A transmitter is delivering radio frequency (RF) energy into a coaxial cable with a characteristic impedance of 50 ohms. The cable is terminated by a purely resistive load. What value of load resistance will absorb all the RF energy it receives?

Maximum power transfer and zero signal reflection occur when the impedance of the load perfectly matches the characteristic impedance of the transmission line. Since the coaxial cable has a characteristic impedance of 50 ohms, terminating it with a purely resistive load of exactly 50 ohms ensures that all the radio frequency (RF) energy is absorbed by the load (such as an antenna or dummy load) rather than being reflected back to the transmitter. If the load were 25, 100, or 200 ohms, there would be an impedance mismatch. This mismatch would cause some of the RF energy to reflect back down the line toward the transmitter, creating standing waves and a Standing Wave Ratio (SWR) greater than 1:1.