It should be stated that the PL-259, a favorite of the ham world, is not a
constant impedance, either. Some hams go nuts if they see you use one of
those on 2 meters or higher. However, it is simple enough to calculate the
impedance bump at a particular frequency simply by determining the impedance
(using the ratio of diameters and the length of the connection), then
determining what that bump is at a particular frequency.

I did that once, to show a friend that he should not lose sleep over the
connector. It is like inserting a 1" length of 75 ohm coax in a 50 ohm
line. Remember that 50 ohm coax is not necessarily 50 ohms. It is a
nominal impedance, which means it might be 50 ohms, or 52 ohms or even 53
ohms. So, if you are worried about the connector, you should measure the
coax to see what impedance you really want.

RCA and GE both used RCA connectors (commonly called phono plugs) at 450
MHz.

Colin K7FM