# Communication Engineering (Test 5)

## Tancet Anna University : Ece Electronics And Communication Engineering

| Home | | Tancet Anna University | | Ece Electronics And Communication Engineering | | Communication Engineering |

Communication Engineering
| Signals and Systems | | Communications | | Networks, Signals and Systems |
Q.1
The raised cosine pulse p(t) is used for zero ISI in digital communications. The expression for p(t) with unity roll-off factor is given by

The value of p(t) at t = 1/W is
A. −0.5
B. 0
C. 0.5
D.
Explaination / Solution:

Workspace
Report
Q.2
A right circularly polarized (RCP) plane wave is incident at an angle 600 to the normal, on an air-dielectric interface. If the reflected wave is linearly polarized, the relative dielectric constant ξr is.

A. √2
B. √3
C. 2
D. 3
Explaination / Solution:
No Explaination.

Workspace
Report
Q.3
One end of a loss-less transmission line having the characteristic impedance of 75Ω and length of 1 cm is short-circuited. At 3 GHz, the input impedance at the other end of transmission line is
A. 0
B. Resistive
C. Capacitive
D. Inductive
Explaination / Solution:

Workspace
Report
Q.4
Which of the following statements is true regarding the fundamental mode of the metallic waveguides shown ?

A. Only P has no cutoff-frequency
B. Only Q has no cutoff-frequency
C. Only R has no cutoff-frequency
D. All three have cutoff-frequencies
Explaination / Solution:

Rectangular and cylindrical waveguide doesn’t support TEM modes and have cut off frequency. Coaxial cable support TEM wave and doesn’t have cut off frequency.

Workspace
Report
Q.5
In the circuit shown, all the transmission line sections are lossless. The Voltage Standing Wave Ration(VSWR) on the 60 Ω line is

A. 1.00
B. 1.64
C. 2.50
D. 3.00
Explaination / Solution:

Workspace
Report
Q.6
A sinusoidal signal of 2 kHz frequency is applied to a delta modulator. The sampling rate and step-size Δ of the delta modulator are 20,000 samples per second and 0.1 V, respectively. To prevent slope overload, the maximum amplitude of the sinusoidal signal (in Volts) is
A. 1/2𝜋
B. 1/𝜋
C. 2/𝜋
D. 𝜋
Explaination / Solution:

For preventing slope overload, we should have
(slope of m(t) ≤ (slope of sampling)
For sinusoidal signal, if

Workspace
Report
Q.7
A band-limited signal with a maximum frequency of 5 kHz is to be sampled. According to the sampling theorem, the sampling frequency which is not valid
A.

5kHZ

B.

12kHZ

C.

15kHZ

D.

20kHZ

E.

Explaination / Solution:

Given, the maximum frequency of the band-limited signal
fm = 5 kHz
According to the Nyquist sampling theorem, the sampling frequency must be greater than the Nyquist frequency which is given as

So, the sampling frequency fs must satisfy

only the option (A) does’nt satisfy the condition therefore, 5K HZ is not a valid sampling frequency.

Workspace
Report
Q.8
A four-phase and an eight-phase signal constellation are shown in the figure below.

Assuming high SNR and that all signals are equally probable, the additional average transmitted signal energy required by the 8-PSK signal to achieve the same error probability as the 4-PSK signal is
A. 11.90 dB
B. 8.73 dB
C. 6.79 dB
D. 5.33 dB
Explaination / Solution:

Here Pe for 4 PSK and 8 PSK is same because Pe depends on d . Since Pe is same, d is same for 4 PSK and 8 PSK.

Workspace
Report
Q.9
Given two continuous time signals  which exist for t > 0, the convolution z(t) = x(t)* y(t) is
A.
B.
C.
D.
Explaination / Solution:

Workspace
Report
Q.10
Two systems with impulse responses h1(t) and h2(t) are connected in cascade. Then the overall impulse response of the cascaded system is given by
A.
B.
C.
D.