NOTE: The information contained on this page are excerpts from Police-Scanner.info's "Inside the World of Police Scanners" eBook. This eBook is included FREE with every police scanner order. This information also appears on Police-Scanner.info's website. An extensive collection of FREE police scanner information can be found at Police-Scanner.info.

A police scanner is the nickname given to a radio scanner. A radio scanner is a special receiver that is capable of receiving wireless radio signal transmissions. These wireless signals include two-way radio transmissions used everyday in public safety and business operations.

A scanner picks up these radio signals, similar to an AM/FM radio. While an AM/FM radio is programmed to pick up only AM/FM band radio signals, a scanner can pick-up multiple radio signals and multiple radio bands simultaneously making it possible to easily keep track of many channels at once. The term "police scanner" comes from the fact that the majority of scanner users enjoy listening to police radio broadcast.

The vast majority of users include:

• Law-abiding citizens
• On/off-duty or volunteer police officers and firefighters
• Family members of police officers and firefighters
• Neighborhood watch groups
• Regional emergency disaster groups
• Public safety organizations
• Amateur/ham operators
• and news media organizations

If you travel a lot or just want to be able to take it along and listen anywhere, then a handheld scanner would be a good choice. Handheld scanners are made for portable use and come with a belt clip so you can carry it on your belt or in your purse.

Handheld scanners are battery operated and can also run on household current or a vehicles power, This type of model requires "AA" sized batteries or may come with a re-chargeable battery pack.

Pros:

• Made for portable use.
• Runs on "AA" sized batteries or re-chargeable battery pack.
• Not affected by power outages.

Cons:

• Range and reception is less than that of other models.
• Higher chance of unit being damaged to accidental dropping.
• Sound volume not as loud as other models.
• Units with re-chargeable battery packs require charging.

A handheld scanner is ideal during a major disaster, severe weather, or other emergency condition where power may be out for extended durations and there?s nothing like having a battery operated scanner to monitor police and fire radio traffic for dangerous conditions and important information!

If you just want to listen to your scanner only when you are at home, a base station or desktop model is ideal for you. Base and desktop models are made for stationary use such as on a bedroom stand or living room table. In addition, most base models are designed all operational controls on the face as well as "plug-in" power cords and "bracket mounting holes" for mounting in a vehicle for mobile use. Desktop models on the other hand are designed for only stationary use. All operational controls on top of the scanner and it has a "screw-in" antenna and dedicated power cord.

Pros:

• All: Range and reception is greater than other models
• All: Sound volume is much greater than handheld models.
• Base/Mobile: Made for both stationary and mobile use.
• Base/Mobile: Runs on household and vehicle power supply with adapter.
• Base Mobile: You can increase reception by using an external antenna.

Cons:

• All: Affected by power outages.
• All: Must be located near power outlet.
• All: Not for portable use.
• Base/Mobile: Mobile use requires cigarette adapter for vehicle power use and a mobile scanner antenna.
• Desktop: Made for stationary use only.
• Desktop: Limited to the ability of it's "screw-in" antenna.

Every country has its own rules governing usage. In the US, the FCC is the government agency that handles issues regarding radio transmissions, usage, and licenses for all non-military radio systems. The Wireless Telecommunications Bureau (WTB) is the branch of the FCC that handles nearly all FCC domestic wireless telecommunications programs and policies. Learn more about the wireless communication services.

The National Telecommunications & Information Administration?s (NTIA) Office of Spectrum Management (OSM) is responsible for managing the Federal Government's use of the radio frequency spectrum.

The US Radio Frequency Spectrum Allocation establishes which radio services operate in a given frequency band. There are thirty different radio services in over 450 separate frequency bands.

You can view the US Radio Frequency Allocation Chart (in pdf format) here. The chart graphically partitions the radio frequency spectrum, extending from 9 kHz to 300 GHz, into over 450 frequency bands, and uses distinct colors to distinguish the allocations for the thirty different radio services. For more information, see: Basic Elements of Spectrum Management.

Radio Frequencies

A frequency is a path or "channel" used for communications. It is a spot on a radio band identified by its number. To hear transmissions for what you want to listen to, you must have the specific frequency for that channel programmed into your scanner. For example, my local police department?s (Covina PD, CA) main dispatch frequency is 154.7250 MHz.

In busy/populated areas, police and fire agencies will most likely have several frequencies that they use for daily operations. You will most likely find a separate frequency for dispatch, car-to-car, tactical use, detectives, and so on. My local police department has a secondary frequency for car-to-car/tactical communications. In addition, there is a separate channel for investigators and mutual aid. For fire agencies, you will most likely find a separate frequency for dispatch, response coordination, on-scene "fireground" tactical use, paramedics, and so on.

In trunk radio systems, frequencies are not assigned to a particular use, they are assigned in a "pool"and usage is based on availability. See our trunk radio page for a complete overview of how trunk radio systems utilize frequencies.

Channel Designations

A channel designation is used to identify a frequency by name rather than by number. For example, Channel-1 (dispatch) and Channel-2, Frequency-1 and Frequency-2, or Blue channel, Red channel, Primary and Secondary, etc.

Continuous Tone Coded Squelch System (CTCSS)

CTCSS (Continuous Tone Coded Squelch System) is a system that is used to avoid interference between separate agencies within close proximity to each other using the same frequency. Each radio for a particular agency is programmed with a CTCSS code so that only those radios can hear and talk with each other and not a neighboring agency.

The system involves an industry standard set of sub-audible tones for controlling radios and associated equipment. The sub-audible tone is added to the transmitted signal. The receiving radio is then set up to listen for this specific tone in the received and demodulated audio. If the matching tone is present, the squelch is opened up, allowing the audio to pass through to the speaker. If the tone is not present, then the radio remains silent, even though there is a signal on the frequency. This allows two or more agencies to use the same frequency (generally on a repeater), but not hear each other's conversations.

CTCSS is also called "PL Tone" and is the Motorola Proprietary name for CTCSS. Several other companies have marketed their own brands of CTCSS under different names including "Channel Guard", "Quiet Channel", "Quiet Mode", and "Private Mode".

DCS on the other hand stands for Digitally Controlled Squelch. It is also called DPL or Digital Private Line and Digital Channel Guard. DCS is a digital code that is sent to open the squelch just like the tone does in CTCSS.

Some newer high-end scanners come with a CTCSS DCS/PL decoder built in it. If an agency is the only user in the area, there's no need to worry about a PL tone to filter out other users. There are advantages however, like in busy metropolitan areas where CTCSS helps keep a lot of unwanted junk out of your speaker. Without CTCSS or DCS, your scanner will pick up a lot of unwanted stuff you just don't want to hear. On the flip side, I live in eastern Los Angeles County where many public safety agencies reside and have never experienced problems without CTCSS capability.

Common Radio Bands for Monitoring:

• 29.000 - 50.000 MHz - Government, business, two-way and cordless phones.
• 50.000 - 54.000 MHz - 6-meter Amateur Radio
• 108.000 - 136.000 MHz - Aircraft
• 138.000 - 144.000 MHz - Government
• 144.000 - 148.000 MHz - 2-meter Amateur Radio
• 150.000 - 174.000 MHz - Shared by Business, Maritime, Weather, & Public Safety
• 406.000 - 420.000 MHz - Government
• 420.000 - 450.000 MHz - Amateur Radio
• 450.000 - 470.000 MHz - Shared by Business, Industry, Gov., & Public Safety
• 470.000 - 512.000 MHz - Public Safety
• 806.000 - 940.000 MHz - "800 Band" Public Safety
• 851.000 - 866.000 MHz - Business & Public Safety
• 866.000 - 869.000 MHz - Public Safety

In a conventional radio system, a frequency is used for each channel of communication. To hear transmissions for what you want to listen to, you must have the specific frequency for that channel programmed into your scanner. For example, a local police department?s dispatch channel would be on one frequency and their car-to-car channel would be on another separate frequency.

In small towns/cities, police and fire agencies will have several frequencies that they will use for daily operations. You will find a separate frequency for dispatch, car-to-car. For fire departments, they may have dispatch, response coordination, on-scene "fireground" tactical, all on one frequencies.

In large towns/cities, police and fire agencies will have several frequencies that they will use for daily operations. You will find a separate frequency for dispatch, car-to-car, tactical use, detectives, and so on. For fire departments, you will find separate frequencies for dispatch, response coordination, on-scene "fireground" tactical use, paramedics, and so on.

How Trunked Radio Systems Work

In a conventional system, frequencies are allocated for channel use by function, i.e., dispatch, car-to-car, tactical, mutual aid, etc. These channels are only used when they are needed leaving some channels such as dispatch busy with radio traffic while mutual aid remained unused. To make efficient use of all frequencies evenly, trunking technology was developed.

In a trunk radio system, all users share a pool of frequencies from five up to a maximum of twenty-eight. Users are assigned a "group id" and field radios are programmed to only pick-up transmissions for that group. A computer, called the "site controller", automatically assigns a frequency for users belonging to the same group to communicate with each other. This is done over a data channel called the "control channel", which carries data that tells field radios what frequency they are on. Trunk radio systems may have one or more control channels and may rotate them every 24-hours.

Sound complicated? Well, let?s say that your local police are communicating on a frequency assigned by the controller. As soon as there is a break in the communications, the controller automatically moves all users in that talkgroup to the next available frequency. At the same time, your local fire department is communicating on another assigned frequency, as soon as there is a break in their communications, the controller moves them to the next available frequency, maybe even the one that the police were just on.

Since communications on a trunked system never stay on one frequency, monitoring these communications with a conventional scanner is virtually impossible, especially in large metro areas where a trunked system can have dozens and dozens of users. Although, theoretically, in a small town system with just a couple of users like police and fire and little radio traffic, you could get by using a conventional scanner by programming all system frequencies and locking out the data channels. Although you will have to guess at who is who when you hear something.

Types of Trunked Radio Systems

There are several different types of analog trunk radio systems, they include;

• Motorola - Type I, II, IIi Hybrid, Smartnet, Smartzone, & Privacy Plus systems.
• EDACS (Enhanced Digital Access Communication System - owned by M/A-COM)
• LTR (Logic Trunked Radio - mainly used in the private business sector)
• iDEN Harmony
• MPT-1327
• OpenSky
• SmarTrunk
• TETRA

The tragic events of 9/11 clarified the critical importance of effective first responder communication systems. The lack of public safety interoperability is a long-standing, complex, and costly problem with many impediments to overcome. Interoperability is the ability of public safety agencies to talk to one another via radio communication systems—to exchange voice and/or data with one another on demand, in real time, when needed and when authorized.

APCO Project 25, or "P-25" for short, is the public safety industry standard developed by the APCO International (Association of Public Safety Communications Officials) to provide a radio solution that would allow different agencies using different radio systems to interoperate according to a public safety industry standard and not by system manufacturer.

The benefits for public safety are:

• Coordinate communications with other agencies and jurisdictions.
• Purchase radios and other equipment from more than one vendor.
• Upgrade or migrate systems without replacing all your equipment.
• Share resources with other organizations to control costs.

The FCC has officially said that "digital is the mode of the future," so more and more public safety agencies will be going digital. Digital systems are far more expensive than conventional analog systems, so I don't think that everyone will be changing to digital anytime soon, but eventually all public safety radio systems will be digital.

Types of Digital Radio Systems

A digital radio system is basically a Project-25 digital solution on top of a conventional or trunked radio system. In a digital system, a computer converts, or " encodes", voice transmissions into streams of data (0's and 1's - similar to a modem) and the receiving-end radio "decodes" it back into audible voice.

Project-25 uses the IMBE ( Improved Multi-Band Excitation) Vocoder and has two types of digital modulation available; Project-25 Digital Trunking and Motorola ASTRO IMBE:

• Motorola ASTRO IMBE - this is Motorola's proprietary APCO-25 compliant digital trunking solution. ASTRO IMBE uses the Project-25 vocoder for digital voice over a standard Motorola Type II Smartzone system allowing for both analog and Project-25 digital radios to operate on the same network.
• Project 25 Digital Trunking - this is the Project 25 Digital trunking solution that is vendor independent and designed around the Project-25 Digital Trunking standards. All radios on a Project-25 Digital trunking system must use digital voice - no analog trunking capability is provided. This is becoming a more popular trunking format for new systems.

The above digital modulations allow for the following four type of conventional and trunking digital radio systems:

• Conventional P-25 - one frequency with digital voice.
• Trunked at 3600 baud - digital voice with analog control channel operating at 3600 baud. This is the most common P-25 system currently in use.
• Mixed Mode at 3600 baud - trunked system with an analog control channel alternating/mixing analog and digital voice communications.
• Pure Digital at 9600 baud - trunked system with digital analog control channel and digital voice operating at 9600 baud.

NOTE: The information contained on this page are excerpts from Police-Scanner.info's "Inside the World of Police Scanners" eBook. This eBook is included FREE with every order. This information also appears on Police-Scanner.info's website. An extensive collection of FREE police scanner information can be found at Police-Scanner.info.