Also known as: LTR, Logic Trunked Radio

LTR (Logic Trunked Radio) is a simple, low-cost trunking protocol from E.F. Johnson. Unlike systems with a dedicated control channel, LTR is distributed: trunking data rides subaudibly on each voice channel, so every channel carries its own low-speed signalling.¹

LTR is distributed trunking: each channel carries its own subaudible signalling, with no separate control channel.

Overview

Because there is no separate control channel, radios monitor the embedded data (logical channel numbers and home-repeater info) to follow calls. This makes LTR cheap to deploy but trickier to monitor than control-channel systems.

Technical characteristics

Property	Value
Access	FDMA, distributed
Signalling	Subaudible data on each channel
Voice	Analog FM

History

Introduced by E.F. Johnson and widely used for business/SMR trunking; variants include LTR-Net and PassPort.¹

Deployment

Common in commercial/business shared systems (taxi, delivery, utilities), especially in North America.

Decoding it with GopherTrunk

See Status for GopherTrunk’s handling of LTR’s subaudible signalling.

Sources

1. Logic Trunked Radio — Wikipedia, for the E.F. Johnson LTR distributed trunking scheme and its subaudible per-channel signalling. ↩ ↩²

See also

• Trunked radio
• Control channel
• Motorola Type II
• EDACS
• MPT 1327

Learn it step by step

• The digital protocol landscape

From the blog

• SDR Internals, Part 10: Protocol decoders & state machines