are using. Radio systems are complex. The more users know about CTCSS/DCS, radio trunking and other radio technologies, the better they will be able to choose and use scanners.

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