Report on Study Tour Of Khulna Television Substation
Course Title: Television Engineering Sessional.
Course No: ECE-3202.
Date of the Tour: 12th November 2016.
Date of Report Submission: 20th November 2016.
Submitted To
S.M. Shamsul Alam
(Associate Professor)
ECE Discipline
Khulna University, Khulna.
&
Md. Abdullah-Al-Mamun Bulbul
ECE Discipline
Khulna University, Khulna.
Submitted By:
Kangkan Bhakta
ID: 130910
3rd Year, 2nd Term
ECE Discipline
Khulna University, Khulna.
Title: Study Tour in Khulna Television Substation.
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 part of the course titled “Television Engineering Sessional”, we get the opportunity to visit the Television station. Television station means where the basic television signals are transmitting and receiving through various equipment and machinery. The main TV station of our country is situated in Dhaka, Bangladesh. Therefore, we have visited the TV substation, which situated in Khulna located at khalishpur 10 km away from Khulna University with all of our classmates and our honorable course teachers.
Objectives
The main objectives of our tour include the practical knowledge on TV signal
transmitting that holds the information of capturing and visualizing the TV programs.
Our tour also includes the technique of LIVE telecasting on TV by receiving the signals from the main station (Dhaka). We can call the Khulna TV Substation as “TV
Transmitting Centre” which has both the entire transmitter and receiver systems.
Though the transmitter and receiver systems have no modern technical equipment but
they are working without any trouble with good performances.
Basic Structure and Operating Principles of Khulna TV Substation
Signal Reception & Transmission
Modulation Modules
Amplifier Section
Mixing Technique
Power system
Transmission System
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 TV set within 80 Km range. Full range of the signal transmission power is not normally used. 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 TV substation is BTCL (Bangladesh Telephone 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. There are two ways or links for the signal reception & transmission in Khulna TV substation.Those are Satellite Link & Microwave 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 TV signals Transmission and reception).The Geo has 3 (three) regions in the world which are Indian ocean zone, Pacific ocean zone, and Atlantic ocean zone. Our TV station named BTV (Bangladesh Television) 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
The Khulna TV substation mainly receives the signal 216 MHz to 223 MHz which means 7 MHz Bandwidth signal from the Jessore substation.Its channel number is 11 (eleven). The substation receives two types of signal, one is AM signal of about 222.75 MHz that used for video information in TV, and another one is FM signal of about 217.25 MHz, which used for audio information in TV. The both received signals are mixing through a demultiplexer machine and then transmit that mixed signal on air by the antenna.
We know that Khulna substation does not get the direct signal from the origin, Dhaka TV station that situated in Rampura. The basic paths for transmitted signals from Dhaka TV station to the Khulna TV substation can be represented by the following block diagram –
From the block diagram, we see that the signal first generated from Dhaka (Rampura)
TV station.Then it firstly received and then transmitted by some substations. Those
substations are Manikganj substation, Faridpur substation, Magura substation, Jhinaidah substation & Jessore substation. At last, the transmitted signal from Jessore substation received by Khulna substation. Those signals transmitted to Sathkira substation. The Sathkhira TV substation and Khulna TV substation uses the same signals. It’s known that the signal transmission and reception depend on the law of “eyesight”.
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 is an air-cooled solid state DD (double drive) device. It installed in Khulna substation in
the year, 2005. It uses Band-3 Transmission with the Transmission power of 10KW.
The exiting section of the transmitter is 2 (two) types such as A-exciter and B-exciter. Every type exciter has 5 (five) modules. Two types of modulation in Khulna TV station discussed on the following -
DHAKA
(RAMPURA)
Station
MANIKGANJ
Substation
KHULNA
Substation
JESSORE
Substation
JHINAIDAH
Substation
MAGURA
Substation
FARIDPUR
Substation
SATHKIRA
Substation
Video Modulation
In AM transmitters where efficiency is the prime the 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 at any stage. The IF stage for video signal is about 38.4 MHz
Audio Modulation
We know that at the transmitter, the audio signal is Frequency Modulated and it transferred to assigned channel sound carrier frequency by the use of multipliers. It later amplified through several stages of power amplifiers to raise the power output to the desired level. Audio monitors are provided at various points to keep a check on the sound quality. In the Khulna TV substation, the IF stage for 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 some months ago. It supports the digital transmission. Now, it is developing its activity for the new Govt. channel ‘Sangsod Bangladesh’ that will be launched soon in Bangladesh through Khulna TV substation.
Amplifier
In the TV substation, the name of the transmitter is THELES (model number: TAV210K0ADDB3) which is made in France. This transmitter follows the heterodyne action. It has 10 amplifiers. The 1st and 10th amplifier used for audio amplification.
They need the power of 1KW for audio transmission. The 2nd to 9th amplifiers used for video amplification. Those amplifiers need 1.25KW for visual transmission. In case of trouble, number four amplifier is missing in the transmitter without creating any problem in the total transmission system.
Mixing
We have discussed previously this section in the signal reception and
transmission section. In this section, the audio and video signals are both multiplexing
through the machinery in a constructive way. The machine is called the Demultiplexer. It has two input section and one output section.The output section sections are joined to the transmission line. The valuable cooling system is needed for the machine to work properly always to continue the signal transmission on the air through the transmission links.
Transmission
After mixing the AM and FM signals by the de-multiplexer machine a path from the machine is constructed to transmit the mixed signal. The path is made of high-quality steel to close the occurrences of errors in line. The antenna through the transmission line transmits the mixed signal. Those transmission equipment placed outside of the TV substation. Some practical information of antenna and transmission line given below –
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.
Transmission Line
Wave-guided lines or Coaxial cables mainly develop the Transmission Line. They have 28000 volts for proper transmission. 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.
To absorb all types of vibration in the line some materials such as raw cooler and
pretext type cover used surrounding all the walls at studios, booths, and the control room.
Power system of TV substation
Two powers suppliers one is National Grid maintains the main power system of the Khulna TV substation and other is Commercial Grid.The national grid controlled by Power Development Board (PDB).It supplies 11KV continuously to the station. If it fails suddenly then the substation has other option to maintain all transmission works simultaneously and that is the Generator of same power 11KV. The generator placed on the ground floor of the substation building. Here, the following block diagram shows the whole power system of the Khulna TV substation.
Observation
We will say in our observation that it is a great achievement for us to visit a TV substation lively. Mainly, it helps us to know about the practical and actual background of the Television broadcasting in an area of a country. With this successful TV tour, we achieve great experiences so that in future it will encourage us most to know more about the modern and advanced TV broadcasting systems. It is real that in our country the modern and advanced technologies are not available in all substations as like Khulna TV substation. However, we have seen that a new digital transmission machine in there which is not properly installed. We get the information that it will be joined with other transmission machines soon for the channel ‘Sangsod Bangladesh’. Then the people of Khulna will enjoy the digital TV system at home.
Conclusion
At last, it’s really a pleasure for us to get an opportunity to make such an amazing educational tour and complete all the works of it successfully.In this stage, we
will give thanks to our honorable course teachers. In addition, especially thanks to the
authority of Khulna TV substation to give us that good opportunity to complete the tour. The assistant engineer of the substation who gives us all the pieces of information and data that we should need to know for the tour. We will give thanks to the police super of Khulna Thana to give them permission to visit the substation.
National grid
11 KV
Step down
transformer
400V
Power factor
Improvement plant
Regulated power supply input
of Thales
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