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Correct answer is (c) \(\FRAC{E_{max} – E_{min}}{E_{max} + E_{min}}\)

Best explanation: Modulation INDEX TELLS us the amount by which the CARRIER wave is varied with respect to the message signal. It is defined as \(\frac{E_{max} – E_{min}}{E_{max} + E_{min}}\) where Emax and Emin are respectively the maximum and minimum voltage of the modulated wave.

The correct answer is (a) (ωc + ωa), (ωc – ωa) and ωc

The BEST I can explain: If we modulate the carrier signal having frequency ωc with respect to the MESSAGE WAVE having frequency ωa, then the RESULTANT MODULATED wave has frequency components(ωc + ωa), (ωc – ωa) and ωc.

The correct option is (a) half the carrier wave

To explain I would say: The SIDEBANDS are IDENTICAL to each other and CONTAIN same information. Thus, for 100% modulation, VALUE of modulation INDEX should be equal to 1. If modulation index, m=1 then total sideband power is equal to the half of carrier wave.

Correct option is (a) by INCREASING its modulation index

The best explanation: Signal to NOISE RATIO is the ratio of signal power to the noise power. It is the measure of signal present with respect to the surrounding noise. It is directly proportional to the modulation index and thus it INCREASES with modulation index.

The correct answer is (C) incompability with ORDINARY AM radio waves

Explanation: Quadrature Amplitude MODULATION (QAM) is widely used for COMBINING two amplitude modulated waves into a single channel. It is both an analog and digital modulation technique. It has many ADVANTAGES over other modulations such as PSK but its disadvantage is its incompability with ordinary radio waves.

Correct choice is (B) False

Best explanation: Amplitude modulation has the CAPABILITY to send audio, video and digital data using different amplitude modulation TECHNIQUES. So the STATEMENT that only audio signal can be sent by amplitude modulation is WRONG.

Correct choice is (a) True

Explanation: In SINGLE Sideband transmission, the carrier is suppressed and only either of the two SIDEBANDS is transmitted. Thus, it REDUCES the total power consumption and also reduces the BANDWIDTH required. For its demodulation it requires a complex demodulator circu

Correct answer is (c) be set to USB MODE and reinsert the carrier

For explanation I would say: Single SIDE band suppresses the carrier and uses only one of the TWO SIDEBANDS. The two sidebands carry exactly the same information and thus removing a sideband does not have any effect on the signal. To demodulate upper sideband of signal it is necessary that the receiver must be set to USB mode and have the ability to reinsert the carrier.

Right answer is (d) Peak Envelope Power

The explanation: PEP in COMMUNICATION stands for Peak Envelope Power. It is the highest envelope power that is transmitted to antenna transmission line by a transmitter. It is used to measure the power of VARYING signals.

Correct CHOICE is (d) ENVELOPE

Explanation: Envelope is basically a SMOOTH curve that outlines the extremes of any baseband signal in the AMPLITUDE modulated wave. So basically it is MESSAGE or baseband signal that determines the envelope.

Correct choice is (d) \(\sqrt{(m_1 \times m_1) + (m_2 \times m_2)}\)

The EXPLANATION is: Modulation index tells us the AMOUNT by which the carrier wave is varied with respect to the message signal. The TOTAL modulation index of TWO waves having modulation index M1 and m2 is\(\sqrt{(m_1 \times m_1) + (m_2 \times m_2)}\).

The CORRECT answer is (B) Two

To explain I would say: Single tone MODULATION is that in which the modulation is CARRIED out with a message signal having single frequency component. Thus, the modulated wave has two sidebands.

Correct CHOICE is (c) same as USB

The BEST explanation: The two BANDS i.e. upper SIDEBAND and lower sideband generally contains same information. They also has same power.

The correct CHOICE is (b) False

The EXPLANATION is: In Single SIDEBAND transmission, the carrier is suppressed and only either of the two sidebands is transmitted. Thus, it reduces the TOTAL power consumption and also reduces the bandwidth required. The two sidebands carries exactly the same INFORMATION and thus removing a sideband does not have any effect on the signal.

The correct answer is (a) suppressed-carrier

To EXPLAIN: DSB-SC stands for Double Side Band- Suppressed Carrier. In SBSC, the carrier is suppressed and only the TWO sidebands are TRANSMITTED. In DSB-SC all the frequencies produced by amplitude modulation are symmetrically ARRANGED above and below the carrier frequency.

The correct answer is (b) decreases with modulation frequency and increases with deviation

Explanation: Modulation INDEX tells us the amount by which the carrier wave is VARIED with respect to the message signal. In FM, modulation index is the ratio of frequency deviation and MODULATING frequency. Frequency modulated modulation index increases as deviation increase. It also decreases with modulation frequency.

Right option is (a) Bessel functions

To explain: Bessel FUNCTION are the SOLUTION of Bessel differential equation which are non-singular at the origin. In COMMUNICATION it is used to calculate FM bandwidth.

Correct option is (a) increases

The best EXPLANATION: If we increase or DECREASE the MODULATION index, ACCORDINGLY the power of amplitude modulated system will also increase or decrease. This is because the power is directly proportional to the modulation index.

Correct CHOICE is (c) same as USB

Easy explanation: Generally, USB (upper sideband) and LSB (lower sideband) contain same INFORMATION and are identical to one another. THUS, both ENTAIL same POWER.

Right ANSWER is (a) 1

The EXPLANATION: For getting maximum power, it is REQUIRED to set the maximum and minimum voltage of the modulated WAVE such that we get modulation INDEX equal to unity. This implies 100% modulation.

The correct answer is (a) by integrating the MODULATING SIGNAL before applying to the PM OSCILLATOR

To explain: Frequency modulation can be derived from phase modulated system, if we integrate our modulating signal before applying our wave to PM oscillator. LIKEWISE, Phase modulation can be obtained from frequency modulated system, if we DIFFERENTIATE our modulating signal before applying our wave to FM oscillator.

Correct option is (a) Carson’s RULE

For explanation 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.

B = 2(fd+fm)Hz.

The correct OPTION is (d) uses DSBSC AM MODULATION

For explanation: A stereo FM contains three MAJOR sections :- monomode, stereo mode and section common to both mono and stereo mode. The stereo section is much complicated than OTHERS. It uses DSBSC AM modulation, in which the carrier is suppressed and only the two SIDEBANDS are transmitted, for its process.

Right answer is (a) True

The BEST explanation: Signal to noise ratio is the ratio of signal power to the noise power. It is often DESCRIBED in decibels. Signal to noise ratio is the ratio of signal power to the noise power. It is the measure of signal present with respect to the surrounding noise. It is directly proportional to the modulation INDEX and thus it increases with modulation index. It is BETTER for FREQUENCY modulated systems.

Correct option is (a) POWER decreases

Explanation: If the distance between the CENTRAL frequency and SIDEBANDS INCREASES, the effective power decreases as BANDWIDTH increases.

Right CHOICE is (d) Maxwell

Explanation: Maxwell was the first person who CAME up with the concept of electromagnetic theory and from there, the theory of radio WAVES was deduced. After some YEARS, it was Hertz who applied Maxwell theories to the production and reception of waves.

Right OPTION is (a) threshold effect

Explanation: Signal to NOISE ratio is the measure of signal PRESENT with respect to the surrounding noise. Threshold effect has low output signal to noise ratio. It contains large noise as compared to input signal in envelope detector. In threshold effect, detection of message signal is difficult.

Correct option is (a) INFINITE

Easy explanation: WIDEBAND frequency modulated SYSTEM has modulation index greater than 1. Thus, if we consider the number of sidebands in wideband frequency modulated system, we find it to be infinite, mathematically SPEAKING.

The correct choice is (d) it can use amplitude as well as frequency modulation and is ALSO MONAURAL

The best explanation: STC stands for SUBSIDIARY Communication Authority. SCA is a separated data channel which is transmitted along with the main signal over a BROADCAST station. It can either be amplitude modulated or frequency modulated. It being monaural means that multiples AUDIO signals are mixed and then passed through a single channel.

The correct choice is (d) to increase the SIGNAL to NOISE RATIO for lower AUDIO frequencies

The best I can explain: Pre-emphasis is applied in communication systems to improve signal strength before transmission. It refers to boosting the amplitudes of the weak modulating voltages for HIGH audio frequencies. It is also helpful in increasing S/N ratio but for lower audio frequencies only.

The correct choice is (a) Narrow BAND frequency MODULATION

Explanation: NBFM stands for Narrow band frequency modulation. For NBFM, modulation index should be less than EQUAL to 1.

Right choice is (d) because the power in the outer sidebands is negligible

Explanation: In FREQUENCY MODULATION system, frequency of the carrier WAVE is varied in proportion with the instantaneous amplitude of the message SIGNAL, which is to be transmitted. IN Wideband FM, the number of sidebands are infinite. Thus, using Carson’s rule, the bandwidth of FM signal is kept limited CONSIDERING the power impact of other sidebands negligible.

Right answer is (a) True

Explanation: The quality factor Q, of a RESONANT circuit is a measure of a 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 application.

The CORRECT option is (b) transit TIME

For EXPLANATION: Transit time is that time which is taken by the CHARGE carriers to MOVE from emitter to collector.

The correct CHOICE is (a) Marconi

For explanation I would SAY: Marconi is the first person who sent the first RADIO signal across the atlantic ocean. It was Maxwell who originated the THEORY of radio waves. After some years, it was Hertz who applied Maxwell theories to the production and reception of waves.

The correct ANSWER is (a) to REMOVE RF from non-RF circuits

To explain I would say: A bypass capacitor is generally used to dampen the AC or NOISE present at all frequencies. In COMMUNICATION, it is used to remove RF from non-RF circuits.

Right option is (a) Modulating amplifier

Easy explanation: In amplitude modulated system, amplitude of the carrier wave is varied in proportion to the amplitude of the original message wave which is to be transmitted. For HIGH LEVEL amplitude MODULATION, power amplifiers are not required and modulating amplifiers is USED to give power to sidebands.

The correct choice is (c) varies the frequency of carrier oscillator

For explanation I would say: Frequency modulated SYSTEM can be PRODUCED either by direct ways or INDIRECT ways. ARMSTRONG METHOD comes under indirect method. Direct FM modulator is generally used to vary the frequency of carrier oscillator, thus being known as frequency discrimination method, while indirect FM modulator varies the phase of carrier oscillator, thus being called phase discrimination method.

Right ANSWER is (b) DSB-SC is required

The best I can explain: Single side band suppressed CARRIER modulation technique suppresses the carrier and transmits EITHER of the TWO sidebands. Thus, this not only reduces the power consumed but also reduces the bandwidth. SSB-SC technique REQUIRES a DSB-SC to be passed through a bandpass filter.

Right choice is (d) varies the phase of carrier oscillator

The EXPLANATION: Frequency modulated system can be produced either by direct ways or INDIRECT ways. Armstrong method comes under indirect method. Direct FM MODULATOR is GENERALLY used to vary the frequency of carrier oscillator, thus being KNOWN as frequency discrimination method, while indirect FM modulator varies the phase of carrier oscillator, thus being called phase discrimination method.