The demiquad is a single-element one wavelength quad antenna. The length of the antenna is, like the cubical quad beam antenna , one wavelength. Figure shows a type of demi-quad based on the tee-cross type of mast.
The impedance-matching section is a quarter-wavelength piece of 75-Ω coaxial cable (RG-58/U or RF-11/U). The length of the matching section is determined from:
L is the overall length, in feet
FMHz is the frequency, in megahertz
V is the velocity factor of the coaxial cable (typically 0.66, 0.70, or 0.80)