Electronics & Communication Engineering Discipline
Course No: ECE 3202
Course Title: Television Engineering Sessional.
Study tour report on Khulna BTV Substation.
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Submitted To:
Md. Shamsul Alam Submitted By:
Associate Professor Kangkan Bhakta
ECE Discipline ID:130910
Khulna University. 3rd Year,1st Term
ECE Discipline
Abdullah Al- Mamun Bulbul Khulna University.
Lecturer
ECE Discipline
Khulna University.
Study Tour Report on Khulna BTV Substation.
Objectives:
1. To know the different types of television transmitter
2. T0 Know about TV signals transmission that holds the information of capturing and visualizing the TV programs.
3. To attain some practical knowledge about the working principle of a TV station.
4. To see the composite video signal and 625 lines of the composite signal separately.
5. To gather knowledge about the other necessary used machines for receiving and transmitting and their working procedure.
6. To know how a TV transmitter transmits and radiates signal for general viewers through television receiver
Introduction:
As the student of Khulna University in Electronics and Communication Engineering Discipline, we have the course titled “Television Engineering” in 3rd year. Therefore, for the purposes of practical observation of the course titled “Television Engineering Sessional”, we get the opportunity to visit the Television station. The main TV station of our country is situated in Dhaka, Bangladesh. Therefore, we have visited the TELEVISION substation, Khulna on 17th November 2016, which situated in Khalishpur, Khulna 10 km away from Khulna University with all of our classmates and our honorable course teachers S.M. Shamsul Alam (Associate Professor) and Abdullah Al Mamun Bulbul (Lecturer) of Electronics and Communication Engineering Discipline. It is to be noted here that this Television Center has been playing a vital role in Broadcasting throughout the country.
Basic Structure and Operating Principles of Khulna TELEVISION Substation:
1. Signal reception & transmission
2. Modulation modules
3. Amplifier Section
4. Mixing Technique
5. Transmission System
6. Power System
Transmitter :
Khulna BTV Substation has 2 transmitters.
1. One analog transmitter Model No : TAV2 10KOA DDB3( THALES)
2. One digital Transmitter Model No : AXERA Solid State Transmitter.
Signal Reception & Transmission:
For the signal transmission, the coverage area of the substation is about 100 km (radius of the circle) as the capacity in Khulna zone. Both sound signals & picture signals are received clearly by the Television within 80 Km range.
The Transmitting power for coverage area is about 10 KW and has the effective radiated power of 96 KW. The supporting tower for the signal reception in Khulna TELEVISION substation earlier was BTCL (Bangladesh Telecommunications Company Limited), Khulna with the height of 500 ft and the height of the antenna is 15 ft, which has a gain of 9.6 dB but recently has launched the new dish and fully depend on Satellite Link. The Satellite Link used mostly for the better Reception & Transmission of signals. Some information about those links are given below:
Satellite Link:
There are three orbital deviations in the whole world for the satellites which are Leo (used for lower communication), Meo(used for mobile communication)and Geo(used in TELEVISION signals Transmission and reception).TheGeo has 3 (three) regions in the world which are Indian ocean zone, Pacific ocean zone, and Atlantic ocean zone. Our TELEVISION station named BTV (BangladeshTelevision) uses Indian Ocean zone. The name of BTV’s satellite is ASIASAT 3S. Its orbital location is 105.5 degrees east which is orbiting the world 36000km away from the ground.
Microwave Link:
Khulna TV substation mainly receives the signal 216 MHz to 223MHz from Jessoresubstation. This substation receives two types of signal, one is AM signal of about 222.75 MHz, which used for video information in TV and the other is FM signal of about 217.25 MHz, which is used for audio information in TV. Both signals are mixing by a multiplexer and then radiate the signal on air by the antenna. Khulna TV Substation doesn’t receive the original signal sent from Rampura Television Centre. In the following figure, I just tried to sketch a connection link between Rampura to Khulna via different substations
Rampura (Mother station)>>Romna>>Manikgonj>>Magura>>Jessore>> Khulna Substation
Modulation:
Two types of modulation occur in the substation.Those are audio modulation and video modulation. Several electrical and mechanical instruments are responsible for both types of modulations. An electrical machine named ‘THELES’ mainly controls the transmission section of modulation unit in Khulna TV Substation.It installed in Khulna substation in the year, 2005. It uses Band-3 Transmission with the Transmission power of 10KW.Two types of modulation in Khulna TV station discussed on the following –
Video Modulation:
In AM transmitters where efficiency is the prime requirement, amplitude modulation is effected by making the output current of a class C amplifier proportional to the modulating voltage. On the other hand, in an AM transmitter, amplitude modulation can be generated at any point after the crystal oscillator. From the transmitter section of Khulna TV substation, the output signal goes to “power amplification section” where rectification of amplitude modulating the signal at 557 MHz happens in many stages. The stage for the video signal is about 38.4 MHz.
Audio Modulation:
We know that at the transmitter, the audio signal isFrequency Modulated and it transferred to assigned channel sound carrier frequency by the use multiplies.In the Khulna TV substation, the IF stage for the audio signal is 34.4 MHz. Though the ‘THELES’ performs both analog system & digital modulation in TV system, there are also two more electrical machines as the transmission section of Khulna TV substation. One is NEC and the other is AXCERA. The NEC is the product of Nippon Electronics of Japan, which used in Khulna Television Substation before the year of 2005. It is tube type transmitter and needs a 400KW power supply to operate.But it is not more efficient than previous TV transmitter THELES. The other one named AXCERA, made by America is the new one, which installed in the substation in 2009. It supports the digital transmission. Now, it is developing its activity for the new Govt. channel ‘Sangsod Bangladesh’ in Bangladesh through Khulna TV substation.
Mixing:
The audio and video signals are both multiplexing through the machinery in a constructive way. The machine is called the De-multiplexer. It has two input section and one output section.The output section sections is joined to the transmission line
Transmission:
After mixing the AM and FM signals by the de-multiplexer machine path from the machine is constructed to transmit the mixed signal.The antenna through the transmission line transmits the mixed signal. That transmission equipment placed outside of the TV substation. Some practical information of antenna and transmission line.
Antenna:
The main antenna of the substation called Dipole antenna, which is Omnidirectional. Its general height is 15ft, which placed on the top of a 500ft high tower on the ground. The antenna power is about 10kw for visual sync peak output. The gain of the antenna is about 9.6 dB. For the better receiving of signals by the TV set, there must have a Yagi-Uda antenna on the roof or open place of the building that is called directional antenna.
Composite video signal
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The composite video signal as seen from the substation is given here. We were not allowed to use any camera, otherwise, genuine photos could be attached to this report. As seen from the figure, there is a pair of signals for two frames taken per steel picture.
Transmission Line
Wave-guided lines or Coaxial cables mainly develop the Transmission Line.The ground coil of the transmission line is 500ft.Within it, only 3ft is used for the ground level to save Arial from thundering. The special setup Austin transformer needed to light the neon light up above the aerial. It transmits the signal that can receive fairly from 90 miles so far, have also the radiation effect around the aerial.
Conclusion
The overall system of the Khulna TV substation corresponds to our theoretical knowledge. But some additional system and their working procedure I have learned through this tour. So this tour has helped me so much to understand the basic operation of the transmitting and receiving procedure of TV signals.So we are thankful to our course teachers for arranging such a tour and also the instructors form the Television Center. It will help us surely in the long run when we will want to work in this particular field.
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