Correct Answer : Envelope
Explanation : An imaginary line connecting the positive peaks and negative peaks of the carrier waveform gives the exact shape of the modulating information signal. This line is known as the envelope.
Correct Answer : Carrier peak line
Explanation : The modulating signal uses the peak value of the carrier rather than zero as its reference point. The envelope varies above and below the peak carrier amplitude. The zero reference line of the modulating signal coincides with the peak value of the unmodulated carrier.
Correct Answer : Distortion
Explanation : The zero reference line of the modulating signal coincides with the peak value of the unmodulated carrier. Because of this, the relative amplitudes of the carrier and modulating signal are important. When the amplitude of the modulating signal is greater than the amplitude of the carrier, distortion will occur.
Correct Answer : 2.35v
Explanation :
Correct Answer : 12
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 Answer : Modulating signal voltage = Carrier voltage
Explanation : 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.
Correct Answer : Modulating signal voltage > Carrier voltage
Explanation : Over-modulation is a condition in which the modulating signal voltage is much greater than the carrier voltage. The received signal will produce an output waveform in the shape of the envelope, whose negative peaks have been clipped off.
Correct Answer : Error information
Explanation : Distortion occurs when the modulating signal amplitude is greater than the amplitude of the carrier, causing incorrect information to be transmitted. In amplitude modulation, it is particularly important that the peak value of the modulating signal be less than the peak value of the carrier.
Correct Answer : Modulator
Explanation : The circuit used for producing AM is called a modulator. It has two inputs, the carrier and the modulating signal, and the resulting output is the modulated signal. Amplitude modulators compute the product of the carrier and modulating signals.
Correct Answer : Modulation index
Correct Answer : Sideband
Explanation : 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.
Correct Answer : 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.
Correct Answer : 30.8KHz
Explanation : Upper sideband frequency = carrier frequency +modulating signal frequency = 3000Hz + 80Hz = 3080Hz = 30.8KHz.
Correct Answer : 3900Hz
Explaination : Upper sideband frequency = carrier signal frequency + modulating signal frequency.Carrier frequency = upper sideband frequency -modulating signal frequency= 4000Hz – 100HZ = 3900hZ.
Correct Answer : Splatter
Explanation : 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 Answer : 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.
Correct Answer : Binary data transmission
Explanation : 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.
Correct Answer : Spectrum analyzer
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.
Correct Answer : 140KHz
Explaination : Bandwidth = upper sideband frequency – lower sideband frequency = 7350 – 7210 = 140KHz.
Correct Answer : 6Khz
Explanation : Bandwidth of a signal is twice the highest frequency of the modulating signal. Thus, bandwidth = 2 x 3KHz = 6KHz.
Correct Answer : Sideband suppressed carrier signal
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.
Correct Answer : Balanced modulator
Explanation : Balanced modulator is a special circuit which produces DSB or Double sideband suppressed carrier signals. It produces the sum or difference of the carrier and modulating signal but cancel or balance out the carrier frequency.
Correct Answer : Reduce in spectrum space
Explanation : 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 Answer : 125W to 166.66W
Correct Answer : 52.8W
Explaination :
Correct Answer : 10A
Correct Answer : Atmosphere
Explanation : Since an AM signal is a combination of waves of different frequencies when it is passed through the atmosphere, they get affected by the ionosphere and the upper atmosphere which attenuate signals below the frequency of 50Hz. If one sideband is above 50Hz and the other one is below 50Hz the atmosphere attenuates one sideband alone. This is known as selective fading.
Correct Answer : No sideband is generated
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.
Correct Answer : Pilot carrier
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.
Correct Answer : Hard to demodulate
Explanation : One of the main disadvantages of the sideband suppressed signal transmission is that it is hard to demodulate or recover. Since the carrier signal is not present, the carrier frequency must be fed into the receiver to completely extract the information signal.
Correct Answer : 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.
Correct Answer : Frequency deviation
Explanation : 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.
Correct Answer : 150MHz
Explaination : Maximum deviation in frequency = carrier frequency + maximum shift in frequencyMinimum deviation in frequency = carrier frequency – maximum shift in frequencyCarrier frequency = Maximum deviation in frequency – maximum shift in frequencyCarrier frequency = 150.03MHZ – 0.03MHz = 150MHz.
Correct Answer : Frequency shift keying
Explanation : 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.
Correct Answer : Depends only on the frequency of the modulating signal
Explanation : 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.
Explanation : 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.
Correct Answer : 70kHz
Explanation : According to Carson’s rule, BW [fd(max) + fm(max)] = 2(30 + 5) = 70Khz.
Correct Answer : 0.25
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 Answer : Narrowband FM
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.
Correct Answer : 1.667
Explanation : mf = fd⁄fm = 25<
Correct Answer : 5
Correct Answer : Velocity of motion
Explanation : Lightning strikes, ignition systems, motors, electronic circuits and weather create interference signals called noise. They are generally of high frequency and spikes of voltages.
Correct Answer : 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 Answer : 0.966
Explaination : ?=sin-1(N/S)(N/S)=sin(?) =sin(75°)=0.966.
Correct Answer : 172Hz
Explaination : δ=?(fm)=0.43(400)=172Hz.
Correct Answer : 12126.09Hz
Correct Answer : 100? and 0.75?F
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 is 100Ω and C is 0.75μF, R x C = 75μs.
Correct Answer : 15.366°
Explanation : ?=sin-1(N/S)=sin-1(2/7)=sin-1(0.265)=15.366°.
Correct Answer : 25.75
Explaination : N/S = Frequency deviation by noise / maximum deviation = 156.42/4000 =0.0391S/N = (N/S)-1=25.57.
Correct Answer : Bandwidth is higher for binary data than audio signals
Explanation : Since binary data is transmitted in square waves or pulses, they are generally made up of numerous fundamental sine waves. This occupies a huge bandwidth as compared to audio signals which are analog in nature and usually comprise of a lesser number of sine waves.
