Extended Monitor Cables info needed

[Dan Razzell]

In article <34 at brazos.Rice.edu>
Stephen Miller <miller at gaia.m2c.org> writes:
>X-Sun-Spots-Digest: Volume 8, Issue 63, message 9 of 14
>
>I am going to purchase an 100 foot cable which will allow me to place my
>Sun 3/260 in the computer room, while locating the monitor an office area.

In article <286 at brazos.Rice.edu>
Paul Allen <bcsaic!paula at beaver.cs.washington.edu> writes:
>
> I have the high-res mono monitors of four 3/280's located on the ends
> of 50-foot cables.  Someone (perhaps my local field engineer) gave me
> a description of Sun's monitor and keyboard cables and I had a local
> cable-maker build 50-foot duplicates.  We've been running this way for
> over 6 months.  The keyboards work fine, but there's noticeable
> horizontal smearing on the monitors.  Switching to a bold font helps.
> For the price we paid, I'm fairly satisfied, but I'm not sure I'd do
> it again.

For the past year or so I have been gathering and testing various bits of
wisdom on the subject of Sun monitor cabling from Sun Spots and elsewhere.
The arrangement I will describe below works perfectly for us with Sun's
high res monitors at fifty feet, and would probably work at 100, at least
I can say so for our particular keyboard cable.  The horizontal smearing
problem that Paul Allen describes is probably caused by a bad impedance
match in the cable.  Check the specs on the cable to be absolutely sure
it's rated at 75 ohms.  If that is okay then I can only think the problem
is inductive.  If so, it should get worse if the cable is coiled, so you
might try that to see what happens.

The Sun monitor cable has a differential video signal as well as
horizontal and vertical retrace.  Phil OKunewick
<okunewck at gondor.cs.psu.edu> claims success using twisted pair for the
differential signal, but the Belden 8777 shielded twisted pair I used had
the wrong impedance and did in fact cause smearing anyway.  I think one of
his arguments against coax was not to carry one of the video signals on
the shield, and of course that makes sense, so if you do use coax you need
to put the signals inside.  I don't understand how he avoided the
impedance problem if he really used plain twisted pair, but there is a
cheap solution if it works.

I'll just mention that for the time when we were using the wrong cable, we
lived with the smearing by making the background raster on the screen a
random dot pattern rather than the usual checkered texture. That keeps
down the resonance at high frequencies.

VIDEO CABLE

  Use any 4 x 75 ohm coax, 22 ga stranded works fine at 50 feet, probably more.
  We used Comprehensive Video CVC-RGBS, which puts four cables in one jacket.
  DB-9 connectors.

  Pin	Signal	    (From Sun Hardware Installation Manual)
  ---	------
   1	video +
   2
   3	H sync
   4	V sync
   5
   6	video -
   7	ground
   8	ground
   9	ground

KEYBOARD CABLE

  We used Belden 8458, 22 ga stranded works fine at 100 feet.
  DB-15 connectors.

  Pin	Signal	    (From Sun Hardware Installation Manual)
  ---	------
   1	recv kbd
   2	ground
   3	trans kbd
   4	ground
   5	recv mouse
   6	ground
   7	trans mouse
   8	ground
   9	ground
  10	power
  11	power
  12	power
  13	power
  14	power
  15	power