Q: VGA video signal specs
Christoph Maier
does anyone know about the specifications of the video and sync signals
for VGA monitors?
I am trying to send VGA signals over some 180 ft. of cable,
so I'd especially be interested in the required line impedance of the
cables.
Is it possible to produce a Composite Sync signal (or maybe even a
composite video signal) that could be fed into an off-the-shelf VGA
monitor, so I could use only 3 instead of 5 coaxial wires in parallel?
Thanx,
Christoph
Sam Goldwasser
> Hi,
> does anyone know about the specifications of the video and sync signals
> for VGA monitors?
Video: .7 V p-p, (more positive -> brighter).
Sync: separate horizontal and vertical TTL signals. May be either polarity.
> I am trying to send VGA signals over some 180 ft. of cable,
> so I'd especially be interested in the required line impedance of the
> cables.
Line impedence: 75 ohms terminated at both ends.
> Is it possible to produce a Composite Sync signal (or maybe even a
> composite video signal) that could be fed into an off-the-shelf VGA
> monitor, so I could use only 3 instead of 5 coaxial wires in parallel?
RG59 75 ohm coax is what is normally used, but you will need a good quality
cable to go 180 feet without too much signal degredation. Of course, it also
depends on what resolution and thus what video bandwidth you need and how
much dispersion (signal delay as a function of frequency) you can tolerate.
It is relatively easy to combine the sync together, and also with the video
(usually the green signal for 'sync-on-green') but most low cost VGA monitors
do not support this mode and you would then need to separate the signals
at the far end. You could come up with alternative ways of combining the
signals to save on cables but these will all complicate your circuitry at
the monitor end. There are multiple coax cables inside a single sheath
for just this purpose.
--- sam
> Thanx,
> Christoph
Denis Marshall
Maier) writes:
>Hi,
>
>does anyone know about the specifications of the video and sync signals
>for VGA monitors?
>I am trying to send VGA signals over some 180 ft. of cable,
>so I'd especially be interested in the required line impedance of the
>cables.
>Is it possible to produce a Composite Sync signal (or maybe even a
>composite video signal) that could be fed into an off-the-shelf VGA
>monitor, so I could use only 3 instead of 5 coaxial wires in parallel?
>
>Thanx,
>Christoph
According to SAMS Publishing Hardware Bible, the analog voltage level of VGA is
0.7 Volts. A composite video signal is 1 volt peak-to-peak.
Composite signals are acceptable for CGA for 40 column color, 80 column
monochrome, but is unintelligble in 80 column color (I know this from
experience).
Mark E. Rekai
: Video: .7 V p-p, (more positive -> brighter).
What exactly is "more positive"?
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