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Maximum Cable Length?  

post #1 of 16
Thread Starter 
I tried searching for this, but nothing came up.

I purchased a 25' breakout cable (HD15 to 5BNC). However, I purchased the cheapest one I could find (It was like $30). Do you think I am experiencing a loss in picture quality? Should I upgrade my cable, and if I go with a quality cable, what would be a good length to shoot for?

Thanks.
post #2 of 16
What projector/source/scaler?

25' is pretty long for a 'cheap' cable, so yes, you are most likely experiencing a loss in picture quality. Ringing/smearing/general softening of the image.

The length to shoot for is: As short as possible, and always try to use the best cable you can. The longer you need to go, the better the cable needs to be. The higher the resolution and the better the equipment, the better you cables need to be in order to not introduce a noticeable loss.

I have a cheap 6' VGA -> 5BNC that I've used in a pinch. Looks like crap. Lots of smearing, generally soft image. Cost about $10.

The cable I have installed permanently is a BetterCables 25' VGA -> 5BNC that cost me 25x as much. No loss in picture quality, but more expensive. see here: http://www.bettercables.com/vgato5bncs.html

The best cables you can use would be ones you make yourself by using high quality runs of Belden cable. I forget what model, but it's their best coax.

If I was doing it all again, I'd probably go the DIY route and solder BNC's onto a panel on the back of my HTPC so that I could make my own 5BNC -> 5BNC cables.

Kal
post #3 of 16
Thread Starter 
I'm running a Marquee 8000 with an HTPC with an older dual-head video card. So, I guess some steps to improve my picture quality would be to upgrade video cards and cables.

I'm interested in how you plan on soldering the 5 BNC connectors onto your HTPC. I guess the main part I am confused on is how you plan to hook the BNCs to the signal from the video card. This sounds like a great plan.

Care to explain? Thanks.
post #4 of 16
The M8000's a great projector so you deserve to feed it with a good quality cable and possibly a newer video card. You don't need anything too fancy on the video card front to get 95% of the picture quality. Any inexpensive video card from the ATI Radeon line will do well, and the newer NVidia cards are getting good marks but I'm not up on what's what on that front really.

To hook BNC's from the video card you simply need to locate where the 5 lines originate from on the video card and solder on mini-coax's or something similar. Good soldering techniques are required since it's pretty fine work.

Here's an example of Mike Parker's MP-1 mod with BNC connectors:

http://www.wisdom-technologies.com/MP-1-2.jpg

While the two sync signals are actually connected to the VGA output pins, the RGB lines are connected before a LCR low-pass filter on the other side. So again, you have to know a bit what you're doing.

If you want to let someone else do it and get a better image to boot because of other mods, get one of Mike's cards. More info here: http://www.wisdom-technologies.com

Kal
post #5 of 16
Thread Starter 
Would you know where to acquire the parts for a DIYer?

Sounds like a fun project.
post #6 of 16
Pretty much any electronics store (Digikey, Mouser, etc) will have BNC connectors and mini-coax. I don't know what type of mini-coax to use... there are many types, so better then others. Try searching this forum for "mini coax" to see what others have used in similar projects.

Kal
post #7 of 16
What about asking Paul (GN2) to make a short breakout cable, then a longer run of 5bnc coax? He makes nice stuff that's affordable with hi quality components.
post #8 of 16
Thread Starter 
I think I'll give this a shot. I notice in a pic of the other side of that 9700 pro (viewable on the wisdom tech site) that there is an extra circuit board (light brown in color) that doesn't seem to be standard with that card. I am assuming that is part of the MP-1 mod.

Is there still a way to tap into the RGB before the low pass filter? Would this project be possible on a Radeon 7500, or what minimum Radeon card would you recommend?

Thanks.
post #9 of 16
Quote:
Originally posted by lanstyle
Is there still a way to tap into the RGB before the low pass filter? Would this project be possible on a Radeon 7500, or what minimum Radeon card would you recommend?
It's possible on any video card... I've been bypassing the low pass filters on video cards since I had a Voodoo1 card in the mid '90's.

To find the right place to connect from, simply trace back the R, G, B lines from the VGA connector one at a time. You want to connect right before you hit the 75Ohm terminating resistor.

The newer Radeon's are supposed to be better, but I'm still running an old 7200. Remember that it's more important to have a good RGB analog output stage then fast 3D graphics, so some of the newer cards will do nothing for you in terms of 2D picture quality. Same is true for some of the OEM card. White the graphics processing unit (GPU) may be from ATI, the rest of the board is sometimes their own so you never know what you're getting in terms of quality in the 2D output section.

Which cards have the best 2D image quality? I have no idea... haven't really looked into this in detail for years I'm afraid.

Kal
post #10 of 16
Thread Starter 
When you say "right before" the 75 ohm resistor... do you mean it is still part of the video chain or is it (effectively) removed from the video chain?

Thanks.
post #11 of 16
Like this:

GPU -> 75 Ohm resistor -> X -> Low pass filter -> VGA connector

You would connect at "X" using good quality mini-coax to your own BNC connectors.

Kal
post #12 of 16
Thread Starter 
Hey kal,

I have sent you a private message asking for locations of the RGB feeds on the Radeon 7500. I was hoping that it might be comparable to your 7-series so that you could provide an explanation of where to look for the low pass filter that you were describing. I am unable to locate it. Feel free to reply here or by private message. I will post an explanation here (and how the project is going) after I get it all figured out.

Thanks.
post #13 of 16
Hi Lanstyle,

Got your private message at the same time I saw this, so I'll answer here:

"I just received my Radeon 7500 and I was looking for where to attach the 5 mini coax cables. I believe I have located where to install the two sync cables (at least in the right region, the exact pin location I have not determined, nor do I know how to figure this out)."

The two sync cables can go right on the VGA connector (as Mike P. does with his MP-1 mods). The other 3 have to go here like I've said:

GPU -> 75 Ohm resistor -> connect mini-coax's here -> low pass filter -> VGA connector

I'm afraid I can't get more descriptive then this without actually seeing the card itself. All cards are laid out differently. It can't be described any other way. You really need to trace back the lines to make sure you get it right.

I'm afraid that if you don't know how to trace back the lines from the VGA connector then I really don't recommend you try attaching these mini-coax's yourself. The cards have tons of small surface mount parts you really need to have some solder experience with small parts like this. You'll most likely break the card by applying too much heat/breaking parts or traces/creating shorts.

Kal
post #14 of 16
I use a 30 foot run of Belden 1694a RGBHV and the pix are superb, this is Mike's cable of choice, forgive me but I trust Mike in whatever he recommends :D

On this subject I just dropped $ on all 100% authentic canare tools to make custom Belden 1694a cables with true 75ohm bnc and rca connectors,
Now I can make anything I want at anytime
I think I will start selling custom made cables as very few places use 1694a to make cables

-Gary
post #15 of 16
Thread Starter 
kal,

I already ordered the parts and I'm not too worried if I break a $39 video card. I understand the risks. Would it be possible for me to take some hi-res pics of my video card and email them to you, and you point out the locations on the pictures? I would need your email (feel free to PM it to me, or my email is mr_lanstyle@hotmail.com).

Thanks again
post #16 of 16
I've sent you an email... Send me the pictures and I'll see what I can do.

I can't guarantee anything, as the easy way to do this would be with a multimeter to check the traces and make sure you've got the right 75 Ohm resistor. (The parts aren't always labelled clearly since they're so small and hard to read).

Kal
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