Most radio and RF distribution systems for transmitters
are 50 Ohms. A lot of test equipment is 50 Ohms.
But TV uses 75 Ohms in both video and RF distribution
systems. I have dug through all of my refference books,
inclding one from 1947 and even that far back, when color
TV was still a dream, they used 75 Ohms.

I must have slept through this in class 30 years ago
becvause I am sure there is a logical explanation.
Does anyone know why TV video, antenna systems?("F" connectors),
and cable all use 75 while real radio uses 50 OHms

Bonus quesiton: How can you tell a 50 Ohm and a 75 Ohm
BNC connector apart just by visual inspection?

And guess which BNC was most commonly used in TV facilities
up until HDTV came along?

Terry