[Oren]

I have an LP530 on order (my first projector!) and now I'm wondering how to run a long s-video cable to it. Right now, my components and the sub are in between the front speakers. But unlike a TV the projector is going to be back behind the viewers--way back. How do you do it? Do you put the components near the projector, and run long wires to the front speakers? Or keep the components near the front and run a long s-video cable to the projector? Does a long (about 30') s-video cable degrade the signal?


[This message has been edited by Oren (edited 09-22-2001).]

 

[JAB]

The preference would be for longer speaker runs and shorter runs to the projector. However, having said that, 30' is not entirely unreasonable for an S-Video run if you use a good cable.


/jab


------------------

a moderator at the TiVo Community Forum

 

[DanHouck]

That's the key. Good, very well shielded cable and the longer it is the better it should be. I'd also look at using component instead of S-video as you'll get a better picture and color, particularly out of a single chip DLP.


Dan

 

[Jon_B]

I'm glad you asked this question. If you had not, I was going to have to some time or another. http://www.avsforum.com/ubb/smile.gif I am looking at using component cables, the price really goes up as you increase the length. So I've been thinking of keeping all of my equipment closer to the projector than the main speakers. IMHO it's much easier to tell the degradation of quality in picture than in sound. Besides, as of right now I don't have that much invested in speaker cables for the main speakers.


Jon

 

[tlum]

Honestly, I moved everything. My 5.1 audio predated my projector by a few years and was set up with the equipment in the front.


The projector went up on the ceiling, and all the equipment moved to the back of the room.


The longer the cable, the more the signal will degrade. Shielding will keep out noise, but, the longer the cable the more it rolls off and the more reflections become a problem. But that is all relative to the equipment which may not be able to resolve in the frequency range where the majority of the degradation occurs.


If your options are open you'd be better of with shorter component video cables and longer speaker cables. But if you're locked into equipment placement, then, using long high quality component cables is the only route. I was considering building my own, but decided to move the equipment in stead. Speaker wire was not an issue since the main front cables were traded with the rear surrounds, all I had to do was purchase a longer cable for the center channel.

 

[Paul_Seng]

Also keep in mind that when using a projector you may want to keep the room as dark as possible. If your DVD player and audio components are next to the screen or wall, it might distract the viewer some. I keep my stuff in a closet (thankfully) so that there are no "cockpit" lights next to the screen. If you have good, quality cable, long runs in a house setting should be OK.

 

[Oren]

Actually, I kind of like the cockpit look. Might as well max out the LPD (lights per dollar).


If I put the stuff in the back, swapping the front & rear speaker wires is a good idea. Of course, then contolling the components is a pain...isn't it funny how people point remotes at the screen instead of the components?

 

[Gary McCoy]

I spent considerable time finding a good grade of copper center conductor, quad-shielded RG-6 cable, and making some little adapters at each end that transition from a pair of F-connectors to S-video connectors at each end, using Radio Shack parts.


The copper inner conductor is critical, because most RG-6 is actually copperplated steel or a stiff copper alloy. At the relatively low frequencies used by video signals, the so-called "skin-effect" penetrates pretty far under the surface of the wire, and if the center conductor is steel, the video signal sees resistive losses. Since I was making a run of almost fifty feet, I wanted to minimize such losses. You could duplicate what I did fairly easily - cut a short S-video cable in half, then reterminate the cut ends with a small plastic box and two barrel (female) F-connectors. Now connect these two "breakout boxes" with a pair of quality RG-6 cables described above. Two RG-6's offer a considerable improvement in picture quality over a standard long S-video cable.


I personally hardly ever use the S-video input, although the wife will simply turn on the S-VHS or cable box and the projector. I prefer the VGA connection and use a HTPC to line double and scale S-video sources - much better picture.


My honest suggestion is to install the projector once, and run cables to the VGA, S-video, and composite video inputs - that gives the most configuration flexibility, and running extra long cables afterwards is a pain. Your particular projector also has a digital input, I have no suggestion to offer on that.


Gary

 

[kstirman]

I would disagree with most on this thread and recommend shorter speaker cable runs, with longer video cable run.


Search for the thread on using shielded Cat5 networking cable for VGA, component, and s-video. It's cheaper than speaker cable, takes up less space, and will not degrade the signal. You can acheive equivalent performance to the $500 video cables for less than 10% of the price.


DVI, I believe, is not suitable for runs greater than 8ft.


Heavy hitters on this forum have weighed in on the use of networking cables for this use, and agree that it is a very, very good idea.


I do agree that running all possible connections at the same time is a very good idea.


Kelly

 

[tlum]

Quote:

...using shielded Cat5 networking cable...

CAT5 STP is a 100 ohm, 50 pf/ft balanced cable. It is not designed for 75 ohm single ended applications.


CAT5 into a 75 ohm connector will reflect 25% of the signal back into the cable, due to the mismatch, which will result in ringing and all kinds of distortion.


CAT5 is designed for balanced application where common mode rejection mostly nullifies crosstalk between pairs, and reduces shielding requirements. Typically, single ended applications would not find CAT5 to be shielded well enough and will have cross talk problems.


CAT5 with the appropriate circuitry to provide loss-less conversion from single ended to balanced mode, and impedance matching, might yield fairly decent long distance transmission capabilities with video.... and with that goes an increase in cost and complexity.


For a quality signal, stick with a properly matched (75 ohm), low capacitance, single-ended coax cable. You don't have to pay an arm and a leg; cable engineered specifically for video applications isn't that expensive. Gepco sells direct to the public, and does sell by the foot. From a recent quote:


RGB250 $ .83/FT.

VS32001 $1.48/FT.

RGBSC260TS $1.39/FT.


Belden, Mohawk-cdt, and many other have similar offerings, but, you usually have to buy in bulk and you usually have to go through distribution.


I am sorry, I'm an electrical engineer, and hearing talk of CAT5 for video applications raises the hair on the back of my neck about the same way as dragging finger nails across a black board... I don't mean to over react.


-Ted-

 

[Ken Blauvelt]

Ted,


Thanks for your comments. However, where were you when we were banging this thread around??? http://www.avsforum.com/ubb/Forum10/HTML/006683.html


I chickened out and built my 55' component cables for HDTV out of clear blue, studio grade, RG6QS Carol cable from Home Depot. The picture is superb! Maybe a little overkill, but with heatshrink tubing over the screw-on connectors they really look nice too.


The lack of shielding for the CAT5/BNC breakouts scared me off. Apparently, folks are having good luck with shielded VGA fittings though. How do you explain that?



------------------

Ken B.

 

[Gary McCoy]

Ted,

I'm an EE as well, and I built and use one of the Cat5e video cables. The trick is, one conductor of the twisted pair, plus the shield itself, are grounded. The effective impedance of the remaining conductor is very close to the ideal 75 ohm impedance. The Cat5e is small in diameter, inexpensive, and available with plenum sheathing.


I haven't made any measurements with test equipment on my cable, but I can see a distinct improvement in video quality using the test patterns on the Avia test DVD, when compared to a conventional bundle of five smaller diameter coaxial cables in a single PVC sheath. I believe the very low dielectric losses and the rigidly controlled and precisely equal length conductors in the cable are responsible for such performance.


I believe the technique is good for runs up to about 50 feet in length - mine is about 48 feet. Beyond fifty feet I would probably use five runs of a good grade of RG-6 with solid copper center conductors (no skin effect at the lower video frequencies, so copper plated center conductors are undesireable).


Gary

 

[tlum]

Quote:

Originally posted by Ken Blauvelt: Apparently, folks are having good luck with shielded VGA fittings though. How do you explain that?

I could only speculate as to the practical results. I should probably also add to my previous post that I am speaking from a purely theoretical perspective. I have not actually attempted to physically implement such a cable and am not in a position to offer more than a theoretical opinion.


I have, however, just come across a document entitled "Video and UTP", originally presented before the SMPTE Advanced Imaging Conference in Washington in February of 1996. Looks like that has been addressed previously...
http://bwcecom.belden.com/college/Techpprs/tpvutp85.htm


-Ted-



[This message has been edited by tlum (edited 09-26-2001).]

 

[Gary McCoy]

Interesting paper - after reading it I see some topics we may wish to investigate further.


There appears to be no exact Belden equivalent documented that corresponds to the shielded twisted pair (STP) we are using, they are documenting UTP or unshielded cables which are far more commonly used. However, the UTP "Media Twist" has a similar specified bandwidth in balanced mode to the STP we have been using. (Not that that matters a whole bunch when your signal is RGB video at up to HDTV resolutions.)


In any case as I mentioned before, we are not using the cable in balanced mode, we are using it unbalanced with one conductor of each twisted pair plus the shield grounded to lower the impedance. Thus we can't really directly use any of the measured data.


However, if we were to apply the baluns mentioned to each end of the STP cable, we may simultaneously be able to acheive the superior noise rejection of shielded cable with the extended range of balanced twisted pair operation. A further advantage of this technique would be that we should be able to acheive an exact 75-ohm impedance match at each end of the cable, not the approximate match we have in unbalanced mode. Finally, with two baluns per twisted pair, we will have interconnected the equipment with no direct ground connection between projector and video source, and no possibility of ground loop interference.


I know some of you are professional cable installers, have you used STP in balanced mode? Are there particular brands and models of baluns most suited to HD video transmission over ranges greater than the 50 feet or so we have acheived in unbalanced operation?


Gary


[This message has been edited by Gary McCoy (edited 09-27-2001).]