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Long cable run before or after signal conversion?

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Jason Twite
Long cable run before or after signal conversion?
on Aug 12, 2013 at 8:00:24 pm

(Also posted in Field Production forum)

Workflow:

Canon XH AI output via HD Component --> BMD Analog to SDI mini converter --> input into switcher via HD-SDI.

Which is the best practice?
A) Have the mini converter right at the camera to go from component out and then make a longer run (100' - 250') of SDI cable to the switcher.

B) Have the mini converter near the switcher and have component cables do the longer run?

Trying to figure out whether I need to buy more component or SDI cables.

Thanks!


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Matt Geiser
Re: Long cable run before or after signal conversion?
on Aug 13, 2013 at 11:57:59 am

You're going to want to do your long run over hdsdi. You'll have less signal loss over distance with the digital format.


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Jason Twite
Re: Long cable run before or after signal conversion?
on Aug 13, 2013 at 3:51:13 pm

Thank you, Matt! I figured that was the way to go, but wasn't sure if the mini adapter nullified any benefit of running one cable a longer distance than the other.


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Bill Davis
Re: Long cable run before or after signal conversion?
on Aug 15, 2013 at 7:01:19 pm

I generally concur, however, the main difference between digital and analog signals is that when an analog signal gets weaker, it gains noise, but is still useful at the far end.

With a digital signal, if it degrades to the point where every packet isn't distinct and can't be recovered, it just STOPS working, period.

Remember every pro sports broadcast for the first 50 years of broadcast was done with LONG analog cables.

Sure digital is preferred. Right up to the point where it isn't. And that's something you have to suss out.

Scopes, as always, are your friend!

Know someone who teaches video editing in elementary school, high school or college? Tell them to check out http://www.StartEditingNow.com - video editing curriculum complete with licensed practice content.


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Jason Twite
Re: Long cable run before or after signal conversion?
on Aug 15, 2013 at 7:42:49 pm

I trust SDI can handle a run up to 300' without completely cutting out. I've had cases of composite signal losing quality at that distance...using cheap coax.

On other forums, users continually ask about degradation of an HD/SD-HDI signal over long distances. My understanding, and based on Bill's statement, it's either all or nothing - no in between.
Correct?

Thanks,
Jason


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Bill Davis
Re: Long cable run before or after signal conversion?
on Aug 17, 2013 at 5:44:25 pm

As I understand it, with any digital packet based transfer that uses checksums - at the receiving point, if the checksums match, the program reassembles and delivers the video stream - or the process simply fails. In a "non-real time" environment like file transfer, the software can request a "re-send" if a packet fails - but in real-time streaming, if the sums don't add up all along the way, the stream stops.

I'll leave it for someone with more technical expertise to clarify if I'm not describing this properly.

Know someone who teaches video editing in elementary school, high school or college? Tell them to check out http://www.StartEditingNow.com - video editing curriculum complete with licensed practice content.


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Jim Brown
Re: Long cable run before or after signal conversion?
on Aug 18, 2013 at 1:15:22 pm

We do this very often to feed projectors from an ATEM switcher. We run coax (quad shield from Home Depot) with good connectors (double bubble) using Black Magic converters. We have run as far as 350 ft from the switcher to the converter at the switcher. It either works or doesn't. No degradation of signal. I mention the Home Depot cable because on some large shows we have needed additional cable and have had to go to Home Depot and terminate it on site.

This weekend I ran a 100 ft to first projector converter and then 250ft to a second projector convertor and then another 100 ft to 2 more convertors. The Black Magic (and I am sure the AJA gives you a loop thorough out which has been resynched. If I was ever in a situation where distance was a problem I would go half the distance, put in a converter and then continue.

We use this setup at least once a week and it works great. An added benefit is I no longer have to worry about hum bars and what phase of power the projector is on!

Works the same way on cameras. We use multiple Sony Z700 robotic cameras for football broadcasts and we convert from RGB at the camera to HDSDI using the Black Magic converters and run long runs of coax back to the broadcast trailer. The Black Magic converter is about a tenth the cost of the SDI option on these cameras!

Let us know how it goes.

Jim Brown
M & M Productions USA


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