Same cable for BNC, SDI and Composite?

kayut

Standard Member
Hi,
I wanted to know if SDI, BNC and Composite cables are all the same (maybe Coax) or not only the connectors but also the cable are different??

Thanks
 

Alan Mac

Well-known Member
SDI and Composite video both use 75 Ω coaxial cable.

SDI uses 75 Ω BNC connectors.

Composite video may also use 75 Ω BNC connectors, though for consumer video applications it is more usual to employ RCA / phono connectors.


Alan
 

kayut

Standard Member
Great!
Many thanks for your answer.

Does it mean that I can use the same 75 Ω coaxial cable with a BNC connector for a SDI input and also for a Composite input??
 
Last edited:

Joe Fernand

Distinguished Member
AVForums Sponsor
Use BNC > BNC for SDI.

You can use the same BNC > BNC cable for Composite to Composite - though you will require BNC to RCA adapters if your Composite video devices have RCA sockets.

Joe
 

Alan Mac

Well-known Member
Does it mean that I can use the same 75 Ω coaxial cable with a BNC connector for a SDI input and also for a Composite input??

In principle you can use the same cable and connectors for SDI and composite video.

BUT:

The SDI cable must of necessity use proper 75 Ω BNC connectors because the digital signal bandwidth extends into the gigahertz region.

However, the BNC connectors fitted to video equipment are often 50 Ω even though the internal terminating impedance is 75 Ω over the video bandwidth. While this has no significant effect on the low-bandwidth composite-video signal, there may be a mechanical problem in trying to mate a 75 Ω plug with a 50 Ω socket.

50 Ω and 75 Ω BNC connectors may differ slightly in their physical dimensions, so that a thinner 75 Ω pin on the SDI cable may not make proper contact with a 50 Ω socket.


Alan
 

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