Extra exam question E9A12

WhyAn antenna with 6 dB gain over an isotropic radiator has about 3.85 dB of gain over a half-wavelength dipole. Since a half-wavelength dipole itself has about 2.15 dB of gain over an isotropic radiator, converting a 6 dBi figure to dBd means subtracting that 2.15 dB: 6 minus 2.15 works out to approximately 3.85 dB over a dipole, answer A. The other figures come from adding instead of subtracting that 2.15 dB conversion, or from an unrelated calculation.