Logic Trunked Radio
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Contents
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 that track LTR Standard systems require that the channels be programmed in proper logical order in order to properly monitor the system. Radio Shack scanners that support LTR Standard systems do not require that the frequencies be in proper order but tracking is less efficiently accomplished.
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.
- "HH" is the home repeater number and has twenty possible values, 01 through 20. A talkgroup will always use its home repeater by default, unless the repeater is already in use by another talkgroup. If the home repeater is in use, the controller will assign another free repeater at random. If no repeater is free (all are in use), then the radio will receive a busy signal.
- "GGG" is the group number and has 254 possible values, 001 through 254.
- Scanners that Track LTR Standard
- Radio Shack Pro-2051
- Radio Shack Pro-2055
- Radio Shack Pro-2067
- Radio Shack Pro-92
- Radio Shack Pro-97
- Uniden BC246T
- Uniden BC250D
- Uniden BC296D
- Uniden BC780XLT
- Uniden BC785D
- Uniden BC796D
- Uniden BC898T
- Uniden BCD396T
- Uniden BCT8
- Uniden BR330T
LTR Passport
Each passport site seems to have at least 3 frequencies:
- A "local" home channel for units that have this site as the home site.
- A "roaming" home channel for units that have another site as the home site.
- 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.