Malcolm Gordon Posted April 26, 2007 Share Posted April 26, 2007 The 500-seater multi-purpose venue we use has a ceiling mounted digital projector (make/model unknown but could be discovered if significant). This has two VGA feeds with cable runs for connection to laptops either in the control room at the back, or dropped down at stage side for control by the lecturer. The input is selected by infra-red transmitter. The control room connection gives a clean signal from the house laptop. However today, using the same laptop but stageside for a PowerPoint presentation, the picture exhibited an echo reminiscent of a TV picture bounced off a gasholder. On a dark slide bright picture elements were repeated more faintly a short distance to the right, displaced I would guess about 1/25th of the frame. Is such an effect likely to be caused by a damaged cable, or perhaps by signal reflection within the cable that is significant because of the increased length? Is there such a thing as an inline attenuator that would suppress such reflections? I am not sure that the fault has been noticed before, but as a regular user moving from 35mm slide illustrations for talks we are anxious to keep the audience's confidence. Link to comment Share on other sites More sharing options...
mac.calder Posted April 27, 2007 Share Posted April 27, 2007 How long is the VGA run? Anything over about 10m and you start asking for trouble. I would look into getting VGA->Cat5 or VGA->fibre if you need long distances - most venues have Cat5, you just need to make sure your cat5 points don't go through any ethernet hardware (switches, routers etc). It is possible that one of the sync lines is dead, but I think if it is an excessively long VGA run, you will want to look into putting the signal down another medium. p.s. Fibrelink (for fibre) and Magenta Research (for Cat5) have always worked for me - Magentas I have often had over 120m of cat 5 (don't ask!) and they have been fine - and fibre... well fibre is the mutts nuts for long distances. Link to comment Share on other sites More sharing options...
Tomo Posted April 27, 2007 Share Posted April 27, 2007 On a dark slide bright picture elements were repeated more faintly a short distance to the right, displaced I would guess about 1/25th of the frame.This is a classic 'excessively long cable' fault. Look into some of the Cat5 video extender units - the Extron and Kramer units I've used in the past could handle 100m without noticable artifacts. Link to comment Share on other sites More sharing options...
Pete McCrea Posted April 28, 2007 Share Posted April 28, 2007 It might also be worth trying a line driver in there to see if boosting the signal helps the receiving device cope a bit better. Quality of the cable might also be an issue. We have 30m VGA lengths in stock supplied by VDC that haven't caused us any issues when used for feeding projectors with Data sources, but then the O/P device is usually a scaler with a fairly powerful output, or driven from a DA. Again Kramer and Extron both offer suitable line drivers, and VGA over CAT5 Systems. Link to comment Share on other sites More sharing options...
Malcolm Gordon Posted April 28, 2007 Author Share Posted April 28, 2007 The cable run I would estimate at about 30m. It has worked satisfactorily in the past, but I believe that the projector has been changed, which may be a factor. Thanks for the suggestions; I'll pass them on. Link to comment Share on other sites More sharing options...
rubber duck Posted June 20, 2007 Share Posted June 20, 2007 Have a look at the Avocent EMP1000P VGA over cat5 solution. This is a cheap but very good solution to use in this case. R D Link to comment Share on other sites More sharing options...
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