What is MIMO

Multiple-Input Multiple-Output (MIMO) technology is a wireless technology that uses multiple transmitters and receivers to transfer more data at the same time. Wireless products with 802.11n support MIMO. This is part of the technology that allows 802.11n to reach much higher speeds than products without 802.11n.

MIMO technology takes advantage of a radio-wave phenomenon called multipath where transmitted information bounces of walls, ceilings, and other objects, reaching the receiving antenna multiple times via different angles and at slightly different times. Multipath is a natural occurrence for all radio sources. Radio signals bounce of objects and move at different speeds towards the receiver. In the past multipath caused interference and slowed down wireless signals. MIMO takes advantage of multipath to combine the information from multiple signals improving both speed and data integrity.

MIMO technology leverages multi path behavior by the use of multiple, smart transmitters and receivers with an added spatial dimension to dramatically increase performance and range. MIMO allows multiple antennas to send and receive multiple spatial streams at the same time. Smart transmitters and receivers are used with all 802.11n devices. Using multiple antennas the data can be sent and received through multiple signals. More antennas usually equates to higher speeds. A wireless adapter with 3 antennas may have a speed of 600 Mbps while an adapter with 2 antennas has a speed of 300mbps. The router also needs to have multiple antennas and fully support all of the features of 802.11n to gain the highest speed possible With this extra bandwidth cannot be needed for achieving high data rate.

MIMO makes antennas work smarter by enabling them to combine data streams arriving from different paths and at different times to effectively increase receiver signal-capturing power. Smart antennas use spatial diversity technology, which puts surplus antennas to good use. If there are more antennas than spatial streams, the additional antennas can add receiver diversity and increase range. In order to implement MIMO, either the station (mobile device) or the access point (AP) need to support MIMO. Optimal performance and range can only be obtained when both the station and the AP support MIMO. Legacy wireless devices can't take advantage of multipath because they use a Single Input, Single Output (SISO) technology. Systems that use SISO can only send or receive a single spatial stream at one time.

How to calculate the value of a ceramic capacitor

You might have come across situations were you needed to calculate the value of a ceramic capacitor. Today a large variety of such capacitors are available in the market but the value calculation of all remains the same. All these capacitors are marked with a three digit number code, say, 104. There are two key points to remember in the value calculation. First point is that in the marked number code the first two digits are the significant digits and the third digit is the multiplier. The second point is that the final value is in the 'pico Farad' unit (without conversion).

For example, a value 104 on the capacitor indicates that the value of the capacitor is 10 x 10⁴ pF or 100 nano Farads (μF) or 0.1 micro Farads (μF). Some other codes and their corresponding values are given below:

Capacitor Code	Value in pF	Value in μF
101	100	0.0001
102	1000	0.001
103	10000	0.01
104	100000	0.1
105	1000000	1

For some capacitors there will be an additional alphabet code at the end of the number marking say 104J. This alphabet code indicates the capacitor tolerance. The tolerance values are calculated as given in the table below

Code	Tolerance
C	±0.25pF
J	±5%
K	±10%
M	±20%
D	±0.5pF
Z	+80% / -20%

For example, 104J coded capacitor has the value 0.1 ± 5% μF. 
For a 104C coded capacitor, the value is 0.1 μF ± 0.25pF

How to Design an Air Core Inductor

An air core coil inductor is made by winding several turns of enameled wire around a none ferromagnetic material core (like plastic, ceramic, or other non-magnetic forms, as well as only with air inside the windings).

These coils have lower inductance compared to the ferromagnetic core coils. Despite of this characteristic, air core coil inductors are often used at high frequencies because they are free from energy losses called core losses that occur in ferromagnetic cores (which increase with frequency).

In air core coils with winding not rigidly supported on a form (core), a side effect called 'microphony' may occur. 'Microphony' refers to the mechanical vibration of the windings which in-turn causes variation in the coil inductance.

The major advantages of air core coils are:

1. The inductance is independent of the electrical current through the coil since there is no ferromagnetic core to get saturated as the current increases.

2. There is no iron loss as in case of ferromagnetic cores, thus giving a better Q Factor and low distortion with increased frequency.

3. They can be operated at high frequencies (upto 1 Ghz).

The inductance of an air core coil inductor can be calculated using the equation shown in the above figure.

here,

    L = Inductance (in uH)
    a = Diameter of the coil (in Inches)
    b = Length of the coil (in Inches)
    c = Diameter of the winding wire (in Inches)
    n = Total turns of wire

Note: The formula is valid only if the value of b is greater than 0.4a.

How a software interacts with hardware? - Basics of Computer Electronics

In modern computer programming, every software is written using a software programming language. This text program (called high level language) is then converted into runnable (executable - low level language) format by special softwares called compilers(or interpreters). The specialty of this low level language is that it could be understood by a hardware (precisely a microprocessor - a type of electronic component which can perform electronic operation based on software codes). The microprocessor reads the program (low level) and perform the corresponding action.

Now the microprocessor understands a particular code by reading (actually, its sensing electronically) the bits in the particular code. For example if a microprocessor is made in such a way that it will make its 5th pin to +5 voltage level when it reads a bit sequence 0010011, then the processor perform the action whenever it reads a 0010011 in the code. In this way the actions to be performed by a particular microprocessor and the corresponding bit sequence is defined at the time the microprocessor is manufactured. As you know, in a computer system, the microprocessor is the brain, so all the operations are carried out by it.

The computer peripherals (like mouse, keyboard etc) are identified by using configuration files called drivers. These files contain the information that is to be used for interacting with the hardware. The Operating System (windows, linux etc) controls and monitors the peripheral (hardware) control and management.

7 TIPS TO PASS ANY EXAM

Here are 7 tips that can help every student to pass exams:

1. No limiting belief please

Remove the limiting belief that you can’t pass. If you believe you can pass or you believe you cannot pass, you are right.

I have seen students under the impression that examiner is their enemy. Please don’t think so. Pass percentage might be low, but students do pass their exams. So, don’t think that you will be in a failure category ever.

2. Understand the structure of paper

First of all, understand the structure of paper – is there any marks allocation for a particular topic? Secondly, if there is marks allocation, is examiner following it? The best thing to do is to review the past five papers.

What is the key topic i.e. examiner’s favorite? Is there any article by examiner in the Students’ Accountant or any other relevant student magazine? Study that topic and prepare for it, even if you don’t like it!


3. Taking notes

Prepare for exams by way of ‘notes’ which you can recall quickly at the time of taking exam. This will help in two manner. First, when you write, you are in better picture of giving your mind instruction through written letters. Secondly, you can revise from your notes instead of opening the book when exam day is near. Here is my strategy for taking notes:

Take a paper and turn it in landscape format. Put three columns in landscape form. Once done, take synopsis of a chapter in smaller fonts and the language which you can easily understand. Write bullet points, important concepts and key ideas which you need to remember.

These notes should be used at the time when paper is on head and you need to revise whole subject in two to three hours.


4. Remembering / memorizing key ideas and formulae

- One of the key ideas to memorize ideas e.g. formulae, is to write them in small charts and hang it in front of your bed.

See those formulae daily before going to bed and rising up. Use different colours and markers.

Believe me, in my statistics paper, I was recalling the formulae in the exact colors which I wrote on charts.


 5. Exam practice

Practice mock exam – be your own examiner. Take any past paper and solve it as a mock exam. Solve past paper in the time allocated in exam. Think you are in exam hall and solve the paper accordingly.

Check your paper and give yourself marks. See how are you performing in mock exam and be sincere to yourself.


6. Time your paper

Here is technique to time your paper: Take total marks and total time. Subtract 10 minutes from the total minutes. Divide the remainder with the marks and you get time per marks

For example: If there are 100 marks for a paper and you have 180 minutes. Subtract 10 minutes. This means you have 170 minutes altogether or 1.7 minutes per mark.

Make sure that you don’t spend more that 1.7 minutes per mark e.g. if a question is of 10 marks, maximum time you should spend should be 17 minutes.

It happens that students try to focus on one particular question and if they are unable to solve it, they get confused. Don’t panic. Start next question. If student has time, he / she can take up that particular question later on.

Try to allocate 10 minutes at the end of exam to review the paper thoroughly.


7. Don’t annoy examiner

See for spelling errors and writing style. Writing needs to be legible and understandable. As a teacher to many students, I have noticed that spelling errors and the way students write, at times, is not understandable. Examiner has very less time to check paper. If your paper is examiner friendly, you are going to attract good marks.

MySQL Server (Windows) - Applying Security Settings Failed

You might have encountered the following 'Applying Security Settings' failure error while installing MySQL Server (more precisely, during the instance configuration) for Windows.

This occurs because an older MySQL database (instance) exists in your system. To find where it is located, open the my.ini file in the MySQL installation folder and find '#Path to the database root' string. The line next to it specifies the default path to the database folder. By default this will be pointing to "C:/ProgramData/MySQL/MySQL Server 5.5/Data/".

Now remove the existing MySQL installation. Next, open the parent folder of the database location ( ie if the path is "C:/ProgramData/MySQL/MySQL Server 5.5/Data/" then open the folder that is the parent of "MySQL" folder). Here it will be "C:/ProgramData". Then delete the "MySQL" folder (with all its contents) in it.

Notes:

1. Deleting only the "Data" folder will also serve our purpose. But it would be better if you delete the entire location as specified above. 

2. The "ProgramData" folder is a hidden/system folder. So in order to access it, type the path  of the folder ("C:/ProgramData") in your windows explorer address bar and press enter.

3. Deleting the database will delete all the data stored in it. You may not be able to recover it. 

Now install a fresh copy. You will see that it works like charm!

How to fix phpmyadmin not found error

Are you getting “404 Not Found” error while you’re trying to load your localhost phpmyadmin (say, http://localhost/phpmyadmin)?

     This happens due to the misconfiguration of apache server settings (or it was not configured at all), during the phpmyadmin installation. To reinstall (reconfigure) the package, run the following command in the Linux terminal (Ctrl + Alt + T):

sudo dpkg-reconfigure -plow phpmyadmin

While reconfiguring, select apache2 as the web server and provide the necessary configuration details.

If the above command does not work, then you may try the following commands in the terminal:

sudo ln -s /etc/phpmyadmin/apache.conf /etc/apache2/conf.d/phpmyadmin.conf
sudo /etc/init.d/apache2 reload

The first command will create a soft (symbolic) link of the apache configuration (that is provided along with phpmyadmin installation package) into the apache installation folder. The second command will restart the local apache server.

Hope this solves your problem.