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The popular End Fed Half Wave is all things to all men, but this article compares an End Fed Half Wave, Inverted L, and Half Wave Dipole with some common parameters:

• frequency: 7.1MHz;
• flat top length: 20m;
• Height above ‘average’ ground (σ=0.005, εr=13): 10m;
• lossless balun / matching device.

Key differences:

• ground connection: Inverted L = 2Ω, End Fed Half Wave = 100Ω; and
• effective common mode choke used on the dipole.

Above is the modelled gain for all three. Continue reading End Fed Half Wave / Inverted L / Half Wave Dipole

I have noted recently the increasing popularity of the so-called End Fed Half Wave antenna, though the term often includes harmonic operation of the antenna.

It seems that at the heart of common ham understanding of this antenna system is that some kind of two terminal feed device creates a scenario with current on the nominal radiator, and zero common mode current on the feed line. If that feed device is small, its contents bears little influence on the current distribution on the feed line and radiator (the device behaviour approaches that of a simple circuit node).

Above is the kind of current distribution envisaged by many. The equivalent source is shown at the end fed feed point The red curve is the magnitude of current, the horizontal line represents the nominal radiator, and the vertical line represents the common mode conductor formed by the feed line. The feed line is often of arbitrary length, arbitrary route, and it may connect to real ground via an arbitrary impedance. Pretty much everything about this antenna system is random save the length of the nominal radiator. Continue reading The magic of End Fed Half Waves / EFHW