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Is it safe to modify a capture card?

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I am probably going to uy a capture card (Compro Videomate X800) soon. Since one of the uses it will have is capturing laserdiscs and this card doesn't have BNC connector, it would have to be put in.
I was wondering if the required modification could result in an increase of interference and/or otherwise potentially harm the image quality of the captured video. If so, I'd like to know how much image quality would I lose using a BNC-to-RCA adapter instead.
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I use a bnc to rca connector that I bought at radioshack and see no lose in quality.
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If anything it will reduce interference and ghosting to add a BNC connector to the card.

You get an impedence mismatch when using an adapter plug.

It is easy to mod a card to have a BNC input, just make sure of three things.

1) The BNC connector you buy is actually 75ohms for video and not 50ohms for networking.
2) You use mini coax to solder it to the board, bluejean sells mini coax or you can cut open an old monitor cord.
3) the BNC connector is isolated from the backplane, you don't want two separate earth paths.

The hardest part is drilling the dirty great hole in the metal backplane to mount it, you will need to centre punch the hole or the drill will walk all over the place.
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Here is what mine looks like (Video 75ohm)
http://www.radioshack.com/product/index.jsp?productId=2102688&cp=2032058.2032231.2032281&parentPage=family
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Originally posted by: Laserman
If anything it will reduce interference and ghosting to add a BNC connector to the card.


How so?

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By not creating an impedance mismatch. RCA is not and cannot be 75ohms impedance. The video needs to stay 75ohms from start to finish.
If it isn't you get signal degradation, ringing or reflections in the signal.

You can read here for a laymans overview of impedance.

http://www.bluejeanscable.com/articles/impedance.htm