Electronics and Communication Engineering Interview Questions and Answers
Question - 21 : - What is a repeater?
Answer - 21 : - A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.
Question - 22 : - What is attenuation?
Answer - 22 : - Attenuation is the reduction in amplitude and intensity of a signal. Signals may attenuate exponentially by transmission through a medium, or by increments calculated in electronic circuitry or set by variable controls. Attenuation is an important property in telecommunications and ultrasound applications because of its importance in determining signal strength as a function of distance. Attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in question.
Question - 23 : - What is multiplexing?
Answer - 23 : - Multiplexing (known as muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire.
Question - 24 : - What is CDMA, TDMA, FDMA?
Answer - 24 : -
Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. CDMA employsspread spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequencydivision multiple access(FDMA) divides it by frequency.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different directions (spatial division).In CDMA, they would speak different languages. People speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.
Question - 25 : - What is Barkhausen criteria?
Answer - 25 : - Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations. “Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network ( the magnitude of the loop gain ) are less than unity”. The condition of unity loop gain Aβ = 1 is called the Barkhausencriterion. This condition implies that | Aβ|= 1and that the phase of – Aβ is zero.
Question - 26 : - Explain Full duplex and half duplex.
Answer - 26 : - Full duplex refers to the transmission of data in two directions simultaneously. For example, a telephone is a fullduplex device because both parties can talk at once. In contrast, a walkietalkie is ahalfduplex device because only one party can transmit at a time. Most modems have a switch that lets you choose between fullduplex and halfduplex modes. The choice depends on which communications program you are running. In fullduplex mode, data you transmit does not appear on your screen until it has been received and sent back by the other party. This enables you to validate that the data has been accurately transmitted. If your display screen shows two of each character, it probably means that your modem is set to halfduplex mode when it should be in fullduplex mode.
Question - 27 : - Advantages of negative feedback over positive feedback.
Answer - 27 : - Much attention has been given by researchers to negative feedback processes, because negative feedback processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a system and can lead a system away from equilibrium states, possibly causingquite unexpected results.
Question - 28 : - Example for negative feedback and positive feedback.
Answer - 28 : - Example for –ve feedback is —Amplifiers
And for +ve feedback is – Oscillators
Question - 29 : - What is Oscillator?
Answer - 29 : - An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.
Question - 30 : - What is a transducer and transponder?
Answer - 30 : -
A transducer is a device, usually electrical, electronic, electromechanical, electromagnetic, photonic, or photovoltaic that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer. In telecommunication, the term transponder (short for Transmitter responder and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) has the following meanings:
An automatic device that receives, amplifies, and retransmits a signal on a different frequency (see also broadcast translator).An automatic device that transmits a predetermined messagein response to a predefined received signal. A receiver transmitter that will generate a reply signal upon proper electronic interrogation. A communications satellite’s channels are called transponders, because each is a separate transceiver or repeater.