Defining Terms Modulation: The process of impressing the source information onto a bandpass signal with a carrier frequenc It s(t)=Relg(t)ejcr] where g(n)is a function of the modulating signal m(t) g(t)=gIm(t) gl- performs a mapping operation on m( t). The particular relationship that is chosen for g( t) in terms of m(r) defines the type of modulation used. Superheterodyne receiver: Most receivers employ the superheterodyne receiving technique, which consists of either down-converting or up-converting the input signal to some convenient frequency band, called the intermediate frequency band, and then extracting the information (or modulation) by using an appropriate detector. This basic receiver structure is used for the reception of all types of bandpass signal such as television FM. AM. satellite, and rada Related Topics 69.2 Radio Broadcasting.70. 1 Coding References L. W. Couch, Digital and Analog Communication Systems, New York: Prentice-Hall, 1995 F. Dejager, Delta modulation of PCM transmission using a 1-unit code, Phillips Res Rep,, no. 7, pp. 442-466 J.H. Downing, Modulation Systems and Noise, Englewood Cliffs, N J. Prentice-Hall, 1964. J. Dunlop and D.G. Smith, Telecommunications Engineering, London: Van Nostrand, 1989 B P Lathi, Modern Digital and Analog Communication Systems, New York: CBS College, 1983 H. Park, Jr, On binary DPSK detection, IEEE Trans. Commun., COM-26, PP. 484-486, 1978 M. Schwartz, Information Transmission, Modulation and Noise, New York: McGraw-Hill, 1980 Further information The monthly journal IEEE Transactions on Communications describes telecommunication techniques. The performance of M-ary QAM schemes is evaluated in its March 1991 issue, pp 405-408. The IEEE magazin IEEE Communications is a valuable source Another source is IEEE Transactions on Broadcasting which is published quarterly by The Institute of Electrical and Electronics Engineers, Inc. The biweekly magazine Electronics Letters investigates the error probability of coherent PSK and FSK systems with multiple co-channel interferences in its April 11, 1991, issue, Pp 640-642. Another relevant source regard ng the coherent detection of MSK is described on Pp 623-625 of the same issue. All subscriptions inquiries and orders should be sent to IEE Publication Sales, P.O. Box 96, Stevenage, Herts, SGl 2SD, United Kingdom 69.2 Radio broadcasting Jefferson F. Lindsey ill and Dennis F. Doelitzsch Standard Broadcasting(Amplitude Modulation Standard broadcasting refers to the transmission of voice and music received by the general public in the 535 to 1705-kHz frequency band. Amplitude modulation is used to provide service ranging from that needed for small communities to higher-power broadcast stations needed for larger regional areas. The primary servic
© 2000 by CRC Press LLC Defining Terms Modulation: The process of impressing the source information onto a bandpass signal with a carrier frequency fc. It can be expressed as s(t) = Re{g(t) ejwct} where g(t) is a function of the modulating signal m(t). That is, g(t) = g[m(t)] g[·] performs a mapping operation on m(t). The particular relationship that is chosen for g(t) in terms of m(t) defines the type of modulation used. Superheterodyne receiver: Most receivers employ the superheterodyne receiving technique, which consists of either down-converting or up-converting the input signal to some convenient frequency band, called the intermediate frequency band, and then extracting the information (or modulation) by using an appropriate detector. This basic receiver structure is used for the reception of all types of bandpass signals, such as television, FM, AM, satellite, and radar signals. Related Topics 69.2 Radio Broadcasting • 70.1 Coding References L. W. Couch, Digital and Analog Communication Systems, New York: Prentice-Hall, 1995. F. Dejager, “Delta modulation of PCM transmission using a 1-unit code,” Phillips Res. Rep., no. 7, pp. 442–466, Dec. 1952. J.H. Downing, Modulation Systems and Noise, Englewood Cliffs, N.J.: Prentice-Hall, 1964. J. Dunlop and D.G. Smith, Telecommunications Engineering, London: Van Nostrand, 1989. B.P. Lathi, Modern Digital and Analog Communication Systems, New York: CBS College, 1983. J.H. Park, Jr., “On binary DPSK detection,” IEEE Trans. Commun., COM-26, pp. 484–486, 1978. M. Schwartz, Information Transmission, Modulation and Noise, New York: McGraw-Hill, 1980. Further Information The monthly journal IEEE Transactions on Communications describes telecommunication techniques. The performance of M-ary QAM schemes is evaluated in its March 1991 issue, pp. 405–408. The IEEE magazine IEEE Communications is a valuable source. Another source is IEEE Transactions on Broadcasting, which is published quarterly by The Institute of Electrical and Electronics Engineers, Inc. The biweekly magazine Electronics Letters investigates the error probability of coherent PSK and FSK systems with multiple co-channel interferences in its April 11, 1991, issue, pp. 640–642. Another relevant source regarding the coherent detection of MSK is described on pp. 623–625 of the same issue. All subscriptions inquiries and orders should be sent to IEE Publication Sales, P.O. Box 96, Stevenage, Herts, SG1 2SD, United Kingdom. 69.2 Radio Broadcasting Jefferson F. Lindsey III and Dennis F. Doelitzsch Standard Broadcasting (Amplitude Modulation) Standard broadcasting refers to the transmission of voice and music received by the general public in the 535- to 1705-kHz frequency band. Amplitude modulation is used to provide service ranging from that needed for small communities to higher-power broadcast stations needed for larger regional areas. The primary service
THE REVOLUTIONARY TECHNOLOGY OF RADIO he beginning of the present century saw the birth of several technologies that were to be revolu tionary in their impact. The most exciting of these was radio or, as it was generally called at the time,"wireless". No other technology would seem to obliterate the barriers of distance in human communication or to bring individuals together with such immediacy and spontaneity. And seldom had there emerged an activity that seemed so mysterious and almost magical to most of the population Radio was mysterious not only to the layman, but also to many engineers and technically informed individuals. The mystery lay largely in radio's application of principles and phenomena only recently identified by physicists and engineers working at the frontiers of their specialties. The existence of electromagnetic waves that traveled like light had been predicted by the brilliant physicist James Clerk Maxwell in the 1860s and proven by the young German Heinrich Hertz in the 1880s. The possible use of these waves for communicating through space without wires occurred to many, however, the first practical steps to making radio useful are generally attributed to Oliver Lodge in England, guglielmo Marconi in Italy, and Aleksandr Popov in Russia. Marconi's broadcast of Morse code across the Atlantic in 1901 first showed the world just what enormous potential radio had for changing the whole concept of long-distance communication. The next few years saw feverish activity everywhere as men tried to translate the achievements of the pioneers into the foundations of a practical technology By 1912, radio technology had attracted a small number of dedicated individuals who identified their own future with the progress of their chosen field. Some of these had organized themselves into small, localized societies, but it was clear to many that a broader vision was needed if radio practitioners were to achieve the recognition and respect of technical professionals. It was with such a vision in mind that representatives of two of these local societies met in New York City in May 1912 to form the Institute of Radio Engineers. The IRE was to be an international society dedicated to the highest professional standards and to the advancement of the theory and practice of radio technology. The importance of radio lay not simply in its expansion of the means of human communication over distances, but also in its exploitation and expansion of very novel scientific and technical capabilities. As the century progressed, radio would give rise to the 20th century's most revolutionary technology of all-electronics. Courtesy of the IEEE Center for the History of Electrical Engineering. rea is defined as the area in which the groundwave signal is not subject to objectionable interference or objectionable fading. The secondary service area refers to an area serviced by skywaves and not subject to bjectionable interference. Intermittent service area refers to an area receiving service from either a roundway or a skywave but beyond the primary service area and subject to some interference and fading Frequency Allocations The carrier frequencies for standard broadcasting in the United States (referred to internationally as medium wave g)are designated in the Federal Communications Commission(FCC) Rules and Regulations, VoL IIL, Part 73. A total of 117 carrier frequencies are allocated from 540 to 1700 kHz in 10-kHz intervals. Each carrier frequency is required by the FCC rules to deviate no more than +20 Hz from the allocated frequency to minimize heterodyning from two or more interfering stations. Double-sideband full-carrier modulation commonly called amplitude modulation(AM), is used in standard broadcasting for sound transmission. Typical modulation frequencies for voice and music range from 50 Hz to 10 kHz. Each channel is generally thought of as 10 kHz in width, and thus the frequency band is designated from 535 to 1705 kHz; however, when the modulation frequency exceeds 5 kHz, the radio frequency bandwidth of the channel exceeds 10 kHz and C 2000 by CRC Press LLC
© 2000 by CRC Press LLC area is defined as the area in which the groundwave signal is not subject to objectionable interference or objectionable fading. The secondary service area refers to an area serviced by skywaves and not subject to objectionable interference. Intermittent service area refers to an area receiving service from either a groundwave or a skywave but beyond the primary service area and subject to some interference and fading. Frequency Allocations The carrier frequencies for standard broadcasting in the United States (referred to internationally as mediumwave broadcasting) are designated in the Federal Communications Commission (FCC) Rules and Regulations, Vol. III, Part 73. A total of 117 carrier frequencies are allocated from 540 to 1700 kHz in 10-kHz intervals. Each carrier frequency is required by the FCC rules to deviate no more than ±20 Hz from the allocated frequency, to minimize heterodyning from two or more interfering stations. Double-sideband full-carrier modulation, commonly called amplitude modulation (AM), is used in standard broadcasting for sound transmission. Typical modulation frequencies for voice and music range from 50 Hz to 10 kHz. Each channel is generally thought of as 10 kHz in width, and thus the frequency band is designated from 535 to 1705 kHz; however, when the modulation frequency exceeds 5 kHz, the radio frequency bandwidth of the channel exceeds 10 kHz and THE REVOLUTIONARY TECHNOLOGY OF RADIO he beginning of the present century saw the birth of several technologies that were to be revolutionary in their impact. The most exciting of these was radio or, as it was generally called at the time, “wireless”. No other technology would seem to obliterate the barriers of distance in human communication or to bring individuals together with such immediacy and spontaneity. And seldom had there emerged an activity that seemed so mysterious and almost magical to most of the population. Radio was mysterious not only to the layman, but also to many engineers and technically informed individuals. The mystery lay largely in radio’s application of principles and phenomena only recently identified by physicists and engineers working at the frontiers of their specialties. The existence of electromagnetic waves that traveled like light had been predicted by the brilliant physicist James Clerk Maxwell in the 1860s and proven by the young German Heinrich Hertz in the 1880s. The possible use of these waves for communicating through space without wires occurred to many; however, the first practical steps to making radio useful are generally attributed to Oliver Lodge in England, Guglielmo Marconi in Italy, and Aleksandr Popov in Russia. Marconi’s broadcast of Morse code across the Atlantic in 1901 first showed the world just what enormous potential radio had for changing the whole concept of long-distance communication. The next few years saw feverish activity everywhere as men tried to translate the achievements of the pioneers into the foundations of a practical technology. By 1912, radio technology had attracted a small number of dedicated individuals who identified their own future with the progress of their chosen field. Some of these had organized themselves into small, localized societies, but it was clear to many that a broader vision was needed if radio practitioners were to achieve the recognition and respect of technical professionals. It was with such a vision in mind that representatives of two of these local societies met in New York City in May 1912 to form the Institute of Radio Engineers. The IRE was to be an international society dedicated to the highest professional standards and to the advancement of the theory and practice of radio technology. The importance of radio lay not simply in its expansion of the means of human communication over distances, but also in its exploitation and expansion of very novel scientific and technical capabilities. As the century progressed, radio would give rise to the 20th century’s most revolutionary technology of all — electronics. (Courtesy of the IEEE Center for the History of Electrical Engineering.) T
adjacent channel interference may occur. To improve the high-frequ formance of transmission and to compensate for the high-frequency roll-off of many consumer receivers, FCC rules require that stations boost the high-frequency amplitude of transmitted audio using preemphasis techniques. In addition stations may also use multiplexing to transmit stereophonic programming. The FCC adopted Motorolas C-QUAM com patible quadrature amplitude modulation in 1994. Approximately 700 AM stations transmit in stereo Channel and Station Classifications In standard broadcast(AM), stations are classified according to their operating power, protection from inter rence,and hours of operation. a Class a station operates with 10 to 50 kw of power servicing a large area with primary, secondary, and intermittent coverage and is protected from interference both day and night. These stations are called"clear channel"stations because the channel is cleared of nighttime interference over a major portion of the country. Class B stations operate full time with transmitter powers of 0. 25 to 50 kw and are designed to render primary service only over a principal center of population and the rural area contiguous thereto. While nearly all Class a stations operate with 50 kw, most Class B stations must restrict eir power to 5 kw or less to avoid interfering with other stations. Class b stations operating in the 1605 to 1705 kHz band are restricted to a power level of 10 kw daytime and 1 kw nighttime. Class C stations operate on six designated channels(1230, 1240, 1340, 1400, 1450, and 1490) with a maximum power of 1 kw or less full time and render primarily local service to smaller communities. Class D stations operate on Class A or B frequencies with Class B transmitter powers during daytime, but nighttime operation, if permitted at all,must be at low power(less than 0. 25 kw)with no protection from interference. Although Class A stations cover large areas at night, approximately in a 1220-km(750-mi)radius, the nighttime coverage of Class B, C, and D stations is limited by interference from other stations, electrical devices, and atmospheric conditions to a relatively small area. Class C stations, for eso be large differences in the ar ce that the station covers daytime versus nighttime. With over 5200 AM stations licensed for operation by the FCC, interference, both day and night, is a factor that significantly limits the service which stations may provide In the absence of interference, a daytime signal strength of 2 mV/m is required for reception in populated areas of more than 2500, while a signal of 0.5 mv/m is generally acceptable in less populated areas. Secondary nighttime service is provided in areas receiving a 0.5-mV/m signal 50% or more of the time without objec tionable interference. Table 69. 4 indicates the daytime contour overlap limits. However, it should be noted that these limits apply to new stations and modifications to existing stations. Nearly every station on the air was allocated prior to the implementation of these rules when the interference criteria were less restrictive Field Strength The field strength produced by a standard broadcast station is a key factor in determining the primary and secondary service areas and interference limitations of possible future radio stations. The field strength limitations are specified as field intensities by the FCC with the units volts per meter; however, measuring devices may read volts or decibels referenced to 1 mw(dBm), and a conversion may be needed to obtain the field intensity. The power received may be measured in dBm and converted to watts. Voltage readings may be converted to ratts by squaring the root mean square(rms)voltage and dividing by the field strength meter input resistance, which is typically on the order of 50 or 75 Q2. Additional factors needed to determine electric field intensity are the power gain and losses of the field strength receiving antenna system. Once the power gain and losses are known, the effective area with loss compensation of the field strength receiver antenna may be obtained (69.14) 4 where A fr =effective area including loss compensation, m?; G= power gain of field strength antenna, w/w; n= wavelength, m; and L= mismatch loss and cable loss factor, W/W. From this calculation, the power density in watts per square meter may be obtained by dividing the received power by the effective area, and the electric field intensity may be calculated as c 2000 by CRC Press LLC
© 2000 by CRC Press LLC adjacent channel interference may occur. To improve the high-frequency performance of transmission and to compensate for the high-frequency roll-off of many consumer receivers, FCC rules require that stations boost the high-frequency amplitude of transmitted audio using preemphasis techniques. In addition stations may also use multiplexing to transmit stereophonic programming. The FCC adopted Motorola’s C-QUAM compatible quadrature amplitude modulation in 1994. Approximately 700 AM stations transmit in stereo. Channel and Station Classifications In standard broadcast (AM), stations are classified according to their operating power, protection from interference, and hours of operation. A Class A station operates with 10 to 50 kW of power servicing a large area with primary, secondary, and intermittent coverage and is protected from interference both day and night. These stations are called “clear channel” stations because the channel is cleared of nighttime interference over a major portion of the country. Class B stations operate full time with transmitter powers of 0.25 to 50 kW and are designed to render primary service only over a principal center of population and the rural area contiguous thereto. While nearly all Class A stations operate with 50 kW, most Class B stations must restrict their power to 5 kW or less to avoid interfering with other stations. Class B stations operating in the 1605 to 1705 kHz band are restricted to a power level of 10 kW daytime and 1 kW nighttime. Class C stations operate on six designated channels (1230, 1240, 1340, 1400, 1450, and 1490) with a maximum power of 1 kW or less full time and render primarily local service to smaller communities. Class D stations operate on Class A or B frequencies with Class B transmitter powers during daytime, but nighttime operation, if permitted at all, must be at low power (less than 0.25 kW) with no protection from interference. Although Class A stations cover large areas at night, approximately in a 1220-km (750-mi) radius, the nighttime coverage of Class B, C, and D stations is limited by interference from other stations, electrical devices, and atmospheric conditions to a relatively small area. Class C stations, for example, have an interference-free nighttime coverage radius of approximately 8 to 16 km. As a result, there may be large differences in the area that the station covers daytime versus nighttime. With over 5200 AM stations licensed for operation by the FCC, interference, both day and night, is a factor that significantly limits the service which stations may provide. In the absence of interference, a daytime signal strength of 2 mV/m is required for reception in populated areas of more than 2500, while a signal of 0.5 mV/m is generally acceptable in less populated areas. Secondary nighttime service is provided in areas receiving a 0.5-mV/m signal 50% or more of the time without objectionable interference. Table 69.4 indicates the daytime contour overlap limits. However, it should be noted that these limits apply to new stations and modifications to existing stations. Nearly every station on the air was allocated prior to the implementation of these rules when the interference criteria were less restrictive. Field Strength The field strength produced by a standard broadcast station is a key factor in determining the primary and secondary service areas and interference limitations of possible future radio stations. The field strength limitations are specified as field intensities by the FCC with the units volts per meter; however, measuring devices may read volts or decibels referenced to 1 mW (dBm), and a conversion may be needed to obtain the field intensity. The power received may be measured in dBm and converted to watts. Voltage readings may be converted to watts by squaring the root mean square (rms) voltage and dividing by the field strength meter input resistance, which is typically on the order of 50 or 75 W. Additional factors needed to determine electric field intensity are the power gain and losses of the field strength receiving antenna system. Once the power gain and losses are known, the effective area with loss compensation of the field strength receiver antenna may be obtained as (69.14) where Aeff = effective area including loss compensation, m2 ; G = power gain of field strength antenna, W/W; l = wavelength, m; and L = mismatch loss and cable loss factor, W/W. From this calculation, the power density in watts per square meter may be obtained by dividing the received power by the effective area, and the electric field intensity may be calculated as Aeff = G L l p 2 4
TABLE 69.4 Protected Service Signal Intensities for Standard Broadcasting(AM) Signal Strength Contour of Area Permissible Protected from Objectionable interfering Cla Power Class of nterference(uIm) Signal 10-50 SC100 SC50050%SW SC 5 AC 500 Gw AC250 0.25-1 Not precise SC 25 ot precis 0.25-50 Clear Not precise SC 25 Not precise AC250 is already limited by interference from other stations to a contour of higher value than that normally protected value contour shall be the established protection standard for such station. Changes proposed by Class A and B stations shall be required to comply with the following restrictions. Those interferers that contribute to another stations RSS using the 50% exclusion method are required to reduce their contribution to that Rss by 10%.Those lesser interferers that contribute I but do not contribute to that stations RSS using the 50% exclusion method may tion Interferers not included in a stations rss using the 25% exclusion method to increase radiation as long as the 25% exclusion threshold is not equaled or exceeded. In no case will a reduction be required that would result in a contributing value that is below the pertinent value specified in the table sKywave field strength for 10% or more of the time. For Alaska, Class SC is limited to 5 uV/m. 'During nighttime hours, Class C stations in the contiguous 48 states may treat all Class b stations assigned to 1230, 1240, 1340, 1400,1450,and in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands as if they were Class C stations. Note: SC= same AC = adjacent channel; Sw= skywave; Gw= groundwave: RSS= root of sum squares. Source: FCC Rules and Regulations, Revised 1991; vol Ill, pt. 73. 182(a) E=、9Z (69.15) where E= electric field intensity, V/m; 9= power density, W/m, and Zs= 120T S2, impedance of free space. The protected service contours and permissible interference contours for standard broadcast stations shown in Table 69.4, along with a knowledge of the field strength of existing broadcast stations, may be used in determining the potential for establishing new standard broadcast stations One of the major factors in the determination of field strength is the propagation characteristic that is described by the change in electric field intensity with an increase in distance from the broadcast station antenna. This variation depends on a number of factors including frequency, distance, surface dielectric constant, surface loss tangent, polarization, local topography, and time of day. Generally speaking, groundwave propagation occurs at shorter ranges both during day and night periods. Skywave propagation permits longer ranges and occurs during night periods, and thus some stations must either reduce power or cease to operate at night to avoid sing interference. Propagation curves in the broadcast industry are frequently referred to a reference level 00 mV/m at 1 km; however, a more general expression of groundwave propagation may be obtained by using the Bremmer series[Bremmer, 1949]. A typical groundwave propagation curve for electric field strength as a function of distance is shown in Fig. 69.9 for an operating frequency of 770-810 kHz. The ground conductivity varies from 0. 1 to 5000 mS/m, and the ground relative dielectric constant is 15 The effective radiated power(ERP)refers to the effective power output from the antenna in a specified direction and includes the transmitter power output, transmission line losses, and antenna power gain. The ERP in most cases exceeds the transmitter output power, since that antenna power gain is normally 2 or more. For a hypothetical perfect isotropic radiator with a power gain of 1, the ERP is found to be ERP。E2r2 (69.16) c 2000 by CRC Press LLC
© 2000 by CRC Press LLC (69.15) where E = electric field intensity, V/m; 3 = power density, W/m2 ; and Zfs = 120p W, impedance of free space. The protected service contours and permissible interference contours for standard broadcast stations shown in Table 69.4, along with a knowledge of the field strength of existing broadcast stations, may be used in determining the potential for establishing new standard broadcast stations. Propagation One of the major factors in the determination of field strength is the propagation characteristic that is described by the change in electric field intensity with an increase in distance from the broadcast station antenna. This variation depends on a number of factors including frequency, distance, surface dielectric constant, surface loss tangent, polarization, local topography, and time of day. Generally speaking, groundwave propagation occurs at shorter ranges both during day and night periods. Skywave propagation permits longer ranges and occurs during night periods, and thus some stations must either reduce power or cease to operate at night to avoid causing interference. Propagation curves in the broadcast industry are frequently referred to a reference level of 100 mV/m at 1 km; however, a more general expression of groundwave propagation may be obtained by using the Bremmer series [Bremmer, 1949]. A typical groundwave propagation curve for electric field strength as a function of distance is shown in Fig. 69.9 for an operating frequency of 770–810 kHz. The ground conductivity varies from 0.1 to 5000 mS/m, and the ground relative dielectric constant is 15. The effective radiated power (ERP) refers to the effective power output from the antenna in a specified direction and includes the transmitter power output, transmission line losses, and antenna power gain. The ERP in most cases exceeds the transmitter output power, since that antenna power gain is normally 2 or more. For a hypothetical perfect isotropic radiator with a power gain of 1, the ERP is found to be (69.16) TABLE 69.4 Protected Service Signal Intensities for Standard Broadcasting (AM) Signal Strength Contour of Area Permissible Protected from Objectionable Interfering Class of Power Class of Interference* (mV/m) Signal Station (kW) Channel Used Day† Night Day† Night‡ A 10–50 Clear SC 100 SC 500 50% SW SC 5 SC 25 AC 500 AC 500 GW AC 250 AC 250 B 0.25–50 Clear 500 2000† 25 25 Regional AC 250 250 C 0.25–1 Local 500 Not precise§ SC 25 Not precise D 0.25–50 Clear 500 Not precise SC 25 Not precise Regional AC 250 *When a station is already limited by interference from other stations to a contour of higher value than that normally protected for its class, this higher-value contour shall be the established protection standard for such station. Changes proposed by Class A and B stations shall be required to comply with the following restrictions. Those interferers that contribute to another station’s RSS using the 50% exclusion method are required to reduce their contribution to that RSS by 10%. Those lesser interferers that contribute to a station’s RSS using the 25% exclusion method but do not contribute to that station’s RSS using the 50% exclusion method may make changes not to exceed their present contribution. Interferers not included in a station’s RSS using the 25% exclusion method are permitted to increase radiation as long as the 25% exclusion threshold is not equaled or exceeded. In no case will a reduction be required that would result in a contributing value that is below the pertinent value specified in the table. †Groundwave. ‡Skywave field strength for 10% or more of the time. For Alaska, Class SC is limited to 5 mV/m. §During nighttime hours, Class C stations in the contiguous 48 states may treat all Class B stations assigned to 1230, 1240, 1340, 1400, 1450, and 1490 kHz in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands as if they were Class C stations. Note: SC = same channel; AC = adjacent channel; SW = skywave; GW = groundwave; RSS = root of sum squares. Source: FCC Rules and Regulations, Revised 1991; vol. III, pt. 73.182(a). E Z = 3 fs ERP = E r2 2 30
KILOMETERS FROM ANTENNA GROUND WAVE FIELD STRENGTH OISTANCE 770-810kHz COMPUTED FOR 790 kHz 0050 KILOMETERS FROM ANTENNA IGURE 69.9 Typical ve propagation for standard AM broadcasting.(Source: 1986 National Association of c 2000 by CRC Press LLC
© 2000 by CRC Press LLC FIGURE 69.9 Typical groundwave propagation for standard AM broadcasting. (Source: 1986 National Association of Broadcasters.)