In a radio station, power is generated by a transmitter, usually housed comfortably in a shack, and the RF power is led to the (usually) remote antenna by a cable, or transmission line, which in short wave stations can be several wavelengths long. An antenna tuner is generally placed at the antenna end of the transmission line. Audio power amplifiers are rated as to how many watts they can put out. For example, an amplifier that is used in a home stereo may have a rating of 100 watts per channel. The mathematical equation for power is as follows: P=VI = I 2 R=V 2 /R If the reflected power is zero there will be no standing wave on the line and no excess stresses on it. If the reflected power is zero the generator can deliver its maximum rated power into the load. The difference between the forward and reflected powers is the real power delivered to the load, but: