Which of the following factors affect the feed point impedance of an antenna?
Transmission line length
Antenna height✓Correct answer
The settings of an antenna tuner at the transmitter
The input power level
Explanation
Ground under an antenna reflects energy back into it, and coupling with that reflection changes the current and voltage at the feed point, so feed point impedance varies with height above ground. Feed line length, tuner settings, and drive level change what the transmitter sees at its end of the line, not the impedance at the antenna itself.