I heard that a 1/2 wave vertical has a Z of about 2000 ohms at the base.
Is this the Z between the base of the vertical and ground that RF at the
resonant frequency
'sees' ?

Doesn't the height that the vertical base is above ground affect this
2000 ohm valve?
Or does then metal car roof nullify any height above ground affects on
the Z?

I've noticed that measuring the return loss of a 1/4 vertical is very low.
But measuring the return loss of a 1/2 wave or 5/8 wave antenna is
higher.??????????????