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Correct option is (B) 100Ω and 0.75μF

Explanation: The TIME constant for a high pass filter to be used in the preemphasis CIRCUIT is 75μs.R x C = 75μs. THUS when R is100Ω and C is 0.75μF, R x C = 75μs.

Correct CHOICE is (b) Preemphasis

Explanation: Preemphasis is a technique in which the HIGH frequency SIGNALS are amplified more than the lower frequency signals to have better resistance to noise. It is USUALLY used to transmit sounds from musical instruments which have high frequency harmonics.

The CORRECT choice is (C) 25.75

To explain: N/S = FREQUENCY DEVIATION by noise / maximum deviation = 156.42/4000 =0.0391

S/N = (N/S)^-1=25.57.

Correct answer is (d) 0.0261

Explanation: δ=ɸ(fm)= 0.436(300)=130.89Hz

Frequency DEVIATION by NOISE / MAXIMUM deviation = 130.89/5000=0.0261.

The CORRECT CHOICE is (a) 15.366°

For EXPLANATION: ɸ=sin^-1(N/S)=sin^-1(2/7)=sin^-1(0.265)=15.366°.

Correct ANSWER is (c) 172HZ

Easy explanation: δ=ɸ(FM)=0.43(400)=172Hz.

Correct ANSWER is (a) True

Explanation: The change in AMPLITUDE by the noise INTRODUCES a phase shift which is reflected as a small frequency variation in the signal. These frequency VARIATIONS changes or distorts the signal.

Right ANSWER is (c) Limiter circuits

Explanation: The receivers in FM contain limiter circuits which RESTRICT the amplitude of the received signal. The noise which only affects the amplitude of the signal causes VARIATIONS in amplitude of the signal. The limiter circuit clips off any VARIATION in amplitude to filter out most of the noise.

Correct choice is (d) Velocity of motion

To ELABORATE: Lightning strikes, ignition systems, motors, electronic circuits and weather CREATE interference SIGNALS called noise. They are generally of HIGH frequency and spikes of VOLTAGES.

The correct option is (a) 70kHz

The explanation is: ACCORDING to CARSON’s rule, BW [fd(MAX) + fm(max)] = 2(30 + 5) = 70Khz.

Correct answer is (c) 0.25

Easiest explanation: When the MODULATION index is AROUND 0.25 the modulation produces only single pairs of significant sidebands LIKE that of AM. This occupies comparatively less SPECTRUM space.

Correct option is (b) NARROWBAND FM

The explanation: A narrowband FM is in which the FM signal occupies the same spectrum space as of its equivalent AM signal. Common FM RADIOS use the narrowband TRANSMISSION to reduce spectrum space.

The CORRECT OPTION is (B) 1.667

The EXPLANATION is: MF = ^fd⁄fm = ^25⁄15 = 1.667.

Correct answer is (a) Depends only on the FREQUENCY of the MODULATING signal

The BEST I can explain: Phase modulation depends on both the amplitude and frequency of the modulating signal. Higher amplitude CAUSES a greater phase shift and higher frequency causes a greater rate of change of phase in the carrier signal.

Correct ANSWER is (c) Modulation INDEX

For explanation I would say: The modulation ratio is defined as the ratio of the frequency DEVIATION to that of the modulating frequency. In communication systems using FM techniques, there are LIMITS put on the maximum frequency and the modulation index.

The correct answer is (a) 5

Explanation: Modulation INDEX= MF = ^fd⁄fm = ^75⁄15 = 5.

Right option is (c) Frequency shift keying

For explanation I would say: Frequency shift keying assigns DIFFERENT VALUES of carrier frequencies for BINARY digits and transmits DATA by varying the frequency of the carrier in accordance with the binary data. This type of modulation is widely used in the transmission of binary data in digital cell phones and in some types of LOW speed modems.

The CORRECT choice is (a) True

The best I can explain: In frequency modulation, the INSTANTANEOUS amplitude of the modulating SIGNAL changes the frequency of the CARRIER. The frequency of the modulating signal has no effect Frequency modulation.

Right option is (b) Angle MODULATION

Explanation: Both FM and PM are collectively referred to as angle modulation. It includes varying the phase or the frequency of the CARRIER WAVE. Frequency and phase of the signal is dependent on the instantaneous angle and HENCE the NAME angle modulation.

The correct choice is (c) Frequency deviation

For explanation I would SAY: The amount of carrier frequency change by the MODULATING SIGNAL is referred to as the frequency deviation. The MAXIMUM frequency deviation OCCURS when the amplitude of the modulating signal is maximum.

Right CHOICE is (d) Pilot carrier

Easy explanation: Since demodulation is hard in SSB signals a LOW power carrier wave is transmitted with the SSB. This can be received and amplified at the receiving end to demodulate the SSB SIGNAL. This TYPE is used in FM STEREO transmissions.

The correct OPTION is (a) 10A

The BEST EXPLANATION: PEP = Vs X Imax

Imax = PEP / Vs = 500/50 = 10A.

The CORRECT option is (c) No sideband is generated

Best EXPLANATION: In an SSB the carrier SIGNAL is suppressed. Also, only when a modulating signal is present the sideband is PRODUCED. When there is no modulating signal there is no sideband produced and the carrier is also suppressed hence NOTHING is transmitted.

The correct answer is (b) Reduce in spectrum SPACE

To EXPLAIN I would say: In a signal, only the sidebands contain the information. Also, there is a DUPLICATION of the information in each sideband. Thus one sideband is sufficient form transmission as compared to DSB where both the sidebands are present. SINCE one of the sideband is also suppressed it reduces the maximum or the minimum FREQUENCY of the signal and hence the spectrum space is reduced in an SSB.

Correct CHOICE is (c) SIDEBAND SUPPRESSED carrier signal

Easy explanation: In an SSB or single sideband signal, the carrier is suppressed LEAVING the upper and lower sidebands. The resulting signal is referred to as the sideband suppressed carrier signal and one of the major benefits of this type of signal is that no power is wasted on the carrier.

The correct OPTION is (a) True

For explanation I would say: DSB or double sideband suppressed carrier does not alter the maximum and minimum FREQUENCY of the SIGNAL. It only suppressed the carrier signal and hence the SPECTRUM space which is dependent on frequency remains UNCHANGED.

The CORRECT option is (d) Splatter

For explanation I would say: Harmonics is generated by distortion due to OVERMODULATION. A harmonic interfere with other SIGNALS and is called splatter because of the way it SOUNDS at the receiver.

Correct choice is (b) MORSE code transmission

Explanation: Code transmission such as morse code are usually called continuous-wave (CW) transmissions. This kind of transmission is ALSO referred to as ON/OFF KEYING (OOK). DESPITE the fact that only the carrier is being transmitted, sidebands are GENERATED by such ON/OFF signals.

The correct choice is (a) Binary data transmission

The explanation is: AMPLITUDE MODULATION by square waves or rectangular binary pulses is REFERRED to as amplitude-shift keying (ASK). ASK is USED in some types of data communication when binary INFORMATION is to be transmitted.

The CORRECT answer is (a) 995Khz

Easiest explanation: UPPER SIDEBAND FREQUENCY = 990KHz + 5KHz = 995KHz.

Correct option is (a) True

Easy explanation: Complex waveform such as square waves, TRIANGULAR waves, sawtooth waves and distorted sine waves are MADE up of numerous FUNDAMENTAL sine waves at different amplitudes, according to Fourier THEORY.

Right OPTION is (a) 6Khz

For explanation I WOULD say: Bandwidth of a signal is twice the HIGHEST FREQUENCY of the modulating signal. Thus, bandwidth = 2 x 3KHZ = 6KHz.

Correct CHOICE is (c) SPECTRUM analyzer

Best explanation: For waveform made up of signals with different frequencies, there is a WIDE range of sideband frequencies produced. To FULLY understand the signal a frequency domain display is used. An instrument known as the spectrum analyzer is used to display the frequency domain information of the signal whereas the amplitude information can be given by an OSCILLOSCOPE.

Right answer is (a) Frequency domain display

Explanation: When a waveform is made up of waves of different frequencies the amplitude INFORMATION is not ENOUGH to fully understand the wave and its PROPAGATION characteristics. In this CASE, a frequency domain display is USED where the frequency of each separate signal is shown according to its frequency and amplitude with respect to time.

The CORRECT choice is (b) 30.8KHz

The BEST I can EXPLAIN: Upper sideband frequency = carrier frequency +modulating SIGNAL frequency = 3000Hz + 80Hz = 3080Hz = 30.8KHz.

Correct choice is (b) Sideband

To explain I would say: New signals at different frequencies are formed when an INTELLIGENCE signal is modulated with a carrier. These signals are CALLED SIDEBANDS and USUALLY have the frequency of the sum and the difference of the carrier and the modulating signal.

The CORRECT answer is (d) 12

Easiest explanation: When the voltage of the MODULATING signal exceeds the voltage of the carrier signal over-modulating occurs. Here, 12/10 = 1.2 which is greater than 1 and HENCE would cause over-modulation.

Correct option is (c) Modulating SIGNAL voltage = Carrier voltage

The explanation is: When the modulation index is 1 or the percentage of modulation is 100, modulating signal voltage is equal to the carrier voltage. This RESULTS in the greatest output power at the TRANSMITTER and the greatest output voltage at the receiver, with no distortion.