Television broadcast towers send over-the-air television signals, which are occasionally referred to as conventional or terrestrial television signals. Over-the air-signals are radio waves that are transmitted from TV towers to the antennas connected to an analog TV set.
Over-the-air broadcast stopped being the only means of watching TV in June 1990 when General Instrument, an American company, showed that digital television signals were possible. These digital signals could produce HDTV signals that provided more than double the resolution of pre-existing analog signal TV images. Additionally, digital TV offered vastly improved sound. Digital television broadcasts through a multiplexed digitally processed signal, involving the transmission of multiple analog message signals that have been combined into just one signal. These digital TV channels can be broken up into multiple subchannels. Conversely, the over-the-air television signals of analog TV are separated by channel.
In June 2009 U.S. television stations ceased the broadcasting of programs in anything but digital TV format. The antennas used to watch over-the-air broadcasts, however, can me modified to allow access to digital programming with the use of a digital-to-analog converter box. Many consumers prefer to use antennas with converter boxes to watch their televisions because they allow free access to local broadcasting channels.