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shielding rca/component video

Discussion in 'General Electronics' started by J, Feb 1, 2006.

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  1. J

    J Guest


    I'm building a snake box for my rca gear. I'm going from rca female on the
    box to a multi cable and probably back again and I can use a panel-mount
    rca, solder a shielded (or unshielded?) wire to an output connector (below)
    (db 25).

    What about a Double shielded twisted pair DB25? if not please recommend an
    available cable/connector.

    If I use plain unshielded cable inside the (metal) box, could I run into

    Do I have to worry about shielding, say, composite video from component or
    audio (-10 or +4) inside the box?

    What do you think my distance limitations will be for component video,
    composite, -10/+4 audio, digital coax, svideo on the DB25 cable??
    I'm thinking 3f patch +1ft in box + 10ft +1ft in box + 3f patch for a total
    of 18 Feet.

    Thank you for your time,
  2. "gear"? audio? video?
    "back again"? not sure what that means? back where?
    "the box"? can you give us a better hint what you are doing?
    What is the signal? audio? video? something else?
    "output connector"? output to where? what kind of cable
    does the db25 connect to?
    DB25 connectors are neither shielded or non-shielded.
    DB25 connectors are neither twisted pair or otherwise.
    You seem to be describing some sort of cable which
    connects to the DB25?
    You have left out too many details for us to have any idea
    what you are trying to do here?
    What kind of signal? audio? video? something else? How far?
    If they are the same picture, probably not.
    If they are different video signals, then, probably yes.
    Depends on how far from the video.
    I would use shielded cable just to be safe.
    Impossible to answer.
    We have no clue what your "DB25 cable" is.
    You have provided only ~40% of the details necessary to answer
    your questions properly. I would be far more concerned about
    the nature of the 10 ft of snake cable than about the details of the
    boxes and connectors.
  3. J

    J Guest

    My goal is a box to which I can connect my stereo receiver inputs and
    outputs that will simplify the connection from one entertainment cabinet to
    another - condensing to a single cable (my dreaded DB25 cable ;). Then
    there's a box on the other end of the multicable which expands the
    connectors back out to their respective composite video, svideo, component
    video, audio(red white), digital multichannel audio, etc. rca panelmount

    My question is:
    While building the box 1) Must I shield individual lines soldered from rca
    panel-mounts to my db25 connector inside the metal box, AND 2), Would a
    doubleshielded twisted pair cable (with db25 connector, standard issue
    printer switch cable) effectively transmit things like component, composite,
    svideo, digital audio which were originally on 75ohm coaxial cables?

    How effective is shielding on a cable when the + solder points are not
    shielded inside of a box?

    I plan to make the connections in the box with Belkin 8451. 22 ga shielded 2


    I very much respect the people involved on these lists. I expect very
    little as I know that it is charity. I understand, and have for years, that
    I am poorly organized -as are my writings, but you are making sport of my
    question. Before writing this paragraph, I looked at your other posts.
    People, indeed, ask a lot of stupid questions, and you are quick to point
    out that they need to pause and reorganize. However, if you read the entire
    question before replying impulsively (as I am replying impulsively here),
    you'll see that your ostensible bewilderment is not justified in all cases.
    What kind of gear was implied when I asked about specific signal types:
    Component video, Composite, Svideo, and audio -10,+4. Translation from one
    set of discrete connectors to a unified multi-cable and 'back again' to a
    bunch of discrete connectors is generally what snakes do. The websites I've
    seen are selling twisted pair double shielded DB25M-DB25M cables. I think
    you can surmise that a double shielded twisted pair DB25 Cable is some sort
    of cable that is double shielded with twisted pairs and DB25 Connectors on
    the ends. ;)
  4. If you keep the audio at one end and the video at the
    other end you *might* be able to get away without
    shielding the internal wiring.
    It is questionable whether it will work acceptably well
    for audio in your application. (See more complete
    discussion below.) I would bet that it will make a hash
    out of any video (particuarly high-quality video) that
    you try to run through it.
    Still quite effective. It is over the length of the cable
    that the shielding is beneficial, not just at the connection
    Assuming you mean "Belden", a well regarded maker of
    wire and cable. That would be great for the audio lines.
    I wouldn't use it for video if I had a choice of proper
    coaxial cable (whether 75-ohm or some other impedance
    which doesn't really matter for short pieces).
    No, I was trying to clarify what you are asking. It may
    appear to you that some of the information you left out
    was not important, but that is because you may not
    understand the scope of the questions you are asking.

    Now, there ARE some people on Usenet who DO make
    sport of people's questions (and far worse). I suggest
    that you need to develop considerably thicker skin and
    get a pair of asbestos undershorts if you intend to hang
    around some of these newsgroups very much. ;-)
    If we can assume from your mention of component video
    that you have high-end video equipment (as contrasted with
    a cheapo 12" TV set), then any thought of running video
    through any kind of printer cable should be put out of your
    mind. The video will look like a "dog's breakfast" when
    you are done and you will have wasted both your time
    and your money.

    People frequently come here [I am reading and posting
    from] and ask about very expensive
    audio and video cables and whether they are worth the
    extra expense. The overwhelming answer is: No, their
    high price only enriches the people selling the premium
    cables and they do nothing discernable for your audio or

    OTOH, you can't expect to run high-quality video over
    cable which was never designed for that kind of band-
    width or impedance-control. Just as there is a threshold
    above with you cannot *improve* your video signals,
    so also there is a threshold below which you are just
    wasting your time and money.

    If you object to the way I cross-examined you or responded
    to your questions, I apologize, I was trying to do a complete
    job of understanding the circumstances in order to give an
    accurate answer.
    You are operating so close to the edge that it was not safe
    to make that kind of assumption. Those cables are likely
    very nice for parallel printers. Maybe even overkill (as
    for the "premium" audio and video cables discussed above)

    That cable *might* even be OK for audio, although the lack
    of shielding between the twisted pairs may give you more
    crosstalk than you would like. Particularly with unbalanced
    sources and inputs. And running something like an unshielded
    tape output and a tape input line next to each other could
    even cause oscillation, audible or supersonic, which could
    actually damage speaker tweeters or other parts of your system.

    I would definitely NOT recommend the type of cable you
    want to use for either audio or video use.

    If you want to make something that has several audio and
    video cables in a long, flat form-factor, you could consider
    taking 10-ft lengths of proper audio and video coax and
    "weaving" them together with cable-lacing twine, where
    the cables form the long dimension, and the lacing twine
    weaves across them to hold them in a flexible ribbon shape.
  5. J: If you use well shielded audio and video cables, and part of the goal
    is to have a nice neat equipment wiring harness, you could pick-up
    plastic split-channel or spiral wrap and use that instead of going to
    all the trouble of lacing wires. Plastic channel is available in a few
    different diameters. Keep the equipment power lines and amplifier output
    wires separate from the others. Another step to include is to make sure
    that you label all connector ends, this will save your sanity and avoid
    guessing games.
  6. Jasen Betts

    Jasen Betts Guest

    why not use a SCART plug?

    how fast is a car with 4 wheels?

  7. J

    J Guest

    I've only seen scart in pictures. I'm in the US and none of our gear has
    it. I'd love to, but it looks like my idea is cost-prohibitive.

    4 wheels, right - point taken.

  8. J

    J Guest

    As it stands with my initial design, component, audio, composite, svideo,
    and digital between 2 boxes would cost $100 after labor, connectors, etc.
    To build it properly would cost a lot more, it seems.
    Haven't been getting much sleep...
    I was basing my design on connectors available on the back of sony's new
    $2000 hifi receiver.
    No monster then, hosa is fine?
    I'm too weak to use monster's toothed RCAs anyways. ;)

    I withdraw my objection. Thanks for your patience.
    That was one of my concerns - what does double shielded mean? I was hoping
    the pairs were shielded, then the whole was shielded. Evidentally not.
    sounds pretty, but it's not a component you can just 'install'.

    NOW I see why the product I'm looking for isn't available. The market won't
    meet the price for the quality, variety, and assembly of the components
    required. You'd have to charge several grand for one with 48 specialized
    connectors and 6 breakout boxes.

    I'm just looking for a way to speed hifi installation/ modification. Hoping
    there's an alternative to crawling around behind someone's tv and
    entertainment center for hours...

    Oh well.

  9. J

    J Guest

    yeah, I've seen those. Better than nothing, but not quite the one cable
    simplicity I'm looking for. What can I say, I'm a perfectionist and a

  10. Monster defines the level where you are paying for the
    name and not for any discernable benefit to you.

    OTOH, if you are a San Francisco 49ers fan, you get the
    benefit of going to "Monster Park" where Noel Lee (who
    started "Monster Cable") likely has a luxurious skybox. While
    I admire Mr. Lee's business success, I am not inclined
    to support it.

    Hosa defines the lower level of acceptable quality. It is
    likely OK for fixed-installations (I use it myself), but many
    have reported failures (breaking at the moulded connectors)
    in repeated portable use.
    "Double-shielded" in a (relatively) inexpensive computer
    cable almost always means two layers of aluminum foil
    over the entire cable. I've never seen a comptuer cable
    with individually-shielded pairs. At least not in 30 years.
    Digital signals don't need it, so there is no profit in doing it.
    I'd bet that somebody could come up with an efficient cable
    "weaving" machine and make a bit of profit providing
    custom flat-cable combinations. Could become the next
    Noel Lee and have their own sports stadium! :)
  11. Ray L. Volts

    Ray L. Volts Guest

    Cat5/e STP (Shielded Twisted Pair; each of the 4 pairs is shielded plus a
    shield around the bundle) cable would certainly support the bandwidth
    requirements, but you'd probably have trouble with the 100-ohm impedance. I
    suppose you could rig up some impedance-matching terminations.

    Some info on grounding shielded cable:
  12. Ray L. Volts

    Ray L. Volts Guest

    Also, check these devices out:
  13. SCART connector and cables are designed to carry video signal
    and stereo audio. There are actually wires for audio and
    video (composite video) for both directions. And there are
    also some unidirectional control signals and RGB video lines for
    one direction.

    The idea of SCART is good. The real life implementation of
    it leaves something to be desired. The connector used for
    SCART is not mechanically or electrically very good
    (connector gets easily loose when cable is moved and
    then pins are not making good contact).

    Then some equipment could have designed the use of some
    control signals better in their equipment...

    And audio/video connections were pretty clear
    (composite video and RGB well specified, nicely
    degrading to use composite video if one of the
    equipment on one end did not support RGB) until someone
    later added S-video support for some SCART connectors
    on some equipment... not amy equipment support those...
    anyway the way S-video was added to scart has caused many
    people to wonder why they get blac&white video where
    they expect to get color video...
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