applications of tv broadcasting
Answers
The various methods of TV transmission
Programming broadcast is the transmission of television stations’ programming (sometimes called channels) that is often directed to a specific audience.
There are several types of TV broadcast systems:
Analogue Terrestrial TV
Systems for sound transmission
Digital Satellite TV
Cable TV: analogue and digital systems
New technologies:
Digital terrestrial TV (DTTV)
High Definition Television (HDTV)
Pay-per-view
Video-on-demand
Web TV
IPTV
ANALOGUE TERRESTRIAL TV
Terrestrial television is a term which refers to modes of television broadcasting which do not involve satellite transmission or via underground cables.
Terrestrial television broadcasting dates back to the very beginnings of television as a medium itself and there was virtually no other method of television delivery until the 1950s with the beginnings of cable television, or community antenna television (CATV).
The first non-terrestrial method of delivering television signals that in no way depended on a signal originating from a traditional terrestrial source began with the use of communications satellites during the 1960s and 1970s of the twentieth century.
Analogue TV encodes the image and sound information and transmits them as an analogue signal in which the message transmitted by the broadcasting signal is composed of amplitude and/or frequency variations and modulated into a VHF or UHF carrier.
The analogue television picture is "drawn" several times on the screen (25 in PAL system) as a whole each time, as in a motion picture film, regardless of the content of the image.
DIGITAL SATELLITE TV
Satellite television is television signals delivered by means of communications satellites and received by satellite dishes and set-top boxes. In many areas of the world it provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.
Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility which have very large uplink satellite dishes, as much as 9 to 12 meters (30 to 40 feet) in diameter what results in more accurate aiming and increased signal strength at the satellite.
The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite, which 'retransmits' the signals back to Earth but at a different frequency band, a process known as “translation”, used to avoid interference with the uplink signal, typically in the C-band (4–8 GHz) or Ku-band (12–18 GHz) or both.
The downlinked satellite signal, quite weak after traveling the great distance, is collected by a parabolic receiving dish, which reflects the weak signal to the dish’s focal point where is a “downconverter” device called LNB (low-noise block) that is essentially a waveguide that gathers the signals, amplifies the relatively weak signals, filters the block of frequencies in which the satellite TV signals are transmitted, and converts it to a lower frequency range in the L-band range.
The evolution of LNB was a need, so the designs for microstrip based converters were adapted for the C-Band taking advantage of its central design that was the concept of a block for down conversion of a range of frequencies to a lower, and technologically more easily handled block of frequencies, the IF - intermediate frequency.
The advantages of using an LNB are that cheaper cable could be used to connect the indoor receiver with the satellite TV dish and LNB, and that the technology for handling the signal at L-Band and UHF was far cheaper than that for handling the signal at C-Band frequencies.
The shift to cheaper technology from the 50 Ohm impedance cable and N-Connectors of the early C-Band systems to the 75 Ohm technology and F-Connectors allowed the early satellite TV receivers to use what were in reality modified UHF TV tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on 70 MHz where it was demodulated. This shift allowed the satellite television industry to change to a far more commercial mass production one.
The satellite receiver demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.) and sometimes, the receiver includes the capability to unscramble or decrypt; the receiver is then called an Integrated Receiver/Decoder or IRD.
The cable connecting the receiver to the LNB must be of the "low loss" type, RG-6 or RG-11 and should not be used the standard RG-59 cable.