Cable runs

S

soundguy

Limp Gawd
Joined
Oct 31, 2007
Messages
419
hi guys, i was just wondering about people's cable runs that they might have to projectors etc, because in the assembly hall at school we have an existing 60m run of standard vga cable and we don't want to have to replace it with dvi or even just cat5. We have a vga over cat 5 kit, but that would mean that we would have to run it through the ceiling as it would not run through the school's current network.

we have a HP Compaq dc7700 with built in GMA 3000 Grpahics built into the G965 chipset. we also have a vga switcher/double adaptor that displays the same signal as is on the 19" monitor we have in the Bio box as on the projector in the rest of the hall. I haven't had time to pull it all apart and see what expansion slots it has, but i would think that it will only have PCI. :confused:

what i want to know is; do any of you think that we will be able to use the existing VGA cable with a better GPU?
 
no one? this is kind of important as it means that we have to use a laptop to do assemblies instead of the more powerful desktop...
 
It would depend on the quality of cable, but 60 metres is really pushing it for most VGA cable. What you really need to do is get a VGA-RGBHV breakout and use high grade coax. That'll go 1km no problem.
 
I don't think switching between GPU brands would have a measureable impact on signal strength.
 
ok thanks, we are running an assembly as i write this so yeh...

we will probably jsut go with the VGA over cat5...
 
I'm not a real fan of that. Cat-5 is lower bandwidth than coax. At 60 meters, you are going to be really pushing it to get 1280x1024, if there's any problems in the cable run it may not work since that requires 100MHz of signal bandwidth. Now I realist that Cat-5 is spec'd to 100MHz, but remember it is normally dealing with a digital signal, so low level noise in it doesn't matter, whereas it'll show up quite clearly in an analogue signal. You'll notice that VGA balnus usually recommend using a STP cable instead of normal Cat-5 UTP cable for this reason.

Using Cat-6 or Cat-6a would help the matter since the cable has more stringent requirements, but I'd still be wary. The best idea, if you are spending the time to do cable runs anyhow, is just 5 coaxial cables. Properly shielded coax just has extremely excellent noise rejection and signal transmission characteristics.

The projector should probably come with an input for it already, 5 BNC connectors. You just get a converter for the computer that goes from VGA to RGBHV and then run the 5 coax cables. That'll get you a clean signal to the projector, pretty much regardless of distance.

While it'll probably be a little more expensive than baluns and Cat-5, it isn't going to be a whole lot more and it'll work really well. The only reason to use the baluns is if you just don't have the room to run the 5 coax cables. In that case you probably shouldn't use regular Cat-5 but something like Belden 1352A, which is shielded (and plenum rated). Just remember that when using shielded cable you have to make sure the grounds get properly terminated and connected, it isn't as easy as UTP.

This is just something you want to do right, since it's a pain to install, and since if you have a bad cabling you are going to get a bad signal.
 
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