Architecture · Passive

Passive DAS

A single bi-directional amplifier distributes public-safety signal over coaxial cable, the most cost-effective path to fire-code compliance. Play the signal flow to follow it from the roof donor antenna to every floor antenna.

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Emergency radio coverage

Passive DAS

An amplifier, one cable and a few ceiling antennas bring emergency radio signal to every floor, so firefighters can talk anywhere inside.

  • Up to 250,000 sq ft
  • One amplifier
  • Alerts the fire panel

Red = no radio for firefighters.

  • Radio works
  • Dead spot
How a passive DAS fixes radio dead spots, building front viewFront view of a 7-floor building. Before the system, red dead spots cover much of each floor, worst on the upper floors and around the central stair and elevator core. A roof antenna catches signal from an emergency radio tower 1.35 miles away. An amplifier with battery backup in a top-floor equipment room boosts it. One cable runs down through every floor, and ceiling antennas on each floor turn the dead spots green.GF2F3F4F5F6F7Radio towerRadio towerRoof antennaRoof antennaAmplifier
A real WZC system, 7-floor hotel. Not to scale.
  1. Ground floor: radio works in about 78% of the floor before, 100% after.
  2. Floor 2: radio works in about 58% of the floor before, 100% after.
  3. Floor 3: radio works in about 41% of the floor before, 100% after.
  4. Floor 4: radio works in about 27% of the floor before, 100% after.
  5. Floor 5: radio works in about 16% of the floor before, 100% after.
  6. Floor 6: radio works in about 8% of the floor before, 100% after.
  7. Floor 7: radio works in about 4% of the floor before, 100% after.

How it works

Architecture · Passive

Passive DAS

How it works

  1. Capture

    An amplifier pulls public-safety signal from a donor antenna mounted outside.

  2. Amplify & distribute

    The amplified RF signal travels entirely over coaxial cable.

  3. Balance

    Splitters, taps, and couplers balance signal levels across floors and zones.

  4. Radiate

    Each coax run feeds indoor antennas placed to meet coverage and code.

Passive DAS signal chain: a roof donor antenna feeds a single bi-directional amplifier, which feeds passive splitters over coax and on to ceiling antennas on every floor. The amplifier reports by dry contact to the fire alarm control panel. Illustrative topology; antenna count and run lengths are set by the RF design.

System components

  • Donor Antenna

    Roof-mounted directional antenna captures the outdoor public-safety signal.

  • Bi-Directional Amplifier (BDA)

    A UL 2524-listed amplifier with battery backup and a code-compliant enclosure.

  • Coaxial Distribution

    Low-loss cabling in fire-rated pathways with proper grounding per code.

  • Passive RF Components

    Splitters, taps, and directional couplers balance signal across floors and zones.

  • Service Antennas

    Ceiling- or wall-mounted indoor antennas placed for coverage and code.

  • System Alarming

    Code-required fault and power alarms via dry contacts to the fire alarm control panel (FACP).

Best fit
Up to 250,000 sq ft
Distribution
All-RF over coax
Core unit
Single bi-directional amplifier
Monitoring
Dry contacts to the fire alarm control panel
Band
VHF / UHF / 700 / 800 MHz, as required by the AHJ

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