Plain-language answer: Fifty ohms is a practical industry compromise between power handling and loss in coaxial systems, so radios, meters, cables, and accessories commonly use it as their reference impedance.
Why it matters in the antenna
It is a system convention, not a natural impedance every antenna must have. Matching networks transform other useful antenna impedances to it.
What to verify
Name the reference plane and impedance for every SWR or power measurement.
The common mistake
Changing a good antenna solely because its natural feedpoint is not 50 ohms.
Operating boundary
Use the exact documented component, geometry, frequency, power, duty cycle, clearances, and feed/return system. Begin tests at low power and stop for heating, arcing, damaged insulation, or unstable supports.
