Calculation method
Linked Dipole Calculation Formula
The basic calculation begins with the wavelength:
λ = c / f
where:
- λ = wavelength;
- c = speed of light;
- f = frequency.
A free-space half-wave is:
L = c / (2f)
A practical wire dipole is normally shorter than the free-space
half-wave, so a correction factor is applied.
Half-Wave Dipole Length
Using frequency in MHz and length in meters:
Total dipole length ≈ 149.896 × K / f(MHz)
where K is the selected correction factor.
For K = 0.95:
Total dipole length ≈ 142.40 / f(MHz)
Each dipole leg is half the total:
Each leg ≈ 71.20 / f(MHz)
The linked dipole calculator applies the same principle to every
selected frequency.
Velocity Factor
The correction factor accounts for the fact that a practical
resonant conductor does not behave exactly like an ideal
free-space half-wave.
If a custom factor is entered, the calculator uses it directly in
the starting-length calculation.
Do not confuse this wire correction with the velocity factor of a
coaxial transmission line. They describe different propagation
conditions and should not automatically be treated as the same
value.
Wire and Insulation Correction
Insulation, conductor diameter, construction, nearby materials,
and end effects can all shift resonance.
For that reason, two antennas cut to the same nominal frequency
can require slightly different final dimensions even when both
calculations are mathematically correct.
Use a wire preset for a convenient starting estimate, then verify
the assembled antenna with an analyzer.
Inverted V Correction
The geometry of an inverted-V changes the electromagnetic
environment of the dipole. Bringing the ends lower and changing
the included angle can affect feedpoint impedance, coupling to
the ground, and resonance.
There is no single universal shortening percentage that
guarantees the correct result for every inverted-V installation.
Calculate a reasonable starting length, install the antenna in
its normal geometry, and tune it by measurement.
