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Author Topic: vga hardsplitter, long run powerpoint issue§  (Read 3386 times)

Jerome Casinger

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vga hardsplitter, long run powerpoint issue§
« on: January 29, 2010, 01:26:01 pm »

Hi there,
an office a couple doors down installed 2 computers with 100' vga cables that are mounted on ends of the hallway.  (They had itsomewhere else and they were never used so they moved them around).  They procurred a new laptop and have a hard split vga cable to send the signal to both big screens.  I assume they need a real distributor/amplifier.
Tv1 if its the only one plugged in works great.
TV2 by itself, image quality is terrible especially with white background (powerpoint is all they are running). When a slide with black background and pictures came up the image quality was excellent. Then a white background would come up and the image was terrible.
TV1 and TV2 plugged in on the splitter, TV1 flashes no input, TV2 shows the same degraded signal.

I imagine an amplifier should fix this as it would split the signal properly, but the screen having bad quality with white backgrounds, but perfect on others has me stunned.  Could that be fixed potentially by the spliter/amplifier as well?

Thanks guys, if you have any good reccomendations for an amplifier it would be appreciated.  100' vga is going to each monitor.

Sorry for mispellings fat fingering on blackberry
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Bernard connolly

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #1 on: January 30, 2010, 05:44:43 am »

Hi
Absolutely sounds like an active splitter is needed. Long VGA runs tend to pick up interference if they have budget then VGA over Cat5 solution would be much better. If not even a cheap splitter will help.

Bernard

Don Boone

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #2 on: January 30, 2010, 04:06:31 pm »

You need a VGA 1x2 DA and maybe another cable.

Don
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Gerry Seymour

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #3 on: March 06, 2010, 04:06:11 pm »

Bernard connolly wrote on Sat, 30 January 2010 04:44

Hi
Absolutely sounds like an active splitter is needed. Long VGA runs tend to pick up interference if they have budget then VGA over Cat5 solution would be much better. If not even a cheap splitter will help.

Bernard


+1

I run an active splitter at conferences. I run 100' VGA to  the splitter, then 100' VGA from splitter to each projector. Never an issue.

That said, if I were starting over today, I'd run it all over ethernet cable with baluns. The overall cost would be similar, with easier replacement of cabling and connectors.
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Gerry Seymour

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Jerome Casinger

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #4 on: March 06, 2010, 08:16:49 pm »

Thanks everyone for the tips, I definitly would not have done VGA but it was the hand that was dealt.  We pickup up an active splitter and of course it made a drastic improvement.  Not perfect, but thats because I know what I am looking for.  One of the tvs shows slight shadows around the text, but unless you are looking for it its not noticible.

Thanks again!
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Jason Rose

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #5 on: April 16, 2010, 01:11:38 am »

The TV with the low quality can have a poor cable to begin with. Id start by swapping the wire and seeing if it improves. A kink or interference can be causing this issue.

An active splitter (I highly recommend Kramer VP200K) would be recommended.

Are we allowed to post links? If not, mod please edit this an notify me.

http://www.avshop.ca/distribution-amplifiers/computer/kramer -vp-200k-1-2-high-resolution-uxga-distribution-amplifier
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Brad Weber

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #6 on: April 16, 2010, 09:32:39 am »

When discussing a product I believe that it is generally preferable to link to the manufacturer where there amay also be supporting information such as product data sheets, manuals, warranty info, etc.


There are some points that are commonly overlooked in discussions like this one.  The first is that "VGA" has become a generic term and now rarely actually means 640x480 resolution.  This is important as the image resolution can have a significant bearing on the viability of long cable runs.  Higher resolution relates to greater bandwidth and greater bandwidth relates to larger cable losses.  So on longer runs what works fine for one resolution may not work as well, if at all, for higher resolutions.

Another factor is the cable itself.  There can be tremendous differences in the performance of various 'VGA' cables, especially if the comparisons may also include bundled 5 wire coax (RGBHV).  One problem is that the "VGA" cables that many people buy don't actually provide much information about the cable much less any technical data such as losses at various frequencies.  But on longer runs the differences can be significant.

The source and display devices are also factors.  How good a signal does the source provide?  How degraded a signal can the display receive and still provide an acceptable image?

The point is that saying simply "we run VGA X feet" has limited meaning, there are multiple factors involved that could potentially make that result specific to that application and not relevant to another application.


You have to look carefully at distribution amplifiers as they are not all the same.  A good example of this is to look at the Kramer Electronics DA products page as they show something like 13 different products that all have one HD15 VGA input and two HD15 VGA outputs but with various bandwidths, with or without audio, with or without cable EQ, etc.  Many lower cost DA devices buffer the outputs and offset the loss of the split but provide no additional amplification or processing.  Other products provide adjustable signal gain and/or cable equalization (which compensates for the greater losses at higher frequencies that are typical of cable losses).  For units with adjustable gain and/or EQ, some products address all outputs the same while others allow individual outputs or groups of outputs to be adjusted independently, which can be useful in situations such as having one short run and one very long run from the DA.  Given the situation with the one display, that indicates that adding a DA that simply offsets the split loss will probably not solve that problem, but one with cable EQ and/or adjustable gain might help.
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Brad Weber
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Don Boone

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #7 on: April 17, 2010, 01:22:53 pm »

The quality of cables vary all over the place, even from reputable manufacturers. Years ago I was in the Infocomm booth with the local rep who told me not to use their prefab VGA cables. He said even the long ones didn't use coax for the RGB part of the signal. I suspect that's changed now but I still get spooked by a VGA cable over about 25 feet.

Don
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Chris Young

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Re: vga hardsplitter, long run powerpoint issue§
« Reply #8 on: April 19, 2010, 03:40:19 pm »

I've had my issues with long runs and 'VGA' cables but I've never had an issue staying at 100' or less, running at 1024X768.

Last year though, through a comedy of errors, I ended up running over 200' using premolded cable, and as a result I learned a few things.

Firstly, I've cut open plenty of these cables and I have never seen 5 coax.  Always 3 coax with the remainder TP.  

I'm pretty sure that on these long runs it's more an issue of skew on the sync than signal attenuation.  The reason that I say this is that I had 2 identical runs going side by side all the way to two identical projectors, and one worked, and the other didn't.  I put in amps at the source and 50' short of the projectors, and they never made much difference.  Ultimately I tried break out cables so that I could go sync on green, and while I got a picture out of it, the box I was using to do it (Extron RGB109 IIRC) degraded the resolution too much, but it did work.  I was lucky really, as it was only certain laptops that wouldn't work.  I never spent the time to troubleshoot further, as the whole installation only lasted a year and now the building is being renovated.

My point is, that from now on, I'll run proper 5 coax cable whenever I have to go more than 100'.  I do a lot of these types of installations, and I usually opt for the pre-molded stuff for a few reasons.  It's cheap, it works, and the id bits remain intact.  This last one is nothing to scoff at these days with laptops getting more difficult to coax a signal out of when they don't think there is something to send a signal to.  The other thing to watch for is whether your particular amplifier strips the id bits out or not.  

Cheers,



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