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Coax>RCA

Discussion in 'Multimedia, Projection, and Show Control' started by Charc, Aug 24, 2008.

  1. Charc

    Charc Well-Known Member

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    Right? If I'm running video, it makes a heck load more sense, to take RCA, run it through a little radio shack converter, to coax, and, and then do whatever.

    Seems like coax is more versatile, and standard. Is cheaper than RCA, and has more options for routing.
     
  2. waynehoskins

    waynehoskins Active Member

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    I think I'm following what you're saying, maybe. An RCA connector is one of many coaxial connectors that can be used on a coaxial cable. Similarly, the type of cable and the connectors on the end don't define the application.

    And you're right, the RCA connector is not standard; the BNC is. Stupind blankity-blank RCA connectors on consumer video gear.

    But in general you're better served by properly distributing good old NTSC video (CVBS) than by modulating that onto a radio carrier with one of those little throwdown low-power exciters.

    So a question about your question, because it sure as heck doesn't make any technical sense as is: You're asking whether 'tis better to distribute composite video as NTSC video or as a low-power television signal?
     
  3. waynehoskins

    waynehoskins Active Member

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    Coax is used many purposes. For video, no matter what connector's on it (BNC, RCA, F, PL-259, TNC, ...), the cable itself is coax. The selfsame cable is also used for television antenna and radio antenna feedlines.

    "RCA cable" doesn't exist. You can put an RCA connector on a variety of cables: zipcord, coax, microphone cable, and so on.

    "Coax connector" or "coax signal" also doesn't exist. Coax is the shortened name for "coaxial cable", which can be a variety of types, all of which are a single conductor with a shield around it, the geometry arranged such that the two share the same center axis, or are co-axial, and thus has a predictable constant impedance. The cable for your car-radio's antenna is coax, as is the big-ass heliax at the cell sites.

    "Coax connector" is like talking about, in lighting, a cable as having a "12/3 connector" on the end.

    You're talking about (here I translate to consumer-talk) converting a composite video signal from the Yellow Jack of a device into a signal that you'd run down coax with the screw-on F connectors and plug into the back of your TV set where the antenna plugs in?

    And you're asking if that's a better way to distribute your signal than using what comes out the yellow jack?
     
  4. waynehoskins

    waynehoskins Active Member

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    Well, the answer depends on your application. I would use RF for feeding things like lobby monitors or other ancillary systems, where you might decide later to add on another TV set in the next room. I would not use RF for feeding a primary system if I could avoid it.

    But as to the issue of only cabling (without regard to what signal is on the cable), there's no difference between the readily-available RG-6 at Radio Shack or Home Depot for your TV antenna and the bulk cable you'd typically use to make video cable from (which is RG-59). Arguably, RG-6 has a bit less loss than 59, though the solid center conductor makes it less flexible in applications where you want that. So there's nothing at all wrong with taking an RG-6 cable with F connectors from the shelf at the Radio Shack, putting adapters on either end (F-RCA or F-BNC), and running composite video down it. It's the right impedance and is suited to the task, and it's readily available for quite cheap.

    (In fact, I've done it the other way around numerous times, using a length of RG-59 with BNCs on it built for video, and adapters to F on both ends, for antenna cable)

    And that's where my question about your question comes in, as to what's on the cable.

    RF can be easily distributed with the little splitter blocks. A video signal proper cannot simply be wyed, because the wye creates an impedance bump first of all, and secondly it double-terminates the line if the destination devices are consumer and don't have looping impedance inputs like broadcast gear has. This double-termination is evidenced in a halving of the brightness of the signal for each wye. Well, not half, but close. To distribute video proper to multiple destinations, you need a distribution amplifier.

    So tell us more about the application. Not trying to make you feel stupid, just trying to figure out what you're asking. :)
     
  5. tech2000

    tech2000 Active Member

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    It does in the consumer mindset.
    No typical consumer is going to call it a coax cable with rca connectors
    ...just a thought
     
  6. museav

    museav CBMod CB Mods Departed Member

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    Put simply, "RCA" is a connector type and "coax" is a cable type. Neither identifies the actual signal, which could be anything but for analog video is primarily baseband (composite video, S-Video, component video, RGBHV, etc.) or broadband (RF, CATV, CCTV, MATV, satellite, etc.).

    Certain connectors are typically associated with specific signal types, e.g. an F connector for broadband and BNC for baseband, but those are not absolutes and some connectors may be used for either, whether it is standard practice or not.

    In regards to the original question, I assume by 'converter' you mean a physical adapter and not an active device to convert (modulate) baseband to broadband or anything like that. If so, then in many cases it would indeed probably be easier and better to use RG-59/RG-6 type coax cabling and adapters.

    To clarify one thing, you can get solid conductor or stranded conductor, highly flexible or very stiff, etc. versions of RG-59 and RG-6. The difference between the two is simply a matter of the size of the center conductor, 20AWG for RG-59 and 18AWG for RG-6 (RG-11 is 14AWG). RG-58 and RG-8 are basically the 50 Ohm antenna cousins of these 75 Ohm video cables. You can also use RG-59 or RG-6 for both video and RF applications, the primary difference between 'video' (baseband) and 'CATV' (broadband) cables is typically the high frequency attenuation of the cable, broadband often involves higher frequency bandwidths and thus high frequency losses can be more critical.
     
  7. wadeace

    wadeace Member

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    the only time converting the composite signal to RF is if you are trying to feed the signal to all the tvs spread thought the whole building. and you don't achieve that with a little rs box. to do that right you need a channel modulator and single combiner. these components placed inline with you main cable feed will distribute whatever you feed to it will be distributed as a cable channel to all of the tvs.

    if however you need a long cable to send a video single over than you can get a thick gauge coaxial cable spool, and put your own connectors on it.
     

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