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The correct answer is (a) lower modulation power is required

To explain: Base modulation is PREFERRED over collector modulation of a class C transistor becauselow MODULATING power is required and collector SATURATION prevents complete modulation of a signal. Generally, Collector modulation has more advantages over Base modulation like high linearity, BETTER collector efficiency and such like.

The correct choice is (a) TELEVISION Transmission

Easy explanation: Vestigial Sideband MODULATION (VSB) is a TYPE of amplitude modulation in which the carrier and only one sideband is COMPLETELY transmitted and the other sideband is PARTLY transmitted. Thus, television production is done using VSB modulation.

Correct OPTION is (a) ARMSTRONG MODULATOR

To explain: Varacter DIODE modulator is not an indirect way of GENERATING FM. Instead it’s a direct way of producing FM with the help of voltage controlled oscillator mechanism. It is Armstrong modulator which is an indirect way of generating FM.

Correct CHOICE is (a) DSB

Explanation: A BALANCE modulator mixes audio signal and RADIO frequency carrier wave, thereby producing a DSBSC wave, by SUPPRESSING the carrier. In DSB_SC, only the two sidebands are present. Thus, it has less power consumption.

Correct choice is (B) DETECTION of full AM is simpler

Explanation: SSB is preferred because of its low bandwidth and lesser power CONSUMPTION. It reduces its bandwidth by suppressing the CARRIER and removing one of the two sidebands since both sidebands are exactly same. But full amplitude modulation is sometimes preferred over it because in its detection of full AM is simpler due to it’s simpler DEMODULATION circuit.

The correct choice is (a) low pass filter

Explanation: Sampling is the conversion of continuous-TIME signal to discrete-time signal by sampling the continuous signal with respect to specific time intervals, thereby discritising it. Now to get back the ORIGINAL signal we have to use low pass filter, which attenuates HIGH FREQUENCIES and ALLOWS only low frequencies to pass.

The CORRECT choice is (a) Varacter diode

The best I can explain: Varactor diode is a diode working in the reverse-bias because of which no current flows through it. It has variable capacitance which varies with applied voltage. Varactor diodes are mainly USED in generation of FM signals USING Voltage Controlled Oscillator.

Correct choice is (a) calculate Bandwidth of FM signal

To explain I WOULD say: According to Carson’s rule, the required bandwidth is TWICE the sum of the maximum frequency deviation and the maximum modulating signal frequency or B = 2(FD + fm)Hz.

Right option is (d) MODULATING signal remains constant

To explain: Delta modulation is USED for TRANSMISSION of voice information where quality is not the primarily importance. Its drawback is it has TWO noises namely slope overload and granular noise. Granular noise is produced due to constant modulating input signal resulting into oscillatory output. So for getting RID from these noises we use ADM (Adaptive Delta Modulation).

Correct answer is (b) Crystal Oscillator

The explanation: In frequency modulation, frequency of the carrier WAVE is VARIED with the INSTANTANEOUS amplitude of message signal. Crystal oscillator is used to GENERATE a carrier signal with a precise or FIXED frequency. But it has no use in frequency modulation.

The correct CHOICE is (a) 20Hz to 20KHz

To explain I would say: The STANDARD FIXED range of AUDIO frequencies is from 20HZ to 20 KHZ.

The correct option is (a) ratio of time on to time off

Best EXPLANATION: DUTY cycle is the FRACTION of time in which the system is active. It can ALSO be defined as the ratio of time on to time off of a system. At times, duty cycle, expressed as percentage, is the ratio of time on to sum of time on and time off.

Right choice is (c) a low pass filter

The BEST I can explain: Pulse Amplitude MODULATION is the TRANSMISSION of data by varying the amplitude of different pulses. A low pass filter is always used to demodulate a PAM as it attenuates high FREQUENCIES and allows only low frequencies to pass.

The correct choice is (c) PCM

The explanation: PULSE code modulation (PCM) is a digital FORM of communication. It has no relation with analog communication. Pulse Code Modulation is a technique in which the amplitude of an analogue signal is CONVERTED to a binary value represented as a SERIES of pulses.

Correct option is (a) PAM

To EXPLAIN I would say: Pulse CODE Modulation deals with converting an analog signal to a digital signal. During it’s demodulation, the WAVE to be treated is to be parallel. The series pulse wave signal is then converted into a parallel digital signal using a serial to parallel converter, after which it is further converted into the original analog signal with the help of a decoder or detector.

The correct option is (a) PCM

For explanation: In PCM, the amplitude of the ANALOG SIGNAL is discritised and CONVERTED into digital form for transmission of binary data. PCM is least PRONE to noise and can travel long DISTANCES.

The correct option is (d) AM

To explain: For narrow and wide BANDS frequency modulation, modulation index is respectively smaller and greater than 1. When BANDWIDTH is considered it can be approximated to AM.

Correct option is (b) False

Explanation: In frequency modulation, frequency of the carrier WAVE is varied with the instantaneous amplitude of the MESSAGE signal. Thus, it requires large BANDWIDTH.

The CORRECT option is (a) PULSE MODULATION

The explanation: In pulse modulation, message signal in the form of pulses are VARIED with respect to WIDTH, amplitude or position. It is mostly used for radio navigation and for many others.

Right choice is (a) VHF

To explain: VHF (very high frequency) is the ITU designation for the range of RADIO frequency from 30MHz to 300MHz. Frequency modulated broadcast band generally lies in it only. HF ranges from 3MHz to 30MHz while SHF ranges from 3GHZ to 30GHZ. And LF ranges from 30KHz to 300KHz.

Right ANSWER is (B) Pulse Modulation

To explain: In pulse modulation, message signal in the form of PULSES are varied with respect to WIDTH, amplitude or position. It is mostly used for radio navigation, microwave band and for MANY others.

Correct answer is (a) PAM

For EXPLANATION: In pulse modulation, message signal in the form of pulses are varied with respect to width, amplitude or position. Pulse amplitude modulation varies amplitude of pulses for transmission of DATA. Its’ output pulses are not at FULL transmitter POWER for a strong signal and thus it is an exception.

Right option is (d) PCM

Easiest explanation: The difference between an input value and its quantized value is called quantization error or we can also SEE it as that when an analog number is not converted into an exact digital number. It TAKES place in pulse CODE modulation (PCM). Pulse Code Modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses.

The correct choice is (C) duty cycle

The EXPLANATION: Duty cycle is the FRACTION of time in which the system is active. It can also be defined as the ratio of time on to time off of a system. At times, duty cycle, expressed as a PERCENTAGE, is the ratio of time on to sum of time on and time off.

Correct OPTION is (c) number of quantization levels

Easiest explanation: Pulse code modulation (PCM) is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization NOISE occurs in PCM only. SIGNAL to quantization noise ratio depends on the number of quantization levels.

The correct choice is (a) True

To explain I would say: In pulse modulation, MESSAGE signal in the form of pulses are VARIED with RESPECT to width, amplitude or position. It is mostly used for radio navigation, microwave band and for many OTHERS.

The correct answer is (a) Pulse Modulation

To elaborate: In pulse modulation, MESSAGE signal in the FORM of pulses are varied with respect to width, amplitude or POSITION. It is mostly used for radio navigation, microwave BAND and for many OTHERS. It is also highly used in data communication.

The CORRECT option is (d) more than 1

Best explanation: For PRODUCING Narrow band frequency modulated wave, modulation index should be LESS than or EQUAL to1. For wideband frequency modulated wave, modulation index should be greater than 1.

Correct choice is (a) less than or EQUAL to 1

The explanation: For producing Narrow band frequency MODULATED WAVE, modulation index should be less than or equal to1. For WIDEBAND frequency modulated wave, modulation index should be greater than 1.

The CORRECT choice is (b) increases by 50%

Best explanation: MODULATION INDEX indicates amount of modulation in the carrier signal. If modulation index changes to 1 from 0, its transmitted power increases by 50%.

Correct choice is (b) EXPONENTIALLY with bandwidth

To explain I would say: Pulse code MODULATION (PCM) is a digital form of communication. Pulse Code Modulation is a technique in which the amplitude of an ANALOGUE signal is converted to a binary value represented as a SERIES of pulses. if we calculate the ratio of signal to NOISE ratio for different bandwidth then we observe that it increases exponentially with it.

Right choice is (b) False

To explain: Companding is the process through which the signal to noise ratio of a WAVE is REDUCED by compressing and expanding the signal. It DECREASES the number of bits required to RECORD the strongest signal. Companding also improves signal to noise ratio.