Should I add a Ferrite Core to a HDMI cable? - AVS Forum
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post #1 of 14 Old 03-04-2013, 01:26 AM - Thread Starter
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I will be ceiling mounting my projector in about a day or two and will be having one cable coming out of a receiver, a 3metre one. Should I add ferrite core to it? They don't cost a lot to get one but I'm just curious if I should bother.

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post #2 of 14 Old 03-04-2013, 06:28 PM
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Are you suffering the effects of some kind of interference?
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post #3 of 14 Old 03-04-2013, 10:06 PM
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Quote:
Originally Posted by olyteddy View Post

Are you suffering the effects of some kind of interference?
More precisely, is your HDMI cable acting as an antenna for noise from the connected devices and interferring with something else? If so, ferrites might be useful. Otherwise, no.
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post #4 of 14 Old 03-04-2013, 10:43 PM - Thread Starter
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Luckily, no. I havnt been seeing any interference or noise yet, but I intend to buy my first extra long HDMI cable, 3 metre, and maybe thought the ferrite core would help against any image artefacts that might happen.

I'll be routing all my cables into an AV Receiver and all the info will come out through that one cable.

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post #5 of 14 Old 03-04-2013, 11:30 PM
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Quote:
Originally Posted by Tyrone Burton View Post

...ferrite core would help against any image artefacts...
No. A ferrite core reduces common mode noise. The video and audio are transmitted using a differential circuit that essentially cancels out common mode noise. So, a ferrite isn't going to do much for those signals. And research has shown that a ferrite core will actually adversely affect the video and audio signals. IOW not only are ferrites pretty useless as far as HDMI goes, they are to be avoided unless you absolutely have to reduce interference with other devices.

HDMI uses digital signalling. A problem will not show itself as a subtle change in color, brightness, sharpness, contrast, or any of the other artifacts we might be familiar with in an analog environment. The first indication of a problem is sparkles, pixels that are just plain wrong. If you don't see sparkles, the picture is as good as it gets.
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post #6 of 14 Old 03-04-2013, 11:38 PM - Thread Starter
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Originally Posted by Colm View Post

No. A ferrite core reduces common mode noise. The video and audio are transmitted using a differential circuit that essentially cancels out common mode noise. So, a ferrite isn't going to do much for those signals. And research has shown that a ferrite core will actually adversely affect the video and audio signals. IOW not only are ferrites pretty useless as far as HDMI goes, they are to be avoided unless you absolutely have to reduce interference with other devices.

HDMI uses digital signalling. A problem will not show itself as a subtle change in color, brightness, sharpness, contrast, or any of the other artifacts we might be familiar with in an analog environment. The first indication of a problem is sparkles, pixels that are just plain wrong. If you don't see sparkles, the picture is as good as it gets.
Ah, great, I don't really need one then. Thanks for your help.

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post #7 of 14 Old 03-13-2013, 07:10 AM
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A ferrite doesn't hurt...and it keeps the internal noise from the projector's power supply and internal digital circuits from radiating down the cable and out in to nearby space.
It's a good idea to put a ferrite on any and all cables that may carry digital signals or noise from switch-mode power supplies.

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post #8 of 14 Old 04-14-2013, 04:51 PM
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I tried them and it did not reduce the dancing pixels.If you do Try it's better too buy one that has ferrite core built in as your not suppose to bend hdmi cable too much.
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post #9 of 14 Old 04-17-2013, 09:14 AM
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Quote:
Originally Posted by kenglish View Post

A ferrite doesn't hurt...and it keeps the internal noise from the projector's power supply and internal digital circuits from radiating down the cable and out in to nearby space.
It's a good idea to put a ferrite on any and all cables that may carry digital signals or noise from switch-mode power supplies.

You said "a ferrite", is it recommended to have one ferrite on each cable end or is only one needed per cable?
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post #10 of 14 Old 04-21-2013, 08:14 AM
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One is usually recommended, located as close as possible to the noise source (usually the TV).
I see no problem with putting one (of each kind) at both ends of a cable that ties two devices together, like a TV and a Cable/Satellite box.

The ones that are provided with most consumer stuff are good from about 25 to 250 MHz.. Adding a lower-frequency mix ferrite, designed for below 30 MHz will get rid of RFI on the AM and shortwave/ham bands, as well. They are also a good thing to add to battery chargers and other switched-made power supplies.

Here's a link, which has some information about those power supplies and about interference:
http://www.avsforum.com/t/1468359/new-uk-website-on-radio-tv-interference

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post #11 of 14 Old 04-21-2013, 01:24 PM
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Got three ferrites with my new plasma TV. Now I know what to do with them.

Thanks for the information.
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post #12 of 14 Old 04-21-2013, 04:15 PM
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Note that Ken recommends ferrites on cables to minimize polution of the airwaves. They won't do a thing for your picture.
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post #13 of 14 Old 04-22-2013, 06:45 AM
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They can prevent the cables from carrying interference in to the TV and other devices, if you have any nearby sources of RFI, including transmitters and other digital devices. They keep the cables from acting like antennas, both transmitting (radiating interference) and receiving (conducting interference into, or between devices).

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post #14 of 14 Old 04-22-2013, 06:48 AM
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Quote:
Originally Posted by JRWalker View Post

Got three ferrites with my new plasma TV. Now I know what to do with them.

Thanks for the information.

Put one on the power cord, as close to the TV as possible. Other ones should go on the RF cable (antenna or Cable TV) or on any other cables (HDMI, audio, video, network, etc) as close to the TV as possible. If you wind up with a spare one, you might put it on the end of the cable that connects the TV and Cable/satellite STB, close to the box.

Ken English, Sr. Engineer, KSL-TV.
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