All About Electronics

Analog Modulation & It’s types

2021-02-06T01:22:00.001-08:00

Analog modulation is further divided into three types:

 Amplitude modulation.

 Frequency modulation.

 Phase modulation.

Amplitude Modulation:

Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Amplitude modulation or AM as it is often called, is a form of modulation used for radio transmissions for broadcasting and two-way radio communication applications. Although one of the earliest used forms of modulation it is still used today, mainly for long, medium, and short-wave broadcasting and for some aeronautical point to point communications. Currently, this technique is used in many areas of communication such as in portable two-way radios, citizens band radio, VHF aircraft radio and in modems for computers. Amplitude modulation is also used to mention the mediumwave AM radio broadcasting.

One of the key reasons for the use of amplitude modulation was its ease of use. The system simply required the carrier amplitude to be modulated, but more usefully the detector required in the receiver could be a simple diode-based circuit. This meant that AM radios did not need complicated demodulators and costs were reduced - a key requirement for widespread use of radio technology, especially in the early days of radio when ICs were not available.

In general, amplitude modulation definition is given as a type of modulation where the amplitude of the carrier wave is varied in some proportion with respect to the modulating data or the signal.

Types of Amplitude Modulation:

o Double sideband-suppressed carrier modulation (DSB-SC).

o Single Sideband Modulation (SSB).

o Vestigial Sideband Modulation (VSB).

Advantages of Amplitude Modulation:

• Easier to implement.

• Simple demodulation circuit.

• Cheap receiver.

Disadvantages of Amplitude Modulation:

• AM signal is not efficient in terms of power usages.

• Use of bandwidth not efficient.

• Noise interference is high.

What is Modulation?

2019-11-28T17:24:00.001-08:00

Modulation is a process through which audio, video, image or text information is added to an electrical or optical carrier signal to be transmitted over a telecommunication or electronic medium.

Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. Most radio systems in the 20th century used frequency modulation (FM) or amplitude modulation (AM) for radio broadcast.

Modulation enables the transfer of information on an electrical signal to a receiving device that demodulates the signal to extract the blended information.

Need for Modulation:

Baseband signals are incompatible for direct transmission. For such a signal, to travel longer distances, its strength must be increased by modulating with a high frequency carrier wave, which doesn’t affect the parameters of the modulating signal.

Modulator used for modulation and demodulator used for demodulating signals in its original form. A modem is a common example of a modulation technique in which the data is modulated with electrical signals and transmitted over telephone lines. It is later demodulated to receive the data.

There are basically two methods of modulations:

1.Analog Modulations Method

2.Digital Modulations Method

What is RF?

2019-01-11T15:14:00.002-08:00

Radio frequency (RF) refers to the rate of oscillation of electromagnetic radio waves in the range of up to 300 GHz lower range exactly we can't define but we measured it from 9KHz, as well as the alternating currents carrying the radio signals. This is the frequency band that is used for communications transmission and broadcasting. Although RF really stands for the rate of oscillation of the waves, it is synonymous to the term "radio," or simply wireless communication.

Radio frequency is being used in a lot of fields, but in the context of information and communications technology it refers to the frequency band at which wireless telecommunications signals are being transmitted and broadcast. The frequency band is being divided into different parts, which are then assigned to different technology industries. This is known as the radio spectrum. For example, the VHF (very high frequency) band, which ranges from 30-300 MHz, is being used for FM radio, TV broadcasts, and amateur radio and its counterparts. For a lot of electronic communication devices, the ultra-high frequency (UHF) band is being used. This is the space used by mobile phones, wireless LAN, Bluetooth, and TV and land radio.

Radio frequency is produced by oscillating current a specified number of times and then radiating it off a conductor, referred to as an antenna, into empty space (this refers to space occupied by air rather than solid objects and does not refer to outer space) as electromagnetic radio waves. RF signals are sent and received using conductors through the phenomenon known as the skin effect, where RF current latches itself and flows through the surface of conductors rather than penetrating and passing through them like it does with other non-conducting solids. This effect is the core and basis of radio technology.

What is anAntenna

2017-11-20T23:39:00.001-08:00

An Antenna is a transducer, which converts electrical power into electromagnetic waves
and vice versa.
An Antenna can be used either as a transmitting antenna or a receiving antenna.
 A transmitting antenna is one, which converts electrical signals into
electromagnetic waves and radiates them.
 A receiving antenna is one, which converts electromagnetic waves from the
received beam into electrical signals.
 In two-way communication, the same antenna can be used for both transmission
and reception.
Antenna can also be termed as an Aerial. Plural of it is, antennae or antennas. Now-a-
days, antennas have undergone many changes, in accordance with their size and shape.
There are many types of antennas depending upon their wide variety of applications.

Transistor

2017-01-28T14:49:00.002-08:00

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal.

How it works

A transistor is really simple and really complex. Let’s start with the simple part. A transistor is a miniature electronic component that can do two different jobs. It can work either as an amplifier or a switch:

When it works as an amplifier, it takes in a tiny electric current at one end (an input current) and produces a much bigger electric current (an output current) at the other. In other words, it's a kind of current booster. That comes in really useful in things like hearing aids, one of the first things people used transistors for. A hearing aid has a tiny microphone in it that picks up sounds from the world around you and turns them into fluctuating electric currents. These are fed into a transistor that boosts them and powers a tiny loudspeaker, so you hear a much louder version of the sounds around you. William Shockley, one of the inventors of the transistor, once explained transistor-amplifiers to a student in a more humorous way: "If you take a bale of hay and tie it to the tail of a mule and then strike a match and set the bale of hay on fire, and if you then compare the energy expended shortly thereafter by the mule with the energy expended by yourself in the striking of the match, you will understand the concept of amplification."
Transistors can also work as switches. A tiny electric current flowing through one part of a transistor can make a much bigger current flow through another part of it. In other words, the small current switches on the larger one. This is essentially how all computer chips work. For example, a memory chip contains hundreds of millions or even billions of transistors, each of which can be switched on or off individually. Since each transistor can be in two distinct states, it can store two different numbers, zero and one. With billions of transistors, a chip can store billions of zeros and ones, and almost as many ordinary numbers and letters (or characters, as we call them). More about this in a moment.

PLC (Programmable Logic Controller)

2014-03-05T07:02:00.002-08:00

A programmable logic controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed-up or non-volatile memory. A PLC is an example of a hard real time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result.

Programmable logic controllers provide dependable, high speed control and monitoring demanded

by a wide variety of automated applications. Before the automotive industry discovered the advantages of PLC’s, the process of modifying relay circuitry was a headache inducing endeavor. In the past, annual car model changes forced plant engineers to constantly modify production equipment managed by relay circuitry. In some cases, the engineers had to scrap entire relay controlled panels and replace them with completely redesigned systems. Now, PLC’s allow engineers to implement numerous manufacturing changes with relative ease, which reduces changeover costs and downtime. Prior to PLC’s, cont-actor or relay controls solved many of these control tasks. This is often referred to as hardwired control. Electricians had to design circuit diagrams, specify and install electrical components, and create wiring lists before wiring the components necessary to perform a specific task. Design errors would force the electrician to trace the wires to identify the problem and then reconnect the wires. A change in function or a system expansion required extensive component changes and rewiring. Now, PLC software programming makes wiring changes between devices and relay contacts easier. Although hard wiring is still necessary for connecting field devices, it’s less intensive than before.

Door Open Sensor

2013-06-30T21:33:00.001-07:00

Each Door Open Sensor is made up of two parts. A magnet and a switch. The magnet will be attached to the door. The switch will be attached to the door frame.

Depending on the relative position of magnet and switch, the switch will open or close. With the proper placement, this will allow the detection of the door being opened or closed

Once the switch is wired to an input of the Frotcom GPS/GPRS device; these changes will be detected and communicated to the Frotcom Data Center.

Then, Frotcom will update the door open status for that vehicle and check for alarm conditions.

Main features

Here are some of the main features of the Door Open Sensor:

Thermoplastic enclosure
Flat design
Long life
Non-contacting principle
1 reed contact
Actuating distance up to 60mm
Actuating surface marked by protrusion
Pre-wired cable with length 1m
Protection class IP 67

BURGLAR ALARM

2013-06-20T07:47:00.000-07:00

A burglar alarm is a system designed to detect intrusion – unauthorized entry – into a building or area. They are also called security alarms, security systems, alarm systems, intrusion detection systems, perimeter detection systems, and similar terms.

Burglar alarms are used in residential, commercial, industrial, and military properties for protection against burglary (theft) or property damage, as well as personal protection against intruders. Car alarms likewise protect vehicles and their contents. Prisons also use security systems for control of inmates.

Some alarm systems serve a single purpose of burglary protection; combination systems provide both fire and intrusion protection. Intrusion alarm systems may also be combined with closed circuit television surveillance systems to automatically record the activities of intruders, and may interface to access control systems for electrically locked doors. Systems range from small, self-contained noisemakers, to complicated, multi-area systems with computer monitoring and control.

GAS SENSOR MQ-6

2013-06-09T22:23:00.002-07:00

Whenever there is LPG concentration of 1000 ppm (parts per million) in the area, the OUT pin of the sensor module goes high. This signal drives timer IC 555, which is wired as an a stable multivibrator. The multivibrator basically works as a tone generator.

Output pin 3 of IC 555 is connected to LED1 and speaker-driver transistor SL100 through current-limiting resistors R5 and R4, respectively. LED1 glows and the alarm sound to alert the user of gas leakage. The pitch of the tone can be changed by varying preset VR1. Use a suitable heat-sink for transistor SL100.

Gas Sensor MQ-6

FEATURES

High sensitivity to LPG, ISO-butane, propane

Small sensitivity to alcohol, smoke.

Fast response.

Stable and long life

Simple drive circuit

APPLICATION

They are used in gas leakage detecting equipments in family and industry, are suitable for detecting of LPG, ISO-butane, propane, LNG, avoid the noise of alcohol and cooking fumes and cigarette smoke.

TEMPERATURE SENSOR LM35

2013-06-04T06:07:00.002-07:00

General description of LM 35

The LM35 is an integrated circuit sensor that can be used to measure temperature with an electrical output proportional to the temperature (in ^oC) The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not require any external calibration or trimming to provide typical accuracies of ±1⁄4°C at room temperature and ±3⁄4°C over a full −55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35’s low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus.

LM 35 Temperature Sensor

Features

1. Calibrated directly in ° Celsius (Centigrade)

2. Linear + 10.0 mV/°C scale factor

3. 0.5°C accuracy guarantee able (at +25°C)

4. Rated for full −55° to +150°C range

5. Suitable for remote applications

6. Low cost due to wafer-level trimming

7. Operates from 4 to 30 volts

8. Less than 60 μA current drain

9. Low self-heating, 0.08°C in still air

10. Non linearity only ±1⁄4°C typical

11. Low impedance output, 0.1 W for 1 mA load

Advantages of LM35 to Measure Temperature?

You can measure temperature more accurately than a using a thermistor.

The sensor circuitry is sealed and not subject to oxidation, etc.

The LM35 generates a higher output voltage than thermocouples and may not require that the output voltage be amplified.

Working of LM35:

The scale factor is .01V/^oC.

The LM35 does not require any external calibration or trimming and maintains an accuracy of +/-0.4 ^oC at room temperature and +/- 0.8 ^oC over a range of 0 ^oC to +100 ^oC.

Another important characteristic of the LM35DZ is that it draws only 60 micro amps from its supply and possesses a low self-heating capability.

The sensor self-heating causes less than 0.1 ^oC temperature rise in still air.

It has an output voltage that is proportional to the Celsius temperature.

All About Electronics: Advantages of optical fiber communication

2013-02-24T21:02:00.001-08:00

All About Electronics: Advantages of optical fiber communication: Let us see the advantages of optical fiber communication over conventional communication system Enormous bandwidth: the informati...

Advantages of optical fiber communication

2013-02-24T20:56:00.000-08:00

Let us see the advantages of optical fiber communication over conventional communication system

Enormous bandwidth: the information carrying capacity of a transmission system is directly proportional to the carrier frequency of the transmitted signals. The optical carrier frequency is in the range of 10^14Hz while the radio frequency is about 10^6Hz. Thus the optical fibers have enormous transmission bandwidth and high data rate. Using wavelength division multiplexing operation, the data rate or information carrying capacity of optical fibers is enhanced to many orders of magnitude.

Low transmission loss: due to the usage of ultra low loss fibers and the erbium doped silica fibers as optical amplifiers, one can achieve almost loss less transmission. Hence for long distance communication fibers of 0.002dB/km are used. Thus the repeater spacing is more than 100km.

Immunity to cross talk: since optical fibers are dielectric wave guides, they are free from any electromagnetic interference (EMI) and radio frequency interference (RFI). Since optical interference among different fibers is not possible, cross talk is negligible even many fibers are cabled together.

Electrical isolation: optical fibers are made from silica which is an electrical insulator. Therefore they do not pick up any electromagnetic wave of any high current lightening. It is also suitable in explosive environment.

Small size and weight: the size of the fiber ranges from 10 micrometers to 50 micrometers which is very small. The space occupied by the fiber cable is negligibly small compared to conventional electrical cables. Optical fibers are light in weight. These advantages make them to use in aircrafts and satellites more effectively.

Signal security: the transmitted signal through the fiver does not radiate. Unlike in copper cables, a transmitted signal cannot be drawn from a fiber without tampering it. Thus, the optical fiber communication provides 100% signal security.

Ruggedness and flexibility: the fiber cable can be easily bent or twisted without damaging it. Further the fiber cables are superior than the copper cables in terms of handling. Installation, storage, transportation, maintenance, strength and durability.

Low cost and availability: since the fibers are made of silica which is available in abundance. Hence, there is no shortage of material and optical fibers offer the potential for low cost communication.

Reliability: the optical fibers are made from silicon glass which does not undergo any chemical reaction or corrosion. Its quality is not affected by external radiation. Further due to its negligible attenuation and dispersion, optical fiber communication has high reliability. All the above factors also tend to reduce the expenditure on its maintenance.

Basic structure of optic fiber cable

2013-02-18T18:43:00.001-08:00

Basic structure of optic fiber cable

An optical fiber can be called as a dielectric waveguide. This waveguide operates at optical frequencies.

The fiber consists of three parts namely

1. Core

2. Cladding and

3. Buffer coating

The core of the fiber is cylindrical and has a radius a. its refractive index is represented by n1.

The core is surrounded by a solid dielectric cladding whose refractive index is n2. The refractive index of the core n1 is always greater than the refractive index of cladding n2. The cladding gives mechanical strength to the inner core.

The buffer coating gives additional strength and prevents any damage to the fiber.

Since the cladding that surrounds the core has lower refractive index than the core, the light is guided through the core due to total internal reflection.

Beverage antenna

2012-12-04T09:42:00.003-08:00

Herold beverage discovered in 20 that an otherwise nearly bidirectional long wire antenna becomes uni-directional by placing it close to the lossy earth and by terminating one end of the wire with a non-inductive resistor with a resistance approximately matched to the characteristics or surge impedance of the antenna. This was the fundamental discovery in his 1921 patent. From the transmission line theory we know that the line terminated with load impedance equal to characteristic impedance (Z๐), there is only a traveling wave present on the line. Since there is no reflected wave, there is no standing wave on the line. Then the line is said to be non resonant.

It consists of a wire one or two wavelength long. Note that the length of 1 or 2λ is not a small length at LF or MF; it is hundreds of feet at MF to several kilometers for LF. The wire runs parallel to the earth’s surface from the receiver towards the direction of the desired signal. The wire is suspended by insulated supports approximately two meters above the ground. A non-inductive resistor of value equal to characteristic impedance is installed from the far end of the wire to the ground. As the wire is properly terminated, the structure becomes a non resonant antenna.

Emulator

2012-07-28T20:08:00.002-07:00

An emulator is a piece of hardware that is placed into application circuit to run and observe that operation of the system without developing stimulus files.

Types of emulators

Software emulators:

A software emulator allows computer programs to run on a platform (computer architecture and/ or operating system) other than the one for which they were originally written. Unlike simulation, which only attempts to reproduce a program’s behavior, emulation attempts to model to various degrees the state of the device being emulated. High- level emulation uses a combination of the two approaches in an attempt to retain as much accuracy as possible while having the advantages of simplicity and speed provided by simulation.

Hardware emulator:

A hardware emulator is an emulator which takes the form of a hardware device. Examples include printer emulators inside the ROM of the printer, and FPGA based emulators.

A popular use of emulators is to mimic the experience of running arcade games or console games on personal computers. Emulating these on modern desktop computers is usually less cumbersome and more reliable than relaying on the original machines, which are often old and hard to find. Emulation of arcade and console systems on home PCs usually includes the practice of illegally downloading software from various electronic distribution sources.

In a theoretical sense, any operating environment can be emulated within any other. In practice, it can be quite difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. It also says nothing about timing constraints; if the emulator does not perform as quickly as the original hardware, the emulated software may run much more slowly than it would have on the original hardware, or it may run too fast to be usable.

Simulators

2012-07-10T19:11:00.001-07:00

A simulator is a program that simulates the functioning of electronic circuits. Simulator allows the designer to determine the correctness and efficiency of a design before the system is actually constructed.

A stimulus file is used for simulating input from external hardware. The stimulus file provides a series of inputs to the simulator to observe the overall behavior of system. The stimulus file for micro controller process consists for cycle counter and pin states.

An important consideration while selecting a simulator is its execution speed i.e. how fast it can execute the application’s instructions. If the execution speed of simulator is less compare to the processor then the simulator may take hours in a simulated environment. The delay may be due to complex interactions within the system being simulated. Therefore the simulator’s result are deviated from the actual operation.

Unit Loudspeaker

2012-06-25T04:44:00.003-07:00

For public address and street announcement purpose we require such type of loudspeaker and a power amplifier which can reproduce the sound waves up to thousand of listeners in a public place. The loudspeaker used for the purposes is called unit loudspeaker. it consists of following two main parts.

1. Pressure units: Its construction is similar to that or p.m. dynamic loudspeaker. The difference is that it has a large voice coil with a small cone. The impedance of voice coil may be up to 160 ohms whereas the impedance of an ordinary loudspeaker is not more than 20 ohms. It employs metallic cone in place of a paper cone. The power rating of a pressure unit varies between 16 and 20 watts whereas that of an ordinary loudspeaker lies between 3 to 8 watts.

The pressure units convert the a.f. voltage received from an a. f. amplifier into powerful sound waves. It is known as drive unit.

Horn: if the sound waves reproduced by a pressure unit are allowed to radiate directly in the atmosphere then they would not be able sound waves in a hemisphere then they would not be able sound waves in a hemisphere area only around it. A pressure unit radiates the of aluminum sheet is attached to the pressure unit. The horn converts sound waves of low pressure and high pressure and low velocity in to sound waves of low pressure and high velocity.

A horn is constructed in such a way that its diameter from its throat to mouth increase in a parabolic or exponential ratio. The total length of an ordinary type of horn is large enough and it does not suit for it to be used on vehicles. Hence, the horns on vehicles are of reflex or folded type. In a reflex horn, the total length of the horn is divided in to two parts and both the parts are fitted in such a way that the total length of the horn is reduced to almost half, whereas its effective length remains the same as of an original type.

COLUMN SPEAKER

It is almost impossible to reproduce the entire a.f. range of 20Hz to 20 KHz with a single loudspeaker, even more; the reproduction of the practical a.f. range of 30 Hz to 12 KHz with a single loudspeaker is quite difficult. If the size of the cone is kept between 25 to 35cm then it can reproduce frequencies above 8,000 Hz at the same level. Similarly, if the size of the between 5 to 15 cm then it can reproduce frequencies of the a.f. range of 8000 Hz to 20,000 Hz is reduced to lower level. Hence, the following two alternatives are employed for the faithful and equal level reproduction of the a.f. range of 30 Hz to 12 KHz.

1. Coaxial and Triaxial speaker:

A coaxial speaker consists of two cones of small and large sizes respectively fitted on the same axis. The smaller speaker is called tweeter and the larger one is called woofer. Tweeter improves high frequency reproduction while woofer improves low frequency reproduction.

Similarly, a triaxial speaker consists of tweeter for high frequencies, a diaphragm for medium frequencies and woofer for low frequencies.

2. Multi speaker system : In this system two of three speakers of different sizes, especially designed to produce maximum output for a low pass filter (a choke of suitable value or a MFD value capacitor) is connected in series with the woofer. Similarly, a high pass filter ( a paper capacitor of suitable value) is connected in series with the tweeter. A box consisting more than one speaker is also known as column speaker.

Microphone mirror

In sound recording, for adding the echos to the fundamental sound of a singer, polished metallic reflectors are used which are called microphone are also microphone mirrors. Besides, it high impedance microphones are called microphone mirrors.

Earphone

2012-06-25T04:43:00.000-07:00

A headphone consists of two receiver units joined together with an iron strip in such a way that the strip rests on the head and both the receiver units rest close to the ears of the listener. An earphone consists if a single receiver unit. Some earphones are made so small in size that they can be easily fitted inside the external cavity of the ear.

An earphone is the miniature form of a loudspeaker. It is used with transistorized receivers and hearings aids.

Loudspeaker

The instrument which converts electrical a.f. waves into sound waves is called a loudspeaker. there are mainly following two types of loudspeakers:

1 Magnetic loudspeaker

2 Dynamic loudspeaker

1. Magnetic loudspeaker: It consists of a permanent magnet and a voice coil wound on it. A diaphragm made of fine iron sheet and a paper cone is mounted in front of the magnet. Its working is identical to that of headphone. It is also known as cone type loudspeaker.

Sometimes, a horn is also attached to the loudspeaker for increasing the loudness of the sound. Such loudspeaker is called horn type loudspeakers.

Both the above explained loudspeakers are outdated since the performance of dynamic loudspeaker is more satisfactory than magnetic loudspeakers.

2. Dynamic loudspeaker: This type of loudspeaker consists of moving or dynamic loudspeakers. There are following two types of loudspeakers :

1. Permanent magnet dynamic loudspeakers :

2. Electro magnet dynamic loudspeakers :

Permanent Magnet Dynamic Loudspeaker

1. Principle. If two magnetic fields are acting at one place than a magnet or magnetic field producing coil can be moved of vibrated due to attraction or repulsion between the two fields.

2. Construction: Its construction is similar to that of a dynamic microphone. The only difference is this that the size of loudspeaker is much bigger than that of a microphone. The diameter of the cone of a microphone is usually 2-3 cm while that of a loudspeaker is usually 3 to 30 cm. it employs an ALNICO magnet.

3. Working: the voice coil established an alternating magnetic field on applying a.f. voltage to it. The coils magnetic field will start to be added to or subtracted from the magnetic field of the permanent magnet consequently, the voice coil will start to vibrate to and fro. The cone sound waves. The frequency and amplitude of cones vibration and the corresponding sound waves are exact replica of a.f. waves applied.

4. Users: Loudspeaker are used for listening a broadcast program from a receiver or for listening a public address through an a.f. amplifier by more than one person at a time.

Electro Magnet Dynamic Loudspeaker

In this of loudspeaker an electromagnet is used in place of the loudspeaker construction is the is same as of a p. m. dynamic loudspeaker.

The coil used in electromagnetic is called humbeking coil of field coil. It is excited with a D.C. source. This type of loudspeaker were used in early type of receiver since the technique of making small sized powerful permanent magnets was not developed till then. Now, those loudspeakers are obsolete.

Marconi Antenna

2012-03-29T18:59:00.000-07:00

It is defined as a two part antenna consisting of a vertical portion and a reflective or ground portion. When constructed properly, it is very similar to a vertically oriented dipole.

The reflective portion is not always a physical element, but often a natural earth ground (where the soil conductivity is sufficient) or ground “radials” (a set of wires just beneath the ground that act as the reflective portion).

For example, a λ/4 vertical antenna when grounded, the earth acts as a mirror and the system acts as an antenna of double size i.e. λ/2 dipole. It is as shown in fig. the radiation pattern of it will be similar to vertical λ/2 Hertz antenna.

Barkhausen criterion and various types of oscillators

2012-02-26T09:11:00.001-08:00

The condition for sustained oscillations in a single valve self excited oscillator worked out by the German scientist Barkhausen is this that the voltage multiplication of the amplifier must exactly counterbalance the voltage dividing of the feedback circuit.

β=1/A

Where, β=feedback factor, A= voltage gain

Various types of oscillators

Various types of oscillator have been designed to meet the requirement of different types of electronic equipments which are follows:

Tuned collector oscillator

Hartley oscillator

Colpitt’s oscillator

Clapp oscillator

Crystal oscillator

Phase shift R-C oscillator

Multi vibrator

Wein bridge oscillator

Neon lamp oscillator

Master oscillator power amplifier

Beat frequency oscillator

TUNED COLLECTOR OSCILLATOR :

It is simplest type of oscillator circuit. It consists of two coils L1 and L2 wound like a transformer. Coil L1 is the connected in the collector circuit and coil L2 in the base circuit. The frequency of oscillations depends of oscillations depends on the values of L1 and C1 capacitor C provides a low reactance path to the oscillations.

When the switch S is put to ON, the collector current starts increasing and charges the capacitor C1. When this capacitor gets fully charged, it starts to discharge through L1 and the circuit begins to oscillate. These oscillations include some voltage in the coil L2 which is applied between the base and emitter of the transistor and the same appears in the amplified form in the collector circuit. The output can be obtained from the collector circuit trough a capacitor C2.

The oscillatory frequency of the circuit is calculated by using the formula

There exists a ‘tuned base oscillator ‘circuit also which is based on a CB circuit.

Oscillators

2012-02-11T02:25:00.000-08:00

Introduction:

The to and fro motion of electronics through a conductor produces electromagnetic waves. In the earliest type of type of transmitters, the electromagnetic or radio waves were produced by means of an electric spark. The to and fro motion of electrons through a conductor is known as oscillation and the devices used to produce them is called an oscillator.

It is inconvenient and nearly impracticable to generate frequencies of the order of kilo hertz and megahertz by means of a generator. Transistor oscillators are suitable are suitable for the production of a defined and stable frequencies of said order.

ESSENTIAL REQUIREMENTS OF AN OSCILLATOR:

Following three items are essential for an oscillator

Transistor amplifier circuit

Feedback circuit

Tank circuit

Amplifier:
An amplifier circuit is modified is such a way that can work as an oscillator.

Feedback circuit:
An oscillator requires positive feedback. A portion of the output is energy is received by the input circuit by means of feedback. If the amplifier circuit then the circuit will not oscillate at all.

Tank circuit:
A resonant circuit consisting of an inductor and a capacitor or crystal is known as tank circuit. This circuit produces oscillation and decides their frequency.

Working of Tank Circuit:

If a capacitor is charged and then connected across an inductor, it will start to discharge. The electrons will start to move from plate 2 to 1 through the coil. An alternating magnetic field will be produced around the coil due to the flow of electrons. A back E.M.F will be induced in due to alternating nature of the of magnetic field which oppose the flow of current and will thus will reduce the current.

When the number of electrons on the two plates becomes equal, the capacitor is fully discharged, the current will reduce further and the magnetic field will begin to contact. The flow of current will continue due to contracting. Magnetic field and the back e.m.f. will now oppose its contraction. The process will continue till the charge of the plate is not lost completely. In this way, the capacitor will be charged in opposite direction.

Now the former action will repeat. Hence, the electrostatic field of the capacitor will continue to transfer energy to the electromagnetic field of coil and vice-versa. As a result, an alternating current will start to flow in the circuit. If there occurs no loss in the transfer of energy, the oscillations will continue indefinitely, but an energy loss always exists in the circuit due to ohmic resistance of coil and on reducing continuously, oscillations goes on reducing continuously are called damped oscillations. The following formula is used for the calculation of oscillatory frequency of the tank circuit:

Where,

ƒ= frequency, hertz

L= inductance, Henry

C= capacitance, farads

2π=2*3.142

If the loss of energy in each cycle of damped waves is compensated regularly, the oscillations will continue. Various types of oscillator circuit have been designed to meet the purpose.

ELECTRON EMISSION

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Certain metals have a property of liberating electrons when they are heated up or subjected to light rays, the effect is known as electron emission. There are following five types of electron emission:

1. Thermionic emission: when a metal is heated up to a certain temperature, it starts emission of electrons which is called thermionic emission. The reason behind this effect is this that the electrons present in the atoms of the metal heated up acquire tremendous kinetic energy and their attraction towards their nucleus is greatly reduced. Some electrons leave the surface of the metal and come out. Pure tungsten metal emits electrons at 2400 to 2500 Kelvin.

2. Photo electric emission: certain metals are very sensitive that they start electron emission even on the incidence of light rays. The emission so caused is called photo electric emission. Sodium and potassium are photo emissive metals.

3. Secondary emission: when electrons or ions moving with fast speed strike a metallic surface they themselves enter the metallic body and they scatter some electrons out of that body. The phenomenon is called secondary emission. The action takes place in tetrode valves.

4. Field emission: when the attraction of a strong magnetic field causes emission of electrons from a metallic surface, the phenomenon is called field emission. The electron emission in a cold cathode valve is field emission.

5. Radioactive emission: there are some elements present in the nature which continue to disintegrate into new elements having lesser atomic number. Such elements are called radioactive elements. During disintegration such elements emit beta rays composed of electrons. The emission is called radioactive emission. Uranium, radium, thorium etc. are radioactive elements.

CLASSIFICATION OF SOUND WAVES

2011-12-26T01:43:00.000-08:00

Sound waves can be classified into following three classes:

1. Audible waves

2. Infrasonic waves

3. Ultrasonic waves

Audible waves:

The waves which can be heard by human ears are called audible waves. Their frequency range extends from 20 Hz to 20 KHz but it may vary from person to person in accordance to his age. Children and youth can hear sounds of up to 20 KHz frequency whereas the audible range of old persons is lesser than 20 KHz.

Infrasonic waves:

Waves having a frequency of less than 20 Hz are called infrasonic waves. These waves cannot be heard by human ears. These waves are produced by the vibration of huge bodies like the earth.

Ultrasonic waves:

Waves having frequency of more than 20 KHz are called ultrasonic waves. These waves also cannot be heard by human ears, but can be heard by bats. The bat can hear waves of frequencies up to 50 to 60 KHz and can produce such waves even.

These waves have proved to be very useful to mankind. These are used for communications and for the determination of depth of sea. Besides it, these are used for increasing agricultural yields, for improving the quality of seeds, for protection against insects and in the field of treatment especially surgery.

ARTICULATION OF SOUND

Articulation or modification of sound is necessary before broadcasting. For this, the following instructions should be observed:

1. The broadcasting room should be perfectly sound-proof so that unwanted sounds may not enter in the room.

2. Microphone, record player, tape recorder and amplifier etc. should have a high efficiently so that all the fundamental and harmonic frequencies remain undistorted.

3. The frequency range of sound is limited between 30 Hz to 12 KHz since the frequency of all sounds produced by man, sound and musical instruments lies between 30 Hz to 12 KHz. By limiting the frequency range, amplification of high quality and high fidelity is easily possible.

4. Before sending the sound signals to the transmitter they should be amplified up to a required level.

SOUND

2011-12-26T01:39:00.000-08:00

It is a form of energy which is experienced by human ears. It is produced by the vibration of bodies, by man, animals and birds and by natural interruptions. Sound is propagated in the form of waves and some medium is essential for its propagation. The medium may be a solid, liquid or gas but it should have sufficient elasticity.

The velocity of sound in dry air at 0˚C is 332 meters per second and in water it is 1435 meters per second. Similarly the velocity of sound in different medium is different medium is different. The velocity of sound in the air is affected by humidity, temperature, density of dust particles and the speed of air circulation.

FREQUENCY AND WAVELENTH

Frequency: for a wave, the number of cycles completed per second is called its frequency. Its symbol is ƒ and its unit is hertz (Hz).

Wavelength: straight distance travelled by a wave in one cycle is called its wavelength. In other words, the distance between the two consecutive particles vibrating in the same phase is called wavelength. Its symbol is λ (lamda, a Greek letter) and its unit is meter.

Time period: the time taken by one complete set of vibration, i.e., one cycle is called time period. Its symbol is T and its unit is seconds. Therefore

T= 1/ƒ or ƒ=1/T

T= time period, seconds

ƒ =frequency, hertz

Relation: the wavelength decreases by increasing the frequency and conversely the wavelength increases by decreasing the frequency, but their product remains constant and it indicates the velocity of the wave. Hence

Ѵ =ƒ.λ or Ѵ = λ/T

Where, Ѵ = velocity of the wave, meters per second

λ = wavelength, meters

ƒ = frequency, hertz

T = time period, seconds

Application of Direct Spread Spectrum Signals

2011-12-15T10:15:00.000-08:00

Here we will discuss three types of applications of direct sequence spread spectrum signals: anti jamming signals, low probability intercept and code division multiple access of allow multiple users.

1. Anti jamming with the help of direct sequence spread spectrum signals

In the frequency band of the interest somebody else transmits the signals intentionally.

Since these signals lie in the frequency band of the transmission, the interfere the required signal. Hence it becomes difficult to detect the required signals. This is called jamming effect.

Such problems normally occur in military applications. If enemy knows the frequency band, then he can send jamming signals intentionally. With the help of spread spectrum method, the transmitted signals are spread over the mid frequency band. Hence these signals appear as noise. Then it becomes difficult for the jammers to send jamming signals. This is called anti jamming. For the anti jamming application three codes are used in conjunction with direct sequence spread spectrum method. These are Golay code (24, 12) expurgated Golay (24, 11) and maximum length shift register code.

2. Low detectability signal transmission or low probability intercept

For this application, the signal spectral density is intentionally kept small with respect to the channel noise and receiver noise so that the presence of the signal is not detected easily. Consider that the average received signal power at the intended receiver is Pav and the noise power is Nav. Then the signal is transmitted at low power levels such that Pav/Nav << 1. Hence the receivers which are in the vicinity of the intended receiver cannot detect the presence of the signal. The intended receiver recovers the information bearing signal with the help of processing gain and coding gain. Other receivers do not know the pseudo-noise sequence hence they cannot receive the information signal with the help of processing gain and coding gain. This is called as the signal has low probability of being intercepted. It is also called low detect ability signal transmission.

3. Code division multiple access with direct sequence SS (SSMA)

In this application, many users transmit their signals on the same channel bandwidth. Each transmitter receiver pair has a distinct pseudo-noise (PN) sequence. Thus signals of a particular transmitter are received by its intended receiver only, even if many users are transmitting at the same time. This method is also called spread spectrum multiple access (SSMA). The signals from other users appear as additive interference which is rejected y the spread spectrum decoder. The level of interference depends upon the number of users transmitting at any time. The main advantage of CDMA is that the number of users sharing the same channel can be increased or decreased very easily. Large number of users can transmit on the same channel if their messages are for short periods of time. For this method it is desirable that the PN sequences be mutually orthogonal.