What is a Bi-Directional Amplifier (BDA)?

A bi-directional amplifier (BDA) is used for on-site radio coverage enhancement. A donor antenna collects signal from the rooftop, where it is strong, and delivers it to the BDA for amplification. The amplified signal is then delivered to one or more distribution antennas in areas that have poor coverage. BDAs typically include a backup power system (UPS) and an alarm output for when there is trouble with the system. They are available in VHF, UHF, 700 MHz, 800 MHz and cellular/LTE bands.

Components of a BDA system

• A donor antenna to pick up signal from a repeater site
• The BDA itself, to amplify the signal
• A distributed antenna network of one or more antennas located in signal-deficient areas, to increase the signal there
• UPS and alarm monitoring, available as options

BDAs are the most common coverage enhancement solution for the E-Comm radio network in the Lower Mainland of BC, used in larger buildings to comply with local bylaws in the District and City of North Vancouver, Burnaby, Surrey, Coquitlam, Port Coquitlam, New Westminster, White Rock, Richmond, Langley and Vancouver. All BDAs must be NFPA and ISED approved, and must provide full coverage throughout the building.

Inside the TX/RX BDA wall mount unit

What is the difference between a repeater and a BDA?

Radio repeaters receive one frequency, strip off the voice or data, and retransmit at high power on a different frequency. A repeater needs two frequencies to operate (an uplink and a downlink channel), and it covers a greater area than a BDA can.

Amplifiers take incoming signals within a band and amplify them for distribution in another area. Because BDAs amplify the same frequency, they can only amplify the signal a limited amount; otherwise they would begin to amplify the already amplified signal and get caught in a loop. A bi-directional amplifier is really two amplifiers in one package: one for amplifying signals from the cell site or repeater, the other for amplifying signals from the mobile device back to the radio network.

Who needs a BDA?

People who do not have radio or cell coverage in specific indoor areas often choose to invest in one or more bi-directional amplifiers.

What is the process to comply with the municipal bylaw?

To make sure contractors gain occupancy in a new facility that requires radio coverage, we include the following services:

• Provide heat maps for coverage, and design and quote accordingly
• Coordinate licence and permissions tracking through E-Comm
• Engage a radio P.Eng. to sign off on the design and stamp the final documents
• Obtain a low voltage building permit for installing the coaxial cable
• Install an NFPA approved amplifier, including antenna network, alarm notification and UPS
• Supply a maintenance and as-built document package

How do BDAs work?

Most places have some signal, just not in all the areas required on site. A hotel, for example, may have signal on the upper floors but none in the parkade. To provide signal in the parkade we install an antenna to pick up signal from the cell site or repeater in a working area, feed it to the amplifier, then out to more antennas located near the areas with deficient coverage.

Will one BDA work for multiple carriers?

There are BDAs that serve multiple carriers (Telus, Bell, Rogers, E-Comm, private trunking, private RF channel), however lower cost BDAs offer the best performance when they are designed for a single RF band or carrier. Higher end BDAs can be designed for multiple carriers and many users without compromise.

Do I really need the best one? I have seen these online for low cost

There are many coverage enhancement solutions available, and some cost only a few hundred dollars. Sometimes they are a perfect solution, but often users quickly have buyer's remorse, because those lower cost BDAs are designed for small areas where very few devices access them at the same time.

What specifications should I look for when buying a BDA?

The figures in bold below are for the TXRX Signal Booster II BDAs we normally supply.

• Gain: 50-80 dB. High gain allows the BDA to amplify very small signals to and from the donor site to its maximum output. Many believe this is the most important specification, but many applications do not require high gain. Gain should be engineered to match the requirement for the building. Too much gain can deliver signal into areas that already have good signal, causing distortion there.
• Output: 30 dBm (1 watt single carrier). The total power the amplifier can deliver, shared amongst all the active transmitters that fall within the BDA's passbands.
• 3rd order output intercept point: 55 dBm. This indicates how well a receiver performs in the presence of other strong nearby signals. If there is one measurement of quality for comparing one amplifier with another, this is it. The higher the number the better, and each 3 dB is twice as good.
• Bandwidth. The bandwidth should only be wide enough to pass the active channels. Too wide and it will amplify other signals and use up available output. Multiple carrier performance needs wide passbands.
• Group delay: under 1 microsecond. Digital systems need the donor and amplified signals to be as close to synchronous as possible, so that locations served both directly and through the BDA are not compromised. BDAs designed with higher delays work poorly for time-sensitive digital signals. The TXRX BDAs we distribute have less than 1 microsecond of delay; the next best amplifiers on the market exceed 6 microseconds.
• Noise figure: 3.5 dB. The lower this number the better. In simple terms it is how much noise the BDA adds to the original signal: nothing to do with a noisy sound from a weak signal, but noise generated by the BDA itself. Unchecked system noise will eventually desense a receiver's front end, making it less sensitive and reducing the effective reception range.

Do BDAs require a licence?

Yes. BDAs need to be registered with Innovation, Science and Economic Development Canada (ISED). The yearly licence fee is typically under $100. If the BDA is a coverage enhancement solution for the E-Comm radio network, E-Comm will take care of the ISED licensing. The BDA RF cable installation also requires an electrical permit from the city or BC Safety Authority.

B.C. Communications BDA installation services

We have an expert team ready to help you with your BDA project. Our scope of work for the installation of 700 MHz E-Comm BDA systems includes:

• Analyzing architectural drawings and consulting with engineers (there is a cost of $2,000 for this phase)
• Applying for the radio licence, and coordinating licence and permissions tracking through E-Comm
• Obtaining a low voltage building permit for installing the coaxial cable
• Installing an NFPA approved amplifier, including alarm notification and UPS
• Liaising with the fire department
• Supplying a maintenance and as-built document package
• Engaging a radio P.Eng. to sign off on the design and stamp the final documents

Our labour services include:

• Staging and assembling components, shipping and delivering in stages
• Installing donor antennas
• Mounting the BDA and UPS
• Providing alarm pigtail wire ends for others to connect to the alarm panel
• Connectorizing cable runs installed by others
• Installing splitters and antennas on 12x12 junction boxes supplied by others
• Sweeping coaxial cables and confirming appropriate losses to each antenna
• Meeting with the fire department and engineers to ensure bylaw compliance

Need a bi-directional amplifier? We can help with design and installation: contact us. You can also read about the other ways to increase radio coverage.