NBSIR 74-361

ELECTROMAGNETIC INTERFERENCE MEASUREMENTS

AT ASA, FORT HUACHUCA, ARIZONA

H. E. Taggart

J. W. Adams

Electromagnetic Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

December 1973

Prepared for:

U. S. Army Security Agency

Test and Evaluation Center

Fort Huachuca, Arizona

NBSIR 74-361

ELECTROMAGNETIC INTERFERENCE MEASUREMENTS

AT ASA, FORT HUACHUCA, ARIZONA

H. E. Taggart

J. W. Adams

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

December 1973

Prepared for:

U. S. Army Security Agency

Test and Evaluation Center

Fort Huachuca, Arizona

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS Richard W Roberts Director

CONTENTS

Page

1.0 INTRODUCTION 1 1.1 Types of Noise 2 1.2 Measurement Sites and Types of Measurements 4

1.3 Shielded Enclosure Measurements 6

2.0 EMI MEASUREMENT TECHNIQUES 6

2.1 Radiated Measurements 6

2.2 Mobile Van 9

2.3 Measurement Equipment in the Mobile Van 11

2.4 Conducted Measurements 11

2.5 APD Measurements 12

3.0 MEASUREMENT RESULTS 17

3.1 Radiated EMI (electric field) 18

3.2 Radiated EMI (magnetic field) 42

3.3 Selected Frequency Radiated EMI (electric

field) 42

3.4 Conducted EMI 4 8

3.5 Mercury Vapor Lamps 4 8

3.6 APD Measurements 4 8

3.7 Evaluation of the Shielded Room 51

4.0 CONCLUSIONS 66

5.0 RECOMMENDATIONS 6 7 ACKNOWLEDGMENTS 6 8

REFERENCES 69

iii

ELECTROMAGNETIC INTERFERENCE MEASUREMENTS

AT ASA, FORT HUACHUCA, ARIZONA

H.E. Taggart and J.W. Adams

This report describes the work performed for

the U.S. Army Security Agency Test and Evaluation

Center (USASATEC), Fort Huachuca, Arizona, during

the period from April 1973 to November 1973. The

purpose of the project was to measure, analyze, and

evaluate the electromagnetic environment at selected

sites and to recommend methods of reducing the present levels of electromagnetic interference (EMI)

Chief sources of EMI were the power lines in the

area and sferics from thunderstorms. Both broadband

EMI measurements and amplitude probability distribution measurements were made . Both electric and

magnetic fields were measured. The frequency range

covered was 15 kHz to 10 GHz. Measurements were

made at three locations: 1) at Fort Huachuca

USASATEC; 2) Willcox Dry Lake; and 3) Boulder,

Colorado. The report contains a description of

the test procedures, test results, conclusions,

and recommendations

Key words: APD measurements; broadband EMI; electromagnetic interference; power line EMI.

1.0 INTRODUCTION

This report describes the work performed for the U.S.

Army Security Agency Test and Evaluation Center (USASATEC)

Fort Huachuca, Arizona, during the period from April 1973

to November 1973.

The purpose of the project was to measure, analyze, and

evaluate the electromagnetic environment at selected sites and

to recommend methods of reducing the present levels of

electromagnetic interference (EMI)
1 . 1 Types of Noise

There are three basic types of interference or "noise"

discussed in this report:

1. Man-made noise: This includes any noise generated by

machines, computers, transmitters, high-voltage lines,

or any other electrical noise caused by human activities.

2. Natural noise: This includes noise that is generated as

a result of natural phenomena such as galactic noise,

solar noise, general atmospheric noise, and local

thunderstorms

.

3. Receiver noise: This is the white noise associated with

receiver input circuits and is always present. If a noise source has a lower level than the receiver noise,

the source cannot be measured using the techniques and

instruments described here. Thus, on data plots where

"receiver noise" is indicated, only noise levels above

this "receiver noise" can be measured.

In this measurement program, man-made noise was of

primary interest and in most cases was the dominating source

of interference. However, during certain parts of the day,

atmospheric noise due to large thunderstorms was dominant.

In most cases, it is possible to distinguish man-made noise

from atmospheric noise. Figure 1 illustrates typical values

of electromagnetic interference (EMI) from various sources.

In the broad sense, sources of man-made noise can be

divided into four categories:

1. CIV signals: Including the various types of communication signals, FM, AM, television, etc. (relatively

narrowband signals)

.

2. Impulsive interference: Caused by electrical motors,

arc welders, ignition noise from gasoline engines,

corona discharge, and computers (broadband noise sources).

3. Power line hum: The result of the 60 Hz line current

and its related harmonics

.

4. Rectangular wave signals: Produced by digital transmission systems including computers, data transmission

lines , etc

.

2
100kHz I MHz 10 MHz 100 MHz I GHz 10 GHz

FREQUENCY

Figure I Typical values of EMI from various sources.

3
All of the above signals contribute to the EMI environment. Since the primary objective of the project was to

determine the amount of EMI, and since the recorded data

contained both broadband EMI and narrowband CW signals,

narrowband signals were deleted from some results. This

allows much easier interpretation of the broadband EMI characteristics. Both the narrowband and broadband signals are

shown in some results. The number and the magnitude of the

narrowband signals vary widely depending on time of day,

polarization, frequency, and location.

An important characteristic of electromagnetic noise is

its variation with time. This is illustrated in figure 2,

which shows typical noise caused by impulsive (lightning)

sources. In digital communication systems, where codes do

not have the redundancy of human voice, these time variations

become increasingly important. Therefore, a basic statistical

form will be used in presenting the measured noise data. This

is the amplitude probability distribution (APD) [1]. This

topic will be explained in the section on Measurement Techniques. One horizontal component of the magnetic field

strength was measured for APD analysis.

1 . 2 Measurement Sites and Types of Measurements

Selected sites for the measurements were the USASATEC

facility and compound (Hayes Hall) at Fort Huachuca, Arizona;

the USASATEC antenna site located at Willcox Dry Lake, near

Willcox, Arizona; and, for comparison, two sites at Boulder,

Colorado

Measurements were made at frequencies from 14 kHz to

10 GHz. Radiated and conducted measurements, including both

the electric (E) and magnetic (H) components of the radiated

field, were measured at Hayes Hall. Only radiated E and H

measurements were made at Willcox Dry Lake.

At Hayes Hall , radiated measurements were made at a number of locations inside and outside the compound. The

location of the 15 -kV power lines, test facilities, and

buildings, as well as the positions where the measurements

were made, are shown in section 3.0 of this report.

Measurements at Willcox Dry Lake were made at ASA

benchmark 102, a location several miles from the nearest

power line. This location was the "best" or quietest of the

sites selected.

4
Figure 2 Three-dimensional illustration of the effects of impulsive noise.

5
Noise energy normally varies with time and can vary

as much as 100 dB over a diurnal cycle. Typical variations

in noise caused by impulsive (lightning) sources are shown

dramatically in figure 3. The upper curve of figure 3 shows

EMI recorded during heavy thunderstorm activity, and the

lower curve shows EMI recorded at the same location on a clear day. Therefore, continuous measurements of EMI at

selected frequencies (25 and 250 kHz and 1, 3, 10, and 30 MHz)

were made for a 24 -hour period so that diurnal variations, as well as other variations of the EMI, could be presented on a statistical basis. Data are presented in amplitude probability distributions.

1 . 3 Shielded Enclosure Measurements

In addition to the EMI measurements discussed above,

plane-wave shielding effectiveness of the shielded enclosure

located in the Hayes Hall Electronics Maintenance Branch was

measured. This test was conducted at two frequencies, 420

and 1000 MHz.

2.0 EMI MEASUREMENT TECHNIQUES

This section discusses the techniques used for measuring

conducted EMI, radiated EMI, and APD 1 s . The types of equipment used for the measurements are also discussed. Calibrations

were done in accordance with NBS calibration techniques [2].

2 . 1 Radiated Measurements

A swept - frequency technique was used to evaluate the

characteristics of the radiated energy. This technique provides a measurement of either the electric or magnetic field

strength. Electric field strength is measured as a function

of receiver bandwidth in decibels above one microvolt per

meter per megahertz, dB (yV/m)/MHz. In the case of magnetic

field strength measurements, the units are decibels above

one microampere per meter per megahertz, dB (yA/m) /MHz

Measurements of radiated interference were made at

various locations during normal working hours (0730 to 1630).

Electric field strength was measured at frequencies from 14 kHz

to 10 GHz, and magnetic field strength was measured at fre^

quencies from 14 kHz to 30 MHz.

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Electric field strength (E) is calculable from the

magnetic field strength (H) by the simple free-space plane

wave condition; E = n 0H, where no i s 377 ohms, the intrinsic

impedance of free space. For approximate comparisons, the

magnetic field strength in dB yA/m can be converted to the

electric field strength in dB yV/m by adding 51 dB to the

magnetic field strength. Where free-space conditions prevail,

use of this 51 dB will allow conversion from either E or H

to the other. Since most of the field strength measurements

at Ft. Huachuca were made near a ground plane, free-space

conditions did not prevail, and exact comparisons cannot

be expected.

Both magnetic and electric fields were recorded. Electrostatically shielded loop antennas were used to detect the

magnetic EMI. Various types of antennas, including monopole,

biconical, log-spiral, and dipole, were used to detect the

electric field EMI. The choice depended upon the desired

frequency

Antennas used from 14 kHz to 200 MHz were positioned for

vertical polarization during the measurements. Above 200 MHz,

circularly polarized antennas were used. Although EMI varies

somewhat as a function of the polarization of the antenna,

measurements indicated that the overall results were not significantly changed by using just one antenna polarization. If

directional antennas were used, the antennas were oriented for

maximum gain in the direction of the nearest power line.

Radiated EMI was continuously recorded on an x-y

recorder using a swept - frequency receiver. Frequency bands

of the receivers were usually about one octave wide. The

bandwidth and frequency range for each band are shown in

Table 1. The receiver was calibrated in terms of an impulse

generator in dB yV/MHz. Receiver bandwidth varies as a function of frequency, but all results are normalized to a one megahertz bandwidth.

2 . 2 Mobile Van

The EMI receivers and all ancillary equipment were housed

in a mobile van with the antennas mounted 20 feet above the

ground on a non-metallic mast. A photograph of the mobile

van with the mast in position is shown in figure 4. All

equipment was operated from batteries so that no EMI was

generated from the vehicle engine or from the gasol ine -driven

motor- generator unit in the mobile van.

9
Table 1. Receiver Bandwidths

(Manufacturer's Specifications)

Receiver A

Band Frequency Ran Bandwidth

1 14 .0 kHz - 30 .0 kHz 4 kHz

2 30 .0 kHz - 60 .0 kHz 4 kHz

3 60.0 kHz - 120 kHz 4 kHz

4 120 kHz - 240 kHz 4 kHz

5 240 kHz - 500 kHz 4 kHz

6 0 .5 MHz - 1.1 MHz 5 kHz

7 1.1 MHz - 2 . 30 MHz 5 kHz

8 2 . 30 MHz - 5.00 MHz 50 kHz

9 5.00 MHz - 11 .

MHz 50 kHz

10 11 .

MHz - 25.0 MHz 50 kHz

11 or n Zo . U MHz - 50 .0 MHz j U U Krl Z 12 b U . U MHz - 100 MHz con j u u Krl Z 13 100 MHz - 200 MHz 500 kHz

14 200 MHz - 500 MHz 500 kHz

15 500 MHz - 1000 MHz 500 kHz

Rece iver B

1 1

- 2 GHz 5 MHz

2 2

- 4.4 GHz 5 MHz

3 4.4 - 10 GHz 5 MHz

10
2 . 3 Measurement Equipment in the Mobile Van

The equipment used included the following:

a. EMI Analyzer (Receiver A)

frequency range: 14 kHz to 1 GHz, see table 1.

b. EMI Analyzer (Receiver B)

frequency range: 1 to 10 GHz, see table 1.

c. x-y Recorder

d. Active, Broadband, Monopole Antenna,

frequency range: 10 kHz to 40 MHz.

e. Biconical Antenna,

frequency range: 20 to 200 MHz.

f. Conical, Log-Spiral Antenna,

frequency range: 200 to 1000 MHz.

g. Conical, Log-Spiral Antenna,

frequency range: 1 to 10 GHz.

h. Collapsible Loop Antenna,

frequency range: 10 to 250 kHz.

i. Loop Antenna,

frequency range: 150 kHz to 30 MHz.

j . Current Probe

frequency range: 20 Hz to 10 kHz.

k. Current Probe,

frequency range: 1 to 1000 MHz.

When possible, equipment was calibrated in terms of NBS

s tandards

2 . 4 Conducted Measurements

The conducted EMI on the power lines was measured at two

locations within Hayes Hall at frequencies from 14 kHz to 1 GHz. Conducted EMI was recorded in terms of voltage in decibels above one microvolt per megahertz of receiver bandwidth

(dB yV/MHz)

11
The conducted EMI measurements were performed by coupling

into the 60 Hz power line by means of a capacitive network.

Swept frequency techniques were used similar to the radiated

measurement techniques.

An attempt to use the current probes listed in this section proved unsuccessful because of insufficient current

probe sensitivity. By direct capacitive coupling the sensitivity of the system was improved by approximately 35 decibels.

Good sensitivity was essential, because some measurements were

performed within a shielded enclosure that used power-line

filters .

This section of the report describes the system used to

measure amplitude probability distribution statistics of

electromagnetic noise. The system is an extension of one

designed by Matheson [3] . The systems used for recording and

data processing are shown in figures 5 and 6. Measurements

were made at the following frequencies: 25 and 250 kHz and

1 , 3 , 10 , and 30 MHz .

In order to characterize time variations of the EMI,

APD ' s are produced which require special techniques and equipment. The final outputs are APD figures. These are plots of

the amplitude of time-varying parameter versus the percent

of time a given level is exceeded. By plotting the cumulative

APD on Rayleigh graph paper, one can clearly show the fraction

of time the parameter exceeds various levels. See figure 7.

The measured parameter is one horizontal component of magnetic

field strength.

The APD's are integrated to give rms and average values

of the field strength, according to the equations

2.5 APD Measurements

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Figure 7 APD, 1 MHz, Horizontal E-W Component of Magnetic.

Field, 1 kHz Predetection Bandwidth, Hayes Hall,

Position 1, 6:00 p.m., July 2, 1973.

15
where H represents the magnetic field strength of the noise,

and p is the probability that measured field strength exceeds

the value H. The rms and average values are identified on

each graph and are time averages (30 minutes) of these timedependent parameters . These quantities are also dependent

upon bandwidth of the system, length of the data run, and

possibly other parameters. Finite series are actually used

for the numerical integration. If the tapes are played into

ordinary rms reading meters, the meter readings will vary

10 to 20 dB over fractions of a second. The rms value is

directly relatable to noise power. With these wide variations

of field strength with time, the most suitable presentations

are statistical ones

The measurement technique is to record on magnetic tape

a time -varying , analog signal that is proportional to the

magnetic field strength as seen through a specific receiver

bandwidth. This analog signal must be converted down to be

within the passband of the tape recorder. Four signals

whose amplitudes are proportional to EMI at four frequencies

are tape recorded simultaneously on four channels for about

30 minutes. 1 MHz and 3 MHz recordings were alternated with

10 MHz and 30 MHz recordings to give better spectral coverage,

while 25 kHz and 250 kHz recordings were made during every

run

The data-processing system consists principally of the

analog magnetic tape recorder as a playback unit, an amplifier, a tuned frequency converter, and a digital level

counter. A stable 25 -kHz signal recorded on channel 4 at the

time of recording is used during playback to control a servo

system to remove flutter and wow. The amplifier is used primarily for impedance conversion between the output impedance

of the tape recorder and the input impedance of a tuned frequency converter. The 40 -kHz output of the tape recorder is

converted up to 455 kHz by the tuned frequency converter in

order to match the response band of the digital level counter.

The digital level counter provides a direct digital display

of the percentage of the time each of 15 levels, 6-dB apart,

is exceeded.

The 3-dB bandwidth of the whole system, including recording, transcribing, and data-processing systems, is primarily

determined by the data-processing system. It was found to be

about 1 kHz for the 25 kHz and 250 kHz data and 1.2 kHz for

other frequencies. For approximate comparison with other data

in the report given in dB (yA/m) /MHz , add 60 dB to the APD

measurement data which is given in dB(uA/m) /kHz

16
The dynamic range of the whole system is about 60 dB.

A portable oscilloscope was used to monitor signal levels to

be recorded in order to use the 60 dB dynamic range to obtain

the most useful part of the noise data.

The calibration of the entire measurement system, including loop antennas, field strength meters, mixers, magnetic

tape recorders, impedance transforming amplifiers, and the

digital level counter, was performed by immersing the receiving

loop antennas in a known field, generated at the NBS field

strength calibration site [2]. Thus all levels of field

strength are given in absolute units

.

Estimated limits of error for the APD noise measurements

are ± 3 dB. Several sources of error that are critical to the

overall accuracy of the measurements are listed below:

1. Calibration of the discrete digital level counter

by means of a 1 dB step attenuator contributes ± 1-dB

quantization error limit.

2. The calibration of the field recording system, i.e.,

recording, and data processing, has an uncertainty of

± 0.5 dB [4]

.

3. The estimated uncertainty involved in using the

tape recorder for record and playback is ± 0.5 dB due to

harmonic distortion, flutter, dropout, cross -talk, gain

instability, etc.

4. Gain instability during measurements, gain

changes between measurements and calibration, and the

nonlinearity of field strength meters and mixers, all

combined, contribute ± 0.5 dB uncertainty.

5. Gain instability and nonlinearity of the digital

level counter, the tuned frequency converter, the amplifier, and attenuators, all combined, contribute ± 0.5 dB

uncertainty

.

3.0 MEASUREMENT RESULTS

This section contains the following measurement results:

1. Radiated EMI (electric field) at three locations,

Hayes Hall, Willcox Dry Lake, and Boulder, Colorado.

17
2. Radiated EMI (magnetic field) at two locations,

Hayes Hall and Willcox Dry Lake.

3. Selected frequency radiated EMI (electric field)

at Hayes Hall.

4. Conducted EMI at Hayes Hall.

5. Evaluation of the mercury vapor lamps at Hayes Hall

as EMI source

6. APD measurements at Hayes Hall and Willcox Dry

Lake .

7. Evaluation of the shielded room in Hayes Hall.

Exact location of the measurement points in the Hayes

Hall Area is shown in figure 8. Numbers listed in this

figure will be referred to by position number throughout

this report.

Measurements at Willcox Dry Lake were made at ASA benchmark number 102, approximately one mile south of the ASA test

s ite buildings

Measurements were made at two locations in Boulder, Colorado: 1) near a 15 kV power line that feeds the Radio Building

at NBS, and 2) at a nearby antenna site where the nearest

power line is approximately 100 meters distant.

3.1 Radiated EMI (electric field)

Measurement results of the radiated EMI (electric field)

at the various locations are shown in graphic form. Each

plot of the spectrum is from 14 kHz to 1 GHz, showing the

magnitude of the EMI in dB (uV/m) /MHz , the frequency, the

date of the measurement, and the approximate time of the measurement. Each scan of the spectrum requires more than one

page to provide adequate resolution of the EMI. The measurement data shown in figures 9 through 13 are only plotted

up to 1 GHz. Measurements were made from 1 to 10 GHz; however, no EMI was detected above 1 GHz that exceeded receiver

noise. Measurements were made at the following locations:

18
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19
position 2. Hayes Hall area (110 volt line);

position 5. Hayes Hall area (outside ASA compound);

position 9. Hayes Hall area (15 KV line);

position 35. Willcox Dry Lake;

position Bl. Boulder, Colo. (15 KV line); and

position B2 . Boulder, Colo, (antenna site).

Figures 9(a), 9(b), 9(c) compare the EMI at position 9

(generally the highest level of EMI) with position 35

(generally the lowest level of EMI)

Figures 10(a), 10(b), 10(c) compare the EMI at position 2 (generally the lowest level of EMI within the ASA compound)

with position 5 (generally the lowest level of EMI outside

the ASA compound)

Figures 11(a), 11(b), 11(c) compare the EMI at position

9 with that at position 5.

Figures 12(a), 12(b), 12(c) compare EMI at position 9

(generally the highest level within the ASA compound) with

that at position 2 (generally the lowest level of EMI within

the ASA compound)

Figures 13(a), 13(b), 13(c) compare the EMI at the two

locations in Boulder, Colorado, Bl and B2

The data in figures 9 through 13 show only the broadband

EMI . The carriers from the numerous transmitters were deleted

in order that the broadband data could be more easily studied

and understood.

Figures 14(a), 14(b), 14(c) and 15(a), 15(b), 15(c) show

only the average cw signals (narrowband) at positions 2 and

35 respectively. The units of measure are decibels above one

microvolt per meter. It should be pointed out that the measured values of all the carriers may not be accurate because

some antennas used to measure the EMI were directional and

may not have been directed toward the carrier sources. Also,

the linearly polarized antennas were always positioned for

vertical polarization. The carrier signals can usually be

identified in the background EMI by their narrowband character.

However, they are not readily discernible in all cases. No

attempt was made to identify the source of each carrier signal in figures 14 and 15

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40
41
3 . 2 Radi ated EMI (magnetic field)

The magnetic field EMI was measured at the following

pos itions

position 5. Hayes Hall Area (outside ASA compound);

position 9. Hayes Hall Area (15 KV line); and

position 35. Willcox Dry Lake.

Figures 16(a) and 16(b) compare the magnetic EMI at

position 9 and 5

Figures 17(a) and 17(b) compare the magnetic EMI at

positions 9 and 35.

3 . 3 Selected-Frequency Radiated EMI (electric field)

In addition to making the swept frequency measurements

just described, radiated electric field measurements were

also made at a number of sites in and about the ASA Compound

at three selected frequencies . The selected frequencies

were 40, 54, and 200 MHz. As a result of these measurements,

an EMI map of the area was drawn, showing the variations in

field strength. This map is shown in figure 18.

The numbers on the map represent the measured EMI in

decibels at that particular location at the respective frequencies of 40, 54, and 200 MHz. The top number is the 40 MHz

measurement followed by the 54 and 200 MHz measurements.

These measurements were made relative to each other; therefore , they can be compared with each other but cannot be

compared with other data in this report.

In general, the EMI levels near Irwin Street (front of

the compound) were higher. This was expected, since the

power lines parallel Irwin Street. As the distance from

Irwin Street (and the power lines) was increased, the overall EMI within the compound decreased. The levels at the

extreme rear of the compound were 10 to 30 decibels lower

than at the front of the compound. Measurements at 40 MHz

were made at two locations approximately 300 feet and 500

feet north of the compound. EMI at these two locations outside the compound were about the same level as that at the

quietest location inside the compound. These two locations

were farthest from the power lines, and here the measured

EMI was the lowest (approximately 30 decibels lower than the

EMI measured at the front of the compound)

42
(fxA/m)/MHz

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43
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47
Additional measurements were also made at the main power

station west of Greeley Hall and at two locations just west

of the ASA compound. These measurements were near power

lines, and, as expected, the EMI levels were comparable to

those measured near the front ,of the compound. The highest

EMI levels were measured at the power station where there are

higher power line voltages

3.4 Conducted EMI

Figures 19(a) and 19(b) compare the conducted EMI in the

110 volt AC line located in the Systems -Evaluation Laboratory

(at a workbench) with the conducted EMI within the Electronics - Maintenance Branch shielded room. The difference between the

curves illustrates the effectiveness of the line filters in

reducing conducted EMI . The bottom curve is the conducted EMI

within the shielded room.

3 . 5 Mer c ury Vapor Lamps

Mercury vapor lamps are positioned at selected points on

the periphery of the ASA compound and are used as security

lights during darkness. The contribution of the mercury vapor

lamps to the total EM environment was not certain. Therefore,

measurements were made in the immediate vicinity of several

of the lamps to determine if they contributed significantly

to the overall EMI environment.

Selection of test locations was based on location of

lamps relative to power lines. In areas where EMI levels

were lowest, such as near the rear of the compound, EMI

generated by the lamps was insignificant compared to EMI

emanating from the power line. The general conclusion is

that mercury vapor lamps at the ASA compound do_ not contribute significantly to the EMI environment.

3 . 6 APD Measurements

Measured data were processed and presented as about 150

APD's. These 150 APD ' s are not included in the body of this

report. These large amounts of data are more easily comprehended in summary forms. Diurnal variation for each frequency

48
dB^V

dBfj.V

%

i

i

/

49
dBu.V

dBp-V

IT) (lb. o 1c * O" CD CO

(U L_ZJO

fu JZ ( o UJ CD

CM

(/) o o LO E

fu kT

to

CO

cz

CI r- O a> CO OrV_ f

>- ^

X)

(11 CU 13 "O D , 1 1 1 Ll_l CD tT\ cn

(~ CD co +- JD >^ U a

zj c _j z> "D (D C c O o LTi u 0) V

ro

(TJ ZJ E

CD o O

CL ro

O

1_ > OH TJ CD UJ c CL i T3

ro Q_ L0 CD JD 13 E "D

CD

to +- CD o 10

L_ ro > JZ CQ _J CO 00

CDJ_CD

A^gp

50
at locations 1 and 35 is compiled from the APD ' s . The 0.001

percent value, the time -averaged rms value, and the 99 percent

value are given for a 24 -hour period. These are shown in

figures 20 to 31.

Also, since time variations versus frequency may be of

interest, these are summarized for locations 1 and 35. The

maximum (.001 percent) value during the 24-hour period, the

linearly averaged rms value, and the minimum (99 percent)

value are plotted in figures 32 and 33.

The detailed information in the APD ' s may be obtained

from the authors

3 . 7 Evaluation of the Shielded Room

In response to a request to measure shielding effectiveness of the shielded room in the Electronics Maintenance

Branch, limited measurements were performed. Since the

original measurements plan did not include evaluation of the

shielded room, NBS personnel did not bring all of the required

equipment necessary for complete evaluation. Therefore,

measurements were made using what equipment was available.

Shielding effectiveness was measured at 420 MHz and

1000 MHz frequencies. Measurements were performed by launching a planewave field from a transmitter approximately 12

meters from the shielded room. Shielding effectiveness was

determined by the difference between measured magnitudes in

dByV/m of the launched field outside and inside the shielded

room. Results are listed below:

frequency type of shielding effectiveness

MHz field decibels

420 planewave > 70

1000 planewave 51

The measurement system dynamic range at 420 MHz was only

70 decibels, and shielding effectiveness of the room exceeded

that value. Primary sources of rf leakage at 1000 MHz were

in the vicinities of the door and the line filters, with the

door leaking the most.

51
<u

«-> 0) s:u

v

P.

0)

I-. <up.6

cto

s~

u

co

a;

O

1) X)JJ

•Hd

to

to z

60

50

40'

30

20

10;

T o.ooi%

(J) rms

]_ 9 9%

July 3', 1973 July 2, 1973

•10!

-20

30

40

OH) <)

l

!

CX)

11 1

7

12 1 2 3-1 9 10 11 12 1 3 4 S 6 7 8 9 10 11 12 N Hour of day

Figure 20. Summary of 25 kHz, H-field variations from

each APD, Hayes , Hall

52
>- e. > o

u

o

a.

<u

a>p.6

ajO

4)Co

o

>

•H

4-> nJ rH

<D «:m

T3

o

4)

c

bo

as

50;

40 L

30

20

10

T o.ooi'

(J) mis

j 99*

July 3, 1973- July 2, 1973

! i

-10,-0

- 2 Op

h

30

•40

T

i

!

()

.u.

(> (>

() ()

i I

i

:

• !

(> o

() <)

i

I

-50,

I

.

i !

12 1 M

55789 10 11 12 1234567

N

j 10 11 12

Hour of day

Figure 21. Summary of 250 kHz, H-field variations from

each APD , Hayes Ha1*1 .

53
30

20

T

t

1

0.001%

rms

99?

July 3, 1973 July 2, 1973

> o

< O - Q — ~:

uJ

s

0)&

a)

4)&

6

rto

u

•H

a>co

o

*J

>

•H

«-> 03

i-HV

Ct,

BQ-0

3

10

."II

20 -

-30

-40

•50

60

-70

! i

j j_

. i i

I'-'-i

12 1 M

3 15 9 10 11 12 1 2 i i 5 N

9 10 11 12M

Hour of day

Figure 22. Summary of 1 MHz, H-field variations from

each APD. Hayes Hall.

54
T»2

<D

4-> 0)

O.

<UU

O

cxs

cdo

u

u

co

4->

4) 05

T3

o

0)3

*-> •Hc

60

20

10!

I I J

0.001*.

<|) rms

July 3, 1973 July 2, 1973

I 991

0r~

•10

20

•30

•40 L

-50

•60

-I L.

-70

i

i

21234567 9 10 11 12 1 2 3 4 5 6 7 N

9 10 11 12 M

Hour of day

Figure 23. Summary of 3 MHz, H-field variations from

each APD, Hayes Hall. •

55
10

;T o.oci'

(J) rms

99%

July 3, 197 3- July 2, 1973

-10

I !

•

j

i- -! i

|

I I I i

I

CDCu

<uM

<DeO

o

20

30

co

40k

c 7- .

> o i < o * Q — -

T3

o

CD3

*J •Hc

-501-

-60

-70

-80

-90

... „

()

!

12 1 2 3 4 5 6 7 9 10 11 12 1 N

2 3 4 5 6 7 10 11 12M

Hour of day

Figure 24. Summary of 10 MHz, H-field variations from

each APD, Hayes HaJ.1.

56
Hour of day

Figure 25. Summary of 30 MHz, H-field variations from

each APD, Hayes Hall.

57
m if, S

> O £ < O i Q-3

(D

IB

J-l o

<DM

1) P<6

O

Co

u

a!

CQ

o

3

55

45

35

25

15

y o.ooi'

q) rms

99%

! 1

i

1

! !

15

^ -25

c . DO

35

i - iI -!-

-4 5.

i

. ...I

. —j

I t

July 6, 1973

—

July 5, 1973

10 11 12N

11 12M

Hour of day

Figure 26. Summary of 25 kHz, H- field variations from

each APD, Willcox Dry Lake.

58
ggtj

m ,

V

*J

<u 3S

(-

p.

<uu

<ue

o

I-o

<uco

o

*->

(D>

•H

*J

C3

r-t 0) 06

PQT3

<4-l O

<D3

4-> •Hc

(30 nJ

40

30

y o.ooi%

<|) rms

99%

July 6, 1973

20

10r

10

•20

30r

-40

•50

•60

!

I

!

I

July 5, 1973

! I

O O

12 1 2 3 4 5 6 7 8 9 10 11 12 1 I 3 4 5 6 7 8 9 10 11 12 M N M

Hour of day

Figure 27. Summary of 250 kHz, H-field variations from

each APD, Willcox Dry Lake.

59
Win m

> o

" < C - Q - 3

<0

<U S

u

V

0)?

0

Sio

<l)

o

•J

0J a;

BP

o

4)3

C

30.

20

J

0.0 OH

<P rms

9 91

July 6, 1973

-5(

1

1

- 1

j

i

i !

i f

\

- - - ;

r -

—

_

If

!••;! ivj ;

: j ; 1 .

|

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1 i

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:

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1 II

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c

>

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1

1

. 1

• • 1 •

I 'i '"i-

<>

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1

i •!

>

c > \

!- : • ' <

1. i i i

1 ... _

>i

: "I

\- j--! -! -!

1 | -I- ! 'I-:!

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i

i i

-

1 :

i

j

1

i

: 1

i

-

1

j

i 1 -i

i- !

-

I -1

-

|

; . i

! i-

-

"

i i -t-

:

1

i

-

-i—i

i -1 —

i .......

: i

i !-.-!:

i . ;

- - - ~-|" :|-"

"

i

i

1

'

i '.r _" j -

:

_

! T i-

; -

•

i i

:~ F

...

! i i P. i -

1

. .. -

- 1 —

~j

i

July 5, 1973

12 1 2 3 4 5 6 7 M

9 10 11 12 1 I 3 4 5 6 7 8 9 10 11 12 N. M

Hour of day

Figure 28. Summary of 1 MHz, H-field variations from

each APD, Willcox* Dry Lake.

60
20

Ul 0) : 30-

a>

»-> 2

a>&

<uP.E

COo

co

PQ

4-1O

<B T33

*-> •Hc

60

tfl 2

r

10

T

1

0.001%

rms

99%

i

!

July 6, 1973

~i : r~ July 5, 1973

!.J. !

: l ;

10r

•20

•30

« -40

•50

-60

70

-80

I •[,;, i l i- •I I -

I.—

-I—-ii • t i

I '.._!.. ".

I.

I -!••

I

-! -I

... _i

i I

12 1 2 3 4 5 6 7 M

9 10 11 12 1 2 3 4 5 6 7 9 10 11 12M

Hour of day

? Figure 29. Summary of 3 MHz, H-field variations from

each APD, Willcox Dry Lake.

61
10

o -

8^

> c ; < O u D — 3 - X *

<u

«->

0)CU

<uu

u

p.e

COo

uo

co

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eM

cs S

T

t

1

0.001%

rms

99%

July 6, 1973

-iotJuly 5, 1973

! I i

-20

-40

<-« -so

•70

80

-90

r

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i

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62
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63
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65
4.0 CONCLUSIONS

An analysis of the measured data shows several factors

that should be considered when planning communication links,

tests and evaluations; evaluating present plant effectiveness;

and planning expanded plant facilities. These are:

(1) The main source of interference is the power lines,

with the highest levels of EMI emanating from the Irwin

Street power lines.

(2) The power lines serve as transmission' lines to bring

in electric field interference over the portion of the

spectrum from 250 kHz to approximately 500 MHz. Above

500 MHz, no noise from the power lines was detected.

Quantitative differences may be obtained from figures 9(a),

9(b), and 9(c) (Hayes Hall vs. Willcox Dry Lake).

(3) Below 250 kHz these same power lines provide some

shielding of electric field noise.

(4) Magnetic field noise comparisons indicate that

power lines have little effect; i.e., magnetic field

noise at Hayes Hall Compound is about the same as that

at Willcox Dry Lake.

(5) EMI generated by the mercury vapor lights is

insignificant when compared to the noise from power

lines .

(6) Time variations of magnetic noise have a diurnal

range of 95 dB at 25 kHz and have a short-term range

of 35 dB at 30 MHz. Results are summarized in

figures 32 and 33. During local thunderstorms, the

amplitude and character of the interference change.

(7) The CW carriers from external transmitters can

provide a serious source of interference at Hayes Hall

in those cases where selectivity or directivity cannot

be used to discriminate against them.

(8) Willcox Dry Lake area is much quieter with

regard to electric field noise than Hayes Hall

Compound.

(9) The shielded room provides only a shielding

effectiveness of 50 decibels at 1000 MHz. A welldesigned-and-constructed room will typically provide

100 to 120 decibels at this frequency.

66
5.0 RECOMMENDATIONS

Specific recommendations must be based on many factors

in addition to electromagnetic noise environment. Consequently,

results and data in this report can be used only in conjunction

with other factors when making future decisions.

For better use of existing facilities, USASATEC testing

should be done near position 2 within Hayes Hall compound, or,

for minimal interference at certain frequencies, at Willcox

Dry Lake

Testing during thunderstorms should be avoided, both for

EMI reduction and for safety.

Power lines should be avoided, especially high-voltage

lines along Irwin Street.

Unless power lines were buried throughout Ft. Huachuca,

little would be gained by burying power lines within Hayes

Hall Compound.

The mercury lights do not make a significant contribution to the EMI environment.

If cw signals are a problem, either (1) tighter control

of local sources will have to be achieved; (2) the shielded

room will have to be used; or (3) a remote site such as Willcox Dry Lake will have to be used. In case (3) , some

carriers would still be present.

Shielding effectiveness of the shielded room can

probably be improved by:

(1) Uniformly tightening the bolts that hold the room

together

(2) Checking the line filters for proper bonding and

tightening if necessary.

(3) Routinely cleaning finger stock on the door.

67
ACKNOWLEDGMENTS

The following people made major contributions to this

work: John Workman, Bob Nelson, Leon Saulsbery, Bill Bensema,

and Nancy Tomoeda. Winston Scott and John Workman processed

the data and assisted with preparation of the final report.

Sharon Foote and Janet Becker typed the drafts and final

report

Steve Lung and Phil Wralstad (USASATEC) made necessary

arrangements to allow measurements at Ft. Huachuca and

Willcox Dry Lake.

68
REFERENCES

W.Q. Crichlow, et al . , Amplitude probability distributions for atmospheric radio noise, NBS Monograph 23, 1960.

Taggart , H.E. and J.L. Workman, Calibration principles

and procedures for field strength meters (30 Hz to

1 GHz), NBS Technical Note 370, March 1969.

R.J. Matheson, Instrumentation problems encountered

making man-made electromagnetic noise measurements for

predicting communication system performance, IEEE Trans,

on EMC, Vol. EMC -12, p. 151, Nov. 19 70.

Greene, F.M., NBS field- s trength standards and measurements

(30 Hz to 1000 MHz), Proc. IEEE, Vol. 55, No. 6, June 1967.

69
NBS-lUA (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 74-361

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Electromagnetic Interference Measurements at ASA,

Fort Huachuca, Arizona

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

H.fc. laggart and J.W. Adams

8. Performing Organ. Report. No.

9. performinGtjrganization name and address

national bureau of standards

department of commerce

washington, d.c. 20234

10. Project/Task/Work Unit No. 2728463

11. Contract/Grant No. ASA Order No.

16 Mar 73 ASA-001*

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U.S. Army Security Agency

Test and Evaluation Center

Fort Huachuca, Arizona

13. Type of Report & Period Covered

Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

*2132040 325-4025 P675701-2550 S02-086 675701-91894-00000-2550-73503(13671)

area 67

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

This report describes the work performed for the U.S. Army Security

Agency Test and Evaluation Center (USASATEC) , Fort Huachuca, Arizona, during the period from April 1973 to November 1973. The purpose of the project was to measure, analyze, and evaluate the electromagnetic

environment at selected sites and to recommend methods of reducing the

present levels of electromagnetic interference (EMI). The chief sources

of EMI were the power lines in the area and sferics from thunderstorms.

Both broadband EMI measurements and amplitude probability distribution

measurements were made. Both electric and magnetic fields were measured.

The frequency range covered was 15 kHz to 10 GHz. Measurements were

made at three locations: 1) at Fort Huachuca USASATEC; 2) Willcox Dry

Lake; and 3) Boulder, Colorado. The report contains the test results, conclusions, and recommendations.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

APD ; field strength; interference; power lines.

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