[mdlug] Looking for a good industrial KVM

[Jeff Hanson]

On Thu, Aug 16, 2012 at 1:37 PM, David McMillan <skyefire at skyefire.org> wrote:
>      My big problem is the VGA.  We just keep having serious problems
> getting the display to work reliably.  The screen tends to be fuzzy,
> have "wipe" effects where certain screen items seem to "smear"
> horizontally, and we've had issues with the color channels losing sync
> (so that an icon would look like three separate red/green/blue copies of
> itself stacked not-quite-perfectly atop each other), and just today the
> KVM that was working halfway decent last week has suddenly lost its red
> channel entirely.  We've confirmed it's the KVM by plugging a test
> monitor directly into the PC's VGA socket, and at that point
> everything's fine.
>
>      The primary constraint I'm dealing with is cable length.  The
> complete cable run is a little over 50 meters.  The KVMs we bought were
> *supposed* to be spec'd for that distance, with a "host" and "slave"
> module linked by a straight Cat5 cable (no TCP/IP involved, no hubs or
> switches, just some sort of proprietary direct protocol) and breaking
> out the VGA and USB cables on each end.  It *looked* like such a simple,
> COTS-solved issue when we started....
>      Adding a remote PC at the far end to act as a VNC or RD client
> isn't in the cards.  I just really need a way to get a plain-vanilla KVM
> to work cleanly and reliably over this kind of distance.
>

That's always a problem with analog connections.  Cat 5E/6 may help
but the symptoms indicate a problem with either the video adapter or
display (borderline signal quality).  It may also be caused by a
grounding problem that is causing a voltage differential across the
cable.  Try connecting the power supplies remote unit to the
workstation's power outlet with a long extension cord to see if it
improves.

One expensive solution is a network-based extender.  This will
eliminate VGA crosstalk problems and you could also use a fiber optic
network connection to isolate grounding differentials.  Fiber is
probably overkill because 10/100/1000-BaseT Ethernet NICs have 2KV
tolerance by design.