Explanation: A directional wattmeter measures both the forward power (from the transmitter to the antenna) and the reflected power (from the antenna back to the transmitter). Standing Wave Ratio (SWR) is a critical indicator derived from these two values, showing how efficiently the antenna system is matched to the transmission line. Placing the directional wattmeter between the VHF transmitter and the coaxial transmission line *connected to the antenna* (Option A) allows for accurate measurement of the entire antenna system's performance under actual operating conditions. This setup determines how much power is delivered to the antenna versus how much is reflected due to impedance mismatch. Option B is incorrect because disconnecting the antenna from the coaxial line would invalidate the SWR measurement; you would essentially be measuring an open circuit, not the antenna system. Option C is incorrect because an artificial antenna (dummy load) is used to test the transmitter itself, not the performance of the installed antenna system. Option D is insufficient because a simple in-line RF power meter measures total power but cannot differentiate between forward and reflected power, which is essential for calculating SWR.