75 Ohm Terminators why?

[ARC Tech-109]

Monitors can sometimes handle the mismatch without issues like streaking, clipping but things like recording equipment need to be terminated as they have a far narrower tolerance before streaking, clipping ect. Digital signalling like SDI & HD-SDI is far less tolerant of the mismatch and must be terminated to work correctly.

[ppppenguin]

SDI and HD-SDI only specify 15dB return loss across the bandwidth but running without a termination will often cause them to fail completely. It's rare to have looping inputs and separate terminations with SDI so the problem doesn't usually arise.

When you come from a traditional professional broadcast environment correct termination isn't even something you think about. You just do it right. I've certainly heard horror stories concerning younger broadcast technicians who have absolutely no idea about how to connect analogue video correctly. One good one was a string of monitors with looping inputs. The tech connected one end of the line to an output of the distribution amplifier. And the other end of the line to another output of the same VDA! Some of the monitors seemed OK, others were mysteriously in monochrome. My friend who was on set told me it took him a while to work out what had happened.

[ChrisW6ATV]

The termination is not super-important when connecting a video source to a single display six or ten feet away, but once you feed a chain of several displays, each 50 feet or more apart, the proper impedance becomes critical.

Think of airport terminals in the days when the arrival and departure displays were all black-and-white. They were all fed with looped composite video in those days. One loose or missing termination (separate piece or built-in switch) would mess up a concourse full of monitors.