ANALOG COMMUNICATION INTERVIEW QUESTIONS1. 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? 20Hz to 20 KHz1. Range of Radio Frequency? 10 KHz to 1000GHz.1. What is modulation? 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? Amplitude Modulation(AM) Frequency Modulation(FM) Phase Modulation(PM)1. What are the types of angle modulations? FM and PM1. 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 transmitters 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 signal26. 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 signals 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 producinga 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 emittedby 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 equalsfcW. The difference between these two frequencies defines the transmission bandwidthBTfor an AM wave.47. Limitations of Amplitude Modulation (DSB-C)? Waste of power in the information-less with-carrier part. Wasteful of power and bandwidth48. How to generate SSB signal? Product modulator to generate DSB-SC signal Band-pass filter to pass 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 Signals50. 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)