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Discussion Starter · #1 ·
Hi there,


All hype appart, what is so special about an SDI cable? I have seen mention of them being difficult to find and web site selling them for a cool 4 digits price by the foot.


But I can't seem to find a basic description of what it is. From what I understand, it seems to me a basic RG59 with 75Ohms BNC at the end should work fine, no?


For a reference, here's my understanding of what a video cable is: RG59 with 75 Ohms connectors. Take 3 for component, 2 for Svideo, 1 for composite, 5 for RGBHV. Use RG6 if you have long run or high frequency requirements (Ghz and the like). RG59/6 derivatives exist for various environments in term of temp/humidity/agression/CFC/size/convenience, but that's basically it, electrically.


Again, please let's keep any hype/marketing out of this. I am just looking for a concise electrical specification on SDI cables, NOT for an explanation of why the nature of the pigment used to color of the connector plastic ring dramatically affects the picture :)


Thanks for any pointers or info


Fred
 

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with the distances involved in HT just about any video cable is fine. When one is talking about big distances (broadcasters) THen you need the good stuff. FOr example, the "standard" would be Belden 8281. Which costs somewhere around .50$ per foot can go about 1000' with an SDI signal with no issues. THat is the standard.


So in an HT, just about anything will work fine.


And while some will disagree, just try some run of the mill stuff and you will find it works just fine. THe sign that an SDI cable is not enough is that you might start to get sparkles on screen. little sparkly dots will appear from time to time.
 

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As Dizzman has already said Belden 8281 is the industry standard for quoting max cable lengths for SDI in Broadcasting.


RG-6 solid core co-ax will be perfect for SDI in an HT.


However the overlooked part for many SDI solutions in the HT world is that most of the products are not designed or built to Broadcast SDI standards and the drive and receive capabilities of the SDI interfaces are rarely, if ever, quoted.


It would be interesting to see how many interfaces have the eye-height set up correctly (or even how many manufacturers even know what eye height is!)
 

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i started talking to somebody about eye height, and reciever thresholds and got a big blank stare.
 

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Discussion Starter · #6 ·
RichardA & Dizzman,


Would you mind educating us on what are the eye height and threshold, on top of providing me with excellent answers?


Thanks:)


Fred
 

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it would be challenging to explain. There may be a good online tutorial for it though. Also one of the challenges is that you can't measure them without specialized scopes.

http://www.extron.com/technology/archive.asp?id=sdi
http://www.extron.com/technology/arc...tifyingcables1


Suffice it to say. when using a good quality RG 59 or 6 cable, you can get upwards of 200 metres without even trying.


The bigger issues come about when using different devices and building a system. When many manufacturers come into the mix, there are tolerance variations (that are not supposed to be there) that make things look like a VTR may be a problem when it is the monitor that has the problem. This can cause one product to be blamed for an issue when it is another. And without the big heavy sampling scopes, you won't always find the problems
 
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