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Microlab In-Building Public Safety SMART Passives System for DAS Integrity Monitoring
April 28, 2021

An Emergency Responder Radio Communications System (ERRCS), also known as a Public Safety or First Responder Distributed Antenna System (DAS), has been mandated by many municipalities for new buildings around the country. The municipal jurisdiction’s code requirements are defined by the National Fire Protection Association (NFPA) and/or the International Fire Code (IFC). Some Authorities Having Jurisdiction (AHJ) over ERRCS (e.g., City of San Francisco) are going above and beyond the IFC and NFPA codes and are recommending that all passive DAS networks be equipped with a remote monitoring system that detects faults in the passive network of RF coaxial cables, components, and antennas deep into a building. Typically, only the active components (BDAs and backup battery power supplies) are monitored. Without real-time passive DAS monitoring and alarming, a Public Safety DAS may not be ready for life safety radio traffic. When the Public Safety DAS is commissioned and accepted, a grid test is conducted for RF signal levels and audio quality. If the Public Safety DAS RF coverage passes in a brand-new building, a certificate of occupancy (CO) will be granted by the AHJ. From the date of commissioning, it is typical for the AHJ to conduct annual testing of the DAS. Therein lies the problem for first responders that rely on the Public Safety DAS during emergency incidents. It can be a year or more between a system’s proof-of-performance testing, which checks for overall radio signal coverage integrity. The probability of damage to RF coaxial transmission lines or components, disconnected antennas, and the like are high over the course of a year. This is due to building maintenance and enhancements with the risers and plenums, including plumbing, HVAC repair, security systems, and computer network cabling work. Something as simple as disconnecting an antenna and forgetting to reconnect it to a DAS transmission line will compromise DAS integrity and impede proper radio coverage performance.

Microlab SMART Passives System

The Microlab System Monitor Alarm Report Technology (SMART) Passives System enables real-time performance monitoring of Public Safety DAS structured cabling, RF components, and antennas deep into a building. The SMART Passives System is made up of a SMART Gateway and SMART Couplers. The SMART Coupler with embedded IoT diagnostics was designed to replace common passive DAS tappers and directional couplers. A building’s DAS network of SMART Coupler nodes is complemented by a SMART Gateway at the head-end’s main RF source. The real-time monitoring capabilities of the SMART Passives System will ensure that Public Safety DAS system integrators, AHJs, building owners, and emergency services personnel can depend on the operation of their critical communication systems. If the SMART Gateway loses DC power or an active Internet of Things (IoT) circuit board fails in a SMART Coupler, all emergency radio traffic will continue to pass through the DAS. The DAS will continue to perform, however, there will be a loss of real-time monitoring until power is restored.

How Does the SMART Passives System Work?

The head-end’s main RF source for a Public Safety DAS will be a bi-directional amplifier (BDA) or a dedicated repeater (e.g., an FDNY ARCS Network). The RF source is connected to the SMART Gateway while maintaining the integrity of radio transmission. There is no signal processing. The SMART Gateway provides a DC bias over the passive DAS coaxial RF transmission lines to power the active portion of the SMART Coupler nodes through the building. All diagnostics and communications between the SMART Couplers and SMART Gateway take place over the coaxial cabling. The SMART Couplers do not require local network or power connections within a building’s ceiling, plenum, risers, or distribution paths. A SMART Coupler uses a specially developed, broadband, passive coupler for 130 – 960 MHz that is enclosed with the active IoT circuitry for communications and diagnostics. SMART Couplers measure the Voltage Standing Wave Ratio (VSWR) at each port based on a calibrated CW tone generated by the SMART Gateway, storing and comparing the timestamped VSWR and RF signal levels at each port. SMART Couplers continuously monitor for changes in VSWR and signals to proactively sniff out failures and degradation, such as an open or short circuit. The SMART Gateway then communicates the alarm via e-mail, SMS, or SNMP. For example, if the SMART Passives System detects a catastrophic change in the Antenna 2 path, which is connected to SMART Coupler #1 or SC-01, then an alarm will be triggered indicating DAS performance has been affected after the SMART Gateway polls the SC-01 unit via SC-01’s MAC address. The SMART Passives System’s GUI connected to the SMART Gateway will provide details based on the embedded IoT diagnostics.


  • Monitors DAS infrastructure health; including antennas, coaxial cables, and other passive components
  • Designed for public safety VHF, UHF, TETRA, 700, 800, 900 MHz bands
  • FirstNet Band 14 Ready
  • Diagnostics, power, and communications provided over RF coaxial cable by the SMART Gateway
  • Alarms communicated via e-mail, SMS, and SNMP
  • SMART Gateway dashboard web server compatible with all modern browsers

Visit Microlab to learn more.



March 2023

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International Wireless Communications Expo (IWCE) 2023
Las Vegas

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