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MOTOTRBO is the Motorola brand name for its DMR product portfolio. Outside of Motorola, MOTOTRBO is known as DMR - though the former has become synonymous for the latter, even when referring to competitor products.

Motorola Solutions was the first to market with a range of mobile and portable radios and repeater. Initially, MOTOTRBO only supported Simplex (with no DCDM) and Single Site. Soon after that, IP Site Connect was introduced along with a number of features. Motorola Solutions generally introduces new features and enhancements to MOTOTRBO every six months.

MOTOTRBO has been promoted - and generally accepted - as a replacement for existing analogue systems. Some see it (specifically Capacity Max) as competitor technology to TETRA. However, TETRA offers a significant higher degree of interoperability, when compared to DMR Tier II and Tier III, and has several important security features not present in any DMR offering.

Advantages when compared to Analogue

Compared to legacy analogue LMR systems, MOTOTRBO offers a number of advantages, some of which include:

Features and Benefits of MOTOTRBO
Feature Benefit
Double spectral efficiency Two channels on a 12,5kHz frequency allocation. One timeslot could be carrying a voice call while the other could be used to send data or carry another voice call. With Capacity Plus; Linked Capacity Plus and Capacity Max, it is possible to pool these slots and allocate them automatically thus increasing the number of number of users that can be supported per channel.
Background noise reduction[1] Messages are not missed, or do not need to be repeated, when users are in a noisy environment (e.g. factory with machinery). MOTOTRBO radios are extremely good at filtering background noise. This makes these radios well suited for users who work in noisy environments. Together with the XBT headset or INC and ANC speaker-microphone, users can communicate with ease.
Better readability in poor signal conditions[1] Messages are not missed, or do not need to be repeated, when users are in an area where the outbound signal is weak. Since MOTOTRBO radios use Forward Error Correction in digital mode, the amount of usable RF coverage is increased. A location where an analogue signal would difficult to hear will be easily readable in digital mode.
Improved security More difficult for others to monitor your communications even without encryption.
Analogue Mode Support All MOTOTRBO radios (except the SL4000 series) support analogue mode operation that allows them to be used on legacy analogue systems and gives the customer the opportunity to easily and smoothly migrate to digital when they are ready[1].
Better Battery Life Since a portable two way radio will only transmit 50% of the time when operating in digital mode, the average current consumption can decrease by up to 40% - this results in longer battery life[1].
Data Support Through Motorola's Application Developer program, customers can source and/or develop software applications around their MOTOTRBO radios. Features like GPS and indoor tracking; job ticketing; data and text messaging extend the use of two way radio beyond just push to talk.
RM and OTAP Due to the data capabilities, radio configurations can be updated over the air using Radio Management and OTAP.
Transmit Interrupt Features like Transmit Interrupt allow a manager to break into an ongoing call to pass an important message. Similarly, Transmit Interrupt can be used to free up a channel to pass an emergency call. The messaging required to interrupt a transmission is sent to the transmitting radio via the other slot (since the radio is only transmitting on one slot).
Interoperability MOTOTRBO radios are able to operate with other DMR vendors equipment. This offers the customer peace-of-mind knowing that their investment in this technology is a safe one.
Reuse of existing hardware and frequencies. Since MOTOTRBO radios operate in the existing PMR frequency bands, customers don't need to replace antennas or RF filtering equipment when upgrading to digital.
Call Capabilities MOTOTRBO radios support Private; Group and All (Broadcast) calls. This allows customers to divide their radio fleet into workgroups and reduces fatigue due to radio chatter.
Location Tracking A number of MOTOTRBO radios support GPS/GLONASS/Beidou (GNSS) and Bluetooth 4.x allow the location of users to be tracked ensuring efficiency and worker safety - both indoors and outdoors.

See differences between analogue and DMR audio.

Forward Error Correction allows better audio performance in poor signal conditions.
Two slot TDMA allows two simultaneous voice or data calls on the same channel at the same time.


Digital Mobile Radio (DMR) is an open digital mobile radio standard defined in ETSI Standard TS 102 361 parts 1–4[2][3][4] and used primarily in professional radio communications equipment around the world. MOTOTRBO is the Motorola brand name for its DMR product portfolio. DMR, along with P25 phase II and dPMR are the main competitor technologies in achieving 6,25 kHz equivalent bandwidth using the proprietary AMBE+2 vocoder[5] from DVSI. DMR and P25 II both use two-slot TDMA in a 12.5 kHz channel, while dPMR uses discrete 6,25 kHz channels using FDMA.

DMR was designed with three tiers. The standards defining DMR Tiers I and II (conventional) were first published in 2005, and DMR Tier III (Trunking) was published in 2012, with Motorola Solutions and other manufacturers producing products within a few years of each publication.

The primary goal of the standard is to specify a digital system with low complexity, low cost and some degree of interoperability between radios and infrastructure, so customers are not locked into a proprietary solution. In practice, most vendors have not fully adhered to the standards and introduced proprietary features that make some product offerings non-interoperable.

MOTOTRBO High Tier Product Portfolio.jpg


The 4FSK Deviation Index used in DMR.

The DMR interface is defined by the following ETSI standards:

  • TS 102 361-1: Air Interface Protocol
  • TS 102 361-2: Voice; General Services and Facilities
  • TS 102 361-3: Data Protocol
  • TS 102 361-4: Trunking Protocol

The DMR Air Interface

MOTOTRBO Workshop Presentation R2.4A.jpg

The DMR standard operates within the existing 12,5 kHz channel spacing used in land mobile frequency bands globally, but achieves two voice channels through two-slot TDMA technology built around a 30 ms structure. The modulation is 4-state FSK, which creates four possible symbols over the air at a rate of 4.800 symbols/s, corresponding to 9,600 bit/s. After overhead, forward error correction, and splitting into two channels, there is 2.450 bit/s left for a single voice channel using DMR, compared to 4.400 bit/s using TETRA and 64.000 bit/s with traditional telephone circuits.

The standards are being continuously developed, with revisions being made regularly as more systems are deployed and improvements are discovered. It is very likely that further refinements will be made to the standard, which will necessitate firmware upgrades to radios and infrastructure in the future to take advantage of these new improvements, with potential incompatibility issues arising if this is not done.

The DMR standard does not define specific frequency bands but only mentions a RF range of 30MHz to 1GHz. The majority of manufacturers produce equipment in the (VHF) 136 to 174MHz and (UHF) 403 to 520MHz bands. In addition to this, Motorola also produces equipment in the 300MHz and 800MHz bands (the latter is only available in some Asian countries and North America where this band is not allocated to GSM).

DMR generally has superior coverage performance to analogue FM. This is because Forward Error Correction used in AMBE+2 is able to cope with bit error rates as high as 5% with no degradation in PESQ.

The DMR Association

In 2005, a memorandum of understanding (MOU) was formed with potential DMR suppliers to establish common standards and interoperability. While the DMR standard does not specify the vocoder, the members agreed to use the half rate DVSI Advanced Multi-Band Excitation (AMBE) vocoder to ensure interoperability. In 2009, the MOU members set up the DMR Association to promote the standard; work on interoperability between vendors equipment; provide information about the DMR standard.

The standard allows DMR manufacturers to implement additional features on top of the standards which has led to practical non-interoperability issues between vendors.

MOTOTRBO System Topologies

Motorola Solutions offers several MOTOTRBO system topologies to address most customer needs.


Simplex Operation

MOTOTRBO DMR radios are able to operate on simplex - both in analogue and in digital mode. When in digital mode, the majority of voice and data features are supported (see List of features not supported on simplex). Simplex is also sometimes referred to as Direct Mode.

Users can optionally use Dual Capacity Direct Mode (DCDM). This feature allows radio radios to synchronize with each other and permits two-timeslot operation without the need for a repeater. Without DCDM, only one timeslot may be used on simplex in digital mode. The first generation MOTOTRBO radios do not support DCDM.

In analogue mode, standard FM is used allowing MOTOTRBO radio radios to be used with existing analogue equipment. Depending on the model, the radio radios and repeaters may support one or more analogue signaling formats.

Single Site

A single site system consists of several (or many) radio radios and one or more repeaters. Radio radios communicate with each other via the repeater which is installed at a high site. There may b more than one repeater at the same, or another, high site to provide additional coverage or user volumes.

In analogue mode, standard FM is used allowing MOTOTRBO radio radios and repeater to be used with existing analogue equipment. Depending on the model, the radio radios and repeaters may support one or more analogue signaling formats. such as PL; DPL; Select-5; MDC1200 or Quik-Call II.

A repeater will typically operate in full-duplex mode - in that it transmits and receives at the same time. This is necessary to relay the signal from the transmitting radio radio to other users on the channel (analogue) or same timeslot and talkgroup (digital). The radio radios consequently operate in semi-duplex mode, in that they transmit while the PTT is pressed and receive when it is released.

Repeater Operation

In order to support full-duplex operation, the repeater requires a frequency pair (a transmit frequency and receive frequency separated by a few Megahertz). In cases where a frequency pair cannot be obtained or is not feasible, MOTOTRBO repeaters can be configured for Extended Range Direct Mode (ERDM) operation (sometimes called Single Frequency Repeater).

When operating as a standard repeater, a duplexer is needed to connect the receiver input and transmitter output to a single antenna. If multiple repeaters, in the same frequency band; are co-located, a multicoupler-combiner network is needed to use a single antenna. Using this hardware is necessary to prevent interference and provide adequate coverage.

When operating in ERDM mode, two separate antennas can be used but an external PIN-diode-based antenna switch will allow the connection of a single antenna. The SLR1000 has an optional built-in antenna-switch that permits this. The other repeater can also control such an antenna switch but this is not available from Motorola and the SLR1000 switch cannot be used on high power repeaters like the SLR5500 and SLR8000.

IP Site Connect

IP Site Connect allows repeaters across dispersed locations to exchange voice, data, and control packets over an IPv4-based backend network. The potential applications of this feature include:

  • Connecting two or more dispersed locations for day-to-day communications. For example, a customer’s manufacturing facility and a distribution facility across towns can be connected using MOTOTRBO repeaters in IP Site Connect mode.
  • Building a larger or more effective RF coverage area. For example, multiple repeaters installed in an amusement park or a high-rise building can be connected to provide a contiguous area of RF coverage. The need for multiple repeaters may stem from any combination of geography (distance or topographical interference problems) and in-building or cross-building RF penetration issues.
  • Broadcasting announcements to all sites. This is useful in case of emergency or special events.
  • Connecting repeaters operating in different RF bands. For example, repeaters operating in UHF (UHF-1 and UHF-2) or VHF frequencies can be combined so that voice or data from one system flows into another.
  • Connecting to IP-based applications. IP Site Connect mode allows the customers to connect to third-party IP-based dispatch consoles, or call logging and recording applications, or routing calls to/from IP-based phones.

Radios in a IP Site Connect system are able to automatically switch between sites in a process called Roaming. The radio continuously monitors the signal strength (RSSI) of the current (home) channel and should this drop below a CPS configured threshold, the radio will search for another channel with sufficient RSSI. In the absence of any transmissions, the repeater generates periodic Beacon transmissions that allow the radio to measure the RSSI and determine i the current channel meets the RSSI threshold criteria.

See IP Site Connect.

Capacity Plus (Single Site)

Capacity Plus is a trunked system consisting of up to eight repeaters all located on one site and supporting a large number of users in a defined area. For data intensive applications, up to 12 data revert repeaters can be added to pass radio to server data such as GPS. Capacity Plus does not require a server and all the intelligence to manage call setup and management is built into the repeaters themselves.

Capacity Plus is a proprietary implementation from Motorola based on the DMR Tier 2 air interface.

Radios which are not party to a call, monitor the Rest Channel. Unless the system is fully loaded, one of the slots (one timeslot on one of the repeaters) on the system is functioning as a Rest Channel. When a call is setup, the Rest Channel becomes a Voice Channel (sometimes called a Traffic Channel) and the function of Rest Channel is transferred to either the 2nd timeslot or next free (idle) timeslot.

Capacity Plus is a single site implementation whereas Multi-Site Capacity Plus supports up to 15 sites per system.

Multisite Capacity Plus

Capacity Plus is a multi-site trunked system consisting of up to eight repeaters per site and up to 15 sites. For data intensive applications, up to 12 data revert repeaters per site can be added to pass radio to server data such as GPS. Like Capacity Plus, all the intelligence to manage call setup and management is built into the repeaters themselves.

Since there is no site controller, Talkgroup Calls are allocated to sites in a static basis.

See - Multisite Capacity Plus

Capacity Max

MOTOTRBO Capacity Max is a multi-site trunked system consisting of up to fifteen repeaters per site and up to 250 sites. For data intensive applications, up to six data revert repeaters per site can be added to pass radio to server data such as GPS.

It uses a central server - known as a CMSS - to process authentication and manage network activity. It is DMR Tier 3 compliant.

Unlike some other DMR Tier 3 system technologies, Capacity Max does not use a site controller. Much like Multi-site Capacity Plus, site activity and registration is processed by the repeaters themselves.

As per ETSI TS 102 361-4, each RF site has a permanently transmitting control channel. All radios which are not in a call monitor the control channel. When a call is made, this is set up on the control channel and the system will allocate a traffic channel to all call parties.

Connect Plus

MOTOTRBO Connect Plus was multi-site trunked system consisting of up to fifteen repeaters per site and up to 250 sites. It used distributed architecture which meant there was a site controller (either a XRT9000 or XRT9100) at each site. Connect Plus was not DMR Tier 3 compliant but used the same layer 1 and 2 signaling defined in ETSI TS 102 361.

Connect Plus functionality in the radios was only possible via an option board.


See List of MOTOTRBO Models.

MOTOTRBO Repeaters

See List of MOTOTRBO Models.

See Also

IP Site Connect

Multisite Capacity Plus


  1. 1.0 1.1 1.2 1.3 Cite error: Invalid <ref> tag; no text was provided for refs named :0
  2. ETSI TS 102 361-1 retrieved 13 April 2019
  3. ETSI TS 102 361-3retrieved 13 April 2019
  4. ETSI TS 102 361-4 retrieved 13 April 2019
  5. DVSI Inc. AMBE+2 retrieved 13 April 2019