What is a Bi-Directional Amplifier (BDA)?

A Bi-Directional Amplifier (or BDA) is used for On-Site radio coverage enhancement. BDA ‘s have a few components: A donor antenna collects signal from the rooftop where it is strong and delivers it to the BDA for amplification. The amplified signal is delivered to one or more distribution antennas in areas which have poor coverage. BDA s typically have a backup power system UPS and alarm output for when there is trouble with the system. BDAs are available in many specific bands: VHF, UHF, 700MHz, 800MHz, and cellular/LTE


Components of a BDA system:

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

BDAs are the most common coverage enhancement solution for the E-Comm radio network in the Lower Mainland of BC in larger buildings to comply with the local bylaws in all municipalities in the lower mainland District of North Vancouver, Burnaby, Surrey, Coquitlam, New Westminster, Port Coquitlam, City of North Vancouver, Whiterock, Richmond, Langley and Vancouver.  All BDA must be NFPA and ISEDC approved, and 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 transmit, then retransmit at high power on a different frequency. Radio repeaters require 2 frequencies to operate; an uplink and downlink channel. They have a greater coverage area than what a BDA can provide.

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. Bi-directional amplifiers are really just 2 amplifiers in one package; one for amplifying signals FROM the cell or repeater, the other for amplifying signals from the mobile device TO the radio network.

Who needs a BDA?

People that do not have radio or cell coverage 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?

In order to ensure contractors gain occupancy in their new facility that requires radio coverage, we include the following services:

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

How do BDAs work?

Most places have some signal, just not in all the areas required on site. For example, a hotel may have signal on the upper floors, but not in the parkade. To provide signal into the parkade, we would install an antenna to pick up signal from the cell site or repeater from working areas, feed it to the amplifier then off to more antennas located near the areas with deficient coverage.

Will one BDA work for multiple carriers?

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

Do I really need to get the best one? I have seen these on line for low cost.

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

What are the key specifications I should look for when buying a BDA?

Specification definitions for BDAs are listed below. The ones for the TXRX Signal Booster II BDA’s we normally provide are in bold:

Gain: 50-80dB. 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, however 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 with good signal causing distortion in those areas.

Output: 30dBm (1 Watt single carrier) the total power the amplifier can deliver. This is output is shared amongst all the active transmitters that fall within the BDA’s passbands.

3rd Order Output Intercept Point: 55dBm. It indicates how well a receiver performs in the presence of other strong nearby signals. If there is one measurement for quality in an amplifier as compared with another, this is the specification to look at. The higher the number the better, and each 3dB is twice as good.

Bandwidth: The bandwidth should only be wide enough to pass the active channels. If it is too wide, it will amplify other signals and use up available output. For multiple carrier performance you will need wide passbands.

Digital systems system require donor and amplified signals to be as close to synchronous as possible. This is to ensure that locations served both directly and also through the BDA are not compromised. BDAs designed with higher delays work poorly for many applications since the signal is typically digital, which is time sensitive. The group delay of the TXRX BDAs we distribute have less than 1µS delay, the next best amplifiers on the market exceed 6µS.

Noise figure: 3.5dB; the lower this number is the better. In simple terms it is how much noise the BDA adds to the original signal. This noise has nothing to do with a “noisy” sound coming from a weak signal. It’s strictly noise being generated by the BDA itself. Higher quality BDAs and specifically amplifiers have lower noise figures. Unchecked system noise will eventually De-sense a receivers “front end” thus making it less sensitive… thereby reducing the effective reception range of the receiver.

Do BDAs require a license?

Yes. BDAs need to be registered with ISEDC (Innovation, Science and Economic Development Canada). The yearly license fee is typically under $100 per year. If the BDA is a coverage enhancement solution for the E-Comm radio network, then E-Comm will take care of the ISEDC licensing

The BDA RF cable installation requires us to acquire an electrical permit for installation from the city or BC Safety Authority.

B.C. Communications BDA System Installation Services

We have an expert team ready to help you with your BDA project.

Our scope of work for the installation of 700MHz E-Comm BDA systems include the following:
  • Analyze architectural drawings and consult with engineers (there is a cost of $2000 for this phase).
  • Apply for radio license. Coordinate the license and permissions tracking through E-Comm.
  • Obtain a low voltage building permit for installing the coaxial cable
  • Install an NFPA approved amplifier, including alarm notification and UPS.
  • Liaise with fire department
  • Supply maintenance and as-built document package
  • Engage radio P. Eng. To sign off on the design and stamp final docs
Our labour services includes the following:
  • Stage and assemble components, ship/deliver in stages
  • Install donor antennas
  • Mount BDA & UPS
  • Provide alarm pigtail wire ends for others to connect to alarm panel
  • Connectorize cable runs by others
  • Install splitters, antennas located on 12x12 junction boxes supplied by others
  • Sweep coaxial cables and confirm appropriate losses to each antenna
  • Meet with fire department and engineers to ensure bylaw compliance.

Need a bi-directional amplifier? We can help with design and installation.

Contact us