Take a look at:http://sosnick.uchicago.edu/BNC_50_75.html
And then look at the BNCs on your equipment.
Unless all of your cables and equipment is new, as in since
~2000, I bet you have a lot of 50 Ohm BNCs in your facility.
It is real simple: plastic "inserts" in the business end mean
you have a 50 Ohm BNC. And for analog/NTSC it doesn't
matter.

Terry