How Do Active HDMI Cables Work?

How do active HDMI cables work?

Modern HDMI cables are incredibly effective cables for video and audio transmission. The latest HDMI 2.1 generation supports resolutions up to 8K (and beyond, with compression), as well as high refresh rates. One downside to this latest crop of cables, though, is their length. Where older generations of HDMI cable could stretch up to 25 feet, standard passive HDMI 2.1 cables are only viable up to nine feet. Beyond that, there’s no guarantee the signal will even be received, let alone at high quality.

To go further than that, you need an active HDMI cable. Active HDMI cables are a good way to enjoy the full bandwidth of new, high-performance standards like HDMI 2.1, without being stuck to very short cables. Active HDMI cables utilize a few intriguing technologies to boost the maximum length of an HDMI cable by huge margins. At the extreme end, there are fiber optic active HDMI cables which can reach up to 300 feet and more – although they are more expensive

Passive HDMI cables have limited maximum lengths, while active HDMI cables can go far longer – many times longer than passive alternatives if you use an active optical cable – without losing signal strength or image clarity.

The functional HDMI max length is directly dependent on whether you're using an active or passive HDMI cable. Here's everything you need to know about active HDMI cables, and if you're on a cutting-edge setup, how to get the best HDMI 2.1 cable for your needs.

What is an Active HDMI Cable?

Traditional passive HDMI cables are merely the HDMI port standard connected to shielded copper wiring. That simplicity makes them great because they can transmit audio and video in either direction – that's where the super handy ARC and eARC technologies come in. Unfortunately, thanks to signal attenuation, there is a maximum HDMI cable length, and on newer standards like the HDMI 2.1 cable, it can be quite limited – even with high-quality HDMI 2.1 cables, like those produced by Cable Matters.

Active HDMI cables solve that problem by incorporating signal boosters to amplify the signal from the source and send it further down the line without it degrading. This lets the cable run far longer without the signal being overly negatively affected, making it possible to have HDMI devices and displays far further apart. This is particularly useful for professional settings like bar TVs, presentation screens in meeting rooms at the office, or for creating a hobby or entertainment room with convenient access to a source device like a Blu-ray player or desktop gaming PC.

The use of signal boosters with an active cable, however, means that it can only run in one direction, so you need to connect the source end to the source and the destination end to your display. Getting it wrong won't break anything, but you won't get any kind of signal either.

An active HDMI cable can boost a signal by up to three times, making it possible to send older HDMI standards over 100ft in some cases. 

Another type of active HDMI cable is a fiber optic HDMI cable. These utilize thin glass fibers instead of twisted coppers pairs to carry the data, transmitting it using light rather than electricity. In Ethernet cables, that allows for greater bandwidths over greater distances for faster data transfers, but for active HDMI cables, it means transmitting high-definition video at much greater distances.

Where a copper active HDMI cable will be able to transmit over 100ft, there are fiber optic HDMI cables which can reach 300ft or even further. These cables do get very expensive, though. Where a passive HDMI 2.1 cable that has a maximum run of nine feet might cost you $10-15, an active HDMI 2.1 cable that runs 100ft might cost you around $80, a fiber optic HDMI cable that runs for 300ft, could cost you well in excess of $120.

How Long Can HDMI 2.1 Cables Be?

Passive HDMI 2.0 cables can extend to 20 or even 30 feet in some cases, but that’s not something the latest standard can manage. While active technology does help them go further, HDMI 2.1 cables are a little different due to their more than doubled high-frequency signaling. That gives them support for higher resolutions and refresh rates, like 8K at 30Hz, and 4K at up to 120Hz, but that added density of data means that the signal strength degrades far faster, so you’ll need an active cable to go further than a few feet.

At a 48Gbps data rate, the best passive Cable Matters HDMI 2.1 cables can reach 10ft before they run into difficulties. That's fine for the average living room setup, connecting your new Xbox Series X, PS5, or RTX 3000/4000 graphics card to your HDMI 2.1 TV, but you'll need an active cable to go further if you want to maintain the full 48Gbps bandwidth of HDMI 2.1

HDMI cable length for active HDMI 2.1 connections can increase dramatically whilst retaining full bandwidth. An active HDMI 2.1 cable can measure up to 25ft without difficulty, giving you much more cable reach to play with. That makes it possible to set up an HDMI 2.1 TV much further from the 4K or 8K source.

At the very high end of active HDMI cables, you also have the option of HDMI 2.1 active fiber optic cables. They offer the highest protection against signal attenuation, therefore letting you run the cable even longer. As with passive and copper twisted pair active HDMI cables, though, there is a wide range of length options available. The best fiber optic active HDMI cables can run over 300 feet and still maintain the full bandwidth of the HDMI 2.1 cable standard, but they do tend to be rather expensive, costing well over $100 at the top end.

For more affordable fiber optic active HDMI cables, you could look to lengths of 200ft or 100ft, though be sure in each case to buy a high-quality cable to ensure that it can maintain the performance claims that it makes.

What About HDMI 2.1a?

With the debut of the HDMI 2.1a amendment to the HDMI 2.1 specification, the HDMI Forum introduced a new feature: HDMI Cable Power. Where previously, active HDMI cables may have required an additional, separate power cable, that’s no longer the case. It should make future active HDMI cable runs far more streamlined, easier to install, and cheaper. 

HDMI Cable Management can be supported by all types of HDMI 2.1 cables. That includes those branded as “Ultra High-Speed HDMI Cable,” as well as “Premium High-Speed HDMI cable,” and their various versions with Ethernet support built-in.

The idea behind this was to make active HDMI cables more viable for use in home settings. At the launch of this new feature, the HDMI Forum noted that most active fiber optic HDMI cables were utilized in professional settings. Making it easier to implement could allow for more home setups to leverage the power of these longer, more capable HDMI cables.

However, the downside to this new feature is that it requires the source device, and the display, both to support HDMI Cable Power too. There are displays and devices out there that support it, but you’ll need to double-check their features and spec list to know for sure.

Outside of that, HDMI 2.1a is exactly the same as HDMI 2.1, so any active 2.1a cables will be subject to the same range limitations as other active HDMI 2.1 cables – they just won’t need an additional power cable, too.

The Best Active HDMI Cable for 4K 120Hz

You don't need an active HDMI cable to enjoy the full potential of HDMI 2.1 on new-generation game consoles and PCs. If you just want to experience high resolution, high refresh rate gaming on your HDMI 2.1 TV or monitor and it sits within 10 feet of your game console or PC, you're in luck. You can use a passive, high-quality HDMI 2.1 cable without any concern about running into the HDMI cable max length.

If you're close to that 10ft threshold, however, or want to run a cable at a significantly longer distance to offer multi-screen compatibility without placing the system and HDMI 2.1 TV side by side with each other, then an active HDMI cable is the way to go.

If you can keep your HDMI length under 25 feet, then you can enjoy all the benefits of HDMI 2.1 with a standard active HDMI 2.1 cable. It has all the shielding and signal boosting you need for 4K and 120Hz gameplay over a more extreme HDMI length.

If your HDMI cable length needs to be as long as physically possible with today's technology, though, then a fiber optic HDMI 2.1 cable is your only option. The best HDMI 2.1 cables built using active fiber optic technology can give you 10 meters or more to work with. 

Cable Matters offers a certified HDMI 2.1 cable with fiber optic technology, available in lengths up to 34.2 feet. This cable is also Designed for Xbox, meaning it is built and tested to meet the demands of 4K 120Hz gaming on the latest Xbox Series X game console.

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