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

Active 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

Active 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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