Also known as: Capacity Plus, Cap Plus, Capacity Max
Capacity Plus is Motorola’s proprietary DMR trunking mode (part of the MOTOTRBO family) that pools several channels and rotates the control signalling among them (see rest channel), giving conventional DMR trunked capacity without a separate, permanently dedicated control channel. Capacity Max is the larger multi-site successor, and Hytera’s Connect Plus is a competing vendor equivalent.12
Overview
Standard DMR Tier III trunking permanently assigns one channel as the control channel. Capacity Plus instead treats a group of channels as a shared pool and lets whichever channel is currently idle carry the trunking signalling — the rest channel. When a call is set up, radios move to a granted timeslot and the rest/control function may hop to a different idle channel. This squeezes more usable capacity out of a small channel count and avoids “wasting” a full channel on control alone, at the cost of being a proprietary, Motorola-specific scheme rather than the open Tier III standard.
Technical characteristics
| Property | Value |
|---|---|
| Air interface | DMR two-slot TDMA, 4FSK |
| Trunking | Proprietary Motorola (Capacity Plus Single-Site / Multi-Site) |
| Control | Rotating rest channel, not a fixed control channel |
| Signalling | CSBK with Motorola grant formats |
| Vocoder | AMBE+2 |
| Squelch / identity | color code, talkgroup, source ID |
Because the control signalling moves, a scanner cannot simply park on one control frequency; it has to track the rest channel as it hops and then follow the granted timeslot for voice.
History
Capacity Plus grew out of Motorola’s MOTOTRBO product line as an entry-level trunking option for customers who wanted more capacity than conventional Tier II but did not need full multi-site Tier III. Capacity Max later extended the concept to larger multi-site networks with centralised control.12
Deployment
Common on business, industrial, and campus MOTOTRBO systems where a handful of channels must serve many users cost-effectively. It competes with open Tier III and with Hytera’s Connect Plus in the same market segment.
Decoding it with GopherTrunk
Following Capacity Plus means tracking the rotating rest/control channel as it hops, reading the Motorola-format CSBK grants, then decoding the granted timeslot — GopherTrunk’s DMR support is vendor-aware of these Motorola grant formats and renders the AMBE+2 voice. See Status.
Sources
-
Digital mobile radio — Wikipedia, for DMR and Motorola’s proprietary Capacity Plus trunking built on the DMR air interface. ↩ ↩2
-
DMR Association — the DMR manufacturer association, for the DMR air-interface basis on which vendor trunking modes such as Capacity Plus are layered. ↩ ↩2