Explanation: A resonant Hertzian (or half-wave) antenna's physical length is approximately half the wavelength of the signal it's designed for. Wavelength and frequency are inversely proportional ($\lambda = c/f$, where $c$ is the speed of light). Therefore, if you reduce the physical length of the antenna, you are making it resonant at a shorter wavelength. A shorter wavelength corresponds directly to a higher frequency. To maintain resonance, a shorter antenna must operate at a higher frequency. Option A is incorrect as it states the opposite of the correct relationship. Options B and C describe issues related to amplifier linearity, mixer performance, or impedance mismatch, not the direct effect of physical length on an antenna's fundamental resonant frequency.