How the calculation works
Frequency and wavelength are related by the propagation speed of the wave. In free space, electromagnetic waves travel at the defined speed of light: 299,792,458 metres per second.
Where λ is wavelength in metres, c is 299,792,458 m/s, and f is frequency in hertz. To work backwards:
Worked example
This is the free-space wavelength. A practical half-wave dipole is not simply cut to exactly half this number in all circumstances; physical construction, conductor diameter, surroundings and end effects alter the resonant length. The dedicated antenna-length calculator will deal with that separately.
Frequency units
- 1 kHz = 1,000 Hz
- 1 MHz = 1,000,000 Hz
- 1 GHz = 1,000,000,000 Hz
Why this calculator uses the exact value of c
Rules of thumb such as 300 ÷ MHz are convenient at the bench and usually adequate for mental arithmetic. This calculator uses 299,792,458 m/s so that the displayed mathematical result is reproducible and unambiguous.
What this calculator does not include
It does not apply coaxial-cable velocity factor, dielectric propagation velocity, antenna shortening factors, loading coils or environmental detuning. Those belong in separate calculators because they represent different physical problems.