Than answer is, each station is on a different frequency, just like the radio in your car. You can pull up to a traffic light, and get noise on one station, another is perfect, yet the antenna cable from the antenna to the radio is the same for both stations. Something could be affecting the frequency specific to the station you are having trouble with, and not affecting other frequencies. Also, if another station is on a frequency close to the one you are getting interference on, or shares that frequency, then it could affect the other station as well.