Playing with a piece of RG-58 coaxial cable.

A length of 7.80 meters of RG-58 coaxial cable is connected to the miniVNA 'DUT' port. The measurments were made with the MiniVNApro and vna/J software in 'reflection' mode.

With the end side of RG-58 cable open.

With the end side of the RG-58 short-circuited.

With the end side of the RG-58 cable left open, we have a low impedance (Z) on each odd multiple of quarter wave length and a high impedance (Z) on each multiple of half wave length.
Is just the opposite if we short-circuited the end of the cable.
For calculation you need to take account of the velocity factor of the cable.