Solutions · DAS (Distributed Antenna Systems)
DAS: we bring the radio signal inside tunnels, metro lines, airports, and large buildings.
We design and install radiating cable and distributed antenna systems for radio coverage in road and railway tunnels, metro lines, airports, and large buildings. On the same line we distribute professional radio networks (TETRA, DMR, VHF/UHF), cellular service (GSM, 3G, LTE, 5G), and FM and DAB+ rebroadcast.
In a tunnel, on a metro line, on underground levels, and inside reinforced-concrete buildings, the radio signal does not get in from outside: the walls attenuate it until it is unusable. The maintenance team loses contact with the control room the moment it passes the entrance, and anyone inside cannot call 112. Raising the power of the outdoor systems does not help, because the signal still stops at the structures it would have to pass through.
A DAS distributes the signal from the inside: a line runs through the space and radiates along its whole length. Radiating cable covers linear environments such as road, railway, and metro tunnels; distributed antennas cover open spaces and multiple levels, such as airport terminals and large buildings.
What makes it hard to bring the radio signal into an enclosed space.
The three problems a DAS has to solve, from the design calculation to day-to-day operation.
Attenuation along the line
The distribution line loses power with every meter of cable, every coupler, and every splitter. If the calculation does not account for all the losses, the last section is left without usable coverage while the first receives more signal than it needs. How uniform the coverage is depends on how the passive components and the line amplifiers are sized.
Several services on the same line
Professional radio networks, cellular service, and FM and DAB+ rebroadcast share the same line, each with its own band and its own power level. That takes filters, combiners, and passive components chosen for the full range of distributed frequencies; otherwise one service interferes with another.
The faults you cannot see
A short circuit on the radiating cable caused by a fire, or an open line from a faulty connector, leaves the whole area served by that section without communications: the equipment in the technical room keeps running and reports nothing. That is why we continuously check the continuity of the line and the presence of the carriers, instead of waiting for the first call that does not go through.
How a DAS is built.
A distribution line seen from beginning to end: the master unit combines the services in the technical room, the remote unit converts the signal back to radio frequency along the route, and the splitter shares it between the radiating cable and the distributed antennas.
- Radiating cable
- Radiating cable is a coaxial line that radiates the signal along its whole length. It is the choice for linear environments such as tunnels, where coverage has to be continuous from one entrance to the other.
- Distributed antennas
- Distributed antennas are fed from the same line and each covers its own area. They are needed in open spaces and across multiple levels, such as airport terminals, concourses, and the underground levels of a large building.
- Passive components
- Splitters, directional couplers, and terminating loads share the signal between the branches and close the end of every section. Line amplifiers recover the attenuation along the route.
- Master unit and remote unit
- The master unit combines the signal sources and feeds the distribution line. The remote units, connected over optical fiber, convert the signal back to radio frequency along the route and feed the more distant sections.
What a DAS includes.
The systems we build and what each one covers, from the master unit to the acceptance measurements.
Master unit and signal sources
- Base stations, repeaters, and FM and DAB+ receivers installed in the technical room or the shelter
- A master unit that combines the services onto the distribution line and sets their levels
- Filters, duplexers, and combiners at the input, one for each distributed band
- Input power levels set service by service to the values specified by the design
- Signal conversion for digital distribution over optical fiber, where the design calls for it
Radiating cable
- Radiating cable laid along the tunnel sidewall or in the building risers, at the height specified by the design
- Fixings at a constant spacing, respecting the minimum bending radius
- Splices, connectors, and terminating loads fitted and sealed against moisture
- Several sections fed separately, where a single line does not cover the full length
- Labeling of the sections and the access points, so maintenance teams can find every branch of the line
Distributed antennas
- Antennas installed on ceilings, on walls, and in niches, at the points indicated by the coverage calculation
- Coaxial connecting cables sized for the length of each branch
- Antennas at the entrances and at the junctions between spaces, where the radiating cable line breaks
- Coverage of shielded areas: underground levels, stairwells, service corridors, and technical rooms
- Verification of the signal level in every area served by the antennas
Passive components
- Power splitters and directional couplers to share the signal between the branches
- Terminating loads at the end of every section
- Fixed attenuators to even out the levels between branches of different lengths
- Connectors and adapters chosen for the full range of distributed frequencies
- Surge arresters on the RF lines and bonding to the earthing system
Line amplifiers and remote units
- Line amplifiers housed in the niches and cabinets along the route
- Remote units that convert the signal arriving over optical fiber back to radio frequency
- Optical links in cascade, star, or redundant topology, depending on the length and the criticality of the section
- Gain settings that keep the levels specified by the design across the whole line
- Dedicated power supply and uninterruptible power supplies for every active device
Monitoring of the line and the services
- TP-CCV2 in the base station cabinet: it reports short circuits and open lines on the radiating cable
- TP-035 and TP-035A passive components, to inject the test signal onto the line without interrupting the services
- TP-RFX connected to an antenna inside the covered space: it checks the TETRA, DMR, FM, and DAB carriers present
- TP-CELLX inside the covered space: it verifies the operators’ 2G, 3G, and 4G cellular coverage
- Track-TP as the supervision platform, with notifications by email, SNMP traps, WhatsApp, and Telegram
Acceptance testing and measurements
- Continuity and insulation test of the radiating cable before the system enters service
- Standing wave ratio (VSWR) on antennas, downlead cables, and radiating cable sections
- Location of line faults, with a measurement of the distance to the fault point
- Attenuation and signal levels along the route, compared with the design calculation
- Coverage and call tests on every distributed service, with a signed acceptance report
Frequently asked questions.
The questions we are asked most often about this type of system.
What is the difference between a passive and an active DAS?
What changes is how the signal reaches the point you need to cover. In a passive system the signal leaves the equipment in the technical room and travels only through cables and passive components: the design is simple and needs no powered equipment along the route, but cable attenuation limits the length that can be served. In an active system the signal travels over optical fiber to remote units installed along the route, which convert it back to radio frequency close to the area to be covered: longer distances can be served and levels can be set service by service, at the cost of equipment that has to be powered and monitored. The choice is made with the link budget, based on the length to be covered and the number of distributed services.
Is the equipment that generates the signal part of the DAS, or does the network owner supply it?
The DAS is the part that carries the signal into the space to be covered: master unit, distribution line, radiating cable, antennas, and passive components. The equipment that generates the signal depends instead on the service being distributed. For the customer’s radio network we supply and install the base stations or repeaters in the technical room ourselves. For cellular service the equipment is supplied by the mobile operator, and the design allows for the rack space, the power supply, and the connection point to the line. For FM and DAB+ rebroadcast the receivers stay in the technical room and take their signal from an outdoor antenna. The split of supply is put in writing before work starts on site, because it also establishes who is responsible for each device once the system is in service.
Can a DAS that is already installed be upgraded with new bands or new services?
Often yes, but the existing system has to be checked first. Radiating cable, antennas, splitters, couplers, and connectors work over a defined frequency range: if the new band falls inside that range, the work usually involves the head-end equipment and the input filters, whereas if it falls outside, the passive components have to be replaced. Before quoting an upgrade we measure the existing lines and compare the values with the original design, because on a system a few years old some sections may already have degraded. The survey tells you whether it is worth upgrading the system or rebuilding the distribution.
Can a DAS also distribute a private LTE or 5G network?
Yes. We already distribute professional radio networks, cellular service, and FM and DAB+ rebroadcast on the same line: the bands of a private LTE or 5G network are added the same way, once the link budget has been checked. The network is supplied by the operator the customer chooses; we design the distribution, install it, and carry out the acceptance testing.
What drives the cost of a DAS?
Cost comes down to four factors: the length or the floor area to be covered, the number of services distributed on the same line, the type of distribution chosen, and the conditions the work is carried out in. A linear environment served by a single run of radiating cable costs far less than an active system with remote units over optical fiber and several distributed bands. Site conditions matter too: in a space that stays in service, work runs in time slots agreed with the operator and the schedule stretches. A reliable figure comes after the coverage study and the link budget, which establish how much equipment and how many passive components are really needed.
Every DAS starts with a site survey and a coverage study.
For every project we provide a tailored technical and commercial proposal based on your requirements — feasibility analysis, RF coverage study, and intervention planning.