41 questions and answers
1. a. State sampling theorem. What is Nyquist rate of sampling?
b. What is pulse amplitude modulation
c. What is meant by flat top sampling? Why is it more preferred than natural sampling?
d. Explain the demodulation of PAM signal using a hold circuit
e. What is the bandwidth required for transmission of PAM signal?
a. The sampling theorem state that A band limited signal of finite energy, which has no frequency components higher than fm Hz, is completely described by its sampled values less than or equal to 1/(2fm ) second apart.
How is a Phase Locked Loop (PLL) used for demodulation of FM signal? Mention the advantage of PLL demodulation.
The PLL is useful in demodulation of FM signals in presence of large noise and low signal power (low signal to noise ratio). It is most switched for using space vehicle to earth data links or where loss along the transmission path is very large recently it has found application is commercial FM receivers.
Explain with suitable block diagram the generation of FM signal using Armstrong method.
The generation of FM waveform by indirect method is also known as Armstrong Method. In the indirect method a narrow band FM signal is generated first after that this NBFM signal is frequency multiplied to generate WBFM.
State Channel capacity theorem
Bandwidth and noise power place a restriction upon the rate of information that can be transmitted by a channel.
What is meant by entropy of a source?
In a practical communication system, we usually transmit long sequence of symbols from an information source. Thus we are more interested in the average information that a source produces than the information contain of a single symbol.
Apply Shannon – Fano algorithm to the source with M = 8 emitting message A, B, C, D, E, F, G, H having probability P(A) = 1/2, P(B) = P(C) = 1/8, P(D) = P(E) = P(F) = 1/16, P(G) = P(H) = 1/32, calculate entropy, average code length and efficiency of coding.
Given that the probabilities of the eight messages are respectively P(A) = 1/2, P(B) = P(C) = 1/8, P(D) = P(E) = P(F) = 1/16, P(G) = P(H) = 1/32
Write short notes on:
The block diagram of voltage control oscillator is given in . 9. In most the cases, the frequency of an oscillation is determined by the time constant RC. However, in cases or applications such as FM., tone generation, and frequency shifting keying (FSK), the frequency is to be controlled by means of an input voltage, called the control voltage.
Write short notes on:
A typical circuit diagram of Ring modulator is given in Figure 10(a). The ring modulator consists of two centre trap transformers T1, T2 and four non-linear devices i.e. p-n junction diodes D1, D2, D3 and D4. Carrier signal c(t) with frequency fc is applied at the center tapes of two transformers.
Write short note on PCM ( Pulse Code Modulation).
Figure shows the basic block diagram of pulse code modulation scheme. The main elements of the PCM systems is \nTransmitter Transmission path (Channel) Receiver
Write a short note on TDM (Time Division Multiplexing).
The Time Division Multiplexing (TDM) is a multiplexing method by which multiple number of channel containinformation passes over a common transmission media or channel at different time slots. In other way TDM is a technique in which combining the digital message signal from different sources on a single data stream and transmit over a common channel at different time slot.
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