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Discussion Starter · #1 ·
I read with interest the thread that described using cat5 cable for vga. I plan to make up the cable described.


I was wondering if I could also use cat5 cable for vga, component video, svideo & composite as well? If yes then do you know what should be pared with what when I build the cable?


Also, if I try to locate a cable similar to cat5 but with more wire pairs, can I then make one cable to run to the Projector that will then let me remotely connect to any of the inputs? Would this cause interference if they were all in the same sheath? Are all the grounds common or should they be isolated?



I know I'm asking a lot of questions here but with the collective knowledge of the group I'm sure this will be a worthwhile thread.


Thanks in advance
 

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So it seems we have 2 things here. One is the type of cable. The second is the connectors on the ends.


The number of wires running through a CAT5 cable is 8. But you only get 4 usable because the other 4 are wrapped around each of the other 4 as shielding. (Hence the name "twisted pair".) I think you'd see a lot of interference if you tried to use all 8. You typically see "2-pair" used for telephones, and "4-pair" used for computers. I did a quick search and didn't find any 5-pair or 6-pair cables available.


Category-5 (aka "CAT5") is basically a quality rating. CAT3 is good for 10mbit networks but not 100mbit. CAT5 is good for 100 and 200mbit speeds. And now there's a "CAT5e" and "CAT6" which you would use for gigabit ethernet. Since it's good at higher speeds, it should provide a cleaner signal. Noticeably cleaner? I have no idea.


There's another classification for these cables: UTP and STP. UTP means "unshielded twisted pair" and will be practically any CAT5 cable you buy. However you can specify you want "STP" (SHIELDED twisted pair) which has an insulation layer around all the pairs. This would be a good option as it's very little extra cost, and would help the cable be resistant to things like running too near some electrical wiring. Notice I said resistant, not impervious.


The connectors on the ends are "RJ" ("registered jack") connectors. RJ-11 and RJ-12 are for telephone. RJ-45 for computers. You can chop the RJ-45 connector off the ends and wire them up however you like. But it can be tricky. The wires are tiny. You can put a lot of work into splicing CAT6 STP cable to be what you want, only to have an UNshielded connector on the end that picks up RF from the projector's power supply.


Now after all that babbling, do I have an answer to your original question? I'm going to take a shot and say NO you cannot run all the signals through one CAT5 cable. But you might can do it with 3 cables.


Another alternative is to draw out exactly what you want and ask about having it special-made. There are a couple companies out there (Cables-To-Go comes to mind) that will make whatever you want. (Something like 4 CAT5e cables wrapped in shrink-wrap tubing, 20 feet long, with VGA/SVID/RCA connectors on each end?) However I don't think you can get a refund on special-made cables so it could turn into a $100 gamble.


For a $15 trip to RSHACK you can get some connectors and a crimper and always do an experiment.
 

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Discussion Starter · #3 ·
Thanks for your very through description of Cat5 cabling. But there is another thread that describes the wiring cat5 cable for vga with excellent results. Just do a search here at avs and you'll find the thread.


Thanks again
 

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Quote:
Originally posted by jcase
Thanks for your very through description of Cat5 cabling. But there is another thread that describes the wiring cat5 cable for vga with excellent results. Just do a search here at avs and you'll find the thread.


Thanks again
Didn't that thread have warnings from several members that CAT5 cable is not suitable for unbalanced video transmission. I know on at least one of those threads I went into this.


I'll say it again as an EE and a 20 year career designing broadcast facilities. IT'S NOT THE PROPER CABLE FOR VIDEO. The impedance is wrong. Unbalanced video requires 75ohms, CAT5 is 110. The construction is wrong.

Unbalanced video needs a coaxial cable. CAT5 is twisted pair. In addition running RGBHV over these pairs will result in substantial crosstalk. Now that doesn't happen (at least not very much) on balaned signals over twisted pairs. Large analog telephone cables have thousands of pairs and yet very little crosstalk.


BUT, you are proposing to send unbalanced video over twisted pairs. No in-phase cancellation can take place, therefore induced voltages tend to add and hence produce crosstalk.


If you want great pictures, do what the pros do. Use coaxial cables designed for the signal impedance which in this case is 75ohms. It you want distorted pictures that look good only because some ill-informed AV magazine editor says so, try the CAT5.
 

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Glimmie,


What kind of defects/artifacts should one see if they are using cat5?


I am currently using a ~25’ cable (including a shielded coupler in the path) without any major complaints (at least compared to regular 3ft vga cable), but would be interested to understand how my picture would improve if I *upgraded*.


Btw, can a cable have an impedance of 75 ohms if it has an HD-15 connector on the end?


Thanks for the info,

jeff
 

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Quote:
Originally posted by Glimmie



Didn't that thread have warnings from several members that CAT5 cable is not suitable for unbalanced video transmission. I know on at least one of those threads I went into this.


I'll say it again as an EE and a 20 year career designing broadcast facilities. IT'S NOT THE PROPER CABLE FOR VIDEO. The impedance is wrong. Unbalanced video requires 75ohms, CAT5 is 110. The construction is wrong.

Unbalanced video needs a coaxial cable. CAT5 is twisted pair. In addition running RGBHV over these pairs will result in substantial crosstalk. Now that doesn't happen (at least not very much) on balaned signals over twisted pairs. Large analog telephone cables have thousands of pairs and yet very little crosstalk.


BUT, you are proposing to send unbalanced video over twisted pairs. No in-phase cancellation can take place, therefore induced voltages tend to add and hence produce crosstalk.


If you want great pictures, do what the pros do. Use coaxial cables designed for the signal impedance which in this case is 75ohms. It you want distorted pictures that look good only because some ill-informed AV magazine editor says so, try the CAT5.
Why did someone have to start a new thread about this?


If the old thread had been continued Glimmie would know that Thumper has installed PLENTY of systems with shielded CAT5 as the distribution method PROFESSIONALLY without fail without baluns. This also means no expensive distribution amplifiers and no $$$ plenum coax cables (that's the real killer for his situation).


Yes, cat5 is between 100-120 ohms but in the case of Shielded Twisted Pair, if the shield is used as an additional ground the cable impedance is lowered. How much? I don't know for certain. When the cable is very long I will see some very slight ghosting on a projector but no detectable crosstalk.


Now has this technique worked for everyone, the answer is "NO". Is this necessary for everyone the answer is "NO". All caveats are mentioned in the original thread. It has worked for plenty of people like Jeff J, but there are either brands of STP that don't work well, people who aren't soldering correctly. or people who can't tell between UTP and STP (seriously).


Please post comments in the other thread.


-Mr. Wigggles
 

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Just got the balun and tested with a 500ft spool of cat5 (not cat5e).

The picture was great, just a little softer than a 5ft cable, not bad for 100 times the distance and no active components!
 

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Don't take this the wrong way, but comparing dual channel 5MHz s-video to three+ channel 30+MHz HD signals is a bit of an apples to oranges comparison.


Thumper install projectors all of the time and the slight softening you are seeing with baluns at 5MHz is unexceptable at 30+MHz. He hasn't found found one that works well with high-def imaging.


Don't get me wrong, 500' of s-video is impressive, but a totally different story.


-Mr. Wigggles
 

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Glimmie is right.


Not only are you straining your in/output circuitry, but video will be affected by standing waves. Standing waves happen when there's an impedance mismatch.


All high-speed transmission lines must have matching impedance in the source, cable, and sink. If it doesn't, waves will not be completely absorbed at the sink, and will bounce back and forth in the line, cancelling new signal, and arriving late.


Higher frequencies will be affected first, giving variously ghosting, blurring, and posterization. PQ will tend to be poor with screens over 96". And you can forget HD.


Do it if you want, but it's ******rigging.
 

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Read everything carefully before commenting.


Also, there are other threads with emperical evidence to the contrary.


Thumpers cat5 signaling is so succesful, that with his help, AMP just created a device made specifically for video over shielded cat 5 with no baluns.


-Mr. Wigggles
 

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I run my video over rusty twisted barb wire, a chain of aluminum foil gum wrappers and some old copper piping. Talk about bandwidth, this is 1/2 inch pipe man, shiet ... that makes rg6 look like drinking straw. And black levels, damn ... crt blacks, hell I have black hole blacks.


:)
 

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Quote:
Originally posted by btmoore
I run my video over rusty twisted barb wire, a chain of aluminum foil gum wrappers and some old copper piping. Talk about bandwidth, this is 1/2 inch pipe man, shiet ... that makes rg6 look like drinking straw. And black levels, damn ... crt blacks, hell I have black hole blacks.


:)
Is the piping schedule 20 or schedule 40?


Don't use the cheap 20 stuff. You'll have ghosting like a mugh'


-Mr. Wigggles
 

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Yeah, and don't skimp with 1/2" connectors...You'll never get the bandwith you will with the 3/4"...and don't get me started about pvc vs. copper...I'll take cast iron any day! Guess I'm old school though...
 

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Mr. Wiggles,


Could you please post note where AMP's device info is located and if not inluded in the reference, what it does? I hope it is a pseudo Extron trype matrix switcher.... :D


Thank you very much


Fury
 

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Srgtfury,


Next week I will post additional info and pictures on the connector assembly and some better screen shots.


This lastest version of the connectors tested just this week are very good. At 50', running 1600x1200, the image is absolutely indescernable when compared to a 6' manufactured RGB cable. We tried it out on Plus, Mitsu and Sanyo projectors (including the XP-21N). I will have the part # hopefully by then and some pix of the assembled products.


BTW, for the EEs out there when the 100 ohm cable was tested in this configuration the cable's impedance on the RGB channels was between 70 & 74 ohms. The H & V channels were higher; around 90 ohms.


Finally, a very low cost, small form factor, easy to assemble connectivity solution for short haul RGB signalling is at hand.


Thumper
 
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