Any recommendations for a KVM extender?

August 28, 2006 5:37 PM

Any recommendations for a KVM extender?

I bought an ATEN KVM extender running 50 feet over STP cat 5e cable, and I'm getting slight sharpening/ghosting on my monitors.

posted by phirleh to Computers & Internet (9 answers total)

We used a Belkin Omniview extender at work. I didn't notice any monitor issues, though the mouse did act a little sluggish sometimes.
posted by Popular Ethics at 8:02 PM on August 28, 2006

Why not network the computers and use some software like Anyplace Control? You are introducing the opportunity for lots of interference along such a long distance. You could try shielding the cable but I'm not usre that would help much.
posted by JJ86 at 6:11 AM on August 29, 2006

The extenders use cat5 network cable, and presumably an IP based protocol. The "interference" issue shouldn't be any greater than any other ethernet network. That said, you can't cram video at 1024 pixels x 768 pixels x 24 bits / pixel * 30 frames / second = 500 Mb/s, down a cable with a maximum throughput of 100Mb/s, without some occasionally noticeable compression.
posted by Popular Ethics at 7:11 AM on August 29, 2006

Just because it's cat5 cable doesn't mean it's using any kind of networking protocol. In fact, you can roll your own "extender" for distances of the order of 50' just by using plugs and wire; no electronics required.
posted by flabdablet at 8:01 AM on August 29, 2006

I found out recently that shielding isn't part of the specification, so not all Cat-5e cable is the same. Foil-wrapped Cat-5e cable grounded at one end may improve your performance (assuming what you have isn't shielded).
posted by cardboard at 8:54 AM on August 29, 2006

I'm just curious why you are trying to access a monitor that is 50' away from one of the computers?
posted by JJ86 at 10:28 AM on August 29, 2006

Response by poster: For JJ86, the computer is an Avid for editing video, when its in the room with me its noisy and hot (many external drives, digital betacam tape deck), so I moved it into an air conditioned machine room and put the wires through the ceiling, so the only thing in the room is my keyboard, mouse, monitors, video screen and mixer. I originally had mistakenly purchased unsheilded cat5 cable (UTP) and it was slightly ghosty, but when I got the sheilded cat5 (STP), I didn't find too drastic an improvement. Thank you for all of the suggestions though.
posted by phirleh at 7:59 PM on August 29, 2006

Does your cat5 adapter in fact just dump the raw video signal straight out of your graphics card onto the cat5 without any kind of electronics in between? If so, does it actually connect the cable shield to the signal ground connections?

According to the forum I linked above, it's that shield-to-signal-ground connection that makes the cable impedance drop from 110 ohms to somewhere closer to 75 ohms, which it needs to be to match the output impedance of your graphics card and the input impedance of your video monitor.

Impedance mismatches cause part of the signal to bounce back along the cable from the point of mismatch, and these reflections will show up on your screen as ghosting.

Also according to the same forum, not all shielded cat5 is created equal; some brands work much better than others.
posted by flabdablet at 6:23 AM on August 30, 2006

Response by poster: flabdablet
The keyboard, mouse and vga run into a console box then they are connected to the cat5 and then a remote box splits the keyboard, mouse and vga back into the computer. It could be the cable brand, I might just have to live with it. If not, maybe I'll try playing around with the refresh rate on the monitor, see if it makes a difefrence, thanks.
posted by phirleh at 6:00 AM on August 31, 2006