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Friday, January 28, 2011

Eamcet - 50% marks in Inter subjects mandatory From this year


Shocking news to Engineering colleges Managements...
From this 2011 50% marks in Intermediate in Maths, Physics and Chemistry to be eligible for admission to engineering colleges. Students from SC and ST should get at least 40%. The new norm may prove disastrous for Engineering colleges as nearly 80,000 students who qualified in Eamcet last year did not secure 50% marks in Inter.
But from next year, those who do no secure 50 per cent marks will not be able to pursue Engineering courses resulting in thousands of seats remaining vacant. The requirement of 50% in Inter was applicable only to Eamcet medical stream students in accordance with the directions of the Medical Council of India two years ago.
The new norm, that is meant to improve standards in professional education, will be incorporated in the Eamcet notification set to be issued in the first week of February.
This follows the decision of the AICTE to increase the qualifying marks from 35% to 50% in 10+2 exams to improve the standards in Engineering.

EAMCET 2011

Eamcet committee will meet on January 29 to finalise the schedule for issuing Eamcet-2011 notification and sale of applications. Eamcet notification is likely to be issued on February 5. JNTU-Hyderabad will conduct the Eamcet for the 12th year in a row. Eamcet committee comprises representatives from 25 universities and the officials of higher and technical education departments. The issue of “hi-tech cheating” in the Eamcet last year using modern gadgets is likely to prominently figure in the meeting. Eamcet committee will examine various options like installing cellphone jammers at Eamcet centers to check hi-tech copying.
Eamcet will be conducted on May 8. Andhra Pradesh government has decided to conduct Eamcet on a Sunday like last year to save students from weekday traffic problems. Eamcet 2011 applications would be available in all Andhra Bank branches, e-seva centers and post offices.

Wednesday, January 26, 2011

SPEECH BY HER EXCELLENCY THE PRESIDENT OF INDIA SHRIMATI PRATIBHA DEVISINGH PATIL TO THE NATION ON THE EVE OF 62ND REPUBLIC DAY OF INDIA



My Fellow Citizens,
On the eve of our 62nd Republic Day, I extend my warmest greetings to all of you across the country and also to those living abroad. I convey my special greetings to the members of our Armed Forces and Para-Military Forces, who guard our frontiers and to our internal security forces. I also compliment every citizen from every walk of life for contributing to the process of nation-building.
26th January is a very significant date in our nation's calendar, when we celebrate the establishment of free India as a Republic based on the ideology of justice and equality. It is a day when we recall with gratitude the sacrifices of our freedom fighters and the work of our Founding Fathers, for giving to us a country where our dignity and individual freedoms are guaranteed by an enlightened Constitution. It must also be an occasion when we rededicate ourselves to maintaining harmony, peace and brotherhood. Most of all, it is a time to introspect about how we have fared so far, and in which direction are we moving.
For our achievements, the foremost credit goes to the drive and the dedicated hard work of millions of men and women of our country. We are witness to the increasing influence of India and its steady economic growth that has brought prosperity to an increasing number of people. We can be proud of our successes, but there are many significant tasks that are yet to be accomplished, in particular the pledge to empower the poor and the marginalized sections of our population so that they too can become a part of the growth story of our nation.
Dear Citizens,
We are fortunate that we are the inheritors of the ideals and values of one of the world's oldest civilizations, which has bequeathed to us a rich treasure of human experiences and thought. The concept of the human race being one, the importance of living in harmony with each other and with nature, the quest for knowledge and truth, find prominence in our age old culture. These ideas provided inspiration for our freedom movement and after our independence found a ready resonance in our Constitution. As citizens of this country each one of us, therefore, has a duty and a responsibility to demonstrate, that these principles have given to us the motivation and the strength to build our great nation.
It is, however, a fact that there can be no society which does not need to evolve to cope with the changing demands of time; and there can be no nation which does not face challenges. India too has its share of problems and obstacles, constraints and difficulties. We cannot evade these or wish them away, but working in different fields, we must together find solutions. The strength of a nation is not determined by the challenges it faces, but by its responses to these challenges, especially so when it stands at a critical juncture and at a decisive point. What we do in this coming decade in terms of leveraging our advantages and addressing our shortcomings, will shape the destiny of the nation. Wherever course correction is required, it must be undertaken unhesitatingly and with urgency. There should be national consensus on critical national goals. Among such goals, eradication of poverty, empowerment of women, access to quality education and affordable health facilities are essential for building human resources. Apart from this, civic discipline, the readiness of people to work with dedication and integrity can make an enormously positive impact.
Dear Citizens,
Among our remarkable accomplishments has been an unwavering adherence to democracy. The people of India have expressed their confidence by participating time and again in the electoral processes. For us, democracy is an article of faith, important both as a basic pillar of our Republic and as a guarantor of our freedoms. Its sustenance is essential for the identity of India, hailed as the largest democracy in the world, and one that functions well even in situations of multiple complexities. We must not only reinforce democratic institutions and processes, but also refrain from any action, taken wittingly or unwittingly, that dilutes or is detrimental to democracy.
The Parliament of the country is the repository of the sovereign will of the people, and its successful functioning is a joint responsibility of both the Government and the Opposition. It is important that the decorum and dignity of the House is upheld at all times. The image of Parliament in the public mind should be one where proceedings, debates and discussions take place with a view to resolve issues through a constructive and co-operative approach. If this does not happen, people's faith in democratic institutions can be affected, resulting in a feeling of despondency which is unacceptable in a healthy democracy, as it may derail democratic institutions. Hence, dialogue among stakeholders in democratic institutions is an integral part of democratic working.
The time has come for us to take a closer look at our social milieu. Is there growing criminalization of our society? Is there increasing apathy towards each other? Are we becoming too materialistic, shortsighted and unconcerned about the impact of our actions on our brethren, society or the environment? It is a matter of anguish and great concern when a person is killed for a petty sum of money; or when a woman is raped because she protests against being teased; or when over small incidents, due to lack of patience, there is a quick flaring of tempers. Cases of ragging in educational institutions are also disturbing. Ragging is violence. It is heinous and should not be tolerated, for it can cause irreparable loss to the parents and to the country. Our social fabric is deeply damaged by such incidents and it is essential that these tendencies are curbed in the interest of social harmony and cohesion. I appeal to my fellow citizens to never resort to violence. Our nation won its freedom by travelling on the high path of non-violence and truth. In our journey as an independent nation too, we must adhere to it and demonstrate moral courage. Societies evolve in a positive direction when people work to bring about constructive changes and to eliminate social evils. In my first address to the nation on the eve of Republic Day in 2008, I had spoken on the need for social, economic, administrative and political activities to be carried out on the basis of moral values and social justice. I reiterate the great importance of integrity, honesty, good conduct and high values, which our culture teaches us.
The youth of our country must carry forward this legacy. As the architects of the future of the country, their upbringing with a value-based education is paramount in the development of their character. It is said that the first teacher of the child is the mother when the child is of tender age, and the next is the primary school teacher. Both make lasting impressions on children in their formative years. In primary schools, teachers are doing good work. We should regularly assess issues relating to training of teachers and quality of education including checking instances of absenteeism of teachers. In addition, our special efforts to reach out to students from tribal and remote areas, Scheduled Castes, Scheduled Tribes and other backward communities must be augmented. Our endeavour should be to create a level playing field in educational competitiveness so that students from all sections of society can enter premier institutions like the Indian Institutes of Technology and the Indian Institutes of Management.
Dear Citizens,
As a nation, our aim is to grow and to create a just society. Our goal of poverty eradication and of inclusive growth that embraces the disadvantaged and marginalized sections of society can be achieved when our actions are guided by a social conscience and are not devoid of sensitivity. We are seeking good governance and a people-centric administration. In this, callous and casual attitudes in the sphere of public service are unacceptable. Delivery systems for schemes and programmes that promote the welfare of the people and spur economic growth should have inbuilt mechanisms for greater transparency and accountability. Education, health and skill building efforts will create productive human resources for the future. Urban and rural development schemes will make our cities and villages sustainable habitats. Programmes for women, the youth, the girl child, the differently-abled and marginalized sections of society will equip them to avail of opportunities and face the future with confidence. We need to address the problems of orphans and street children, as well as of the old and destitute. For the success of welfare schemes, the total sum of developmental funds must reach the intended beneficiaries. Corruption is the enemy of development and of good governance. Instead of getting lost in this mire, it is necessary to rise above it and seriously look at bringing systemic changes to deal more effectively with corruption. Financial institutions, the corporate world and civil society - all must uphold high standards of probity in their working. Only a genuine partnership between the Government and its people can bring about positive change to create a just society.
The media plays an important role in bringing information, news and views to the public. This generates awareness, promotes discussion on issues and creates perceptions. There are numerous examples of outstanding conduct in the country where good samaritans are rendering yeoman service to society, some civil society organizations are putting in selfless work in the field as are some philanthropists, scientists and educationalists doing pioneering work. By highlighting such actions the media can inspire others to follow good examples, and I would urge the media to work in a positive spirit, as it expands its reach and coverage. A responsive and responsible media is an asset in maintaining the vitality of democracy and its institutions.
Fellow citizens,
It is heartening that our economy is progressing at a stable pace and that even in the face of difficult circumstances during the global financial downturn, its performance was appreciable. We are now returning to the pre-crisis growth pattern and are confident of growing at over 9 percent next year. All sectors of the economy will be contributors to our growth trajectory. However, rising inflation particularly food prices, are a cause of serious concern and draw attention to the urgent need to take suitable action, and also look at more innovative approaches towards food security, agricultural production and rural development.
The Green Revolution which made our nation self sufficient in foodgrains has run its course. We need a Second Green Revolution that maximizes productivity, and yet generates income and employment opportunities for the rural population. The First Green Revolution was almost confined to irrigated areas, and now we should also focus on rain fed areas, which could become the cradle for the Second Green Revolution. We should bear in mind that our agricultural holdings are fragmented, small and are likely to further decrease in size; making economic viability of farming a big issue. It is said that small farmers are leaving farming, because of poor returns and scarcity of agricultural labour. In such a situation, it would be advantageous to think of modernization and mechanized farming, and there should be deliberations on evolving suitable models for partnerships between farmers, private sector and the Government in agriculture and rural development. In any arrangement, it should be kept in mind that farmers are stakeholders in every aspect related to agriculture, whether it is cultivation related activities, warehousing, processing, marketing, research or development. Farmers, therefore, must be involved in all these various activities, with a sensitivity that safeguards their rights on their land and its produce. The corporate sector should take up responsibility to make agriculture productivity remunerative, particularly in rain fed farming areas, as food security is of prime importance for our country.
Every year there is drought in some or the other part of the country. A national campaign for foodgrain productivity should be undertaken to create awareness about sustainable food production for food security in every State and in every block. Similarly, national planning for integrated production, particularly of foodgrains like cereals, oilseeds and pulses is needed and should be implemented, given that our population in the next 20 years is likely to become 148 crore. Each State should, as far as possible and as per local conditions, try to produce food grains required by it. This will result in saving transport and storage costs, as also prevent wastage during transport and handling, besides helping in quicker distribution of foodgrains.
In agriculture as in all other fields we need innovations more than ever before. This decade has been designated as the 'Decade of Innovation' in India. Our scientists and researchers have the talent and the capacity to look at high-end technology as also at cost-effective, location-specific and affordable innovations for wider use in the country. Access to innovations is an integral part of their practical use. In a situation of rapidly moving global knowledge economy, our pace of research must accelerate. Larger funds should be allocated for science and technology so that such scientists can undertake in depth research in a wide range of subjects.
Development and progress require an environment of stability and security. The work of our police and internal security agencies is critical in this field, as also is our cooperation and dialogue with our neighbours for stability in our region, and with the international community to create a peaceful world. Terrorism poses the single most detrimental threat to the progress of humankind. There is a crucial need for concerted action by all members of the international community to eradicate the threat of terrorism. India's profile in global affairs is the focus of international attention today. As India assumes its seat as a non-permanent member of the UN Security Council, it will intensify efforts to effect concerted and collective global action against terrorism, and will also work with a deep sense of responsibility on all global issues.
Fellow Citizens,
Many developments in the last few years have brought to our attention the importance of united action to achieve our goals besides emphasizing the need to continue to adhere to the basic values of our country. Here, I am reminded of some lines of a well-known poem:-
Speech
Which means:-
Compassion, non-violence, goodwill
May always flow in unison.
With these words, I once again greet all fellow citizens on the occasion of Republic Day.
Jai Hind!


*********Source :- President of india .nic ,(content is provided by President’s Secretariat. in that site ) 

Republic day wishes

Freedom in Mind,
Faith in Words,
Pride in our Heart,
Memories in our Souls.
Lets Salute the Nation on
REPUBLIC DAY.
==–..__..-=-._.
!!==–..__..-=-._
;
!!==–..*..-=-._;
!!==–..__..-=-._;
!!
!!
!!
“VANDEMATARAM”
HAPPY REPUBLIC DAY..

31 States,
1618 Languages,
6400 Castes,
6 Religions,
6 Ethnic Groups,
29 Major Festivals
1 Country!
Be Proud To Be An Indian!…
Great Republic…
Happy Republic Day !!

Tuesday, January 25, 2011

Padma Awards 2011

The Padma awards for this year have been declared today. Hyderabad-born Indian cricketer, VVS Laxman has been awarded the Padma Shri for his outstanding performance in Indian cricket. Laxman is the one of the finest batsmen of Indian test cricket, known for pulling off India out of many crisis situations. Yesteryear film actress, Waheeda Rahman will receive this year's Padma Bhusan for her outstanding contribution to Indian cinema. Earlier, she had won the Padma Shri in 1972. Indian music composer Mohammed Zahur "Khayyam" Hashmi, better known as Khayyam has been declared the winner of 2011's Padma Vibhusan. Earlier in 2007, Khayam was awarded the Sangeet Natak Akademi Award in Creative Music, by the Sangeet Natak Akademi, India. Other     
Padma Shri Awardees are: Kajol, Sushil Kumar.
Padma Bhusan Awardees are: Shyam Saran , Chanda Kochar,Sashi Kapoor. 
Padma Vibhusan Awardees are: Kapila Vatsyan, Montek Singh Ahluwalia, Aziz Premji, Vijay Kelkar, Brojesh Mishra and A Nageshwar


                    
The Bharat Ratna is likely to be awarded to none other than cricketing legend, Sachin Tendulkar. Tendulkar's name has already been nominated for the Bharat Ratna awards, confirmed Ambika Soni, the Information and Broadcasting Minister.  If Sachin wins the Bharat Ratna this time, it will be the first time the Bharat Ratna will be given to any sportsperson in India. The Padma awards and the Bharat Ratna will be awarded to their respective recipients on January 26, 2011- India's Republic Day.



*****  After all discussions there is no Bharat Ratna Award This Year

Tuesday, January 18, 2011

Here are some things apart from working on your engineering concepts, that you should do for a complete preparation for GATE:
1. Solve previous years GATE papers: Solving previous years papers gives you a fair idea of what the actual paper would be like. It also brushes up your basics and exposes your areas of improvement.
2.  Solve as many test papers as possible. This actually is the best way to keep improving as you prepare for GATE.
3. Analyze : Analyzing your test results is a very important part of taking the test. If you do not analyze, the test does not add value. You should minutely analyze and define as to where you could have scored more; analyze your accuracy rates in various topics and maintain a topic wise datasheet which lists your performance topic wise for different test papers.
4. Simulate actual test environment : This is very important. The actual test happens in a classroom, and is timed. When you take up the test, switch off your cell phone, have a timer which times your tests, and avoid taking any breaks. Also, if possible, take up a mock test series which enables you to take the test in a classroom environment.

Monday, January 10, 2011


How to Prepare For GATE With One Month to Go



As GATE exam is just a month around, most of the students started heating up for GATE exam. This is the time when students are done with their regular engineering exams and it’s time to get really serious about GATE. If someone misses this month or doesn’t get serious with preparation then cracking GATE would just be a nightmare.
With a short time to prepare for GATE, that consists of four years of engineering courses, it can be a really a confusing task. Even students preparing yearlong could be puzzled about their approach for preparing for GATE. In this post I tried to give my approach toward competitive exams specially at the verge of the exam.
I know most of the students think that saying it is easier than doing it. But remember that to be successful, doing and trying hard is more important than just keeping on thinking. With this post I call all of you to leave your beds for a month. Exhaust yourselves, work hard and stay focused for GATE. Believe me you will make it happen or at least you will feel great that you gave a sincere try.
If you want to do great in GATE then there are five essential things you need to follow at this moment.
  1. Easy subjects first
    When time is less for preparation, the best thing do is to start preparing with the subjects you feel easy about. As I mentioned in my earlier post that makes a priority of subjects when you have sufficient time to prepare and clear your doubts. If you analyze deeply, most of the subjects have almost the same weight age.
    Easy subjects will finish quickly and make you more confident. As soon as you finish a topic you will see more energy and excitement of cracking the GATE.
  2. Use Short notes
    Try to collect short notes, such as brilliant tutorials, GATE forums or some other study material. This will help you speed up your preparation, as the notes don’t go into every detail of the subject, cover the essential concepts needed for the exam and save time.
    Do follow only one note as different notes may use different analogy and may lead to confusion.
  3. Get Question banks
    Have a question bank or GATE questions’ answer book for sure. As soon as you finish a topic you can refer to different types of questions that can be asked. Don’t worry if you cannot solve all the questions. At least you will get an idea of the type of question you can expect and where do you stand.
  4. Previous year papers
    Every GATE aspirant must solve previous year question papers. First and foremost it gives an idea about the GATE question paper. Secondly, sometimes you may get some questions from previous papers.
  5. Avoid reading from soft copies
    It’s very common among student to search and download the soft copies of the books and notes. These soft copies can be easily found, downloaded and shared. But the disadvantage with soft copies is that you will read them on computer and can be easily distracted to other things like music, videos, internet … etc.
    It is always beneficial to make a hard copy of the important pages and avoid computer to concentrate well on the desired subject. You can also write down some important points if don’t want to have printed copy.
    The idea is to avoid all kind of distraction that prevents GATE preparation.

GATE Video Lectures and Video Tutorials


This is tuff time to prepare for GATE 2011, these video can help GATE 2011 aspirants to learn basic engineering concepts and speedup the preparation of GATE in last stages. I also hope that these will help in IIT M.Tech interviews.

Sunday, January 9, 2011

 History of Mobile / Cell Phone

The development and history of the mobile phone has seen a tremendous number of changes since the first cell phones were introduced. It was only at the beginning of the 1980s when mobile phone technology started to be deployed commercially. Since then there have been many new cell phone or mobile phone systems introduced, and many improvements have been made in this form of radio communications technology. The mobile phones themselves as well as the associated equipment including base stations and the other network equipment and cellular technology has become much cheaper and far smaller.

One of the major changes is the level of market penetration that has been achieved. Cellular technology has enabled many people to have phones where it would not otherwise be possible. In many countries there are more mobile phone accounts than people, i.e. many people have more than one account, possibly one for private use and one for work. In this way cellular technology has enabled market penetration to become more than 100%.
With the development of cellular technology, mobile phones now have many more facilities and capabilities than the first ones to be sold. Mobile phone history will show a steady increase in the capabilities of these phones.

Mobile phone history overview

The phones themselves have undergone many changes during their history. Cellular technology that has been used has improved dramatically. The first systems to be launched were based on analogue technology. The early phones were very large and could certainly not be placed in a pocket like the phones of today.
The first generation (1G) phone systems as they are now known were overtaken in the early 1990s by the first digital systems.
The high levels of use and limited frequency allocation meant that greater spectrum use efficiency was needed. Accordingly the next or second-generation (2G) phone systems were introduced to meet this need.
As the usage of phones increased and people became more mobile, new possibilities emerged for using the phones for data transfer. They could be used to download information from the Internet, or to send video. The first stage in this migration was to provide a medium speed data transfer capability. These systems were accordingly known as 2.5G.
However the ultimate aim was to provide a relatively high-speed data transfer capability. These full third generation (3G) systems took longer to develop and roll-out than had been originally anticipated as a result of higher development costs and a downturn in the global economy. However they are able to provide a significant improvement in capability over the 2.5 G systems


Analogue Systems

There was an enormous variety of first generation systems that were introduced. Much of the early development of cellular systems had been undertaken in the USA, but the first fully commercial system to be launched was the Nordic Mobile Telephone (NMT) system. Shortly after this a system known as the Advanced Mobile phone systems (AMPS) was launched commercially. This was developed primarily by Bell and was introduced in the USA although many other countries used this system later. A further system known as Total Access communication systems (TACS) developed by Motorola was introduced in the UK and many other countries.
These were the main systems that were developed, although around the globe many variants were developed to suit the needs of the individual countries.
Although there were differences in the specifications of the systems, they were all very similar in concept. The voice information was carried on a frequency-modulated carrier. A control channel was also used to enable the mobile to be routed to a suitable vacant channel. The channel spacing for each system was different. NMT used a 12.5 kHz channel spacing, AMPS, a 30 kHz spacing and TACS a 25 kHz spacing. A later development of AMPS called NAMPS or narrowband AMPS used a 10 kHz channel spacing to conserve spectrum.

Digital Systems

The analogue systems were very successful, but their very success started to show some of their shortcomings. The main one was the inefficient way in which they sued the spectrum. With the growth rates that were being seen, there was insufficient spectrum to support the quality of service that was required. By converting to a digital system, considerable savings could be made. A number of systems arose from this initiative. These second-generation systems as they were termed, started to be deployed in the early 1990s and their history is just as remarkable.
The system that was developed in Europe was the result of 26 telecommunications companies working together. Work actually started in 1982, and the roll-out commenced in 1991. The system known by the letters GSM was originally called Groupe Speciale Mobile but this was later changed to Global System for Mobile communications in view of the wide involvement in its development. It used time division multiple access (TDMA) to allow up to eight users to use each of the channels that are spaced 200 kHz apart. The basic system used frequencies in the 900 MHz band, but other bands in the 1800 and 1900 MHz (USA) bands were added. New bands in the 850 MHz region were also added.
In the USA a system specially designed to operate alongside their AMPS system was devised. The system was known under a variety of names including Digital AMPS or DAMPS, and US Digital Cellular (USDC), although it is normally known just as TDMA today as it relies on TDMA technology. The system was originally defined under standard number IS-54, although this was later updated to IS-136 and it uses a 30 kHz channel spacing to make it compatible with the existing AMPS systems in operation.
Another development in the USA from Qualcomm took a major leap in technology. It introduced a totally new concept for multiple access. Based on direct sequence spread spectrum (DSSS) that had previously been used for military transmissions, it used a multiple access system known as code division multiple access (CDMA). The new system offered far greater levels of spectrum efficiency although it required more complicated circuitry in the handsets. The system was defined under standard IS-95 and each carrier had a bandwidth of 1.25 MHz, although many users could use the same channel. The specification was updated from IS-95A to IS-95B. It was this later standard that went under the trade name cdmaOne.

2.5G

Once the second-generation systems became established it soon became apparent that the limited data capabilities of some of the 2G systems were a significant disadvantage. Many applications  for data transfer with the increased use of the Internet and laptop computers were seen. Even though the third generation systems were on the horizon, developments were needed to provide a service before they entered the market. One of the first was the General Packet Radio Service (GPRS) development for the GSM system. Its approach centred on the use of packet data. Up until this time all circuits had been dedicated to a given user in an approach known as circuit switched, i.e. where a complete circuit is switched for a given user. This was inefficient when a channel was only carrying data for a small percentage of the time. The new packet switched approach routed individual packets of data from the transmitter to the receiver allowing the same circuit to be used by different users. This enabled circuits to be used more efficiently and charges to be metered according to the data transferred.
Further data rate improvements were made using a system known as EDGE (Enhanced data Rates for GSM Evolution). This basically took the GPRS system and added a new modulation scheme, 8PSK, to enable a much higher data rate to be achieved. Whilst the symbol rate remained the same at 270.833 samples per second, each symbol carried three bits instead of one.
Whilst GPRS and EDGE were applied to GSM networks, enhancements were also applied to the CDMA system that originated in the USA. Here an evolutionary path from 2G through 2.5G to 3G was created. The intermediate stage was development of cdmaOne was CDMA2000 1X. This scheme retained the 1.25 MHz bandwidth of IS95 / cdmaOne, but by adding further channels enabled data transfer rates of 307 kbps to be achieved, thereby doubling the capacity of IS95B.

Third Generation

Although technologies such as GPRS, EDGE and CDMA2000 1X were able to deliver significantly higher data rates than their predecessors, the final migration was to the full 3G service. There were three main technologies.
From Europe there was the UMTS (Universal Mobile Telecommunications System) using wideband CDMA (W-CDMA). This system used a 5 MHz channel spacing and provided data rates of up to 2 Mbps.
Then there were the CDMA2000 evolutions. The first to be launched was CDMA2000 1xEV-DO. Here the letters EV-DO stood for Evolution Data Only. The idea for this system was that many of the applications would only need a data connection, as in the case of a data card for use in a PC to provide a wireless Internet capability over a mobile phone system. For any applications needing both data and voice a standard 1X channel would be required in addition. Although using CDMA technology, the EV-DO system also used TDMA technology as well to provide the throughput whilst still maintaining backward compatibility with IS95 (cdmaOne) and CDMA2000 1X.
The next evolution of the CDMA2000 family was CDMA2000 1xEV-DV. This was an evolution of the 1X system, and totally distinct from 1xEV-DO and it provided a full data and voice capability. Again this system was able to provide backward compatibility with IS95 (cdmaOne) and CDMA2000 1X whilst still being able to provide a data capability of 3.1 Mbps in the forward direction.
These major two players in the 3G scene both used what is called frequency division duplex (FDD) where the forward and reverse links used different frequencies. Within UMTS there is a specification covering a time division duplex (TDD) system where the forward and reverse links used the same frequency but use different timeslots. However the TDD version is not being deployed for some time.
A third 3G system that originated in China uses TDD. Known as time division synchronous CDMA (TD-SCDMA) this system used a 1.6 MHz channel spacing and was thought to be likely to take a significant portion of the Chinese market along with those in neighbouring countries

Summary

The history of the mobile phone has taken place over a comparatively short time, but cellular technology has been seen to develop at a tremendous rate. As a form of two way radio communications, cellular technology has outstripped every other form of radio communications technology. It took just over 20 years to migrate from the first analogue systems to the 3G systems capable of high data rate transfers. Now development of cellular technology is looking at 4G standards capable of data rates of over 100 Mbps. With many developments still taking place, the outlook for cellular technology looks as if it will be particularly interesting.

Monday, January 3, 2011

Resistor attenuator circuits

- for use in radio frequency circuits including receivers and transmitters, etc

Attenuator circuits are used in a variety of radio frequency circuit design applications. The attenuators reduce the level of the signal   and this can be used to ensure that the correct radio signal level enters another circuit block such as mixer or amplifier  so that it is not overloaded. As such attenuators are widely used by radio frequency circuit designers. While it is possible to buy ready made attenuators, it is also easy to make attenuators for many applications. Here a simple resistor network can be used to make attenuators that provide levels of attenuation up to figures of 60 dB and at frequency of 1 GHz and more, provided that care is taken with the construction and the choice of components.
One important feature that is required for radio frequencyapplications is that the characteristic impedance should be maintained. In other words the impedance looking into and out of the attenuator should be matched to the characteristic impedance of the system.


T and Pi networks

There are two basic formats that can be used for resistive attenuators. They are the T and pi networks. Often there is little to choose between them and the choice is often down to the preference of the designer.
As the name suggests the "T"section attenuator is in the shape of the letter T with two resistors in the signal line and one in the centre to ground.
T section attenuator

T section attenuator

The two resistor values can be calculated very easily knowing the ratio of the input and output voltages, Vin and Vout respectively and the characteristic impedance Ro.


T section attenuator equations



The pi section attenuator is in the form of the Greek letter pi and has one in line resistor and a resistor to ground at the input and the output.
Pi section attenuator



Pi section attenuator

Similarly the values for the pi section attenuator can be calculated


Pi section attenuator equations


Practical aspects


It is generally good practice not to attempt to achieve any more than a maximum of 20 dB attenuation in any one attenuator section. Even this is possibly a little high. It is therefore common practice to cascade several sections. When this is done the adjoining resistors can be combined. In the case of the  T section attenuator this simply means the two series resistors can be added together. For the pi section attenuators there are parallel resistors.
When making large value attenuators, great care must be taken to prevent  the signal leaking past the attenuator and reaching the output. This can result from capacitive or inductive coupling and poor earth arrangements. To overcome these problems good earth connection and careful layout, keeping the output and input away from one another are required. It may also be necessary to place a screen between the different sections.
Using these attenuators a surprisingly good frequency response can be obtained. Non-inductive resistors are required to ensure the best performance, and using good printed circuit board techniques and surface mount resistors, a good performance at frequencies in excess of 1 GHz are easy to achieve.