PART-A (2-MARK QUESTIONS)

1. Define Transducer?

It is device used to convert one form of energy into another form of energy. For example solar

panel, it is converting the solar energy into Power.

2. What is voice coil?

It is defined as, coil of wire attached to the apex of a loudspeaker cone. It provides the motive

force to the cone by the reaction of a magnetic field to the current passing through it. It is referred

as voice coil.

3. What is composite video signal?

Composite video (1 channel) is an analog video transmission (no audio) that carries

standard definition video typically at 480i or 576i resolution. Hence this type of video signal is

called as composite video signal

4. Define CRT?

It stands for cathode ray tube. It contains two ends (i.e) Narrow tube that contains electron gun at

one end and a phosphorous coated region at another end. It is used to produce the video signal.

5. What is ERCO?

It is noting but Error detection and error correction, used in CD system.

6. What are the various layers present in the disc?

There are 3 different layers will present in the disc. They are (i) transparent layer, (ii)

Protection layer, (iii) Reflection layer.

7. Define switching system?

It is a system used to enable any type of terminal, in order to pass the information from one place

to another place. The different types of switching system are circuit switching, packet switching

and message switching etc.

8. What is WLL?

Wireless local loop (WLL), is a term for the use of a wireless communications link as the

"last mile / first mile" connection for delivering plain old telephone service (POTS) or Internet

access (marketed under the term "broadband") to telecommunications customers. Various types

of WLL systems and technologies exist.

9. Define Magnetron?

The microwave radiation of microwave ovens and some radar applications is produced by

a device called a magnetron. The magnetron is called a "crossed-field" device in the industry

because both magnetic and electric fields are employed in its operation, and they are produced in

perpendicular directions so that they cross.

10. What is refrigerator?

A refrigerator or fridge is a common household appliance that consists of a thermally

insulated compartment and a heat pump that transfers heat from the inside of the fridge to its

external environment so that the inside of the fridge is cooled to a temperature below the ambient

temperature of the room.

PART-B (11 MARKS)

11. Discuss the principle of operation of electrostatic loudspeaker along with its diagram?

An electrostatic loudspeaker (ESL) is a loudspeaker design in which sound is generated

by the force exerted on a membrane suspended in an electrostatic field.

The speakers use a thin flat diaphragm usually consisting of a plastic sheet coated with a

conductive material such as graphite sandwiched between two electrically conductive grids, with a small air gap between the diaphragm and grids. For low distortion operation, the diaphragm must operate with a

constant charge on its surface, rather than with a constant voltage (charge and voltage is not the same

thing). This is accomplished by either or both of two techniques: the diaphragm's conductive coating is

chosen and applied in a manner to give it a very high surface resistivity, and/or a large value resistor is placed in series between the EHT (Extra High Tension or Voltage) power supply and the diaphragm

(resistor not shown in the diagram here). However, the latter technique will still allow distortion as the

charge will migrate across the diaphragm to the point closest to the "grid" or electrode thereby increasing the force moving the diaphragm, this will occur at audio frequency so the diaphragm requires a high

resistance (Meg ohms) to slow the movement of charge for a practical speaker.

The diaphragm is usually made from a polyester film (thickness 2–20 µm) with exceptional

mechanical properties, such as PET film. By means of the conductive coating and an external high voltage supply the diaphragm is held at a DC potential of several kilovolts with respect to the grids. The

grids are driven by the audio signal; front and rear grid is driven in ant phase. As a result a uniform

electrostatic field proportional to the audio signal is produced between both grids. This causes a force to

be exerted on the charged diaphragm, and its resulting movement drives the air on either side of it.

In virtually all electrostatic loudspeakers the diaphragm is driven by two grids, one on either side, because the force exerted on the diaphragm by a single grid will be unacceptably non-linear, thus causing

harmonic distortion. Using grids on both sides cancels out voltage dependent part of non-linearity but

leaves charge (attractive force) dependent part.[1]

The result is near complete absence of harmonic distortion. In one recent design, the diaphragm is driven with the audio signal, with the static charge

located on the grids (Transparent Sound Solutions).The grids must be able to generate as uniform an

electric field as possible, while still allowing for sound to pass through. Suitable grid constructions are

therefore perforated metal sheets, a frame with tensioned wire, wire rods, etc.

To generate sufficient field strength, the audio signal on the grids must be of high voltage. The electrostatic construction is in effect a capacitor, and current is only needed to charge the capacitance

created by the diaphragm and the stator plates (previous paragraphs referred to as grids or electrodes).

This type of speaker is therefore a high-impedance device. In contrast, a modern electrodynamics cone

loudspeaker is a low impedance device, with higher current requirements. As a result, impedance

matching is necessary in order to use a normal amplifier. Most often a transformer is used to this end. Construction of this transformer is critical as it must provide a constant (often high) transformation ratio

over the entire audible frequency range (i.e. large bandwidth) and so avoid distortion. The transformer is

almost always specific to a particular electrostatic speaker. To date, Acoustic built the only commercial

"transformer-less" electrostatic loudspeaker. In this design, the audio signal is applied directly to the stators from a built-in high-voltage valve amplifier (as valves are also high impedance devices), without

use of a step-up transformer.

12. Explain the concept of carbon Microphones?

A carbon microphone, also known as a carbon button microphone (or sometimes just a button

microphone), use a capsule or button containing carbon granules pressed between two metal plates like the Berliner and Edison microphones. A voltage is applied across the metal plates, causing a small current

to flow through the carbon. One of the plates, the diaphragm, vibrates in sympathy with incident sound

waves, applying a varying pressure to the carbon. The changing pressure deforms the granules, causing the contact area between each pair of adjacent granules to change, and this causes the electrical resistance

of the mass of granules to change. The changes in resistance cause a corresponding change in the current

flowing through the microphone, producing the electrical signal. Carbon microphones were once

commonly used in telephone

Unlike other microphone types, the carbon microphone can also be used as a type of amplifier, using a

small amount of sound energy to control a larger amount of electrical energy. Carbon microphones found

use as early telephone repeaters, making long distance phone calls possible in the era before vacuum tubes. These repeaters worked by mechanically coupling a magnetic telephone receiver to a carbon

microphone: the faint signal from the receiver was transferred to the microphone, with a resulting stronger

electrical signal to send down the line.

Moving-coil microphones use the same dynamic principle as in a loudspeaker, only reversed. A small movable induction coil, positioned in the magnetic field of a permanent magnet, is attached to the

diaphragm. When sound enters through the windscreen of the microphone, the sound wave moves the

diaphragm. When the diaphragm vibrates, the coil moves in the magnetic field, producing a varying current in the coil through electromagnetic induction. A single dynamic membrane does not respond

linearly to all audio frequencies. Some microphones for this reason utilize multiple membranes for the

different parts of the audio spectrum and then combine the resulting signals. Combining the multiple

signals correctly is difficult and designs that do this are rare and tend to be expensive. There are on the other hand several designs that are more specifically aimed towards isolated parts of the audio spectrum.

The AKG D 112, for example, is designed for bass response rather than treble.[16]

In audio engineering

several kinds of microphones are often used at the same time to get the best result.

Ribbon microphones use a thin, usually corrugated metal ribbon suspended in a magnetic field. The ribbon is electrically connected to the microphone's output, and its vibration within the magnetic field

generates the electrical signal. Ribbon microphones are similar to moving coil microphones in the sense

that both produce sound by means of magnetic induction. Basic ribbon microphones detect sound in a bi-

directional (also called figure-eight, as in the diagram below) pattern because the ribbon, which is open to sound both front and back, responds to the pressure gradient rather than the sound pressure. Though the

symmetrical front and rear pickup can be a nuisance in normal stereo recording, the high side rejection

can be used to advantage by positioning a ribbon microphone horizontally, for example above cymbals, so that the rear lobe picks up only sound from the cymbals. Crossed figure 8, or Bulletin pair, stereo

recording is gaining in popularity, and the figure 8 response of a ribbon microphone is ideal for that

application.

Other directional patterns are produced by enclosing one side of the ribbon in an acoustic trap or baffle,

allowing sound to reach only one side. The classic RCA Type 77-DX microphone has several externally adjustable positions of the internal baffle, allowing the selection of several response patterns ranging from

"Figure-8" to "Unidirectional". Such older ribbon microphones, some of which still provide high quality

sound reproduction, were once valued for this reason, but a good low-frequency response could only be obtained when the ribbon was suspended very loosely, which made them relatively fragile. Modern

ribbon materials, including new non materials have now been introduced that eliminate those concerns,

and even improve the effective dynamic range of ribbon microphones at low frequencies. Protective wind screens can reduce the danger of damaging a vintage ribbon, and also reduce plosive artifacts in the

recording. Also there are new ribbon materials available that are immune to wind blasts and phantom

power.

13. Explain the composite video signal?

14. Discuss the NTSC color TV system in detail?

15. Write briefly about the Processing of an audio signal?

17. Write briefly about the PAPX Switching?

A private branch exchange (PBX) is a telephone exchange that serves a particular business or office,

as opposed to one that a common carrier or telephone company operates for many businesses or for the

general public. PBXs are also referred to as:

PABX – private automatic branch exchange

EPABX – electronic private automatic branch exchange

PBXs make connections among the internal telephones of a private organization—usually a business—

and also connect them to the public switched telephone network (PSTN) via trunk lines. Because they incorporate telephones, fax machines, modems, and more, the general term "extension" is used to refer to

any end point on the branch.

PBXs are differentiated from "key systems" in that users of key systems manually select their own

outgoing lines, while PBXs select the outgoing line automatically. Hybrid systems combine features of

both.

Initially, the primary advantage of PBXs was cost savings on internal phone calls: handling the circuit

switching locally reduced charges for local phone service. As PBXs gained popularity, they started offering services that were not available in the operator network, such as hunt groups, call forwarding,

and extension dialing. In the 1960s a simulated PBX known as Centrex provided similar features from the

central telephone exchange.

Two significant developments during the 1990s led to new types of PBX systems. One was the massive

growth of data networks and increased public understanding of packet switching. Companies needed packet switched networks for data, so using them for telephone calls was tempting, and the availability of

the Internet as a global delivery system made packet switched communications even more attractive.

These factors led to the development of the VoIP PBX. (Technically, nothing was being "exchanged" any

more, but the abbreviation PBX was so widely understood that it remained in use.)

The other trend was the idea of focusing on core competence. PBX services had always been hard

to arrange for smaller companies, and many companies realized that handling their own telephony was

not their core competence. These considerations gave rise to the concept of hosted PBX. In a hosted

setup, the PBX is located at and managed by the telephone service provider, and features and calls are delivered via the Internet. The customer just signs up for a service, rather than buying and maintaining

expensive hardware. This essentially removes the branch from the private premises, moving it to a central

location.

The term PBX was first applied when switchboard operators ran company switchboards by hand. As automated electromechanical and then electronic switching systems gradually began to replace the

manual systems, the terms PABX (private automatic branch exchange) and PMBX (private manual

branch exchange) were used to differentiate them. Solid state digital systems were sometimes referred to as EPABXs (electronic private automatic branch exchange). Now, the term PBX is by far the most widely

recognized? The acronym is now applied to all types of complex, in-house telephony switching systems,

even if they are not private, branches, or exchanging anything.

PBXs are distinguished from smaller "key systems" by the fact that external lines are not

normally indicated or selectable at an individual extension. From a user's point of view, calls on a key system are made by selecting a specific outgoing line and dialing the external number. A PBX, in

contrast, has a dial plan. Users dial an escape code (usually a single digit; often the same as the first digit

of the local emergency telephone number) that connects them to an outside line (DDCO or Direct Dial Central Office in Bell System jargon), followed by the external number. Some modern number analysis

systems allow users to dial internal and external numbers without escape codes by use of a dial plan

which specifies how calls to numbers beginning with certain prefixes should be routed.

PBX functions

Functionally, the PBX performs four main call processing duties:

Establishing connections (circuits) between the telephone sets of two users (e.g. mapping a dialed

number to a physical phone, ensuring the phone isn't already busy) Maintaining such connections as long as the users require them (i.e. channeling voice signals

between the users)

Disconnecting those connections as per the user's requirement

Providing information for accounting purposes (e.g. metering calls)

In addition to these basic functions, PBXs offer many other calling features and capabilities, with

different manufacturers providing different features in an effort to differentiate their products. Common

capabilities include (manufacturers may have a different name for each capability)

18. Explain the UHF/VHF radio system with necessary diagrams?

Ultra-high frequency (UHF) designates the ITU radio frequency range of electromagnetic waves

between 300 MHz and 3 GHz (3,000 MHz), also known as the decimeter band or decimeter wave as the

wavelengths range from one to ten decimeters; that is 10 centimeters to 1 meter. Radio waves with

frequencies above the UHF band fall into the SHF (super-high frequency) or microwave frequency range.

Lower frequency signals fall into the VHF (very high frequency) or lower bands. UHF radio waves

propagate mainly by line of sight; they are blocked by hills and large buildings although the transmission

through building walls is high enough for indoor reception. They are used for television broadcasting,

cordless phones, walkie-talkies, satellite communication, and numerous other applications.

Characteristics

The point to point transmission and reception of TV and radio signals is affected by many variables. Atmospheric moisture; solar wind; physical obstructions, such as mountains and buildings; and time of

day all affect the signal transmission and the degradation of signal reception. All radio waves are partly

absorbed by atmospheric moisture. Atmospheric absorption reduces, or attenuates, the strength of radio

signals over long distances. The effects of attenuation degrades in increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, such as VHF TV signals. The

ionosphere, a layer of the Earth's atmosphere, is filled with charged particles that can reflect some radio

waves. Amateur radio enthusiasts primarily use this quality of the ionosphere to help propagate lower frequency HF signals around the world: the waves are trapped, bouncing around in the upper layers of the

ionosphere until they are refracted down at another point on the Earth. This is called sky wave

transmission. UHF TV signals are not carried along the ionosphere but can be reflected off of the charged

particles down at another point on Earth in order to reach farther than the typical line-of-sight transmission distances; this is the skip distance. UHF transmission and reception are enhanced or

degraded by troposphere ducting as the atmosphere warms and cools throughout the day.

The main advantage of UHF transmission is the short wavelength that is produced by the high frequency.

The size of transmission and reception antennas is related to the size of the radio wave. The UHF antenna

is stubby and short. Smaller and less conspicuous antennas can be used with higher frequency bands.

The major disadvantage of UHF is its limited broadcast range, often called line-of-sight between the TV

station's transmission antenna and customer's reception antenna, as opposed to VHF's longer broadcast

range.

UHF is widely used in two-way radio systems and cordless telephones, whose transmission and reception

antennas are closely spaced. Transmissions generated by two-way radios and cordless telephones do not travel far enough to interfere with local transmissions. Several public-safety and business

communications are handled on UHF. Applications such as GMRS, PMR446, UHF CB, 802.11b

("WiFi") and the widely adapted GSM and UMTS cellular networks, also use UHF cellular frequencies.

A repeater propagates UHF signals when a distance greater than the line of sight is required.

Applications

UHF television broadcasting fulfilled the demand for additional over-the-air television channels in urban areas. Today, much of the bandwidth has been reallocated to land mobile, trunked radio and mobile

telephone use. UHF channels are still used for digital television.

Radio

UHF spectrum is used world-wide for land mobile radio systems for commercial, industrial, public safety,

and military purposes. Many personal radio services use frequencies allocated in the UHF band, although

exact frequencies in use differ significantly between countries.

VERY HIGH FREQUENCY:

Very high frequency (VHF) is the ITU-designated range of radio frequency electromagnetic waves from 30 MHz to 300 MHz Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF).These names referring to

frequency usage originate from the early 20th century, when regular radio service used the terms LF (low

frequencies), MF (medium frequencies), and HF (high frequencies). These names were standardized by the International Telecommunications Union (ITU) and extended to higher frequency ranges. Common

uses for VHF are FM radio broadcasting, television broadcasting, land mobile stations (emergency,

business, private use and military), long range data communication up to several tens of kilometers with

radio modems, amateur radio and marine communications. Air traffic control communications and air navigation systems (e.g. VOR, DME & ILS) work at distances of 100 kilometers or more to aircraft at

cruising altitude.

Propagation characteristics

VHF propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF waves (called sky wave propagation) so

transmissions are restricted to the local radio horizon less than 100 miles. VHF is also less affected by

atmospheric noise and interference from electrical equipment than lower frequencies. Whilst it is blocked by land features such as hills and mountains, it is less affected by buildings and other less substantial

objects than UHF frequencies.

Line-of-sight calculation

For analog TV, VHF transmission range is a function of transmitter power, receiver sensitivity, and distance to the horizon, since VHF signals propagate under normal conditions as a near line-of-sight

phenomenon. The distance to the radio horizon is slightly extended over the geometric line of sight to the

horizon, as radio waves are weakly bent back toward the Earth by the atmosphere.

20. Explain the principle operation of Microwave oven with block diagram?