EPA-520/1-74-005 RF PULSE SPECTRAL MEASUREMENTS IN THE VICINITY OF SEVERAL AIR • TRAFFIC CONTROL RADARS $1$ ' U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Radiation Programs ------- RF PULSE SPECTRAL MEASUREMENTS IN THE VICINITY OF SEVERAL AIR TRAFFIC CONTROL RADARS m \ Richard A. Tell John C. Nelson* * Current address: Department of Physics, Midwestern University, Wichita Falls, Texas 76308 May 1974 U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Radiation Programs Field Operations Division Electromagnetic Radiation Analysis Branch 9100 Brookville Road, Silver Spring, Maryland 20910 ------- FOREWORD The Office of Radiation Programs carries out a national program designed to evaluate the exposure of man to ionizing and nonionizing radiation, and to promote the development of controls necessary to pro- tect the public health and safety and assure environmental quality. Office of Radiation Programs technical reports allow comprehensive and rapid publishing of the results of intramural and contract projects. The reports are distributed to State and local radiological health offices, Office of Radiation Programs technical and advisory committees, universities, laboratories, schools, the press, and other interested groups and individuals. These reports are also included in the collec- tions of the Library of Congress and the National Technical Information Service. i I encourage readers of these reports to inform the Office of Radiation Programs of any omissions or errors. Your additional comments or requests for further information are also solicited. W. A. Mills, Ph.D. Acting Deputy Assistant Administrator for Radiation Programs iii ------- CONTENTS Page FOREWORD Hi ABSTRACT viii BACKGROUND 1 OBJECTIVES 1 FAA FACILITIES AND EQUIPMENT 2 MEASUREMENT APPROACH 12 RESULTS AND OBSERVATIONS • 21 CONCLUSIONS 35 RECOMMENDATIONS 36 ACKNOWLEDGMENTS 37 REFERENCES 38 APPENDIXES A. Summary of Pertinent Radiation Standards 39 B. Field Strength and Power Density in Free Space 41 C. Voltage and Power Ratios to dB 43 D. Attenuation Effectiveness of Wire Mesh Cloth . 45 LIST OF FIGURES 1. Map of FAA Aeronautical Center, Oklahoma City, Oklahoma, showing radar locations and measurement sites 3 2. ASR-7 radar installation 5 3. ASR-4B radar installation 5 ------- Page 4. ARSR-1D radar installation 6 5. Measurement layout at location 1 ...... 7 6. Three radars as viewed from location 1 7 7. Equipment in hallway of CAMI top floor 8 8. Antenna on roof of CAMI 9 9. Roof access door at CAMI and signal cables 9 10. Radar configuration from second floor of MPB, location 3 . . 10 11. Measurement setup in computer room, ground floor MPB .... 11 12. Block diagram of measurement system 13 13. Arrangement of measurement equipment in station wagon .... 15 14. Mean gain of AEL APX-1293 crossed planar log periodic antenna 16 15. Typical signal cable loss 16 16. Typical signal cable VSWR 17 17. VSWR of AEL APX-1293 crossed planar log periodic antenna . . 18 18. Typical pulse spectrum from laboratory generator 19 19. Main lobe of pulse spectrum 19 20. Picture in time domain of PRF 20 21. ARSR-1D spectrum signature 32 22. ASR-4B spectrum signature 32 23. Spectrum scan, 0-2 MHz, observed inside building, on ground floor at location 2 34 24. VHF scan in computer room, center frequency 100 MHz, 2 MHz/division 34 vi ------- LIST OF TABLES Page 1. Specifications of radars at FAA Center 4 2. Salient characteristics of anticipated new ARSR-3 12 3. Measurement equipment summary 14 4. Measurement system correction summary 21 5. Summary of radars and measurement locations 22 6. List of supplementary measurements 22 7. Results at location 1; ASR-7, attenna stopped ... 24 8. Results at location 1; ASR-4B, antenna rotating 24 9. Results at location 1; ARSR-1D, antenna rotating 25 10. Results at location 2; ASR-4B, antenna stopped 25 11. Results at location 3, computer room; ASR-4B, antenna rotating 26 12. Results at location 3, computer room; ARSR-1D, antenna rotating 26 13. Results at location 3, MPB-North Lobby; ASR-4B, antenna rotating 27 14. Results at location 3, 2nd floor-MPB; ARSR-1D (500 kW) , antenna stopped 27 15. Results at location 3, 2nd floor-MPB; ARSR-1D (4 MW), antenna stopped 28 16. Results at location 3, 2nd floor-MPB; ARSR-1D (4 MW, maximum field), antenna stopped 28 17. Results at location 3, 2nd floor-MPB; ASR-4B, antenna rotating 29 18. Measured PRE and pulse width 31 vii ------- ABSTRACT The purpose of this study was to determine the response character- istics of a microwave scanning spectrum analyzer in the presence of a relatively intense and complex electromagnetic environment. Measure- ments of ambient field intensities in the vicinity of three different ground radars used in air-traffic-contrbl operations. Maximum peak field strengths of 960 V/m were measured about 1000 feet from the radar site. Characteristic radar spectrum signatures were recorded by photographing visual displays on the analyzer CRT. viii ------- BACKGROUND The Office of Radiation Programs within EPA conducts an environmental nonionizing radiation program. Specific objectives of this program include: determination of requirements for environmental incident monitoring capabilities; evaluation of needs and requirements for environmental surveillance and inspection; evaluation of the needs and requirements to provide technology assessment; identification of nonionizing radiation effects research requirements; and the determi- nation of needs, rationales, and alternatives for establishment of environmental nonionizing radiation guidelines or standards, and the effects of such guides or standards. Before environmental guides or standards can be developed the electromagnetic environment must be characterized in quantitative exposure terms. In support of these goals, the Electromagnetic Radiation Analysis Branch conducts a pro- gram of identification and investigation of radiofrequency and micro- wave sources whose environmental radiation fields may be potentially hazardous (1). Ground-based, high-powered radars are a class of microwave emitting sources with potential for significant environmental exposure. Because of their pulsed nature and the rotation of the antenna, this class of source presents measurement problems which are not encountered when using the spectrum analyzer to measure the emission of continuous wave sources. Proper adjustment of spectrum analyzer controls, commensurate with the radars pulse spectrum, are required before accurate interpretation of the exposure fields are possible. To properly evaluate equipment and measurement techniques under field conditions, it is necessary to know the frequency of the source, its location, and to have control over the operation of the source. Thus the effects of rotation and other variables can be controlled and the results used to interpret real electromagnetic environments. Through the kind cooperation of the Federal Aviation Administration (FAA) we were able to conduct the field evaluations under the required conditions at the FAA Aeronautical Center, Oklahoma City, Oklahoma. The radars at this site are used for training purposes and not for air traffic control. The measurements reported in this study were made September 4-7, 1973. OBJECTIVES The objective of this study was to observe the response character- istics of a microwave spectrum analyzer to high level, pulsed fields with the analyzer when situated in an electromagnetically complex environment and to arrive at conclusions, based on our experience, which could be used in future measurements of this type to facilitate the data collection in the field. ------- No detailed attempt has been made to compare measured values of field intensity with expected values based upon calculation. Such calculations require more information than was possible to obtain at the time of this study and involve complex analytical approaches beyond the scope of this report. The reader is directed to appropriate reference material for accomplishing this additional task (2^3). Values of measured radiation levels may be compared with existing RF exposure standards. Appendix A presents a summary of pertinent radiation standards. FAA FACILITIES AND EQUIPMENT One primary purpose of the FAA Aeronautical Center is training of personnel for subsequent jobs within the FAA (e.g., air traffic controllers, radar operators, and maintenance crews). In this context, the Air Navigation Facilities Training Branch currently maintains three different radars which are commonly used in daily ATC situations across the Nation. These three radars—the ASR-4B, ASR-7, and ARSR-1D—at different times of the day were made available to us for field measure- ments from various locations at the Center. The FAA Center, itself, is located in the southwestern part of Oklahoma City and is directly adjacent to the Oklahoma City Will Rogers World Airport. Though the Center is adjacent to the airport, the Center's radars are not used in any way for purposes of directing air traffic at Will Rogers—the airport maintaining its own radar equipment. Figure 1 is a map of the general layout for the Center with identification of the three measurement locations that were used and shows their proximity to the three radars located at the Center. Prior to the field trip, a computer search was made of all unclassified RF sources in the vicinity of the Center. This source search, accomplished by the DOD's Electromagnetic Compatibility Analysis Center, Annapolis, Maryland (4_), revealed the FAA Center to be in the midst of a very complex source environment. Forty-six sources were indicated as being within one mile of the ARSR-1D coordinates. These sources had transmitter powers between 1 W and 4 MW, and frequencies between 1.85 MHz and 2.82 GHz. Specifications for each of the three radars measured were also obtained and these are indicated in table 1. The ARSR-1D is capable of operating at two power levels—500 kW and 4 MW—and represents the highest power radar unit in operation at the FAA Center and at most FAA airport installations across the Nation. Antennas employed with all of these radars were rectangular in shape and perforated for minimum wind loading. This perforation accounts, however, for reduced front-to-back ratios as opposed to solid reflectors. This observation is evident in data which will be presented shortly. Figures 2, 3, and 4 show the ------- FIDIXAL AVIATION AnONAUTICAL CtNTt* OKUHOMA CITY, OKLA. Figure 1. Map of FAA Aeronautical Center, Oklahoma City, Oklahoma, showing radar locations and measurement sites ------- Table 1. Specifications of radars at FAA Center ! Specification ! ; i Frequency (MHz) ' ! i Peak Power (kW) ! Average Power (W) ! Pulse Width (usec) ! Pulse Repetition Frequency ! (Hz) ! Duty Factor ! Antenna Gain (dBi) ! Antenna Rotation Rate (RPM) ! j 3dB Horizontal Beam Width ! (degrees) ! i Pencil ! CSC2 ! Manufacturer ! i Antenna Height (ft.) ! Antenna Width (ft.) ! Height above Ground (ft.) ! j ASR-7 2820 425 336 0.833 950 0.00079 34.0 12.6 1.4 4.9 Texas Instruments 9.0 17.5 27 i ; » i i i i i j i i i t i j i i t j Radar Unit ASR-4B 2720 425 403 ' 0.833 1140 0.00095 34.0 15 1.4 4.9 Texas Instruments 9.0 17.5 75 j i i j i t j i i j j i t j j i i ; j j ARSR-1D 1335 500 ; 4000 360 ; 2880 2 360 0.00072 34.2 3 or 6 1.35 6.2 Rathe on 18.0 42.0 80 ------- Figure 2. ASR-7 radar installation Figure 3. ASR-4B radar installation ------- Figure 4. ARSR-1D radar installation antenna-mount configurations for the ASR-7, ASR-4B, and the ARSR-1D, respectively. Individual antenna heights above ground may be found in table 1. Measurement locations, numerically designated and shown in the map of figure 1, are described as follows in the order in which they were surveyed: Location 1. This location was on a service road of the Center generally to the west of the transmitter site and was used for measure- ments from the stationary ASR-7 radar antennas. Measurements were made at ground level with the radar antenna pointed directly toward us within the accuracy of visual means. A portable electric generating unit powered the measurement instrumentation contained in the rear of a station wagon vehicle. Figure 5 depicts the general measurement layout at location 1. Figure 6 shows the ASR-7 antenna in the background (the closest radar to our location) at a distance of approximately 880 feet. ------- Figure 5. Measurement layout at location 1 Figure 6. Three radars as viewed from location 1 ------- Location 2. This measurement site was located atop the roof of the Civil Aeromedical Institute (CAMI) building, almost due south of the transmitter site. The site was chosen because of the inclement weather conditions; it allowed the instrumentation to be located in the hallway of the CAMI top floor (figure 7) and the reception antenna could be placed on the roof for correct alignment (figure 8). The signal cables were connected to the instrumentation via an access door in the roof and a janitor closet below, leading to the hallway (figure 9). This arrange- ment was convenient to carefully view the stationary ASR-4B radar antenna located atop the Air Navigation Facilities Building Number 2 approximately 1790 feet away. The receiving antenna height was approximately 45 feet as compared with the ASR-4B antenna height of 75 feet, placing us more into the radar antenna's main lobe than previously. At this position, a measurement was made of the ASR-4B front-to-back ratio by carefully rotating the antenna exactly 180 degrees from our monitoring location. Figure 7. Equipment in hallway of CAMI top floor ------- Figure 8. Antenna on roof of CAMI Figure 9. Roof access door at CAMI and signal cables 9 ------- Location 3. The final measurement location consisted of three positions within the boundaries of the multiple purpose building (MPB). This building houses the FAA's extensive Oklahoma computing center. Concern over actual radar fields permeating this complex had been expressed by Data Services personnel prior to our field trip. This con- cern was directed toward the anticipated installation of a series of new computer terminals, with the possible consequent interference problems, in the second floor of the multiple purpose building. This area is directly in the line-of-sight to two of the three radars in daily operation and only about 750-1000 feet away, depending on the particular radar. Figure 10 shows the radar configuration as viewed from the second floor. The monitoring site elevation on the second floor was approximately 15 feet above ground as.compared to the ARSR-1D antenna at 80 feet above ground. During the trip, coordination was made with the Data Services ARSR-1D I ASR-4B Figure 10. Radar configuration from second floor of MPB, location 3 10 ------- Division, and field measurements were subsequently made in the ground floor computer operations room (see figure 11), the north ground level lobby, and the proposed terminal installation area. EMI potential to the terminals was of concern due to the existing radar installations and to the expectation of the installation of a new ARSR-3, more powerful than any the radars in current operation. Based on measurements of the presently used ARSR-1D and specifications for the new ARSR-3, it was hoped that estimates of anticipated radiated fields might be made prior to the new radar installation. A brief summary of the salient characteristics of the ARSR-3 is given in table 2. Spectral measure- ments in the computer room at location 3 included a look at the AM standard broadcast and the FM broadcast bands. Measurement data indicat- ed the shielding effectiveness of the computer room itself. Figure 11 shows the vertical antenna setup for low frequency band measurements. The field measurements made at location 3, on the second floor, represented the highest intensities found at any of the locations and, consequently, were the most interesting. ' Figure 11. Measurement setup in computer room, ground floor MPB 11 ------- Table 2. Salient characteristics of anticipated new ARSR-3 Approximate frequency : 1260 MHz Peak transmitter power : 5 MW Pulse width : 2 sec Pulse repetition frequency: 294-389 Hz (nominally 350 Hz or more) Antenna gain : 34.5 dB MEASUREMENT APPROACH This section describes the approach used in making field measure- ments of the radars and gives the analysis of a representative sample measurement. Figure 12 presents in block format the measurement system consisting of the following essential components: (a) a calibrated microwave frequency range spectrum analyzer, (b) a set of two calibrated transmission lines, (c) a dual polarized planar log periodic antenna, and (d) an oscilloscopic camera for recording spectral data from the spectrum analyzer. Also shown in the diagram is a microwave tracking preselector and a 100 dB variable step attenuator. Table 3 lists specific instrument models used in this study. The attenuator provided spectrum analyzer input protection from unusually high fields while the preselector was available to minimize intermodulation products, if necessary. Figure 13 depicts the actual instrumentation arrangement. The basic measurement process consists of making a signal amplitude determination on the spectrum analyzer. This amplitude is that of the signal arriving at the analyzer input port via the transmission line and is ultimately related to the total power absorbed by the reception antenna. A special technique of correcting the observed signal amplitude must be made to compensate for pulse desensitization in the analyzer due to the pulsed nature of the incident fields. This correction procedure will be discussed after a description of the characteristics of the remaining measurement system. 12 ------- DUAL POLARIZED LOG PERIODIC ANTENNA VERTICAL SIGNAL CABLE c HORIZONTAL SIGNAL CABLE STEP ATTENUATOR TRACKING PRESELECTOR SPECTRUM ANALYSER OSCILLOSCOPE CAMERA Figure 12. Block diagram of measurement system 13 ------- Table 3. Measurement equipment summary Equipment Designation Spectrum analyzer: Variable persistence display High resolution IF section RF tuning section (10 MHz -18 GHz) RF tuning section (500 kHz-1250 KHz) Tracking preselector Precision step attenuator Dual polarized planer log periodic antenna Biconical dipole antenna Broadband rod antenna Model 141T 8552B 8555A 8554L 8445A AE 119-99-01-01 APX-1293 94455-1 95010-1 Manufacturer HP HP HP HP HP Weinschel ! AEL i ! Singer t ! Singer 1 14 ------- Figure 13. Arrangement of measurement equipment in station wagon Through the relation between an antenna's effective capture area, Ae, and its gain, G, and the free space wavelength X, Ae = G A2 4 TT the effective area of the log periodic was obtained by reference to figure 14, a plot of antenna gain vs. frequency. Next the signal is coupled to the selected transmission line A or B and is fed to the analyzer input. In actuality, a part of this signal power is not effectively coupled into the analyzer due to both attenuation effects of the transmission line coax and mismatch losses, both at the antenna- coax junction and the coax-analyzer junction. Accordingly, a characterization of the signal cables was obtained through use of an automated microwave network analyzer to determine both loss (attenuation) and VSWR (a measure of mismatch); see figures 15 and 16, respectively. 15 ------- 8.4 - 8.2 8.0 7.8 7.6 S 7.4 S7-2 7.0 6.8 6.6 6.4 I _L DATA SUPPLIED BY AEL I I 456 FREQUENCY (GHZ) 8 -10 Figure 14. Mean gain of AEL APX-1293 crossed planar log periodic antenna 30 z o D Z 25 20 15 10 I I I J I S .6 .7 .8 .9 1 FREQUENCY (GHZ) 16 Figure 15. Typical signal cable loss ------- e I 1.1 — 1.0 - FREQUENCY (GHZ] Figure 16. Typical signal cable VSWR Using the VSWR calibration of the antenna from figure 17, a complete analysis of the signal path loss was obtained for each measurement frequency. In this fashion observed received powers could be related to the actual incident field densities. The dual polarized antenna was utilized to facilitate measurements of both horizontal and vertical field components of the incident radiation, and thus through addition of components arrive at the total radiated field intensity (expressed either in terms of power density or field strength—see appendix B for the relationship between field strength and power density in free space). In practice, the antenna was oriented such that one array was positioned vertically and the other horizontally. Once the signal is applied to the spectrum analyzer input, a careful interpretation of the resulting pulsed spectrum must be made. Details of the theory of pulsed spectra analysis will not be given here but only the procedures for recording and reducing the collected data. Readers are referred to reference 4 for specific details regarding the theory. 17 ------- 4 5 FREQUENCY (GHZ) Figure 17. VSWR of AEL APX-1293 crossed planar log periodic antenna In essence, a measurement of the signal's pulse width and PRF are made by observing the signal display with different analyzer settings. From these measurements and knowledge of the analyzer's bandwidth, the observed signal amplitude (power) may be corrected for the desensitiza- tion caused by application of pulsed, low-duty-cycle signals. In this process various conditions must be met to allow an accurate measurement of the signal power. These conditions can be found in reference 4. Nevertheless, two essential displays of the received signal must be produced: (1) the main lobe of the received pulsed spectrum from which the width is determined, allowing identification of the pulse width of the signal, and (2) the pulse repetition rate of the signal by looking in the time domain. Figure 18 shows a typical pulse spectrum from the analyzer's display. This display was produced from a laboratory micro- wave pulse generator. In practice, radars show nonsymmetrical spectra due to frequency modulation (FM) occurring during the pulse process. The dispersion in this example was 2 MHz/division. Figure 19 shows a more careful examination of the main lobe of a pulsed spectrum (ASR-7 as observed from location 1) where it is seen that the dispersion is approximately 2.6 MHz wide. Finally-, in the time domain of the ARSR-1D, from Figure 20, we see the PRF to be about 356 Hz (a 5 msec/div. time base was employed for this case) . From measurements similar to these 18 ------- Figure 18. Typical pulse spectrum from laboratory generator Figure 19. Main lobe of pulse spectrum. Spectrum analyzer scan width/division set at 1 MHz 19 ------- Figure 20. Picture in time domain of PRF and relating to the analyzer's bandwidth characteristics, the peak and average power, pulse width, PRF, and duty factor of the observed signal may be determined. Using this procedure, measurements were obtained on the radars described to determine principally the peak and average incident power density and field strength. Again, it must be stressed that proper operation of the spectrum analyzer must be maintained by carefully observing control settings for the specific analyzer function. For example, loading of the first mixer in the analyzer must be controlled in order that saturation does not occur, thereby, causing an erroneous indication of detected power. When spectral observations were made at lower frequencies, two different antennas were available for use: (1) a biconical dipole for the VHF band and (2) a broadband vertical monopole for the MF-HF spectrum. A summary of the specific equipment which was used is given in table 3. 20 ------- Table 4. Measurement system correction summary I J Frequency J (MHz) i ! j 1335 ! ! 2720 ! j 2820 ! t Ae (cm2) 185.7 55.2 51.9 j j j j J j ! t ! ; t t Insertion Cable A 12.5 21.6 22.4 j j J ! ; j j ! i Loss (dB) Cable B 12.2 20.8 21.2 RESULTS AND OBSERVATIONS Reduction of all data was done on the basis of the spectral photographs of oscilloscopic displays after returning from the field trip. As an aid in reducing the data, a system correction summary (see table 4) was prepared which incorporated the necessary correction terms for antenna effective area and cable insertion losses (both attenuation and mismatch loss). Table 5 gives a summary of the totality of field measurements made; principally the radar measurements are the only absolutely quantitative results, while any other measurements at lower frequencies were of a relative amplitude nature. Only relative field values were considered because of the problem of antenna directionality and source geographic distribution. To obtain absolute amplitude measurements of field intensity it is necessary to know the sensing antennas gain in the direction of each specific source. When making swept frequency measurements of signals arriving from many different directions, the use of an omni-directional antenna is necessary to allow accurate comparisons of signal intensities. Additionally, it was not the real purpose of this study to investigate non-radar signals. A listing of these supplementary measurements is given in table 6. All results of radar field intensity measurements have been reported in terms of both incident power density and field strength. Values are indicated for measurements of peak and average field levels for each polarization component (vertical and horizontal) and the total resultant field levels. For convenience of the reader the measurements have been reported in the following manner: 21 ------- Table 5. Summary of radars and measurement locations j i Radar Fields Measured ! ASR-4B Location 1 2 3 Computer room North lobby i ! Rotating i j ! X J j j i ! ! X j i ! X j 2nd floor! x i j ! Stopped i t ! i ! -X j j ! i i i ! ; i j ! ! ASR-7 ! ARSR-1D i ! Rotating t t t ; [ j i ! t j i t j t i ! i ! Stopped ! Rotating ! i i t ! ! ! ! X ! X ! ! ! ! ! ! ! it • ! ! 1 ! j ; i i i j j ! : J J 1 X ! i j ! i i i t Stopped X Table 6. List of supplementary measurements 1. Spectrum search of the frequency range 1160 MHz to 1360 MHz taken from the roof at location 2 with the reception antenna looking north. 2. Measurement of the front-to-back ratio of the ASR-4B antenna taken at location 2. 3. Spectral scan of frequency range *\» 0 to 200 MHz taken in computer room at location 3. 4. Spectral scan of frequency range y 0 to 2 MHz taken in computer room at location 3. 5. Spectral scan of portion of FM broadcast band taken in ground floor laboratory at location 2. 6. Spectral scan of frequency range *> 0 to 2 MHz taken in ground floor laboratory at location 2. 22 ------- Power density : mW/cm2 and dBm/cm2 Field strength: V/m and dB/yV/m where 0 dBm/cm2 is equivalent to 1 mW/cm2 and 0 dB/yV/m is equivalent to 1 yV/m. Results are extensively recorded in tables 7 through 17 . Resultant peak power densities ranged from 90 yW/cm2 to 245 mW/ctn2 and resultant average power densities ranged between 0.06 yW/cm2 and 0.17 mW/cm2. The highest fields measured were at the MPB location on the second floor level, looking out of the window directly toward the ARSR-1D antenna. After our initial measurements at this location with the receiving antenna tripod fixed in height, a survey of the room was accomplished by moving the antenna and looking for the maximum signal. In this fashion, it was observed that the highest power density that could be found was 245 mW/cm2 peak or 961 V/meter. The repetitive auto- matic firing of the electronic shutter in our oscilloscope camera (due to RFI) attested to the fact that the fields permeating the room were high. Yet, in terms of levels which are considered thermally hazardous to humans, no fields which were monitored exceeded any U.S. safety standards on an average power density basis. Reference to appendix A will reveal some current RF safety standards. In comparing measured exposure values with various personnel exposure standards, it should be pointed out that the values indicated in tables 7 through 17 have not taken into account antenna rotation duty factor. If the ARSR-1D antenna is assumed to be rotating, the exposure at the MPB location would be approximately 3 yW/cm2 when averaged over one rotation. In computing the antenna rotation duty factor the 3 dB beam width of the ARSR-1D antenna, using a cosecant-squared beam, was used as the active part of the beam for calculation purposes, where . . a i. c *. 3dB beam width in degrees Antenna duty factor = x>n , a 3 360 degrees With respect to the potential for RF interference to computer terminals which may be installed in the measurement area of the MPB second floor, the following information is taken from the AFSC Design Handbook on Electromagnetic Compatibility (6): "In a typical computer many circuits of the computer do not malfunction under intense electromagnetic field radiation. Circuits in this category are high-level circuits such as flip-flops, AND and OR gates, pulse amplifiers, relay drivers, level inverters, and cathode followers. Low-level circuits of the computer, whose normal input is within the range of 50 mV to 2 V peak-to-^peak, do malfunction when subjected to 23 ------- Table 7. Results at location 1; ASR-7, antenna stopped Field Component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average Power mW/cm2 17.2 0.0160 0.180 1.70 x lO-1* 17.4 0.0160 Density | dBm/cm2 j ! +12.3 j ! -17.9 j ! - 7.5 i ! -37.8 j ! +12.4 i ! -17.9 j j Field ; v/m ; ! 255 ; ! 7.80 j I 26.0 i j 0.80 j ! 256 j ! 7.80 j Strength j dB/yV/m j i 168 i j 138 i I 148 j 5 118 i I 168 j ! 138 ! Table 8. Results at location 1; ASR-*4B, antenna rotating Field Component .- j i Peak vertical ! j Average vertical ! i Peak horizontal ! j Average horizontal ! j Total peak ! j Total average ! ! Power mW/cm2 0.0340 3.30 x 10-5 1.02 x ID"3 5.50 x 10"5 0.0350 8.80 x 10-5 Density j i 5 i t i j j j ! i J j i dBm/cm2 | t -14.7 J i -44.8 i i -29.9 I i -42.6 1 i -14.5 i i -40.5 i ! Field Strength V/m J t 11.3 I 1 0.350 i i 1.96 i t 0.460 t I 11.5 j j 0.570 i i dB/yV/m 141 111 126 113 141 115 24 ------- Table 9. Results at location 1; ARSR-1D, antenna rotating Field Component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Power Density mW/ cm2 0.350 2.30 x'lO'1* 1.48 9.80 x 10~k dBm/ cm2 - 4.6 -36.4 + 1.7 -30.1 1.83 ! + 2.6 Total average ! 1.21 x 10~3 ! -29.2 Field V/m 36.3 0.930 74.7 1.92 83.1 2.10 Strength J dB/viV/m i ! 151 t ! 119 i ! 157 ! 126 i ! 158 ! 126 Table 10. Results at location 2; ASR-4B, antenna stopped t i Field Component J— Peak vertical ! i Average vertical ! Peak horizontal ! j Average horizontal ! j Total peak ! Total average ! Power mW/cm2 5.30 x 10-3 5.20 x 10"6 5,10 x ID'1* 2.71 x 10-5 5.82 x 10~ 3 3.20 x 10-5 Density J dBm/ cm2 ! -22.7 j J -52.8 ! -32.9 j ! ^ -45.6 i ! -22.4 ! -44.9 j t r ! t ! ; i t j t j ! Field Strength V/m j 4.47 i i 0.140 i 1.38 J j 0.319 ! i 4.68 I 0.347 ! dB/uV/m 133 103 123 110 133 111 25 ------- Table 11. Results at location 3, computer room; ASR-4B, antenna rotating • Field Component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average Power Density , Field Strength • mW/cm2 2.71 x 10-1* 2.60 x 1(T7 3.42 x 10~5 3.31 x 10-8 3.00 x 10-1* 2.90 x 10- 7 dBm/cm2 ! V/m • -35.7 -65.8 -44.7 -74.8 -35.2 -65.3 1.01 0.0313 0.358 0.0111 1.06 0.0330 dB/yV/m 120 89.9 111 80.9 120 90.4 Table 12. Results at location 3, computer room; ARSR-1D, antenna rotating Power Density Field Strength e lejua component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average mW/cm2 3.50 x 10-5 2.30 x 10-8 ! 5.51 x 10-5 ! 3.60 x 10~8 9.01 x 10~5 5.93 x 10-8 dBm/cm2 -44.6 -76.4 -42.6 -74.4 -40.5 ! -72.3 j j j 19. I I I I I I I I V/m '/ 0.363 30 x 10- 3 0.455 0.0116 0.582 0.0149 dB/yV/m 111 79.3 113 81.3 115 1 83.5 26 ------- Table 13. Results at location 3, MPB-North Lobby; ASR-4B, antenna rotating Field Component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average i i j ! j ! j j t j i ! j i i Power mW/cm2 0.107 1.04 x 10~4 0.0337 3.30 x 10"5 0.141 1.37 x lO"4 i Density J J dBm/cm2 J ; i ! - 9.7 ! i i ! -39.8 ! i i ! -14.7 ! i t ! -44.8 ! j ; ! -8.5 ! j j ! -38.6 ! Field V/m 20.1 0.626 11.3 0.353 23.0 0.719 Strength j dB/yV/m j ! 146 ! ! 116 i ! 141 j ! Ill j ! 147 ! ! 117 Table 14. Results at location 3, 2nd floor-MPB ARSR-1D, (500 kW) J Power Field Component . J mW/cm2 i- Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average 0.0778 5.30 x 10-5 7.78 5.31 x 10-3 7.90 5.42 x 10- 3 , antenna stopped Density J Field 1 1 J dBm/cm2 J V/m • • ! v ! ! -11.1 i ! -42.8 ! + 8.9 i ! -22.8 ! + 6.2 ! -22.7 17.1 0.447 171 4.47 172 4.5 • » Strength • dB/yV/m 147 113 ! 165 ! ! 133 I 165 ! 1.33 27 ------- Table 15. Results at location 3, 2nd floor-MPB; ARSR-1D, (4 MW) , antenna stopped Field Component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average i j ; i i • i • i i j i Power Density J Field Strength mW/cm2 J dBm/cm2 J V/m i 0.980 ! - 0.1 6.60 x 10-1* ! -31.8 i 61.8 0.0418 62.8 0.0425 +17.9 -13.8 +18.0 -13.7 60.8 1.58 483 12.6 487 12.7 dB/yV/m 156 124 174 142 174 142 Table 16. Results at location 3, 2nd floor-MPB; ARSR-1D, (4 MW, maximum field), antenna stopped Field Component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average Power mW/cm2 49.1 0.0332 196 0.132 245 0.165 Density J dBm/cm2 I +16.9 Field Strength V/m ; dB/viV/m 430 I -14.8 i 11.2 t +22.9 i 860 ! - 8.8 i 22.3 ! +23.9 ! 961 » - 7.8 i 24.9 173 141 179 147 180 148 28 ------- Table 17. Results at location 3, 2nd floor-MPB; ASR-4B, antenna rotating Field Component Peak vertical Average vertical Peak horizontal Average horizontal Total peak Total average J Power Density j mW/cm2 j j j ! 0.673 ! ! ! ! 6.61 x 10-1* ! j 1 ! 0.0847 ! ! 8.30 x 10-5 ! i i ! 0.758 ! j j ! 7.43 x 10-" ! i j dBm/ cm2 - 1.7 -31.8 -10.7 -40.8 -1.2 -31.3 • J ; • » j j j ! ; j ! j t j Field Strength V/m J dB/yV/m 50.4 1.6 17.9 0.600 154 1.24 145 115 1 53.5 ! 155 j 1.7 ! 125 ! 29 ------- moderate field intensities. Sense amplifiers of the memory element malfunction at a field intensity in the region of 15 V per meter peak; the tuning fork oscillator of the out- put section will malfunction near 40 V per meter peak. Data conversion receivers of the input section malfunction at 50 V per meter peak. The flux amplifier of the output section fails at 100 V per meter. In actual usage, the susceptibility data levels of malfunction must be identified with the specific parameters which characterize the radar." The reference also states "In the remaining group, which represents most of the computer circuits, malfunction does not occur at field intensity levels as high as 400 V per meter peak." It is also noted that susceptible circuits are usually more sensitive when subjected to radiation nearer the low end of the 450-2900 MHz band than to higher frequencies. Polarization is said to be very significant, depending upon the particular computer unit but in general vertical polarization causes more problems than horizontal." On the basis of this information it is not possible to say definitely that a computer terminal placed on the second floor of the MPB would experience interference, but certainly the possibility should be con- sidered when locating the terminals. Peak fields nearing 1 kV/m are very intense fields from almost any electronic equipment interference standpoint. By comparing measured field intensities from the ASR-4B radar made in the computer room vs. the north lobby of the MPB, an estimate of the building attenuation effectiveness was determined. A nominal 26 dB shielding effect was found at the ASR-4B frequency of 2720 MHz. During the process of measuring field levels we also determined, by measurement, the observed PRF and pulse width of each radar. Table 18 reviews the observed values. / An interesting effect observed was that of signal polarization. It was found, as one would expect, that the extent of depolarization of the emitted radar signal seemed to be a function of the complexity of the surrounding reception environment; the more complex the environment, the more equal the two wave components became. For example, the ratio of vertical to horizontal field density was 15.2 dB at location 1 where the area was fairly in the clear. When determined at location 2 the ratio was 10.2 dB, apparently due to the roof top clutter of air conditioning equipment and other nearby obstacles. The computer room measurement made inside the MPB with building shielding showed the ratio to be only 9.0 dB. 30 ------- Table 18. Measured PRF and pulse width Location Radar Measured PRF Measured Pulse Width (Hz) (ysec) 1 1 1 2 , 3 ASR-7 ASR-4B ARSR-1D ASR-4B ARSR-1D 1185 1079 356 1083 355 0.77 0.91 1.85 0.91 1.90 Figures 21 and 22 are included for illustration of typical pulse spectra observed from the ARSR-1D and ASR-4B, respectively. Notice the effect of frequency modulation resulting in a nonsymmetrical signature. A measure of the front-to-back ratio of the ASR-4B radar antenna was accomplished at location 2. A picture of the radar spectrum was taken when the antenna was pointed directly toward our reception antenna. Subsequently the same spectrum was photographed when the ASR-4B antenna was directed 180 degrees opposite to our location. An F/B ratio of 16 dB is apparent from the relative power at the peaks of each signal. F/B ratios on this order are typical when the paraboloidal reflector is not solid in construction. It was noted in the course of these measurements, that when the radar antenna was rotating, it was much more difficult to generate a useful spectral display on the analyzer. This is related to the obvious interplay between spectrum analyzer scan time and antenna rotation rates. Thus, when the radar is beaming only momentarily toward the receiver, it rapidly becomes difficult to utilize appropriately fast enough scan rates on the analyzer to produce a meaningful display. Under these circumstances the use of a variable persistence oscilloscope screen becomes mandatory for meaningful and relatively rapid identification of radar spectra from rotating antennas. Once the primary peak of the radar spectrum signature was located, it was found that a useful technique for accurately determining the peak signal amplitude involved reducing the analyzer's 31 ------- Figure 21. ARSR-1D pulse spectrum. Center frequency = 1335 MHz, 2 MHz/division Figure 22. ASR-4B pulse spectrum. Center frequency = 2720 MHz, 5 MHz/division 2 ------- frequency dispersion such that it was displaying essentially only the peak lobe of the pulse spectrum. Then the scan rate of the analyzer was increased until many repetitive frequency scans occurred during the time of radar field illumination thus raising the probability of detecting the actual peak power of the signal at precisely the time that the main beam of the radar was directed at the reception antenna. Of course, during this process care must be exercised that an uncalibrated condition does not develop (i.e., analyzer scan time does not become too fast for the bandwidth and scan width settings). Our experiences with using a spectrum analyzer for these types of field measurements did not reveal a significant problem with intermodula- tion products giving rise to erroneous signals on the spectrum display. One good test for determining the validity of the observed signals is to insert a fixed amount of attenuation into the input port and look for a corresponding decrease in measured signal amplitude. Spurious responses will decrease by significantly more than the amount of added attenuation. In certain circumstances intermod was observed when all three radars were operating simultaneously and all three antennas became momentarily synchronized and illuminated our sampling locations at the same time. Under such conditions it became tedious to extract a good spectrum signature from a revolving antenna. Figure 23 shows the spectrum, ^0 to 2 MHz, observed inside the building, on the ground floor at location 2. The local standard AM broadcast stations are visible with the center frequency on the display set at 1.0 MHz. Local radio station KOMA transmitting on 1.520 MHz is seen as the strongest signal being received at that location. Figure 23 is a plot of the relative power of the received signals and shows-that KOMA had a signal strength on the order of 10 times that of any other broadcast signal (a 20 dB greater received power). Also notice, though, the extensive noise peaks, particularly below about 600 kHz. A similar measurement in the computer room at location 3 showed essentially no AM radio signal reception but a lot of broadband noise across the band. Such noise pickup was probably due to the electric motors used in air conditioning equipment located inside the room at many locations for maintaining correct room temperature. A scan around 100 MHz in the computer room (figure 24) showed large amounts of broadband noise and what appeared to be some FM signals penetrating the building shielding. 33 ------- Figure 23. Spectrum scan, 0-2 MHz, observed inside building, on ground floor at location 2 Figure 24. VHF scan en computer room, center frequency 100 MHz, 2 MHz/division 34 ------- CONCLUSIONS Experience obtained during this field study verified that the use of spectrum analyzers as sensitive scanning detectors is required for accurate and meaningful quantitation of microwave exposure from radar. The spectrum analyzer allows accurate determination of exposure levels from rapidly rotating radar antennas unlike conventional microwave hazard survey meters with fairly long response times. The high sensi- tivity provides a capability of examining radiation levels, signifi- cantly below thermalizing levels, which may be significant in device interference problems. Additionally the spectrum analyzer provides a means of searching through a wide spectrum of frequencies for identification of particular radiofrequency sources of interest from an exposure standpoint. Though spectrum analyzers provide a practical means of monitoring environmental electromagnetic radiation exposures, accurate determina- tion of mean exposure levels from bands containing a multiplicity of intermittent radiofrequency signals (not under the observer's control) requires the addition of some form of automated spectral data collection system with an interface to the analyzer. A description of such a system currently under development by EPA will be forthcoming in the near future. Typical fields and specific technical comments on the application of spectrum analyzers to their measurement as determined in this study are summarized below. (a) Accurate radar field measurements from rotating antennas are possible though more difficult than from non-rotating antennas. Appropriately narrow frequency scans facilitate accurate identifica- tion of the spectrum signatures of individual radars when the antennas are rotating and more than one radar is operating in the same general geographic vicinity and frequency range. (b) When making measurements in an area of relatively intense radar fields, appropriate shielding of the equipment is useful to prevent inadvertent radiofrequency interference to the spectrum analyzer itself and consequent erroneous signal power determination. (c) For relatively wide frequency scans, the use of frequency pre-selection via filters is useful to prevent intermodulation pro- ducts from occurring in the spectrum analyzer and consequent indica- tion of false signals. (d) Exposure field distributions, particularly inside of buildings, may be very complex with the resulting field intensity being extremely dependent on position. Thus, a careful survey of the general area of interest may reveal significantly different exposure levels. 35 ------- (e) Ground level peak field intensities from any one of the radars monitored are high enough to warrant consideration of the potential for interference to susceptible electronic equipment. In addition to these conclusions, several observations were made which may have practical implications in terms of FM operations at the Center. The relatively high levels of radiation found on the second floor of the MPB may degrade terminal performance due to radio- frequency interference. Peak field strengths as high as 961 V/m were observed on the second floor t>f the MPB due to the ARSR-1D radar where new computer terminals may be situated in the future. Maximum average power density was measured as 0.165 mW/cm2 at this location. The planned installation of a new ARSR-3 in the near vicinity with its higher peak power, will add to the potential for equipment degradation. Shielding could be an effective way to reduce radiofrequency inter- ference by covering windows with a fine wire mesh. A significant reduction in electromagnetic fields in the shielded computer room of the MPB is demonstrated by the 65 dB lower'intensity values as compared with those on the second floor. Appendix D contains shielding data for two types of wire mesh for a wide range of frequencies. Ground level peak field strengths as high as 256 V/m were measured from the ASR-7 radar. Average power density was 0.0160 mW/cm at this location. Radiation levels found in any location measured from any source did not exceed the OSHA guide (8) for occupational personnel microwave exposure. RECOMMENDATIONS Since all high power civilian ATC radar installations are operated by the FAA, a review of records might not prove too difficult to attempt identification of other geographic areas where unusual exposure condi- tions may exist. For example, a search for radar installations in close proximity to multi-story buildings might reveal areas where potential RFI could be detrimental to critical electronic systems. For purposes of relating measured field intensities to predicted values based on the radar's power and antenna characteristics, it is important to be able to accurately determine the elevation angle from the reception point to the radar antenna. This would probably best be accomplished by use of a precision transit. Additionally, some means must be provided for accurately measuring the distance from the radar to the reception site. Finally, as an aid in precisely directing the main antenna lobe toward the measurement location, some form of con- venient communication should be available, such as walkie-talkies, so that measurement personnel may indicate to the radar operator when maximum signal strength is observed. 36 ------- ACKNOWLEDGMENTS The authors are especially grateful to those individuals who assisted in the successful conduct of this field trip: Dr. Robert N. Thompson and Mr. Jim Langwell of the Industrial Hygiene Section in the FAA's Civil Aeromedical Institute, for their excellent cooperation and coordination of facilities and personnel involved in this measurement study; Mr. Clayton A. Taylor of the Radar Section, Airway Facilities Branch, FAA Academy for his coordination of equipments, assistance, and patience during the measurement period; Mr. John F. Rieger of the FAA Data Services Division for his cooperation and coordination of the measurements at the computing center in the multipurpose building; Mr. Tom Andrews and Mr. Peter Brown of the Walter Reed Army Institute of Research, Department of Microwave Research, Silver Spring, Maryland, for their assistance in calibration of the signal cables used in this project. Finally, the authors wish to acknowledge Mrs. Vicki Gocal for her assistance in the typing of this manuscript. 37 ------- REFERENCES 1. TELL, R. A. Environmental Nonionizing Radiation Exposure: A Preliminary Analysis of the Problem and Continuing Work Within EPA, in Proceedings of a Session on Environmental Exposure to Nonionizing Radiation, Annual Meeting of the American Public Health Association, Atlantic City, New Jersey, November 14, 1972. USEPA publication EPA/ORP 73-2. 2. MUMFORD, W. W. Some Technical Aspects of Microwave Radiation Hazards, Proceedings of the IRE, February 1961, pages 427-447. 3. U.S. AIR FORCE. Technical Manual T. 0. 31Z-10-4, Electromagnetic Radiation Hazards, August 1, 1966, revised June 1, 1971. 4. Data base request DB-1579, ACV-1, from the Electromagnetic Compatibility Analysis Center, North Severn, Annapolis, Maryland, August 22, 1973. 5. HEWLETT PACKARD. Spectrum Analysis...Pulsed RF, Application Note 150-2, Hewlett-Packard, 195 Page Mill Road, Palo Alto, California 94306, printed November 1971. 6. U.S. AIR FORCE. U.S. Air Force Design Handbook AFSC DH 1-4, Electro- magnetic Compatibility, second edition, revision No. 2, issued at Wright-Patterson Air Force Base, Ohio, January 10, 1973. 7. AMERICAN NATIONAL STANDARDS INSTITUTE. Safety Level of Electromagnetic Radiation with Respect to Personnel. Rep. ANSI-C 95.1, 1966. 8. DEPARTMENT OF LABOR. Occupational Safety and Health Administration, Federal Register, Vol. 36, No. 105, May 29, 1971, Section 1910.97 Nonionizing Radiation. Effective August 27, 1971. 9. U.S. DEPARTMENTS OF THE ARMY AND THE AIR FORCE. Control of Hazards to Health from Microwave Radiation, Rep. TB MED 270/AFM 161-7, December 1965. 10. AMERICAN CONFERENCE OF GOVERNMENTAL INDUSTRIAL HYGIENISTS. Threshold Limit Values of Physical Agents with Intended Changes Adopted by ACGIH for 1971 (Amer. Conf. of Governmental Industrial Hygienists Publ.), Cincinnati, Ohio, 1971. 11. ACADEMY OF MEDICAL SCIENCE. Safety Standards and Regulations for Handling Sources of High, Ultrahigh and Superhigh Frequency Electro- magnetic Fields, AMN (Academy of Medical Sciences), USSR, Russian, No. 848-70, March 30, 1970, pp. 3-34. 38 ------- APPENDIX A. SOME SELECTED MICROWAVE EXPOSURE STANDARDS , ANSI. OSHA110 MHZ-100 GH2KREFEHENCES 7,81 ,,U.S. ARMY-AIR FORCE (300 MHZ-300 GHZ) {PRACTICAL ENFORCEMENT LIMIT. 55 mW/cm2) (REFERENCE 91 VACGIH 1100 MHZ-100 GHZ) (REFERENCE 10) USSR (300 MHZ-300 GHZ) (REFERENCE 11) USSR NON.OCCUPATIONAL (300 MHZ-300 GHZ) (REFERENCE 11) TIME OF EXPOSURE (mini Notes on Exposure Standards U.S. Army-Air Force The exposure power density may increase to a maximum of 100 m for periods of exposure less than 60 minutes according to the relation- ship: T = 6000 where w2 T = time for exposure permitted w = power density in mW/cm^ 39 ------- Under no circumstances may the exposure exceed 100 mW/cm^. In actual practice the maximum allowable exposure is limited to 55 mW/cm^ which corresponds to a 2 minute duration from the above formula. For scanning antennas, the stationary exposure is first determined and then the rotational property of the antenna is taken into account to arrive at a calculated time-averaged exposure. However, if the stationary exposure is 100 mW/cm2 or greater access is forbidden and the reduction in exposure which might be obtained by taking rotation into account is not allowed. The higher exposures may occur during a one-hour period after which it may be repeated. ANSI-OSHA The ANSI and OSHA standards are practically the same and specify that for exposure periods less than 0.1 hour, an exposure energy density of 1 mW-hr shall not be exceeded. These standards, then, place no upper cm^ limit on the allowable exposure as long as an appropriately short period is used. The higher exposure may occur during a 0.1 hour period after which it may be repeated. Exposure for periods greater than 0.1 is 10 USSR The Soviet standard also specifies allowable exposure fields for other frequency bands: 100 kHz - 30 MHz, 20 V/m electric field 100 kHz - 1.5 MHz, 5 A/m magnetic field 30-300 MHz, 5 V/m electric field. In the frequency range of 300 MHz to 300 GHz, occupationally exposed individuals are limited to 10 yW/cm^ for periods greater than 2 hours; from 15 minutes to 2 hours the limit is 100 yW/cm^, and for exposures shorter than 15 minutes, 1 mW/cm . For non-occupationally exposed per- sons the Soviet standard specifies an upper limit of 1 yW/cm (this level might be interpreted as an environmental level standard for the public as a whole) . 40 ------- POWER DENSITY (dBm/cm2) CU O CO a> a> •H CO § I 1 +J bO C Q) i-i 4-1 CO § ("•/A) H19N3H1S Q13M 41 ------- Appendix C. Voltage and power ratios to dB VOLTAGE RATIO 1.0000 .9988 .9977 .9964 .9954 .9943 .9931 .9920 .9908 .9897 .9886 .9772 .9661 .9550 .9441 .9333 .9226 .9120 .9016 .8913 .8810 .8710 .8610 .8511 .8414 .8318 .8222 .8128 .8035 .7943 .7*52 .7762 .7474 .7586 .7499 .7413 .7328 .7244 .7161 .7079 .6998. .6918 .6839 .6761 .6683 .6607 .6531 .6457 .6383 .6310 .6237 .6166 .6095 .6026 .5957 .5888 .5821 .5754 .5689 .5623 .555* .5495 .5433 .5370 .5309 .5248 .5188 POWER RATIO 1.0000 .9977 .9954 .9931 .9908 .9886 .9863 .9840 .9817 .9795 .9772 .9550 .9333 .9120 .8913 .8710 .8511 .8318 .8128 .7943 .7762 .7586 .7413 .7244 .7079 .6918 .6761 .6607 .6457 .6310 .6166 .6026 .5888 .5754 .5623 .5495 .5370 .5248 .5129 .5012 .4898 .4786 .4677 .4571 .4467 .4365 .4266 .4169 .4074 .3981 .3890 .3802 .3715 .3631 .3548 .3467 .3388 .3311 .3236 .3162 .3090 .3020* .2951 .2884 .2811 .2754 .2692 dB 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 VOLTAGE RATIO .0000 .0012 .0023 .0035 .0046 .0058 .0069 .0081 .0093 .0104 .012 .023 .035 .047 .059 .072 .084 .096 .109 .122 .135 .148 .161 .175 .189 .202 .216 .230 .245 .259 .274 .288 .303 .318 .334 .349 .365 .380 .396 .413 .429 .445 .462 .479 .496 .514 .531 .549 .567 .585 .603 .622 .441 .640 .679 .698 .718 .738 .758 .778 .799 .820 .841 .862 .884 .905 .928 POWER RATIO .0000 .0073 .0046 .0069 .0093 .0116 .0139 .0162 .0186 .0209 .023 .047 .072 .096 .122 .148 .175 .202 .230 .259 .288 .318 .349 .380 .413 .445 .479 .514 .549 .585 .622 .440 .498 .738 .778 .820 .862 .905 .950 .995 2.042 2.089 2.138 2.188 2.239 2.291 2.344 2.399 2.455 2.512 2.570 2.630 2.692 2.754 2.818 2.884 2.951 3.020 3.090 3.162 3.234 3.311 3.388 3.447 3.548 3.631 3.71S VOLTAGE RATIO .5129 .5070 .5012 .4955 .4898 .4842 .4786 .4732 .4477 .4424 .4571 .4519 .4447 .4416 .4345 .4315 .4266 .4217 .4169 .4121 .4074 .4027 .3981 .3936 .3890 .3846 .3802 .3758 .3715 .3673 .3431 .3589 .3548 .3508 .3467 .3428 .3388 .3350 .3311 .3273 .3234 .3199 .3142 .2985 .2818 .2441 .2512 .2371 .2239 .2113 .1995 .1884 .1778 .1585 .1413 .1259 .1122 .1000 .03162 .01 .003142 .001 .0003142 .0001 .00003142 io-» POWER RATIO .2430 .2570 .2512 .2455 .2399 .2344 .2291 .2239 .2188 .2138 .2089 .2042 .1995 .1950 .1905 .1862 .1820 .1778 .1738 .1698 .1440 .1422 .1585 .1549 .1514 .1479 .1445 .1413 .1380 .1349 .1318 .1288 .1259 .1230 .1202 .1175, .1148 .1122 .1094 .1072 .1047 .1023 .1000 .08913 .07943 .07079 .04310 .05623 .05012 .04467 .03981 .03548 .03142 .02512 .01995 .01585 .01259 .01000 .00100 .00010 .00001 -JO-' 10-' 10" io-» io-« cffi 5.8 5.9 6.0 .1 .2 .3 .4 .5 .4 .7 4.8 4.9 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 16.0 17.0 18.0 19.0 20.0 30.0 40.0 50.0 40.0 70.0 80.0 90.0 100.0 VOLTAGE RATIO 1.950 1.972 1.995 2.018 2.042 2.045 2.089 2.113 2.138 2.143 2.188 2.213 2.239 2.245 2.291 2.317 2.344 2.371 2.399 2.427 2.455 2.483 2.512 2.541 2.570 2.400 2.430 2.441 2.492 2.723 2.754 2.784 2.818 2.851 2.884 2.917 2.951 2.985 3.020 3.055 3.090 3.126 3.162 3.350 3.548 3.758 3.981 4.217 4.447 4.732 5.012 5.309 5.423 4.310 7.079 7.943 8.913 10.000 31.420 100.00 316.20 1,000.00 3.162.00 OfflOO.OO 31,420.00 10' POWER RATIO 3.802 3.890 3.931 4.074 4.149 4.244 4.345 4.447 4.571 4.477 4.786 4.898 5.012 5.129 5.248 5.370 5.495 5.623 5.754 5.888 6.026 6.144 4.310 6.457 6.407 6.741 6.918 7.079 7.244 7.413 7.586 7.742 7.943 8.128 9.318 8.511 8.710 8.913 9.120 9.333 9.550 9.772 10.000 11.22 12.59 14.13 15.85 17.78 19.95 22.39 25.12 28.18 31.62 39.81 50.12 63.10 79.43 100.00 1,000.00 0,000.00 10" 10' 10' 10* 10* 10" 43 ------- Appendix D. Attenuation effectiveness of wire mesh cloth" Frequency (MHz) 0.01 0.03 0.06 0.1 0.3 0.6 1.0 3.0 r Attenuation of Copper 18x18 22x22 103 104 105 105 105 103 101 94 6.0 89 10.0 ! 85 30.0 ! 75 60.0 ! 69 100.0 ! 65 300.0 ! 55 600.0 ! 49 1000 ! 45 3000 ! 35 6000 ! 29 10000 ! 25 ! t . .6 ! 109.1 .7 ! 110.2 .4 ! 110.2 .4 ! 113.6 .0 I 110.5 .4 ! 108.9 .3 ! 106.8 .5 I 100.0 .3 ! 94.8 • -L .8 Q .6 Q .9 • J .9 .9 • J 90.6 81.3 • 75.4 71.0 61.4 55.4 51.0 41.4 35.4 31.0 Radiated Field i • i • i * T • t • t • t • i . t • i • i • t • ! i i t (dB) Galvanized 22x22 137.7 135.4 132.1 129.1 120.8 115.1 110.8 101.4 95.4 91.0 81.4 75.4 71.0 61.4 55.4 51.0 41.4 35.4 31.0 i . t • t • i • i . t • i . i . i • t • i I ! i I Steel 26x26 143.9 141.6 138.3 135.3 127.0 121.3 117.0 107.6 101.6 97.2 87.6 81.6 77.2 67.6 61.6 57.2 47.6 41.6 37.2 jData taken from reference 6. 45 ------- THE ABSTRACT CARDS accompanying this report are designed to facilitate information retrieval. They provide suggested key words, bibliographic information, and an abstract. The key word con- cept of reference material filing is readily adaptable to a variety of filing systems ranging from manual-visual to electronic data processing. The cards are furnished in triplicate to allow for flexibility in their use. ------- RF PULSE SPECTRAL MEASUREMENTS IN THE VICINITY OF SEVERAL AIR TRAFFIC CONTROL RADARS, EPA-520/1-74-005, May 1974. Richard A. Tell and John C. Nelson. ABSTRACT: The purpose of this study was to determine the response characteristics of a microwave scanning spec- trum analyzer in the presence of a relatively intense and complex electromagnetic environment. Measurements of ambient field intensities in the vicinity of three different ground radars used in air traffic control operations. Maximum peak field strengths of 960 V/m were measured about 1000 feet from the radar site. Characteristic radar spectrum signatures were recorded by photographing visual displays on the analyzer CRT. KEY WORDS: Microwave exposure; nonionizing radiation; radar; radiofrequency hazard. RF PULSE SPECTRAL MEASUREMENTS IN THE VICINITY OF SEVERAL AIR TRAFFIC CONTROL RADARS, EPA-520/1-74-005, May 1974. Richard A. Tell"and John C. Nelson. \ ABSTRACT: The purpose of this study was to determine the response characteristics of a microwave scanning spec- trum analyzer in the presence of a relatively intense and complex electromagnetic environment. Measurements of ambient field intensities in the vicinity of three different ground radars used in air traffic control operations. Maximum peak field strengths of 960 V/m were measured about 1000 feet from the radar site. Characteristic radar spectrum signatures were recorded by photographing visual displays on the analyzer CRT. KEY WORDS: Microwave exposure; nonionizing radiation; radar; radiofrequency hazard. RF PULSE SPECTRAL MEASUREMENTS IN THE VICINITY OF SEVERAL AIR TRAFFIC CONTROL RADARS, EPA-520/1-74-005, May 1974. Richard A. Tell and John C. Nelson. ABSTRACT: The purpose of this study was to determine the response characteristics of a microwave scanning spec- trum analyzer in the presence of a relatively intense and complex electromagnetic environment. Measurements of ambient field intensities in the vicinity of three different ground radars used in air traffic control operations. Maximum peak field strengths of 960 V/m were measured about 1000 feet from the radar site. Characteristic radar spectrum signatures were recorded by photographing visual displays on the analyzer CRT. KEY WORDS: Microwave exposure; nonionizing radiation; radar; radiofrequency hazard. AU.S./QOVERNMENT PRINTING OFFICE: 1974 546-319/398 1-3 ------- |