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

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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

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                                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

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                               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

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                                                                   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

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                            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

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                                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

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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.

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     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

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                                                                              FIDIXAL AVIATION
                                                                               AnONAUTICAL CtNTt*
                                                                               OKUHOMA CITY, OKLA.
Figure  1.   Map of  FAA Aeronautical Center,  Oklahoma City, Oklahoma,
            showing radar locations and measurement  sites

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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

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Figure 2.  ASR-7 radar installation
  Figure 3.  ASR-4B radar installation

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                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.

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  Figure 5.  Measurement layout at location 1
Figure 6.  Three radars as viewed from location 1

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     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

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         Figure 8.  Antenna on roof of CAMI
Figure 9.  Roof access door at CAMI and signal cables
                                                                9

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     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

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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

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      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

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              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

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             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

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   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

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      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

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 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

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                               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

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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

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             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

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          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

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       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

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        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

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           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

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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

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           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

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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

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               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

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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

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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

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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

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                                       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

-------