Above answers are correct. The real question you need to answer is how far appart in angular extent are your favorit stations. The 3db down point either side of the antenna's main axis is refered to by non engineers as the acceptance angle. This means if you slew the antenna that many degrees off the main axis (bore site on the station's transmit antenna)you lose 50 percent of the power at your receiver as delivered by the antenna. So if you have an acceptance angle of 5 degrees (a fairly high gain antenna) and your two favorit stations are 20 degrees appart, there is no way you can receive both stations properly without a rotor to move the axis of the antenna from one direction to the other. On the other hand if you live very close to your stations get an omin directional antenna with a gain of 1 and an acceptance angle of 360 degrees.
