Antennas

Antenna Length (1)

  • A half wavelength in free space is 150 ÷ ƒMHz metres long
  • The velocity of a wave in antenna wire is less that in free space, so antenna lengths are shorter than equivalent free space lengths
  • This fact coupled with the capacitive effect of end insulators mean that a half wave antenna is about 5% shorter than its free space length.  Use of insulated wire reduces this by a further 3 – 4%
  • The starting figure generally used for the length of a half wave antenna is:
           142.5 ÷ ƒMHz (metres)   or   468 ÷ ƒMHz (feet)