Would someone like to explain to a thicko (me) what is the actual difference between a 75
and 50
BNC and would I tell them apart?
Easy with a new toy like capt bullshot has got....a VNA ! ![DMM :-DMM](https://www.eevblog.com/forum/Smileys/default/smiliey_dmm.gif)
To spot that difference, one must have $$$ cal kit and cables, too ...
Only for accurate measurement as you will still see the differences. ![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)
What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm? Does it reflect energy at higher frequencies, or something like that?
I don't have a 75Ohm cable with a 50Ohm connector fitter (or vice versa), so I can't show that.
I've compared two BNC tees using a very simple (and non-calibrated) setup here. The VNA shows the "open" response, which ideally should be just a flat line at 0dB):
It's one of the "better" 50 Ohm cables (checked using the 1502 TDR), connected to an 50Ohm tee and a 75Ohm tee (by the looks, don't have any specs of them).
So the result isn't totally as expected, as the 50Ohm tee looks worse than the 75Ohm one hat higher (some GHz) frequencies. Normally, one would expect the 50Ohm one to look better in a 50Ohm setup
Comparing the tees at the TDR does judge the 75Ohm "better" than the 50Ohm tee in a 50Ohm setup, too ...