Rhombic Math & Design
Updated: Nov 25
Good symmetry is of vital importance for the performance of this antenna. The width of the antenna's main lobe is determined by the angles q and a, often referred to as tilt and apex angle. In general, the wider the rhombic (greater a and smaller q) the wider the beam and vice versa. Of coarse q and a are linked since the sum of half the tilt angle and apex angles is always 90 degrees: q/2 + a/2 = 90
Effective Antenna Aperture Calculator below is useful. Antenna gain G is directly proportional to the antenna aperture A and is increased by means of focusing radiation in only one direction while reducing radiation in all other directions. So, the narrower the width of the beam, the higher the antenna gain.
a 14dBd antenna on 7 MHz is Ae 6,014.99624 m²
a 14dBd antenna on 14 MHz is Ae 1,503.74976 m²
Capture area or Effective Aperture is determined by antenna gain and the wavelength, not by antenna physical size.
The big antennas use wire rope, not copper wire to carry the weight and to keep wire sag lower. The most suitable metal is relevant in relation to the mechanical properties of the install. For rhombic antennas the concern should be using maximum size wire/cable rather than the conductivity of the material. Larger is also better for RF skin effect, and a traveling wave antenna will be terminated anyway.
General Steve Walz, V31KW/K0UO