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'[OT]:Video card output in dos?'
2000\05\25@044301 by Graham North

Hi all.

You may remember a post by me asking how many monitors could be powered from
one graphics card.  Well I am still playing with multiple monitors.

Here is my problem.

I race model cars and my local club is holding a regional event in a couple
of weeks.  The software used runs in dos (it needs total control of the com
ports).  We would like to have monitors around the track for the refs and

There is a system we could buy but it would cost over £400.

My friend suggested the idea of using a TV card with an analogue output and
send the picture via coax to portable TV's set up around the track.

What I am trying to ask is whether there will be an output from the card
while the dos software is running?

Sorry for the long post, hope someone can help me on this.  If you have any
other ideas how I could do this then please let me know.


Graham North

2000\05\25@045344 by Michael Rigby-Jones

{Quote hidden}

The answer is a definate maybe.  I have an NVIDIA Riva128 card with TV out,
and also an ATI Expert@Play (Rage Pro chipset I think).  TV out works OK,
under windows, but when the PC is booting and still in text mode, my TV
(addmitedly rather ancient) dosen't seem to be able to handle whatever
refresh rate the card is giving out, I get a flickering, rolling picture
(maybe defaulting to NTSC?).  I've not tried booting striaght into DOS which
I imagaine would give the same results, but I can use a DOS box under

The composite output is a 50 Ohm source which must be correctly terminated.
You can't just feed it to lots of TV's without serious picture degradation
(and it's bad enough to start with)  You will need some kind of distibution
amp, which should be reasonably simple to make using e.g. high speed op-amps
or a discreet transistor design.

So I guess the answer is that it probably depends if the card you are going
to use has some kind of dos support such as a utility run from
autoexec.bat/config.sys to setup the TV mode properly.



2000\05\25@050629 by Graham North

Thanks for the info.

What exactly do you mean when you say it must be terminated properly?

I was planning on connecting the output from the card into a cheap TV mains
amplifer, and connecting the other TV's to this.

Is this OK?


Graham North
       {Original Message removed}

2000\05\25@055944 by Michael Rigby-Jones

No, the output of VGA cards with TV out is not a (75 Ohm) UHF signal, it's a
50 Ohm composite video signal, at least on all the cards I've seen it is.
You will need to have some form of composite video in on the TV's, such as
either the old phono style connector or the newer Scart type.  The video
output from the card has an impedance of 50 Ohms.  To correctly terminate
this and stop reflections which really upset the picture, you must terminate
this with a 50 Ohm load.  Now the TV composite in is a 50 Ohm load, so
normally you would just plug the video out on your card to the back of the
TV and everything would be fine.  If, however, you try to connect the same
source to two TV's, it will see a load of 25 Ohms (50/2).  You will still
get some kind of picture, but the chances of "ghosting" occuring are quite
high, and on a computer generated signal this means that any text will be
pretty well unreadable.

You could ouput the compostite signal into a modulator to convert this UHF
and then distribute it with an aerial amp, but you will definately lose a
lot of quality.  The modulators come in small metal cans that accept video
in, sometimes sound in, power and have a coax connector for the TV out.
Nintendo etc use them to connect their consoles to a TV.

The proffesional solution would be a proper distribution amplifier, but I
suspect that this item will have a "professional" price tag!



> {Original Message removed}

2000\05\25@060607 by Graham North

Thanks Mike

Not had any experience with TV cards as you may be able to tell!

I made a 'splitter' ( two monitors from one graphics card ) last night and
witnessed the degradation of the signal.

However this may well be the way to go.


Graham North
       {Original Message removed}

2000\05\25@111937 by Alan Brumley

What I would do is this:
Sorry to hear you talking in Pounds, cause I don't know if we will have the
same stores in common.
Buy/Rent/Steal a vga to NTSL/PAL converter people use them for presentations
to hook into a TV.  Feed the output of that into the input of a VCR.  Take
the output of the VCR (what you would normally run to the TV) and if
necessary, run that through a signal amplifier.  They sell them at "Radio
Shack's (American store that we love to hate).  The one I have here has a
plug (for 110V) and a coax input.  Then it has two coax outputs.(A splice of
the first one)  They are useful for pulling weak VHF TV stations.  Since
your VCR is "broadcasting" on VHF, that should let you run several TV's just
by splicing the coax.  And setting each TV to channel 3 or 4, whatever your
VCR is set to.

You should be able to do it all for under $100 (again, US money)  The VGA to
PAL/NTSC would cost the most.  We ran three TV's from one VCR at an old
apartment, and we didn't even have the signal amp.  Signal was perfect.  (Of
course that could depend on the VCR)

{Original Message removed}

2000\05\25@185031 by Gennette, Bruce

Several problems here -

1. Turning 25line x 80char x 16colour text video display into domestic video
2. Turning video into a TV channel
3. Transporting the TV signal all around your venue

For 1. You have to buy a VGA-to-video converter, you have several choices,
the best being a video card with TV out, next best is a presentation quality
external VGA-to-video converter
For 2. You could buy a dedicated modulation unit, but every video recorder
has one already built in . . . [Attach a TV antenna to the VCR too to make
the system more user friendly - everyone can watch the news while waiting
for the races to start]
For 3. You need either -
       A. For a few short, separate runs, a distribution amplifier (store
bought about US$50, home built about US$25), a 4 way splitter and a maximum
of 100m of co-axial cable (75ohm).
       B. For a single long cable run with multiple taps along it, a
powerful distribution amplifier, and a series of progressively weaker 'T'
taps and up to 500m of co-ax.  This system amplifies the signal way above
what a TV can handle to pump it through to the end of the cable, so each tap
has to divide the signal into a full strength pass-through and a reduced
strength local signal.  All unused taps (and the end of the cable) need a
75ohm terminator fitted to avoid unwanted reflections of the TV signal.

3.B. is the best method.  If you go this route you will need to study
distribution (not hard) to work out what values each tap should be.  I would
also suggest making the cable runs a permanent installation, so buy good
quality (not domestic) co-ax.


       {Original Message removed}

2000\05\26@030749 by Robert Rolf

picon face
If you are planning to be ONLY in DOS mode, then option one has few
choices. Only the ATI 'all in wonder' cards will come up in TV mode
in DOS. All the others (AFAIK) require the winblows driver to be
The ATI card autosense a connection on it's video out connector and
automatically comes up in the appropriate refresh rate.

The ATI card also fiddles with the color burst phase to remove 'dot
which can make graphics blurry. (Don't know if it does this in PAL mode
since PAL is more picky about it's line to line phasing).

I wonder why you can't run the program in a DOS box in Winblows.
does a really good job of 'virtualizing' the I/O ports, and if you go
the the DOS prompt properties you can give the program 'exclusive' use
of the ports, and high enough priority that it shouldn't screw up.
Have you also tried 'booting to DOS' which usually leaves the winblows
device drivers in place?

The ELSA synergy video card has a neat feature in that you can run
Windows 9x, and have the video output come from any ONE subwindow,
including a DOS box (or the whole screen).

Remember that encoded video (PAL or NTSC) has substantially LESS
than your basic VGA screen. Unless the text is quite fat, it will be
UNREADABLE, particularly if you distribute it as RF rather than base
video. (NTSC RF BW is 4Mhz, about 240 lines of resolution, vs the 320
(since its 'cycles' of resolution) of a 640 pixel wide display. PAL RF
is about the same. Only SECAM has better RF bandwidth because the
scheme is much different.

1-C would be, point a good quality camera at a good monitor, and
that signal. The camera optical system then performs the antialiasing
function. You'd want an older, tube type camera because it's longer
persistance will mask out the banding flicker that you usually see with
CCD cameras pointed at monitors. (Or use are really MODERN CCD camera
which has a 'low speed' sutter (15Hz).

3-C If your venue is small enough get one of those 'TV Rabbit' type of
signal rebroadcasting devices (like used to 'view your VCR/DTH anywhere
in the house) ($50US) and ship the signal to the TV's over-the-air in
the UHF

Have fun, and be sure to test the system well before race day.

"Gennette, Bruce" wrote:
{Quote hidden}

>         {Original Message removed}

2000\05\26@071539 by Albert Noah

Actually, the STB Velocity 128 runs in DOS just fine. Be sure to have the
RCA jack connected and the monitor cable disconnected when you boot. I got 2
at a local computer show for $30 each. They actually work pretty good.

{Original Message removed}

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