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Bi-directional Amplifier- Why you Need a Bi-directional Amplifier

The fundamental role of amplifiers is to intensify the incoming signal. But, in some cases, amplifying signs in the receiving and transmission modes are handy for reliable communication. It is why a bi-directional amplifier is essential. Take a look at this system’s features, components, and uses. 

What is a Bi-Directional Amplifier?

A typical audio amplifier

Figure 1: A typical audio amplifier

Also called a BDA, a bidirectional amplifier facilitates two-way communications. Primarily, it enables radio signal strength amplification in the transmit and receive modes. The two-way radio system features a power amplifier (PA) on the transmission end, while the receiving end has a low noise amplifier (LNA). 

In principle, it’ll receive a weak input signal during the receive phase and amplify it. Next, it sends the RF signals to the radio. Next, during its transmit mode, it’ll boost the radio frequency from the radio, thus enhancing more extensive transmission. Therefore, it facilitates proper radio coverage by increasing the signal range. 

Thus, bidirectional amplifiers boost the cellular coverage of signal distribution. 

Components of a BDA System

Radio Terminals in a typical audio amplifier

Figure 2: Radio Terminals in a typical audio amplifier

Radio communication enhancement systems with the BDA sport the following components: 

  1. Donor Antenna

The cellular signal amplifier system features a donor antenna system to collect the radio repeater site’s signal.

  1. BDA

It enables a boost in radio signals by causing amplification.

  1. Distributed antenna network

It features an architectural design of antennas. Often, It’s common in signal-deficient zones and acts as a band-selective radio signal booster system. 

  1. UPS

It provides power in times of outages to ensure continuous building coverage. 

  1. Alarm Monitoring. 

Alarm systems are a critical component of the public safety radio system.

The BDA system is the most common booster in building radio frequency applications. It improves critical radio coverage, especially in more significant buildings and dead spots. 

Types of Bi-Directional Amplifiers

A guitar amplifier

Figure 3: A guitar amplifier

Primarily, there are two kinds of bi-directional amplifier (BDA) systems. 

  1. Full-duplex Bidirectional Amplifier

There is a frequency division multiplexing (FDM) function in some cases. Such an amplifier is capable of simultaneous transmission and receiving of the signal. Primarily this is because it features a separate transmit and a different receive frequency feature. 

A full-duplex bi-directional amplifier also sports duplex filters that hinder signal interference of the transmit signal and the systems receive channel. 

  1. Half-duplex Bidirectional Amplifier

Radio communication enhancement systems with this amplifier perform signal receiving and transmission on separate occasions. Also, they feature a switch on the input terminals and output ports that aids the selection of either the transmit or receive operation. 

Besides, half-duplex bi-directional amplifiers rely on intelligent biasing to choose the operation mode. 

Factors that affect the performance of a bi-directional amplifier

An audio mixer sound amplifier

Figure 4: An audio mixer sound amplifier

Radio system coverage in BDA systems depends on factors such as the following: 

Bi-directional Amplifier: Gain

It is the function of the amount of signal undergoing amplification. Thus, the higher the amplifier’s gain, the higher the amount of incoming cell signal it can amplify. The typical radio communication enhancement system’s gain is approximately +60 to +65 decibels. 

Bi-directional Amplifier: Uplink-output power

It gives the maximum boost in radio signal a BDA can send from the source to the surrounding receivers. The units of this feature are Decibel Milliwatts (dBm). 

Bi-directional Amplifier: 3rd Order Output Intercept Point

This property measures a receiver’s performance in the presence of other strong signals in its vicinity. Hence, when comparing the quality of one BDA to another, you must focus on this feature as it’s very significant. 


An amplifier’s bandwidth should be extensive enough to outweigh the active channels. But, an ample bandwidth is not good enough as it’ll induce amplification of other signals. Consequently, this will interfere with the available output. 

To ensure multiple carrier performance, it’s imperative to have relatively wide passbands. 

Noise Figure

It measures the amount of noise the BDA puts into the primary signal. Therefore, the lower the noise figure, the more influential the BDA. 

What is the Difference Between a Repeater and a BDA?

Portable radio transceivers

Figure 5: Portable radio transceivers

Radio Repeaters

They receive a single frequency, remove the data/voice, transmit, and finally retransmit on high power at a different frequency. Therefore, they need two frequencies for effective functioning that include;

  • Uplink Channel
  • Downlink Channel

Additionally, they have a more excellent outreach/coverage than the average BDA. 


On their part, BDA will receive the incoming signal and later amplify it to enable distribution. Notably, BDAs boost the same sign. 

Thus, they’re capable of amplification for a limited number of times. Otherwise, they’ll amplify an already amplified signal causing a problem in the loop. 

Also, note that BDAs operate as two separate amps in one package. Hence, one amplifies the repeater’s signal while the other amplifies the mobile device signal to the radio network system. 


In a nutshell, the bi-directional amplifier (BDA) system is essential in enabling adequate radio coverage. For further queries on the working principle of this analog two-way radio system, reach out, and we’ll get back to you promptly. 

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Emma Lu
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