Antennas can pick up digital or analog signals.
In June 2009, all television broadcasting in the United States switched over to digital, replacing the old analog signals. You may have had a technician knocking on your door to ask if you needed a digital-to-analog converter box. Digital broadcasting works differently, and carries extra benefits over analog. It also behaves differently when there is interference or signal loss.
Analog TV
For analog television, the signals are sent out from the broadcasting station at certain radio frequencies, ranging from 54 to 890 MHz. Each channel falls at a different frequency; really, it's a pair of frequencies: one for video and one for audio. On the receiving end, the television set is constantly scanning across the screen, drawing the image frame by frame. The signal it receives is used to modulate the brightness and color of each pixel as it scans across.
Digital TV
Digital television compresses all the audio and visual data into a single digital signal. This signal, rather than being composed of real-time modulating brightness and color information, is simply made of pulses representing digital bits. The television set, or digital-to-analog converter box, can then interpret these bits to produce audio and video in much the same way that a media player on a computer can read a video file.
Free Space
Representing the information as a single signal of bits allows broadcasters to use less of the frequency spectrum to transmit the same amount of information. This frees up radio frequencies that can be put to use for other things. Some of it is allotted to emergency services, such as police, fire and rescue communications. Other parts of the spectrum have been bought by commercial companies for use in wireless Internet and phone service.
Quality
The compressed digital format of the signal makes it more efficient, so that even while it takes up less of the radio spectrum, digital TV can transmit more information. This allows one television channel to use a higher resolution of picture and sound data (that's what HDTV is), or to send out more than one signal at normal quality, dividing the channel into multiple sub-channels.
Bad Reception
With analog TV, a poor signal can result in a fuzzy picture and distortion in the sound. A little bit will happen with even mild interference, and it gets worse as the interference grows. With digital TV, something different happens. If there is a little interference, the receiver can still put together the signal alright, and you won't notice a thing. At some point, however, the signal degradation is enough that it can't be interpreted. All at once, the picture freezes, goes black or experiences other bizarre, dramatic distortions.
Tags: analog signals, brightness color, digital-to-analog converter, information This, radio frequencies