[btmoore]

I have 2 HDTV displays, a front projector in the HT room and a direct view CRT in the family room. I am considering centralizing the HD STB to feed both displays. I currently run an ~35 ft run from the component switch to the projector over 3 rg6 cables. Does anyone know what the distance limitation are (while still maintaing quality) for component HD video over a copper core rg/6 cable?


Regards,


Brian

 

[RobertCooper]

btmoore,


This is a bit of an "educated guess", but hope it helps....


The cable companies run hundreds and hundreds of feet of RG-59 and RG6, and their signal is at a much higher frequency. If I recall... each signal of a component run is maxed out at 6 MHz (usually the bandwidth limitation of the DVD players). Therefore, it is my conclusion that 35 feed of component run will be no problem. Why else do I conclude this....?


I run about 35 feet of component to my projector from my DVD. Also, I run 3-foot RCA's to the wall jack. In the wall is the 35 feet of RG6 for each of Y, Rg, and Rb, and then to another wall jack... and another 3-foot of RCA (radioshacks gold jobs)... and I see very few easily noticable artifacts with the run when compared to just hooking my DVD player right to the projector with one 3-foot run of RCA's. I think my problem is that I'm changing types of cables twice, with non 50-ohm interfaces between the cables. If contemplated just pulling the RG6 a few feet out of the wall and terminating it with RCA's. It won't look as pretty, but I won't change cable medium so many times.


I think you'll be fine and completely happy with RG6, esp. if that's the ONLY wire you're signal will be traveling over. May I recoomend getting double-shielded RG6... just for extra goodness. It is only a few cents more per foot.


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-Rob Cooper


[This message has been edited by RobertCooper (edited 08-21-2001).]

 

[work permit]

RG6 cable will still have a -3db bandwidth of 200MHZ at 100'. Shielding is probably a greater factor than bandwidth at long distances.


Off the top of my head, I would think that if you run a few hundred feet of this stuff, the relative delay between the three cables could create some problem. Even if the physical length of the cable is the same, loose tolerances could create a difference in electrical length.


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Alex


[This message has been edited by work permit (edited 08-21-2001).]

 

[Glimmie]

The CATV analogy makes sense but there is a difference between baseband video and an RF signal. With RF, as long as the receiver can recover the loss, the signal can attenuate.


But as baseband video attenuates, detail is lost. In your application up to 100 feet of RG6 is not a problem. As far as length between the three cables, within two inches is fine.

 

[Ken H]

Yes, even for higher bandwidth computer RGB signals, 100' is usually fine. I suppose the Canare cable helps too, but a good RG6 should work for HDTV at that distance.


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"Better living thru modern, expensive electronics devices"

tm

 

[thomasb]

For 1080i, Component video pixel rate is 1080*1920*30 =

62 million pixels/sec. The signal in the cables is analog, so you need a bandwidth of at least 5*60 = 300 MHz to pass the

signal accurately. This is high enough that the slower rolloff of RG6 compared to RG59 is preferable for runs over 30-50 ft.


At the speed of light the "length" of each pixel is about 300/60 = 5 meters = 16 feet. The dielectric in the cable slows things down, shortening the "length" to about 12 feet. Slight variations in length between the 3 cables would therefore not be significant. However, major discontinuities, such as wall jacks or changes in cable impedance, separated from either end by more than a few feet, might cause noticeable reflections (ghosts). Transitions between RG6 and

RG59 should not matter, since both have 75 ohm impedances.

F-type video jacks have much better impedance match than RCA jacks.


With good RG6 cable and good connections, you should be able to run at least 150 feet with only a slight softening of the picture.