VGA over CAT5e

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Hi Guys,

I need to get a VGA signal from the Nav Station in my boat to the
monitor in the bridge. I could just run a VGA cable (about 4m worth)
but I need to pass the cable through some small holes for the looming
(sp?) and the DB15 connectors wont fit unless I make the hole bigger.

I am thinking about running the VGA singal over CAT5e, which a Google
search seems to suggest is possible. I was wondering if anyone had any
better ideas, keeping costs fairly low.

Has anyone here had any success cutting the end off a VGA cable and
wiring on a new DB15 for example?

Thanks in advance,

-Al

Re: VGA over CAT5e


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Al

Well I was going to say different cable for different uses, but then I found
this site:
http://www.geocities.com/dougburbidge/vgaovercat5.html
The author says they've achieved 15 metres.
For the cost of the cable and solder time, worth trying.

If that doesn't work you can get gadgets that convert from VGA to RJ45 and
back again:
http://www.svideo.com/vgacat5.html

Best
Paul.


Re: VGA over CAT5e



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I used to make up  VGA cables for control room applications. 15M using
individual screened conductors was about the recommended limit

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mmm wouldn't surprise me.
I've seen VGA extension cables as short as 2M exhibit ghosting.

P.


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There are well built VGA extension cables (use 75 ohm mini coax cables
at least for RGB signals). Those work generally well.
Also there are those crappy cables built just from general purpose
computer cable with lots of wires inside one outer shield. Those
cheap cables have typically wrong impedance and considerable
crosstalk between signals -> ghosting problems

Then the used resolution + refresh combination has effect.
Almost any crapphy cable works for 640x480 60 Hz resolution
but for 1280x12o4 and higher resolutions the quality of the cable
starts really slow up.

--
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
http://www.epanorama.net /

Re: VGA over CAT5e


On Sun, 5 Oct 2008 21:05:00 -0700 (PDT), BigAl.NZ@gmail.com wrote:

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http://www.google.com/search?hl=en&q=ethernet+vga+extender

generates 257,000  hits.

http://www.google.com/search?hl=en&q=kvm+cat5+extender

generates 140, 000 hits.

Here's a few that look promising:

http://sewelldirect.com/KVMcat5extender.asp

http://www.cablestogo.com/product.asp?cat_id=503&sku=39970






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You would need the skills of a micro-surgeon and a very fine solder
tip.




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I am liking the ethernet idea. I found these mounts I could use which
have sealed end caps for when not in use:

http://au.farnell.com/1254803/connectors/product.us0?sku=3Damphenol-pcd-rjf =
rb71

This way it has a fighting chance of surviving in the marine
enviroment!

-Al

Re: VGA over CAT5e


BigAl.NZ@gmail.com wrote:

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The impedance is different enough that you will get visible reflection
at anywhere close to VGA frequencies.  I believe VGA, like most analog
video signals, is 75 ohm coax (unbalanced).  Matching that to 100 ohm
balanced line is not easy with passive parts.   Using active circuitry
you can generate the balanced signal needed, and convert it back
at the other end.  That takes a number of very fast amplifiers
(I think three video, plus two sync, but I am not so sure about sync
signals for VGA.)

I believe the boxes are commercially available, because it is sometimes
the best way to send video long distance.  (The cheaper cable makes
up for the added cost of conversion.)

If you find the connectors with separate pins that you solder and
then install it isn't too hard.  You still want the appropriate
multiple coax cable, though.

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Finding ready made cables has been easy enough, and finding the
required cable in bulk hard enough, that I haven't tried.

-- glen


Re: VGA over CAT5e


BigAl.NZ@gmail.com writes:

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How about cutting the connector from one cable end, pulling
the cable and then soldering a new one to the end.
Or building entirely new VGA cable the length you want
by soldering the connectors yourself to both ends.
The soldering the cable consisting of several mini
coax condictors and many other conductor DB15 VGA connector
is not the easiest job, but doable if you are good
at building cables. I have done that kind of soldering
myself when I have needed some custon VGA cables for
some applications.    

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Runnign VGA over CAT5e is possible.
There are commercial active adapters that do the conversion  
"right" and work even for some longer distances. Those
cost money but work quite well.
Then in Internet there are some simple plans to run
VGA over CAT5e cables. When you use a shielded CAT5e cable
and not too long distances, those hacks can work quite well
but might not give perfect "crystal clear" picture like
a real VGA cable or commercial converter would give.
Running VGA signal on unshielded CAT5e cable with simple
DIY passive adapters is not a vry good idea: the image
quality will get worse and your cable will radiate
out considerable RF interference which could interfere
for example with boat radios.

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I just gave you several ideas.
 
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Yes. I have done this several times.  

--
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
http://www.epanorama.net /

Re: VGA over CAT5e


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You have lots of replies to this already, but just curious as to whether
you've considered instead putting a small laptop in your "bridge" and using
remote desktop or vnc to control your "Nav Station" (assuming its a standard
pc). You could even go wireless and avoid the need for cable runs all
together.
--
Brian Cryer
www.cryer.co.uk/brian


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VGA cable is shielded
and CAT5 is not, so you would get some horrible ghosting.

BTW, there may still be some ghosting even with VGA cable



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STP CAT5e or CAT 6 would do the trick, and at these lengths the cost
difference isn't an issue.

-John O



Re: VGA over CAT5e


JohnO wrote:

(snip)

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There might be a minimum amount that they will sell, but the
real problem isn't shielding but impedance and
balanced/unbalanced line.

If you transition from a balanced line (UTP) to an unbalanced
line (coax), unless exactly impedance matched, it won't
work right.   UTP cable depends on the voltage and currents
on the two wires being exactly opposite to cancel out and
not radiate the signal.  Coax depends on the voltage on the
shield being zero.  To couple between them you either need
a transformer (if there is no DC component), or active
circuitry such as differential amplifiers.  VGA has a
DC component so you can't use transformers.

-- glen


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You can use a transformer, but wired as a *balun* (coils in series with
the lines instead of across them); this provides the required impedance
transformation while still passing DC.


--
Rich Seifert              Networks and Communications Consulting
                          21885 Bear Creek Way
(408) 395-5700            Los Gatos, CA 95033
(408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

Re: VGA over CAT5e


Rich Seifert wrote:
(snip)

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So that is how they do it.

TV baluns, from 300 ohm balanced to 75 ohm coax, don't do that.

http://en.wikipedia.org/wiki/Balun

Does that restrict which impedance transformation you can make?

-- glen


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The impedance transformation is determined by the winding ratio,
regardless of whether the coils are in series or parallel with the
lines.

Putting the balun in series provides better low-frequency response (down
to DC), but of course this configuration does not provide any electrical
isolation. It functions very much like a common-mode choke, with an
impedance change.


--
Rich Seifert              Networks and Communications Consulting
                          21885 Bear Creek Way
(408) 395-5700            Los Gatos, CA 95033
(408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

Re: VGA over CAT5e


(some newsgroups removed)
Rich Seifert wrote:
(snip)

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(and later wrote)

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I could get out pencil and paper and go through it.

It seems to me that in the series configuration the current
in the center conductor of the coax is the same as in one
wire of the balanced line.  Also, that the transformer has
to be configured so that the shield is at 0VAC.  Again,
with out actually drawing it on paper, I believe that
indicates a 1:1 transformer.

-- glen


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Thethe wrong cable impedance and lack of shileding between
RGB signals will not cause ghosting. Most ghosting will
be caused by the impedance mismatches.

The lack of shield in cable will cause that that cable  
will pick up more easily external interference
and will radiate out more RF interference and properly
shielded VGA cable.


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True. The VGA cables vary in quality. The good ones are good
but there are also bad ones. One thing to keep in mind
in VGA connections is that it is a good idea to keep the
number of VGA connectors along the link minimum (ideally
only at source and destination), because the VGA connector
impedance is not exactly 75 ohms as the system is designed
for, and having many such wrong impedance connectors on
the way will cause impedanc mismatches that cause
reflections. For VGA cables is best to use a correct
length cable in the beginning, and avoid using
orignal cable + extension cable combinations.    
  

--
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
http://www.epanorama.net /

Re: VGA over CAT5e


On Sun, 5 Oct 2008 21:05:00 -0700 (PDT), BigAl.NZ@gmail.com wrote:

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If you are handy with a soldering iron there is no problem. You may
have to buy a new plug/socket though as the one you cut off may be
potted.

Re: VGA over CAT5e


It might be worthwhile to think-out a bit beyond the size of the hole
though which you want to pass this signal.  Stuff like "what will
hold-up best when I'm at the bridge, in a storm, near a rocky shore
and I really need to know where I am?"  I say that only half in jest.

rick jones
--
oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

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