Bandpass Modulation MCQ || Bandpass Modulation Questions and Answers

Answer.1. log₂m

Explanation:-

The transmission bandwidth for a m-ary PSK is given by:

BW = 2R_b/N

Rb = Bit rate = 1/Tb

Tb = bit duration

N = log₂m

For Binary transmission:

BW = 2R_b/log₂2 = 2R_b/1

We can see that the m-ary transmission bandwidth is smaller than binary by log2m

Answer.1. ASK

Explanation:-

ASK is also called on-off keying because, in the case of ASK, the carrier waves continuously switch between 0 and 1 according to the high and low levels of the input signal. In the ASK modulation scheme the signal attains either maximum amplitude or zero point. Thus it is also called on-off keying.

Answer.4. Frequency shift keying

Explanation:-

Analogue modulation techniques:

1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation

Digital Modulation Techniques:

1. Amplitude shift key
2. Frequency shift key
3. Phase Shift key
4. QAM

Amplitude-shift keying (ASK), frequency-shift keying (FSK), and phase-shift keying (PSK) are digital modulation schemes. FSK refers to a type of frequency modulation that assigns bit values to discrete frequency levels. FSK is divided into noncoherent and coherent forms.

ASK, PSK and FSK are signaling schemes used to transmit binary sequences through free space. In these schemes, bit-by-bit transmission through free space occurs.

Answer.1. Base bandwidth

Explanation:-

• Transmission bandwidth:- The maximum amount of data transmitted over an internet connection in a given amount of time.
• A baseband bandwidth is equal to the highest frequency of a signal or system, or an upper bound on such frequencies, for example, the upper cut-off frequency of a low-pass filter
• In amplitude shift keying, transmission bandwidth is equal to Base bandwidth.

Answer.3. 45

Explanation:-

The combination of ASK and PSK is called APK.

APK illustrates a hypothetical eight-vector signal set on the phase-amplitude plane. Four of the vectors are at one amplitude, and the other four vectors are at a different amplitude.

Each of the vectors is separated by 45°. When the set of M symbols in the two-dimensional signal space are arranged in a rectangular constellation, the signaling is referred to as quadrature amplitude modulation (QAM).

Answer.2. Frequency mixing

Explanation:-

Heterodyning, or mixing, is the process of multiplying a weak signal by a strong sinusoidal carrier, sometimes called the local oscillator, to shift the frequency of the signal in such a way that the information carried by the signal is preserved.

Answer.2. Predetection point

Explanation:-

In the first step, the received waveform is reduced to a single random variable or to a set of random variables formed at the output of the demodulator and sampler at time t = T where T is the symbol duration.

In the second step, a symbol decision is made on the basis of comparing to a threshold or on the basis of choosing the maximum.

Step 1 can be thought of as transforming the waveform into a point in the decision space. This point can be referred to as the pre-detection point, the most critical reference point in the receiver.

The first step of the detection process is to reduce waveform into a single or group of random variables. This first step in the transformation of the waveform into a point in signal space. This point is called a pre-detection point.

Answer.3. Both 1 and 2

Explanation:-

Heterodyning is used to shift one frequency range into another, new frequency range, and is also involved in the processes of modulation and demodulation.

The two input frequencies are combined in a nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a mixer.

Answer.4. All of the above

Explanation:-

Bandpass modulation techniques encode information as the amplitude, frequency, phase, or phase and amplitude of a sinusoidal carrier.

These bandpass modulation schemes are known by their acronyms to ASK (amplitude shift keying), FSK (frequency shift keying), PSK (phase shift keying), and QAM (quaternary amplitude modulation), where keying or modulation is used to indicate that a carrier signal is modified in some manner.

Answer.3. Both 1 and 2

Explanation:-

Demodulation of bandpass digital communication systems can be accomplished either coherently, where the receiver internally produces a reference signal of the same frequency and phase as the input signal, or noncoherently, where the receiver does not use a reference signal but employs either differential encoding of the information or even simpler means.