Logic Trunked Radio
Trunked radio system without a dedicated control channel.
Logic Trunked Radio (LTR) is a trunked radio system that was created by the E. F. Johnson Company in the late 1970s. Unlike many other trunked systems, LTR has no dedicated control channel. Each site in an LTR system is limited to 20 repeaters, and sites operate independently without being linked. Every repeater has its own controller, and these controllers work together; one controller is designated as the master, and the others report to it. On standard LTR systems, each controller typically sends out a data burst about every 10 seconds. This burst lets subscriber units know the system is present and which channels are in use or free. The system operator can choose to turn off these idle data bursts. Some systems send idle bursts only on channels used as home channels, not on overflow channels. To a listener, the burst sounds like a short blip of static, similar to a radio being keyed and unkeyed in about a quarter of a second. The bursts are not sent simultaneously across all channels but occur randomly throughout the system.
- Developer
- E. F. Johnson Company
- Maximum channels per site
- 20
- Idle data burst interval
- approximately every 10 seconds on LTR Standard systems
Lore & Background
LTR systems are limited to 20 channels (repeaters) per site, and each site stands alone, not linked to others. 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, each controller periodically sends out a data burst (approximately every 10 seconds on LTR Standard systems) so that subscriber units know the system is there and which channels are in use or available. 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 listener, the idle data burst will sound like a short blip of static, as if someone keyed up and unkeyed a radio within about 1/4 second. This data burst is not sent at the same time by all channels but happens randomly throughout all the system channels.
Reader's Guide
LTR's significance lies in its unique architecture, which eliminates the need for a dedicated control channel, a feature that distinguishes it from many other trunked radio systems. This design simplifies system operation and reduces the risk of a single point of failure, as control functions are distributed across all channel controllers. The system's limitation to 20 channels per site and its standalone site operation make it suitable for localized, medium-capacity trunking applications. The periodic idle data bursts, while optional, serve as a beacon for subscriber units to maintain awareness of system status. The random timing of these bursts across channels helps prevent interference and ensures that the system remains responsive. LTR's development by the E. F. Johnson Company in the late 1970s represents an early approach to trunked radio that prioritized simplicity and distributed control over centralized channel management.
Did You Know?
- LTR does not have a dedicated control channel.
- Each repeater in an LTR system has its own controller, with one master controller coordinating the others.
- The idle data burst on LTR Standard systems is sent approximately every 10 seconds.
- The idle data burst sounds like a short blip of static, about 1/4 second long.
Frequently Asked Questions
What is Logic Trunked Radio (LTR)?
LTR is a trunked radio system developed by the E. F. Johnson Company in the late 1970s. It is distinguished by the fact that it operates without a dedicated control channel, instead relying on a network of distributed repeater controllers to manage channel assignment.
How does LTR coordinate channels without a control channel?
Each repeater in the system houses its own controller, and all controllers work together as a group. One controller is designated as the master, and the remaining controllers report to it, which allows the system to allocate and manage channels without needing a separate control frequency.
What is the maximum number of repeaters a single LTR site can support?
A single LTR site is capped at 20 repeaters. Sites also operate independently of one another and are not linked, meaning each location functions as a fully standalone system.
How often do LTR Standard controllers send their idle data burst?
On LTR Standard systems, each controller transmits a data burst approximately every 10 seconds. This periodic signal lets subscriber units confirm that the system is active and ready to accept calls.
Why is LTR considered different from other trunked radio systems of its era?
Most trunked systems of that period relied on a single dedicated control channel for all coordination. LTR eliminated that requirement by embedding a controller in every repeater and using a master-slave hierarchy among them, which made the architecture more distributed and site-independent.
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