I wish my 'scope (DSO-X 2024A) had switchable input Z (50/75/1M) as I do loads of RF and video work.
I have to use T pieces and terms - very messy - easy to use the wrong term.
Using a spectrum analyzer and a tracking generator is a great way to show the effect of a stub.
Why would anyone put a 75 ohm terminator on a 50 ohm connector. There are 75 ohm BNCs, although they are rare these days. Beware of these things, as they cross-mate mate too easily with a 50 ohm BNC, and bust it.
Adding 50 ohm termination is not cheap if you do it right. You need a switch, and it probably needs to be a physical switch. If you switch in a 50 ohm terminator while the maximum permitted voltage is applied to the input there would be considerable power dissipated, so you also need protection too.
When the input switching of scopes was largely mechanical a 50 ohm terminator setting was much more common. Quite a few scope didn't have proper protection, though, and dealing with overdissipation in the terminator was a common reason for repairs.
When working with video you have to use a 75 ohm term. I use 75 ohm cable and a 75 ohm term plugged into a 50 ohm T-piece into the 'scope. The T-piece doesn't appear to suffered having the wrong BNC plugged into it. I would not risk a 75 ohm BNC plugged directly into the 'scope.
If you weren't meant to look at video then why give us all those video triggering modes?
Oscilloscopes are meant for the viewing of many types of signal, but the oscilloscope doesn't provide every possible interface needed for that.
If you have a real 75 ohm BNC it has a thinner pin in the middle, so its impedance is higher. They easily mate with a 50 ohm BNC, but the narrower socket will be stretched by the thicker pin. I have no idea when they didn't make the outside part of the 75 ohm version fatter to get the right impedance in a way that wouldn't allow false mating.
These days its common to find a 50 ohm BNC on the end of 75 ohm cables. YMMV.
Sorry,but that doesn't make sense!
If a 75 Ohm BNC centre pin was narrower than that of a 50 Ohm one, how could that damage the latter?
Perhaps the other way round!.
Over many years of dealing with 75 Ohm video systems in analog TV Broadcasting,I have found it was standard practice to use "50 Ohm" BNCs on the end of 75 Ohm coax--- they make them to fit RG59,etc.
With the advent of Digital TV,& the necessity of piping baseband digital video around the Studio,the racks were rewired with "real" 75 Ohm BNCs,as were any test leads,etc.
At the time,(1999),the only difference I could discern with the plugs was that the insulation on the 50 Ohm ones was brought right up to the front of the connector,whereas with the 75 Ohm one it was not.
There was never any question of incompatibility.
Looking at a manufacturer's site,unless I misread,the part number for the centre pin is the same for both versions,but the different insulation coverage is plain in the diagrams.
http://www.gordontech.com.au/catalog.htmThere is a definite difference in centre pin size in
"N" connectors,where the 75 Ohm one will cause damage to the 50 Ohm version,but that is a different matter.