Diplexer: What Is It?!

A diplexer is an RF (radio frequency) coaxial device that operates and looks quite similar to a standard RF splitter/combiner. The diplexer is a reversible three-port device.One port can be used as an input, and the other two ports as outputs. In this fashion, the diplexer acts as a splitter.When reversed, two ports can be used as inputs and the third, as an output. The diplexer then acts as a combiner.

However, the diplexer is a bit more specialized than the standard splitter/combiner. Unlike the splitter/combiner, the diplexer is a frequency-selective device. When the diplexer is used as a combiner, filters inside of the diplexer allow two different frequency bands, each at its own power level, to be multiplexed and outputted on a single coaxial cable. The signals are not mixed, meaning that at the output of the diplexer, there are two distinct frequency bands, instead of just one wide band, and the power levels are not added together. Diplexers are typically used with high frequency satellite signals, and low frequency CATV/OTA (over-the-air) antenna signals, for transmission down a single coaxial cable.

A second diplexer, acting as a splitter at the opposite end of the coaxial cable, then separates the two frequency bands, each with its own respective power. The satellite signal goes out of one port to the satellite receiver, and the CATV signals go out the other port to the TV tuner.

Here are two diplexer products.

• The first is the OnQ Diplex Filter Assembly. One filter assembly is required at each of of the coaxial cable.
• The second is the OnQ 1×4 Satellite Diplexer Module. The module is designed for installation within an OnQ enclosure, and multiplexes the signals together for distribution out to four locations. Do note that four Diplex Filter Assemblies are required to complete the system, one at the far end of each coaxial cable coming from the 1×4 module.

So there you go. The next time you encounter an installation requiring both satellite and CATV/OTA, or even modulated signals from a security camera, and all you have to work with is a single coax cable, break out with the diplexers, and call it a day.