Which of these cables is better for digital coax?

Discussion in 'Accessories, Cables, and Remotes' started by Vincent_S, Dec 22, 2003.

  1. Vincent_S

    Vincent_S Second Unit

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    I am going to order a new digital coax with Eichmann Bullet ends and was wondering which would be better suited for the job and why. Canare L-5CFB, Canare LV-77S or Belden 89259. Will be installed from DVD player to receiver BTW. Stiffness should not be an issue. Thanks.

    P.S. I already have the LV-77S with rca ends, just wanting to do a comparison between the two.
     
  2. Bob McElfresh

    Bob McElfresh Producer

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    Vincent: Can you tell if I am posting this from:

    - A 386 PC with a StarBand Sat modem
    - A Pentium with a cable modem
    - A Sun Workstation with a T1 internet connection

    In truth - you cannot. By it's nature, the digital connection hides/removes you knowing the quality of my equipment or wires.

    The digital signal from a DVD player is very INSENSITIVE to the cable. You are not going to hear any difference between what you have now (the LV-77S) and any of the others.

    And I suspect/theorize that a cable with Eichmann plugs might be worse than your current Canare based cable. Canare's claim-to-fame is it's RCA plugs. They have proven themselves over and over again.

    There has been some controversy over the Eichmann plugs for HD video and since the SPDIF specification calls for a "75 ohm" path - you might actually be damaging the signal.

    So my advice is: save the money to upgrade some analog-video cable in your system. This is where it MIGHT make a difference. Not for a digital signal.
     
  3. Chu Gai

    Chu Gai Lead Actor

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    You're using a Pentium
     
  4. Bob McElfresh

    Bob McElfresh Producer

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    Nope. Athlon [​IMG]
     
  5. Matt_Doug

    Matt_Doug Stunt Coordinator

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    If we were net video conferencing I would be able to guess which computer and definitely which connection you're using. My point being that the equimpent can make a difference. As per connection; the copper clad RG6 the CATV company uses with Canare 75 ohm type RCA connectors will more than suffice for any consumer digital connection. Cables can't hold a candle to upsamplers, re-clockers and electrical isolation as a tweak for cosumer dif's
     
  6. Chu Gai

    Chu Gai Lead Actor

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    You're getting very sleepy...tired...your wallet is empty from shopping. I tried [​IMG]
     
  7. Matt_Doug

    Matt_Doug Stunt Coordinator

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    Yes, Empty,Empty, Empty, Empty, Empty, Emp
     
  8. Mark Rich

    Mark Rich Second Unit

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    Try and find belden 1506a or 1695a (Both have a solid core, high level of shielding and use teflon for the dielectric)with either Bullets or Vampire RCA connectors.
    The Canares are not true 75ohm connectors and I've found that a decent,well made RCA connector (Vampire, Cardas,WBT etc.)works as well and often better than the Canare's in most applications. The down side to the Bullets is the lack of shielding (plastic body) and poor strain relief (plastic on plastic construction).
     
  9. Alf S

    Alf S Cinematographer
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    Just use a $3 RCA video cable (or a free one you probably have layin' around the house)and save your cashola..it serves the same purpose!

    [​IMG]

    Happy Holidays BTW!
     
  10. Bob McElfresh

    Bob McElfresh Producer

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    Ok, here is how an engineer would select a coax for a particular application:

    - He would first determine the highest-frequency signal the coax would have to carry. For the coaxial-digital connection, the baudrate is about ... 400 Khz. Let's round to 500 Khz.

    - He would multiply the max frequency by 4. This gives us 2 Mhz

    - Then he would look at the frequency-response table for the various coax. He would look at the frequency over 100 feet where the signal has dropped/attenuated by 3 db (or 50%). Any coax that had less than 3 db drop at 2 Mhz would be a canidate for this application.

    Then he would look at the second-order issues with the coax. The first issue would be price, followed by any/all of these depending upon the application:

    - Availability
    - Durability (different materials have different usage life)
    - Flexability
    - Pull Strength (if you are pulling 100's of yards through couduit). This is often a trade-off with Flexability.
    - Appearance
    - Cost & availability of tools and connectors
    - Return loss (for long runs)

    Note: the nature of the signals (Digital vs Analog) also has an effect. The frequency response data is good, and necessary for analog - but digital has a few special issues that analog can ignore. This is mainly caused by digital signals trying to instantly jump to some voltage, or to zero volts. The materials used in the coax now affect some obscure parameters like "Reactive Capacitance", and others.

    Without having had a recent course in electromagnetics, my best advice is to read the "Application Notes". Every coax has one of these. This is where the cable designers tell you what type of application (digital/analog/speed/environment) they had in mind when they designed the cable.

    Does that help with the "Why"?
     
  11. Vincent_S

    Vincent_S Second Unit

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    Thanks, I think I am going to try and find a good pair of analogs since I don't even own a set:b Maybe next time I have some spare $$ I might try a different dig coax. Thanks for the input guys!
     
  12. MarkStash

    MarkStash Stunt Coordinator

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    Alf:

    I'm just setting up my new HT. I'm still waiting for some components to be delivered. In the meanwhile I'm researching and learning. Right now I'm on the coaxial audio cable/s piece as I currently have optical cables. Is it true that an RCA cable serves the same purpose? Do I need to spend $40+ for new cables? Thanks (I know, I may be naive as I am a newbie to this).
     
  13. Bob McElfresh

    Bob McElfresh Producer

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    No..and Yes.

    The people who designed the coaxial-digital interface had a Video cable in mind. Use a video cable (with yellow markings on the plug) for the coaxial-digital connection.

    It's a bit of a myth that "..any RCA cable will work" because:
    • Cable makers sometimes use video-cable coax for the L/R audio cables.
    • An audio cable made with with the wrong type of coax will appear to work for the coaxial digital connection. But the sound can drop-out every few minutes during the movie.

    A short video cable should run you ~$15 at Radio Shack or the AR Pro brand from Best Buy/Sears if you dont have an old one lying around.
     

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