Everything you ever needed to know about attenuation and cable length

| Jul 11, 2013


Cable Length Infographic
Click on the image for a larger view

When it comes to transmitting signals through any cable, one of the biggest obstacles is signal attenuation. Attenuation refers to the reduction in the strength of a signal over distance. Think of the sound comming from your speaker. If you are standing right next to your speaker, the sound is very loud and strong. But, the farther you move away, the quieter the sound gets. Eventually, you won't be able to hear it at all. That's because the sound is being affected by attenuation as it moves through the air. The extent of attenuation is usually expressed using decibels (dBs). This reduction is a natural consequence of sending signals over a given distance, and it happens with any type of signal being transmitted over the air, through cables, or through any other medium.

Attenuation and Signals

Why do we have attenuation? Well to understand that, we need to take a look at what makes a signal. When you turn on your TV, watch a video on the internet, or listen to music on a stereo, you need to transmit data from a source (like your DVD player, receiver box, stereo, etc.) to a receiver (like your TV, monitor, speakers, etc). Some devices need to send and receive data. Any time data needs to be sent from one place to another, an electric current or electromagnetic field is used to convey that data. In a sense, the electric current acts like a car, taking the data from point A to point B. That current is the signal.

What Causes Attenuation?

Wreck it Wralph Data Transfer
These video game characters are data, the subway car acts like the signal,
transmitting the data from place to place

So, when we say that attenuation affects the signal, it is affecting the current that is carrying the data. Just like there are different factors that affect how far you can drive in your car, there are a variety of factors that affect attenuation. The first thing is the type of conductor that is in your cable. Copper, being one of the most conductive metals available, has long been the standard for all kinds of cables. But, since it’s expensive, some people use less conductive metals instead. The less conductive your cable, the more attenuation you will have.

Even with the best possible cable you will have to deal with attenuation. That’s because all electrical signals transmitted down conductors cause an electromagnetic field around the transmission. This field causes energy loss down the cable and gets worse depending on the frequency of the signal and the length of the cable.

Think of our car example. Even with newer, more advanced cars, we can only go so far before we have to refill the tank (or plug it in if you are being eco-friendly). The same basic idea carries over to attenuation.


Knight Rider Boost
Your signal needs a boost

Fortunately there is an easy solution to this problem, and that is through amplification. Amplification is an increase in signal strength, making it the opposite of attenuation. You can buy repeaters (sometimes called signal boosters) to amplify the signal, which help you to make it go farther. You can even get anHDMI cable with a built in repeater, which allow you to get more length without having to buy extra equipment.

Whenever you go to buy cable, make sure and check how long you need it to go. Then, check the hardware you’re getting. Do you know how far your cable will reliably transmit a signal? Once you know that, you can get what you need for your installation and overcome the obstacle of attenuation.