The Evolution of Police Scanners

Welcome to the "Evolution of Police Scanners". This section provides an overview of how police scanners have evolved around public safety radio systems. 

The information in this section is divided into the following topics:

• The Early Years: Conventional Police Scanners

• The Next Generation: Trunking Police Scanners

• The New Frontier: Digital Police Scanners

Note: This section is also the first part of the six-part Police Scanners & Accessories section. 

Monitoring police communications goes back to the early 1930's when police broadcast were done through local AM radio stations. Field units would monitor the radio for calls and anyone with a radio would also hear the broadcast. For a detailed overview of how this all worked, check out this page. It is also helpful to read Harry Marnell's "LAPD Communications Division History." Jump forward to the early 70's.      

Crystal-Controlled Scanners

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. 

The first generation police scanners were crystal-controlled conventional scanners, with 4 or more channels. To monitor a particular frequency, you had to have a quartz-crystal tuned to that frequency and plugged into one of the scanner's internal slots (one for each channel). Each crystal cost around $7.00 and got a little expensive once 16 and 20-channel scanners came out. Crystal-controlled scanners can still be found in yard sales and even on ebay. 

Programmable Scanners 

In the late 70's, programmable scanners were introduced and it was heaven! NO MORE CRYSTALS! These new scanners came with a keypad that allowed you to directly enter frequencies into the scanner's memory (one per channel) just as today's scanners do! 

Note: Conventional scanners are capable of picking up only conventional analog (non-digital) radio transmissions. This type of scanner is perfect is you do not need trunking or digital-capable scanner in your area. 

Click here for a more detailed look at Conventional Radio Systems.

The next generation of police scanners where analog trunking-capable scanners. This type of scanner was needed to monitor and track communications on a Trunked Radio System. In a trunk radio system, users share a pool of frequencies from 5 up to 29 frequencies, depending on the size and number of users. 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. Click here for a more detailed look at Trunked Radio Systems.

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 with 800MHz-capability 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. 

Besides it's ability to function as a "conventional" scanner, there are some important things to know when it comes to trunking scanners. First off, not all trunking scanners can track all trunk system types. This limitation only applies to first generation trunking scanners that are only able to follow Motorola trunked systems, one of the three most common trunked radio systems in use in the United States. Trunking scanner technology, called "TrunkTracker", has since evolved into several generations, each expanding the capability of previous generations to track all public safety trunked radio systems.  

TrunkTracker Technology

A TrunkTracker is a special scanning receiver which has been programmed to decode, monitor, and track communications on a Trunked Radio System. TrunkTracker technology was developed by Uniden back in 1997 and was the biggest advancement in scanner technology in 20 years. Since it's arrival, trunking technology now spans four generations from the original TrunkTracker models to the current TrunkTracker IV models. 

TrunkTracker - the first TrunkTracker scanners (BC235XLT, BC895XLT, PRO-90, PRO-91, PRO-2050 and PRO-2066), could only monitor Motorola systems in the 800MHz frequency band and only one system at a time.

TrunkTracker II  - TrunkTracker II expanded monitoring capabilities of trunked systems to include Motorola Type I, Type II, Hybrid, SMARTNET, Privacy Plus, GE/Ericsson EDACS systems (which is now owned by M/A-Com) and systems located in the VHF/400/500/ 800/ 900 MHz frequency bands. Another major improvement was "Multi-Track", giving uses the ability to not only monitor both non-trunked conventional and trunked systems at the same time, but multiple trunk systems as well. The BC245XLT is the only TrunkTracker II scanner made.  

TrunkTracker III - TrunkTracker III technology adds the ability to monitor EF Johnson LTR systems along with the ability to monitor EDACS 4800, 9600 and SCAT* analog systems. TrunkTracker III scanner include the BC780XLT, BC246T, BC898T, BC785D and BC250D - BCT-8?. *(EDACS SCAT is only available in the BC785D and BC250D). 

TrunkTracker IV  - TrunkTracker IV technology adds the ability to monitor APCO 25 Digital Trunking Systems including 3600 & 9600 Baud, C4FM, & CQPSK.

In a digital radio system, a computer encodes voice transmissions into streams of data (0's and 1's - similar to a modem) and then the radio on the receiving end converts it back into audible voices. In order to follow these digitized transmissions, you need a digital-capable scanner. Click here for a more detailed look at Digital Radio Systems.

Digital scanners are the newest generation of scanners to hit the market. These new scanners are basically trunking scanners with the ability to decode and track APCO 25 Systems digital radio systems in addition to regular analog trunked and conventional systems. Because this scanning technology is relatively new, there are only a few digital scanner models available on the market to choose from, and by only two manufacturers, Uniden and Radio Shack 

Uniden was the first to put out digital scanners in late 2002, the BC250D (handheld model) and the BC786D (base model). A year later in September 2003, Radio Shack released its much-anticipated digital scanner, the Pro-96. More recently, Uniden has put out second-generation digital scanners, the BC296D (handheld model), the BC796D (base model) and the new BC369T. Radio Shack has their second generation digital scanner due out in late 2005.

It's important to note that the BC250D and the BC785D are limited to only decoding and tracking APCO 25 digital transmissions with 9600-baud control channels and cannot decode and track APCO 25 digital transmissions with 9600-baud control channels or CQPSK and C4FM modulation types. All other modes have the ability to decode and track all of the above digital types. More details can be found in the Digital Scanner page.

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