The "EDACS" (Enhanced DigitalAccess Communications System) system is one of a few different commercially available trunking systems. These systems are made by M/A-COM Wireless Systems and are usually supported by local communications companies.
Each EDACS system operates on a different group of 800 / 900 MHz frequencies where many agencies share groups of channels. A typical system has 2 or more geographically spread out tower systems. Where these systems are used, most county, local government and emergency services will be found using this system.
Each transmitter tower has it's own group of frequencies, one of which is a control channel. The system can choose ANY of the frequencies for the Control Channel. EDAC Systems are limited to 25 frequencies per tower site. The computer controlled radio system instantly assigns a random channel for each transmission by sending digital information over the control channel. Each call will be on a different channel. Transmissions can be simulcasted over all transmitter towers or sent to an individual tower to cover only a certain area.
The system controller is programmed to detect interference on any of the frequencies and cease all operations on that frequency until a specified time elapses after the interference stops. If the radio is lost or stolen, it can be locked out by the system.
EDACS systems currently supports a max of 2,047 talk groups or virtual channels, a max of 16,382 individual Logical ID's (LID). A LID is a numeric ID assigned to each radio during it's programming that will specifically ID that radio on the system. It is used to display the name or ID of the individual originating the transmission as well as to the system for it's permissions and denials of groups/features. The dispatcher can detect if a person is transmitting on a portable or a car radio because each unit has a different ID. Some radios are not allowed to use the telephone interconnect, make individual calls and some are not even allowed to transmit. This is all controlled via the logical ID of the radio. The LID is also used to make individual calls, you have to know or have pre-programmed the LID of the radio you want to have an I-Call with.
EDACS systems are able to connect a user to the telephone system. All telephone interconnect activity is usually on one frequency of each system. The calls are in conventional mode, but when no calls are taking place the frequency reverts back to a trunk channel.
The system can be patched to any VHF or UHF frequency that is available in the Comm Center. The patches can also be used to patch different talkgroups / agencies together. When two or more talkgroups are patched together, you will only hear the transmission on the patch talkgroup, not the originating talkgroups. A patch disables the original talkgroups.
EDACS systems are also capable of transmitting in ProVoice Digital Mode. There are no scanners available that will be able to hear or follow this mode. Your scanner will give no indications that digital communications are even taking place when it is Trunk Tracker mode. If you scan the system in conventional mode you will only be able to hear the digital data bursts. Presently their are no scanners available that follow digital communications. Some county and city detective divisions have talkgroups that use this mode.
Agency Call - Allows a supervisor to communicate to all fleets and subfleets
within the agency. (AFS XX-000)
Fleet Call - Allows a supervisor to communicate to all radios within a fleet or
Subfleet. (AFS XX-XX0)
I-Call - Individual call allows a one-on-one conversation not overheard by
other radios in the system or most Scanners. It is just like
using a cellular phone.
Wide Area - Countywide, usually the dispatch talkgroup. Communications are repeated
on all tower sites.
Each Motorola system operates on a different group of 400 / 800 / 900 MHz frequencies where many agencies share groups of channels. A typical system has 1 or more geographically spread out tower systems. Where these systems are used, most county, local government and emergency services will be found using this system.
Each transmitter tower has it's own group of frequencies, one of which is a control channel. The system can choose ANY of the frequencies for the Control Channel. Motorola Systems are limited to 28 frequencies per tower site. The computer controlled radio system instantly assigns a random channel for each transmission by sending digital information over the control channel. Each call will be on a different channel. Transmissions can be simulcasted over all transmitter towers or sent to an individual tower to cover only a certain area.
The system controller is programmed to detect interference on any of the frequencies and cease all operations on that frequency until a specified time elapses after the interference stops. If the radio is lost or stolen, it can be locked out by the system.
Motorola systems currently supports a max of 4,096 talk groups or virtual channels, a max of 65,535 individual Logical ID's (LID). A LID is a numeric ID assigned to each radio during it's programming that will specifically ID that radio on the system. It is used to display the name or ID of the individual originating the transmission as well as to the system for it's permissions and denials of groups/features. The dispatcher can detect if a person is transmitting on a portable or a car radio because each unit has a different ID. Some radios are not allowed to use the telephone interconnect, make private calls and some are not even allowed to transmit. This is all controlled via the logical ID of the radio. The LID is also used to make private calls, you have to know or have pre-programmed the LID of the radio you want to have an I-Call with.
Motorola systems are able to connect a user to the telephone system. All telephone interconnect activity is usually on one frequency of each system. The calls are in conventional mode, but when no calls are taking place the frequency reverts back to a trunk channel.
The system can be patched to any VHF or UHF frequency that is available in the Comm Center. The patches can also be used to patch different talkgroups / agencies together. When two or more talkgroups are patched together, you will only hear the transmission on the patch talkgroup, not the originating talkgroups. A patch disables the original talkgroups.
Motorola systems are also capable of transmitting in APCO 25 Digital Modes. Some systems also use encryption on some talkgroups. These talkgroups cannot be monitored by any scanner.
In a conventional radio system, the user may only have access to a single channel. If the user wishes to make a call, he must first monitor the channel to make sure it is clear. If the channel is busy, the user must continue to monitor the channel until the co-channel user has terminated the conversation. By contrast, in a LTR trunked system the channel selection is automatic. When the user initiates a call, the trunking system electronically "monitors" each channel in the system and automatically selects one of the clear (unused) channel. Once a channel is selected, it becomes exclusive for the duration of the transmission and cannot be interrupted by other users.
Logic Trunked Radio (LTR) Trunk Systems do not have a control channel such as Motorola or Ericsson Trunked systems. On a LTR Trunk System a data burst can be heard on each frequency of the system around every 10 to 20 seconds. Also LTR frequencies do not have any CTCSS or DCS tones (pl tones). LTR Trunked systems are also known as SMR (Shared Mobile Radio) systems.
Each business user on a LTR Trunked system is assigned a talkgroup ID(s) that consists of an Area Code, a Home Channel
and a User ID.
Area Code - It is used if two different nearby LTR Trunked systems are using the same frequency(s).
The Area Code can be either 0 or 1.
One system is assigned an Area Code of 0 and the other is assigned an Area Code of 1.
Home Channel - Each user is assigned a home channel (frequency). If the system is not very busy, then all
conversations can be heard on the home channel. When the system starts getting busy, one or more of the users
will change over to another free home channel (frequency) or to one of the overflow channels. Overflow
channels have no assigned users. An LTR system can have a maximum of 20 channels (frequencies).
User ID - Each business user is assigned a single or a group of ID's (user identification) from 000 to
254. Most small business users will only have a single ID. Each home channel (frequency) can have a maximum
of 255 user ID's.
Example:
0-05-098
0 = Area Code (0 or 1)
05 = Home Channel (01 to 20)
098 = User ID (000 to 254)
The systems on the website have their home channels and frequencies listed. The frequencies listed without channel numbers are the overflow frequencies and still need their channel numbers figured out.
Some LTR Trunk Systems are single frequency (channel) systems. They use the talkgroup ID's in the same way as pl tones are used. On a single channel system the scanner will display other active talkgroups besides the one that it is locked on.
Most LTR Trunked Systems are PassPort (LTR-Net) enabled. The LTR Passport-enabled service allows multiple sites to be linked together and includes "follow-me roaming" features that are similar to the automatic handoff of radio signals characteristic of cellular radio systems.
Example: A Taxicab leaving Melbourne going to Orlando automatically switches to one of the Orlando systems after it gets out of the range of the Melbourne system. All communications will then be linked back to Melbourne via the Orlando system.
A dispatcher has the ability to contact a selected group of users, contact an individual user or to use Fleet Call to contact all users. Some systems can also have telephone interconnect.
These systems are used by taxicabs, pest control, wreckers, repairmen etc. The system owners lease air time to individual business users. The individual users do not need a separate license, only the system owner needs a license. Because of this the only way of finding out who is using these systems is by monitoring them.
Digital Packet Data talkgroups are used to send computer information that can contain vehicle location (GPS), status or any other type of digital information. All that can be heard on these talkgroups are bursts of digital data.
The frequencies with channel numbers are in LCN order and must be entered into the scanner in this order. Channels not listed must be left blank.
Example:
Ch. Frequency
1 461.6250
2 blank
3 461.3750
4 blank
5 461.2750
6 blank
7 461.8000
You can only enter one LTR Trunk System per bank.
Courtesy of http://home.roadrunner.com/~scanner/
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