United States
Environmental Protection
Agency
^—
Radiation
Office of
Radiation Programs
Las Vegas, Nevada 89114
ORP/EAD-77-2
April 1977
1EPA
Technical Note
An Investigation of
Broadcast Radiation
Intensities at
Mt. Wilson, California
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Technical Note
ORP/EAD-77-2
AN INVESTIGATION OF BROADCAST RADIATION INTENSITIES
AT MT. WILSON, CALIFORNIA
Richard A. Tell
and
Patrick J. O'Brien
APRIL 1977
U.S. Environmental Protection Agency
Office of Radiation Programs
Electromagnetic Radiation Analysis Branch
P.O. Box 15027
Las Vegas, Nevada 89114
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DISCLAIMER
This report has been reviewed by the Office of Radiation
Programs Las Vegas Facility, U.S. Environmental Protection
Agency, and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recom-
mendation for their use.
11
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PREFACE
The Office of Radiation Programs of the U.S. Environmental Protection
Agency carries out a national program designed to evaluate population
exposure to ionizing and nonionizing radiation, and to promote develop-
ment of controls necessary to protect the public health and safety. This
report describes a survey conducted at Mt. Wilson in the Los Angeles area
to evaluate ambient radio frequency and microwave radiation intensities.
Readers of this report are encouraged to inform the Office of Radiation
Programs of any omissions or errors. Comments or requests for further
information are also invited.
loyd L. Galpin, Director
Environmental Analysis Division
Office of Radiation Programs
111
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CONTENTS
Page
PREFACE iii
LIST OF FIGURES vi
LIST OF TABLES vii
ACKNOWLEDGMENTS viii
INTRODUCTION 1
EQUIPMENT USED IN THE STUDY 6
RESULTS 12
CONCLUSIONS 19
REFERENCES 20
v
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LIST OF FIGURES
Number Page
1 Mt. Wilson Broadcast Complex 2
as Seen from Pavilion Parking Lot
Map of Major Tower Complex on 5
Mt. Wilson
Antenna Factor Graph for Dipole 10
Antenna with 20 Ft of Cable
Dipole Antenna Arrangement; 14
Measurement of Radiation Intensity
at Antenna with NBS Probe
Field Intensities in Post 16
Office, Residence and Yard as
Measured with NBS Probe
VI
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LIST OF TABLES
Number Page
1 TV Stations on Mt. Wilson 3
2 FM Stations on Mt. Wilson 4
3 Technical Specifications for NARDA 7
Electric and Magnetic Field Monitors
4 Technical Specifications for NBS 8
Model EDM-3 Electric Energy
Density Meter
5 Technical Specifications for IFI 9
Model EFS-1 E-Field Sensor
6 Technical Specifications for 10
Tektronix Spectrum Analyzer
Model 7L-13
7 VHP TV Exposure Measurements 17
in Parking Lot
8 UHF TV Exposure Measurements 17
in Parking Lot
9 FM Radio Exposure Measurements 18
in Parking Lot
VII
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ACKNOWLEDGMENTS
The authors would like to extend their appreciation to
the County of Los Angeles Department of Health Services,
Division of Occupational and Radiation Management, and in
particular to Messrs. Bruce Ault, Adam Wiley, and Joe Karbus,
for cooperation and assistance in the support of this study.
The loan of portable survey instrumentation for use in this
study from the National Bureau of Standards, Electromagnetics
Division, Boulder, Colorado, and the Narda Microwave Corporation,
Plainview, New York is also gratefully acknowledged. Special
thanks are given to Mrs. Lois McAllister and Miss Sue Hager
for their efforts in typing this report.
Vlll
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INTRODUCTION
This report describes an investigation of electromagnetic
field intensities at the multistation broadcast installation
located at the top of Mt. Wilson near Los Angeles, California.
Mt Wilson supports transmitting antennas for a total of 27
broadcast stations (12 FM radio stations and 15 television
stations). In June 1975, a gross hazard survey was performed by
the Los Angeles County Department of Health Services using a
Narda Microwave Corporation electric field probe. The results of
this survey indicated that exposures of 6 mW/cm were found near
the Mt. Wilson Post Office. Based on this finding a preliminary
analysis was performed to estimate the potential broadcast radia-
tion levels at Mt. Wilson [1]. The analysis concluded that
ground, level radiofrequency exposures would lie within the 1 28
mW/cm range with the exact exposure level being dependent upon
the particular vertical radiation patterns of the transmitting
antennas which were involved. The vertical radiation pattern is a
measure of the transmitting antenna's ability to focus the power
in the vertical plane with the main beam aimed generally at the
horizon [2]. Past experience by EPA has shown that some FM radio
transmitters emit a radiation lobe almost straight down with an
intensity equal to or greater than that emitted in the main beam.
This finding supported the conclusion that ground level exposures
exceeding 1 mW/cm2 could exist on Mt. Wilson, but due to an
insufficiency of data pertaining to vertical radiation patterns
of VHP and UHF TV stations the upper limit was estimated, con-
servatively, to be as high as 28 mW/cm2.
Exposures of this magnitude (28 mW/cm2) are unquestionably
considered hazardous, and since it was unclear as to what exposure
levels exist on Mt. Wilson, a field investigation was performed
in November of 1975 to conduct measurements of actual radiation
levels. In addition to determining the exposure, it was con-
sidered important to evaluate different measurement techniques
and instrumentation; this was partially accomplished by making
use of a number of different microwave survey probes and a spec-
trum analyzer and sets of calibrated dipole antennas. It was
hoped that the results of this field study could also help to
evaluate other high intensity broadcast source locations throughout
the country and aid EPA in evaluating population exposure to
radiofrequency and microwave fields.
The Mt. Wilson site is probably unique to the entire nation
in terms of source density and total number of stations. It was
even considered that the Mt. Wilson complex might produce an
upper limit nationally for public exposure to electromagnetic
radiation.
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Figure 1 depicts part of the extensive Mt. Wilson broadcast
complex. A station listing is given in Tables 1 and 2 giving
pertinent technical parameters of all FM and TV stations atop Mt.
Wilson. There are no AM standard broadcast stations on Mt.
Wilson. All of the stations together account for a total of 10.2
MW of effective radiated power CERP); 586 kW of this total is due
to the FM radio stations. FM station antennas vary in height
above ground from 100 to 492 feet while TV antenna heights vary
from 82 to 490 feet. Figure 2 is a map of the major tower
complex on Mt. Wilson. It was produced by copying an aerial
photograph and then reducing the size. Cross references for
purposes of station identification and location were made with a
number of information sources [3,4] and personal inspection and
discussion with station personnel on the mountain. There exists
a lower density antenna complex, principally KNXT-TV (channel 2)
and KNX-FM, to the west of the area shown on the map. The Post
Office is seen to be situated within several hundred feet of the
major concentration of broadcast towers on Mt. Wilson.
FIGURE 1. MT. WILSON BROADCAST COMPLEX
AS SEEN FROM PAVILION PARKING LOT
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TABLE 1. TV STATIONS ON MT. WILSON
Power
Visual Aural
KNXT-TV (2)
KNBC-TV (4)
KTLA-TV (5)
KABC-TV (7)
KHJ-TV (9)
KTTV-TV (11)
KCOP-TV (13)
KWHY-TV (22)
KCET-TV (28)
KMEX-TV (34)
KLXA-TV (40)
KBSA-TV (46)
KBSC-TV (52)
KLCS-TV (58)
KVST-TV (68)
46.8
42.7
50.1
166
162
166
170
64.6
1200
500
622
219
800
1906
1925
9.33
7.41
10
25.7
22.9
20
32.4
9.12
240
100
123
138
120
380
385
Latitude
34-13-57
34-13-33
34-13-35
34-13-36
34-13-38
34-13-29
34-13-42
34-13-36
34-13-27
34-13-35
34-13-42.5
34-13-35
34-13-27
34-14-26
34-13-36
Longitude
118-04-18
118-03-55
118-03-56
118-03-59
118-04-00
118-03-47.1
118-04-02
118-03-59
118-03-47
118-03-56
118-04-01
118-03-58
118-03-45
118-03-45
118-03-59
Ant. Ht.
Above
Ground
(Ft)
466
490
240
234
199
237
200
132
363
170
200
138
82
180
126
Total
Power
56.1
50.1
60.1
191.7
184.9
186.0
202.4
73.7
1440.0
600.0
745.0
357.0
920.0
2286.0
2310.0
These data pertain to the stations at the time of the field study, November 1975.
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TABLE 2. FM STATIONS ON MT. WILSON
Call
KPFK-FM
KFAC-FM
KNX-FM
KMET-FM
KLOS-FM
KRTH-FM
KUTE-FM
KKDJ-FM
KOST-FM
KBIG-FM
KBCA-FM
KLVE-FM
Freq.
(MHz)
90.7
92.3
93.1
94.7
95.5
101.1
101.9
102.7
103.5
104.3
105.1
107.5
Total Power =
Power
(kW)
no
59
54
58
68
58.8
0.7
8
12.5
105
18
34
586
Ant.
Ht.
(Ft)
170
142
466
237
234
199
no
200
492
120
100
Latitude
34-13-45
34-13-29
34-13-29
34-13-29
34-13-36
34-13-38
34-13-35
34-13-36
34-13-34
34-13-47
Longitude
118-04-03
118-03-46
118-04-18
118-03-47
118-03-59
118-04-00
118-03-59
118-03-57.
118-03-55
118-04-03
These data pertain to the stations at the time of the field study, November
1975.
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MICROWAVE
KBCA-FM
KPFK-FM
KLVE-FM
KCOP-13
TO OBSERVATORY
KCOP-AUX
KABC-7
KLOS-FM
KWHV-22
KHJ-9
KATH-FM
POST OFFICE
KMEX-34 TRA-|L
KBIG-FM
PAVILLION
MEASUREMENT LOCATION
SIGNAL POINT LOOKOUT
SCALE. Ft
FIGURE 2. MAP OF MT. WILSON BROADCAST COMPLEX
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EQUIPMENT USED IN THE STUDY
Several different types of survey instruments were taken to
Mt. Wilson for the purpose of determining actual radiation
levels and instrument intercomparison. Two survey type monitors
manufactured by Narda Microwave Corporation were used: a model
8321 electric field probe with a model 8310 readout unit and a
model 8316 B readout unit; a model 8616 readout unit with a model
8631 magnetic field probe. Pertinent technical specifications
for these instruments are given in Table 3. The major features of
these instruments are: a) all instruments are isotropic in
response; i.e., they are independent of orientation in a field;
b) the electric field responding instruments are designed for
radiation detection in the 300 MHz to 18 GHz frequency range; c)
the magnetic field instrument is designed to measure radiation
levels in the 10 to 300 MHz frequency range; d) all instruments
provide a readout in units of mW/cm2 power density. A detailed
description of the development of these probes, which utilize
thermocouple techniques to measure power absorption, can be found
in the literature [5].
Another survey instrument, developed by the National Bureau
of Standards, was utilized during the investigation. This de-
vice, the model EDM-3, uses an orthogonal array of very short
dipole elements which contain diodes for immediate detection of
the incident electric fields and conversion to a dc voltage.
This voltage is fed to the readout instrument via extremely high
resistance leads which give the probe a non-perturbing feature
with respect to the field. The predecessor developments to this
particular instrument have been described in the literature [6].
Table 4 lists pertinent technical specifications for the NBS EDM-
3. The unique feature of this device is its flat response to
incident fields from 10-1000 MHz and its readout in units of
yj/m3 electric field energy density.
Yet another device used in the study consisted of the In-
struments for Industry E-field sensor, model EFS-1. This device
responds to the electric field and provides a readout directly in
terms of the electric field strength (Volts/meter). A single rod
type of antenna is used as the pickup and consequently the in-
strument can only be used for measurement of one spatial field
component at a time. Each of the three orthogonal components are
measured by re-orienting the instrument. The EFS-1 has a flat
response from 10 kHz to 200 MHz. Table 5 provides technical
specifications for the EFS-1.
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TABLE 3. TECHNICAL SPECIFICATIONS FOR NARDA ELECTRIC
AND MAGNETIC FIELD MONITORS
Instrument/Probe
Characteristics
Response Time (sec)
Dynamic Range
Probe Responds to
Accuracy at Calibration
Frequencies
Frequency Sensitivity
1-12 GHz
0.85-18 GHz
0.30-18 GHz
10-200 MHz
10-300
Isotropic Response
Drobe Overload
Readout Instrument
8310 8316B 8616
1.2 1.0,3.0
.1-20 mW/cm2 0.02 -20 mW/cm2
Electric Field
+ O.SdB
+ O.SdB
± 0.5-1 dB
± 0.5-3 dB
Magnetic Field
± 0.5 dB
- 0.5, +2 dB
+ 0.5 dB maximum deviation from energy
incident is any direction except from
and through handle
100 mW/cm2 CW 60 mW/cm2 CW
60 W/cm2 Peak 60 W/cm2 Peak
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TABLE 4. TECHNICAL SPECIFICATIONS FOR NBS MODEL EDM-3
ELECTRIC ENERGY DENSITY METER
Frequency Range
Electric Energy Density
Range
Dynamic Range
Overall Accuracy
10 MHz-1 GHz
Isotropic Response
3-3,000 MHz
full scale ranges of 3, 1, 0.3, 0.1, 0.03,
0.01, 0.003, 0.001, 0.003 yJ/m3
50 dB(0.00003-3.OyJ/m3)
±1 dB
±1 dB
TABLE 5. TECHNICAL SPECIFICATIONS FOR IFI MODEL EFS-1 E-FIELD SENSOR
Frequency Range
Accuracy
Meter Calibration
Field Strength Ranges
10 kHz to 200 MHz
better than 5% of full scale
direct reading in volts per meter
1-3 V/m
3-10 V/m
10-30 V/m
30-100 V/m
100-300 V/m
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Because more conventional methods of measuring electric
field strength revolve around the use of a frequency selective
receiver coupled to a calibrated antenna, a Tektronix spectrum
analyzer, model 7L13, was used in the study. A set of cali-
brated, tuned dipole antennas were used in conjunction with the
spectrum analyzer. Table 6 provides a specification summary for
the spectrum analyzer and Figure 3 is a graph of the calibration
factor for the dipole antennas. The dipole antennas were cali
brated by EPA by referencing them to a set of standard dipole
antennas constructed by the National Bureau of Standards. The
antenna factor shown in Figure 3 includes the effect of the 20
foot connecting cable between the antenna and the spectrum
analyzer. The spectrum analyzer produces a display on a CRT
which appears as a graph of signal amplitude in terms of power
vs. frequency. With knowledge of the antenna calibration factor,
the received signal powers can be corrected to yield the incident
electric field strength. In order to obtain a measure of the
total power density at a given point, measurements in at least
two orientations 90 degrees with respect to each other, must be
made. In general, three orthogonal measurements will be required.
The equivalent power density then can be computed using the
relations which follow.
In free space the plane wave rms electric and magnetic fields
are related through the impedance of space by
- = Z where Z is typically taken to be 377 fl
HO O
-
where
= permeability of free space = 1.257x10
"
eo = permittivity of free space = 8. 854x10" 12 F/m
The time average of the energy flow, S, or power density is
given by
The total energy density U for an electromagnetic wave is
„ = 1 (e0 E2 + y0 H2) = UE + UH) and
2
UE where Ug = electric field energy density
UH UH = magnetic field energy density
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TABLE 6. TECHNICAL SPECIFICATIONS FOR TEKTRONIX
SPECTRUM ANALYZER MODEL 7L-13
Tuning Range
Display Flatness
Reference Level
1 kHz-1.8 GHz
+1, -2 dB over any selected frequency span with
respect to 50 MHz
Calibrated in decade steps from -100 dBm to +30 dBm
SINGE* DIPOLE CftUMATION
CD
•o
cc
o
o
<
UJ
O MEASURED DATA
SOLID LINE IS LEAST SQUARES FIT
MAXIMUM DEVIATION FROM MEASURED DATA
IS 1.3dB
WITH 20' RG-55 CABLE
30
50 70
100 200
FREQUENCY (MHZ)
300
500 700
FIGURE 3. ANTENNA FACTOR GRAPH FOR THE DIPOLE
ANTENNA WITH 20 FT OF CABLE
10
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Based on these relations, the following result for plane waves:
S (mW/cm2) = [E(V/mj]2
3770
and s (mW/cm2) = 60.0 UE (yj/m3).
Thus, measurements of electric field energy density may be
converted into far field (plane wave) equivalent power density
[7]. Electric field energy density measurements made in the near
field of an antenna (where E and H are not related as in plane
waves) can not be simply converted into power density, but the
expression S = 60 Up will give an upper limit for the actual
power density.
11
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RESULTS
The approach used to measure radiation levels on Mt. Wilson
consisted of surveying the general area using the various types
of survey instruments available. This allowed a determination of
the specific areas where relatively intense radiation levels
exist, determination of the magnitude of these levels, and pro-
vided insight to some of the deficiencies of the instruments.
The Narda electric field monitors are not designed for frequencies
below 300 MHz. Thus these measurements were used to evaluate
their performance in an environment where they would not neces-
sarily be expected to respond reliably. In general, maximum
field intensities were observed beneath FM broadcast transmitting
antennas. Typical exposure levels were found to lie in the range
of 1-7 mW/cm2; exposures in open areas, i.e., not close to con-
ducting structures, did not exceed about 2 mW/cm2 equivalent
power density. During the course of the measurements it was
determined that the Narda electric field monitors yielded in-
consistent readings of power density. The responses were char-
acterized by significant changes in meter reading due to probe
lead stretching and orientation. This phenomenon was first
observed when an exposure reading at one point could not be
reproduced at a later time. As an example, at one location the
Narda electric field instruments could be made to read anywhere
between 1 and 13 mW/cm2, depending on probe lead and readout
meter orientation. Another factor of considerable significance
was an apparent pickup of 60 Hz ac power line electric fields
from the nearby commercial power transformers. Though it was not
conclusively proved, there was suspicion that the lower frequency
fields, i.e., approximately 100 MHz, of the FM stations, were
permeating the readout enclosure and possibly producing undesir-
able currents on the probe lead causing the observed interference
effect. The Narda electric field monitors are designed for
broadband response from 300 MHz to 18 GHz. It is not clear what
effect the presence of a relatively intense field at 100 MHz will
have. Because of the presence of significant fields below 300
MHz and the inconsistencies of the readings the Narda electric
field monitors were not used to collect data.
In contrast to the Narda electric field monitors, the new
Narda magnetic field instrument seemed to exhibit far superior
performance in the Mt. Wilson environment. This instrument was
essentially independent of probe lead stretch effects and was far
less dependent on 60 Hz ac field pickup. This is probably due to
two major reasons; (a) the monitor has a self contained pre-
amplifier within the probe handle and, (b) the probe is designed
to respond to fields from 10 to 300 MHz, which is the frequency
range for the most intense ground level fields measured. However,
12
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it is not clear just what effect would be seen if there are
present relatively intense UHF fields, e.g., from UHF TV sta-
tions. It is possible that the orthogonal loop array in the
probe may exhibit a resonance response at some high frequency
causing an erroneous reading on the meter. Thus, when used in a
multiple frequency environment, where signals span the 54-800 MHz
range, there is still a degree of uncertainty in the readings.
The NBS probe, designed for uniform sensitivity over the 10-
1,000 MHz region, proved very consistent in readings, from one
location to another. The availability of a peak or average
detector function provided a means of identifying the presence of
60 Hz pickup and, for the types of sources present at Mt. Wilson,
allowed the determination of actual RF field density. A number
of comparisons were performed with the NBS electric field and
Narda magnetic field meters. The findings are to a degree not
completely clear. At certain locations, the two instruments
provided almost an identical response when the meter indications
were converted to the same units. This occurred in fairly clear
locations i.e., not immediately next to a reflecting object.
Nevertheless, even under such conditions, at other locations, the
instruments did not correspond in reading. This was particularly
true when measuring the fields in a clump of trees next to an ac
transformer and near the KBIG-FM radio tower. Here, we observed
that the fields were relatively more intense, up to about 5 mW/cm2,
near the surface of the tree trunks using the NBS meter. Such a
conclusion was not as evident using the Narda magnetic field
meter. On the basis of the limited tests performed during this
study, it is presumed that any differences seen in the two meters
are principally due to the fact that one responds to the electric
field while the other responds to the magnetic field. Furthermore,
in situations which are not considered far field, the two field
parameters, electric and magnetic field strength, will not have a
fixed and known relationship. This phenomenon should be further
and more rigorously defined. It became apparent that field
comparisons of different meters can be difficult, due to exact
spatial relocation problems.
A maximum observed electric field energy density of 0.12yJ/m3
or 7.2 mW/cm2 equivalent was measured on the ground beneath KLVE-
FM. This measurement was near the steel pole supporting the
'antenna and is not representative for distances beyond several
feet from the tower. KLVE-FM uses an unguyed steel pole type of
tower rather than a conventional triangular self-supporting or
guyed type of arrangement.
On a driveway near the base of KBIG-FM, a measurement of the
field strength of KBIG-FM was made using the spectrum analyzer
and a tuned, half-wave dipole. Figure 4 illustrates the dipole
antenna arrangement and a measurement of the radiation at the
13
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FIGURE 4. DIPOLE ANTENNA ARRANGEMENT; MEASUREMENT OF
RADIATION INTENSITY AT ANTENNA WITH NBS PROBE
antenna with the NBS probe. The results of the measurement
showed that the FM station field was predominant in terms of
other field components produced by other nearby stations. With
the spectrum analyzer the field was measured as equivalent to
2.30 mW/cm2 including vertical and horizontal field components.
Using the NBS meter to measure the field at the center of the
dipole antenna a reading of 0.032 yj/m3 equivalent to 1.92 mW/cm2
was obtained. This is equivalent to a 0.8 dB difference and
represents excellent agreement.
An estimate of the expected power density at ground level
was performed for KBIG-FM. The distance to the center of radia-
tion of the antenna was taken as 90 feet (27.4 m) and the power
density was calculated by assuming that the total ERP in both
horizontal and vertical planes was effective at this steep verti-
cal angle (not usually valid). In this case the computed value
14
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was 2.2 mW/cm2 appearing to be in good agreement with the measured
values. This agreement is probably fortuitous since the vertically
polarized component of the field will normally be very low at a
steep depression angle and since the presence of reflections can
cause the resultant power density to vary by a factor of four
over calculated free space values.
An attempt was made to correlate the findings obtained with
the NBS meter and the spectrum analyzer with the IFI probe.
Experience with the IFI showed that the readings were difficult
to make in that the orientation of the IFI was so critical for
finding the maximum value that one could not easily reproduce the
readings. The best that could be done with the IFI was a reading
of 39 V/m equivalent to 0.40 mW/cm2 on the driveway near the base
of KBIG-FM. The IFI is apparently very significantly affected by
the presence of a ground plane and thus the readings obtained are
of questionable value. A block of polyetyrene foam was used to
support the instrument during the measurements but further investi
gation is desirable to fully define the usefulness of this device
in field situations similar to the Mt. Wilson site. It is pos-
sible that higher frequency field components, above 200 MHz may
have disturbed the readings to some extent.
A detailed survey, using the NBS probe, was made of the in-
terior of the Post Office and attached residence. Figure 5 is a
diagram of the Post Office and residence showing measured field
intensities in terms of yJ/m3 and mW/cm2. Typical maximums were
0.12 mW/cm2 equivalent except very near some conducting objects
such as the light switch where a reading of 0.48 mW/cm2 was en-
countered. Outside the Post Office in the backyard was a rabbit
hutch for a pet rabbit. At this location the measured field was
equivalent to 1.2 mW/cm2.
A value of 0.003 mW/cm2 was observed in a tree house in the
backyard of the residence. Measurements were made in the tree
house because of its elevated location and minimum shielding.
Measurements were also conducted in the large parking lot
near the Pavillion using the spectrum analyzer and tuned dipole
arrangement. From this location almost the entire broadcast
complex could be viewed. A sequence of measurements were made
for each FM and TV station operating at the time of measurement
from Mt. Wilson. These results are tabulated in Table 7
for the VHP TV stations, Table 8 for the UHF TV stations,
and in Table 10 for the FM stations.
15
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0.001 uJ/m3 (0.06 mW/cm2) in the
P.O. Lobby
0.008 uJ/m3 (0.48 mW/cm2) at 2"
from the light switch
at®
0.002 uJ/m3 (0.12 mW/cm2) at 2"
from the wall at (§)
0.001 uJ/m3 (0.06 mW7cm2) max. in
Livingroom
0.003 uJ/m3 (0.18 mW/cm2) at 2"
from the end of TV
antenna lead at (C)
<0.001 uJ/m3 (0.06 mW/cm2) in the
kitchen
0.001 uJ/m3 (0.06 mW/cm2) in the
Master Bedroom
0.0012uJ/m3 (0.072 mW/cm2) in corner
of Master Bedroom at(D)
0.002 uJ/m3 (0.12 mW/cm2) in corner
of Master Bedroom at (E
0.001 uJ/m3 (0.06 mW/cm2) inAux.
bedroom
AUX.
BEDROOM
D .-.(^LOBBY
POST
OFFICE
MASTER
BEDROOM
0.01 uJ/m3 (0.6 mW/cm2) at 2"
from light fixture (
0.008 uJ/m3 (0.48 mW/cm2) near gate at (G)
0.02 uJ/m3 (1.2 mW/cm2) on the Rabbit Cage
RABBIT CAGE
0.08 uJ/m3 (4.8 mW/cm2) near a 6" coil of wire at (H)
0.02 uJ/m3 (1.2 mW/cm2) near antenna
TV ANTENNA
0.012 uJ/m3 (0.72mW/cm2) general level in the back yard
0.003 uJ/m3 (0.18 mW/cm2) in the Tree House
^mfiK
0.03 uJ/m3 (1.8 mW/cm2) near the end of a wire in the upper level
of the Tree House
FIGURE 5. FIELD INTENSITIES IN POST OFFICE, RESIDENCE
AND YARD AS MEASURED WITH NBS PROBE
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TABLE 7. VHP TV EXPOSURE MEASUREMENTS IN PARKING LOT
Channel
2
4
5
7
9
11
13
Call
KNXT-TV
KNBC-TV
KTLA-TV
KABC-TV
KHJ-TV
KTTV-TV
KCOP-TV
Freq (MHz)
55.25*
59.75**
67.25
71.75
77.25
81.75
175.25
179.75
187.25
191.75
199.25
203.75
211.25
215.75
E (V/m)
0.279
0.110
0.507
0.181
0.415
0.158
3.71
1.48
2.76
1.13
4.15
1.52
1.77
2.32
Total
S (nW/cm2)
0.0207
0.0032
0.0683
0.0086
0.0456
0.0066
3.64
0.58
2.02
0.336
4.57
0.611
0.832
1.43
14.18
* Visual carrier.
** Aural carrier.
TABLE 8. UHF TV EXPOSURE MEASUREMENTS IN PARKING LOT
Channel
22
28
34
40
58
Call
KWHY-TV
KCET-TV
KMEX-TV
KX LA-TV
KLCS-58
Freq (MHz)
519.25
523.75
555.25
559.75
591.25
595.75
627.25
631.75
735.25
739.75
E (V/m)
0.09
0.09
2.56
0.92
0.97
0.87
0.41
0.33
5.52
2.48
Total
S GaW/cm2)
0.0021
0.0021
1.74
0.225
0.250
0.201
0.0446
0.0289
8.08
1.63
12.21
17
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TABLE 9. FM RADIO EXPOSURE MEASUREMENTS IN PARKING LOT,
Call
KPFK-FM
KFAC-FM
KNX-FM
KMET-FM
KLOS-FM
KRTH-FM
KUTE-FM
KKDJ-FM
KOST-FM
KBIG-FM
KBCA-FM
KLVE-FM
Freq (MHz)
90.7
92.3
93.1
94.7
95.5
101.1
101.9
102.7
103.5
104.3
105.1
107.5
E (V/m)
0.287
4.36
0.257
2.35
2.35
4.50
0.306
1.808
0.577
7.68
0.118
0.408
Total
S (yW/cm2)
0.0219
5.04
0.0175
1.47
1.47
5.37
0.0248
0.867
0.0882
15.65
0.0037
0.0442
29.54
Exposure from VHP TV = 14.18 yW/cm2
Exposure from UHF TV = 12.21 yW/cm2
Exposure from FM radio = 29.54 yW/cm2
Total exposure
55.93 yW/cm'
Thus we see that the major proportion of total exposure is due to
the presence of the FM broadcast stations, it being greater than
the VHP and UHF TV combined. This observation is due to the
broader radiation pattern of FM station antennas in the vertical
plane when compared to TV type transmitting antennas.
18
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CONCLUSIONS
Measurements of electric field intensity in the unique
environment of broadcast emitters at Mt. Wilson indicate that
maximum radiation levels lie in the range of 17 mW/cm2 and are
very dependent on location. Small distance changes can result in
very large changes in exposure and as such introduce significant
uncertainties in predictive modeling. The higher end of this
range will be encountered near conducting objects and usually
encompass only relatively small areas of concern. Levels near 1
mW/cm2 may be more common and are likely to be present in areas
near the base of FM broadcast towers. Ground level values of
field intensity are typically far less for VHP and UHF TV emis-
sions, even though the TV stations have higher ERP.
Care must be used when making surveys of radiation levels in
a multiple frequency environment such as at Mt. Wilson with
emissions as low as 54 MHz since commonly used survey instruments
may exhibit frequency dependencies or interference susceptibili
ties which lead to erroneous indications of exposures.
Localized hotspots, resulting from reflections in a multiple
source environment, are most easily identified with a broadband
survey probe. While the broadband probe is most efficient in
determining the existence of a relatively intense field, a tun-
able device, such as a spectrum analyzer, is required to isolate
the field components. Exposure levels reported here do not
exceed the OSHA guide of 10 mW/cm2 established for the working
environment [8], however the maximum values are several orders of
magnitude greater than median environmental levels found in
certain urban environments [9]. Radiation levels encountered
while working on the broadcast towers themselves can be much
higher and are the subject of separate consideration [10].
19
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REFERENCES
1. Tell, R. A., An analysis of potential broadcast radiation
levels at Mt. Wilson, California, technical memorandum, U.S.
Environmental Protection Agency, September 1975.
2. Tell, R. A., and J. C. Nelson, Calculated field intensities
near a high power UHF broadcast installation, Radiation Data and
Reports, 15:401-410 (1974).
3. Television Factbook 1974-75 stations volume, Published by
Television Digest, Inc., Washington, D.C. (1974).
4. Broadcasting Yearbook 1975, Published by Broadcasting Pub-
lications, Inc., Washington, D.C. 20036 (1974).
5. Asian, E. E., Electromagnetic Radiation Meter, IEEE Trans-
actions on Microwave Theory and Techniques, MTT-19: 249-250
(1971) .
6. Bowman, R. R., Some recent developments in the character-
ization and measurement of hazardous electromagnetic fields, In
Biologic Effects and Health Hazards of Microwave Radiation,
proceedings of an international symposium, Warsaw, October
15-18, 1973, published by Polish Medical Publishers, Warsaw,
1974.
7. Bowman, R. R., Quantifying hazardous electromagnetic fields:
practical considerations, National Bureau of Standards Technical
Note 389, April 1970.
8. Department of Labor. Occupational Safety and Health Admin-
istration, Section 1910.97, Federal Register: 36: 105 (May 29,
1971), Nonionizing Radiation, Effective August 27, 1971.
9. Janes, D.E., R.A. Tell, T.
frequency Radiation Levels in
AB-4A, Microwave Measurements
Biological Effects, USNC/URSI
15, 1976.
W. Athey, and N.N. Hankin, Radio-
Urban Areas, presented in Session
and Exposure Systems, Series on
Meeting, Amherst, MA, October 10-
10. Tell,
immediate
Technical
R. A., A measurement of RF field intensities in the
vicinity of an FM broadcast station antenna, EPA
Note, February 1976.
20
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TECHNICAL REPORT DATA .
(Please read Instructions on the reverse before completing)
1. REPORT NO.
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
An Investigation of Broadcast Radiation
Intensities at Mt. Wilson, California
April 1977_
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Richard A. Tell and Patrick J. O'Brien
8. PERFORMS
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELET
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
4. SPONSORING AGENCY CODE
EPA/200/03
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report describes a series of measurements made to determine radio
frequency exposure from television and FM broadcast stations located
on Mt. Wilson to areas near the tower bases and within about 2,000 feet.
Portable broadband survey instruments and a spectrum analyzer with
dipole antennas were employed in these measurements and used in a com-
parison of indicated radiation levels and assess difficulties or pecu-
liarities of the specific types of equipment. Maximum ground level
exposure values were in the 1-7 mW/cm range. Intensities of about
0.1 mW/cm were measured inside the Mt. Wilson Post Office which is
located in the immediate vicinity of a large number of towers. Ground
level intensities were predominantly due to the presence of FM broad-
cast installations even though the FM stations used much lower effective
radiated powers. This phenomenon is due to the much broader vertical
plane pattern of FM stations and the presence of grating lobes
associated with some FM antennas. It was found that wide ranges in
exposure could occur over very small geographic areas revealing the
potential for significant uncertainties in predictive modeling.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
.IDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
13. DISTRIBL
3. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
27
D. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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