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Difference between revisions of "Logic Trunked Radio"

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Revision as of 05:20, 29 December 2010

Overview

Logic Trunked Radio, or LTR, was originally developed by E. F. Johnson in the early 1980s. LTR systems do not have a dedicated control channel like Motorola and EDACS systems. Each repeater has its own controller and all of these controllers are coordinated together. Even though each controller monitors its own channel, one of the channel controllers is assigned to be a master and all the other controllers report to it.

Typically on LTR systems, each of these controllers periodically sends out a data burst (approximately every 10 seconds on LTR Standard systems) so that the subscriber units know that the system is there. The idle data burst can be turned off if desired by the system operator. Some systems will broadcast idle data bursts only on channels used as home channels and not on those used for "overflow" conversations. To a scanner user the idle data burst will sound like a short blip of static like someone keyed up and unkeyed a radio within about 1/2 second. This data burst is not sent at the same time by all the channels but happen randomly throughout all the system channels.

LTR Standard

LTR Standard systems have no dedicated control channel. All control data is sent as subaudible data along with voice transmissions. Systems can have any number of channels from 1 through a maximum of 20. Each channel in the system is assigned a unique number (01 through 20) and these need not be sequentially assigned. Each subscriber radio must be programmed with all channels in the system in proper logical channel order (the same requirement as EDACS systems).

Uniden scanners and Radio Shack scanners that track LTR Standard systems require that the channels be programmed in proper logical order in order to properly monitor the system, with exception of the Radio Shack Pro-92 and Pro-2067, that do not require that the LTR frequencies be in proper order but tracking is less efficiently accomplished. This ordering is referred to as the Logical Channel Number or LCN.

LTR Standard talkgroups are written in the format A-HH-GGG.

  • "A" is the area code and is either 0 or 1. The area code is the same for all talkgroups in a given system and is arbitrarily chosen by the system operator; the most common use is to simply distinguish between talkgroups on multiple systems.
  • "GGG" is the group number and has 254 possible values, 001 through 254.

If there are no LTR systems in the Radio Reference Database for your general location, Mapping an LTR System describes how find and determine the proper channel order using Uniden Scanners

Scanners that Track LTR Standard

LTR Passport

Each passport site seems to have at least 3 frequencies:

  1. A "local" home channel for units that have this site as the home site.
  2. A "roaming" home channel for units that have another site as the home site.
  3. A "registering" channel that is used by roaming units to register with the site.

The local home channel is programmed into the radio. The roaming home channel is assigned when the unit registers with a site and seems to be the same for all units that register at that site. The registering channel is the frequency broadcast by neighboring sites in their "neighbor" information.

Passport bands:

  • Band 0 800 MHz
  • Band 1 900 MHz
  • Band 2 400-420 MHz
  • Band 3 420-440 MHz
  • Band 4 440-460 MHz
  • Band 5 450-470 MHz (this is the one used by most UHF Passport systems in the United States)
  • Band 6 460-480 MHz
  • Band 7 470-490 MHz
  • Band 8 480-500 MHz
  • Band 9 490-512 MHz
  • Band 10 409-430 MHz
Scanners that Track LTR Passport

No scanners are currently available that will track LTR Passport systems.

LTR Standard and Passport

LTR Standard and Passport systems are hybrid systems that have some LTR Standard talkgroups and some LTR Passport talkgroups.

LTR MultiNet

LTR MultiNet systems are APCO-16 compliant and thus are mostly found in use as public safety systems. LTR MultiNet systems usually have one or more "status channels" that act like a control channel in a Motorola or EDACS system, however these channels can also carry voice transmissions simultaneously.

Scanners that Track LTR MultiNet

There are no scanners currently available that will track LTR MultiNet systems.

LTR-Net

An enhanced version of LTR Standard that is backward compatible with LTR Standard. LTR Standard radios can be used on an LTR-Net system.