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 or site. Ericsson EDACS systems are
limited to 25 frequencies per system or site. Motorola and EDACS systems can be either analog, digital, or mixed (digital and analog talkgroups). Mixed
Motorola systems should be programmed as Motorola systems and not P25 digital systems. That way the talkgroup options will allow you to select if it is a
digital or analog.
LTR systems
work a little differently. LTR systems typically
do not have a dedicated control channel. This type of system encodes all trunking information
as digital subaudible data that accompanies each transmission. The frequencies also have to be in LCN (Logical Channel Number) order or the correct
'slot' for the system to trunktrack properly. The Auto-Move feature will accomplish this for you. 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 channel controllers is assigned to be a master that
all controllers report to. Each of these controllers sends out a data burst approximately every 10 seconds so that the subscriber units know that the system
is there. This data burst is not sent at the same time by all the channels, but happens randomly throughout all the system channels. If you listen to the
frequencies of an LTR system in manual mode (not trunking), on every channel in the system you will hear this data burst that will sound like a short blip of
static like someone keyed up and unkeyed a radio within about 500 msec. LTR systems are limited to 20 frequencies per system.
Trunkscanning
is basically scanning IDs that are programmed into ID locations (same concept as frequencies into channels). You can then trunkscan just
the programmed IDs.
Trunktracking
is searching for
all
IDs in a system (same concept as searching for frequencies in a band).
Understanding Multi-Site Trunking
Some Motorola and EDACS systems covering a very large geographic area use multiple antenna sites that each operate on different frequencies and use
the same talkgroup IDs for traffic. You can program up to 32 frequencies for each trunking system (all you need are the
control channel frequencies
) but if
you have more than 32 frequencies for a system (such as large multi-site system), you will have to split it into separate sites (or groups of sites) and
duplicate the IDs for each site (or group of sites). Each talkgroup object can be assigned to one or more scan lists but only assigned to one trunking
system or site.
Radio Reference.com
has an excellent page explaining the various types of trunking systems in more detail
.
Understanding IDs
ID Formats
Motorola IDs
come in two display formats: Type I and Type II. Each format displays and uses Talk Group IDs in slightly different ways.
Type I/II hybrid
systems use both Type I and Type II formats for Talk Group IDs.
Type I IDs
are in the format
BFF-SS
where
B
is the block,
FF
is the fleet, and
SS
is the sub-fleet. Type I systems are usually organized with
different IDs assigned to different fleets. For example, a valid fleet/subfleet ID identifying all detectives within a police department might be 000-12,
where 000 identifies all police IDs and 12 identifies the Detective division. To properly trunk a Type I system, you have to program the fleet map for
the system.
Type II IDs
are identified by a 5-digit number. Valid (programmable) Talk Group IDs are divisible by 16.
EDACS IDs
come in two display formats:
AFS
(Agency-Fleet-Subfleet) and
Decimal
.
AFS IDs
are in the form
AA-FFS
where
AA
is the agency,
FF
is the fleet, and
S
is the sub-fleet. EDACS systems are organized with different IDs
assigned to different fleets and agencies. For example, a valid agency/fleet/subfleet ID identifying all detectives within a police department in an
agency might be 06-101, where 06 identifies the agency (Police), 10 identifies the Police division (East side), and 1 identifies the Detective
division.
Decimal IDs
are shown as a decimal number from
0
to
2047
.
You can find a chart showing Decimal and AFS equivalents here:
LTR IDs
are in the format
A-HH-UUU
where
A
is the area code (0 or 1),
HH
is the home repeater (01-20), and
UUU
is the user ID (000-254).
ID Types
Group Wildcard IDs
will monitor
all
talkgroup
IDs on the trunked radio system. A wildcard TGRP object allows you to receive IDs that are not already
stored as objects in the radio's memory.
Group IDs
will only monitor
talkgroup
radio traffic on that specified TGID.
Private Wildcard IDs
will monitor
all
private
IDs on the trunked radio system.
Private IDs
will only monitor
private
radio traffic on that specified private TGID.
Radio IDs
are group or private IDs associated with individual radios.
Understanding Receive Modes
Each conventional channel can have its own receive mode:
Auto
,
AM
,
FM
, or
NFM
.
Auto
- Receives transmissions in the modulation sent.
AM
- Receives transmissions in AM modulation.
FM
- Receives transmissions in FM modulation.
NFM
- Receives transmissions in NFM modulation.
Understanding CTCSS/DCS/NAC
Each conventional channel can have its own squelch mode:
None
,
CTCSS
,
DCS
,
P25
, or
Search
.
None
no codes will be searched.
CTCSS
- PL codes appear (if received) in the format
xxx.x
, where
xxx.x
is a frequency in Hz.
DCS
- DPL codes appear (if received) in the format
xxx
, where
xxx
is an octal code.
P25
- NAC codes appear (if received) as a 3-digit hexadecimal number.
Search
- the scanner will search and display
any
codes (if received).
Continuous Tone Coded Squelch System (CTCSS), Digital Coded Squelch (DCS), Network Access Code (NAC), are three methods used to prevent
interference by other radio communications. Your scanner can receive transmissions that use these codes (or sometimes referred to as tones).
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
