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

Reply to
Don
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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

Reply to
John - KD5YI

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

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Reply to
CJT

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

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Reply to
Peter Bennett

Check out

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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.

Reply to
Glenn Gundlach

If it's just analog video you probably don't need a lot of bandwidth, just about any RG59 will do. NTSC not only tops out around 3.58MHz, but corrects amplitude with the color burst...

Reply to
William P. N. Smith

RGB, implies this is not NTSC... Depending on the resolution, bandwidth can be significant. 300MHz for modern large monitors. Most cable maufacturers will offer 'triple co-ax', or 'triple + sync', and for a PC monitor, it'll be the latter that is needed. How careful you need to be, will depend massively on the monitors resolution, and sync rate.

Best Wishes

Reply to
Roger Hamlett

Sorry, last time I did video over coax it was mostly NTSC, either RGB, Y/C, or Composite. Could be anything, the OP probably needs to tell us what bandwidth he needs, though 15 feet isn't too significant, connector losses will probably swamp any differences in cable type over that kind of distance.

Reply to
William P. N. Smith

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

I
Reply to
Don

You could look for a monitor extension cable:

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Good Luck! Rich

Reply to
Rich Grise

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

1600 x 1200 x 75 = 144e6

That's a maximum pixel clock of 144MHz.

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.

Reply to
David Jordan

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:

Reply to
Chuck Wozniak

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

I
Reply to
Don

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

DEC

I

greatly

Reply to
Don

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