OFDM definition

Before we learn about OFDM, first let we check it out what is full form of OFDM. OFDM is a modulation format used for the latest wireless communications technology. 

OFDM is a multi-carrier transmission technology. OFDM is used to obtain a higher data rate in the multipath fading environment of mobile communication.

In mobile communication, the selection of digital modulation is dependent on three parameters. They are listed below :
  • Narrower bandwidth 
  • Efficient power utilization
  • Elimination of intermodulation products

CDMA definition

Code division multiple access (CDMA) is one type of channel access method, In this method user, may transmit at the same time using same frequency band but with different codes so that we can easily decode to identify a particular user. 


CDMA definition
CDMA

TDMA definition

Time division multiple access (TDMA) is one type of multiple access method. In each user allowed to transmit only in a specified time slot with a common frequency band. It allows several users can transmit to share the same frequency band at a different time, so each using its own time slot.

TDMA

OSI full form

What is the full form of OSI?


Answer:

  • Open Systems Interconnection


What does OSI mean?


 OSI is an effort to standardize networking that was started in the year 1977 by the ISO. 

It is a conceptual model so that it characterizes and standardizes for the communication functions such as the telecommunication or computing system without regard to its internal structure and technology of a system. 

The OSI model comprises seven layers following below:

  • Layer 1 -  Physical Layer
  • Layer 2 - Data link layer 
  • Layer 3 - Network layer 
  • Layer 4 - Transport Layer 
  • Layer 5 - Session layer 
  • Layer 6 - Presentation layer
  • Layer 7 - Application layer

FDMA definition

Frequency division multiple access (full meaning of FDMA) is a frequency band, it is one types of channel access method and it can be divided small frequency channel and also have different channel are allocated to different users. Multiple users can transmit at the same time but on different frequency channel as shown in the figure below :

FDMA



How FDMA work

FDMA is a channel access method can be implemented at the MAC full form is a media access control layer of the data link layer in the OSI full form open systems interconnection reference model for networking protocol stacks. 

 First, let we check it out the full meaning of FDMA. It is a frequency band, it is one types of channel access method and it can be divided small frequency channel and also have different channel are allocated to different users. The user can be assigned a specific frequency band in the electromagnetic spectrum and at that time a call that user is the only who has the right to access the specific band. 

 In the AMPS cellular phone system, the frequency band is allocated from the electromagnetic spectrum as follows :

Two different frequency bands are used to allow full duplex communication between the base and mobile stations. 

Transmission by mobile station used AMPS cellular phone: 824 MHz to 849 MHz
Transmission by base station used AMPS cellular phone: 869 MHz to 894 MHz

 Both of these band are then divided into discrete channels that are 30 KHz wide in bandwidth.

FDMA applications

Frequency division multiple access is a frequency band, it is one types of channel access method and it can be divided small frequency channel and also have different channel are allocated to different users. Now here check it out the application of FDMA  to know more details about FDMA. 

 Applications :
  • Telephone system
  • Radio system 
  • Cable TV
  • Walkie talkies
  • Mobile network for a closed user group. e.g. Wi-Fi
  • Total access communication systems (TACS)
  • 2G mobile communication
  • GSM uses FDMA in combination with TDMA
  • UMTS in combination with other multiplexing techniques 


Full form of MAC

What is full form of MAC?

 Answer :
  • Media Access Control

What does MAC mean?

A MAC is a unique identifier assigned to a network interface controller for communication on the physical or data link layer of the network segment. MAC addresses are the most common network used for IEEE 802 network technology, Including Wi-Fi.

Difference between Hub and Switch

This article gives information about like layers, purpose, functionality, number of the port, speed, cost, elements to know more details about hub and switches.
  • Hub uses physical layer, Switch uses a data link layer.
  • Hub is a passive device, Switch is an active device.
  • Hub is to connect a network of personal computers together, they can be joined a central hub while Switch is to allow connection to multiple devices, manage ports and also have manage VLAN security settings.
  • In when we use hub electronics device that connects many networks device together so that device can exchange data while using networks switches is a computer networking device that is used to connect many more devices together on a computer network.
  • When we are using Hub data transmission using electrical signal or bits while When we are using switch data transmission using frame and packet.
  • Hub has 4/12 port while switches are multiport bridges that have 24/8 port.
  • Hub cannot learn or store MAC address and switch store MAC addresses in a lookup table.
  • In using hub speed up to 10 Mbps, using switch speed up to 10/100 Mbps or 1 Gbps.
  • A switch is an intelligent device, a hub is not an intelligent device.
  • Hub has one broadcast domain while a switch is one broadcast domain (unless VLAN implemented.
  • When we use switches many spanning-tree is possible and when we use hub there is no spanning-tree is possible.
  • When we have use hub transmission mode has a half duplex and when we use switches transmission mode has half/full duplex.
  • Sun system, Oracle, and Cisco are the manufactures of the hub while Cisco and D-link juniper are manufactures of switches.
  • Hubs were less cheap in the past but switch prices have come down significantly.
  • Switches have replaced hubs in most modern day application nowadays.
  • Collision doesn't happen in switches but are very common in hubs.
  • Bandwidth is shared among network elements causing slowdown.
  • The number of elements is severely limited for hubs as compared to switches.

Difference between thyristor and transistor

Before we learn about the difference between thyristor and transistor first let we understand the difference between two types of transistor called NPN and PNP transistor and thyristor meaning. Now let us talk about the difference between thyristor and transistor to know more details about this topic.
  • The thyristor is a four-layer semiconductor device, the transistor is a three-layer semiconductor device.
  • Thyristor having better power handling capacity than a transistor.
  • Thyristor having high current and voltage rating while transistor having too much low current and voltage rating.
  • In thyristor internal loss is less as compared to a transistor device.
  • Thyristor having suitable for high power applications but the transistor is suitable for a high-frequency application.
  • Rating in thyristor is in kW while the transistor is always in measure watt.
  • A transistor having too much light in weight.
  • The thyristor can be used as switches while transistors can be used as switches or amplifiers.
  • Thyristor requires more time to turn on and turn off but transistor require takes very less time to turn on and turn off.
  • The thyristor can be considered as a tightly couple pair of a transistor in an analysis.
So in this above difference we can to conclude that thyristor and transistor both devices are switching devices but thyristor is not suitable for the high-frequency application and the same way the transistor is not suitable for high power application nowadays.  

 Explore more information:
  1. Difference between IGBT and BJT
  2. Difference between NPN and PNP transistor
  3. Difference between BJT and MOSFET
  4. Difference between JFET and MOSFET
  5. Difference between IGBT and MOSFET
  6. Difference between GTO and thyristor
  7. Difference between IGBT and Thyristor
  8. Difference between thyristor and MOSFET
  9. What is NPN transistor
  10. What is BJT
  11. Difference between NMOS and PMOS

Advantages and disadvantages of electric drive

The machining equipment designed to convert electrical energy into mechanical energy and provide electrical control is called electric drive. This article gives information about the advantages and disadvantages of the electrical drive to know more details about the electrical drive. 
    Advantages of electric drive :
    • Very large range torque, speed, and power
    • Free from pollution
    • It can operate on all the quadrants of speed torque plane side
    • Working is independent of the environment condition
    • The efficiency of the drive is high
    • No starting problem easily start so not require any refueling
    Disadvantages of electric drive :
      • Cause noise pollution
      • An initial cost of the system is high
      • Application of the drive is limited
      • Poor dynamic response
      • The output power obtained from the drive is too much low
      • The output power obtained of conductor or short circuit, the system may get damaged due to which several problems occur

      Advantages and disadvantages of cycloconverter

      Cycloconverter is actually AC-AC converter. It converts a constant voltage and constant frequency AC waveform to another AC waveform. This article gives information about some advantages and disadvantages of cyclo-converter to know more details about cyclo-converter. 

      Advantages of cyclo-converter :
      • Efficiency is very high compared to other converters
      • Four quadrant operation is possible because cyclo-converter is capable of power transfer in both the directions
      • AC power at one frequency is directly converted to a lower frequency in a single conversion
      • If one of the SCR fails, the cyclo-converter operates with a distorted output
      • In this converter, power transfer is possible from supply load and vice versa at any power factor
      • Dynamic response is good 
      • Smooth low-speed operation
      Disadvantages of cyclo-converter :
      • Control circuit become complex so difficult to design
      • The output frequency of the cyclo-converter is 1/3th or 1/2th for responsible power output and efficiency
      • Power factor is too much poor at large values of α
      • More distortion at low frequencies
      Explore more information:

      Application of cycloconverter

      Cyclo-converter is basically converted input power at one frequency to output power at a different frequency with one stage of conversion.

      Basically, cyclo-converter is two types namely :  
      • Step down cyclo-converters
      • Step-up cyclo-converters
      The application of cyclo-converters include the following :
      • Speed control of high power ac drives.
      • Static VAr compensation.
      • Induction heating.
      • Synchronous motor.
      • Rolling mill drives.
      • Mine winders.
      • Cement mill drives.
      • This converter also has used for converting variable speed alternator to constant frequency output with age for use as a power supply in aircraft or shipboards.
      • HVDC transmission system.
      • Grinding mills.
      Explore more information:

      Cycloconverter operation

      A principle of cyclo-converter operation :
      • A cyclo-converter is a one types of device that converts AC power at a certain frequency into AC power but lower frequency.
      • The principle of cyclo-converter is described given below by using a single phase to single phase step-up converters and single phase to single phase step down converters.
      Cyclo-converter operation
      Types of cyclo-converter :
      1. Single phase to single phase cyclo-converter 
      2. Three phases to three phase cyclo-converter 
      Single phase to single phase bridge type cyclo-converter 
      • The operation of bridge type cyclo-converter shown in the figure. It can be easily explained for both discontinuous and continuous load current. The voltage and current waveform would again be as shown in the figure. 
      • It consists of a total of eight thyristors, four for the positive group and four for the negative group. 

      Bridge type single phase to single phase cyclo-converters
      This converter having to back to back connection of full wave rectifier. We have to assume that get on forth of the input voltage as the output.  For the first two cycles of  VS the positive converters operate supplying current to the load and the input voltage get rectified. In the next two cycles, the other converter called the -ve converters, it will operate the current load in the opposite direction called a reverse direction. so we also conclude that one converter is an operation the other converter will be disabled conditions, therefore, there is no current circulating between rectifiers.

      Three phases to three phase cyclo-converters 

      Out of the several configurations of 3 phase to 3 phase cyclo-configuration as shown in the figure. Here only one important scheme used for a large industrial drive is presented. Each phase of the 3 phase output must have a displacement of 120 degrees. The figure shows the circuit arrangement of 3-phase to three phase cyclo-converter using three sets of three-phase half wave circuit employing a total of 18 thyristors. 

      3-phase to 3-phase cyclo-converters
      Applications :
      The application of cyclo-converters include the following :
      • Speed control of high power ac drives.
      • Static VAr compensation.
      • Induction heating.
      • Synchronous motor.
      • Rolling mill drives.
      • Mine winders.
      • Cement mill drives.
      • For converting variable speed alternator to constant frequency output with age for use as a power supply in aircraft or shipboards.
      • HVDC transmission system.
      • Grinding mills.

      CRT advantages and disadvantages

      CRT full form stands for cathode ray tube also known as the picture tube. It is less bulky, as well as used in various applications. This article gives the advantages and disadvantages of CRT to give more information about CRT.

      Advantages of CRT :
      • Less expensive than other display technology
      • Fast response time
      • It can operate at any resolution, geometry and also for aspect ratio without the need for rescaling the image
      • Highest pixel resolutions generally available
      • They produce more colours
      • CRT also suitable for use even in dim or dark light
      • Produce a very dark black and grayscale and are the reference standard for all professional calibrations
      • Easily increases the monitor's brightness by reflecting the light
      • Fast response times and no motion artifacts
      Disadvantages of CRT :
      • Big back and take up space on a desk
      • Not suitable for very bright environments because less bright than LCD
      • They are large, heavy and bulky
      • Consume a lot of electricity and  also produce a lot of heat
      • Geometrical error at edges
      • Flickering at 50-80 Hz
      • Harmful DC and AC electric and magnetic fields
      Explore more information:

      What is electric drive

      • In many of industrial applications, electricity is one of the most important components. 
      • An electric motor is the most important part,  it is an energy transmitting device and the working machine.
      • An electric motor is the source of the motive power. An energy transmitting device delivers power from electric motor to the driven machine, it usually consists of a shaft, belt, rope, etc. 
      • An electric drive together with its working machine constitute is an electric drive system.
      • A ceiling drives together with its speed regulator but without blades is an example of an electric drive.
      • In short, a drive is a combination of the various system combined together for the purpose of motion control, so it is many more benefits of electric drive to motion control.
      • Electric drive is mainly two types: AC drive and DC drive In that drive motive power in dc and AC drive is provided by dc motors and ac motors respectively. This electric drive uses many devices like pumps, fans, robots, etc.
      DC drives :

       DC motors are used extensively in adjustable speed drive and position control applications. It can be also used conjunction with power electronic converters are dc separately excited motor or dc series motor. So depending upon the type of AC source or the method of voltage control, dc drive classified as under :
      Advantages and disadvantages of an electrical drive :

      The following advantages of electrical drive given below :
      • It has a very large range of torque, speed, and power.
      • It is very free from pollution.
      • It can operate on all the quadrants of speed torque plane.
      • Their working is independent of the environment condition.
      • The efficiency of the drive is high.
      • The drive can easily be started and it does not require any refueling.
      The following disadvantages of electrical drive given below :
      • It can cause noise pollution.
      • The initial cost of the system is high.
      • The application of the drive is limited.
      • It has a poor dynamic response.
      • The output power obtained of conductor or a short circuit device so the system may get damaged due to which several problems occur.
      • The output power obtained from the drive is low.
      Application of electrical drive :
      • A ceiling fan motor with a regulator.
      • A motor and conveyor belt with material on its belt.
      • Food mixer without food is processed.
      • It is also used as a large number of industrial and domestic applications.
      • It is also used Rolling mills and textile mills as well as some machine tools.
      • Some other applications like pumps, robots, washing, etc.
      • It can also use various traction like an electric train, electric buses, trams, trolleys, battery-driven solar power vehicles.

      Single phase DC drives feature

      Electric drive is designed to convert electrical energy into mechanical energy and provide electrical control.  Let we check features of single-phase DC drives one by one below :
      • Linear torque control
      • Adjustable current limit
      • Maximum speed settings
      • Stall relay contact
      • Armature voltage
      • Speed reference 0-10V 
      • Ramp single output
      • Current single output
      • Speed single output
      • Control fuses fitted
      • Stability adjustment
      • Suitable for shunt
      • Calibration range switches
      • Total demand signal output
      • Zero speed relay contact
      • IR compensation
      • Total demand signal output
      • Speed signal output
      • Current signal output
      • Power on and stall indicator LEDs

      Single phase DC drives

      • Electric drive is a combination of the various system combined together for the purpose of motion control, so it is many more benefits of electric drive to motion control.
      • Some basic features of single-phase DC drives is that speed single output, control fuses fitted,  and it can provide stability adjustment etc.
      • The general circuit arrangement for single phase dc drives as shown in the figure.
      • The arrangement for the speed control of a separately excited for dc motor from single phase source.
      • In this circuit to shown in the figure, it can insert inductor in series with the armature circuit to reduce the ripple in the armature current and also to make the armature current continuous for low values of motor speed to shown in the figure. 
      Single phase DC drives 
      Single phase dc drive may be subdivided as under :

      Three phase half wave converter drives

      • Three phases half wave converter drive consisting of two converts and a separately excited dc motor.
      • The armature circuit of the motor is fed through a three-phase half wave converter whereas its field is energized through a three-phase semi-converter.
      • Two quadrant operation can also be obtained from three phases half wave converter drive in case motor field winding is energized from a single phase or three phases full converter.
      Three phases half wave converter drive 


       V0 = Vt =  3Vml / 2∏ * Cos ɖ  for the  0< ɖ <  ∏

      The voltage expression is valid only for the contentious armature current. for three phase semi-converter, the average value field voltage from the equation given by this equation given below,

                                              Vf =  3Vml/2∏ * (1+Cos  ɖ1 ) for 0<  ɖ1 <  ∏


        Vml = Is the maximum value of line voltage and ɖ is the firing angle for converter 1.

      Application :

      A three-phase half wave converter drive is not normally used in the industrial application as introduce dc component in the ac supply lines.

      Three phase dual converter drive

      • The schematic diagram of three phases dual converter d drive as shown in the figure.
      • As per the circuit diagram converter, 1 allows motor control 1 and 4 quadrants whereas with converter 2 the operation in 2 and 3 quadrants obtained
      • For reversing the polarity of motor generated emf for regeneration purpose, field circuit must be energized from a single phase or three phases full converter.
      Three phases dual converter dc drive
      When converter 1 or 2 is in operation

      Average output voltage,

      V0 =  Vt is =  3Vm l/ 2∏  * Cos  ɖ1  for 0<  ɖ1 <  ∏

      With a 3 phase full converter in the filed circuit,

      Vf  =  3Vml/2∏ * Cos  ɖf  for 0<  ɖf <  ∏

      In case of circulating types of dual converter, ɖ1  + ɖ2 =180 degree

      Application :

      • Direction and speed control dc motors.
      • Applicable wherever the reversible dc is required.
      • Industrial variable speed dc drive.
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