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a/v cables for component video???


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8 replies to this topic

#1 of 9 OFFLINE   Bob Kavanaugh

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Posted May 24 2003 - 04:31 PM

Alright, please help me to help out my friend. He has a Toshiba 34HF81 and a Toshiba progressive scan dvd player. The thing is, he has his component video hooked up with old monster a/v cables ( you know L audio R audio and composite video in one cord). Sure, it works, but I think it is tragic to hook up a 2500 dollar digital tv's video with some audio cables. Maybe I am crossing the line, by offering advice that is not asked for, and he tells me he is pleased with the video quality. I've offered to set up a double-blind test with my component cables, and he is not interested... yet. I think that if I come up with a good reason(s) for him to get real cables he'll do it. So... what would be the reason YOU would not use a/v cables for component video ,or would you, and I am the one who is wrong here? Thanks.

#2 of 9 OFFLINE   MikeShea

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Posted May 24 2003 - 05:40 PM

If they're decent quality monster audio cables, they are probably fine. I've seen some relativly inexpensive Monster component cables for the $40 pricetag. You can always pay more but I doubt if you can ever justify the cost.
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#3 of 9 OFFLINE   Inspector Hammer!

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Posted May 24 2003 - 11:54 PM

Bob,

this "friend" is you isn't it? Come on, you can admit it. I'm kidding. Posted Image

To be quite honest Bob, I would NEVER use those types of cables for progressive scan or componant video and I would advise anyone who has progressive and componant video capability to go and pick up a set of real componant cables that are designed to carry that particular signal.

Your friend may be getting signal degradation by using those types of cables for componant, in fact I can almost guarentee he is. If you were to test those cables using the resolution patteren on the AVIA calibration dvd, he's probably got video noise like mad with those cables, and that noise is present in his picture all the time. It's not hard to upgrade to the real cables and his picture quality would probably be better once or if he does so.

But, RCA A/V cables used as componant cables, nope. You could always pick up a set for him and have him pay you back, just a friendly suggestion. Posted Image Either way, try as hard as you can to steer him from the cables he's currently using.

His equipment is only as good as the cables used to connect them, if he's got good equipment, he's shortchanging it's performance by skimping.

Good luck. Posted Image
"That's Jack Bauer!!!!!! He's coming for me!!!!!" - Charles Logan

#4 of 9 OFFLINE   Allan Jayne

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Posted May 25 2003 - 12:21 AM

If you pick up a set of audio cables regardless of price and use them for video, you will get a picture, but the quality is unpredictable. The longer the cable, the more likely you will see degradation.

If you were lucky, the audio cable might actually be video grade, for example if during manufacture they made all three cables in the set from the same spool of wire for manufacturing simplicity.

If your friend never complains about the picture, leave him alone. But if he ever tries calibrate or run a test pattern, let him know that all bets are off unless he upgrades the cables. Even what looks like misconvergence can be blamed on the cables as chroma delay and he could waste money on a service call there.

Video hints:
http://members.aol.c...ynejr/video.htm
.

#5 of 9 OFFLINE   Bob McElfresh

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Posted May 25 2003 - 01:16 AM

You could try telling him these facts: - Video cables should be made with 75 ohm coax. - Audio cables can be made with any of the popular impedences: 50, 75, 110, 300 ohms (Sometimes the L/R/Video bundles were all made with 75 ohm coax - this might be why your friend is getting away with it.) While you CAN use component cables for progressive/HD, the 3 video formats have different maximum frequency: Component Video: 4 Mhz Progressive Video: 13 Mhz 1080 HD Video: 35 Mhz So for HD, you really want cables designed for HD, not just component. If you do get some different cables and try a comparison, DONT just fire up a DVD and look for differences. It's hard to notice/remember the fine details on moving pictures. Get a copy of Avia (the setup DVD) and pick some of the static, fine-focus or contrast test patterns. Do the A/B comparison with one of these patterns frozen on the screen.

#6 of 9 OFFLINE   Bob Kavanaugh

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Posted May 25 2003 - 12:48 PM

Thanks guys. No, this friend isn't me Posted Image .

We each have the Avia calibration disc, so i'll see if he's up to doing a heads up comparison. Sounds like that might work.

Thanks!

#7 of 9 OFFLINE   ChristW

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Posted May 26 2003 - 11:55 AM

So how does this differ from using RG6 cable and attaching the correct connector to each end? I've read in numerous places that this works fine and am thinking about doing it in my theater (which just began construction this past weekend!) CW

#8 of 9 OFFLINE   Bob McElfresh

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Posted May 26 2003 - 12:49 PM

[quote] So how does this differ from using RG6 cable ... [quote]
I assume you are talking about CATV grade RG6? The often-recommended Belden/Canare cables from the custom sites almost all use RG6 form-factor.

But just being "RG6" does not tell you the coax is built for video frequencies.

Here is how engineers pick coax for an application:

- Determine the maximum frequency signal you will send. For this example, let's pick 35 Mhz for 1080 video.

- Multiply the max frequency by 2 and 4 to give you an acceptible range. For our example, this would be 70 - 140 Mhz.

- Now look at the specs on the Belden or Canare web site and select a coax that has less than 3 db drop over 100 feet of coax.

Belden gives tables of numbers, but Canare has a nice chart:

Posted Image

Look at the horizontal line that indicates 3db of "attenuation" (attenuation = reduction)

The V-5CFB hits the 3db line at around 250 Mhz. - This coax would work well for 1080 video.

The V-4CFB and V-3CFB both hit the 3db line at about 150 Mhz. The V-4 would be a better choice as it hits a bit higher.

CATV Coax - Before you just go down and buy RG6 coax from the local store, remember that CATV signals only go to about .. 1 Mhz. Component video goes up to 4 Mhz, let alone Progressive or 1080. See the roll-off in the Canare graph? The hardware-store RG6 coax will look much worse than this in the 1-35 Mhz range.

Yet, it will APPEAR to work. There will be a loss of focus because the higher-frequency signals are rolled off, but you will "see" video. This is why the rumor that any-old RG6 coax will work came about.

Note: People will say that some CATV coax is rated to the GigHz range for Sat/cable modems. But these signals are DIGITAL so they are a lot more robust/forgiving of the cable. Dont buy coax rated for 1.1 Ghz digital and then assume it works for 35 Mhz analog. Read the fine print.

The other issue: the RCA connector.

Think of the RCA plug as a "speed-bump". You really want to get a RCA plug that as closely matches the 75 ohm impedence of the coax. While it's impossible to exactly match this, some RCA plugs like the Canare plugs come darn close.

The generic RCA plugs from Radio Shack - could be 30 ohms, 50 ohms, 90 ohms... etc. Audio is NOT sensitive to the impedence like video. Try to find RCA plugs with impedence ratings, or any verbage like "Component Video" or "HD Video" compatible.

The Price: See the Canare graph? See the really good V-5CFB coax? How much WOULD you pay?

$5.00 /ft

$4.00 /ft


But wait. If you call now, you can buy this 3-conductor, HD Grade RG6 coax for:

$1.52/ft

This is what production studios/broadcast stations pay.

(Yes, they have to buy spools of 300 feet at a time.)

If you have long runs, contact the custom web sites. They will likely charge you more than the bulk price (because there is storing, cutting, measuring, handling involved), but you WANT them to put the good Canare RCA plugs on the ends (the tools cost about $300 to do it right).

A cable made with this stuff will rival/beat the Monster CX-300 component cable set that sells for $220 for 6 feet.

#9 of 9 OFFLINE   DaveWUSAF

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Posted May 29 2003 - 12:03 PM

Cable TV frequencies go alot higher than just 1 Mhz. Ch 2 starts at about 54 Mhz and the upper channels on a small system are between 450 and 650 Mhz. RG-59 handles it fine on shorter runs but I agree that RG-6 would be the better choice for use in a home theater setting. I would imagine that you would loose less than 1/4 db from the lowest freqs to the highest (1 to 30 Mhz)in a pair under 6 ft long.




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