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Thread: Genlock Loop through

  1. #1
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    Genlock Loop through

    Genlock loop with self terminating output jack. This device is not the end of the signal path, the video passes through so should the genlock.

  2. #2
    Grizzled Veteran jcupp's Avatar
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    Yeah, but if you're looping black burst through several inputs it will be progressively further off because of cable lengths. Good engineering practice would suggest a DA and equal length cables for black burst.
    -Jeff


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    Product and Vertical Market Manager - Digital Broadcast
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    You beat me to it Jeff.
    Zane Condren
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    Quote Originally Posted by Sound Man
    Genlock loop with self terminating output jack. This device is not the end of the signal path, the video passes through so should the genlock.
    Jeff's right about looping not being a good idea. I don't think it's a problem on small systems with few components and short cable runs, but the better way is to send it all from DA's. Nothing wrong with Loop Outs; a lot of manufacturers include them, some don't.

    Quote Originally Posted by jcupp View Post
    Yeah, but if you're looping black burst through several inputs it will be progressively further off because of cable lengths. Good engineering practice would suggest a DA and equal length cables for black burst.
    I don't believe equal-length cables are necessary for blackburst. In my experience in broadcast television, you run the amount of cable required for each piece of gear (video and BB), then adjust the individual pieces' SC and H-Phase to match House Black. Never any problems from the different lengths of BB cable. I may be wrong, but that's how I, and all broadcast engineers I've worked with, have always done it.

  5. #5
    Grizzled Veteran jcupp's Avatar
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    If you have equal cable lengths you don't need to adjust to compensate. I'm just old-school.
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  6. #6
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    Genlock Loop through

    My system is already configured with a DA on the BB and I agree that good practice is to connect equipment in that manor. It is still a need that sometimes arises that the next piece of equipment in the signal flow is just a short distance away and it may be a long run back to the DA.

    Bob

  7. #7
    We've got it simple. Jim_C's Avatar
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    When matching cable length goes bad.

    Quote Originally Posted by Tim Ward View Post
    I don't believe equal-length cables are necessary for blackburst. In my experience in broadcast television, you run the amount of cable required for each piece of gear (video and BB), then adjust the individual pieces' SC and H-Phase to match House Black. Never any problems from the different lengths of BB cable. I may be wrong, but that's how I, and all broadcast engineers I've worked with, have always done it.
    At the first TV station I interned at while still in school, I was looking behind the production desk and I noticed about 100' of bnc going from one output, to the ground in a big jumbled mess, then back up and plugged into another piece of equipment 2" below where it came out.

    I asked the 'engineer' what it was for and he said it was black burst and that is was that long to match the other genlock runs.


    Good Times.


  8. #8
    Paintball Video Geek billmi's Avatar
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    I saw a couple of set-ups like that in Central California back in the 90s, usually with the cable still on a spool. Typical set-up would be using a Video Toaster as a M/E bus fed to their main switcher. Cameras would loop from the Toaster to the swticher, but the delay added by the Toaster meant its output was out of synch, so they'd add enough cable to delay it to be in synch with the next frame as a cheaper alternative to getting a TBC to resynch it's output to the house.
    Toasting with NewTek since 1991 - Corinthian Media Services
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  9. #9
    We've got it simple. Jim_C's Avatar
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    Quote Originally Posted by billmi View Post
    I saw a couple of set-ups like that in Central California back in the 90s, usually with the cable still on a spool. Typical set-up would be using a Video Toaster as a M/E bus fed to their main switcher. Cameras would loop from the Toaster to the swticher, but the delay added by the Toaster meant its output was out of synch, so they'd add enough cable to delay it to be in synch with the next frame as a cheaper alternative to getting a TBC to resynch it's output to the house.
    Well..... it WAS the mid 90's, they were using a Toaster 4000 in the chain somewhere, and this was a bare bones NO budget WB station.........so you may be on to something.


  10. #10
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    Quote Originally Posted by jcupp View Post
    If you have equal cable lengths you don't need to adjust to compensate. I'm just old-school.


    In most situations not requiring ridiculously long lengths, I tend to do the same with camera feeds, in fact.

    Woah. 'Guess that makes me old, huh...
    Last edited by Quiet1onTheSet; 08-06-2009 at 05:01 PM.

  11. #11
    The "Engineering Term" for that is "Delay Loop".

    Making them is fun:
    Put the full spool in place.
    Check offset on scope.
    Snip off some cable.
    Check scope.
    Snip.
    Check again, closer.
    Snip.
    Scope.
    Snip.
    Scope.
    Snip.
    Scope. Almost there.
    Snip.
    Scope. Too much, ARRGH!
    New Spool...


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