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Question about whats going on in a long SVGA cable

B

Biftheunderstudy

Senior member
Whilst procrastinating at work, I noticed that the three colours on the monitor for the security cameras in the store are all separated. What this means is that there are 3 images in red and green on top of the regular picture. The image is after a couple hundred feet of SVGA cable.

Some of the employees seem to think its interference, but I find this unlikely. I've been pondering it for a while and as a physicist I must get to the bottom of it. My friend and I have come up with a few candidates but I'd like to hear some input from you guys.
 
Originally posted by: Biftheunderstudy
Wrong BNC cable for the security cameras? Or just slight impedence changes over the length of the cable?
Click to expand...

It can be either one or both.

I would guess though that its the length of the cable.
Probably a cheap cable that does fine in short lengths.
 
Yeah.. If you're doing long runs SVGA over the 15 pin cable is a pretty terrible idea. Break out each line to BNC 🙂

~MiSfit
 
You're obviously just not up to snuff on the most recent tech that your company has installed. Bust out the 3-D glasses and all will become clear to you. 😛
 
Sounds like the vga cable is running from the DVR/switcher to a remote monitor. I doubt it is a problem with the camera drops themselves.
Those are usually RG59 siamese cable, and I've run that several hundred feet on a regular basis. I've made 100' runs with vga with no problems, but no farther.
Can you view a monitor that is located closer to the DVR for comparison?
 
Different colors are modulated at different frequencies and multiplexed over the line. If there is any nonlinear phase shift in the transmission line, it will be amplified due to the long length. The different colors, being at different frequencies, will be shifted differently and end up out-of-sync with each other resulting in color separation.
 
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