Receiving Signals
The television system for each country will specify a number of television channels within the UHF or VHF frequency ranges. A channel actually consists of two signals: the picture information is transmitted using amplitude modulation on one frequency, and the sound is transmitted with frequency modulation at a frequency at a fixed offset (typically 4.5 to 6 MHz) from the picture signal.
The channel frequencies chosen represent a compromise between allowing enough bandwidth for video (and hence satisfactory picture resolution), and allowing enough channels to be packed into the available frequency band. In practice a technique called vestigial sideband is used to reduce the channel spacing, which would be at least twice the video bandwidth if pure AM was used.
Signal reception is invariably done via a superheterodyne receiver: the first stage is a tuner which selects a television channel and frequency-shifts it to a fixed intermediate frequency (IF). The signal amplifier (from the microvolt range to fractions of a volt) performs amplification to the IF stages.
Read more about this topic: Analog Television
Famous quotes containing the words receiving and/or signals:
“The same polarity of the male and female principle exists in nature; not only, as is obvious in animals and plants, but in the polarity of the two fundamental functions, that of receiving and penetrating. It is the polarity of earth and rain, of the river and the ocean, of night and day, of darkness and light, of matter and spirit.”
—Erich Fromm (19001980)
“The term preschooler signals another change in our expectations of children. While toddler refers to physical development, preschooler refers to a social and intellectual activity: going to school. That shift in emphasis is tremendously important, for it is at this age that we think of children as social creatures who can begin to solve problems.”
—Lawrence Kutner (20th century)