Maximum distance for DVI-D Cable Run

[jonnybrandon]

Sorry to hijack the thread but I have a related question.

 

Can somebody tell me what the maximum distance is that I can realistically run DVI-D cable from Mac to projector, without the need for a driver/amp? Would there, in fact, be any signal loss? And would it make a significant quality difference over using a VGA run (with DVI-VGA conversion at source)?

 

I am touring a projection system and have the option of a straight DVI run, up to a maximum of 40m.

 

Having researched this issue I'm a bit confused and hope that somebody can set me straight!

[AHYoung]

realistically 40m is beyond the limit of dvd -d but its down to many factors as lower resolutions will probably travel further and some cables are better than others. A lot of manufacturers say 10m is the max, ive run lower res up to 25m without problems, but any further would probably be pushing it. there are extenders/ repeaters which should make a 40m run possible, and if you want to spend more both cat 5 based and fibre baluns allow dvi to run up to 100m {and beyond}, but it will cost.

 

however why go dvi d, im assuming the projector has vga in, your mac certainly will output it and 40m over vga is no problem. So unless there is a convincing reason to go digital, analogue is the easy option.

 

you also want to consider how you power the projector as you can get nasty ground loops if you dont consider the mains as if you power both from the nearest supply, you may well leave yourself open to earth loop problems which can be tricky to resolve. We have looms with mains and signal together so you power the projector from the same feed as the source which cuts out most mains bourne problems.

 

cheers alastair

[jonnybrandon]

you also want to consider how you power the projector as you can get nasty ground loops if you dont consider the mains as if you power both from the nearest supply, you may well leave yourself open to earth loop problems which can be tricky to resolve. We have looms with mains and signal together so you power the projector from the same feed as the source which cuts out most mains bourne problems.

 

Thanks for the help. I'd thought that VGA would probably be the way to go but needed somebody to confirm!

 

As for power, I'm not sure I understand what you mean when you say you powered the projector from the same feed as the source? Should I run my 13A from the same socket/extension as my Mac?

 

Cheers.

[Freddie]

As for power, I'm not sure I understand what you mean when you say you powered the projector from the same feed as the source? Should I run my 13A from the same socket/extension as my Mac?

 

Yep, it'd be good practice to run the Mac from the same socket as the projector :)

[AHYoung]

assuming you went with the easiest option....

 

 

You might plug the projector into the nearest circuit on the truss / lighting bar, mac into whatever 13a is at FOH. the projector probably has a 50m cable to get back to the mains distribution, which itself could have a long run to the supply, so you could be looking at 100m of cable. the 13a foh socket could be on a completely seperate supply or at the very least an a long run back to the common point. this in iself isnt a problem, but as the earths will probably have a small potential due to the long runs and the fact that cable has a finite resistance, when you join the 2 together with the signal cable you get a ground loop and the picture rolls. Its exactly the same as a ground loop or Mains hum in the audio world and its difficult to get rid of.

 

You can generally avoid it by attemting to run the projector and mac from the same supply, and as you have to run signal between them its no hardship to run the mains from foh up to the projector. Its also worth noting that if you are running sound as well as video from the mac, if you want an easy life stick it all on the sound supply.

 

an easy test for mains hum is to unplug the mains from your laptop and see what happens as this will break the loop. You get Opto and transformer isolaters or humbuckers which are effectively DI boxes for video and isolate the grounds, and if you use fibre it also gives isolation, but its easier to be carefull with mains distribution.

 

cheers

 

Alastair

[jonnybrandon]

Thanks Alastair for your helpful explanation :)