Why A half wavelength in free space is 150/f(MHz) meters, so at 14.10 MHz that is 150/14.10 = 10.64 meters. An air-insulated open-wire line has almost no dielectric loading, so its velocity factor is essentially 1.0 and the physical length matches the free-space electrical length. In feet the same calculation is 492/f(MHz) = about 34.9 feet.