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)