Analog Communication Interview Questions 4o20

ANALOG COMMUNICATION INTERVIEW QUESTIONS 1. What are the main components needed for a communication? 

Sender, Transmission line and Receiver.

1. What is Radio communication? 

Radio communication uses electrical energy to transmit information. Radio transmitter converts audio (sound) signals to electrical signals that are sent over wires or through space. A radio receiver converts the electromagnetic waves so that the information can be found out.

1. Range of Audio Frequency? 

Ø 20Hz to 20 KHz

1. Range of Radio Frequency? 

Ø 10 KHz to 1000GHz.

1. What is modulation? 

Ø Modulation is the process of changing the characteristics of the carrier signal with respect to that of the message signal.

1. What are the principle forms of modulation? 

Ø Amplitude Modulation(AM)



Ø Frequency Modulation(FM)



Ø Phase Modulation(PM)

1. What are the types of angle modulations? 

FM and PM

1. What is a mixer? 

An electronic circuit that combines two frequencies.

1. What is a product detector? 

It is a detector whose audio frequency output is equal to the product of the Beat Frequency Oscillator (BFO) and the RF input signal.

1. What is a Beat Frequency Oscillator (BFO)? 

An oscillator whose output frequency is approximately equal to the transmitter’s carrier frequency.

1. What is known as Bandwidth? 

Bandwidth is the frequency range, in hertz (Hz), between the upper and lower frequency limits. 12. What is Harmonics?



Harmonics is the signals with frequencies that are an integral multiple of the fundamental frequency. 13. What is the range of frequency in commercial AM broadcasting?



540 KHz to 1600 KHz has a 10 KHz bandwidth. 14. Range of frequency in AM baseband?



100KHZ to 5 KHz. 15. What is baseband?



It is a band of frequencies occupied by a message signal. 16. What you mean by frequency translate?



It is the process of displaying the frequency contents of a signal to another place in the frequency spectrum. 17. Modulation index?



Modulation index (m) is the ratio between the amplitude of the message signal to the amplitude of the unmodulated carrier signal. 18. What is percentage of modulation?



The modulation index (M) is expressed as a percentage.(%m) 19. Transmission efficiency?



It is the ratio of the total AM power to that of the sideband. 20. What is Splatter?



Adjacent channel interference due to over modulation of carrier signal by abrupt peak message signal.

21. What is the selectivity of a radio receiver? The ability of a radio receiver to select a desired signal frequency while rejecting all others is called selectivity.

22. What are the

main components of a RF receiver? 

RF filter, RF amplifier, mixer. Local Oscillator, IF filter, IF amplifier and Envelope Detector.

23. What is RF stage? 

It is the first input stage in which primary selection, filtering and amplification of the input RF signal is performed.

24. What is IF stage? 

It is the section of the receiver between the mixer and the detector. The IF stage operates at a fixed intermediate frequency (FIF) and it is where most of the amplification and filtering occurs.

 

24. What is local oscillator? An oscillator in which a piece of electronic equipment that is usually used as a source of electromagnetic wave frequencies for mixing with other frequencies that the equipment handles.

25. What is envelope detector? 

A circuit containing a diode in series with an RC network, used to perform demodulation. An envelope detector, which demodulates an AM signal, cannot demodulate an SSB signal

26. What is a diode detector? 

A diode detector is a nonlinear charging circuit formed by a diode in series with a parallel with RC network.

27. What is a balance modulator? 

Balance modulators translate a message signal to two sidebands and suppress the carrier signal frequency to produce a DSB signal.

28. What is up conversion? 

The process of increasing the frequency of a signal to a higher frequency for transmission is up conversion. The mixer, which is a balanced modulator, performs the up-conversion.

29. What is the function of AGC circuit? 

A circuit that maintains the output volume of a receiver, regardless of the variations in the received signal power.

30. What is centre frequency? 

Centre frequency is the frequency of the unmodulated FM carrier signal.

31. What is frequency deviation?



Frequency deviation – the maximum frequency change between a modulated and unmodulated carrier signal.

32. What is discriminator? 

Discriminator is a device that demodulates an FM signal.

33. What is Quadrature? 

Quadrature is the phase relationship between two equal frequency signals that are 90° out of phase.

34. FM modulation index? 

FM modulation index – the ratio of frequency deviation to the message signal frequency.

35. What is signal to noise ratio? 

A signal-to-noise ratio is the ratio of the magnitude of the signal to that of noise (often expressed in decibels).

36. What are varactor diode and schottky diode? 

Varactor diode is a diode that changes capacitance with a change in input voltage.



Schottky diode is diodes that have a low forward voltage drop in the range of 0.2V to 0.4V.

37. What is phase-locked loop (PLL)? 

Phase-locked loop (PLL) is a circuit that locks onto a phase relationship between an input signal and a VCO signal, and produces an error signal. The error signal is fed back to control the VCO frequency so that it equals the input frequency.

38. What is Frequency-Shift Keying (FSK)?



Frequency-Shift Keying (FSK) is shifting an analog signal’s frequency between two values to represent the binary states high and low of a digital signal. A modem uses FSK to transmit digital signals over analog telephone lines.

39. What is voltage controlled oscillator (VCO)? 

Voltage controlled oscillator (VCO) an oscillator that uses an input voltage to control its output frequency.

40. What are the advantages and applications of PLL? 

PLLs have high degree of noise immunity and a narrow bandwidth.



Do not require complex coil adjustments.



PLLs are also used for Frequency-Shift Keying (FSK) operations in digital communications.



A PLL operates by producing a voltage controlled oscillator (VCO) frequency (f vco) that matches the RF frequency (fi).



PLLs are used in FM and AM demodulation because they do not require complex coil adjustments.

41. What is noise? 

An unwanted signal that will disturb the transmission or processing of signals in communication systems. Eg. Shot noise, Thermal noise.

42. What is shot noise? 

A noise arises from the discrete nature of diodes and transistors. E.g., a current pulse is generated every time an electron is emitted by the cathode.43.

What is thermal noise? 

A noise arises from the random motion of electrons in a conductor.

44. What is white noise?



A noise is white if its PSD (Power Spectral Density) equals constant for all frequencies.

45. What is modulation? 

A process by which some characteristic of a carrier is varied in accordance with a modulating wave (baseband signal).

There are, 

Amplitude modulation



Angle modulation (Phase modulation, Frequency modulation).

46. What is Transmission Bandwidth? Transmission bandwidth of an AM wave, 

For positive frequencies, the highest frequency component of the AM wave equalsfc + W, and the lowest frequency component equals fc – W.



The difference between these two frequencies defines the transmission bandwidthBT for an AM wave.

47. Limitations of Amplitude Modulation (DSB-C)? 

Ø Waste of power in the information-less “with-carrier” part.



Ø Wasteful of power and bandwidth

48. How to generate SSB signal? 

Ø Product modulator to generate DSB-SC signal



Ø Band- filter to only one of the sideband and suppress the other.

49. Vestigial Sideband Modulation?



Instead of transmitting only one sideband as SSB, VSB modulation transmits a partially suppressed sideband and a vestige of the other sideband.

Eg: Television Signals 50. What is Angle Modulation? 

The angle of the carrier is varied in accordance with the base band signal. Commonly used angle modulation



Phase modulation (PM)

Frequency modulation (FM)