75 Ohm Coax Recommendation for an RGB Cable
 

From what I have read, RGB video cables are 75 ohm impedance. However, I
have never seen a recommendation for the RG number (or other qualifier). I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be greatly
appreciated!!

Thanks!

Don

Don wrote:
From what I have read, RGB video cables are 75 ohm impedance. However, I
have never seen a recommendation for the RG number (or other qualifier). I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be greatly
appreciated!!

Thanks!

Don


RG59. Belden 1426A has 8.5 dB/100ft loss at 1 GHz.

Alternately, RG6. Belden 1694A is 5.9 dB/100 ft at 1 GHz.

If you can't find those, just pick up any old RG59 at Radio Shack or Fry's
and try it.

Good luck.

John

Don wrote:
From what I have read, RGB video cables are 75 ohm impedance. However, I
have never seen a recommendation for the RG number (or other qualifier). I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be greatly
appreciated!!

Thanks!

Don




Probably RG-6 would do the job -- cheap and reasonably low loss.

--
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minimize spam. Our true address is of the form .

On Thu, 14 Jul 2005 01:34:37 GMT, "Don" wrote:

From what I have read, RGB video cables are 75 ohm impedance. However, I
have never seen a recommendation for the RG number (or other qualifier). I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be greatly
appreciated!!

RG-59 seems to be the standard small (0.25 inch) 75 ohm coax -
however, different makes may be of differing qualities.




--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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John - KD5YI wrote:
Don wrote:
From what I have read, RGB video cables are 75 ohm impedance. However, I
have never seen a recommendation for the RG number (or other qualifier). I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be greatly
appreciated!!

Thanks!

Don


RG59. Belden 1426A has 8.5 dB/100ft loss at 1 GHz.

Alternately, RG6. Belden 1694A is 5.9 dB/100 ft at 1 GHz.

If you can't find those, just pick up any old RG59 at Radio Shack or Fry's
and try it.

Good luck.

John

Check out
http://www.belden.com/
We use 1505 at work for component serial digital video 270 Mbit rate
and for short runs of 1.5Gbit (HDTV) and plain old analog video. 1505
is 7.6dB/100 ft at 1GHz. We get it for $180/1000 ft and Kings BNCs for
$1.45 each. For the longer runs its 1694. I use 1694 at home for off
air HDTV antenna lead. It was the lowest loss RG-6 size I found.

GG
Always make NEW mistakes.

First of all, "Thanks!" to everyone who has commented so far! Your insights
have been extremely helpful.

Some additional info for things that folks have had to make assumptions
about:

The signal is an RGB video signal with sync on green (i.e. there are only
three outputs - RGB - from the video card to the monitor.

The system is an old DEC Alpha VME system. I have not been able to dig up
any info on the video output. General consensus in the lab is that the
display is running at 1280x768, but since the system is currently down for
maintenance, no way of really checking.

The monitor is a DEC 21" VRCX1-WA with RGB and high density DB15 inputs.
Obviously, we are using the RGB inputs. The monitor it self is spec'ed at
1600x1200 at a 75Hz update rate. This should give the upper end of the
video bandwidth, but I am not sure how to convert it into an equivalent
video bandwidth in MHz.

Right now I have got my hands on some double shielded RG-59 and looking for
some 75ohm BNCs. Our lab has a boat load of 50 ohm stuff, but one poster's
comments about the connectors being the weak link have me real concerned and
I am going to try to minimize any impedance mismatch. Unfortunately, the
video card end is a basic DB-15 (not the normal high density type used for
PC video).

Again, thanks for the help!

Don







"Don" wrote in message
nk.net...
From what I have read, RGB video cables are 75 ohm impedance. However, I
have never seen a recommendation for the RG number (or other qualifier).
I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be greatly
appreciated!!

Thanks!

Don

On Fri, 15 Jul 2005 02:18:05 +0000, Don wrote:

The signal is an RGB video signal with sync on green (i.e. there are only
three outputs - RGB - from the video card to the monitor.

The system is an old DEC Alpha VME system. I have not been able to dig up
any info on the video output. General consensus in the lab is that the
display is running at 1280x768, but since the system is currently down for
maintenance, no way of really checking.

The monitor is a DEC 21" VRCX1-WA with RGB and high density DB15 inputs.
Obviously, we are using the RGB inputs. The monitor it self is spec'ed at
1600x1200 at a 75Hz update rate. This should give the upper end of the
video bandwidth, but I am not sure how to convert it into an equivalent
video bandwidth in MHz.

You could look for a monitor extension cable:
http://www.google.com/search?q=monitor+extension+cable

Good Luck!
Rich

On Fri, 15 Jul 2005 02:18:05 GMT, "Don" wrote:

First of all, "Thanks!" to everyone who has commented so far! Your insights
have been extremely helpful.

Some additional info for things that folks have had to make assumptions
about:

The signal is an RGB video signal with sync on green (i.e. there are only
three outputs - RGB - from the video card to the monitor.

The system is an old DEC Alpha VME system. I have not been able to dig up
any info on the video output. General consensus in the lab is that the
display is running at 1280x768, but since the system is currently down for
maintenance, no way of really checking.

That's an odd size, 1280x1024 or 1024x768 would be normal.

The monitor is a DEC 21" VRCX1-WA with RGB and high density DB15 inputs.
Obviously, we are using the RGB inputs. The monitor it self is spec'ed at
1600x1200 at a 75Hz update rate. This should give the upper end of the
video bandwidth, but I am not sure how to convert it into an equivalent
video bandwidth in MHz.

1600 x 1200 x 75 = 144e6

That's a maximum pixel clock of 144MHz.

Right now I have got my hands on some double shielded RG-59 and looking for
some 75ohm BNCs. Our lab has a boat load of 50 ohm stuff, but one poster's
comments about the connectors being the weak link have me real concerned and
I am going to try to minimize any impedance mismatch. Unfortunately, the
video card end is a basic DB-15 (not the normal high density type used for
PC video).

You'll be glad of that when you solder your RG59 to it, the
high-density DE-15s are a pig to solder conductors that thick to.


Dave.

Actually, the pixel clock rate may be closer to about 190 MHz.

A typical raster scan monitor uses a horizontal retrace blanking time
that is typically 20% of the total horizontal line time. In this
particular case the monitor would need 2000 pixel clock cycles/line
(1600 Active and 400 Blanking). That takes the clock rate up to 180 MHz.
Adding in some additional blanking time for vertical retrace and you are
close to a 190 MHz dot clock

--
Chuck Wozniak

David Jordan wrote:



1600 x 1200 x 75 = 144e6

That's a maximum pixel clock of 144MHz.

Thanks to everyone who responded!!

Looks like I am going to go the RG-59 cable with BNCs on one end and the DEC
DB-15 on the other.

Don





"Don" wrote in message
nk.net...
From what I have read, RGB video cables are 75 ohm impedance. However, I
have never seen a recommendation for the RG number (or other qualifier).
I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be greatly
appreciated!!

Thanks!

Don

Used about 18ft of RG-59 and BNCs and it works!





"Don" wrote in message
hlink.net...
Thanks to everyone who responded!!

Looks like I am going to go the RG-59 cable with BNCs on one end and the
DEC
DB-15 on the other.

Don





"Don" wrote in message
nk.net...
From what I have read, RGB video cables are 75 ohm impedance. However,
I
have never seen a recommendation for the RG number (or other qualifier).
I
am looking for a good quality cable as we want to go about 15ft with the
signal. (Moving a monitor from one part of our lab to another.)

Any suggestions, recommendations, links to FAQs, etc, etc will be
greatly
appreciated!!

Thanks!

Don