What is a use for an antenna analyzer other than measuring the SWR of an antenna system?
A. Measuring the front to back ratio of an antenna
B. Measuring the turns ratio of a power transformer
C. Determining the impedance of an unknown or unmarked coaxial cable
D. Determining the gain of a directional antenna
Well, you’re not going to use an antenna analyzer to try and figure out the windings on a power transformer. At least I hope not. Totally the wrong tool for the job.
Actually measuring the front to back ratio and the gain of a directional antenna requires specialized equipment, since it needs to measure the power output by a radio. An antenna analyzer generally doesn’t do that.
So, we’re left with C. Determining the impedance of an unknown or unmarked coaxial cable.
But why are we able to do this with an antenna analyzer?
Simply put, to the point of view of the analyzer, the coax is just another antenna. It has two components, the center conductor and the shield, and therefore a labeled 50Ω length of cable should have a characteristic impedance of 50Ω. If you measure this differently, then it means there is a problem with the cable. Either a section is open, shorted, or damaged in such a way that it allows the two conductors to interact. In fact, many antenna systems rely on the antenna-like properties of coaxial cable to function, requiring specific feed-line lengths, etc.