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HDMI: Extension, Distribution and Switching via Cat5e/6

post #1 of 11
Thread Starter 
HDMI: Extension, Distribution and Switching via Cat5e/6
Author - Jeffrey Herman, Muxlab


Structured cabling plays a major role in audio-video systems today with Cat5e/6 being the most cost-efficient method to interconnect AV equipment in a multi-room or large venue environment. As more and more AV content is transmitted at HD resolution, there is a growing demand for the structured cabling system to support HD transmission over Cat5e/6 and therefore a greater need for HDMI over Cat5e/6 products. Furthermore the recent AACS Adopter Agreement pertaining to copy protection (Analog Sunset) and the gradual move away from unprotected component analog video is encouraging integrators to analyze future AV installations more closely in order to future proof them in support of HDMI. This article will focus on the key components needed to manage HDMI cabling over Cat5e/6.

Read the complete article at HomeToys.com
post #2 of 11
I just hope everyone will use shielded cable and proper ferrites and torroid cores on all their cabling, to reduce not only incoming interference, but also interference produced by their electronic devices.
Polluted spectrum is Useless spectrum.
post #3 of 11
Quote:
Originally Posted by kenglish View Post

I just hope everyone will use shielded cable...
Polluted spectrum is Useless spectrum.

I thought shielded cable was considered overkill for the standard residential environment (basement home theater)?
post #4 of 11
Quote:
Originally Posted by skillz2882 View Post

I thought shielded cable was considered overkill for the standard residential environment (basement home theater)?

I have to agree with kenglish there is a lot of interference out there. Some of it is a simple fix there is a lot of power ran from big companies all the way down to homes that is not properly grounded and you get weird loop back interference among other weird problems I.R. leaks ect. We really need to redo a lot of power grids and ground homes better. This is just a small part of what he is talking about sadly. I am not an expert but I do know what he is talking about we had that problem at my work.
post #5 of 11
Quote:
Originally Posted by kenglish View Post

I just hope everyone will use shielded cable and proper ferrites and torroid cores on all their cabling, to reduce not only incoming interference, but also interference produced by their electronic devices.

Ferrites will certainly help reduce RFI emissions. They might help improve the signal on the single-ended lines. But they won't do a thing to improve the signals on the TMDS pairs that carry video and audio. In fact they will actually degrade the signals on the TMDS lines slightly according to a research report on the subject I read. The eye pattern used to test HDMI cables closed in when ferrites were used.
post #6 of 11
Quote:
Originally Posted by skillz2882 View Post

I thought shielded cable was considered overkill for the standard residential environment (basement home theater)?

HDMI cable is shielded. The balanced pairs are shielded, and the whole cable is shielded. Cat 5/5e/6 is inferior for the purpose. You would have to use Cat 7/Class F cable to equal HDMI cable, and properly ground it. Shielded cable that is not properly grounded is no better than unshielded cable, and sometimes worse. Maybe you are thinking of cable for networking, not HDMI.
post #7 of 11
Sure Cat 5e/6 is cheaper than HDMI, but if I had a run less than 100', I'd still go HDMI. Per the article "Through the wall - use the existing installed Cat 5e/6... really not that many homes have this, and (IMHO) if I'm making holes and putting in wire, it's just as easy to use HDMI. This seems more for commercial applications rather than home entertainment applications
post #8 of 11
Quote:
Originally Posted by AVTrauma View Post

Sure Cat 5e/6 is cheaper than HDMI, but if I had a run less than 100', I'd still go HDMI. Per the article "Through the wall - use the existing installed Cat 5e/6... really not that many homes have this, and (IMHO) if I'm making holes and putting in wire, it's just as easy to use HDMI. This seems more for commercial applications rather than home entertainment applications

I had existing Cat5e in my walls when I bought an HDMI plasma. SO I used an $80 active, dual-wire extender to get the HDMI signal to the set.

After dealing with the headaches and handshake issues for a year, I tore off the baseboard, ran an HDMI cable in a groove Icheselled in the wall, and replaced the baseboard. 2-3 hours of labor and $30 bucks for the cable. I wish I'd done that in the first place...
post #9 of 11
Quote:
Originally Posted by Colm View Post

Ferrites will certainly help reduce RFI emissions. They might help improve the signal on the single-ended lines. But they won't do a thing to improve the signals on the TMDS pairs that carry video and audio. In fact they will actually degrade the signals on the TMDS lines slightly according to a research report on the subject I read. The eye pattern used to test HDMI cables closed in when ferrites were used.

If the ferrites can degrade the signal that should be INSIDE the pairs, then the pairs must be capable of radiating noise and interference.

My biggest gripes, though, are the noise given off by plasma and LCD TV's and monitors, computer routers, and bad power lines.
HDMI cables are a big culprit, carrying the noise from the big TV's to other devices, as well as acting as a radiating "antenna" for such noise.
post #10 of 11
Quote:
Originally Posted by kenglish View Post

My biggest gripes, though, are the noise given off by plasma and LCD TV's and monitors, computer routers, and bad power lines.
HDMI cables are a big culprit, carrying the noise from the big TV's to other devices, as well as acting as a radiating "antenna" for such noise.

Sounds like a problem with the originating equipment, not the cable. Ferrites on the cable are just a cheap fix that lets manufacturers avoid fixing the underlying problem.

Considering you are a broadcast engineer, I can understand your feelings about noise. For most of the rest of us, I think it is much less of an issue. With NTSC I used to be annoyed by the way impulse noise affected the picture on my TV when tuned to VHF low stations. Now that we have ATSC, the picture is rock solid as long as the signal to noise ratio is sufficient. I get all my local stations with no problems, and regularly get stations from 100 miles away in the evenings. The only problem I can attribute to noise now that affects me is with WiFi. Sometimes I lose the connection, apparently because of noise (neighbor's microwave?). Doesn't happen enough to be a big deal. But it would be an annoyance if I were using it to stream video. Have to go hardwire for that.
post #11 of 11
Quote:
Originally Posted by kenglish View Post

If the ferrites can degrade the signal that should be INSIDE the pairs, then the pairs must be capable of radiating noise and interference.

Theoretically, there should be no noise with the differential transmission system used for the TMDS lines. Ideally, the fields of the the wires will cancel out. Of course, we don't live in an ideal world. I think what is happening is that because of intra-pair skew and other problems, the differential signal is not completely in sync, and a small part of it essentially looks like common mode noise, and is therefore attenuated by the ferrites. And there are also single ended lines in the cable. FWIW in a HDMI cable, unlike a Cat 5/5e/6 cable, the individual TMDS pairs are shielded, and the whole cable is shielded. So, noise should be less of a problem with HDMI cables than with a media adapter using Cat 5/5e/6. Using shielded cable with media adapters is problematic because most of them are not designed to ground shielded cable.
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