Television transmission and reception:
The plan of television system is to expand sense of sight beyond its natural limits and to transmit
sound associated with scene. Picture signal is generated by Television camera and the sound signal by microphone. In the 625 line CCIR monochrome and PAL-B colour Television systems adopted by India, the picture signal is amplitude modulated and sound signal frequency modulated before transmission. The TV receiver has tuned circuits in its input section called ‘tuner’. It selects desired channel signal out of the numerous chosen up by antenna. The preferred RF band is transformed to a common fixed IF band for convenience of providing large amplification to this .Amplified IF signals are detected to obtain the video and audio signals.
Digital Transmission :
All “free-to-air” TV stations are now transmitting “free-to-air” television in digital form also traditional analog transmission. The coverage and diversity of digital transmission will increase progressively over the next few years. The Australian Government has set a deadline for analog “free-to-air” transmission to be terminated by December in the year 2013. After analog transmission is ceased in the year 2013 Television transmission will be in digital form only.
Picture information is optical in the character and might be thought of as grouping of large
number of tiny areas representing picture details. These basic areas into which the picture details
might be broken up are known as the ‘picture elements’ or ‘pixels’, which when viewed together represent visual information of scene so that at any instant there are almost an infinite number of pieces of Hierarchical transmission.
Channel coding is conducted in units of the OFDM segments. So that division of a single television channel can be used for fixed reception service and rest for mobile reception service. This signal transmission is defined as hierarchical transmission. Each of the hierarchical layer consists of one or more the OFDM segments and parameters such as a carrier modulation scheme the inner-code coding rate and the time interleaving length can be specified for each hierarchical layer. Up to three hierarchical layers may be provided and that segment used for the partial reception is also counted as one hierarchical layer.
Basic configuration of channel coding:
Multiple TSs output by the MPEG-2 multiplexer are fed to TS re-multiplexer such that the TSPs can be properly arranged for signal processing one data segment at a time. In the re-multiplexer, each TS is first changed into 188-byte burst-signal form by means of a clock having a rate four times higher than that of the IFFT sample clock. An outer code is then applied, and these TSs are converted into a single TS. That need to be picked up simultaneously for transmitting picture details.
The receiving antenna intercepts radiated RF signals and the tuner selects desired channel’s frequency band and converts it to the common IF band of the frequencies. Receiver employs 2 or 3 stages of intermediate frequency amplifiers. Output from last IF stage is demodulated to the improve video signal. This signal that carries picture information is amplified and coupled to the picture tube which converts electrical signal back to picture elements of identical degree of black and white. Glass envelope contains the electron-gun structure that produces a beam of electrons aimed at the fluorescent screen. When electron beam strikes screen the light is emitted. Beam is deflected by a pair of deflecting coils mounted on neck of picture tube in a same way as beam of camera tube scans the target plate. The amplitudes of currents in the horizontal and vertical deflecting coils are adjusted that entire screen called the raster which gets illuminated because of fast rate of the scanning.
Question & answers:
Q1: What is Partial reception ?
Ans: As for an OFDM segment at the center of a television-broadcasting signal consisting of 13 segments it is possible to conduct the channel coding so that range of frequency interleaving is limited within segment. This configuration enables the ISDB-TSB receiver to the receive 1 segment service embedded in the hierarchical television signal.
Q2: What is TELEVISION TRANSMITTER ?
Ans: The luminance signal from camera is amplified and synchronizing pulses added before feeding it to modulating amplifier. The synchronizing pulses are transmitted to keep the camera and picture tube beams in step. The allotted picture carrier frequency is generated by a crystal controlled oscillator. The continuous wave sine wave output is given large amplification before feeding to the power amplifier where its amplitude is made to vary in accordance with the modulating signal received from the modulating amplifier.
Q3:Expalin the Sound Transmission of television?
Ans: There is no distinction in sound transmission between the monochrome and the colour TV systems. Microphone converts sound associated with picture being televised into proportionate electrical signal, which is normally voltage. This electrical output, regardless of complexity of the waveform, is a single valued function of time and so needs a single channel for the transmission. Audio signal from the microphone after amplification is the frequency modulated, employing assigned the carrier frequency.
Q4 . For TND service licensed to a Broadcaster which area is served ?
Ans: Batchelor is served.
Q5: Give explanation for the Spectrum Requirements for the Television Broadcast Services using Cellular Transmitters?
Ans: Television broadcast services have strongly shaped the social and cultural development during the last century and are considered an important cultural good. The traditional means of providing Television programs to the households is by means of terrestrial broadcast distribution. Now terrestrial broadcast distribution is still used by approx. 10% of households in the USA as their sole means of receiving the television. Spectrum bands that are allocated to the Television broadcast transmission in US – after switchover from the analog to the digital transmission are from 54 to 72 MHz, from 76 to 88 MHz, from 174 to 216 MHz and from 470 to 698 MHz. These sums up to total of 300 MHz of the Television broadcast spectrum. Majority of households however the receive Television programs now via cable, satellite, and recently also via the Internet connections.