Chart of end-effect correction factors
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An end-effect correction factor is applied to calculations of antenna wire lengths, and is dependent on
the ratio of wavelength to wire diameter, the λ/d ratio.
This λ/d ratio can take a wide range of values, as shown by this table:
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λ/d ratios by band and wire diameter
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Chart of dipole feed-point impedance vs. apex angle
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A flat dipole in free space has a characteristic feed-point impedance of ~73.1 Ω. When situated above real ground,
however, the impedance will be somewhat less.
When a dipole is configured as an inverted vee, the feed-point impedance will depend on the included apex angle of the
antenna: the smaller the apex angle, the smaller the impedance.
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Feed-point impedance by apex angle
The table and chart show the variation by included apex angle for an inverted-vee dipole in ideal conditions over
perfectly conducting ground.
It is recommended to keep the included apex angle between 90° and 180° - if it is less than 90°, the feed-point impedance
rapidly decreases, thereby lowering the radiation resistance, and will lead to increased coupling between the two legs of the
antenna. This will result in poor antenna performance.
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Chart of dipole feed-point impedance vs. antenna height
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A flat dipole in free space has a characteristic feed-point impedance of ~73.1 Ω. When situated above real ground,
however, the impedance will be somewhat less.
When a dipole is situated above real ground, its' feed-point impedance is found to vary with its' height above
the ground.
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Feed-point impedance by antenna height
The table and chart show the variation by height in wavelengths above ground for a flat dipole in ideal conditions over
a perfectly conducting ground.
Situating a dipole antenna too low above the ground can result in a low feed-point impedance, low radiation resistance, and
increased capacitive coupling of the RF field with the ground, leading to poor antenna performance.
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Chart of inverted-Vee dipole length correction factor vs. antenna apex angle
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A flat dipole in free space will resonate at its' design frequency. In the real world, however, in a dipole configured as an
inverted-vee, the resonant frequency will be found to increase with the antenna's central apex angle, while the bandwidth at
resonance will decrease.
In order to counteract such an increase in resonant frequency, it is necessary to lengthen the dipole "legs" by
a small amount, dependent on the apex angle, to bring the antenna to resonance at the desired frequency.
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Inverted-vee dipole - length correction
factors by apex angle
The table and chart show the variation by apex angle for a dipole configured as an inverted vee.
An inverted-vee dipole antenna with an apex angle between 180° (a flat-top) and 90° will function well; angles below 90° will
result in poor performance.
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