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Effects of joining BNC cables on HD-SDI

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Rob Davy
Effects of joining BNC cables on HD-SDI
on Dec 9, 2011 at 7:23:34 am

Hey,

Has anyone had any experience with the effects of joining BNC cables (probably Belken 1505a) together with BNC barrels? Specifically on HD-SDI...
Eg, is there a major issue in using 3 x 100ft cables vs 1 x 300ft cable?

Cheers!


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Tom Sefton
Re: Effects of joining BNC cables on HD-SDI
on Dec 9, 2011 at 12:11:43 pm

Hi Rob,

We haven't joined 3 cables, but due to the logistics of running cables under flooring and through guttering at trade shows we have used one loom with 12 I/O and then connected cameras locally with shorter runs (control room being at least 250ft run with the loom).

Didn't have any noticeable dropout or signal loss - this was using the output from XLH1's, via matrix switchers, to watchout, to 4 video walls for live camera feed.


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Peter Emminger
Re: Effects of joining BNC cables on HD-SDI
on Dec 9, 2011 at 5:56:53 pm

The max cable length you want to run with HD-SDI is 100m or approx 330'
Everytime you add a connection with any cable you're adding resistance and you increase the potential for a problem.
If this were a critical application i would try to get a longer cable OR i would put a DA at one of your connection points. Something like this:
http://www.aja.com/products/converters/converters-hd-hd10da.php

If its not a critical application i say set it up and see how it works for you. There's a lot of variables involved so you might be fine.

--
Peter Emminger
Project Manager & Technical Director
Yellow Light Live, Inc.


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Gary Snyder
Re: Effects of joining BNC cables on HD-SDI
on Dec 10, 2011 at 2:45:42 am

Here is a great link that gives distance - vs cable type
for SD and HD video..

http://www.gepco.com/technical/sdi_distance_chart.htm

Gary C. Snyder
President / Engineer
Clark Media
610-694-9800
HD rentals in New York and Philadelphia
Panasonic, Sony and Arri Alexa


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Rob Davy
Re: Effects of joining BNC cables on HD-SDI
on Dec 10, 2011 at 3:01:17 am

This one is more useful for my cables... http://www.belden.com/pdfs/Techpprs/Maximum_Transmission_Distance_at_Serial..., but still doesn't help with the effects of adding barrels...


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Scott Sheriff
Re: Effects of joining BNC cables on HD-SDI
on Dec 11, 2011 at 6:43:40 pm

[Peter Emminger] "Everytime you add a connection with any cable you're adding resistance and you increase the potential for a problem."

While that is technically true, IRL well made BNC cables joined with quality connectors are not that big of an issue. The insertion loss for MIL-Spec BNC connectors is only 0.2db at 3ghz.

[Peter Emminger] "If this were a critical application i would try to get a longer cable OR i would put a DA at one of your connection points"

A longer cable is probably the best choice, but I would go with a passive connector, over a DA, unless I really needed a DA to split the signal. DA's can fail, or cause drift in levels. A well made passive component is virtually fool-proof.

Scott Sheriff
Director
http://www.sstdigitalmedia.com


"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." ---Red Adair

Where were you on 6/21?


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Phil Senger
Re: Effects of joining BNC cables on HD-SDI
on Dec 12, 2011 at 5:21:51 pm

I would suggest using a quality barrel, I know some are actually endorsed for HD/SD-SDI. I have had on numerous occasions a cheap barrel fail, in fact, sometimes the guts fall out completely. The higher quality barrels are much more robust and feel (cause it's all about the feel) much better.

Phil Senger

SW Audio+Visual
Vancouver, BC
http://www.sw-online.com


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Michael Sisko
Re: Effects of joining BNC cables on HD-SDI
on Nov 12, 2012 at 1:38:37 pm

Only use 75ohm BNC Barrels (they often have a purple ring on them) You can extend HD-SDI that far but a single cable with a reclocking DA would be best. Even with multiple cables you should either be using a reclocking DA or a signal extender. AJA makes several great pieces to do this as well as Extron (HDSDI-101) 100m is pushing the limits of most cables and rental cables should not be used more then 75m. In my experience, I will not run SDI longer then 125ft without some type of resync or reclock.


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