Which of the following improves the efficiency of a ground-mounted quarter-wave vertical antenna?
Installing a ground radial system✓Bonne réponse
Isolating the coax shield from ground
Shortening the radiating element
All these choices are correct
Explication
A ground-mounted quarter-wave vertical returns its antenna current through the earth, and soil is a poor conductor, so that return path dissipates power as heat. Buried or elevated radials give the return current a copper path instead, cutting loss resistance and raising efficiency; shortening the element lowers radiation resistance and makes efficiency worse.