Sunday, July 16, 2017

Bangabandhu-1: First Satellite of Bangladesh

Bangabandhu-1 is the first Bangladeshian geostationary communications satellite . The satellite was ordered in November 2015 from Thales Alenia Space, who will build, launch and operate the satellite for the Bangladesh Telecommunication Regulatory Commission (BTRC). It will be stationed at an orbital slot at longitude 119.1° east with 40 transponders (Ku and C-band) with a capacity of 1600 megahertz. The total cost of the satellite is 248 million US dollars (Tk 19.51 billion).

Fig: Bangabandhu-1 [Thales Alenia]

Bangabandhu-1 is a satellite telecommunications system, comprising a satellite and the complete ground segment (control, mission and user segments). Thales Alenia Space is also in charge of building two facilities in Bangladesh for all ground support equipment needed to control the satellite and operate the telecom system. There will be two ground stations for satellite operation and control, one as the primary site (Gazipur) and other as the backup site (Betbunia). Thales Alenia Space Belgium, Thales Alenia Space Italy and Thales Alenia Space Spain are all involved in this project, as suppliers of various ground and satellite components.

Details about this satellite

Satellite Name
Bangabandhu-1 (BD-1)
Nation
Bangladesh
Type / Application
Communication
Position
119° E (119.1° E)
Operator
Bangladesh Telecommunication Regulatory Commission (BTRC)
Manufacturer
Thales Alenia Space, France
Equipment
16 standard C-band, 24 Ku-band transponders
Model (bus)
Spacebus-4000B2
Propulsion
S400
Power
2 deployable solar arrays, batteries
Lifetime
15+ years
Mass (kg)
3500
Orbit
GEO
Launch Date
December, 2017 (Estimated)
Launch Site
Cape Canaveral, USA
Launch Vehicle
Falcon 9 v1.2, SpaceX
Commercial Activity
April, 2018 (Estimated)

The priority satellite applications are Direct to Home (DTH), VSAT, Backhaul and Trunking, Network Restoration, Disaster Preparedness and relief etc. The Primary Service Area (PSA) would be Bangladesh and neighboring countries and the Secondary Service Area (SSA) would be South East Asia, Europe, MENA, and East Africa depending on orbital slot.

Fig: System Concept of Bangabandhu-1 


Once the satellite is launched, Bangladesh is expected to save $14 million annually and earn around $1 billion by leasing and renting the satellite. There will be a huge improvement in various sectors including information communication, e-learning, healthcare as well as early warning system and emergency relief efforts during natural disasters. Over 150 channels with high-definition quality will be available in the country as well.

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Friday, July 14, 2017

Network Connection

Type of Connection

For communication occur, two devices must be connected in some way to the same link at the same time. There are two possible types of connection: 1) point-to-point connection, 2) multipoint connection.

Point-to-point

This type of connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices.

Connection medium: cable, wire, microwave, satellite links.


Multipoint

A multipoint (multidrop) connection is one in which more than two specific devices share a single link. If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshared connection.


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Wednesday, July 12, 2017

Difference between UPS and Inverter

সাধারণত দুইটাই সমান। ইনভার্টর ডিসি পাওয়ার সাপ্লাইকে এসি পাওয়ার সাপ্লাইয়ে কনভার্ট করে।




অন্যদিকে ইউপিএস (Uninterrupted Power Supply) একটা ইলেক্ট্রনিক ডিভাইস যাতে ইনভার্টের টেকনোলজি ব্যাবহার হয়। ইউপিএসের ইনপুট পাওয়ার থাকে এসি পাওয়ার সাপ্লাই তারপর তা ডিসি পাওয়ারে কনভার্ট করে এবং তা জমা রাখে। তারপর আবার ডিসি পাওয়ারকে এসি পাওয়ারে কনভার্ট করে এবং স্ট্যান্ডবাই পাওয়ার প্রদান করে যখন ইলেক্ট্রিসিটি চলে যায়। 

UPS
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Tuesday, July 11, 2017

Generator faults and protections

Faults

  • Failure of prime mover 
  • Failure of field 
  • Over current 
  • Over speed 
  • Over voltage 
  • Stator winding fault 
  • Unbalanced loading

Protection 

  • Stator protection 
  • Differential protection (Merz price circulating current scheme) 
  • Protection against motoring 
  • Negative phase sequence protection against unbalanced loading 
  • Field failure protection 
  • Reverse power protection 
  • Inter turn fault protection 
  • Rotor earth fault protection 
  • Overcurrent relays in stator and rotor circuit 
  • Over voltage protection 
  • Over speed protection 
  • Rotor fault protection

Fig: GE Power Generator

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Electro-mechanical relay (EMR) / ইলেক্ট্রো-মেকানিক্যাল রিলে

ইলেক্ট্রো-মেকানিক্যাল রিলে (EMR)

ইলেক্ট্রো-মেকানিক্যাল রিলে হচ্ছে এমন একটি রিলে যার মুভিং কন্টাক(contact) সক্রিয় হয় ম্যাগনেটিক ফিল্ডের প্রভাবে। এই ম্যাগনেটিক ফিল্ড একটি কয়েলের মধ্যে দিয়ে প্রবাহিত ইলেক্ট্রিক কারেন্টর ফলে সৃষ্ট হয়। যখন কয়েলটি প্রবলভাবে সক্রিয় করা (energized) হয় তখন ইহা মুভিং কন্টাকে স্থির (stationary) কন্টাকের দিকে আকর্ষণ করে। এক কথায় বলতে গেলে, ইলেক্ট্রো-মেকানিক্যাল রিলে কয়েলের মধ্যে দিয়ে প্রবাহিত ইলেক্ট্রিক্যাল কারেন্ট ফলে সৃষ্ট ম্যাগনেটিক ফিল্ড ব্যাবহার করে এক বা একাধিক মেকানিক্যাল সুইচ বন্ধ করে।

ছবিঃ ইলেক্ট্রো-মেকানিক্যাল রিলে
ছবিঃ ইলেক্ট্রো-মেকানিক্যাল রিলে


ব্যবহারঃ

  • সলিনয়েড এক্টিভ কন্ট্রোল।
  • ইলেক্ট্রনিক কন্ট্রোল সার্কিট এবং পাওয়ার সার্কিট আলাদা করতে পারে।
  • অটোমোটিভ অ্যাপ্লিকেশান (ইলেক্ট্রিক ফুয়েল পাম্প)।
  • মোটর কন্ট্রোল।

ইলেক্ট্রো-মেকানিক্যাল রিলের সুবিধাঃ

  • কন্টাক এ.সি অথবা ডি.সি সুইচ করতে পারে।
  • খরচ কম।
  • কন্টাকের ভোল্টেজ ড্রপ কম, যার ফলে হিট সিঙ্ক দরকার পড়ে না।
  • উচ্চ প্রতিরোধক (resistance) হয় অস্থায়ী (transient) ভোল্টেজ প্রতিরোধ করার জন্য ।
  • ওপেন কন্টাকের মাধ্যমে কোন অফ-স্টেইট (state) লিকেজ(leakage) কারেন্ট হয় না।

ইলেক্ট্রো-মেকানিক্যাল রিলের অসুবিধাঃ

  • লোডের উপর নির্ভর করে কন্টাক ওয়ার (wire) এবং তাদের স্থায়িত্ব।
  • কন্টাকের স্থায়িত্ব কমে আসে যখন দ্রুত (rapid) সুইচিং অ্যাপ্লিকেশান এবং উচ্চ (high) লোডের জন্য।
  • কর্মক্ষমতা (performance) কম হয় যখন সুইচিং উচ্চ বেগে (inrush) কারেন্ট প্রবেশ করে।

উল্লেখ যোগ্য বিষয়ঃ

  • কয়েল ভোল্টেজ (Coil Voltage)- ভোল্টেজ সুইচিং এর সময় দরকার হয়।
  • কন্টাক রেটিং (Contact Rating)- কতটুকু কারেন্ট রিলে ধারণ করতে পারে।
  • নরমালি ওপেন (NO) অথবা নোরমালি ক্লোজড(NC)

ইলেক্ট্রো-মেকানিক্যাল রিলের অভ্যন্তরঃ



উপরের ছবিটি হল ইলেক্ট্রো-মেকানিক্যাল রিলের বেসিক ছবি। একটি স্প্রিং, সচল আর্মেচার(movable armature), ইলেক্ট্রো-ম্যাগনেট, সচল কন্টাক (movable contact) এবং স্থির কন্টাক (stationary contact)। স্প্রিংটি দুই কন্টাকে আলাদা করে রেখেছে যতক্ষণ না পর্যন্ত ইলেক্ট্রো-ম্যাগনেট সক্রিয় হয়ে দুই কন্টাকে একসাথে করেছে।

ইলেক্ট্রো-মেকানিক্যাল রিলের ওয়ারিং অবস্থায়ঃ


উপরে আমরা দেখতে পারছি যে ইলেক্ট্রো-মেকানিক্যাল রিলের ওয়ারিং অবস্থা। যখন কন্ট্রোল সার্কিট ইলেক্ট্রো-ম্যাগনেটকে অন করে তখন সচল আর্মেচার ইলেক্ট্রো-ম্যাগনেটের প্রতি আকৃষ্ট হয় এবং সচল কন্টাক ও স্থির কন্টাককে যুক্ত করে। এইটা সার্কিটটা সম্পূর্ণ করে এবং লোডের কাছে পাওয়ার সররাহ করে।

ইলেক্ট্রো-মেকানিক্যাল রিলের উদাহরণঃ

ধরি, পানি নিস্কাশনের (drain) জন্য একটি সলিনয়েড বাল্ব কন্ট্রোল করা প্রয়োজন। এই কন্ট্রোলটা হবে মাইক্রো-কন্ট্রোলার দ্বারা। সলিনয়েড বাল্ব খোলার জন্য দরকার ১২০ ভোল্ট এ.সি। ধরি, ওই ১২০ ভোল্ট এ.সি পাওয়ার সাপ্লাইও আছে। এখন কিভাবে ৫ ভোল্ট ডি.সি পাওয়ার সাপ্লাই দিয়ে মাইক্রো-কন্ট্রোলার দ্বারা সলিনয়েড বাল্ব কন্ট্রোল করা যাবে। 

রিলে দ্বারা সহজে এই সমস্যা সমাধান করা যায়। অনেক রিলে আছে যারা ৫ ভোল্ট ডি.সি কয়েল দ্বারা বাল্ব অন অফ করা যায়। রিলে মাইক্রো-কন্ট্রোলার এবং ১২০ ভোল্ট এ.সি পাওয়ার সাপ্লাই এর মধ্যে ইন্টারফেস প্রদান করে যা বাল্ব খোলার ও বন্ধ করার জন্য প্রয়োজন। 



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Wednesday, July 5, 2017

The History of First Mobile Phone (video)


Video courtesy of ColdFusion

The world’s first mobile phone call was made on April 3, 1973, when Martin Cooper, a senior engineer at Motorola, called a rival telecommunications company and informed them he was speaking via a mobile phone. The phone Cooper used, if you could call it that, weighed a staggering 1.1kg and measured in at 228.6x127x44.4mm. With this prototype device, you got 30 minutes of talk-time and it took around 10 hours to charge



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Saturday, July 1, 2017

Network and Network Criteria

Network

A network is a set of devices (nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending or receiving data generated by other nodes on the network.


Fig: Network

Network criteria


A network must be able to meet a certain number of criteria.


Performance
Performance can be measured in many ways, including transit time and response time. 
  • Transit time: The amount of time required for a message to travel from one device to another.
  • Response time: The elapsed time between an inquiry and a response.
  • Performance factor
    1. Number of users
    2. Transmission medium
    3. Capabilities of connected hardware
    4. Efficiency of the software
  • Performance evaluated by two networking metrics: throughput and delay. We often need more throughput and less delay.
Reliability 
Reliability measured by
  • The frequency of failure
  • The time it takes a link to recover from a failure
  • The network’s robustness in a catastrophe
Security
Network security issues include protecting data from
  • Unauthorized access 
  • Damage and development 
  • Implementing policies and procedure for recovery from breaches and data losses.
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Friday, June 30, 2017

Data Communication

Data Communication(DC)

Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable, wireless or optical fiber etc. For data communications to occur, the communication devices must be part of a communication system to made up of a combination of hardware (physical equipment) and software (programs).

Characteristics of data communication 

  1. Delivery: Must deliver data to the correct destination
  2. Accuracy: Must deliver the data accurately
  3. Timeliness: Must deliver data in a timely manner. (For video and audio, timely deliver means delivering data as they are produced, in the same order as they produced and without significant delay. This kind of delivery is called real-time transmission. 
  4. Jitter: Jitter refers to the variation in the packet arrival time. (Example: video packets are sent every 30-ms if some of the packets arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the result.) 

Components

There are five components of data communications.

  1. Message: text, numbers, pictures, audio, and video. 
  2. Sender: person, computer, telephone, video camera etc. 
  3. Receiver: same as sender and television. etc. 
  4. Transmission medium: cable (twisted-pair, coaxial), radio waves, optical fiber. 
  5. Protocol: Protocol is a set of rules that govern the data communications. Actually, it represents an agreement between the communicating devices (sender and receiver).

Fig: 5 components of data communication 

Data Representation


Text 

Texts are represented as a bit pattern, a sequence of bits (0s or 1s). Different sets of bit patterns have been designed to represent text symbols. Each set is called code and the process of representing symbols is called coding. Today, the prevalent coding system is called Unicode, which uses 32-bits to represent a symbol or character used in any language in the world. 


Number
Numbers are also represented by bit patterns. The number directly converted to a binary number to simplify mathematical operations. 

Image 
Images are also represented by bit patterns. First, an image divided into pixels then each pixel is assigned a bit pattern

Audio 
Audio is by nature different from text, numbers, or images. It is continuous, not discrete. 

Video 
Video can either be produced as a continuous entity (TV camera), or it can be a combination of images, each a discrete entity, arranged to convey the idea of motion.

Data Flow 

Communication between two devices can be simplex, half-duplex, or full-duplex. 

Simplex Mode 
In simplex mode, the communication is unidirectional (one-way street). Only one of the two devices on a link can transmit and the other can only receive.
Fig: Simplex
Half-Duplex Mode
In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.
Fig: Half-duplex

Full-Duplex
In full-duplex mode, both stations can transmit and receive simultaneously.
Fig: Full-duplex
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Wednesday, June 14, 2017

The Terrifying True Scale of Nuclear Weapons (video)


Nuclear weapons have come a long way and come in all types of different sizes. Some are relatively small while others are enormous, so big they boggle the mind at what they can be capable of. This video analyzes the sizes and impacts of various different nuclear devices, the history of nuclear weapons and what countries in the world are in possession of such devices.

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Saturday, June 10, 2017

The Biggest Rocket ever Designed (video)




That one rocket, which is still the Tallest, heaviest and most powerful ever built, was the Saturn V, which was designed to take men to the moon and later launched the first American Space station, Skylab. 

But if things had been a little different back in the 60’s we might have had a different rocket to hang on the bedroom walls of the space fans of the 70’s and 80’s.

In the early 1960’s, a rocket was designed which made the Saturn V look small comparison.
This was the Sea Dragon, a super heavy lift rocket that would have been 10 times more powerful with 80 Million lb’s of thrust compared to the Saturn’s 7.8 million and that was from just one massive engine. 

It was designed to lift a payload of 1,100,000 lbs into orbit, compared to the 310,000 lbs of the Saturn V. This meant it could have lifted an entire space station into Low Earth Orbit in one mission.

The rocket bell of this single engine would be so large at 75 feet in diameter, that you could fit the entire first stage of a Saturn V with all 5 of its F1 engines inside with room to spare.
So what happened to the Sea Dragon and why didn’t it get built ?. 

At the time of the design in 1962, it was thought that by the 1970’s, 80’s and beyond, thousands of people would be working in space and on the moon, even on Mars and as such, rockets with huge lifting capabilities would have been in great demand as they would dramatically lower the cost of getting materials into space.

The sea dragon was designed by Robert Truax, a US navy Captain and Rocket engineer. He was one of the pioneers of American rocketry and worked on the Thor and Polaris missiles amongst others. His team debriefed the German Rocket engineers at the end of World War 2 including Werner Von Braun who went on to design the Saturn V.

Traux believed it was complexity that drove up the cost of rockets and not their size. His designs for the Sea Dragon were very simple but very big. The sea dragon would have been 75 ft in diameter and 500ft tall, half the Hight of Chrysler building. 

This type of low-cost super heavy rocket is now known as a “big dumb booster” due to its simplistic design.
Instead of having very complicated turbopump driven engine like the Saturn’s, his were the simplest possible design for a rocket engine. 

In place of having powerful fuel pumps to push the huge amounts of rocket fuel and oxidizer in the engine, he proposed a pressure fed system with a separate liquid nitrogen tank to pressurise the fuel tanks, this would push the fuel into the massive combustion chamber.

His engines were literally not much more than the valves to turn on the fuel and the huge engine bell, this would make them not only much cheaper to manufacture but much easier to refurbish and reuse, unlike the F1 engines of the Saturn which were left crash in the sea and be discarded.

The rocket would be a two-stage design, the first stage would lift it to a height of 130,000 ft before it separated and fell back into the sea, using drag bags to slow it impacts with the water, where it would be recovered for reuse.



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Friday, June 9, 2017

What Happened on the Moon Before Apollo? (video)


The Apollo landings from 1969 to 1972 marked a high point in lunar exploration but Apollo didn’t just rock up on to the moon out of the blue, it took many, many missions by probes and landers over the preceding years to establish if we could send men to the moon and get them back



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Wednesday, June 7, 2017

How Far have we gone into the Universe? (video)





Humanity is a fledgling space-faring species, with only a tiny percentage of people who have traveled into space. Most people throughout history have lived their whole life on our tiny rock, but how far have those select few explorers gone? How far into the void of space have we extended our reach? 


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How big is the Universe? (video)





The universe is about 13.8 billion years old, so any light we see has to have been travelling for 13.8 billion years or less – we call this the 'observable universe'. However, the distance to the edge of the observable universe is about 46 billion light years because the universe is expanding all of the time.

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Crashing Into Saturn: Cassini's last Mission (video)




NASA's Cassini spacecraft begin the last chapter of its 20-year mission to Saturn. Diving deeper into Saturn's rings than ever before, scientists hope that the data from Cassini's final orbits will help to improve our understanding of the giant ringed planet. The probe's last act will be to plunge itself into the planet's atmosphere, where it will burn up and become part of the planet itself.

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Tuesday, June 6, 2017

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