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Any issues using a 90 degree BNC adapter for SDI recording?


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#1 Vincent Sweeney

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Posted 10 March 2011 - 06:14 AM

Anyone out there have an opinion on whether or not its ok to use a 90 degree BNC adapter on a short, on-camera HD-SDI cable that is recording out from camera? I need to use one to make cable routing more comfortable on the camera.

It seems obviously ok to me but I'd like to make sure there isn't some odd little factor that I am not figuring in here. It's a critical connection so of course I want to make sure I'm not introducing some possible problem by using one.
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#2 Phil Rhodes

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Posted 10 March 2011 - 06:46 AM

Mnnnnn. Probably.

Theoretically, HD-SDI should be transported down low-capacitance cable assemblies, and it even then has a greatly reduced maximum distance specification against the SD version. Nyquist's theorem states that the minimum electrical bandwidth for HD-SDI is 3GHz, and 6GHz for the "3 gig" version. This is properly fast, in order to fit unadulterated HD video down a serial link. There are (admittedly older) high performance search radars that don't get up that high. BNCs do not match very well at these frequencies and their insertion loss is fairly terrible. You could reasonably consider HD-SDI to be a fairly well stressed specification and taking liberties with it is probably not a good idea long term.

As a practical matter, I have never had a problem with any old cable I happened to grab, although I was never anywhere near the maximum cable length. If it works it will probably go on working, at least for short periods while components are fresh and new and unworn, and while the joints don't have dampness in them, and while the temperature and humidity are stable. The only definite no-no is to ensure you're using 75-ohm adaptors and connectors; until fairly recently, 50-ohm computer networking stuff was easier to find, and the pins are a different size - enough to damage connectors, although they will fit if you lean on them.

So I guess you'll be fine. But if it breaks, you can't really complain. 3 gig breaks all the time anyway...

P
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#3 Vincent Sweeney

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Posted 10 March 2011 - 04:30 PM

Thanks Phil. The cable in this case is 1.5ft. long. I would think that if there were any loss or issue the KiPro would warn me. I will give them a call to check as well.

This is the (75ohm) connector I am using:
http://www.filmtools.com/bncelbow.html
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#4 Phil Rhodes

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Posted 10 March 2011 - 05:07 PM

Try it. I suspect you'll be fine.

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#5 Chris Keth

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Posted 11 March 2011 - 07:18 PM

You would probably be fine but if you're recording that HDSDI signal, why don't you have a cable made with a right angle end and eliminate the extra connection?
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#6 Vincent Sweeney

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Posted 12 March 2011 - 12:08 AM

You would probably be fine but if you're recording that HDSDI signal, why don't you have a cable made with a right angle end and eliminate the extra connection?


Still may happen... its been an insane time crunch. Testing so far shows no issues at all.
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#7 Vincent Sweeney

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Posted 24 March 2011 - 03:35 PM

To follow up: Markertek came through with a custom one for $32

IMG_2323.JPG
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