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» Film-Tech Forum   » Operations   » Digital Cinema Forum   » Maximum distance for VGA signals.

   
Author Topic: Maximum distance for VGA signals.
Stephen Furley
Film God

Posts: 3057
From: Coulsdon, Croydon, England
Registered: May 2002


 - posted 08-17-2013 01:02 AM      Profile for Stephen Furley   Email Stephen Furley   Send New Private Message       Edit/Delete Post 
I should know this, but I don't. What's the maximum distance that VGA signals from a computer can be sent if broken out onto five strands of good quality 75 Ohm co-ax?

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Scott Norwood
Film God

Posts: 7991
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 08-17-2013 08:29 AM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
Isn't this resolution-dependent?

I am sure that there is real answer to this, but the practical side is that the image will get unacceptably smeary before you lose sync.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12206
From: Annapolis, MD
Registered: Dec 1999


 - posted 08-17-2013 12:27 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Scott is correct. It is all about bandwidth and attenuation. How high is the frequency and what is the attenuation of the cable at what distance and at what frequency.

A typical mini-coax cable can go about 10.5m without visible degradation on XGA signals (1024x768). While you can certainly run longer and get an image...it WILL start to smear. As you move up in frequency (higher refresh rates and resolutions), the distance before smearing drops (geometrically). If you move up to a full-size RG59 or RG-6 (times 5, plus, if you want EDID to travel, you'll need to add additional conductors), you can push that out a bit...as I recall, RG-6 can carry XGA a full 100 meters. Note, only the R, G and B really need the fatter cable...the sync cables can be smaller and survive.

What is more popular is to use an Interface of some kind to boost the overall level as well as high frequency (think of it as a slit-loss correction) so that at the other end of the cable, you have essentially the same signal as if it was coming out of the device.

http://www.extron.com/product/product.aspx?id=rgb160xi&subtype=1&s=3

What most have taken to is to run everything on a CAT 5 style solution. Most are proprietary.

http://www.extron.com/product/product.aspx?id=mtpt15hda&subtype=5&s=4

Generally, the twisted pair solutions start to be more cost effective on longer runs. The cable is cheaper and easier to pull in though more fragile.

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Stephen Furley
Film God

Posts: 3057
From: Coulsdon, Croydon, England
Registered: May 2002


 - posted 08-17-2013 05:10 PM      Profile for Stephen Furley   Email Stephen Furley   Send New Private Message       Edit/Delete Post 
No Cat. 5 installed, but there is some old co-ax. I don't know exactly what it is, but it's only about 25 metres, so it's worth giving it a try.

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Kris Verhanneman
Expert Film Handler

Posts: 182
From: Belgium
Registered: Dec 2009


 - posted 08-18-2013 04:13 AM      Profile for Kris Verhanneman   Email Kris Verhanneman   Send New Private Message       Edit/Delete Post 
Hello,

might be cheaper to add an cat 5 cable but if not you can alway have a look at scalers that give you an output on HD SDI (or SDI).
Like this one for example
Link

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999


 - posted 08-18-2013 05:04 PM      Profile for Bruce Hansen   Email Bruce Hansen   Send New Private Message       Edit/Delete Post 
The VGA to cat5 converters that I have seen suck. Stick with coax. Don't forget that VGA is ANALOG.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12206
From: Annapolis, MD
Registered: Dec 1999


 - posted 08-18-2013 10:28 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
It all depends on what you use. The Extron ones are generally pretty good and even better if they are set up properly. To the point, you'd be hard pressed to know that the Cat 5 solution was used...even with an O'scope (because that is how I set them up for proper level and frequency response).

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Stephen Furley
Film God

Posts: 3057
From: Coulsdon, Croydon, England
Registered: May 2002


 - posted 08-20-2013 04:01 AM      Profile for Stephen Furley   Email Stephen Furley   Send New Private Message       Edit/Delete Post 
Tried it, and it works ok. Five strands for the VGA plus a sixth carrying S/PDIF from an amp for a mic. Not ideal, but it's there and available, and it will do the job. It's only needed for a few minutes.

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