Understanding Trunking - Uniden BCD396T Manual

Owner's manual (156 pages)

Owner's manual (156 pages)

Owner's manual (154 pages)

Table of Contents

Easier to Read BCD396T/UBCD396T Digital Scanner Manual

Continuous Tone Coded Squelch System (CTCSS) and Digital Coded Squelch (DCS) are two methods used to prevent interference by other radio communications. Your

scanner can receive transmissions that use these codes (or more commonly referred to as tone codes).

CTCSS and DCS systems all use some form of coded squelch. Coded squelch techniques involve the transmission of a special 'code' signal along with the audio of a radio

transmission. A receiver with coded squelch only activates when the received signal has the correct 'code'. This lets many users share a single frequency, and decreases

interference caused by distant transmitters on the same channel. In all major metropolitan areas of the United States, every available radio channel is assigned to more

than one user. Public safety radio systems on the same frequency are usually set up at a distance of 40 miles apart, or more. This means that you may hear transmissions

from a distant system when your local system is not transmitting. By programming the CTCSS tone for a local channel the scanner will not stop on transmissions from the

distant system. With few exceptions, such as the VHF Aircraft and Marine bands, almost every other VHF or UHF radio system uses some form of coded squelch. By far,

CTCSS is the most popular mode among non-trunked systems.

For more information visit Radio Reference's respective pages on

Trunking systems let a large group of 2-way radio users (or even different groups of 2-way radio users) efficiently use a set of frequencies. Instead of selecting a specific

frequency for a transmission, the user's radio selects a programmed trunking bank in the system when that user presses their PTT (push to talk) button. The trunking

system automatically transmits the call on the first available frequency, and also sends (on a different frequency called a Data or Control channel) a code that uniquely

identifies that transmission as a talkgroup ID (or just ID.) So when you are trunktracking a system, you are listening to active IDs transmitting in the system (each using the

first available frequency in the system.) Trunking systems in general allocate and use fewer frequencies among many different users.

Since the trunking system might send a call and its response on different frequencies, it is difficult to listen to trunked communications using a conventional scanner. These

scanners let you monitor the control channel frequency so you can hear calls and responses for users and more easily "follow" conversations than with a conventional

scanner.

These scanners trunktrack the following types of systems:

Motorola Type I

Motorola Type II

Motorola Type IIi Hybrid

Motorola Type II Smartnet

Motorola Type II Smartzone

Motorola Type II Smartzone Omnilink

Motorola Type II VOC

When you program Motorola frequencies into the scanner, one frequency is the control (or data) channel, and the rest are voice frequencies shared by all the users. There

may be 3 or 4 frequencies assigned as (primary or alternate) control channels but only one control channel will be active at a time. These scanners will allow you to

program just the Motorola control channels into the trunking system and the voice channels will automatically be found. EDACS systems need all the frequencies for the

system programmed and in the correct LCN (Logical Channel Number) order.

The control channel is continually transmitted to the field units and has a sound similar to listening to a boat engine over the phone (in manual mode; you won't hear this

when you are trunking the system.) This control channel is also a good check to see if you can trunktrack the system. If you can't hear a control channel when you step

through the trunking frequencies (in manual mode), you either don't have all the frequencies or are too far away to receive the control channel and the system. Motorola

systems are limited to a maximum of 28 frequencies per system, Ericsson EDACS systems are limited to 25 frequencies per system.

LTR systems work a little differently. This type of system encodes all trunking information as digital subaudible data that accompanies each transmission. LTR systems

typically do not have a dedicated control channel. The frequencies also have to be in LCN (Logical Channel Number) order or the correct 'slot' for the system to trunktrack

properly. Each repeater has its own controller, and all of these controllers are synchronized together. Even though each controller monitors its own channel, one of the

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CTCSS

and DCS.