If you made a quarter-wavelength vertical antenna for 21.125 MHz, approximately how long would it be?

To find the practical length of a quarter-wavelength antenna in metres, you use the standard metric formula: Length (m) = 71.3 / Frequency (MHz). The constant 71.3 naturally accounts for both the quarter-wave division (300 / 4) and the velocity factor of the wire. Plugging in the given frequency: 71.3 divided by 21.125 MHz equals approximately 3.37 metres. The distractor 6.77 metres would roughly be a half-wavelength for this frequency, which is why using the correct formula multiplier is essential.