General exam question G9D01

WhyA horizontal dipole placed between 1/10 and 1/4 wavelength above the ground is most effective as a near vertical incidence skywave antenna for short-skip communications on 40 meters during the day. For NVIS-style short-skip communication on 40 meters, a horizontal dipole mounted low, between about 1/10 and 1/4 wavelength above ground, throws most of its radiated energy nearly straight up, which is exactly the steep, high-angle path NVIS propagation depends on, answer A. A vertical antenna, regardless of height, favors low radiation angles rather than the straight-up angles NVIS needs, and a horizontal dipole raised to a half wavelength shifts toward lower-angle DX radiation instead of the steep NVIS angle, so B, C, and D are wrong.