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Correct choice is (b) Transformer COUPLING

To explain: Impedance matching is the input impedance of an electrical LOAD or the output impedance of corresponding electrical signal SOURCE to maximize power transfer or minimize signal REFLECTION from the load. Transformer coupling is basically used for impedance matching in RF amplifiers. It is usually used with a small load for power AMPLIFICATION.

The correct OPTION is (d) EITHER MIXER or detector or IF amplifiers

Easy explanation: Distortion in a receiver can OCCUR in either mixer or in the detector. It can also occur in IF amplifiers. Distortion is the change in the shape of the waveform.

The correct answer is (b) False

Easy explanation: Neutralization CANCELS unwanted feedback by adding feedback out of PHASE with the unwanted feedback. It is a METHOD of filtering noise out of signals.

Correct OPTION is (b) by the noise that is GENERATED in the RECEIVER

For explanation I would say: The response of a receiver to weak SIGNALS is limited by the noise. This noise is generated in the receiver only. Noise is the unwanted signal that is PRESENT in the passband of the signal.

The CORRECT choice is (a) Sampling signals less than Nyquist Rate

The best I can explain: ALIASING causes different signals to become indistinguishable when sampled. It happens when the sampling rate is less than Nyquist rate. To PREVENT aliasing, sampling signals should be at a rate which is TWICE of Nyquist Rate.

The correct option is (a) True

Explanation: The quality FACTOR Q, of a RESONANT circuit is a measure of quality of resonant circuit, thus indicating the PERFORMANCE of the resonant circuit. BANDWIDTH can be seen as the ratio of the resonant frequency to quality factor. A higher value for Q means a more narrow bandwidth, which we want in many applications.

Correct OPTION is (B) all RF amplifiers can be linear

The best I can explain: For LOW level AM, modulation is done at low power of carrier and modulating signal, so power amplifiers are used to BOOST the carrier and modulating signal. Therefore, output power is low. THUS, the amplifiers used are linear.

Right choice is (b) all RF amplifiers can be nonlinear

To elaborate: In high level AM, modulation is done at high POWER of CARRIER and modulating SIGNAL therefore output power is high. Therefore, power amplifiers are not used to BOOST the carrier and modulating signal. Thus, all RF amplifiers are non-linear.

Right OPTION is (a) pi NETWORK and T network

For explanation I would say: If a source with low IMPEDANCE is connected with a LOAD with high impedance then the power that can PASS through the connection is limited by higher impedance. Generally the two networks, pi and T are used for impedance matching.

Right option is (b) they are essentially class C AMPLIFIERS

For explanation: FREQUENCY MULTIPLIER multiplies the frequency of the input by an integer, such that the output is a multiple of the input. Frequency MULTIPLIERS are generally class C amplifiers.

Right option is (d) a small range of amplitude

The best explanation: A SIGNAL compression method in a wireless NETWORK provides EFFICIENT transfer of COMPRESSED signal SAMPLES over serial data links in the system. Baseband compression produces a small range of amplitude.

The CORRECT answer is (d) has VARIABLE amplitude

For explanation I would say: If any SIGNAL has variable amplitude then its AMPLIFIER must be linear. Others may or may not have the same but can possess non-linear amplifiers.

Correct choice is (a) True

The explanation is: ALC STANDS for Automatic Level CONTROL. It is a technology which is used for automatic control of output power. It HELPS in maintaining the output when there are varying CHANGES in the INPUT.

Correct choice is (a) 50 ohms RESISTIVE

The best explanation: Transmitter is an ELECTRONIC DEVICE that produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. Transmitters are usually designed to DERIVE a load impedance of 50 ohms resistive.

The correct option is (d) a BALANCE MODULATOR

To EXPLAIN I would say: A mixer is the ONE which mixes the audio frequency with the carrier frequency. A transducer converts a signal from one form to another. Balance modulator suppresses the carrier and leaves only the sidebands.

Correct ANSWER is (c) a dummy LOAD

To explain: If a transmitter is CONNECTED to RESISTOR not antenna than it is called dummy load. Such a load is USED for testing purposes to set the parameters of the transmitter, as it would have behaved in presence of an actual antenna.

Correct answer is (d) to change the carrier frequency to any required value

To EXPLAIN: Mixing is used to change the frequency of carrier by mixing it with a radio frequency signal or audio signal. The frequency can be CHANGED to any required value in COMMUNICATION.

The CORRECT option is (a) baseband frequency range

Explanation: BANDWIDTH can be SEEN as a range of frequencies WITHIN a band, that is used for transmitting a signal. A signal bandwidth depends on the baseband frequency range.

Right answer is (d) MULTIPLEXING

The explanation is: Multiplexing is a method by which multiple analog or digital SIGNALS are combined to FORM a single complex signal. In multiplexing, many signals are combined into one signal and passed through a single channel, thus sharing the same medium.

Correct answer is (a) True

Best explanation: Miller effect is responsible for LIMITING the gain of an AMPLIFIER at HIGHER frequencies due to Miller capacitance between the output and input. Also, OSCILLATIONS in amplifier occur due to input/output FEEDBACK.

The CORRECT CHOICE is (a) True

Best explanation: Phase distortion is the CHANGE in shape of the waveform. Thus, if we SHIFT the phase relationships between BASEBAND frequencies, it will ultimately result in distortion.

The correct answer is (a) sensitivity and selectivity

To elaborate: Sensitivity and selectivity are the TWO key specifications for any receiver, which is used for the PURPOSE in communication. Sensitivity is the ability of the receiver to amplify WEAK signals, WHEREAS Selectivity is the ability of the receiver to reject UNWANTED signals.

Correct ANSWER is (b) Armstrong

The best EXPLANATION: SUPERHETERODYNE uses frequency mixing to convert a received RF signal to a fixed IF(INTERMEDIATE frequency). This method is known as heterodyning.This IF can be processed more easily than the original carrier frequency. It was INVENTED by Armstrong.

The correct ANSWER is (C) is above the RF frequency

Explanation: The frequency of the local OSCILLATOR is not fixed. It is mostly above the RF frequency.

The correct choice is (a) the increase of wire RESISTANCE with frequency

Easiest explanation: SKIN effect becomes more and more apparent as frequency increases as skin DEPTH becomes smaller. It is due to alternating current FLOWING through the outer surface of conducting material. It refers to the increase of wire resistance with frequency.

Correct choice is (b) color VIDEO receivers

To elaborate: Phase DISTORTION is a change in the SHAPE of the waveform. It occurs when filter’s do not have a sharp CUT off frequency thus not properly filtering a wave. Thus, phase distortion is important in color video receivers.

The CORRECT answer is (c) approximately 3KHz

Best explanation: The FIXED standard baseband bandwidth for a voice GRADE SIGNAL is approximately close to 3KHz.

Correct answer is (a) True

For EXPLANATION I would say: Miller effect is responsible for limiting the gain of an amplifier at higher frequencies DUE to Miller capacitance between the output and INPUT. ALSO, oscillations in the amplifier occur due to input/output feedback.

The correct answer is (d) base-to-collector capacitance

The EXPLANATION: Miller EFFECT is responsible for the increase in EQUIVALENT input capacitance of an inverting voltage amplifier. The increase equivalent input capacitance is given by, CM = C(1 + AV). In BJT, miller effect is due to base-to-collector capacitance.

The CORRECT option is (a) Intermediate Frequency

To elaborate: IF stands for intermediate frequency. It is a frequency to which a carrier wave is SHIFTED, with the help of a mixer, as an intermediate step in TRANSMISSION and RECEPTION. This IF is more suitable for executing further processes.

Right CHOICE is (d) SMALL ADJUSTABLE capacitors

Easiest explanation: Trimmers and padders are the two types of small adjustable capacitors. Its capacitance can be ADJUSTED to the required VALUE.

Right CHOICE is (a) weakest SIGNAL that is received at the receiver

Explanation: Sensitivity and SELECTIVITY are two key components of any circuit. Sensitivity is USED to MEASURE the weakest signal that is received at the receiver.

The correct choice is (a) Automatic Gain Control

The explanation: AGC stands for Automatic Gain Control. It is closed loop FEEDBACK REGULATING circuit. Its purpose is to PROVIDE a CONTROLLED signal amplitude at its output, IRRESPECTIVE of changes in it’s input signal amplitude.

Right answer is (a) the range of frequencies that RECEIVER can select

Easy EXPLANATION: Sensitivity and Selectivity are two key components of any circuit. Selectivity is used to measure the range of frequencies that the receiver can select. Sensitivity is the ABILITY of the receiver to amplify WEAK SIGNALS.

The correct option is (B) it is a bit-oriented protocol

Easy EXPLANATION: HDLC is a high-level data link control. It is a bit-oriented protocol. HDLC is GROUP of rules for transmitting data between NETWORK points.

Right answer is (b) over short distances only

The BEST EXPLANATION: In serial transmission, bits are transmitted one at a TIME over a single channel. In parallel transmission bits are sent simultaneously over their own individual channel. It sent DATA over short distances only.

Correct choice is (a) Dual-Tone MULTI frequency

Easiest explanation: DTMF is an in-band telecommunication signal. It uses the voice-frequency band over TELEPHONE lines. It was developed by Bell SYSTEMS in United States.

Right choice is (d) Emile Baudot

For EXPLANATION: Emile Baudot invented the FIVE-level teletype code. Each character in ALPHABET is represented by a SERIES of five BITS.

Right CHOICE is (b) False

The BEST explanation: In Asynchronous TRANSMISSION, each character is signified by start and stop bits. Thus, the transmitter and receiver are synchronized frame-by-frame using the start and stop bits, not by data bits.

Correct ANSWER is (C) Local Access and TRANSPORT Area

Easy explanation: LATA stands for Local Access and Transport Area and is used in the U.S. for a geographical area covered by one or more local telephone companies. It is legally REFERRED to as local EXCHANGE carriers.

The correct answer is (a) it has no START and stop bits

The explanation: In synchronous TRANSMISSION both SENDER and receiver access the data according to same clock. It has no start and stop bits and thus it has more EFFICIENT. However, it is more expensive than ASYNCHRONOUS transmission and has highly complex circuit.

Correct choice is (c) PARITY

For explanation: VRC is generally used in COMMUNICATION. It STANDS for VERTICAL Redundancy Check. It is same as parity.

Right OPTION is (a) correct bit errors

Best explanation: ARQ is an error control method.It is used for data transmission that uses ACKNOWLEDGMENTS and inputs to ACHIEVE RELIABLE data transmission.

Correct CHOICE is (a) Public Switched Telephone Network

Explanation: PSTN stands for Public Switched Telephone Network. It is the aggregate of the WORLD’s circuit-switched telephone network. It helps in providing SERVICES for public TELECOMMUNICATION.

Correct answer is (d) BIT stuffing

Easiest explanation: SDLC stands for Software Development LIFE Cycle. It consists of a DETAILED PLAN describing how to develop, analyze and maintain software for it’s business value. Bit stuffing is required in it if we want to use flags.