RGBHV over shielded Cat 5 success! - Page 7 - AVS Forum

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Digital Hi-End Projectors - $3,000+ USD MSRP

J.F's Avatar J.F
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I have a progresive scan DVD player with BNC output, so making a BNC to CAT5 conection is what I need, but I am a little lost here. How to connect the ground? Where to put the H/V connections? I read the whole thread above, but didn't really find a definitive answer.

Did anyone do that and get a better results as with plain VGA cable, I have 30ft run of VGA cable which is connected to a DVD player with 2ft VGA to BNC 'adapter'.

Any help appreciated
Chuck_McDevitt's Avatar Chuck_McDevitt
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Just some comments:

If you are sending regular composite video or s-video,
it should work fine to use unsheilded cable (even for hundreds of feet).

For RGBHV, unshielded has a problem: There is one too few twisted pairs to send 5 signals properly. People using shielded cable are using the shield as the return for H and V, and using one of the twisted pairs as if it was two separate lines to send H and V (suboptimal, but it works).

If you try to use unshielded, or use shielded with the shield improperly connected, it might cause severe ghosting.
You can generally get rid of most of this if both the sending side and recieving side equipment has a grounded (three pin) power plug, and you have both plugged in to a common electrical circuit.

Another approach to using unshielded cable would be to run TWO
cat 5e cables, so that you can have a full twisted pair for H and V each (as well as the other signals RGB).
gireesh's Avatar gireesh
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If you look at VGA specs, sync signals do share the same return. Therefore, using nine conductors, including the shield, you have RGB with thier returns on three twisted pairs and H and V have their own signal lines, but share the same return conductor. I have read somewhere that all the return signals are grounded on the cards, so in theory you could get away with just five conductors and a shield.

Gireesh.
J.F's Avatar J.F
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RGB have each their own pair for ground and signal, but HV are on one twisted pair, is this good to have these two signals twisted together?
Anyone tried if it is better to put RH together keep V wiht R ground or something similar?
Chuck_McDevitt's Avatar Chuck_McDevitt
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Of course it is bad having H and V twisted together....
Twisted pairs are meant for a balanced signal, and if the signals
on the different wires aren't mirror images, you get lots of crosstalk. So H gets a small ghost of V, and V gets a small ghost of H.

But because H and V are only sync signals, this doesn't matter a whole lot unless you try to have a really really long run.
As long as the signal from the crosstalk doesn't exceed sync level,
it shouldn't be visible in any way.



As far as getting away with fewer conductors by sharing the return for R,G and B, this would be a bad idea, exactly for this reason of crosstalk.

For a very very short run, straight through cable (rather than twisted pairs) work for this approach (very cheap VGA cables work this way). But for long runs, you will get crosstalk.
centaur's Avatar centaur
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Mods delete posts, so I do.
cybrvanr's Avatar cybrvanr
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post #187 of 524
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i would like to try this on my Toshiba at home. But one thing's not very clear. A standard piece of cat5 cable only has 4 pairs of conductors, and would work for RGBS, but most video cards put out RGBHV, requiring a 5th pair of conductors.

Are you guys just connecting your systems up with RGBS, using the horizontal connection only, are you using more than 1 piece of wire to deliver RGBHV to the projector, or did you find a supplier of 5-pair cat-5 cable?
MrWigggles's Avatar MrWigggles
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Quote:


Originally posted by centaur
Right.

Ideally H & V would each be twisted with their own returns, but this is overkill. Common ground/shield is fine, twisted with these.

I will make this, and also will attach shield to only one end, to eliminate ground loop. Also will solder shield to connector shell, (hence the hood) for further shielding. (Less heat than it seems)

The point some make about the -'s & ground being commoned internal to the VGA card or display is true on many cards, but I'll connect private returns for the colors in anticipation of higher-quality cards.

Thanks Thumper & MrWigggles. I never would have dreamed the impedance of SCat5 would be close enough. What I think is happening here is the long runs you are using are reducing the effective impedance to the correct amount. Still though, I am surprised.

I'll let you know how it works with my Marantz VP12s1 on HD. Right now I have a 25' shielded VGA cable, and have one level of ringing (faint), only on black text with white bg.

The term ground loop is very poorly understood. Having two ground conductors doesn't make a ground loop. Ground loops cause problems when power ground current goes through signal lines.

The grounding mentioned in this design idea is all common. The R-, G-, B-, H-, V- etc. are all the same signal which is ground or GND. Length has nothing to do with lowering characteristic impedance, Z, of a cable. Having additional conductors, in this case the shield, in close proximity is what lowers the characteristic impedance.

Also, please bear in mind this Cat 5 technique is generally meant for cables that use HD-15 connectors on one or both ends. If you have a component output and a component input, I would recommend miniature bundled coax over what I have described here in a heart beat. Belden makes some good cable as well as others.

-Mr. Wigggles
centaur's Avatar centaur
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Chuck_McDevitt's Avatar Chuck_McDevitt
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There is both shielded and unshielded Cat-5e,
and both shielded and unshielded Cat-5.

Shielded Cat 5-e is a specially item, not likely to be carried
in a local store, but you can get it from Belden.
Chuck_McDevitt's Avatar Chuck_McDevitt
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Oh, and as far as Cat 5e (or Cat 6) being a sham... They are not.

For balanced signals, the more twists per foot, the less loss to radiation and higher bandwidth.

Cat 5e can handle 350mhz balanced with no problem.

Cat 6 can handle 350 mhz balanced with so little signal
getting lost to radiation that it can meet FCC class "B",
just as good as a coax.

But in this application, you AREN"T sending balanced,
and aren't sending anything near that bandwidth.

Due to the unbalanced signal, I'm not sure if shielded CAT 5e
would work better or worse than shielded CAT 5. Probably
better, but it would require testing.
audiman's Avatar audiman
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I didnt see if someone ran a test between a VGA 30 feet run, and a cat5 30 feet run.

Is the cat5 supposed to be better ?

Anyone tried it with a crt pj ?

Thx
centaur's Avatar centaur
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audiman's Avatar audiman
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Was your cat5 shielded ?
centaur's Avatar centaur
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gireesh's Avatar gireesh
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I am sorry that your experiments with Cat5e and Cat6 were disappointing. I was going to make some cables myself, specifically to easily switch between different sources.

Can you clarify a couple of things...

What resolution are you running ? 1080i or 540p from DTC100 ?

When using with the PC, what resolution were you using and what refresh rate ?

I understand your projector does native 1280x720.

Gireesh.
JeffDM's Avatar JeffDM
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I am using General Cable's Command Linx Cat 5e cable from Home Depot, maybe 50ft of it, with Radio Shack connectors, but for 480i and 480p signal. In some cases I do see faint ghosting.

I guess in some cases such as SXGA resolution, that it's simply too much to ask of twisted pair not intended for this use, it might be better to get five coaxes and bundle them together or just buy a premade long cable.
centaur's Avatar centaur
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Speedy's Avatar Speedy
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Quote:


Originally posted by Swampfox
Mr. Wiggles,
You may be an excellent engineer, but you are not a marketing executive. What the videophile community wants is a cable that "increases the realism and color saturation, rendering an image that exceeds the original source, causing the viewer to be immersed in a three dimensional pan-reality!"

@Swampfox

Do you know what your saying? An image can get as good as the weakest point of your equipment. By eliminating the weakest point will truly improve image quality. But then again you my have your weakest point somewhere else.

Fact is, a videophile as for audiophiles want to have their playback as close to the original as possible. You will achieve best image quality by calibrating your system using an Avia video calibration dvd.

If your source is bad, though luck.

There are methods to give you the impression that the image is better by screwing up calibrated systems. That is what all showrooms do for TV display's. But this is out of topic.
QQQ's Avatar QQQ
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Speedy:

I hate to break this to you but I think Swampfox was making a harmless joke. As far as your comment that Swampfox may have his weakest point someplace else, I think you may have your weak point someplace else if you didn't get the joke.
Speedy's Avatar Speedy
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@ QQQ and Swampfox

OK, I missed the joke and apologize for my mistake. Shame on me I read it again and got it right this time.

Everybody has some weak point
JP's Avatar JP
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I just got some shielded cat5e and tore away the rubber insulation to see what I had to work with. Here are a few questions I have if anyone has the knowledge to help:

1. are you guys using wire strippers to tear away the insulation of each individual strand? My wire strippers only go to 20 gauge and this isn't small enough to strip away the insulation on these tiny cat5e cables. Are you guys using a different process where wire strippers are not needed? I tried using an exacto knife but the wire is solid core and the pressure I need to strip away the insulation causes the knife to go completely through the wire.

2. Thumper mentioned early on in this post that he has done quite a few of these and he says for a performance increase go ahead and tie all the grounds together as well as the shield and the ground wire. I assume this one ground would be designated on just one pin of the hd15 plug. Is the consensus that this is worth the effort? I would think it would actually be easier to go through only one solder connection rather than 4 but I haven't gotten my hd15 plug yet so I might be wrong. Any thoughts on this are greatly appreciated.
QQQ's Avatar QQQ
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Speedy:

No problem.

Thanks
JasG's Avatar JasG
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Quote:


Originally posted by JP
...are you guys using wire strippers to tear away the insulation of each individual strand?

I think I used my fingernails - I might have nicked it slightly to make it easier to strip.
lewis's Avatar lewis
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I too would like to know the answer to that question. If the grounds are grouped together where are they soldered, to one particular pin or to the actual casing of the HD-15 connector.

Also should the metal foil be completely striped back or soldered to something?

Thanks
Lewis
J.F's Avatar J.F
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I made a cable with shielded cat5e length 10 meters, and the result was not only very dissapointing but completely horrific. 7 or 8 ghost images at 800x600 resolutin and 60Hz refresh. Usless, I connected all grounds and shield wire and everything as described, but the result was as above.

It seems that the length was too long or cable type was wrong or this method just plain sucks for my application.

So 'your milage my vary' .... I junked it immediately afterwards and am now using my old vga cable, bought at computer store, real cheap, 10m long, with only one very slight almost invisibly light 'ghost' only seen with computer desktop not on any kind of video.
MrWigggles's Avatar MrWigggles
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I am really suprised with some of the results posted.

I am still using the my shielded cat 5 cable as I type this message. Maybe I am lucky with the cable I bought at Fry's I really don't know what to say.

The benefits for this cable design are listed early on in the thread. The image quality that I have currently doesn't surpass the finest cables in the world but does equal it in my situation.

Anyway, it is a cheap alternative for the enthusiast out there who want to give it a shot.

But as just mentioned, aparantly your millage may vary.

-Mr. Wigggles
jaymer's Avatar jaymer
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I'm puzzled by all this as well, and esp. all the deleted posts... don't know whats going on, but...

I found a local supply of cat5 back in October and made myself a cable per MrWiggles fine instructions. Since then I've enjoyed my LT150 via 35ft of DIY cable - no probs or regrets. This works as many have stated early on in the thread. My cable has 2 male db-15s on each end and connects my video card directly into the RGB input on the LT150.
centaur's Avatar centaur
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I am quite sure I've found the answer, but am no longer contributing here due to Mods' propensity to stifle free speech.
tahustvedt's Avatar tahustvedt
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I ordered some shielded Cat-5 a week ago. It arrived today but it was not shielded. They even put a sticker on the bag saying "shielded Cat-5e". They obviously think the "enhanced" stands for shielded.

I'm glad the cable is so cheap. I'll have to order some more, but I'm ordering from somewhere else now.

I hate it when this happends!!!!! Everything I buy has to malfunction in one way or another. I tend to expect a fault now with everything I buy.

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