How Does a Duplexer Work?

Duplexers sound like they might be perplexing and complicated, but the concept is simple. Did you know you’re already using a duplexer on your mobile phone?

A duplexer could revolutionise how you use your radio device, so let’s find out more.

Here, we will take a close look at duplexers and explain how they work and what they do.

What Is a Duplexer?

A duplexer is a three-port filtering electronic device which allows bi-directional or duplex communication. Put simply, it is a three-port device that separates transmit and receive signals from an antenna into different signal paths. 

Mobile phones all contain a transceiver device for simultaneous communication.

Duplexers aren’t to be confused with emerging technology in specialist digital radios that mimic duplex operation by quickly switching the receiver and transmitter on and off. This technology isn’t an authentic duplex operation.

Put simply, when a transmitter and a radio receiver use the same antenna for communications, an electrical switch is used. This electronic switching system is known as a duplexer. Without a duplexer, signal and frequency interference between the transmitted frequency and the received frequency can damage the radio receiver.

A duplexer is very important for radio apparatus as it allows the switching of the pathway of the signals toward either the transmitter or the radio receiver.

Why not just use two antennas? Well, that’s a fair question. Two antennas need to be far enough apart so that the transmitter signals don’t interfere with the receiver. The type of antennas and their orientation to one another is also critical, and you’ll need two transmission lines. Other antennas on the same tower will also affect the antenna-to-antenna isolation.

How Do Duplexers Work?

It’s simple! The transmitter and radio receiver are split so they work together rather than in opposition whilst the transmission is ongoing. 

The mechanics include two band pass filters which connect in parallel. One filter provides a path between the antenna and the transmitter and the other between the radio receiver and the antenna. 

There’s no direct connection between the transmitter and the radio receiver.

The signals are isolated from each other using two or multiple resonate circuit cavities. Typically, there’s one circuit for the transmitter and one for the radio receiver. 

Theoretically, only two cavities are needed, but radio experts will always suggest having more as this delivers the best quality output by increasing the isolation between transmission and reception.

When the radio receiver is in use, one circuit is dominant and works until that function is complete and the opposing process is required.

What Are the Advantages of a Duplexer?

Send and Receive Functionality

A duplexer allows users to send and receive messages from one device with a single antenna, making for a more straightforward radio set up..

Trying to do this without a duplexer will result in interference and poor-quality function.

Minimises Space and Cost of the System

Sharing the same antenna for a radio transmitter and radio receiver minimises space and cost.

Protects the Radio

Trying to send and receive messages on a unit with one antenna will overload the radio receiver and may even destroy it. Radio receivers can become damaged if high-level RF signals are applied to the receiver antenna.

A duplexer protects the radio receiver from high-power transmitters by isolation.

Frequently Asked Questions

What Is a Duplexer Used to Prevent?

Duplexers have several advantages, but one of the main benefits of a duplexer is protecting the radio eeceiver from high-power transmitters because of the isolation.

Radio receivers are vulnerable to overheating and damage if they receive high-level RF signals from the antenna.

What can a Duplexer be used for?

Duplexers can be used to:

• TX and RX from two radios at the same time into a dual-band antenna
• Combine a dual-band radio with separate outputs into a dual-band antenna
• Separate a single connector duplexed radio into separate antenna systems
• Allow a single coax run into two antennas at the top of the tower, and two radios at the bottom by using a duplexer at both ends of the coax run, avoiding cost and weight.

Final Thoughts

So, duplexers aren’t as complicated as you might think, and they offer plenty of advantages for radio users.

Want to try one for yourself? Shop Moonraker for a wide range of duplexers from all the top brands and prices for every budget.