edited ttc report -final

Bangladesh Telecommunications Company Limited Telecom Training Center (TTC), Tejgaon, Dhaka

JOB ATTACHMENT REPORT Date : From : 01-04-2010 To : 24-07-2011

Date of Submission : 25 July, 2011

Submitted To : Ms. Mst. Mallika Akar Khanom Superintendent (Exam & Program), TTC, Tejgaon, Dhaka.

Submitted By : Mohammad Mijanur Rahman Roll No.01, Batch-TCM (Ext.)-09-10 TTC, Tejgaon, Dhaka.

Authorized Officer’s Signature : ...........................................

Job Attachment Report On “Mohakhali Standard-A Satellite E/S”

1

Mohakhali Satellite Earth Station, Karail, Banani, Dhaka

At a glance Mohakhali Standard-A Satellite Earth Station

IOR (Indian Ocean Region) & GEO (Geostationary Earth Orbit) 64° East

C Band Carrier : works with INTELSAT

TX Frequency : 6 GHz

RX Frequency : 4 GHz

Antenna Size (Diameter) : 16 M

Antenna’s Weight : 35 tons

Total International Circuits : 5,000

Total Carriers : 30 with 12 countries

AZ : 230.77

EL : 049.55


2

Methodology

Primary Source of Information:

Classes provided by concerned officer

Group discussion with colleagues

Relevant manual study on provided by the officers concerned

Secondary Source of Information:

Website of BTCL.

Annual Report of BTCL

Relevant books, Newspapers and Journals

Technical-related internet web sites

Lecture sheets provided by TTC’s honourable teachers


3

Introduction

The first commercial communications satellite, INTELSAT (known as ‘Early

Bird’), was launched in April, 1965. Since then, Satellite communications have

become a major means for international as well as domestic communications

over long or moderate distances.

There are artificial man made satellite revolving around earth which help us to

communicate. In fact they help us in many ways. The television that we watch

and the internet that we browse all work through the satellite technology. The

technology is in fact used at all those places where the use of cables and wires is

practically impossible.

It first and most important applications was in inter country long distance

telephony. These satellite phones get connected directly through geostationary

satellite and then the signals are transmitted to teleport which is connected to a

satellite phone system. The technology is used in the regions or places where

the submarine communication cables and fiber optic cables are not possible.

In Bangladesh, Mohakhali Satellite E/S is playing a great role to expand new

circuits and carriers in tele-communication. Through this Satellite E/S along with

International Trunk Exchange, 30 carriers, 5000 international circuits are running

well with 12 countries. It is now also being used as stand by submarine

communication cables. This E/S is contributing greatly to revenue income of the

government.

The knowledge and experience which achieved in the field training in my job

area, here I have presented this with most key-points of satellite communication

system. I think it will fulfill the requirements of Job attachment report.


4

What is a Satellite ?

A satellite is a specialized wireless receiver/transmitter that

repeats radio-frequencies.

It is launched by a rocket and placed in orbit around the earth.

There are hundreds of commercial satellites in operation

throughout the world.

These satellites are used for a wide range of purposes

including Internet access, television broadcasting, wide-area

network communication, weather forecasting, amateur radio

communications and the Global Positioning System.


5

Various Purposes For Satellites

Satellites are used for many purposes such as :

Communications

Remote Sensing

Navigation

Atmospheric Conditions

Weather

Search and Rescue

Astronomy


6

Some World Satellite Communication Providers

Telesat

MSV

Intelsat

PanAm Sat

Eutelsat

Loral Skynet

HNS-Spaceway

Inmarsat

SES Astra

Arabsat

SMART-ACeS


7

What Is An Orbit?

After launch, a satellite is placed in orbit around the earth.

The earth’s gravity holds the satellite in a certain path as it

revolves around the earth.

This path is called an “orbit”.

There are several kinds of orbits. They are :

I) LEO, or Low Earth Orbit

Ii) MEO, or Medium Earth Orbit

Iii) GEO, or Geostationary Earth Orbit-Mohakhali Satellite

E/S is on this orbit.

Iv) HEO, or Highly Elliptical Orbit


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GEO, or Geostationary Earth Orbit

A GEO is 35,650 Km above our planet’s surface.

A satellite in geosynchronous orbit circles the earth in 24 hours-

the same time it takes the earth to rotate once.

These satellites are positioned over the equator and travel in

the same direction and speed as the earth and therefore

appear “fixed” with respect to a given spot on earth.

In this high orbit, GEO satellites are always able to “See” the

receiving stations below, and their signals can cover a large

area of the earth.

Three GEO satellites can cover the globe, except for the parts

at the North and South poles.

Most communication satellites

Mohakhali Standard-A Satellite E/S is on the GEO.


9

How a Satellite Works

Satellites have a few basic parts. They are the :

Command and Telemetry

Power source

Pointing Control

Mission payload

Communications


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Tracking Telemetry and Control This is the on-board computer of the satellite which controls all the

tracking, telemetry and control functions of the spacecraft. It records every activity of the satellite, receives information from the

ground station and takes care of any general maintenance items the

satellite needs to do.

Power Supply The power supply to satellites is provided primarily by means of the

solar arrays.

The solar arrays convert sunlight to electricity which is stored in

batteries and distributed to all the satellite’s instruments.

Batteries are required to power the satellite during eclipse when the

earth blocks the sun’s rays.

Pointing Control The pointing control system keeps the satellite course and pointing in

the correct direction.

The system utilizes sensors to obtain pointing control.

A propulsion mechanism or momentum wheel provides the satellite

with a ways to move into the proper position when required.

Communications

The communications system is made up of a transmitter, a receiver

and several antennas to relay messages between the satellite and

earth.

Ground control also uses it to send operating instructions to the

satellite’s computer (telecommand)

This system also sends health information generated by the satellite

back to earth (telemetry)


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Uplink / Downlink

An uplink is the transmission of a signal from an earth station to a satellite

in orbit.

A downlink is characterized by the satellite receiving the uplinked signal,

amplifying it, shifting it to a lower frequency and then re-transmitting from

the satellite antenna to an earth station(s) on the ground.

C-band uplink frequencies are from 5.925GHz to 6.425 GHz and the

downlink frequencies are from 3.7GHz to 4.2GHz.

Satellite Transponder Capacity

A transponder is the part of the satellite that receives signals and

transmits signals back to Earth.

A typical Ku band satellite and C band satellite have 32 (27 MHZ wide)

transponders and 24 (36 MHZ wide) transponders respectively.

A single transponder on one of these satellites is capable of handling an

immense capacity of information which typically corresponds to the double

of is bandwidth in million bits of information per second, i.e., 72 Mbit/s

and 54 Mbit/s for C band and Ku band transponders respectively.

Today’s communication satellites are an ideal medium for transmitting and

receiving almost any kind of content, from simple data to the most

complex and bandwidth-intensive video, audio and data content.


13

Satellite Frequency Bands and Antenna Size

Commonly used satellite frequency bands are L, C, and Ku.

C and Ku are the most common frequencies for fixed satellite services

such as video, data and voice.

L is the most common frequency for mobile satellite services such as

voice and data.

Ka-band will be used in the near future for video and data services.

The frequency and power output of a satellite signal determine the size

of the earth station antenna. When the frequency increases, the

wavelength decreases. As wavelength increases, larger antenna are

necessary to gather the signal.

Frequency Review : C-Band

Introduced in the 1970’s.

Occupies the 4-6 GHz frequency band.

Shared band with terrestrial microwave.

C band channels are typically 36 MHz.

Typically provides national domestic, regional or even global coverage.

Characterized by higher availability links that are less susceptible to

rain fade.

Lower cost per MHz when compared to other frequency bands.

Larger antennas required when compared to other frequency bands.


14

Mohakhali Standard-A Satellite Earth Station Link

The Satellite Earth Station Link of Mohakhali Standard-A Satellite E/S

comprises of the following equipments :

1. Modem (Modulator/demodulator)

2. Combiner

3. Divider

4. Upconverter

5. Downconverter

6. HPA (High Power Amplifier)

7. LNA (Low Noise Amplifier)

8. DCME (Digital Circuit Multiplication Equipment)

9. LRE (Low Rate Encoding)

10. Antenna

TX

RX

M O D E M

COM

UC

HPA

DIV

DC

LNA

D C M E

COM

UC

HPA

DIV

DC

LNA

M O D E M

TX

RX

ITX

IGW

ITX

IGW


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Modem (Modulator/demodulator)

A device that converts binary data streams, such as those from a PC, to

communicate over an analog transmission medium such as telephone lines or

on a carrier wave for wireless transmissions. The satellite modem can either

connect to the computer serial port, or to a network device via an Ethernet

connection.

Combiner

Combiner is used for 6 GHz band signal in satellite communication E/S. This

equipment requires no power supply and does not need any adjustment.

Electrical performances are as follows :

Frequency range 5850 to 6425 MHz

Insertion loss is more than 5 dB

Input/Output impedance 50 ohms

Return loss : unbalanced more than 17 dB

Isolation : more than 40 dB

Upconverter

A device that increases the frequency of the carrier, typically from

Intermediate Frequency (IF) to Radio Frequency (RF). The upconverter is

used in the transmission system or satellite communication earth station

which converts a 70 MHz or 140 MHz IF signal into a 6 GHz RF signal.

Downconverter

A device that lowers the frequency of the carrier, typically from Radio

Frequency (RF) to Intermediate Frequency (IF). It provides frequency

conversion of 4 GHz band received signal into a 70 MHz or 140 MHz IF signal

in satellite communication.


16

HPA (High Power Amplifier)

A device that amplifies a specific band of frequencies by a large amount,

sufficiently large to enable the antenna to beam them up to the satellite. This

equipment has the following advantages :

High reliabilities

Solid-state IPA

Low noise figure

High gain stability

Automatic recycling

Low in rush current

All air-cooled ventilation

The frequency range of HPA is 5.850 MHz to 6,425 MHz

HPA works in two circuits polarization :

RHCP (Right Hand Circuit Polarization)

LHCP (Left Hand Circuit Polarization)

LNA (Low Noise Amplifier)

A device to amplify the received modulated carrier while minimizing noise.

The LNA subsystem which is designed for use in the satellite communication

earth station, offers ultra low noise performance over the receiving frequency

band of 3.625 GHz to 4.2 GHz. Three FET Low noise Amplifier is mounted in

a redundant configuration.


17

DCME Digital Circuit Multiplication Equipment (DCME) is a type of voice

compression equipment that is installed at either end of a long-distance link

(typically communications satellite or submarine communications cable). There

are five types of DCME used in Mohakhali Standard-A Satellite Earth Station.

They are as follows-

1. DCME DX-3000 made by Mitsubishi Corporation of Japan

2. DCME DX-7000 made by Mitsubishi Corporation of Japan

3. DCME L3 MAX Pro made by UK

4. DCME DTX-240 made by ECI Telecom

5. DCME DTX-360 made by ECI Telecom

LRE (Low bit Rate Encoding)

Low bit Rate Encoding. One LRE is used in Mohakhali Satellite E/S and it is

made by Tellabs Ltd of Ireland.

Antenna

A device for transmitting and receiving radio waves, usually designed to focus

the waves to or from one direction. The antenna is often referred to as a dish.

The antenna also contains the feedhorn. The feedhorn is piece of antenna

hardware, located at the focal point of the parabolic reflector, that radiates RF

energy toward the antenna reflector and collects (received) RF energy from

the antenna reflector.


18

Power System of Mohakhali Satellite E/S

Generally power supply comes from PDB. If PDB fails, power

supply comes from UPS battery instantly and uninterruptly.

After a few seconds generator will start automatically and takes

load until PDB power supply comes.

My Job Responsibilities

Run international circuits smoothly

Observe & operate communication equipments with frequency

level analysis

Recover communication hindrance through manually and with

application software

Maintain international incoming and outgoing calls

Conclusion

Every organization needs well-adjusted, trained and experienced

people to perform its activities. In this regard, employee training is a

must because it is learning experience which seeks a relatively

permanent change in employees. The knowledge and practical

experience achieved in the field training provided by our concerned

officers has greatly benefited us to enhance our technical job skills

and overall improve our job performance.


19

25 July, 2011 To Ms. Mst. Mallika Akar Khanom Superintendent (Exam & Program), Telecom Training Center, BTCL, Tejgaon, Dhaka.

Subject : Submission of Job Attachment Report. Dear Madam,

Here is the Job Attachment Report on “Mohakhali Standard-A Satellite E/S”

where I have achieved my experience at my job area Mohakhali Satellite Earth

Station, Karail, Banani, Dhaka. The duration of Job attachment Programme was

one year. I have worked in the Earth Station as a Telecom Mechanics (TCM). I

have gathered practical knowledge in “Satellite Communication System” I have

found it interesting and acquired valuable practical knowledge while working for

this report.

I am very much grateful to you for your valuable advice, suggestion and co-

operation in preparing this report. I sincerely believe that this report would be

interesting, informative and acceptable to you.

Sincerely yours,

(Mohammad Mijanur Rahman) Roll No.-1, Batch- TCM (Ext.)-09-10 Telecom Training Center, BTCL, Tejgaon, Dhaka.

edited ttc report -final

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