What is the approximate length for a 1/4 wave monopole antenna cut for 28.5 MHz?

Explication

A quarter-wave monopole is half the length of a half-wave dipole, so its length is 234/f = 234/28.5 = 8.2 feet, about 8 feet. The 16 foot choice is the half-wave dipole length at 28.5 MHz.