TechNote September 2020

PORTABLE REPEATERS The U.S. Department of A is a device that receives a radio and re-transmits an Homeland Security (DHS) established the System amplified, but otherwise identical, signal. Repeaters are used to extend the Assessment and Validation for range of radio systems where coverage gaps are present. Coverage gaps can Emergency Responders be caused by signal obstructions, topology, or distance. Repeaters can also (SAVER) Program to help be implemented to mitigate coverage gaps in indoor and subterranean emergency responders environments. Radio repeaters are commonly deployed in three forms: improve their procurement human-portable, cell-on-wheels (COW) and cell-on-light truck (COLT) systems. decisions. Each type has specific applications and limitations; users should choose Located within the Science which is best suited to the environment where a repeater is needed. and Technology Directorate AEL reference number: 06CP-01-REPT (S&T), the National Urban Security Technology Overview Laboratory (NUSTL) manages the SAVER Program and Radio communication conducts objective coverage can be limited operational assessments of for a variety of reasons, commercial equipment and including excessive systems relevant to the emergency responder distance in a remote community. rural area or line of sight (LOS) obstructions in The SAVER Program gathers indoor or subterranean and reports information about equipment that falls within the environments. categories listed in the DHS Employing radio Figure 1. Indoor and Subterranean Coverage Gaps Authorized Equipment List repeaters can eliminate Image courtesy of DHS SAVER (AEL). these coverage gaps. SAVER publications focus on A basic radio repeater contains a receiver, duplexer, controller, , answering two main and antenna. The receiver amplifies radio from the antenna and filters questions: “What equipment out noise. The duplexer isolates the receiver from the transmitter to reduce is available?” and “How does signal interference. The controller uses software to communicate with the it perform?” transmitter and receiver. The transmitter converts the received audio signal’s SAVER knowledge products frequency and amplifies the signal before sending it to the antenna. The are created for the nation’s antenna initially receives the source signal and later transmits the processed first responders and made signal. (Repeaters that lack a duplexer require separate antennas for the available to help them make operational and procurement receiver and transmitter.) All of these components work together to complete decisions. the repeater’s function. Important uses for first responders include enhancing two-way radio communication in areas with unreliable coverage and For more information on this and other technologies, supplementing limited or damaged communications infrastructure during an contact NUSTL by e-mail at emergency. [email protected] or visit the When selecting what type of repeater to use, emergency responders should SAVER website: consider its frequency and operating mode (analog or digital transmission) to www.dhs.gov/science-and- ensure it is compatible with the radio equipment used by their agency. technology/SAVER. Transmitting power should also be considered: in general, power levels required to mitigate outdoor coverage gaps are higher than those required to mitigate indoor gaps. Higher levels of power, however, may result in the repeater retransmitting a noisier signal.

Approved for Public Release SAVER-T-TN-20

TechNote

Radio Repeater Variants and Uses These systems can also be used in rural areas to supplement a limited radio network. Because COWs Human-Portable Radio Repeaters are towed by another vehicle, this type of system is appropriate for agencies who only occasionally Human-portable radio deploy repeaters for outdoor operations. COWs can repeaters are designed to serve as makeshift cellular infrastructure and often provide a communication provide greater transmission power levels than solution to areas where human-portable repeaters. vehicle access is not possible. A typical human- Cell-on-Light Truck portable radio repeater COLT systems are weighs less than 50 pounds complete cellular systems and is contained within a that are integrated into a Figure 2. Human-Portable single case. They can be vehicle and allow for both powered externally via an Radio Repeater Image courtesy of radio and satellite AC supply or by battery, an Motorola communication. COLT alternative which limits their systems generally include service time. Systems that require external power a power generator Figure 4. Cell-on-Light Truck may limit placement options of these repeaters or separate from the Image courtesy of FEMA may require supplemental equipment, such as a vehicle’s engine to provide generator or battery, to maintain portability. Antenna power to the communication system. The generators connections for human-portable repeaters are often allow for system operation without external power as limited by range as well as power, making system long as requirements such as fuel availability are location and position very important to achieving met. These systems are highly customizable for peak performance. specific scenarios and are intended for use by Cell-on-Wheels multiple operators. COLTs are limited to areas with vehicle access. COW systems are trailer- mounted communication Similar to COW systems, COLT systems can be used systems that provide to provide network coverage when regular easily transportable radio infrastructure is insufficient or damaged. Due to its repeater solutions. These integration into a vehicle, a COLT system may be systems can be configured more appropriate than a COW system for agencies for both satellite and radio that regularly or frequently deploy outdoor communication repeaters. Like COWs, COLTs often provide greater capabilities and may also Figure 3. Cell-on-Wheels transmission power than human-portable repeaters. include onboard power Image courtesy of General generation. COWs are Dynamics Mission Systems References limited by potential 1) “Portable Communication Repeaters Technology external power requirements as well as by vehicle Guide.” DHS S&T SAVER Program. 2007. access to the desired area of operation. COWs can [Limited Distribution]. be used to support public events (e.g., concerts) and 2) “Portable Cellular Systems Application Note.” natural disaster response when cell networks are DHS S&T SAVER Program. 2014. [Online URL]. overloaded and/or where network infrastructure has been damaged.

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