Communications - Online Test
Q1. Two 4-array signal constellations are shown. It is given that φ1 and φ2 constitute an orthonormal basis for the two constellation. Assume that the four symbols in both the constellations are equiprobable. Let N0/2 denote the power spectral density of white Gaussian noise.
If these constellations are used for digital communications over an AWGN channel, then which of the following statements is true ?
Answer : Option A
Explaination / Solution:
No Explaination.
Q2. FM Radio set used in cars is
Answer : Option D
Explaination / Solution:
Radio means sending energy with waves. In other words, it's a method of transmitting electrical energy from one place to another without using any kind of direct, wired connection. That's why it's often called wireless. The equipment that sends out a radio wave is known as a transmitter; the radio wave sent by a transmitter whizzes through the air—maybe from one side of the world to the other—and completes its journey when it reaches a second piece of equipment called a receiver((here a radio).
Q3. For a Hertz dipole antenna, the half power beam width (HPBW) in the E-plane is
Answer : Option C
Explaination / Solution:
The beam-width of Hertizian dipole is 1800 and its half power beam-width is 900
Q4. TV set used in a typical house is
Answer : Option D
Explaination / Solution:
The equipment that sends out a radio wave is known as a transmitter; the radio wave sent by a transmitter whizzes through the air—maybe from one side of the world to the other—and completes its journey when it reaches a second piece of equipment called a receiver.A television antenna, or TV aerial, is an antenna specifically designed for the reception of over-the-air broadcast television seignal, which are transmitted at frequencies from about 41 to 250 MHz in the VHF band, and 470 to 960 MHz in the UHF band in different countries..
Q5. Consider the amplitude modulated (AM) signal 
For demodulating the signal using envelope detector, the minimum value of Ac should be
For demodulating the signal using envelope detector, the minimum value of Ac should be
Answer : Option A
Explaination / Solution:
Q6. Attenuation is
Answer : Option D
Explaination / Solution:
Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes calledloss, attenuation is a natural consequence of signal transmission over long distances.
Q7. The driving point impedance of the following network is given by
The component values are
Answer : Option D
Explaination / Solution:
Q8. Amplification is the
Answer : Option C
Explaination / Solution:
It is the process of increasing the amplitude and hence the strength of an elctrical signal by using an electric circuit having atleat on transistor is called amplifier.Amplification is rerquired to compensate for the loss of strenght of a signal during its transmission.The additional energy is otianed from a dc source.The process of amplification is done at a location betwen the sources and the destination where the strength of signal becomes weaker than the required level.
Q9. The circuit shown in the figure is used to charge the capacitor C alternately
from two current sources as indicated. The switches S1 and S2 are mechanically
coupled and connected as follows:
Assume that the capacitor has zero initial charge. Given that u(t) is a unit step function , the voltage vc(t) across the capacitor is given by
Answer : Option C
Explaination / Solution:
Q10. Range of an electronic communication system
Answer : Option C
Explaination / Solution:
As the distance between the source and the destination increases the strenght of the transmitted signals become weaker and weaker and the distance where it loses energy to travel any more is range of the signal.
