There is a clear consensus among poskim that one may not listen to the radio or watch television on Shabbat. Even if the radio or television is turned on before Shabbat so that no melakha is performed on Shabbat, it is forbidden, and for several reasons. First, if there are Jews who work at the station, one may not derive enjoyment from Shabbat desecration.
Second, even if all the station’s workers are non-Jewish, one may not listen to or watch broadcasts because it belittles and detracts from the honor of Shabbat. We already saw (2:9) that some maintain that one may not leave a flour mill running before Shabbat if it will continue to run on Shabbat, because the noise of the grinding detracts from the honor of Shabbat. Listening to the radio and watching television are much more serious. While the mill makes noise that no one wants to hear, one who turns on the radio or television before Shabbat indeed wishes to listen or watch on the holy Shabbat. All would agree that this infringes upon Shabbat’s honor.
Third, it is a weekday activity. Just as the prophets and Sages forbade many things that are reminiscent of weekdays, so that our behavior on Shabbat would be different from that of the workweek, so too we should prohibit listening to the radio and watching television on Shabbat.
Fourth, there is a concern that the radio or television might malfunction, and the listeners or viewers might try to fix it on Shabbat. One might want to raise or lower the volume or adjust the device in some other way (see above 17:2). A similar concern led to the ban on using musical instruments, and the same ban should apply.
For all these reasons, one may not listen to radio or watch television on Shabbat, even when they are turned on before Shabbat. For the same reasons, it is also forbidden to set a timer to turn on a recording device or video or audio player (see Yesodei Yeshurun vol. 3, pp. 50-55; Tzitz Eliezer 3:16; SSK 42:43; Yabi’a Omer 1:20; Yalkut Yosef 318:34-38).