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Joining component cables

Discussion in 'Accessories, Cables, and Remotes' started by Cameron Yee, Dec 17, 2003.

  1. Cameron Yee

    Cameron Yee Executive Producer
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    Would there be any issues with my joining two sets of component cables with RCA couplers (female-female adapter)? Signal loss? If the standard audio grade not recommended, any available for video? Sources? Thanks.
     
  2. Chu Gai

    Chu Gai Lead Actor

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    Well you can and the signal loss would be neglible it's just that it's one of those inelegant solutions. Kind of like hooking up 2 extension cords for a temporary solution to a problem. You know, for a few dollars more you'd probably have the length you need...what length are you looking for?
     
  3. Bob McElfresh

    Bob McElfresh Producer

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    Signal loss is not the problem. Impedence matching is the issue.

    The coax is 75 ohms to match the input impedence on your television. The RCA plugs can get close to 75 ohms if your cables have good ones, but these can often be 40/50/... because Audio cables dont care about the impedence.

    The couplers/barrel connectors - are a un-known impedence. (If you find any RCA couplers that ARE rated for 75 ohms - let me know. I've never found any. BNC connectors - different story).

    An impedence mis-match is like a speed-bump in a road. Not a problem for the slow speeds like 5-10 mph, but hit the same bump at 60 - big shock.

    Your video signals run from 1-4 mhz (for ordinary component video), but can run from 1-35 Mhz for HighDef.

    The higher-frequency signals will hit the impedence mis-match and can reflect in the cable. This can result in a "ghost" or a loss of sharpness/resolution on the screen.

    So it really depends on your system. For a 19" TV running component signals - it will likely not cause a problem.

    A 50" HDTV from a 720/1080 source - much more likely to have an impact.
     
  4. Cameron Yee

    Cameron Yee Executive Producer
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    Thanks for the info. I found some of your previous responses on the subject but it wasn't the easiest thing to search for. I'm mainly just curious as I've invested in some higher quality cables and know how I like to try different things when I get bored or am just itching for some change.
     
  5. Chu Gai

    Chu Gai Lead Actor

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    Well...

    To determine if an impedance mismatch is relevant here, we need to compare the length of the signal being transmitted to the offending item.

    v * l = c

    where c is the speed of light in a vacuum, v is the frequency of the signal, l is the length of the signal.

    if we assume the frequency is 37 MHz (running our DVD player at top resolution) and we take 0.8 as an arbitrary value for the velocity of propagation (speed of an electromagnetic signal is different in different media...greatest in a vacuum) and solve for l we get the following length of the signal: approximately 250 inches.

    The net length of our coupling RCA we'll say is an inch (less actually). A general rule of thumb is that the impedance mismatch needs to be 1/10 of the frequency in question to pose problems. So I wouldn't expect this to pose a difficulty. Also bear in mind that your equipment, source and destination, also has 75 ohm terminating resistors at both ends. However, it still is an inelegant solution.
     
  6. Bob McElfresh

    Bob McElfresh Producer

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    I know the feeling.

    Try doing a "HT Cleanup" by laying out your rack differently, labeling and bundling your cables and trimming your speaker wires.

    If you want to try and compare different video cables, I would suggest:

    - move the source close enough to the TV that you have a un-broken run with the cable.

    - Use some of the fine-detail test patterns in the Avia or VE disks. If not, try the "THX Optimizer" on some DVD's, or find a DVD that has a scene with lots of bright, contrasting colors and straight lines. Freeze the frame and use this for your A/B comparisons.

    - Re calibrate your speaker system. Use a laser-pen to check the speaker alignment and adjust as necessary.

    - Use this Viewing Distance Calculator and adjust your seating to match the THX optimal seating distance.

    Hope this helps.
     
  7. Cameron Yee

    Cameron Yee Executive Producer
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    We ARE a wild and crazy bunch [​IMG]

    Actually I've been thinking I should trim the ends of my speaker wire.
     

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