How DMR Tier II Repeater Sites Increase Radio Range and Add Useful Features
What is Digital Mobile Radio?
Digital Mobile Radio (DMR) is the open radio industry standard developed by the European Telecommunications Standards Institute (ETSI) and promoted worldwide by the DMR Association. Hytera was instrumental in the development of the DMR standard, and the initial launch of fully compliant DMR two-way radios.
DMR is a digital radio standard used in professional mobile radio applications. DMR uses two-slot TDMA (Time Division Multiple Access) technology to divide a single 12.5kHz channel into two time slots, allowing two separate conversations to take place at the same time. DMR with TDMA and 12.5kHz channel spacing offers numerous advantages over analog radio systems:
- Improved voice quality
- Longer battery life
- Dual-slot operation doubles the number of users that can operate on a single frequency
- Interoperability with existing analog systems
DMR radio systems also support a variety of call types:
- Group Call – a one to many call, and probably the most often used type of call
- Private Call – Individual radio-to-radio calls
- Emergency Call and All Call – A special call that will broadcast to every radio on a channel, or with XPT, all the radios on the system.
- Priority Calls – Emergency and All Calls have a higher priority than Private or Group Calls and DMR radio systems end the lower priority call to receive the higher priority call.
- Text Messaging – Free form texting, or text messages can be pre-programmed to specific buttons
- Dedicated data channels – If the radio system involves heavy GPS data, large fleets, DMR delivers GPS data via specific data channels so as not to interfere with voice traffic.
DMR systems typically support the 150 to 174 VHF and 400-512 UHF frequency ranges. DMR systems are also available in the low band of 66-88MHz (rarely used) and high band range of 806-941MHz.
DMR Tier II repeaters are deployed when a radio-to-radio system (a group of radios talking to each other) requires farther range or more capacity due to a growing number of users.
DMR Tier II (Licensed Conventional)
A DMR Tier II radio system is a professional two-way radio system that uses repeaters for voice and data communications. Tier II uses DMR standard compliant radios and requires FCC licenses. Both DMR radios and Analog radios can be deployed on Tier II repeater systems.
Tier II systems are for medium and large size organizations that require wide-area coverage throughout a school campus, business complex, or open rural area. DMR Tier II radios are available from several manufacturers, allowing for easy integration with existing analog radio systems.
How It Works – The Components of Tier II Repeater Site
A DMR Tier II Repeater Site consists of a DMR repeater, antenna systems, and supporting equipment which typically includes power supplies, backup batteries, and monitoring systems. The repeater and associated equipment that makes up a Conventional Tier II system is sometimes referred to as a Base Station.
DMR Tier II repeater systems are installed by authorized radio system dealers who are professional radio system integrators that can configure and install all the necessary radio system components.
DMR Tier II Repeaters – the repeater is the heart of a professional DMR radio system. It is responsible for receiving and transmitting radio signals over a wide area. Repeaters receive low‐level signals from handheld and mobile DMR radios and retransmit the information at a higher power level over a greater area. This is commonly referred to as the range of the repeater, the area within which you can activate the repeater with the transmitted signal. Two or more repeaters can be deployed together and assigned to different call groups.
Repeaters provide an intelligent and seamless communication platform with the flexibility to connect with a variety of systems. Repeaters can provide inter-system connectivity to SIP/PBX/VoIP phone systems, dispatching systems, and DMR Tier II, Tier III, and XPT Trunking Systems.
Repeaters are available as network equipment that can be installed in a standard 19” rack typically found in a data closet, and as compact repeaters that have integrated antennas for applications like use in tight spaces like farm enclosures, rural outbuildings, or on ships and yachts. Compact repeaters can also support portable applications like racing teams and feature integrated battery packs for carrying the repeater in mobile applications like fighting wildfires and search and rescue operations.
The repeater typically consists of a receiver, transmitter, and a duplexer. The receiver receives incoming radio signals and filters them to ensure that only the desired signals are transmitted to the transmitter. The transmitter then amplifies and retransmits the signal over a wider area. The duplexer is used to separate the incoming and outgoing signals, allowing the repeater to operate on two frequencies (Tx and Rx) on one antenna.
Multiple repeaters can be deployed in Tier II systems for additional channel capacity.
Antenna Systems – Antenna systems are used to transmit and receive radio signals between the base station and mobile and portable radios. A DMR base station can consist of several antennas, including a main antenna and auxiliary antennas. The main antenna is used to transmit and receive radio signals over a wide area, while the auxiliary antennas are used to provide coverage in specific areas, such as buildings or tunnels. Some DMR Tier II systems use more than one frequency and have a separate antenna for each frequency. Antenna patterns can be adjusted so that a repeater range can cover a certain area or direction only, but the majority of antennas are omnidirectional.
Supporting Equipment – Additional equipment is used to provide power and network connectivity for the repeater site. This equipment typically includes power supplies, backup batteries for mission critical operations during natural disasters. The power supplies provide the necessary power to operate the base station, while backup batteries are used to provide backup power in case of a power outage. Repeater sites may also include optional network infrastructure such as servers, routers, switches, and other networking equipment required to connect the different components of the DMR Tier II radio system.
Dispatching and Monitoring Systems – A dispatch application (also called a dispatch console) is a client software application that provides centralized control and monitoring of the DMR Tier II radio system, including voice calls, GPS location tracking, messaging functions, and voice recording. It enables the dispatcher to communicate with multiple radio terminals simultaneously and monitor the activity on the system. A dispatcher will communicate with the radios on the system using a microphone and speaker connected to the PC running the dispatch application.
Monitoring applications provide alerts if a repeater has a power failure, antenna issue, and can monitor the call traffic and generate alerts for dropped calls. Both dispatching and monitoring applications run on PCs connected to the repeater; either through a direct connection to the Ethernet port, or through an IP network linked to the repeater.
Key Benefits of DMR Tier II Repeater Systems
Enhanced Coverage and Range – DMR Tier II conventional repeater systems significantly enhance coverage and range compared to direct radio-to-radio communication. By strategically placing repeaters at elevated locations, these systems can extend the signal coverage area, overcoming obstacles such as buildings and terrain. This ensures that users can communicate seamlessly over a broader geographic area, improving overall operational efficiency.
Improved Signal Quality – One of the primary benefits of DMR Tier II conventional repeater systems is the improvement in signal quality. The repeaters receive weak signals from portable or mobile radios and retransmit them at a higher power level, resulting in clearer and more reliable communication. This ensures that messages are transmitted with minimal distortion or interference, leading to enhanced clarity and intelligibility.
Increased Group Calling Capacity – Conventional repeater systems allow for simultaneous communication between multiple users to increase call capacity. With DMR Tier II, users can access the repeater and communicate with one another concurrently, promoting efficient group communication. This feature is particularly beneficial in scenarios where multiple teams or individuals need to coordinate their activities in real-time.
Scalability and Flexibility – DMR Tier II conventional repeater systems offer excellent scalability and flexibility. As the system’s capacity is determined by the number of available channels, it can be easily expanded by adding more repeaters or increasing the number of available channels. This scalability enables organizations to adapt their communication infrastructure to growing needs without the need for a complete overhaul.
Enhanced Privacy and Security – Privacy and security are paramount in professional communication systems, and DMR Tier II conventional repeaters offer robust features in this regard. Encryption capabilities are built into DMR Tier II, ensuring that sensitive information remains protected and confidential. Additionally, repeaters can be configured with advanced access control features to limit unauthorized usage, providing an additional layer of security.
Interoperability – This is a crucial advantage of DMR Tier II conventional repeater systems. DMR is an open digital radio standard, ensuring compatibility among different manufacturers’ equipment. This allows organizations to choose from a wide range of DMR-compatible radios and infrastructure components, promoting interoperability and eliminating vendor lock-in.
Enhanced Management and Monitoring – DMR Tier II conventional repeater systems offer advanced management and monitoring capabilities. System administrators can remotely monitor and manage the repeaters, perform diagnostics, and optimize system performance. These features enable proactive maintenance, efficient troubleshooting, and swift resolution of any issues, leading to increased uptime and operational reliability.
Advanced Features and Functionality – Repeater systems offer additional features and functionality that can enhance operational efficiency. These include features like emergency signaling, remote monitoring, network connectivity, and dispatcher consoles.
