Tech Desk 5: Components of a PS-DAS

What are the components of a Public Safety-DAS?

The main high level components of a Public Safety – Distributed Antenna System are the rooftop donor antenna, coaxial cables, radio repeater or bi-directional amplifier, and a series of aesthetically pleasing antennas that are typically mounted to ceiling tiles. For larger buildings and campus wide solutions, fiber optic cabling is used to overcome the loss inherent to longer coaxial cable lengths.  The radio or RF site survey within the building will drive the system design and complement the information gathered through the authority having jurisdiction. The AHJ may even require a design review prior to the build.

The donor antenna is directional and mounted outdoors atop the building that requires the PS-DAS. Donor antennas point toward the radio tower with the antennas providing the emergency first responder dispatch and tactical radio communications. Transmissions to and from the building are carried by this antenna.

Coaxial cable is run between the donor antenna and the PS-DAS repeater or bi-directional amplifier BDA.  Coaxial cables for in-building purposes are plenum rated.  A plenum rating means the cable is suitable for use in air space and emits less smoke and toxic fumes in the event of fire.  If the signal loss is high through the coaxial cabling a fiber optic network will be used instead.  This requires converting the electrical radio signals to optical signals to pass through the fiber optic cabling.

The repeater or bi-directional amplifier (BDA) filters and amplifies the signal received by the donor antenna as well as the DAS antenna network. The building distribution side of the BDA distributes the radio transmissions over a network of coaxial or fiber optic cabling throughout each floor of the building. The coax or fiber terminates at each PS-DAS antenna typically mounted to the ceiling.