- What are the main components needed for a communication?
- Sender, Transmission line and Receiver.
- 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.
- Range of Audio Frequency?
- Ø 20Hz to 20 KHz
- Range of Radio Frequency?
- Ø 10 KHz to 1000GHz.
- What is modulation?
- Ø Modulation is the process of changing the characteristics of the carrier signal with respect to that of the message signal.
- What are the principle forms of modulation?
- Ø Amplitude Modulation(AM)
- Ø Frequency Modulation(FM)
- Ø Phase Modulation(PM)
- What are the types of angle modulations?
- FM and PM
- What is a mixer?
- An electronic circuit that combines two frequencies.
- 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.
- What is a Beat Frequency Oscillator (BFO)?
- An oscillator whose output frequency is approximately equal to the transmitter’s carrier frequency.
- 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).
- 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 equals fc + W, and the lowest frequency component equals fc – W.
- The difference between these two frequencies defines the transmission bandwidth BT 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-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 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)