PinoyBIX Engineering Problem Solving and Reference

This is the summary notes of the important terms and concepts in Chapter 14 of the book COMMUNICATIONS ELECTRONICS by Louis E. Frenzel. This book introduces basic communication concepts and circuits, including modulation techniques, radio transmitters and receivers. It also discusses antennas and microwave techniques at a technician level and covers data communication techniques (modems, local area networks, fiber optics, satellite communication) and advanced applications (cellular telephones, facsimile and radar). The work is suitable for courses in Communications Technology. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

CHAPTER 14

Modern Communications Applications

1. Facsimile or fax is an electronic communication technique for transmitting printed documents including text, line drawings, photos, and other graphical information via telephone lines or radio.

2. Fax machines scan the document to be transmitted using photo-optical techniques to create a baseband signal that modulates a carrier prior to transmission.

3. The receiving fax machine demodulates the carrier to recover the baseband signal which is sent to a printer where the original document is faithfully reproduced.

4. The quality of reproduction is a function of the scanning resolution in lines per inch. The greater the number of scan lines, the finer the definition.

5. The most widely used device to convert the scanned lines into an electrical signal is a light-sensitive semiconductor component known as a charge coupled device (CCD).

6. The CCD contains thousands of tiny capacitors that charge to a value proportional to the light intensity. The capacitors are sequentially sampled. Their charges are read out, creating an analog signal corresponding to the lines scanned.

7. The baseband signal modulates a carrier prior to transmission; AM, FM, and PSK are commonly used.

8. Facsimile standards for modulation, transmission speed, and other factors are set by the International Telegraph and Telephone Consultative Committee (CCITT). There are four basic standards designated group 1 through 4.

9. Group I fax machines are analog and use FM where black is 1500 Hz (or 1300 Hz) and, white is 2300 Hz (or 2100 Hz). Resolution is 96 lines per inch, and transmission, speed is 6 min per page. Group 1 machines are no longer used.

10. Group 2 machines are analog and use FM or vestigial sideband AM with a 21O0-Hz carrier. Resolution is 96 lines per inch, and transmission speed is 3 min per page or less.

11. Group 3 machines use digital techniques and PSK or QAM to achieve speeds of up to 9600 baud over the telephone lines. Resolution is 200 lines per inch, and transmission times are less than I min, with less than 30s being common. Most modern fax machines are of the group 3 type.

12. Group 4 fax machines are digital and are designed for wideband telephone lines. Digital transmission rates are 56 kbits/s. Resolution is 400 lines per inch. Few group 4 machines are in use yet.

13. Most fax printers are of the thermal type and use special heat-sensitive paper, although laser printers using xerography are used in some higher-priced machines.

14. Fax is widely used by newspapers, business, and the military. Radio fax is used for transmitting weather satellite photos to earth.

15. Cellular radios provide telephone service in vehicles and are used as portable telephone units.

16. The area served by cellular telephones is divided into small zones called cells.

17. Each cell is served by a repeater containing a low-power transmitter and a receiver.

18. The cells are connected by wire to a computer-controlled master station called the mobile telephone, switching office (MTSO). The MTSO links to the telephone system.

19. By operating at high frequencies in the spectrum and through the application of frequency reuse, many channels are available to users.

20. There are 666 full-duplex telephone channels in most service areas.

21. The receive frequencies are in the 870-to 890-MHz range.

22. The transmit frequencies are in the 825-to 845-MHz range.

23. Channel spacing is 30 kHz.

24. Spacing between the simultaneously used transmit and receive frequencies is 45 MHz.

25.Cellular radios use' FM with a maximum deviation, of 12 kHz.

26. Mobile cellular transmitters have a maximum output power of 3 W which can be decreased in steps under the control of the MTSO to minimize adjacent cell interference.

27. Mobile cellular receivers are of the dual conversion type with a 45- or 82.2-MHz first IF and a 10.7-MHz or 455 kHz second IF.

28. Both transmit and receive frequencies are determined by PLL frequency synthesizers that are set by the MTSO to a clear channel.

29. The MTSO monitors received cell signal strength [received signal strength indicator (RSSI) and transmitter power output and makes decisions about when to "hand off" the mobile unit to another cell to maintain optimum signal strength.

30. The MTSO controls transmitter power as well as transmit and receive frequencies. Serial digital data containing this information is transmitted to the mobile unit whose logic section interprets it and effects the changes.

31. Each cellular radio contains a PROM called the number assignment module (NAM) which stores the unit's telephone number referred to as the mobile identification number (MIN).

32. Most cellular radios contain two microprocessors, one for controlling the logic section and another for operating the displays and dialing circuits in the handset and control section.

33.Radar is the acronym for radio detection and ranging.

34. Radar uses a reflected radio signal from a target to determine its distance, azimuth, elevation, and speed.

35. Radio waves travel at a speed of 186,000, mi/s or 162,000 nmi/s. Knowing the speed of radio waves permits the distance (range) of a remote target to be determined.

36. Radio signals travel at a speed of 5.375 S/nmi or 6.18 S/nmi.

37. The distance D in nautical miles to a target can be computed by knowing the total delay time T in microseconds for a signal to reach the target and return. (D = T/12.36).

38. The strength of the reflection is a function of the wavelength of the radar signal and its relationship to the size of the target. Optimum reflection is obtained when the size of the target is one-quarter wavelength or larger of the signal frequency. Most radars operate in the microwave part of the spectrum.

39. The bearing or azimuth of a target with respect to the radar set is determined by a highly directional antenna. A narrow beam-width antenna is rotated continuously over 360° and the detection of a reflection from a target at a given bearing gives the target's direction.

40. There are two basic types of radar: pulse and continuous wave (CW).

41. In pulse radar, the transmitter emits microwave energy in the form of repetitive sine wave bursts or pulses.

42. The pulse repetition time (PRT) is the time interval between the beginning of successive pulses.

43. The pulse repetition frequency (PRF) or the pulse repetition rate in pulses per second is the reciprocal of PRT (PRF = 1/PRT).

44. The ratio of the pulse burst duration to the PRT is known as the duty cycle and is usually expressed as a percentage.

45. The PRT and duty cycle set the range of a radar: a short PRT and pulse width for short range, and a long PRT and pulse width for long range.

46. The reflection from the target occurs in the interval between successively radiated pulses.

47. In CW radar, constant-amplitude-constant frequency signal is continuously radiated. If the target is stationary, the reflected signal contains no distance information.

48. Continuous wave radar relies on the Doppler effect to produce frequency modulation of the carrier.

49. The Doppler effect is the change in frequency that occurs as the result of relative motion between the transmitter and a target. The Doppler effect occurs with sound, radio, and light signals.

50. The relative speed between transmitter and target is directly proportional to the amount of Doppler frequency shift.

51. The CW Doppler radar is used for speed measurement. Police radars are an example.

52. By frequency modulating a CW radar with a sawtooth or triangular wave, the frequency difference between the transmitted and received signals can be used to compute the distance or range to a target.

53. Radar sets consist of a transmitter, a receiver, an antenna, a master timing section, and a display.

54. Most radar transmitters use a magnetron oscillator, although some high-power radars use klystrons or TWTs. Low-power radars use a Gunn diode oscillator.

55. Radar receivers are super heterodynes with diode mixers.

56.The radar antenna is usually a horn with a parabolic reflector that rotates over a 360 angle.

57. A duplexer is a waveguide assembly that allows both transmitter and receiver to share the same antenna.

58. Spark-gap tubes called transmit-receive (TR) and anti-transmit-receive(ATR) tubes prevent high-power energy from the transmitter from getting into and damaging or desensitizing the receiver.

59. The radar display is normally a cathode ray tube (CRT) that is calibrated to read out the range, bearing, and other data.

60. The most common CRT readout is the plan position indicator (PPI) where the radar is at the center and a radius rotates to reveal reflected targets as blips.

61. Phased array radars use a matrix of dipoles or slot antennas with variable phase shifters to permit automatic, high-speed, electronic beam switching; beam width changes; and sweeping or scanning.

62. Television is the radio transmission of sound and pictures in the VHF and UHF ranges. The voice signal from a microphone frequency modulates a sound transmitter. A camera converts a picture or scene into an electrical signal called the video or luminance Y signal, which amplitude modulates a separate video transmitter. Vestigial sideband AM is used to conserve spectrum space. The picture and sound transmitter frequencies are spaced 4.5 MHz apart with the sound frequency being the higher.

63. TV cameras use either a vacuum tube imaging device such as a vidicon or a solid-state, imaging device such as the charge coupled device (CCD) to convert scene into a video signal.

64. A scene is scanned by the imaging device to break it up into segments that can be transmitted serially. The National Television, Standards Committee (NTSC) standards call for scanning the scene in two 262 ½ line fields which are interlaced to form a single 525-line picture called a frame. Interlaced scanning reduces flicker. The field rate is 59.94 Hz, and the frame or picture rate is 29.97 Hz. The horizontal line scan rate is 15,734 Hz or 63.6 S per line.

65.The color in a scene is captured by three imaging devices which break a picture down into its three basic colors of red, green, blue using color light filters. Three color signals are developed (R, G, B). These are combined in a resistive matrix to form the Y signal and are combined in other ways to fonti the I and Q signals. The I and Q signals amplitude modulate 3.58 MHz subcarriers shifted 90° from one another in balanced modulators producing quadrature DSB suppressed signals that are added to form a carrier composite color signal. This color signal is then used to modulate the AM picture transmitter along with the Y signal.

66. A TV receiver is a standard superheterodyne receiver with separate sections for processing and recovering the sound and picture. The tuner section consists of RF amplifiers, mixers, and a frequency synthesized local oscillator for channel selection. Digital infrared remote control is used to change channels in the synthesizer via a control microprocessor.

67. The tuner converts the TV signals to intermediate frequencies of 41.25 MHz for the sound and 45.75 MHz for the picture. These signals are amplified in IC IF amplifiers. Selectivity is usually provided by a surface acoustic wave (SAW) filter. The sound and picture IF signals are placed in a sound detector to form a 4.5 MHz sound IF signal. This is demodulated by a quadrature detector or other FM demodulator to recover the sound. Frequency multiplexing techniques similar to those used in FM radio are used for stereo TV sound. The picture IF is demodulated by a diode detector or other AM demodulator to recover the Y signal.

68. The color signals are demodulated by two balanced modulators fed with 3.58-MHz subcarriers in quadrature. The subcarrier is frequency- and phase-locked to the subcarrier in the transmitter by phase-locking to the color subcarrier burst transmitted on the horizontal blanking pulse.

69. To keep the receiver in step with the scanning process at the transmitter, sync pulses are transmitted along with the scanned lines of video. These sync pulses are stripped off the video detector and used to synchronize horizontal and vertical oscillators in the receiver. These oscillators generate deflection currents that sweep the electron beam in the picture tube to reproduce the picture.

70. The color picture tube contains three electron guns that generate narrow electron beams aimed at the phosphor coating on the inside of the face of the picture tube. The phosphor is arranged in millions of tiny red, green, and blue color dot triads or stripes. The electron beams excite the color dots or stripes in proportion to their intensity and generate light of any color depending upon the amplitude of the red, green, and blue signals. The electron beam is scanned or deflected horizontally and vertically in step with the transmitted video signals. Deflection signals from the internal sweep circuits drive coils in a deflection yoke around the neck of the picture creating magnetic fields that sweep the three electron beams.

71. The horizontal output stage, which provides horizontal sweep, is also used to operate a flyback transformer that steps up the horizontal sync pulses to a very high voltage. These are rectified and filtered into a 30- to 35-kV voltage to operate the picture tube. The flyback also steps down the horizontal pulses and rectifies and filters them into low-voltage dc supplies that are used to operate most of the circuits in the TV set.

72. Cable television is the transmission of multiple TV signals which are frequency multiplexed on a single cable to be used in lieu of over-the-air signal transmission. The headend of a cable TV station collects TV signals from local stations and from other sources by satellite and then modulates and multiplexes these signals on a cable that is sent to subscribers.

73. The main cable from the headend, called the trunk, takes the signals to other distribution points and to other cables called feeders, which transmit the signals to neighborhoods. The feeders are then tied to cable drops connected to each house. The cable signals are amplified at several points along the distribution path to maintain strong signals. A cable TV decoder box or tuner selects the desired channel and converts it into a channel 3 or 4 TV signal that connects to the TV receiver for presentation.

Complete List of Reviewers in Communications Electronics per Chapter

Important List of Communications Engineering Materials

Share your Notes in Modern Communications Applications

If you have some important review notes on this topic kindly write the notes on the comment section below. This will absolutely beneficial to those aspiring to become professional engineers by taking the Board Exam and eventually to become successful in their chosen field. Thank you.

---

This is the summary notes of the important terms and concepts in Chapter 13 of the book COMMUNICATIONS ELECTRONICS by Louis E. Frenzel. This book introduces basic communication concepts and circuits, including modulation techniques, radio transmitters and receivers. It also discusses antennas and microwave techniques at a technician level and covers data communication techniques (modems, local area networks, fiber optics, satellite communication) and advanced applications (cellular telephones, facsimile and radar). The work is suitable for courses in Communications Technology. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

CHAPTER 13

Fiber-Optics Communications

1. The information-carrying capacity of a cable or radio channel is directly proportional to its bandwidth.

2. The RF spectrum is heavily used and occupied. Only in the microwave region is there room for expansion.

3. Light is an electromagnetic signal like a radio wave but is much higher in frequency. It can be used as a carrier for information signals.

4. Because of the very high frequency of light compared to typical information signals, tremendous bandwidth is easily available.

5. Light waves carrying data signals can be transmitted in free space but are greatly attenuated by atmospheric effects and require pinpoint alignment.

6. Most light-wave communication is by way of a glass or plastic fiber cable that acts as a "light pipe" to carry light modulated by information signals.

7. The main components of a light-wave communications system are an AID converter, a light source transmitter, a fiber optic cable, a photo- or light detector with amplifier and shaper, and a DIA converter.

8. Because of the great attenuation of light in a fiber-optic cable, repeater units are used to amplify and regenerate the signals over long distances.

9. The primary application of fiber-optic communications is in long-distance telephone systems.

10. The primary advantages of fiber-optic cables over conventional cables and radio are wider bandwidth, lower loss, lightweight, small size, strength, security, interference immunity, and safety.

11. The main disadvantage of fiber-optic cable is that its small size and brittleness make it more difficult to work with.

12. Light waves, like radio waves, are a kind of electromagnetic radiation.

13.Light waves occur at very high frequencies in the range of 3 x 10¹¹ to 3 x 16¹⁶ Hz.

14. Wavelength rather than frequency is used to express the place of light in the spectrum.

15.The wavelength of light is expressed in terms of nanometers (1 nm = 10^-9 m) or micrometers (1m = 10^-6 m). Micrometers are also called microns.

16. The visible light spectrum is from 700 nm (red) to 400 nm (violet).

17. The optical spectrum is made up of visible light, infrared at lower frequencies and ultraviolet at higher frequencies.

18. Infrared rays cannot be seen, but they act like light waves and can be manipulated in similar ways as with a lens or mirrors.

19. Light waves, like microwaves, travel in a straight line.

20. The angle at which light strikes a surface is called the angle of incidence. The angle at which light is reflected from a surface is called the angle of reflection. The angle of incidence is equal to the angle of reflection.

21. When a light ray passes from one medium to another, it is bent. This is called refraction.

22. The amount of refraction is called the index of refraction n and is the ratio of the speed of light in air to the speed of light in another medium, such as water, glass, or plastic (n = 1 in air, n = 1.3 in water, n = 1.5 in glass).

23. The angle of the incident light ray determines whether the ray will be reflected or refracted.

24. The critical angle is the angle of incidence that causes the refracted light to travel along the interface between two different media.

25. If the angle of incidence is made greater than the critical angle, reflection occurs instead of refraction.

26. Light entering a fiber-optic cable has an angle of incidence such that the light is reflected or bounced off the boundary between the fiber and the external media. This is called total internal reflection.

27. Fiber-optic cables are made from glass and plastic. Glass has the lowest loss but is brittle. Plastic is cheaper and more flexible, but has high attenuation.

28. A popular fiber-optic cable with a glass core and plastic cladding is called plastic clad silica (PCS).

29. The cladding surrounding the core protects the core and provides an interface with a controlled index of refraction.

30. Step index means there is a sharp difference in the index of refraction between the core and cladding.

31. Graded index means that the index of refraction of the core varies over its cross section, highest in the center and lowest at the edges.

32. A single-mode cable is very small in diameter and essentially provides only a single path for light.

33. Multimode cores are large and provide multiple paths for the light.

34. Multiple light paths through a step-index core cause a light pulse to be stretched and attenuated. This is called modal dispersion and it limits the upper pulse repetition rate and thus the information bandwidth.

35. Multiple light paths in a graded-index core are controlled so that they converge at multiple points along the cable. Modal dispersion does occur, but it is not as severe as that caused by a step-index core.

36. Modal dispersion does not occur in single mode cores.

37. The three most widely used types of fiber optic cables are multimode step-index, single-mode step-index, and multimode graded-index.

38. The primary specification of a fiber-optic cable is attenuation which is usually expressed as the loss in decibels per kilometer.

39. Light loss in a fiber-optic cable is caused by absorption, scattering, and dispersion.

40. Cable attenuation is directly proportional to its length.

41. Cable losses range from 1 dB/km in glass single-mode step-index cable to 100 dB/km for plastic multimode step-index cable.

42. Fiber-optic cables can be spliced by gluing.

43. Special connectors are used to connect cables to one another and to the equipment.

44. Fiber-optic systems use light-emitting diodes (LEDs) and semiconductor lasers as the main light sources.

45. Light-emitting diodes are used in short distance low-speed systems. Injection laser diodes (ILDs) are used in long distance, high-speed systems.

46.Most LEDs and ILDs emit light in the in. visible near-infrared range (0.82 to 1.55 m).

47.A popular operating frequency is 1.3 m because fiber-optic cable has an attenuation null at this wavelength.

48. Laser diodes emit monochromatic or single-frequency light. The light waves are coherent, so they reinforce one another to create an intense and finely focused beam.

49. Intense laser light is produced by an ILD because reflecting surfaces in the structure form a cavity resonator for the light waves.

50. The most commonly used light sensor is a photodiode.

51. A photodiode is a PN junction that is reverse-biased and exposed to light. Light increases the leakage current across the junction. This current is converted into a voltage pulse.

52. PIN junction diodes are faster and more sensitive than conventional photodiodes.

53. The fastest and most sensitive light detector is the avalanche photodiode (APD).

54. The APD operates with a high reverse bias so that when light is applied. Breakdown occurs and produces a fast, high-current pulse.

55. The receiver portion of a fiber-optic system is made up of a photodiode, amplifier, and shaper.

56. Fiber-optic systems are rated by the speed and the product of the bit rate and the distance.

57. A measure of the quality of a fiber-optic system is the maximum distance between repeaters.

Complete List of Reviewers in Communications Electronics per Chapter

Important List of Communications Engineering Materials

Share your Notes in Fiber-Optics Communications

If you have some important review notes on this topic kindly write the notes on the comment section below. This will absolutely beneficial to those aspiring to become professional engineers by taking the Board Exam and eventually to become successful in their chosen field. Thank you.

---

This is the summary notes of the important terms and concepts in Chapter 12 of the book COMMUNICATIONS ELECTRONICS by Louis E. Frenzel. This book introduces basic communication concepts and circuits, including modulation techniques, radio transmitters and receivers. It also discusses antennas and microwave techniques at a technician level and covers data communication techniques (modems, local area networks, fiber optics, satellite communication) and advanced applications (cellular telephones, facsimile and radar). The work is suitable for courses in Communications Technology. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

CHAPTER 12

Data Communications

1. Data communications is the transmission and reception of binary data between computers and other digital equipment.

2. The earliest form of electronic communications, the telegraph, was a type of data communications.

3. Turning a carrier off and on in a code of dots and dashes is a kind of data communications known as continuous wave (CW).

4. Teletype is a form of telegraph that uses the 5-bit Baudot code to transmit between typewriters like units.

5. The most widely used binary data communications code is the 7-bit American Standard Code for Information Interchange (ASCII).

6. Another popular code is the 8-bit Extended Binary Coded Decimal Inter- change Code (EBCDIC) used mainly in IBM systems.

7. The two main methods of data transmission are serial and parallel. In serial transmission, each bit is transmitted sequentially. In parallel transmission, all bits are transmitted simultaneously.

8. Serial transfers are slower than parallel transfers but require only a single line or channel. Parallel transfers require multiple channels of lines called a bus.

9. The speed of data transmission is designated in terms of bits per second (bits/s) or baud. 10. Baud rate is the number of symbol changes per second. A symbol is an amplitude, frequency, or phase change.

11. The channel-or bit-rate capacity of a channel is directly proportional to the channel bandwidth and the time of transmission.

12.The channel capacity or binary signal transmission speed C in bits per second is equal to twice the channel bandwidth B when no noise is present (C = 2B).

13.When multiple levels or symbols are used to encode the data, the channel capacity C is greater for a given bandwidth B, or C = 2BLog2N where N is the number of symbols used.

14.The channel capacity C in bits per second is proportional to the channel bandwidth B and the power S/N ratio, or C = Blog₂ t1 + SIN).

15. The, bit rate is higher than the baud (symbol) rate if multiple-level (symbol) encoding is used.

16. The two methods of data transmission are asynchronous and synchronous. In asynchronous transmission, data is sent one character at a time with start and stop bits. In synchronous transmission, data is sent as a continuous block of multiple characters framed with synchronization characters.

17. Synchronous transmission is faster than asynchronous transmission.

18. In data communications, a binary 1 is referred to as a mark and a binary 0 as a space.

19. Signals, whether voice, video, or binary, transmitted directly over a cable are known as baseband signals.

20. Voice and video signals are analog but may be converted to digital for data communications transmission.

21. Signals that involve a modulated carrier a called broadband signals.

22. Communications of binary data signal over the telephone network which is designed for analog signals is made possible by using a modem.

23. A modem is a modulator-demodulator unit that converts digital signals to analog and vice versa.

24. The most commonly used modulation techniques in modems are frequency-shift keying (FSK), phase-shift keying (PSK), and quadrature amplitude modulation (QAM).

25. Frequency-shift keying uses two frequencies for binary 0 and 1 (1070 and 1270 Hz or 2025 and 2225 kHz). It operates at speeds of 300 baud or less.

26. Modems capable of transmitting at standard higher rates of 1200, 2400, 4800, and 9600 bits/s use PSK and/or QAM.

27. Binary PSK (BPSK) uses a carrier of 1600 or 1700 Hz where a phase of 0° represents a binary 0 and a 1800 phase shift represents a binary 1, or vice versa.

28. Binary PSK is generated by a balanced modulator.

29. Binary PSK is demodulated by a balanced modulator.

30. To properly demodulate BPSK, the carrier at the demodulator must have exactly the same phase as the transmitting carrier.

31. A special carrier recovery circuit in the receiver produces the correct phase carrier from the BPSK signal.

32. Differential PSK eliminates the need for a special reference phase carrier by using a coding technique where the phase of each bit is referenced to the previous bit.

33. Quadrature PSK uses four equally spaced phase shifts of the carrier to represent two bits (dibit). For example, 00 = 45°, 01 = 135°,11 = 225°, 10 = 315°.

34. In 8-PSK, 3 bits are coded per phase change. In 16-PSK, 4 bits are coded per phase change. Thus the bit rate is 3 or 4 times the symbol rate change or baud rate.

35. Quadrature amplitude modulation uses a combination of QPSK and two-level AM to code 3 bits per baud. Each of the eight possible 3-bit combinations is represented by a unique phase and amplitude signal.

36. A protocol is a rule or procedure that defines how data is sent and received.

37. Protocols include "handshaking" signals between the transmitter and receiver that indicate the status of each.

38. The Xmodem protocol is widely used in personal computers.

39. In synchronous communications, a variety of special characters are sent before and after the block of data to ensure that the data is correctly received.

40. Bit errors that occur during transmission are caused primarily by noise.

41. The ratio of the number of bit errors that occur for a given number of bits transmitted is known as the bit error rate (BER).

42. Error-detection and -correction schemes have been devised to reduce bit errors and increase data accuracy.

43. One of the most widely used error detection schemes add a parity bit to each character transmitted, making the total number of binary Is transmitted odd or even. If a bit error occurs, the parity bit derived at the receiver will differ from the one transmitted.

44. Parity generator circuits are made up of multiple levels of exclusive OR (XOR) gates.

45. Another name for parity is vertical redundancy check (VRC).

46. The longitudinal redundancy check (LRC) is another way to test for errors. Corresponding bits in adjacent data words are exclusive-ORed to generate a block check character (BCC) that is appended to the transmitted block.

47. The VRC and LRC provide a coordinate system that will identify the exact location of a bit error so that it may be corrected.

48. A widely used error-detection scheme is the cyclical redundancy check (CRC) where the data block is divided, by a constant to produce a quotient and remainder. The remainder is the CRC character which is attached to the transmitted data block and compared to the CRC computed at the receiver.

49. A network is any interconnection of two or more stations that can communicate with one another.

50. An example of a wide area network (WAN) is the telephone system. An example of a metropolitan area network (MAN) is a cable TV system.

51. A local area network (LAN) is an interconnection of stations in a small area over short distances such as in an office building, on a military base, or on a college campus.

52. Local area networks were conceived to allow PC users to share expensive peripherals such as hard disks and printers but are now used for general communication and the sharing of software and data.

53. The most common physical configurations or topologies of LANs are the star, ring, and bus.

54. The bus is the fastest. The ring is the least expensive but is disabled if one station fails.

55. The star configuration is commonly used to connect many terminals and PCs to a larger mainframe or minicomputer.

56. The three most commonly used transmission media in networks are twisted pair, coax, and fiber-optic cable.

57. Twisted pair is inexpensive and easy to work with and is widely used for short distance, low-speed LANs. It is not shielded, so it is susceptible to noise.

58. Coax is the most widely used medium because of its high-speed capability and its shielding against noise.

59. Fiber-optic cable is growing in usage as its price declines. It has the highest speed capability of any medium.

60. Local area networks use both baseband and broadband techniques. Baseband refers to transmitting the information signal directly on the medium.

61. Broadband refers to using modulation techniques to transmit the data on carriers that can be assigned specific channels over a wide frequency range on a common medium.

62. Broadband systems require the use of modems at each node.

63. Spread spectrum (SS) is a modulation and multiplexing technique used primarily in data communications that deliberately spreads the signal out over a wide bandwidth rather than trying to restrict it to a narrow band.

64. The two most widely used types of spread spectrum are frequency hopping (FH) and direct sequence (DS).

65. Spread spectrum offers the benefits of privacy or security of communications, immunity to jamming, and lower sensitivity to frequency-selective fading.

66. In frequency-hopping SS, the serial binary data usually modulates a carrier by FSK. The FSK signal is mixed with a sine wave from a frequency synthesizer to form the final RF signal. The frequency synthesizer is switched at a rate of speed higher than the rate of the data signal, dwelling only briefly on each of many channel frequencies. Thus, the signal is broken up into small pieces and spread over a wide frequency range.

67. The frequency-hopping scheme is controlled by a pseudorandom binary code that switches at random from binary 0 to 1 and vice versa. The random nature of the signal causes the frequency to jump all over the band, distributing pieces of the signal hither and yon. The pseudorandom code acts like digital noise and thus is called a pseudorandom noise (PSN) code.

68. In direct-sequence SS, the serial data is mixed with a higher-frequency PSN code in an X-OR circuit. The resulting higher frequency binary signal produces more higher-frequency sidebands, thereby spreading the signal out over a wider bandwidth. The X-OR output usually phase-modulates the final carrier.

69. Because an SS signal is spread out randomly over a wide bandwidth, many signals can share a band without interference. A narrowband receiver will no respond to an SS signal except to interpret the random signals as a form of low-level noise.

70. The main problem in receiving SS signals is in acquiring the signal and synchronizing the transmitted PSN code to the same internally generated PSN code in the receiver. In direct-sequence SS, an electronic correlator circuit is responsible for achieving synchronism.

71. Different stations sharing a given band are defined and identified by their unique PSN code.

72. Spread spectrum was originally developed for and used in military equipment. In 1985, the FCC authorized SS for commercial or civilian use in the 902- to 928-, 2400- to 2483-, and 5725- to 51150-MHz bands.

73. The new applications for spread spectrum include wireless LANs, wireless computer modems, and telemetry systems.

Complete List of Reviewers in Communications Electronics per Chapter

Important List of Communications Engineering Materials

Share your Notes in Data Communications

If you have some important review notes on this topic kindly write the notes on the comment section below. This will absolutely beneficial to those aspiring to become professional engineers by taking the Board Exam and eventually to become successful in their chosen field. Thank you.

---

This is the summary notes of the important terms and concepts in Chapter 11 of the book COMMUNICATIONS ELECTRONICS by Louis E. Frenzel. This book introduces basic communication concepts and circuits, including modulation techniques, radio transmitters and receivers. It also discusses antennas and microwave techniques at a technician level and covers data communication techniques (modems, local area networks, fiber optics, satellite communication) and advanced applications (cellular telephones, facsimile and radar). The work is suitable for courses in Communications Technology. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

CHAPTER 11

Introduction to Satellite Communications

1. A satellite is a physical object that orbits a celestial body.

2. A communications satellite containing electronic equipment acts as a repeater or relay station between two earth stations.

3. The basic component of a communications satellite is a receiver-transmitter combination called a transponder.

4. A satellite stays in orbit because the gravitational pull of the earth, is balanced by the centripetal force of the revolving satellite.

5. Satellite orbits about the earth are either circular or elliptical.

6. Satellites orbit the earth from heights of 100 to 22,300 mi and travel at speeds of 6800 to 17,500 mi/h.

7. A satellite that orbits directly over the equator 22,300 mi from earth is said to be in a geostationary orbit. It revolves in synchronism with the earth's rotation, so it appears to be stationary when seen from points on the earth.

8. A satellite is stabilized in orbit by spinning it on its axis or building in spinning flywheels for each major axis (roll, pitch, yaw).

9. Attitude adjustments on a satellite are made by firing small jet thrusters to change the satellite's position or speed.

10. The location of a satellite is determined with latitude and longitude measurements that designate a point on the earth subsatellite point (SSP) directly below the satellite.

11. Azimuth and elevation angles determine where to point an earth station so that it intercepts the satellite.

12. Satellites are launched into orbit by rockets that give them vertical as well as forward motion.

13. A geosynchronous satellite is initially put into an elliptical orbit where its apogee is 22,300 mi high. The apogee kick motor is then fired to put the satellite into its final circular geostationary orbit.

14. Many satellites are put into orbit by launching them from NASA's space shuttle.

15. Most satellites operate in the microwave region.

16. Microwave satellites operate on assigned frequency bands designated by a letter. Common communications satellite bands are the C (3.4 to 6.425 GHz) and Ku (10.95 to 14.5 GHz) bands.

17. Satellite bands are typically 500 MHz wide and are divided into 12 segments, each 36 MHz wide. A transponder is used to cover each segment.

18. Frequency reuse is a technique that allows two sets of transponders to operate on the same frequency, thus doubling channel capacity. The two sets of channels use antennas of different polarizations to prevent interference with one another.

19. Spatial isolation is another technique for frequency sharing. It uses highly directional spot-beam antennas to prevent interference between stations on the same frequency.

20. The main subsystems in a satellite are the communications; power; telemetry, tracking; and control (TIC); propulsion; attitude stabilization; and antenna subsystems.

21. A transponder consists of a low-noise amplifier (LNA) that receives and amplifies the up-link signal, a mixer that converts the signal to another (lower) frequency, and a high-power amplifier that retransmits the signal on its new down-link frequency.

22. Double-conversion transponders use two, mixers, one to translate the up-link signal to an IF where it is amplified and filtered, and another to translate the signal to its final down-link frequency.

23. Regenerative transponders demodulate the up-link signal to recover the baseband signals and then use them to remodulate a downlink transmitter. This improves the SIN ratio.

24. In a broadband transponder, a single mixer converts all channels within the 500-MHz bandwidth simultaneously to their downlink frequencies. These are selected by channel bandpass filters and then amplified by individual power amplifiers.

25. In a channelized transponder, each channel has its own LNA, bandpass filters, mixer, and high-power amplifier.

26. The power subsystem consists of solar panels, batteries, dc-to-dc converters, and regulators. The solar panels convert sunlight into de power to operate all satellite electronics and to charge the batteries that take over when sunlight is blocked.

27. The TTC subsystem contains a receiver that picks up commands from a ground station and translates them into control signals that initiate some action on board. The telemetry system monitors physical conditions within the satellites and converts them into electrical signals that are transmitted back to earth.

28. The propulsion system consists of the apogee kick motor that puts the satellite into final orbit and the jet thrusters that are used for positioning and attitude control.

29. The stabilization subsystem for attitude control consists of spin components or three-axis flywheel gyros.

30. The antenna system consists of one or more highly directional horn or parabolic antennas and an omnidirectional TTC antenna.

31. Earth stations consist of transmit, receive, power, antenna, TIC, and ground control equipment (GCE) subsystems.

32. The transmit subsystem takes the baseband voice, video, or computer data signals: multiplexes them; and uses the composite signal to modulate a carrier. An up converter translates the signal to its final up-link frequency before it is amplified and transmitted.

33. The most common forms of modulation used are FM and QPSK.

34. Transistor power amplifiers are used in low-power earth stations; klystrons are used in high-power narrowband stations; and TWTs are used in high-power broadband stations.

35. Earth stations feature large- parabolic dish antennas with high gain and directivity for receiving the weak satellite signal.

36. The receive subsystem in an earth station amplifies the signal with an LNA and then separates the channels with bandpass filters. Down conveners translate the signals to a lower IF where they are demodulated and demultiplexed.

37. The GCE in an earth station interfaces the baseband signals to the transmit and receive subsystems. The receive GCE performs demodulation and demultiplexing. The transmit GCE performs modulation and multiplexing.

38. The most common application for satellites is communications.

39. Another major use of satellites is surveillance and reconnaissance.

40. Film cameras, TV cameras, infrared sensors, and radars are all used to observe a variety of conditions on earth from surveillance satellites.

41. Satellites play a major role in military and defense systems not only for communications but also for surveillance.

42. The 24-satellite Global Positioning System (GPS) makes accurate navigation possible anywhere on earth with a low-cost microwave receiver.

43. Consumers use satellite TV receivers to intercept TV signals transmitted by networks and cable TV companies.

Complete List of Reviewers in Communications Electronics per Chapter

Important List of Communications Engineering Materials

Share your Notes in Introduction to Satellite Communications

If you have some important review notes on this topic kindly write the notes on the comment section below. This will absolutely beneficial to those aspiring to become professional engineers by taking the Board Exam and eventually to become successful in their chosen field. Thank you.

---

This is the summary notes of the important terms and concepts in Chapter 10 of the book COMMUNICATIONS ELECTRONICS by Louis E. Frenzel. This book introduces basic communication concepts and circuits, including modulation techniques, radio transmitters and receivers. It also discusses antennas and microwave techniques at a technician level and covers data communication techniques (modems, local area networks, fiber optics, satellite communication) and advanced applications (cellular telephones, facsimile and radar). The work is suitable for courses in Communications Technology. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

CHAPTER 10

Microwave Techniques

1. Microwaves are radio signals in the frequency range from 1 to 300 GHz.

2. The RF spectrum below UHF is mostly already fully occupied leaving little or no room for the growth of new radio services.

3. At microwave frequencies, tremendous bandwidth is available for new radio services as well as for wide-bandwidth signals such as TV, multiplexed signals, or computer data.

4. The microwave frequencies are used primarily for telephone communications, radar, and satellite communications.

5. Other microwave applications include cable TV, space communications, radio astronomy, and heating.

6. The primary benefit of microwaves is wide bandwidth availability.

7. The main disadvantages of microwaves are that they are limited to line-of-sight transmission distances, conventional components are not usable, and circuits are more difficult to analyze and design.

8. The allocation of the RF spectrum is handled by the Federal Communications Commission (FCC) in the United States.

9. Balanced transmission line is not used for microwaves because of radiation losses. Coaxial cable is not used because of its high attenuation.

10. The preferred transmission line for microwaves is waveguides.

11. Because of the short physical length of transmission lines at microwave frequencies, quarter- and half-wave lines are commonly used for tuned circuits and filters.

12. Two printed circuit board implementations of transmission lines, called stripline and microstrip, are widely used to create resonant circuits and filters.

13. A waveguide is a hollow metal pipe with a circular or rectangular cross section used for carrying microwave signals from one place to another.

14. A waveguide acts like a high-pass filter, passing all frequencies above its cut-of frequency and rejecting those below it.

15. The cutoff frequency f_co of a waveguide depends upon its physical size. For a rectangular waveguide, it is 300/2a. where a is the wide dimension of the waveguide in meters.

16. The microwave signal carried by a waveguide is made up of electric (E) and magnetic (H) fields that bounce off the walls of the waveguide as they propagate along its length.

17. The modes of a waveguide describe the various patterns of electric and magnetic fields that are possible.

18. A transverse electric (TE) mode is one where the electric field is transverse or perpendicular to the direction of propagation.

19. A transverse magnetic (TM) mode is one where the magnetic field is perpendicular to the direction of propagation.

20. Waveguides are available in standard lengths and sizes, and special pieces are used for right-angle bends and 90° twists.

21. Half-wavelength sections of waveguides with shorted or closed ends are known as resonant cavities since they "ring" or oscillate at the frequency determined by their dimensions.

22. Cavity resonators are metallic chambers of various shapes and sizes that are used as parallel-tuned circuits and filters. They have a Q of up to 30,000.

23. Point-contact and Schottky or hot-carrier diodes are widely uses as mixers in microwave equipment as they have low capacitance and inductance.

24. Varactor diodes are widely used as microwave frequency multipliers. Multiplication factors of 2 and 3 are common with power levels up to 20 Wand efficiencies up to 80 percent.

25. Step-recovery or snap-off diodes are also widely used as frequency multipliers with multiplication factors up to 10, power ratings up to 50 W. and efficiencies approaching 80 percent.

26. A Gunn diode is a microwave semiconductor device used to generate microwave energy. When combined with a microstrip, stripline or resonant cavity, simple low power oscillators with frequencies up to 50 GHz are easily implemented.

27. Both I MPATT and TRAPATT diodes are GaAs devices operated with high reverse bias to produce avalanche breakdown. Both are used in microwave oscillators.

28. A klystron is a vacuum tube used for microwave amplification and oscillation.

29. Klystrons use a cavity resonant or to velocity modulate an electron beam which imparts energy to another cavity, producing power amplification. Klystrons are available which produce from a few to many thousands of watts.

30. A single-cavity reflex klystron is used as a microwave oscillator.

31. Klystrons are being gradually replaced by Gunn diodes and traveling-wave tubes.

32. A magnetron is a diode vacuum tube used as a microwave oscillator in radar and microwave ovens to produce powers up to the megawatt range.

33. In a magnetron, a strong magnetic field creates circular paths of electron flow to excite cavities into oscillation.

34. A traveling-wave tube (TWT) is a microwave power amplifier with very wide bandwidth.

35. A microwave signal applied to a helix around the TWT produces velocity and density modulation of the electron beam over a long distance which induces a higher-power signal in the helix.

36. The most commonly used microwave antenna is the horn, which is essentially a rectangular waveguide with a flared end.

37. A pyramidal horn flares in both waveguide dimensions. A sectoral horn flares in only one dimension.

38. Horn antennas are directional and produce a beam width in the 10° to 60° range with a gain in the 10- to 20-dB range, depending upon dimensions.

39. A parabolic or dish-shaped reflector is used with most microwave antennas to focus the RF energy into a narrow beam and increase gain.

40. The parabolic reflector usually has a diameter that is no less than 10 wavelengths at the operating frequency.

41. The gain and directivity of a parabolic reflector antenna is directly proportional to its diameter.

42. Parabolic reflector antennas are fed by placing a horn antenna at the focal point or by placing the horn at the center of the reflector and placing a small reflector at the focal point. The latter is known as Cassegrain feed.

43. A helical antenna is made up of six to eight turns of heavy wire or tubing to form a coil or helix. It is fed with coax and is backed up with a reflector.

44. Helical antennas are used at UHF and microwave frequencies and have a gain in the 12- to 20-dB range and a beam width in the 12° to 45° range.

45. Helical antennas produce circular polarization where the electric and magnetic fields rotate. The polarization may be right-hand or left-hand depending upon the direction in which the helix is wound.

46. Helical antennas can receive either vertically or horizontally polarized signals but can only receive a circularly polarized signal of the same direction.

47. A popular omnidirectional microwave antenna is the bicone.

Complete List of Reviewers in Communications Electronics per Chapter

Important List of Communications Engineering Materials

Share your Notes in Microwave Techniques

If you have some important review notes on this topic kindly write the notes on the comment section below. This will absolutely beneficial to those aspiring to become professional engineers by taking the Board Exam and eventually to become successful in their chosen field. Thank you.

---

This is the summary notes of the important terms and concepts in Chapter 9 of the book COMMUNICATIONS ELECTRONICS by Louis E. Frenzel. This book introduces basic communication concepts and circuits, including modulation techniques, radio transmitters and receivers. It also discusses antennas and microwave techniques at a technician level and covers data communication techniques (modems, local area networks, fiber optics, satellite communication) and advanced applications (cellular telephones, facsimile and radar). The work is suitable for courses in Communications Technology. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

CHAPTER 9

Antennas and Transmission Lines

1. A transmission line is a two-wire cable used to carry RF energy between two different pieces of communications equipment or between an antenna and a receiver or transmitter.

2. The two most common types of transmission lines are balanced and coaxial.

3. The primary feature of a transmission line is its characteristic or surge impedance Zo which is a function of the distributed inductance L and the capacitance C per unit length (Zo = L / C).

4. The characteristic impedance of a balanced line is determined by its physical dimensions. [ Zo =276 log (2 S I D) where S is the center-to-center spacing of the conductors and D is the diameter of the conductors.]

5. The characteristic impedance of coax also depends on its physical dimensions. [ Zo = 138 log (D I d) where D is the inside diameter of the shield and d is the diameter of the inner conductor.]

6. The proper use of a transmission line is to terminate it in a load impedance equal to its surge impedance. All the power applied to the line will be absorbed by the load.

7. Wavelength is the distance between adjacent peaks of a RF wave. It is also the distance traveled by a signal in one cycle. Wavelength (λ) is computed with the expression λ = 300 / f where f is the frequency in megahertz and is in meters, Or λ = 984 / f where A is in feet.

8. If a transmission line is not terminated in its characteristic impedance, the load will not absorb all the power. Some of it will be reflected back toward the generator.

9. If the load on a transmission line is an open or short, all the power applied to the line will be reflected back to the generator.

10. The forward or incident power applied to the line combines with the reflected power to produce a pattern of voltage and current variations along the line known as standing waves.

11. If the load impedance matches the line impedance, there are no standing waves.

12. A measure of the mismatch between line and load impedances or the maximum and minimum voltage and current variations along, the line is the standing-wave ratio (SWR) which is a number always greater than 1.

13. The SWR indicates how much power is delivered to the load and lost in the line. With SWR = 1, all power is delivered to the load.

14. The ratio of the reflected voltage V, to the incident voltage V, on a transmission line is caIled the reflection coefficient R (R = Vr I Vi). A properly terminated line will have R = O. A shorted or open line will have R =1.

15. The SWR in terms of the reflection coefficient is

16. The SWR = ZO I ZL, or ZL l Zo where ZO is the characteristic impedance and ZL is the load impedance.

17. Every effort is made to reduce the SWR by using impedance-matching circuits to ensure that maximum power is delivered to the load.

18. Transmission lines, one-quarter or one-half wavelength long and either shorted or open, act like resonant or reactive circuits.

19. At UHF and microwave frequencies where one-half wavelength this less than 1 ft., transmission lines are commonly used to replace conventional LC tuned circuits.

20. A shorted quarter wave and an open half wave act like a parallel resonant circuit.

21. Both an open quarter-wave circuit and a shorted half-wave circuit act like a series resonant circuit.

22. The velocity of propagation of a radio signal is slower in a transmission line than in free space. This difference is expressed as the velocity factor F for different types of lines. Coax has a velocity factor of 0.6 to 0.7. The velocity factor of open wire line or twin lead is in the 0.7 to 0.8 range. In computing the length of a transmission line at a specific frequency, the velocity factor must be considered ( = 984 F/f).

23. An antenna or aerial is one or more conductors used to transmit or receive radio signals.

24. A radio signal is electromagnetic energy made up of electric and magnetic fields at right angles to one another and to the direction of signal propagation.

25. The polarization of a radio signal is defined as the orientation of the electric field with respect to the earth and is either vertical or horizontal.

26. The most common antenna is the half wave dipole or doublet that has a characteristic impedance of approximately 73 flat the center. Its length in feet is 468/f where f is the frequency in megahertz.

27. The dipole has a bidirectional figure-eight radiation pattern and is usually mounted horizontally but may also be used vertically.

28. A popular variation of the dipole is the folded dipole which is one-half wavelength long and has an impedance of 300 .

29. Another popular antenna is the quarter-wave vertical. The earth acts as the other quarter wave to simulate a half-wave vertical dipole.

30. The quarter-wave vertical is referred to as a ground plane antenna. It is fed with coax with the center conductor connected to the antenna and the shield connected to earth ground, to an array of quarter-wave, wires m called radials, or to a large, flat, metal surface. Its length in feet is 234/f where f is in megahertz.

31. The characteristic impedance of a ground plane is about 36.5. It has an omni directional radiation pattern that sends or receives equally well in all directions.

32. A directional antenna is one that transmits or receives over a narrow range in only one direction.

33. Directional antennas made up of two or more elements focus the radiation into a narrow beam, thus giving the antenna gain.

34. The gain of the, antenna is the power amplification resulting from the concentration of power in one direction. The gain may be expressed as a power ratio or in decibels.

35. The effective radiated power (ERP) of an antenna is the power input multiplied by the antenna power gain.

36. Directional antennas with two or more elements are caIled arrays. There are two types of arrays: parasitic and driven.

37. Parasitic elements called reflectors and directors when spaced parallel to a half wave dipole driven element help focus the signal into a narrow beam.

38. The measure of the directivity of an antenna is the beam width or beam angle measured in degrees.

39. A parasitic array made up of a driven element, reflector, and one or more directors is known as a Yagi or beam antenna and has a gain of 10 to 20 dB with a beam width of 40° to 20°.

40. Driven arrays consist of two or more half wavelength elements, each receiving power from the transmission line.

41. The three most popular driven arrays are the collinear, end-fire, and broadside.

42. A widely used driven array is the log periodic antenna which exhibits gain, directivity, and a wide operating frequency range.

43. A radio wave propagates through space in one of three ways: ground wave, sky waves, or direct waves.

44. The ground or surface wave leaves the antenna and follows the curvature of the earth. The ground wave is only effective on frequencies below 3 MHz.

45. The skywave propagates from the antenna upward where it is bent back to earth by the ionosphere.

46. The ionosphere is a portion of the earth's atmosphere 30 to 250 mi above the earth that has been ionized by the sun.

47. The ionosphere is made up of three layers of different ionization density: the D, E, and F layers. The F layer is the most highly ionized and causes refraction or bending of radio waves back to earth.

48. The refraction of the ionosphere causes a radio signal to be bent back to earth with little or no attenuation long distances from the transmitter. This is known as a skip or hop.

49. Multiple skips or hops between the ionosphere and earth permit very long distances, even worldwide, communications. This effect is useful over the 3 - to 30-MHz range.

50. At frequencies above 30 MHz, propagation is primarily by the direct or space wave which travels in a straight line between transmitting and receiving antennas. This is known as line-of-sight communications.

51. Radio waves ate easily blocked or reflected by large objects. This is particularly true of VHF, UHF, and microwave signals.

52. The communications distance at VHF, UHF, and microwave frequencies is limited to the line-of-sight distance between transmitting and receiving antennas.

53. The line-of-sight distance (D) is limited by the curvature of the earth and is dependent upon the heights h_t, and h_r, of the transmitting and receiving antennas, respectively.

54. To extend transmission distances at VHF, UHF, and microwave frequencies, relay stations known as repeater stations receive and retransmit signals.

Complete List of Reviewers in Communications Electronics per Chapter

Important List of Communications Engineering Materials

Share your Notes in Antennas and Transmission Lines

If you have some important review notes on this topic kindly write the notes on the comment section below. This will absolutely beneficial to those aspiring to become professional engineers by taking the Board Exam and eventually to become successful in their chosen field. Thank you.

---