What is an End Fed Half Wave (EFHW) Antenna?

What is an End Fed Half Wave (EFHW) Antenna?

Going through the QRZ.COM pages of many Amateur Radio operators, I came across EFHW or End Fed Half Wave Antenna often. Unlike the centre fed half-wave dipole antenna, feed point is at a high voltage point of the radiating element instead of at the high current point. While the centre fed half-wave dipole resonates at odd multiples of half-wave length, EFHW operates at odd and even multiples of a half wavelength. This would mean a truly multi-band operation for the Radio Amateur!

But EFHW has high feed point impedance of around 5000 Ohms unlike the 72 Ohms of the centre-fed half wave dipole which matches easily with a 50 Ohms coaxial cable. This necessitates the use of a matching transformer for EFHW. This matching transformer is called ‘unun’ as it matches an unbalanced antenna to an unbalanced feed line. A small counterpoise is used beyond the feed point. As EFHW is a single wire, it is easy to setup, especially for portable operation.