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ADVANCED TELEVISION SYSTEMS
List the merits of Digital TV receiver. / List the merits of digital TV receivers that are not achievable in a analog receiver.
Reduction of 50Hz flicker
High resolution pictures
Slow motion action
What do you mean by EDTV.
EDTV is mainly intended for direct broadcasting satellite system.
To improve the performance of the TV system it requires different transmission standards but it maintain the present line numbers and field rates.
Why FM is used in satellite TV system?
If we compare analog frequency modulation (FM) with analog amplitude modulation (AM), the FM better performance is due to the fact that the signal to noise ratio at the demodulator output is higher for wideband FM than for AM. For the transmission of a television signal over a satellite, the amplitude modulation would be severely affected by losses, various forms of interference, and nonlinearities in the transponder.
By the other hand frequency modulation is also more robust against signal amplitude fading phenomena. For a video signal, using the Carson’s rule, the required bandwidth is 32.4 MHz, thus a bandwidth of 36 MHz was originally chosen for a satellite transponder in order to accommodate one analog FM television channel.
And since the FM television channel occupies the entire transponder bandwidth, this can be operated at full power without any inter modulation interference caused by the nonlinear transfer characteristic.
State the use of geostationary satellite for TV system.
The shear range of programmes currently available on satellite channel is very much impressive such as 24-hour music videos, news, and feature films.
Commercial radio, TV broadcasting, telecommunications, weather forecasting, Global positioning
A variety of general entertainment programmes, sports, children’s programmes, foreign language broadcasts and cultural programmes are all available for the keyboard dish owner.
Some of these come through subscription channels and others by free to watch channels which are sponsored by advertising
What are the advantages of HDTV?
High quality image and sound
Wide screen aspect ratio for 103 cm trinitron(16 : 9)
The HDTV has the resolution of approximately twice the vertical and horizontal resolution of ordinary TV
Differentiate DVD from CD.
Distinguish between VCD and DVD.
Programmes on DVD can be four times longer than VCD
DVD video disc holds over 4 hours while the VCD holds 74 minutes.
DVD video has up to 8 digital audio tracks. Each track can hold uncompressed audio with quality better than audio CD
The quality of DVD video vast exceeds that of video CD, with 4 times the resolution in normal mode and 5.5 times in wide screen mode.
What are the transmission principles behind digital TV?
Analog to digital conversion
Video / Audio signal quantizing
What is the value of characteristic impedance of coaxial cable used for CATV?
The value of characteristic impedance of coaxial cable (RG-59U ½ inch flexible cable) used for CATV is 75 Ω
What are two types of video disc system?
Laser or optical disc system
Capacitance disc system
What do you mean by longitudinal video recording?
A method in which video signals are recorded on at least several tracks along the length of the tape.
Give the applications of video tape recorders.
Smaller and lower priced video tape recorders using ½ inch tape are available for closed type circuit TV or for use in the home. They can record and playback programs on a television receiver in color and monochrome.
In addition to that small portable cameras are provided for a complete television system with the recorder. These portable systems are also employed for taping television programs from a remote are also employed for taping television programs from a remote location for away from the TV broadcast studio.
Define bullet amplifier.
The LNA low noise amplifier is provided in the middle of coaxial cable to compensate any losses in it. This LNA is often called as bullet amplifier.
What do you mean by helical scan recording?
In helical scan recording, the two recording heads ‘look at ‘ the tape surface as it is drawn past them through two tiny rectangular slits mounted on opposite sides of the drum. The heads thus trace out diagonal tracks across the tape, one track per head.
Why are up-link and down-link frequencies chosen to be in the GHz range and kept fairly apart from each other?
The transponder cannot transmit and receive on same frequency, because the transmitter signal can overload the receiver and block the small up-link frequency signal and thereby prohibiting the communication.
The frequencies used for this purpose are in microwave frequency range from (3 to 30 GHz). During UHF, the atmosphere does not act as a barrier and signals can able to travel out into space and return back without any absorption or deflection.
Write short notes on CATV.
CATV stands for community antenna television systems. The CATV system is a cable system distributes good quality television signal to a very large number of receivers throughout an entire community.
Generally this system gives increased TV programmes to subscribers who pay a fee for this service. A cable system may have many more active VHF and UHF channels than a receiver tuner can directly select.
What do you mean by translator?
Translator is a frequency converter which heterodynes the UHF channel frequencies down to a VHF channel.
Define uplink frequency in satellite communication.
The frequency at which the information signals are transmitted from earth station to the satellite is called uplink frequency. Most the communication satellite uses C band frequencies.
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