projector setup over 20mtr cable run

jackrussell007

hi folks

I'd appreciate some help for anyone that can advise me on how to get the below setup working properly.

we have a NEC projector at work that I need to celing mount. I cant remember the exact model. (will post tomorrow). The cable run is approx 20mtr. The projector has VGA and DVI-I inputs. I want to use both, one will be connected to a board room computer, the other will be connected to a desktop electrical box that we have fitted into the board room table. The idea was that the DVI-I should go into the board room pc and the VGA port is available for anyone with a laptop that needs to use the projector (by plugging into the outlet box)

the setup I was advised to get by a leading cable manufacturer was to buy 2 of their VGA to CAT5 converters and set it all up using them, I can convert the DVI-I to VGA using a spliter cable. they had sent on a bunch of long cabling at first but non of it worked(long story). anyway the testing I did with a hp pc I had around the place demonstrated that it would work perfectly well if the resolution was set at 1280 x 1024 on VGA. When I connect a laptop however with the very same settings, I get a lot of distortion on screen. the top of the projection is being pulled off to the side, why does this happen?? Why would it display differently between the desktop pc and the laptop, both are set to display at 1280 x 1024.

If I set the laptop to 800x600 it steadies the image and displays it properly but this is useless to us, (high end workstation used for CAD applications) I havent even got to trying the DVI-I setup yet.

How do people send video over very long distances, such as in university lecture halls, is it sent over CAT5 or is there so other way of boosting VGA or DVI-I?


any help is greatly appreciated

ZENER

Unlikely that an analogue video signal of such high frequency will take kindly to that sort of journey. You will need to spend a few bob on a well screened cable for it to work and even then you may just about manage 1024 x 768.

Given that most modern laptops and computers now come with a HDMI socket (If they only have DVI then use a DVI<>HDMI convertor) why not use a DVI to HDMI convertor at the projector and use a HDMI<>CAT5/6 converter for the long cable runs over CAT6 cabling terminating in a HDMI Switcher into which you can connect your sources ?

I'm sure there are probably better options but that's just one that came to mind for such a long run.

Ken

jackrussell007

Hi Ken

thanks for your reply.

I began my search by looking for a couple of high quality 20mtr cables. When the cable manufacturer explained that this may still be an excessive length to get a reliable signal over, it was instead advised that buying 2 x 10mtr cables with a booster in the middle might be a better option. In the event what they actually sent was 2 x 10mtr VGA cables with a VGAto CAT5 converter in the middle. This did not work at all but after some testing I found that the problem was not the CAT5 extender but was the length of the cables being plugged in. I found that the cat5extenders worked fine with a standard VGA cable out of the pc, into the extender, over 20mtr of cat5, into another converter, back into standard length VGA cable and into the projector. I even tested this same setup using 50mtr of CAT5 and while there was some loss of picture clarity, it was more than useable. THe only difference is that this was all tested on top of a table with the cable sitting on the table rather than running through walls over power lines etc. This was tested and worked fine at 1280 x 1024 resolution.

I should mention that when I setup the original pc that I did all my tests on, the picture is fine, its just when I setup the laptop for testing that I run into trouble. Is there a difference in signal strength or power output from laptop to laptop?

Is there some other way of getting a signal over that distance? Can it be sent wirelessly? (edit....I would only need to send a wireless signal about 12 foot from floor to ceiling) I'd love to know how they were sending it over such a long distance in my old lecture hall, it must've been over 25mtr and didnt seem to be at a low resolution.

jackrussell007

Its a NEC NP500G by the way
thanks

ZENER

With that setup you still have over 25 meters of unbalanced video cable which will be susceptible to local interference as you've already discovered.

If the DVI<>HDMI option really isn't a goer then try removing the 20 meter VGA cable and use a standard 1.5 or 2 meter cable but replace the shortfall with longer CAT6 cabling. I suggest CAT6 rather than CAT5 because of the higher spec and technical capabilities regarding higher frequencies.

In other words try to reduce as much as possible the length of unbalanced cable. If you're unsure about the difference have a look here. Primarily refers to audio but the principles are the same.

Ken