What does a combiner do?

A combiner is a very important part of a headend system. It’s the part that allows the full signal to travel over a single wire. Without that, there would be no headend system. And yet a combiner is usually the least expensive part of a headend system, because it doesn’t have to be expensive or fancy.

What a combiner does

A combiner’s job is simple. It just takes the signals coming into it and combines all of them. Sort of like this:

There’s no real intelligence to a combiner. It mixes signals indiscriminately. It’s up to the other parts of the system to know how and why to combine things. And when it comes to a headend, this is done through a mix of magic and science.

Understanding baseband video

When a video signal goes through a wire, it uses the entire wire. We call this baseband video. The entire signal capacity of the wire is used up by this one video and audio signal. Baseband video is used for the highest possible quality.  Baseband signal on a wire could be imagined to look like this:

The red signal takes up the entire capacity of the wire it’s on.

However, it doesn’t make a lot of sense to use baseband video to distribute signals. You would need one wire for each channel you wanted to watch, and that would become a real mess, real fast. The solution is a “modulated” system, which allows for more than one signal on a wire.

Understanding modulated video

A modulator is a device which takes that entire baseband video signal and forces it to use only a small portion of the capacity of a wire. This generally means that there is some quality loss, but if it’s done well, the loss in quality is so small that you just don’t notice.

A modulator doesn’t just keep all the signal in a small space, it also keeps the rest of the signal capacity clear. That means a modulator needs some sort of noise filter to make sure that it’s not adding noise.

When we talk about the capacity of a wire, we refer to the frequencies it carries. In the case of most coaxial cable, you have a span from 5MHz to 3000MHz to work with. A typical modulated video signal takes up between 5 and 15MHz. So, there’s the possibility of storing a lot of channels on one wire, as long as they don’t interfere with each other.

What a combiner does

As I said the job of the combiner is pretty simple. Each modulated signal uses a frequency range that none of the other modulated signals use. So, all the combiner does is pour all those signals onto a wire. It’s literally as simple as connecting the wires together. Because none of the signals interfere with each other, it all lines up very nicely, like this diagram.

Now all that’s left is for a TV to receive the signal and use its tuner to choose which of those signals to display.

Combiners for home use

You can use a combiner with two over-the-air antennas. The antennas can be pointed in two different directions to get different signals, or pointed in the same direction so you get a stronger signal. You can also use a combiner to add radio signals.

No matter which combiner you need, or what you’re going to use it for, you can find the best selection when you shop at Solid Signal.

 

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 7,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.