Chapter 18 Terrestrial Microwave Communication Systems Objectives 18.1 Introduction 18.2 Terminal and Repeater Siting 18.3 Path Calculations 18.4 Fixed Microwave Links 18.5 Local Microwave Distribution systems Chapter 18 Terrestrial Microwave Communication Systems Objectives 18.1 Introduction 18.2 Terminal and Repeater Siting 18.3 Path Calculations 18.4 Fixed Microwave Links 18.5 Local Microwave Distribution systems Objectives After completing this chapter, you should be able to: • Describe the basic structure and uses of microwave radio links, • Explain the methods used in choosing site for repeaters, • Calculate the signal strength at the receiver for a variety of transmitter, antenna, and terrain configurations • Calculate the required clearance of a microwave path from an obstacle, • Calculate the noise temperature and carrier-to-noise level of a microwave system, • Calculate the noise temperature and carrier-to-noise level of a microwave system. you should be able to: • Describe the basic structure and uses of microwave radio links. • Calculate the signal strength at the receiver for a variety of transmitter.Objectives After completing this chapter. antenna. . • Explain the methods used in choosing site for repeaters. and terrain configurations • Calculate the required clearance of a microwave path from an obstacle. . • Explain fading and describe the diversity schemes that are used to overcome it. SSB.Objectives • Calculate the energy per bit per noise density ratio for a microwave system. • Describe the transmitting and receiving equipment used for FM. • Describe the types of repeaters used for analog and digital systems and perform frequency calculations for these systems. and digital systems. • Describe the place of microwave systems for terrestrial broadcasting. SSB. • Describe the place of microwave systems for terrestrial broadcasting. and digital systems. .Objectives • Calculate the energy per bit per noise density ratio for a microwave system. • Describe the transmitting and receiving equipment used for FM. • Explain fading and describe the diversity schemes that are used to overcome it. • Describe the types of repeaters used for analog and digital systems and perform frequency calculations for these systems. 3 Path Calculations 18.Chapter 18 Terrestrial Microwave Communication Systems Objectives 18.5 Local Microwave Distribution systems .4 Fixed Microwave Links 18.1 Introduction 18.2 Terminal and Repeater Siting 18. 1 Introduction 18.3 Path Calculations 18.2 Terminal and Repeater Siting 18.5 Local Microwave Distribution systems .Chapter 18 Terrestrial Microwave Communication Systems Objectives 18.4 Fixed Microwave Links 18. Electronics Rewind . .Microwaves in Long-Distance Telephony • The first fixed microwave link for telephone communications in North America was established in 1947 between New York and Boston. Microwaves in Long-Distance Telephony • The first fixed microwave link for telephone communications in North America was established in 1947 between New York and Boston. . .Microwaves in Long-Distance Telephony • By 1951 a transcontinental system was in place using 107 repeaters to cover the distance from New York to San Francisco. .Microwaves in Long-Distance Telephony • By 1951 a transcontinental system was in place using 107 repeaters to cover the distance from New York to San Francisco. or television signals. They can be used as studio-to-transmitter (STL) links for radio and television broadcasting stations. data. 1 Introduction • Point-to-point microwave radio links have many uses. and they can also link the head-ends (antenna sites) of many cable television installations to their distribution systems. .18. Another very common application of microwave links is as part of a communications network involving telephone. 18. . Another very common application of microwave links is as part of a communications network involving telephone. or television signals. and they can also link the head-ends (antenna sites) of many cable television installations to their distribution systems. 1 Introduction • Point-to-point microwave radio links have many uses. They can be used as studio-to-transmitter (STL) links for radio and television broadcasting stations. data. so microwave systems are easier to install in difficult terrain. The bandwidth available with fiber-optic systems is greater than with radio. There is no doubt that terrestrial microwave systems will continue to be part of the evolving communications grid. On the other hand. . such as in mountainous or wilderness areas. and they require less maintenance. 1 Introduction • Fiber-optic systems are being installed in preference to microwave radio for some fixed point-to-point services. microwave relays are needed only at intervals of approximately 40 km.18. and they require less maintenance. There is no doubt that terrestrial microwave systems will continue to be part of the evolving communications grid.18. The bandwidth available with fiber-optic systems is greater than with radio. On the other hand. . 1 Introduction • Fiber-optic systems are being installed in preference to microwave radio for some fixed point-to-point services. such as in mountainous or wilderness areas. so microwave systems are easier to install in difficult terrain. microwave relays are needed only at intervals of approximately 40 km. while others are multihop systems that use repeaters to extend the system beyond the line-of-sight range of a single link.18. Figure 18.1 shows the two types of systems. 1 Introduction • Some microwave systems use only one link or hop. . while others are multihop systems that use repeaters to extend the system beyond the line-of-sight range of a single link.1 shows the two types of systems.18. . 1 Introduction • Some microwave systems use only one link or hop. Figure 18. Transmitter Receiver Antenna Antenna (a) Single link Repeater Transmitter Antenna Antenna Receiver Antenna Antenna (b) System with repeater Figure 18.1 Microwave communication systems . Transmitter Receiver Antenna Antenna (a) Single link Repeater Transmitter Antenna Antenna Receiver Antenna Antenna (b) System with repeater Figure 18.1 Microwave communication systems . 1 Introduction • Microwave systems can also be classified by the modulation technique used. .18. most employ frequency modulation. All of these techniques have been discussed in previous chapters. since the radio propagation part of the system is the same for both. generally quadrature amplitude modulation (QAM). Older systems are analog. The modulation and demodulation techniques and the design of repeaters are the main difference between the two types. The analog and digital systems are similar in many aspects. Many of the newer systems use digital modulation schemes. though some use single-sideband AM. most employ frequency modulation. since the radio propagation part of the system is the same for both. though some use single-sideband AM. All of these techniques have been discussed in previous chapters. generally quadrature amplitude modulation (QAM). 1 Introduction • Microwave systems can also be classified by the modulation technique used. . The modulation and demodulation techniques and the design of repeaters are the main difference between the two types. Older systems are analog. Many of the newer systems use digital modulation schemes. The analog and digital systems are similar in many aspects.18. 18. or even less.99%. both analog and digital. Practical systems often have reliability in the range of 99. 1 Introduction • This chapter will first review microwave propagation and then discuss the components used in microwave links. Because these systems are used in commercial applications were reliability is of utmost importance. we will also consider the means of ensuring the greatest possible reliability. . that is the system may be “down” for about one hour per year. 99%. or even less.18. 1 Introduction • This chapter will first review microwave propagation and then discuss the components used in microwave links. we will also consider the means of ensuring the greatest possible reliability. that is the system may be “down” for about one hour per year. both analog and digital. . Practical systems often have reliability in the range of 99. Because these systems are used in commercial applications were reliability is of utmost importance. This chapter concludes with a look at some of these systems.18. 1 Introduction • Recently there has been considerable interest in the use of terrestrial microwave links for broadcasting. . but two-way systems that allow interactive television and Internet access have also been introduced. Most of these systems are used as substitutes for television distribution using coaxial cable. . 1 Introduction • Recently there has been considerable interest in the use of terrestrial microwave links for broadcasting. Most of these systems are used as substitutes for television distribution using coaxial cable.18. This chapter concludes with a look at some of these systems. but two-way systems that allow interactive television and Internet access have also been introduced. Chapter 18 Terrestrial Microwave Communication Systems Objectives 18.1 Introduction 18.3 Path Calculations 18.2 Terminal and Repeater Siting 18.5 Local Microwave Distribution systems .4 Fixed Microwave Links 18. 5 Local Microwave Distribution systems .4 Fixed Microwave Links 18.2 Terminal and Repeater Siting 18.Chapter 18 Terrestrial Microwave Communication Systems Objectives 18.3 Path Calculations 18.1 Introduction 18. and one increases the chances of an equipment breakdown that can disable the link. Repeaters cost money. a microwave system should use as few repeaters as possible. of course. More importantly.2 Terminal and Repeater Siting • In general. additional links contribute to noise levels in analog systems and increase the jitter in digital ones.18. . 2 Terminal and Repeater Siting • In general. additional links contribute to noise levels in analog systems and increase the jitter in digital ones. More importantly. Repeaters cost money. . a microwave system should use as few repeaters as possible.18. and one increases the chances of an equipment breakdown that can disable the link. of course. 18. and the topography must be inspected for the best repeater sites. preferably on high points of the terrain. . and all sorts of practical considerations can prevent certain sites from being used for repeaters. repeater stations must not be located beyond line-of-sight propagation range from each other. Land must be acquired.2 Terminal and Repeater Siting • On the other hand. access and electrical power must be arranged. . repeater stations must not be located beyond line-of-sight propagation range from each other. preferably on high points of the terrain.2 Terminal and Repeater Siting • On the other hand.18. and the topography must be inspected for the best repeater sites. Land must be acquired. and all sorts of practical considerations can prevent certain sites from being used for repeaters. access and electrical power must be arranged. By concentrating the transmitted power into a narrow beam.18. these antennas increase the effective power and reduce interference to and from other systems.2 Terminal and Repeater Siting • Terrestrial microwave systems use relatively low power transmitters with high-gain parabolic or hog-horn antennas. however. . There are limits to antenna gain. Gain figures greater than 45 dB should be avoided because antennas with this much gain have such narrow beamwidth (less than one degree) that mounting requirements are severe—slight motion of an antenna tower due to wind can be sufficient to cause signal loss with such narrow antenna beams. Gain figures greater than 45 dB should be avoided because antennas with this much gain have such narrow beamwidth (less than one degree) that mounting requirements are severe—slight motion of an antenna tower due to wind can be sufficient to cause signal loss with such narrow antenna beams. these antennas increase the effective power and reduce interference to and from other systems. however. There are limits to antenna gain. .2 Terminal and Repeater Siting • Terrestrial microwave systems use relatively low power transmitters with high-gain parabolic or hog-horn antennas. By concentrating the transmitted power into a narrow beam.18. to reduce losses. .18. At lower frequencies.2 Terminal and Repeater Siting • Feedlines between transmitters and/or receivers and antennas are almost always constructed from waveguide at frequencies at 2 GHz. coaxial cable may be used. coaxial cable may be used. . to reduce losses. At lower frequencies.2 Terminal and Repeater Siting • Feedlines between transmitters and/or receivers and antennas are almost always constructed from waveguide at frequencies at 2 GHz.18. 2 Terminal and Repeater Siting Path Calculations .18. 2 Terminal and Repeater Siting Path Calculations .18. Path Calculations • To be continued by the next reporter… .
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