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I need about a 9ft. HDMI cable to go from my HDDVD player to my HDTV. I notice that places like monoprice.com have different gauges of HDMI cable. They have 28, 26 and 22 gauge. I know for a longer run, a larger gauge matters. Can I get the cheapest 28 gauge and be okay for a run under 10ft.? Would getting a larger gauge make any difference?
 

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Quote:
Originally Posted by mediahound /forum/post/0


Can I get the cheapest 28 gauge and be okay for a run under 10ft.?


Would getting a larger gauge make any difference?
Yes.


No.
 

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The HDMI specification puts minimum requirements in place for any HDMI connector and cable, no matter what material they are made with (including what gauge of wire). We designed the HDMI spec so that any cable that meets the specification will be able to reliably transmit the HDMI signal between compliant devices. In addition, there are size requirement on the overmold of the plug so that cables always be inserted into devices which have multiple HDMI connectors stacked next to each other. Beware of non-compliant cables with large overmolds (the part of the cable that you grab to push it in or pull it out)- we have seen some that create interference such that you can not put 2 cables into the TV. We are certainly doing our best to monitor to market and get such non-compliant devices out of the market.


That said, I have been told by electrical engineers that a wire with thicker gauge should impart less attenuation to the HDMI signal compared to a thinner gauge, so the message from cable makers is that a thicker gauge allows you to make a compliant cable that is a longer length. But again:

1) HDMI requires all cables to meet a minimum requirement for attenuation (thus, a cable is either compliant or it's not)

2) the quality of the HDMI receiver chip will have a significant impact on the ability to recover an attenuated signal. Receiver chips with equalizers have been shown by manufacturers to be able to fully recover a signal that is attenuated even more than the HDMI spec allows.
 

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The thicker gauge cables are most useful for when you are using a switch or a splitter without a repeater and you need to compensate for the total length needing to support the signal.


PS remember smaller number guages are thicker wires
 

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Quote:
Originally Posted by HDMI_Org /forum/post/0


That said, I have been told by electrical engineers that a wire with thicker gauge should impart less attenuation to the HDMI signal compared to a thinner gauge, so the message from cable makers is that a thicker gauge allows you to make a compliant cable that is a longer length. But again:

1) HDMI requires all cables to meet a minimum requirement for attenuation (thus, a cable is either compliant or it's not)

2) the quality of the HDMI receiver chip will have a significant impact on the ability to recover an attenuated signal. Receiver chips with equalizers have been shown by manufacturers to be able to fully recover a signal that is attenuated even more than the HDMI spec allows.
You should ask your engineers about the downside of larger wires which is very critical in high speed (high frequency) digital signalling, i.e. capaticance. Yes attenuation decreases as the gauge increases but capacitance increases with gauge.


Why is that a big deal??


Because a higher capacitance means that the signal will not transition sharply from a low to high state or visa-versa as sharply, i.e. your signal goes from...
Code:
Code:
__    ____
__|  |__|    |____           to..

   __    ____
__/  \\__/    \\____
it is no longer the same signal.


The eye chart shows this as a squeezing from the left and right sides, where attenuation issues bring the top and bottom closer together.
Code:
Code:
________                  ___
  /        \\                /   \\             ________
 /          \\              /     \\           /        \\
 \\          /              \\     /           \\________/
  \\________/                \\___/


    Normal               Capaticance         Attenuation
 

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Actually capacitance is not the issue with TMDS signals through HDMI cables. If you study the telegraphers equations related to transmission lines the RC effect of a cable only is relevant at low frequencies - sub MHz. And the cable looks like a lumped element generally. Once you get up high enough in frequency the dominant effect is an LC, or travelling waves. The loss is due to skin effect, i.e. the signals at high frequency ride on a thinner and thinner layer of conductor as frequency increases essentially making the cable seem more resistive.


The skin effect loss in long HDMI cables is the dominant force that closes the eye diagram. Skin effect loss is directly related to the gauge of the wire. The larger the gauge the less the loss. Dielectric absorbtion also could contribute but that doesn't kick in until even higher frequencies than we have to worry about with HDMI. Also, the loss tangent of the insulation material in cables is pretty low.


The skin-effect loss starts to kick in once you are up in the MHz range. The loss increases relative to the square root of frequency. This is the dominant force for closing the eye diagram. But note that it not only slows the edges but also closes the eye in the vertical dimension as well. So you can end up with a very small eye opening (or none at all) at the end of a long cable.


But making a large gauge cable has its own issues - thick, heavy, lots of copper, stiff, and expensive.
 

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Quote:
Originally Posted by FiberOpticDude /forum/post/0


The skin-effect loss starts to kick in once you are up in the MHz range. The loss increases relative to the square root of frequency. This is the dominant force for closing the eye diagram. But note that it not only slows the edges but also closes the eye in the vertical dimension as well. So you can end up with a very small eye opening (or none at all) at the end of a long cable.


But making a large gauge cable has its own issues - thick, heavy, lots of copper, stiff, and expensive.

Correct me if I am wrong but HDMI
 

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HDMI 1.2 actually works up to 1.65Gbps. The 165MHz is the pixel frequency. There are 10bits/pixel (using the standard 24bit color - 8 bits per RGB lane, then TMDS coding that adds 2 more bits per lane). Note that the minimum 20% to 80% transition time for HDMI 1.2 is 75 picoseconds. So even HDMI 1.2 can contain some very high frequency energy.


So the characteristic impedance (Z0) of a transmission line is the square root of (L/C). Using a large gauge only increases the capacitance minutely. Capacitance is related to the closeness of the two wires, the dielectric constant of the material between the wires, and the amount of surface area where the electric field developes. Increasing the gauge only increases the surface area component, and increases capacitance. But note that increasing the gauge decreases inductance. Inductance relates to the area between the wires, the dielectric, and the current density flowing down the wires. When gauge is increased, the inductance would decrease as long as the spacing between the wires was kept the same. So to keep the characteristic impedance the same (100ohms differential for HDMI TMDS pairs) the spacing would need to increase (to reduce capacitance). since inductance would decrease with the larger gauge.


So for the 10 gauge example. You could run high frequency signals down a 10 gauge cable if the geometry creates a matched impedance. This of course would require a large amount of dielectric material. Speaking of this situation. Imagine the transmission lines that run to television antennas. These are huge gauge "cables" that carry thousands of watts to the antennas. Check out:
http://www.dielectric.com/broadcast/...s/FLEXLine.pdf

These are very large - not sure the fit on the gauge scale - cables that operate with low loss up to nearly the GHz range.
 

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What gets more exciting is that HDMI uses TMDS, and multiple balanced pairs of wire, so the simple manchester coding shown in the original explanation is nowhere near the truth for HDMI. The "MHz" really is the bandwidth of the cable; however, HDMI uses several of these cables, and also uses a lot of the frequencies under the ceiling to cram the most information across the least amount of bandwidth.


As an interesting aside, HDMI can't send signals with frequencies less than 25 MHz (this is likely to avoid capacitance issues), so really low-quality signals (like 480i) have to have their bandwidth usage raised to fit the cables!
 

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Quote:
Originally Posted by vantagesc /forum/post/0


Sounds like for really short runs, like 3ft - 6ft, it doesn't really matter. 26 guage will be fine?

See my response posted three months ago!
 

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What about 28 gauge. I am in a house temporarily till it sells so I want to set my equipment up temporarily with 3-6 ft HDMI for the time being on the cheap till I move, so for such short runs, what I read here tells me I can get away with the 28 gauge correct?
 

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Quote:
Originally Posted by smakovits /forum/post/11916649


so for such short runs, what I read here tells me I can get away with the 28 gauge correct?

Certainly!
 
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