Dipole Antenna

The dipole is a half-wave wire antenna fed at its center. It is the classic reference antenna for HF work: simple, predictable and effective.

Configuration

The wire runs horizontally along the azimuth direction and is fed in the center. The default wire length is 10.1 m; a length of 0 selects the resonant half-wave length for the operating frequency automatically.

Characteristics

• Typical gain around 5.5 dBi over ground, broadside to the wire (peaks perpendicular to the wire run).
• Non-directional in practice: a figure-eight pattern with broad lobes and shallow nulls off the wire ends.
• Typical takeoff angle around 30 degrees at the default 10 m height. Radiation angle depends strongly on height, see below.
• Moderate bandwidth: SWR stays reasonable over several percent of the center frequency; odd multiples of the resonant frequency are also usable.

Height

Height above ground is the dominant tuning knob:

• Below roughly a quarter wavelength, the dipole radiates mostly straight up. That is excellent for short-range regional coverage (a few hundred kilometers via near-vertical ionospheric reflection) and poor for long distance.
• Around half a wavelength and above, a strong low-angle lobe forms and long-distance performance improves markedly.

Sizing

A practical resonant half-wave length in meters is approximately 143 divided by the frequency in MHz (see Antenna Calculations). Examples: about 40 m at 3.6 MHz, about 20 m at 7.1 MHz, about 10 m at 14.2 MHz. Leaving the length at 0 lets SimTX use the resonant length directly.

When to use

A resonant dipole at a sensible height is a strong general-purpose choice on any HF band and a good baseline against which to compare other antennas.