Cable length and then some

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Cable length and then some
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Mindblower
Montreal, Canada
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March 21, 2009 - 9:51 am
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I plan on using two computers that share one monitor. Both systems would be used infrequently, thus the question of how long can the cable connecting computer to monitor be? I'd need to at the very least double the cable length if I decide to manually disconnect each time I plan on using one setup. Ideally a cable switch box would work best, but it does add to the length. I have (can get access to all the parts), so this is not my problem. I notice some form of coupler (shielding) at either end of this cable, so is there another problem I need to address in this cable switch box (with the short length of wire)?

Kindly don't keep me in suspense too long, Mindblower!

"Light travels faster than sound;
That is why some people seem bright until you hear them speak"

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David Hartsock
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March 22, 2009 - 1:57 pm
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Wow, Mindblower, that's kind of a loaded 'what if' question!

There are a lot of variables here, but this will give you a rough idea...

1. If your connection is VGA or DVI(analog) the max theoretical length is probably around 100ft. The max real life distance is probably closer to 50ft without a device to buffer/isolate the signal. Now the longer the cable the lower the bandwidth it will be able to transmit without one. This means lower resolution and less color depth. This assumes you are using high quality cable. Lower quality cable will mean less distance and less resolution/color depth. Another issue would be grounds and this would depend on your home/office wiring. Monitors on different outlets using a simple switch may have different ground potentials. This would result in a noisy display or rolling video to a point where it may not be useful.

Now, adding a switch where you would have to alter the shielding of a quality cable would also lessen the usable length. Your best bet is a good quality KVM switch. A quality KVM can go from over $100 for a simple 2 port unit to $1000 for a professional 8 to 16 port unit. A high quality switch is going to run upwards of $50. Might as well go with a KVM.

2. The DVI(digital) spec is 5 meters, but they are usually good out to 25th. They do make amplifiers which allow you to go well past 25ft and closer to 50. Ground issues would not be an issue because the signal is digital, nor would resolution/color depth issues. It's either there or it isn't.

3. HDMI is usually good to 50ft with quality cables. Ground issues would not be an issue because the signal is digital, nor would resolution/color depth issues. It's either there or it isn't. If you need more distance than that you will need to look into external devices, which will be pricey and may not work if you require HDCP(high bandwidth digital copy protection) connections. HDCP is a pain in the a** and (in my mind) the main failure of HDMI, but that is another story.

The most important aspect when using any long cable connection is well made quality cable with large conductors and high quality shielding - and they aren't cheap. This is especially true with the increasing cost of copper.

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Mindblower
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March 23, 2009 - 11:18 am
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Thanks Dave. I'm only planning to spend less than $25.00 CAD (taxes included) for the entire project. My price list (not actual).
1 to 2 video cables about $2.00 each
1 to 3 male to female adaptors about $3.00 each
1 box about $5.00
either several dpdt switches about $0.35 each
or 1 above switch with several relays about $2.00 each

I can purchase a monitor used for under $40.00 (20'') or new under $150.00 (14"). The switch box would only save me the disconnect/connect time (since I'd still be using two cable lengths for each with one adapter) but this is where shielding kicks its ugly roots. The unshielded wire length is less than a foot (being generous here).

Guess I should of mentioned this previously, Mindblower!

"Light travels faster than sound;
That is why some people seem bright until you hear them speak"

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David Hartsock
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March 23, 2009 - 10:38 pm
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If it's only $25 I would give it a try. It will be a fun project either way. If the monitors are close it will probably work. You may also do some searching on line. You may be able to find a cheaper KVM for close to that price.

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Mindblower
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April 8, 2009 - 5:06 pm
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Problem solved. Checked out an electronics outlet (no big brand name - just low prices on parts) and to my delight found an already built switch box which can supply 5 outlets for $15.00 (CDN). Blows the mind since I thought that if they made switches for printers (back in the days before the USB port), why not for VGA monitors.

Important lesson to learn is to visit (if in you area) such places since great deals seldom. I've tried using 2 6' cables with the box and see no loss of signal. Since the store sells cable lengths up to 100 ', my tiny extra is nothing, Mindblower!

"Light travels faster than sound;
That is why some people seem bright until you hear them speak"

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David Hartsock
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April 8, 2009 - 7:48 pm
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Glad to hear it Mindblower!

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