Before this:The birth of trunking: sharing channels
The analog trunking era: SmartNet, EDACS, LTR & MPT-1327
Key takeaways The first big trunked systems carried analog voice but digital control. The major families were Motorola Type I/II/IIi (branded SmartNet/SmartZone), GE/Ericsson EDACS, LTR (Logic Trunked Radio — distributed control, sub-audible data, no dedicated control channel), and MPT-1327 (the British/European standard). These architectures invented the vocabulary digital systems inherited: dedicated vs distributed control, and message vs transmission trunking. Many are still on the air, and GopherTrunk decodes them.
Trunking arrived years before digital voice. For a long while the state of the art was a clever hybrid — your voice still went out as ordinary FM, but a computer chose the channel and announced it as data. This lesson surveys those analog trunked systems, because the concepts they pioneered shape every digital standard that came after.
The hybrid idea: analog voice, digital control
Picture the trunking machinery from the last lesson — a controller, a channel pool, a control channel handing out assignments — but the audio on each voice channel is plain analog FM. That’s the whole analog trunking era in one sentence. The organising layer was digital and modern; the voice layer was the same FM that had been around for decades. This split is why a single system could enjoy trunking’s spectrum efficiency without anyone needing a vocoder.
These systems also settled two design questions that still matter:
- Dedicated vs distributed control. A dedicated-control system reserves one channel full-time as the control channel (SmartNet, EDACS). A distributed-control system has no single control channel; the signalling rides along with the voice on each repeater (LTR).
- Message vs transmission trunking. Transmission trunking releases a channel the instant a user unkeys; message trunking holds it through a short hang time so a conversation stays put. The trade-off is faster channel reuse versus smoother back-and-forth.
The major families
Motorola Type I/II/IIi is the most widespread legacy family, sold under the SmartNet and SmartZone brand names. Type I, Type II, and the hybrid Type IIi differ mainly in how they encode talkgroup and radio identity, and SmartZone added multi-site coverage. Type II in particular blanketed North American public safety and business for years.
EDACS (Enhanced Digital Access Communications System) came from GE, later Ericsson. It used a dedicated control channel with very fast channel assignment and a distinctive signalling scheme, and was common in public-safety and utility deployments.
LTR (Logic Trunked Radio) is the conceptual outlier. It has no dedicated control channel: each repeater carries sub-audible data beneath the voice, and the radios coordinate channel use collectively — distributed control. That made LTR inexpensive and simple, which is why it was popular for smaller business systems.
MPT-1327 is the British/European standard, an open specification widely deployed outside North America for business and government trunking. Like the Motorola and EDACS families, it uses a dedicated control channel.
How they compare
| System | Origin | Control | Typical use |
|---|---|---|---|
| Motorola Type I/II/IIi (SmartNet/SmartZone) | Motorola | Dedicated | US public safety & business |
| EDACS | GE / Ericsson | Dedicated | Public safety, utilities |
| LTR | E.F. Johnson | Distributed (sub-audible) | Small business systems |
| MPT-1327 | UK / open standard | Dedicated | Business & government outside US |
The shared thread is analog voice, digital control. Where they diverge — dedicated vs distributed control, and how they encode IDs — is exactly the kind of difference that decides how a monitor follows them.
What digital inherited
When the digital standards arrived, they didn’t reinvent trunking — they reused it. Dedicated control channels, talkgroups, affiliation, and the message/transmission trunking distinction all came straight out of this era. P25, DMR Tier III, and TETRA are, at the trunking layer, refinements of ideas that SmartNet and EDACS proved in the field. The big addition was digital voice — vocoders, error correction, and built-in encryption — on top of a trunking model that already worked.
These systems haven’t vanished. Many are still on the air, and GopherTrunk decodes a range of them, so they’re not just history. The Status reference tracks which it handles.
Recap
- The first big trunked systems carried analog voice with digital control.
- Motorola Type I/II/IIi (SmartNet/SmartZone) and EDACS used dedicated control channels.
- LTR was different — distributed control with sub-audible data and no dedicated control channel.
- MPT-1327 was the open British/European standard, dedicated-control, used worldwide outside North America.
- They invented dedicated vs distributed control and message vs transmission trunking, which digital systems inherited; many are still on the air and GopherTrunk decodes them.
We dig into these per-system in Motorola SmartNet and EDACS, LTR & MPT-1327, and compare every flavour in Trunking flavours. Next, we cross the line into digital voice in The digital leap.
Frequently asked questions
What is the difference between analog and digital trunking?
Analog trunking carries the voice as ordinary FM but uses digital signalling to assign channels — the control is digital, the audio is analog. Digital trunking carries the voice itself as bits through a vocoder. Many ideas, like dedicated control channels and talkgroups, were invented in the analog era and carried straight into digital systems.
What is the difference between message and transmission trunking?
In transmission trunking, a channel is assigned for a single transmission (one press of the key) and released the instant the user lets go. In message trunking, the channel is held through a short hang time so a back-and-forth conversation stays on one channel. Message trunking feels smoother; transmission trunking returns channels to the pool faster.
What was LTR and why was it different?
LTR (Logic Trunked Radio) used distributed control with no single dedicated control channel. Each repeater carried sub-audible data alongside the voice, and the radios worked out channel assignments collectively. That made LTR cheap and simple for business systems, but it signals very differently from dedicated-control systems like SmartNet or EDACS.
Are analog trunked systems still on the air?
Yes. Motorola Type II, EDACS, LTR, and MPT-1327 systems still operate in places, even as many agencies migrate to P25 and DMR. GopherTrunk decodes a range of these legacy systems, so understanding them is still useful for a scanner enthusiast.