Predicted and Measured Field Strengths 

in the Boulder, Colorado, Area from 

Two Proposed Terrestrial Digital 

Television Tower Sites 

Christopher L. Holloway, Frank H. Sanders, and Paul M. McKenna 

NIST Technical Note 1519 

and 

NTIA Report 01-387

Institute for Telecommunication Sciences

National Telecommunications and Information Administration

U.S. Department of Commerce

National Institute of Standards and Technology

Technology Administration

U.S. Department of Commerce
NIST Technical Note 1519 

and 

NTIA Report 01-387 

Predicted and Measured Field Strengths in the

Boulder, Colorado, Area from Two Proposed 

Terrestrial Digital Television Tower Sites

 Christopher L. Holloway 

 Radio-Frequency Technology Division 

 Electronics and Electrical Engineering Laboratory 

 National Institute of Standards and Technology 

 Boulder, CO 80305 

 Frank H. Sanders and Paul M. McKenna 

 Institute for Telecommunication Sciences 

 National Telecommunications and Information Administration 

 Boulder, CO 80305 

 May 2001 

U.S. Department of Commerce 

Donald L. Evans, Secretary 

National Institute of Standards and Technology National Telecommunications and Information Administration 

Karen H. Brown, Acting Director John F. Sopko, Acting Assistant Secretary for Communications and Information
National Institute of Standards U.S. Government Printing Office For sale by the 

and Technology Washington: 2001 Superintendent of Documents 

Technical Note 1519 U.S. Government Printing Office 

Natl. Inst. Stand. Technol. Stop SSOP, 

Tech. Note 1519 Washington, DC 20402-0001 

144 Pages (May 2001) Phone: (202) 512-1800 

CODEN: NTNOEF Fax: (202) 512-2250 

 Internet: bookstore.gpo.gov 

and 

National Telecommunications and 

Information Administration 

Report 01-387 
Executive Summary 

In this report, we have analyzed the expected electric (E) field strengths in the Boulder 

area from two proposed terrestrial DTV transmitter locations, the Eldorado Mountain site 

and the Squaw Mountain site. The Eldorado Mountain and Squaw Mountain sites were 

selected from the set of candidate sites because these two possible sites bound the 

propagation environment that would occur at both the Table Mountain National Radio 

Quiet Zone (NRQZ) and the Department of Commerce (DOC) Laboratories in Boulder. 

The Eldorado Mountain site affords substantial line-of-sight coverage over the Boulder 

area, while the Squaw Mountain site affords only indirect (diffractive) coverage over the 

same area. The other possible tower sites fall between these two types of propagation 

conditions. 

The goals of this work were to determine the expected E-field strengths at the Table 

Mountain NRQZ located north of Boulder, Colorado and at the DOC Laboratories 

located at 325 Broadway in Boulder, Colorado. This study also assessed the potential 

impacts of the proposed sites on a broad range of Federal Government research and 

metrology programs that depend upon a relatively quiet radio-frequency electromagnetic 

environment (see Section 8). The DOC conducted tests and analyses to assess whether Efield strengths produced by the DTV transmissions from either proposed site could meet 

the FCC’s regulatory limits for the Table Mountain NRQZ. In addition, tests and analyses 

were performed to ascertain the impact of DTV transmissions from either proposed site 

on measurement efforts that are performed on a regular basis at the DOC Laboratories. 

In this study, measured and predicted E-field strengths are used to estimate the E-field 

strengths in the Boulder area for the proposed transmitter antenna heights of two possible 

transmitter locations, Eldorado Mountain and Squaw Mountain. With these predictions, 

we were able to determine the E-field strengths at both the DOC Laboratories and at the 

Table Mountain NRQZ. The results show that at the Table Mountain NRQZ, the 

predicted E-field strengths are about 0.3 V/m for a single transmitter on Eldorado 

Mountain at 1.0 MW EIRP. This number exceeds the FCC’s regulatory (47 CFR 

73.1030) limit by about an order of magnitude (approximately a factor of 10). At that 

level, research at the Table Mountain NRQZ will be compromised. The results also show 

that the E-field strengths at the DOC Laboratories for a single transmitter located on 

Eldorado Mountain are about 1 V/m for 1.0 MW EIRP. These field strengths are high 

enough to possibly jeopardize the sensitive measurements done on a routine basis at the 

DOC Laboratories, as discussed in Section 8. By comparison, the results show that, at 

the Table Mountain NRQZ, the predicted E-field strengths are about 0.002 V/m for a 

single transmitter located on Squaw Mountain with 1.0 MW EIRP. These field strengths 

are within the FCC’s Table Mountain NRQZ regulatory (47 CFR 73.1030) limit. Thus, 

the results indicate that a transmitter could be located at Squaw Mountain without 

violating the FCC’s regulatory limit or adversely impacting research at the Table 

Mountain NRQZ. 

The data presented in this report illustrate that E-field strengths on the order of 0.5 V/m

to 1 V/m could be present at the DOC Laboratories. The studies presented in Section 8 

iii
illustrate only a few of the potential problems that may be experienced at the DOC 

Laboratories. 

The measured and modeled data presented in this report are for an EIRP of 1 MW. As 

indicated in the report, some of the DTV channels have maximum power allocations of 

1.64 MW EIRP. The E-field strengths presented here can be transformed to a 1.64 MW

EIRP by multiplying the data shown in all the figures by a factor of 1.3 (which would 

increase the E-field strengths by 30 %). This would result in even higher E-field strengths 

in the Boulder–Denver area than those presented here, and could cause even greater 

interference at both the DOC facilities (see Sections 5 and 9). The FCC indicated in 

references cited in the report that in the future, adjustments to the allocated power levels 

may be granted under some situations, in order to allow power levels higher than 1.64 

MW. If these higher power levels are granted, the result would be even higher E-field 

strengths in the Boulder–Denver area than those presented here. 

For DTV reception, the FCC specifies a minimum (i.e., for noise limited DTV reception) 

E-field strength of 41 dBμV/m (0.11 mV/m) for a receiving antenna at a height of 9.14 m

(30 ft). Using the ITM prediction model, we also predicted the coverage areas where the 

FCC’s minimum field strength for acceptable reception is met or exceeded. From the 

results shown here, it is seen that the two proposed transmitter locations (Eldorado 

Mountain and Squaw Mountain) have basically the same DTV coverage areas (see 

Section 6). However, the data in these results show that a transmitter on Squaw Mountain 

will not violate the FCC’s regulatory limits protecting the Table Mountain NRQZ, if 

these transmissions occur on the currently allotted DTV frequencies. 

In a recent document (cited in this report, see Section 9), the Advanced Television 

Systems Committee (ATSC) Task Force on RF System Performance has suggested that 

in order to overcome the indoor DTV reception problem, field strengths at the 9.14 m

(30 ft) reference height may need to be increased substantially to 97 dBμV/m. This is an 

increase of 56 dB over the FCC minimum E-field strength, which is equivalent to an 

increase by a factor of approximately 631 in field strength. This 56 dB increase can be 

obtained by either substantially reducing the coverage area of DTV reception, by 

reducing the DTV payload data rate or by increasing the allocated transmitter power 

levels by an unrealistic 56 dB. Obviously, if transmitter power levels are increased to 

compensate for the indoor reception problem, higher E-field strengths than those 

presented in this report could occur at both the Table Mountain NRQZ and at the DOC 

Laboratories, as well as at other areas throughout Boulder. 

While the results presented in this report are for omnidirectional or omni-azimuthal 

directional antenna patterns, the actual antennas that will be used for the proposed tower 

will have some type of antenna pattern associated with them. The report discusses 

(Section 7) how the results presented here can be used once the antenna pattern of the 

proposed towers are known. 

iv
Contents 

1. INTRODUCTION................................................................................................. 2 

1.1 Electric Field Strength ................................................................................ 2 

1.2 Organization of the Report...........................................................................6 

2. SPECTRUM SURVEY AT THE NRQZ AND AT THE DOC 

LABORATORIES FOR 30 MHz TO 960 MHz..................................................8 

2.1 Measurement System...................................................................................8 

2.2 Measurement System Calibration and Correction to Incident Field 

Strength........................................................................................................9 

2.3 Measurement System Data Collection Algorithms and Parameters............9 

2.4 Data Storage and Analysis.........................................................................10 

2.5 Table Mountain NRQZ Spectrum Survey Results: Vertically Polarized 

Measurements............................................................................................11 

2.6 DOC Laboratories Spectrum Survey Results: Vertically Polarized 

Measurements............................................................................................11 

2.7 Analysis of Existing Television Signal Environment: Horizontally 

Polarized Measurements............................................................................11 

3. DESCRIPTION OF THE MEASUREMENT SYSTEM FOR DTV E-FIELD 

STRENGTH MEASUREMENTS ......................................................................19

3.1 Calibration of System ................................................................................20 

3.2 Data Analysis: Measured E-field Strengths...............................................20 

4. COMPARISON OF MEASURED AND PREDICTED E-FIELD 

STRENGTHS.......................................................................................................25 

5. PREDICTED E-FIELD STRENGTHS FOR THE PROPOSED TOWER 

HEIGHTS.............................................................................................................28

6. DTV E-FIELD STRENGTH REQUIREMENT...............................................29

7. ANTENNA PATTERN EFFECTS.....................................................................30 

8. EFFECTS OF BROADBAND TRANSMISSION ON SENSITIVE 

MEASUREMENTS .............................................................................................31

9. SUMMARY AND CONCLUSION ....................................................................35

10. REFERENCES.....................................................................................................39

APPENDIX A: MEASURED E-FIELD STRENGTHS OF THE 1998 AND 2001 

SPECTRUM SURVEY............................................................................................101

APPENDIX B: MEASURED POWER LEVELS .................................................125 

v
Trade Name Disclaimer 

Certain commercial equipment, instruments, or materials are identified in this report to 

adequately specify conditions used in obtaining the reported information. Such 

identification, implied or specific, does not represent a recommendation or endorsement 

of the companies or the products by the National Institute of Standards and Technology 

or the National Telecommunications and Information Administration, nor does it imply 

that the materials or equipment identified are necessarily the best available for the 

purpose. 

vi
Predicted and Measured Field Strengths in the Boulder, Colorado, Area from 

Two Proposed Terrestrial Digital Television Tower Sites

Christopher L. Holloway 

National Institute of Standards and Technology 

Boulder, Colorado 80305 

Frank H. Sanders and Paul M. McKenna 

National Telecommunications and Information Administration 

Boulder, Colorado 80305 

A study was performed to determine the increase in ambient electromagnetic 

field strengths that would result from a proposal to locate a cluster of terrestrial 

digital television (DTV) transmission towers in proximity to the Department of 

Commerce (DOC) Laboratories in Boulder, Colorado. The primary objective of 

this study was to assess the impact on a broad range of Federal Government 

research and metrology programs that depend upon the relatively quiet radiofrequency electromagnetic environment. Radio-wave propagation measurements 

were performed for two terrestrial DTV frequencies (533 MHz and 772 MHz), 

and used to verify predicted DTV electric field strengths obtained from the DOC 

Irregular Terrain Model (ITM). The measured data were also used to determine 

the variation in received signal strength over small distance intervals. Radiowave propagation measurements were performed at both frequencies using two 

possible mountaintop transmitter locations, Eldorado Mountain and Squaw 

Mountain. The first (Eldorado Mountain) affords substantial line-of-sight 

coverage over the Boulder area, and the second (Squaw Mountain) affords only

indirect (diffractive) coverage over the same area. The two propagation 

conditions from each site, direct and indirect, respectively, are compared to the 

ITM predictions. The relative variations in measured and predicted signal 

strengths are compared as a function of frequency and of propagation conditions. 

Measured and predicted data were found to be in close agreement. This provides 

confidence that the theoretical predictions of received signal strengths at given 

locations in the Boulder area are accurate. It was found that in some locations, 

the ambient field strengths for 1 MW of transmitter power from a single station 

will exceed 1 V/m. 

Key words: digital television (DTV), field strength measurements, Irregular 

Terrain Model (ITM), National Radio Quiet Zone (NRQZ), 

propagation modeling, spectrum survey

1
1. INTRODUCTION 

The Federal Communications Commission (FCC) has mandated that all full-service 

(high-power) television broadcasters be transmitting a digital television (DTV) signal and 

be prepared to terminate their analog television (TV) broadcasts by 2006 [1]. In the 

United States, the analog television broadcast standard, or National Television System

Committee (NTSC), allocates 6 MHz of bandwidth per channel [2, 3]. The high-power 

TV broadcasters have each been provided with a paired digital channel, usually in the 

“core” TV channels (2 through 51). If market penetration of digital television is 

sufficient, then the intent of the FCC directive is for analog TV broadcasts to cease and 

for some of the analog spectrum to be returned to the public for other communication 

services. In this report, the term DTV includes high-definition digital TV (HDTV). 

Current analog TV channels 52 through 69 will be reassigned to other uses, including the 

provision of additional spectrum for public-safety users (including a number of 

interoperability channels); some of this spectrum will also be auctioned for commercial 

wireless telecommunications network applications. Table 1 shows the present analog 

frequencies for the different TV channels along with the new DTV frequencies for some

TV channels in the Denver, Colorado, Designated Market Area (DMA). Some of these 

TV channels have been authorized to transmit at effective radiated power (ERP) levels as 

high as one megawatt (1 MW), where ERP is defined as the product of the power 

supplied to the antenna and its gain relative to a half-wave dipole in a given direction [4]. 

The allocated power levels for these TV channels are also shown in table 1. Also shown 

in this table are the allocated power levels in units of equivalent isotropically radiated 

power (EIRP), defined as the product of the power supplied to the antenna and its gain 

relative to an isotropic antenna in a given direction [4]. Note, EIRP = 1.64 ERP. EIRP is 

used throughout this report. 

In Reference [1], the FCC indicates that in the future, adjustments to the allocated power 

levels may be granted under some situations, which would allow transmitter power levels 

higher than 1 MW ERP (1.64 MW EIRP). The Further Notice of Proposed Rulemaking 

(FNPRM) [5] indicates that maximum ERP of 5 MW (or 8.2 MW EIRP) is possible. 

1.1 Electric Field Strength 

 

A minimum DTV E-field strength of 41 dBμV/m (1.12 V/m) at a receiving antenna 

height of 9.14 m (30 ft) is assumed adequate to provide satisfactory reception, as 

recommended by the FCC [1]. Note that dBμV/m refers to decibels relative to 1 μV/m.

The table of allotments was designed to essentially replicate a broadcaster’s current 

analog Grade B coverage area with digital signal strengths greater than or equal to the 

minimum DTV electric field strength, while attempting to minimize analog-into-digital, 

digital-into-analog, and digital-into-digital co- and adjacent-channel interference with 

signals of other broadcasters. Transmitter power consumption is a significant operational 

cost, and it is therefore critical for broadcasters to have confidence that field strength 

prediction models are accurate, so that excessively high power levels are not transmitted. 

(High transmitter power can also increase deleterious interference, both into-digital and 

4

x10−

2
into-analog, for distant stations.) It is also critical for broadcasters to understand the 

amount by which received DTV signal strengths may vary spatially within predicted 

contours, so that power levels throughout the coverage area will be high enough to 

compensate for localities at which the actual field strength drops below the noise-limited 

field strength. 

Reception may be possible with a 9.14 m outdoor antenna (this height assumes mounting 

3 m above the rooftop of a two story residence) or indoor antenna; however, significant 

problems with reception with indoor antennas have been reported [6]. In this report, the 

Advanced Television Systems Committee (ATSC) Task Force has suggested that in order 

to overcome the indoor DTV reception problem, field strengths at the 9.14 m (30 ft) 

reference height may need to be increased substantially to 97 dBμV/m. This is an 

increase of 56 dB over the FCC 41 dBμV/m, which is equivalent to an increase by a 

factor of approximately 631 in field strength. This 56 dB increase can be obtained by 

either substantially reducing the coverage area of DTV reception or by increasing the 

allocated transmitter power levels by an unrealistic 56 dB. 

In the Colorado Front Range (the Denver metropolitan area), several sites have been 

proposed as possible locations for the new DTV transmitting antenna towers. Two of 

these proposed sites are addressed in this report. They are on Eldorado Mountain, which 

is located just south of Boulder, Colorado, and on Squaw Mountain, which is located just 

south of Idaho Springs, Colorado. Note, the Eldorado Mountain and Squaw Mountain 

sites were chosen in this study because these two possible sites bound the propagation 

environment that would occur at both the Table Mountain NRQZ and the DOC 

Laboratories. The Eldorado Mountain site affords substantial line-of-sight coverage over 

the Boulder area, and the Squaw Mountain site affords only indirect (diffractive) 

coverage over the same area. The other possible tower sites fall between these two types 

of propagation conditions. The Department of Commerce (DOC) conducted tests and 

analyses to address whether DTV transmissions from these two proposed sites will 

produce E-field strengths that exceed the regulatory FCC limits for the Table Mountain 

National Radio Quiet Zone (NRQZ) north of Boulder, Colorado [8]. In addition, these 

tests were used to ascertain whether DTV transmissions from these proposed sites will 

have an adverse impact on measurement efforts that are performed on a regular basis at 

the DOC Laboratories located at 325 Broadway in Boulder, Colorado (hereafter referred 

to as the DOC Laboratories). 

The DOC Laboratories in Boulder comprise three Federal research agencies: the National 

Institute of Standards and Technology (NIST), the National Telecommunications and 

Information Administration’s (NTIA) Institute for Telecommunication Sciences (ITS), 

and the National Oceanic and Atmospheric Administration (NOAA). All three of these 

laboratories perform different types of measurement activities at both the Broadway 

location and at the Table Mountain NRQZ. The Table Mountain NRQZ is one of only 

two national radio quiet zones in the United States (the other being the National Radio 

Quiet Zone in West Virginia/Virginia [9]). The Table Mountain NRQZ provides 

scientists and engineers with a research environment where external radio signals 

(sometimes called “ambient radio noise”) are kept to a minimum. The integrity of this 

NRQZ is mandated by both Federal regulation and state law, [8] and [10] respectively. 

3
These regulations and laws require that signal strengths from various transmitters must 

not exceed specified E-field strengths within the Table Mountain NRQZ in frequency 

bands above 1.6 MHz (table 2). Other public and private institutions besides the DOC 

Laboratories use this NRQZ for research purposes. These include the United States 

Geological Survey (USGS), the National Center for Atmospheric Research (NCAR), the 

Deep Space Exploration Society (DSES), the Radio Amateur Satellite Corporation 

(AMSAT), and Coherent Technologies, to name a few. 

In order to address the concerns of the DOC, propagation models were used to predict the 

E-field strengths at the two DOC locations (the Broadway Laboratories and the Table 

Mountain NRQZ). Various wave-propagation models have been developed that can be 

used for this task. They range from very simple free-space models to more complex 

irregular terrain models. Unfortunately, simple free-space models can be used only under 

certain conditions. A simple free-space model will give accurate results only when 

scatter-free line-of-sight conditions exist. However, the free-space model is a good 

starting point in considering broadcast field strengths and will be briefly summarized. 

Consider the antenna in figure 1, which is connected to a transmitter. Assume that this 

system is isolated in free space (i.e., no scattering objects are in the vicinity of the 

antenna). With this assumption, it can be shown [11-14] that the power density (P), and 

E-field can be related as follows 

 2 4

EIRP

πR

P = [W/m2] (1) 

and 

| E | = η P [V/m], (2) 

where 

EIRP = PtGt . (3) 

In these two expressions, EIRP is the equivalent isotropically radiated power, is the 

input power at the transmitter antenna terminals (in units of watts), and is the gain of

the transmitter antenna, which is in general a function of directional angles 

Pt

Gt

θ (elevation) 

and φ (azimuth), relative to the antenna, in spherical coordinates. is the gain relative 

to an isotropic antenna (often expressed in units of dBi, where dBi refers to antenna gain 

in decibels relative to an isotropic antenna). 

Gt

R is the distance (in units of meters) from

the transmitter antenna to an observation point (the location of a receiver), and η is the 

free-space wave impedance given by the following 

η = 120π ≈ 377 [Ω]. (4) 

4
From the expressions given in equations (1) and (2), it is observed that the power density 

P decays as 2

1

R

and the magnitude of the E-field decays as R

1 . This is illustrated in 

figures 2 and 3, where the magnitude of the E-field and the power density are plotted as a 

function of R for an EIRP of 1 MW. Also shown in these figures are the IEEE radio 

frequency (RF) population exposure limits for a typical TV frequency [15], as well as 

some international limits [16]. Figure 2 also shows the 30 mV/m FCC Table Mountain 

NRQZ limit [8], which is given in table 2 for the DTV frequencies. Notice that for a 

distance of 23 km (the distance from Eldorado Mountain to the Table Mountain NRQZ) 

the free-space field value is about an order of magnitude higher than the FCC NRQZ 

limit. By inserting the NRQZ E-field limit into the expression given in equations (1) and 

(2), the minimal distance at which the FCC NRQZ requirement is met for a given 

transmitter power level and antenna gain can be obtained as follows: 

1/ 2

min 2

4 















= E

PG R t t

π

η [m]. (5) 

For E = 30 mV/m, = 1MW, Pt Gt = 1(EIRP=1 MW), this reduces to 

183 Rmin = [km] (or 114 mi). (6) 

Figure 1 represents an idealization of a realistic wave-propagation environment. A more 

realistic environment is depicted in figure 4. The figure shows a transmitting antenna on 

a hillside that propagates energy toward a receiving antenna near the ground. In this 

scenario the radio waves that propagate toward the receiving antenna are not simply the 

free-space environment shown in figure 1. As the receiving antenna moves along the 

ground and traverses the terrain profile, the E-field strength deviates from the free-space 

calculations due to effects of the terrain. In a line-of-sight (LOS) path, the transmitter can 

be physically seen from the receiver location, e.g., points A or C in figure 4. The E-field 

for a LOS path has contributions from a direct ray, reflected ray(s), and, to a lesser extent, 

from diffracted rays. The direct ray corresponds to the free-space result discussed above. 

The reflected rays are caused by multiple reflections due to objects in the environment 

(e.g., the ground, mountains, hillsides, trees, rocks, cars, buildings, people, etc.). The 

diffracted rays result from scattering from the edges of these objects. In a non-line-ofsight (non-LOS) path, the transmitter cannot be seen from the receiver location, e.g., 

point B in figure 4. The E-field for a non-LOS path is the result of contributions from

only reflected rays and diffracted rays. In these cases, the direct, reflected, and scattered 

rays may add up constructively or destructively to cause the received signal strength to be 

larger or smaller than that predicted using the free-space model. In order to calculate the 

field strength in these more complex environments, sophisticated irregular terrain models 

must be used. 

There are various irregular terrain models available for these calculations [17-19]. In the 

calculations presented in this report, the ITS Irregular Terrain Model (ITM) developed at 

5
the DOC Laboratories is used [17-20], which is based on the work of Longley and Rice 

[21]. This model was developed during the 1950’s and 1960’s and has been continuously 

improved throughout the years. For the predictions reported here, this model uses USGS 

digital terrain elevation data to determine the actual terrain profiles for the area of

interest. Once the terrain features are determined, electromagnetic models are used to 

calculate the E-field strengths at any desired location given a transmitter’s height, 

antenna gain, and power level. The ITM is widely used by the broadcast and 

communication industries. 

In this report, we use the ITM to predict the E-field strengths at the DOC Laboratories 

and at the Table Mountain NRQZ for transmitters located at the proposed Eldorado 

Mountain and Squaw Mountain sites. However, to verify that the modeled results for the 

two proposed locations and tower heights are accurate, comparison to measured data is 

required. Since measurements of E-field strengths based on proposed transmitter tower 

heights (approximately 116 m (380 ft) at Eldorado Mountain and approximately 60.96 m

(200 ft) at Squaw Mountain), and at the maximum proposed transmitting power levels 

(i.e., 1 MW ERP or 1.64 EIRP) are impractical, measurements were carried out at 

reduced transmitter antenna heights and power levels. The proposed transmitter tower 

heights for the two sites were obtained from either the landowners or public documents. 

The measurements were performed in the geographic area of interest to the DOC 

Laboratories at 533 MHz and 772 MHz, i.e., frequencies near the lower and upper ends 

of the UHF DTV spectrum allotment for several of the local broadcast stations. The 

propagation measurements were performed with fixed transmitters placed on the two 

mountaintops and a land-mobile receiver and data recording system. The two 

mountaintop locations used were the proposed Eldorado Mountain and Squaw Mountain 

sites. The mobile van-based receiver system was driven throughout the Boulder area, and 

E-field strengths were measured as a function of location across the area. Both line-ofsight and obstructed (shadowed) propagation paths were encountered during the 

measurements. For model validation, measured field strengths were compared to ITM 

calculated data as a function of location and frequency. The data also revealed the 

variation in received field strength as a function of location, for both line-of-sight and 

shadowed propagation. Once the model predictions were confirmed with the 

measurements, the ITM propagation model was used to calculate the E-field strengths for 

the proposed transmitter heights and power levels at the two proposed sites. 

1.2 Organization of the Report 

This report is organized as follows: Section 2 presents recently measured E-field strength 

at both the Table Mountain NRQZ and the DOC Laboratories, illustrating that the FCC 

E-field strength limits are currently maintained at the NRQZ and exhibiting the current 

field strengths at the DOC Laboratories. In Section 3, the measurement system is 

described and the measured data for the two different transmitter sites are shown. Also in 

Section 3, the measured data were scaled to the proposed transmitter power level to 

indicate the expected E-field strengths at both the DOC Laboratories and at the Table 

Mountain NRQZ north of Boulder. In Section 4, predicted E-field strengths obtained 

from the ITM are compared to the measured data. In Section 5, calculated E-field 

6
strengths are presented for the proposed antenna heights and power levels for the two 

different proposed transmitter sites. Section 6 discusses the FCC field strengths 

recommended for DTV reception. Also in this section, field strength plots for the FCCrecommended 9.14 m (30 ft) receiving antenna height are presented to illustrate predicted 

DTV reception in the Boulder–Denver area from the two proposed sites. In Section 7, 

antenna pattern effects are discussed. Section 8 discusses the effects of broadband 

transmission on sensitive measurement systems. Finally, we summarize the results and 

discuss the possible impact of the proposed sites on the scientific activities at both the 

DOC Laboratories and at the Table Mountain NRQZ facility. 

In this report all measured data are scaled to a 1 MW EIRP and all the predicted E-field 

strengths are calculated for a 1 MW EIRP. Use of a 1 MW EIRP facilitates rescaling 

both the measured and calculated field strengths to any other desired EIRP level, as the 

need arises. 

Table 1. Frequencies and power allocations for analog frequencies for the different TV 

channels along with the new DTV frequencies for some TV channels in the Denver, 

Colorado, Designated Market Area (DMA). 

Current 

NTSC 

channel 

Current 

frequency

bands (MHz) 

New 

DTV 

channel 

New DTV 

frequency bands 

(MHz) 

Allocated DTV 

ERP 

(MW)

Allocated DTV 

EIRP 

(MW)

2 54-60 34 590-596 1.0 1.64

4 66-72 35 596-602 1.0 1.64

6 82-88 18 494-500 1.0 1.64

7 174-180 17 488-494 1.0 1.64

9 186-192 16 482-488 1.0 1.64

12 204-210 38 614-620 1.0 1.64

14 470-476 15 476-482 0.099 0.164

20 506-512 19 500-506 0.248 0.407

31 572-578 32 578-584 0.233 0.383

41 632-638 40 626-632 0.0748 0.129

50 686-692 51 692-698 0.0817 0.134

59 740-746 43 644-650 0.01448 0.024

Table 2. Specified E-field strength limits for the Table Mountain NRQZ for the VHF and 

UHF frequency bands. 

Frequency band (MHz) E-field limit (μV/m) E-field limit (dBμV/m)

1.6-470 10,000 80.0

470-890 30,000 89.5

>890 1,000 60.0

7
2. SPECTRUM SURVEY AT THE NRQZ AND AT THE DOC 

LABORATORIES FOR 30 MHz TO 960 MHz

Spectrum occupancy measurements provide data on expected E-field strengths and 

probabilities of occurrence that are essential for assessing the degree of utilization at a 

given site or in a given area. NTIA has published a set of reports [22-25] documenting 

spectrum occupancy between 100 MHz and 19.7 GHz in some of the largest metropolitan 

areas in the United States. 

In June 1998, a spectrum survey (E-field strength measurements) was performed inside 

the Table Mountain NRQZ and at the DOC Laboratories to determine E-field strengths 

using a vertically polarized receiving antenna. In April 2001, a spectrum survey was 

performed inside the Table Mountain NRQZ and at the DOC Laboratories to determine 

E-field strengths for a horizontally polarized receiving antenna. The results of these 

surveys are presented in this section. 

2.1 Measurement System

The NTIA Radio Spectrum Measurement System (RSMS) was used to perform the field 

strength measurements (or spectrum survey). Hardware, software, and methodology used 

for this survey were the same as for earlier surveys referenced above. Those reports may 

be consulted for detailed descriptions of broadband spectrum survey techniques used at 

the Table Mountain NRQZ. 

The RSMS is a mobile, self-contained computer-controlled radio-receiving system

capable of many measurement scenarios over a frequency range of 30 MHz to 22 GHz. 

Figure 5 is a view of the RSMS with telescoping masts raised and antennas mounted for a 

broadband spectrum survey such as was performed at Table Mountain. The large box on 

the rear of the RSMS is an RF-shielded enclosure containing the measurement 

equipment. 

The masts may be raised to as much as 9 m above ground level. For collection of 

spectrum data between 30 MHz and 960 MHz at Table Mountain, the forward mast was 

raised to full height. An omni-azimuthal directional antenna with a nominal frequency 

range of 30 MHz to 1000 MHz was used to receive signals. A 12 m RF cable connected 

the antenna to the measurement system input port, located inside the van. 

The RSMS measurement system is shown as a block diagram in figure 6. It consists of 

two independent systems, each with its own antennas, receiver and signal processing 

equipment, and controller/data-recording computers. The two are designated System 1 

and System 2. System 1 is on the right-hand side of figure 6. For the Table Mountain 

NRQZ survey, this system was used to measure signals between 30 MHz and 960 MHz. 

System 1 is built around a Hewlett-Packard 8566B spectrum analyzer and a HewlettPackard 85685A preselector. The preselector provides low-noise preamplification for a 

typical measurement system sensitivity of about 10 dB across the range of 30 MHz to 

960 MHz. The preselector also provides bandpass filtering ahead of the preamplification, 

8
to protect the measurements from the effects of strong signals in close proximity to the 

measurement frequencies. Bandpass filters are varactors below 500 MHz and are yttriumiron-garnet (YIG) above 500 MHz. Variable attenuation is available ahead of the 

bandpass filtering in the 85685A, but was not required for the NRQZ measurements. 

The measurement system was controlled via a PC-compatible controller running customdeveloped ITS measurement software. The computer program set all measurement 

parameters to operator specifications. Parameters are varied on a band-by-band basis (see 

measurement system data collection algorithms, below). The computer performed 

measurements on a band-by-band basis, in accordance with a preconfigured sequence for 

the bands between 30 MHz and 960 MHz. The computer recorded all measurement data 

to an internal hard drive for subsequent retrieval and analysis at the NTIA/ITS laboratory. 

2.2 Measurement System Calibration and Correction to Incident Field Strength

The measurement system was calibrated at least once every 24 hours during the spectrum

survey. RSMS calibrations make use of a NIST-traceable standard noise diode at the 

antenna connection point. The procedure is standard Y-factor, in which measured power 

with the noise diode turned on is compared to measured power with the noise diode 

turned off. System noise figure and gain are computed across the entire frequency range 

to be surveyed. Reports [22] through [25] contain detailed descriptions of this technique 

as implemented for the RSMS. 

As data are collected, all measured amplitudes are corrected for the system gain. 

Corrected amplitudes are stored for later retrieval and analysis. These data are in units of 

decibels relative to 1 mW (dBm) for a measurement system with 50 Ω impedance. 

Measured data are converted to other units, if necessary, during post-measurement data 

analysis. The conversion to incident field strength is accomplished by implementing the 

following equation (see References [11] and [26] for details): 

meas Gr | E |= P + 77.2 + 20log( f ) − , (7) 

where |E| is the magnitude of the E-field strength at the antenna in units of dBμV/m,

Pmeas is the measured power in units of dBm, f is the frequency in units of megahertz 

(MHz), and Gr is the gain of the measurement antenna (the receiver antenna) at frequency 

f in units of dBi. Note, dBm refers to decibels relative to 1 mW, and dBi refers to 

antenna gain in decibels relative to an isotropic antenna. 

2.3 Measurement System Data Collection Algorithms and Parameters

RSMS data collection algorithms and parameters are tailored to the characteristics of the 

signals that typically occupy each spectrum band. The two fundamental algorithms that 

are used are swept-frequency and stepped-frequency. Swept-frequency measurements 

require that data be collected as the measurement system is continuously tuned across a 

9
frequency range of interest. Swept-frequency measurements are used in non-radar bands. 

Stepped-frequency measurements require that data be collected at fixed-tuned 

frequencies, with detectors (usually peak) operated at each frequency for specified 

intervals of time. Stepped-frequency measurements are used in radar bands. For the 

purposes of this survey, stepped-frequency measurements were performed between 

420 MHZ and 450 MHz and between 900 MHz and 930 MHz. All other bands utilized 

swept-frequency measurements. 

Measurement parameters within each band are specified for maximum probability of 

intercept (POI). POI is maximized through careful selection of intermediate frequency 

(IF) bandwidth, video (post-detector) bandwidth, and detector type (e.g., peak versus 

average). The IF bandwidth is selected to match or slightly exceed the typical signal 

bandwidth within each band. Video bandwidth equals or slightly exceeds IF bandwidth. 

Detection may be either peak or sample, depending upon signal characteristics. Details 

are provided in References [22] through [25]. 

During the one-week period of this survey, the bands were visited in accordance with a 

preconfigured measurement sequence. The sequence was designed to ensure that each 

band was measured at least once during each hour of the diurnal cycle, and usually bands 

were measured several times during each hour. Bands that normally show highly 

dynamic changes in activity (e.g., land mobile radio bands) were visited much more 

frequently than low-dynamic bands (e.g., broadcasting). Details are described in 

References [22] through [25]. 

2.4 Data Storage and Analysis

All data for the Table Mountain NRQZ survey were recorded to the controller PC’s 

internal hard drive. The data were later archived. Data initially recorded within each band 

showed maximum, minimum, and average signal strengths for periods of about a minute 

each, as described more fully in Reference [22] through [25]. Typically, each of these 

raw recordings was produced from dozens or even hundreds of individual spectrum

analyzer sweeps. 

When data were retrieved for analysis, all raw recordings for each band were combined 

to show the overall maximum, minimum, and average signal strengths within each band 

during the entire measurement period of one week. The cumulative data for all bands 

between 30 MHz and 960 MHz for the 1998 spectrum survey for a vertically polarized 

antenna are presented in Appendix A of this report (figures A.1 through A.34), and 

discussed in Sections 2.5 and 2.6. The cumulative data for all bands between existing TV 

channels from the 2001 spectrum survey for a horizontally polarized antenna are 

presented in Appendix A of this report (figures A.35 through A.43), and discussed in 

Section 2.7. 

10
2.5 Table Mountain NRQZ Spectrum Survey Results: 

Vertically Polarized Measurements 

Table 3 summarizes the measured occupancy and strengths on a band-by-band basis for 

the Table Mountain NRQZ. All signals that are required to meet the 47 CFR 73.1030 

limits within the Table Mountain NRQZ were observed to be in compliance. Moreover, 

virtually all other measured signals within the NRQZ also meet the limits. This may be 

partly due to the relatively rural location of the NRQZ. Of the handful of signals that do 

not meet the limits (and which are not required to meet them, because they are mobile 

systems), the measurement data indicate that field strengths are typically exceeded only 

briefly. 

The results of this spectrum survey allow us to conclude with certainty that for vertically 

polarized measurements the NRQZ is, in fact, quiet. It therefore remains a useful and 

necessary location for radio experiments that cannot be performed in the presence of 

high-level background signals. 

2.6 DOC Laboratories Spectrum Survey Results: 

Vertically Polarized Measurements 

As a comparative data set, a spectrum survey identical to the one at the Table Mountain 

NRQZ was performed at the DOC Laboratories in June 1998. The same measurement 

hardware and software were used as that for the Table Mountain survey. The RSMS was 

located next to the NIST groundscreen, an outdoor antenna range located on the west side 

of the DOC site. The location afforded a limited line-of-sight view of the city of Boulder, 

but was well within a propagation shadow for most Denver-area broadcast transmitters 

(on Lookout Mountain, near Golden, Colorado). 

The groundscreen measurements were run for a week. Plots of the measured E-field 

strengths are shown in Appendix A, figures A.18 through A.34. Table 4 summarizes the 

measured occupancy and strengths on a band-by-band basis for the NIST groundscreen. 

In most bands between 30 MHz and 960 MHz, the NIST groundscreen shows 

significantly higher signal strengths, and often more ambient noise, than the same bands 

within the Table Mountain NRQZ. Therefore, the Table Mountain NRQZ is an important 

resource for carrying out high-sensitivity, low-noise radio-wave measurements in these 

bands. 

2.7 Analysis of Existing Television Signal Environment: 

Horizontally Polarized Measurements 

The 1998 spectrum surveys at the Table Mountain NRQZ and the NIST groundscreen at 

the DOC Laboratories were performed with vertically polarized measurement antennas. 

This polarization, although useful for measuring most incident signals (land mobile radio, 

and radar, for example), was cross-polarized to most (horizontally polarized) television 

signals. To provide maximum coupling to television signals, the 1998 measurements 

were repeated between April 12–20, 2001, at the Table Mountain NRQZ and at the NIST 

groundscreen at the DOC Laboratories, this time using a horizontally polarized log 

11
periodic antenna (LPA). Measurements were also performed with the LPA at a second 

location at the DOC Laboratories, at the end of Wing 4 of Building 1 (the Radio 

Building). Other than the antenna used, all measurement conditions and parameters at 

these locations matched those of the 1998 spectrum survey. 

The LPA was pointed in azimuth to maximize received signal strength from ambient 

television signals at these locations (that is, approximately toward Lookout Mountain). 

The gain of the LPA was factored into resulting measurements of incident field strength 

at these locations. 

Because several television stations were already transmitting in the Denver area when the 

Table Mountain NRQZ was created, transmissions from those stations were 

grandfathered at preexisting levels exceeding the Table Mountain NRQZ limits. Those 

stations, and the strengths at which they are permitted to exceed the NRQZ thresholds, 

are shown in table 5. 

The measurement results are shown in figures A.35 through A.43 and are summarized in 

tables 6 through 8. In these figures, maximum, minimum, and mean levels during the 

measurement period are shown. Additionally, note that the relatively high level of 

television carriers at the Table Mountain NRQZ required the insertion of 10 dB of 

attenuation in the bands with grandfathered signal strengths when the polarizations were 

matched. This attenuation was also used in the measurements in the other television 

bands, and at the other measurement locations, for the sake of consistency. This need for 

insertion of such attenuation is, in general, undesirable for DOC research programs 

conducted at the Table Mountain NRQZ and at the DOC Laboratories (see Section 8). 

Table 6 summarizes the measured occupancy and strengths at the different locations for 

the 54 MHz through 88 MHz frequency range. Television signal strengths at the Table 

Mountain NRQZ are currently at the prescribed limits, including grandfathered signal 

strengths for Channels 4 and 6. Background noise levels on Channel 3 (unoccupied) are 

somewhat higher with horizontal polarization than with vertical polarization. Comparison 

of the Table Mountain NRQZ measurements with those performed on the NIST 

groundscreen facility and the end of Wing 4 of the NIST/ITS Radio Building on 

Broadway in Boulder, shows that the received television carrier field-strengths are higher 

within the NRQZ than at the DOC Laboratories on Broadway. But, apart from the TV 

signals, the spectrum is typically quieter at the Table Mountain NRQZ than at the 

Broadway locations. The noisier environment at the DOC Laboratories is due presumably 

to extensive development in the Boulder area. The characteristics of the ambient noise on 

the DOC Laboratories vary somewhat as a function of antenna polarization and precise 

location, but in no case is the ambient noise on the campus totally abated by polarization 

or location. 

Table 7 summarizes the measured occupancy and strengths at the different locations for 

the 174 MHz through 216 MHz frequency range. Television signal strengths at the Table 

Mountain NRQZ are currently at the prescribed limits, including grandfathered signal 

strengths for Channels 7 and 9. Background noise strengths are comparable with 

horizontal and vertical polarizations. Comparing the Table Mountain NRQZ 

12
measurements with those performed on the NIST groundscreen and at the end of Wing 4 

of the NIST/ITS Radio Building at the DOC Laboratories, the received television carrier 

field strengths are higher within the Table Mountain NRQZ than at the DOC 

Laboratories. But apart from the TV signals, the spectrum is typically quieter at the Table 

Mountain NRQZ than at the DOC Laboratories. The noisier environment at the DOC 

Laboratories is due presumably to extensive development in the Boulder area. The 

characteristics of the ambient noise at the DOC Laboratories vary somewhat as a function 

of antenna polarization and precise location, but in no case is the ambient noise on the 

campus totally abated by polarization or location. The overall higher level of maximum

noise in the 1998 groundscreen measurements, relative to the 2001 groundscreen data, 

may be due to the longer period over which the 1998 measurements were conducted. 

Table 8 summarizes the measured occupancy and strengths at the different locations for 

the 512 MHz through 806 MHz frequency range. Television signal strengths at the Table 

Mountain NRQZ are currently at the prescribed limits. Channel 41 appears to exceed the 

limit by 1 dB in the graph, but this is within the uncertainty of the measurement (a 

conservative estimate of the measurement uncertainty is ± 2 dB). Comparison of 

measurements at Table Mountain with those performed on the NIST groundscreen and at 

the end of Wing 4 of the NIST/ITS Radio Building at the DOC Laboratories, shows that 

the received television carrier field strengths are typically higher within the Table 

Mountain NRQZ than at the DOC Laboratories. But apart from the TV signals, the 

spectrum is typically quieter at the Table Mountain NRQZ than at the DOC Laboratories. 

The noisier environment at the DOC Laboratories is due presumably to extensive 

development in the Boulder area. The characteristics of the ambient noise at the DOC 

Laboratories are noted to vary somewhat as a function of antenna polarization and precise 

location, but in no case is the ambient noise on the campus totally abated by polarization 

or location. 

Although existing television signals are somewhat higher in amplitude at the Table 

Mountain NRQZ than at the DOC Laboratories (due to direct LOS propagation to the 

Table Mountain NRQZ versus indirect propagation to the DOC Laboratories), the 

ambient noise level at the Table Mountain NRQZ is typically less than at the DOC 

Laboratories. The ambient carrier strengths within the Table Mountain NRQZ are within 

the limits described in 47 CFR 73.1030, with the exceptions of the grandfathered limits 

for Channels 4, 6, 7, and 9. 

Due to terrain shadowing of transmissions from Lookout Mountain to the DOC 

Laboratories location, NTSC television signals typically have lower field strengths at the 

NIST groundscreen facility than within the NRQZ (which has line-of-sight coverage 

from most Denver-area NTSC broadcast station locations). This situation will change, 

and the Boulder DOC Laboratories will be subjected to significantly higher television 

signal strengths, if DTV transmitters are located in line-of-sight proximity to the DOC 

Laboratories. If that occurs, it will make the NRQZ environment even more important as 

an asset for measurements in the bands occupied by broadcast television. If new DTV 

transmitter locations do not have line-of-sight coverage of the DOC Laboratories, then a 

situation somewhat similar to the current propagation conditions may continue. 

13
Table 3. Summary of the Table Mountain NRQZ spectrum survey: vertically polarized 

measurements. 

Frequency

range 

(MHz) 

Description of activity measured at the Table Mountain 

NRQZ during one week in June 1998 

30-54 This band shows little activity. Only one signal is present full-time. Even the highest 

signal measured was more than 20 dB below the NRQZ limit. 

54-88 Television channels 2, 4, and 6 (measured with a vertically polarized antenna) are the 

significant occupants. All these signals are at or below the NRQZ limit. 

88-108 This is the FM broadcast band. All signals are below the NRQZ limit.

108-136 Air-traffic-control voice communications and aeronautical navigation aids are observed 

in this band. Although not subject to the NRQZ limits, none of these signals exceeded 

the limit. 

136-174 Land mobile radio signals are observed in this band. Most of these are intermittently 

transmitted. Some approached the NRQZ limit, but none exceeded it. Mobile signals are 

not required to meet the NRQZ limits. 

174-216 Television channels 7, 9, and 12 (measured with a vertically polarized antenna) are the 

significant occupants. All these signals are at or below the NRQZ limit. 

216-225 Little traffic is observed in this band, and all signals are well below the NRQZ limits. 

225-400 Little traffic is observed in this band, which is used primarily for military 

communications, military air traffic control, and some aeronautical radio navigation

aids. Although these signals do not need to meet the NRQZ limit, all were measured at

strengths below the limit. 

400-406 A few signals are observed in this band, which is used primarily for meteorological

transmitters. None approached the NRQZ limit. 

406-420 One signal in this land mobile radio band approached, but did not exceed, the NRQZ 

limit. These signals are not required to meet the limit. 

420-450 No activity is observed in this band, which is used for long-range military radars. No 

such radars are operated in the Table Mountain area. 

450-470 Heavy traffic is observed in this land mobile radio band. Although these transmitters do 

not need to meet NRQZ limits, only three exceeded the NRQZ limit, and then only 

momentarily.

470-512 Only television channels 14, 17, and 20 (measured with a vertically polarized antenna) 

are observed in this part of the spectrum. Their measured signals are below the NRQZ 

limit. 

512-812 UHF television signals (measured with a vertically polarized antenna) are the only

occupants observed in this part of the spectrum. Their measured signal strengths are 

well below the NRQZ limit. 

806-902 Despite heavy observed traffic in the cellular telephone and trunked radio bands in this

part of the spectrum, only a single, mobile signal (not subject to the NRQZ limits) 

momentarily exceeded the NRQZ threshold during the survey. 

902-928 Although signals in this industrial, scientific, and medical (ISM) band are not subject to

NRQZ restrictions, all observed signals were below the NRQZ limit, with a single, 

momentary exception for a single signal. Stepped measurements, performed to observe 

radar signals, show no activity. No such radars operate near Table Mountain. 

928-932 Pager signals are observed in large numbers and densities, and do exceed the NRQZ 

limit. They are not, however, required to meet the limit. 

928-960 Special mobile radio (SMR) traffic in this band is observed, and the signal densities 

were moderate compared to major metropolitan areas [22-25]. Many of these signals 

exceed the NRQZ limit, although typically for short intervals. These signals are not 

required to meet the NRQZ limits. 

14
Table 4. Summary of NIST groundscreen spectrum survey at the DOC Laboratories: 

vertically polarized measurements. 

Frequency

range 

(MHz) 

Description of activity measured at the DOC Laboratories, 

during one week in June 1998 

30-54 This band shows substantial ambient noise. The same spectrum within the Table 

Mountain NRQZ is quieter. 

54-88 Carriers for television channels 2, 4, and 6 are 20 dB to 30 dB (measured with a 

vertically polarized antenna) lower at the groundscreen than within the NRQZ. This is

due to terrain shadowing of the DOC Laboratories from the transmitter locations. 

Table Mountain obtained line-of-sight propagation to these transmitters. 

88-108 This is the FM broadcast band. Signals at the DOC Laboratories are 10 dB to 15 dB

higher than within the NRQZ. 

108-136 Air-traffic-control voice communications and aeronautical navigation aids are 

observed in this band. Power levels are comparable to those measured within the 

NRQZ, as would be expected for predominantly airborne signals. 

136-174 Land mobile radio signals are observed in this band at strengths about 8 dB higher 

than within the NRQZ. 

174-216 The highest-level carriers in this band at the NIST groundscreen are in the range of 

60 dBμV/m to 70 dBμV/m field strength, comparable to the highest carriers in this 

band at the NRQZ (one of which is as high as 78 dBμV/m). But the groundscreen 

environment is noisier, with peak noise envelope amplitudes of between 35 dBμV/m

and 40 dBμV/m. At the NRQZ, by comparison, the peak noise envelope is between 

28 dBμV/m and 30 dBμV/m.

216-225 The groundscreen shows more signal activity, and significantly more noise, than 

within the NRQZ. 

225-400 This spectrum is significantly noisier, and is occupied by more signals for a higher 

percentage of time, than within the NRQZ. 

400-406 This spectrum is noisier, is occupied by more signals, and shows as much as 40 dB

higher signal amplitude, than within the NRQZ. 

406-420 Occupancy of this band is comparable in amplitude and number of signals to the 

NRQZ. The Boulder campus shows more noise (up to about 30 dBμV/m) than the 

NRQZ (at about 20 dBμV/m). 

420-450 Noise at the groundscreen location occurs between 70 and 90 dBμV/m, as compared 

to peak strengths of only 60 to 70 dBμV/m within the NRQZ. 

450-470 Signals at the groundscreen are 5 dB to 10 dB higher than within the NRQZ. 

470-512 Due to terrain shadowing from television broadcast locations to the DOC

Laboratories, television signals (measured with a vertically polarized antenna) in this 

band are equal to or lower in power at the groundscreen than within the NRQZ. 

512-812 Terrain shadowing of the groundscreen location provides UHF television signal

strengths (measured with a vertically polarized antenna) that are comparable to those 

within the NRQZ. 

806-902 Cellular base station signals are about 8 dB higher at the groundscreen location than 

within the NRQZ. 

902-928 At the groundscreen, peak envelopes of signals in this industrial, scientific, and 

medical (ISM) band are typically at field strengths of 50 dBμV/m to 65 dBμV/m.

This is significantly higher than the typical peak envelope strengths of 40 dBμV/m to 

45 dBμV/m within the NRQZ. 

928-932 Pager signals at the groundscreen are comparable to those within the NRQZ. 

928-960 Special mobile radio (SMR) traffic in this band occurs at about 10 dB higher 

strengths than within the NRQZ. Pager signals at the two locations are comparable. 

Above 940 MHz, signals at the groundscreen are typically about 20 dB to 30 dB

higher than within the NRQZ. 

15
Table 5. Grandfathered television signal strengths at the Table Mountain NRQZ. 

Current 

NTSC 

channel 

Grandfathered signal strength within the 

Table Mountain NRQZ (dBμV/m)

Decibels exceeding the Table Mountain 

NRQZ limit of +80 dBμV/m

4 84.1 4.1

6 81.8 1.8

7 94.4 14.4

9 94.3 14.3

Table 6. Television signals between 54 MHz and 88 MHz at the different measurement 

locations. 

NTSC 

channel 

Table Mountain NIST groundscreen End of Wing 4, Bldg. 1 

2 With matched polarization on 

the measurement antenna, 

signal power is just below the 

limit (at +79 dBμV/m). 

With matched polarization 

on the measurement 

antenna, Channel 2 

maximum signal is

+70 dBμV/m.

Maximum measured signal

strength is +65 dBμV/m,

5 dB less than on the 

groundscreen. 

4 With matched polarization on 

the measurement antenna, 

grandfathered signal strength 

is just below the limit (at 

+83 dBμV/m). 

With matched polarization 

on the measurement 

antenna, Channel 4 

maximum signal is

+78 dBμV/m. A transient 

noise spike at 69 MHz 

occurred. 

Maximum measured signal

strength is +72 dBμV/m,

6 dB less than on the 

groundscreen. 

5 With matched polarization on 

the measurement antenna, 

weak signal from a distant 

Channel 5 transmitter is 

observed at a maximum of 

about +55 dBμV/m.

With matching

measurement antenna 

polarization, a significant

signal (+60 dBμV/m) from 

a distant Channel 5 

transmitter is noted. 

Maximum measured signal

strength is +57 dBμV/m,

3 dB less than on the 

groundscreen. 

6 With matched polarization on 

the measurement antenna, 

grandfathered signal strength 

is just below the limit (at 

about +81 dBμV/m). 

With matched polarization 

on the measurement 

antenna, Channel 2 

maximum signal is

+73 dBμV/m.

Maximum measured signal

strength is +78 dBμV/m,

5 dB more than on the 

groundscreen. 

16
Table 7. Television signals between 174 MHz and 216 MHz at the different measurement 

locations. 

NTSC 

channel 

Table Mountain NIST groundscreen End of Wing 4, Bldg. 1 

7 With matched

polarization on the 

measurement antenna, 

signal power is just below 

the grandfathered limit (at 

+93 dBμV/m). 

With matched polarization on 

the measurement antenna, 

maximum signal is

+61 dBμV/m.

Same comments as for the 

groundscreen 

measurements. 

9 With matched

polarization on the 

measurement antenna, 

grandfathered signal

strength is below the limit 

(at +91 dBμV/m). 

With matched polarization on 

the measurement antenna, 

maximum signal is

+61 dBμV/m.

Same comments as for the 

groundscreen 

measurements. 

10 With matched

polarization on the 

measurement antenna, a 

weak signal from a 

distant Channel 10 

transmitter is observed at 

a maximum of about

+35 dBμV/m.

On vertical polarization, a 

signal (+25 dBμV/m) from a

distant Channel 10 transmitter 

is noted. This is not seen in

the horizontally polarized 

measurement, likely because 

of temporal variation in the 

indirect propagation of this

signal.

Not observed in this 

measurement. This may be 

due to temporal variation 

in the indirect propagation 

of this signal. 

11 With matched

polarization on the 

measurement antenna, 

signal strength is well

below the limit (at about

+68 dBμV/m). 

With matched polarization on 

the measurement antenna, 

maximum signal is

+79 dBμV/m. This transmitter 

is located on a high rooftop a 

few blocks from the DOC

Laboratories. 

Same comments as for the 

groundscreen 

measurements. 

12 With matched

polarization on the 

measurement antenna, 

signal strength is below 

the limit (at about

+75 dBμV/m). 

With matched polarization, a 

weak signal (+35 dBμV/m) is 

noted. This Channel's service 

is carried on Channel 11 in the 

Boulder area. 

Same comments as for the 

groundscreen 

measurements 

17
Table 8. Television signals between 512 MHz and 806 MHz at the different measurement 

locations. 

NTSC 

channel 

Table Mountain NIST groundscreen End of Wing 4, Bldg. 1 

31 

and 

32 

Channel 31 is notable for 

having a paired digital

transmission at Channel 32. 

Maximum measured carrier 

strength of +75 dBμV/m is 

typical for UHF television 

signals measured at Table 

Mtn. NRQZ 

With matched polarization on 

the measurement antenna, 

maximum signal is 

+62 dBμV/m.

Similar results as for the 

groundscreen 

measurements. 

41 With matched polarization 

on the measurement 

antenna, maximum signal

strength is +91 dBμV/m.

This matches the maximum 

allowed at the quiet zone, to 

within the measurement 

uncertainty of the RSMS. 

With matched polarization on 

the measurement antenna, 

Channel 41 maximum signal

is +96 dBμV/m. This is the 

highest television signal

strength measured at any site 

during any measurement. 

Similar results as for the 

groundscreen 

measurements. 

Others With matched polarization 

on the measurement 

antenna, typical maximum

signal strengths are between 

+70 and +85 dBμV/m. A 

total of about 14 television 

signals are measured within 

the band. 

With matched polarization on 

the measurement antenna, 

typical maximum signal

strengths are between +60 and 

+80 dBμV/m. Two signals are 

observed at strengths of +86 

and +92 dBμV/m. A total of

about 15 television signals are 

measured within the band.

Similar results as for the 

groundscreen 

measurements. Note 

higher overall noise 

strengths than at the 

groundscreen. 

18
3. DESCRIPTION OF THE MEASUREMENT SYSTEM FOR DTV E-FIELD 

STRENGTH MEASUREMENTS 

In this section, the measurement system is explained, and measured results are presented 

and discussed. The transmitter systems on each mountaintop and the receiver 

measurement system in the van were configured as shown in the block diagram of figure 

7. The transmitter consisted of two signal generators coupled into a single power 

amplifier via a combiner. The amplifier output incorporated a low-pass filter to reduce 

harmonic emissions. Figure 8 is an annotated photograph of the transmitter system used 

on both mountaintops. The signal was radiated from the first mountaintop (Eldorado 

Mountain) near Boulder (see the map in figure 9) via an omni-azimuthal directional 

antenna (with 1.9 dBi gain), mounted 3.66 m (12.0 ft) high at the edge of a cliff that 

overlooks the Boulder–Denver metro area. The second mountaintop (Squaw Mountain) is 

located significantly farther from Boulder (also shown in the map in figure 9), giving 

little line-of-sight coverage over the measurement area. The transmitter at this site was 

similar to that at Eldorado, but a different transmitter antenna was used. The transmitter 

antenna was a log periodic array with 6.5 dBi gain and was mounted 8.2 m (26.91 ft) 

above the ground. This array had a 3 dB beamwidth of 90 deg, and the beam was 

centered on the measurement area. 

The transmitted signals were continuous, sinusoidal waves. This allowed the 

measurement bandwidths in the receivers to be set at sufficiently narrow values to 

observe the transmitted signals with nominal signal-to-noise ratios of 10 dB or more. The 

EIRP levels transmitted from the Eldorado Mountain site were 22.5 dBm and 30.5 dBm

for the 533 MHz and 772 MHz systems, respectively. The EIRP levels transmitted from

the Squaw Mountain site were 35.1 dBm and 43.5 dBm for the 533 MHz and 772 MHz 

systems, respectively. 

The mobile measurement system, shown in figure 5, used a 1.9 dBi gain omni-azimuthal 

directional antenna mounted on a vehicle rooftop at 2.95 m (9.68 ft) above the ground. 

As shown in figure 7, the antenna line was routed to a splitter, and from there the 

received signal was coupled to a pair of receivers. Each receiver was dedicated to a single 

frequency (533 MHz or 772 MHz). Each receiver included a pre-selector (a varactor 

bandpass filter to reject strong adjacent-frequency signals) and a low-noise preamplifier 

(affording a noise figure of approximately 10 dB for the measurement system). 

The preselector outputs were routed to spectrum analyzers. Each spectrum analyzer was 

tuned to the applicable frequency, with a zero Hertz frequency span. The IF bandwidth 

was set to 10 kHz, and the lowpass video bandwidth was set slightly wider. Positive peak 

detection was used. The sweep time was set to 60 s, so that each spectrum analyzer would 

record the received signal strength at the applicable frequency for 1 min at a time. 

Each spectrum analyzer was controlled via a laptop PC-compatible computer. The 

computer downloaded each minute’s-worth of data to data files, and then automatically 

reconfigured the spectrum analyzers and preselectors for the next minute of data. These 

systems were set to run continuously. Thus, received signal strength was continuously 

19
measured at each frequency. Seventeen peak amplitude strengths were measured and 

recorded per second at each frequency during data acquisition runs. 

As the mobile measurement system was driven throughout the Boulder area, a global 

positioning system (GPS) receiver was used to track the vehicle’s position. Notes were 

also kept on the vehicle’s location as a function of local landmarks (e.g., road 

intersections). The routes driven for this study are shown in figures 10a, 10b, and 10c. 

The measurements for each mountaintop were performed on separate days during the 

week of January 22, 2001. 

3.1 Calibration of System 

The transmitter signal strengths coupled to the antennas were verified directly using 

calibrated spectrum analyzers. Antenna gain characteristics were taken from

manufacturers’ data sheets for the individual antennas used in the study. 

The receiver system was calibrated at the antenna output using a noise diode and a 

standard Y-factor excess noise ratio calibration technique in which power is measured in 

the receiver system with the diode alternately turned on and then off. The complete 

system path of RF line, splitter, preselectors, and spectrum analyzers was calibrated with 

this technique. System noise figure was typically about 10 dB, and the correction factor 

between spectrum analyzer output and true power level was typically about 20 dB. These 

numbers were obtained from a noise diode calibration. The noise diode output levels are 

traceable to NIST. 

Noise diode calibration data were stored in computer look-up tables, and were added 

automatically to all measured power levels. All stored data were corrected at the time of 

collection. Antenna factor data were not incorporated into these stored data; field 

strengths were computed after the measurements were completed, by adding antenna 

factor data to the measured power levels in the measurement system circuitry. A 

conservative estimate of the measurement uncertainty is ±2 dB. 

3.2 Data Analysis: Measured E-field Strengths 

Recorded data were reduced from noise-diode-corrected measurement units in the 

receiver system circuitry (dBm) to peak received field strength in free space. This was 

accomplished by adding the appropriate antenna correction factors. Four different sets of 

data were collected for the two measured frequencies (533 MHz and 772 MHz) at the two 

different transmitting sites (Eldorado Mountain and Squaw Mountain). For each 

frequency and transmitter location, data were collected at various locations around the 

Boulder area. Appendix B presents the actual measured power levels for all the various 

locations, frequencies, and transmitter sites. From the Eldorado Mountain location the 

input power to the antenna was 0.115 W (20.6 dBm) and 0.724 W (28.6 dBm) for the 

533 MHz and 772 MHz systems, respectively. The gain of the transmitting antenna at 

the Eldorado Mountain site was 1.9 dBi. From the Squaw Mountain location the input 

power to the antenna was 0.724 W (28.6 dBm) and 5.0 W (37 dBm) for the 533 MHz and 

20
772 MHz systems, respectively. The gain of the transmitting antenna at the Squaw 

Mountain site was 6.5 dBi. 

In this analysis, we are interested in the field strengths for 1 MW power radiating out of 

the transmitter (i.e., 1 MW EIRP). In lieu of transmitting 1 MW in this experiment, the 

measured power level in Appendix B can easily be transformed to any desired transmitter 

power level. Since Maxwell’s equations are linear, it can be shown that by using the 

measured power level presented in Appendix B, received power levels for any given 

transmitter power in dBm can be obtained. For a given frequency, gain, and distance, 

received power is proportional to transmitted power (hence logarithms add) and the 

results for an arbitrary transmitter power can be obtained by scaling the measurements 

P = Pmes − Pt + Peff [dBm] . (8) 

Here, Pmes is the measured power level given in Appendix B, Pt is the power level at the 

input to the antenna for the different systems (defined below), and Peff is the input power 

level to the antenna that would correspond to 1 MW (90 dBm) EIRP, and is given by the 

following 

Peff = EIRP − Gt = 90 − Gt [dBm] , (9) 

where is the transmitter antenna gain. Recall that for the Eldorado Mountain site the 

transmitting antenna gain was 1.9 dBi, and for the Squaw Mountain site the transmitting 

antenna gain was 6.5 dBi. Therefore, for the Eldorado Mountain site 

Gt

Peff = 88.1 [dBm], (10) 

and for the Squaw Mountain site 

Peff = 83.5 [dBm]. (11) 

Pt is different for the different sites and the different frequencies used. For the Eldorado 

Mountain site 

Pt = 20.6 [dBm] for 533 MHz (12) 

Pt = 28.6 [dBm] for 772 MHz (13) 

and for the Squaw Mountain site 

Pt = 28.6 [dBm] for 533 MHz (14) 

Pt = 37.0 [dBm] for 772 MHz. (15) 

21
With these various values of and , the following expressions can be used to 

transform the measured power levels to the power level that would be received assuming 

1 MW EIRP. For the Eldorado Mountain site 

Pt Peff

P = Pmes − 20.6 + 88.1 [dBm] for 533 MHz (16) 

P = Pmes − 28.6 + 88.1 [dBm] for 772 MHz, (17) 

and for the Squaw Mountain site 

P = Pmes − 28.6 + 83.5 [dBm] for 533 MHz (18) 

P = Pmes − 37.0 + 83.5 [dBm] for 772 MHz . (19) 

In order to obtain the E-field strengths, the transformed power levels given in equations 

(16) through (19) need to be converted to power densities. Given the power in dBm, the 

power density is given by the following: 

1000

1 10(P /10)

Aeff

P = [W/m2

], (20) 

where Aeff is the effective area of the receiving antenna, which is a function of wavelength 

and the receiving antenna’s gain [11]: 

π

λ

4

10 2 ( /10) Gr

Aeff = [m2] , (21) 

where Gr is the receiving antenna gain and is 1.9 dBi (1.55) for all the measurements. λ is 

the wavelength, which is equal to 0.563 m (1.85 ft) and 0.389 m (1.27 ft) for a frequency 

of 533 MHz and 772 MHz, respectively. Thus, the effective areas for the two different 

frequencies are: 

Aeff = 0.0391 [m2], for 533 MHz, and (22) 

Aeff = 0.0186 [m2], for 772 MHz. (23) 

Once the power density is obtained, the E-field can be calculated from equation (2) given 

in Section 1. 

Figures 11 through 48 show the measured E-field scaled to 1 MW EIRP for the two 

proposed sites and the two different frequencies. Figures 11 through 20 are the measured 

E-field strengths for a transmitter on Eldorado Mountain operating at 533 MHz. 

Figures 11 and 12 are the measured data for the DOC Laboratories and the Table 

Mountain NRQZ, respectively, while figures 13 through 20 show the measured E-field 

strengths for various other locations throughout the Boulder area. It was necessary to 

perform measurements over a broader geographic area than just the DOC properties to 

validate the area-specific propagation models that formed the basis of this assessment. 

22
Figures 21 through 30 are the measured E-field strengths for a transmitter on Eldorado 

Mountain operating at 772 MHz. Figures 21 and 22 are the measured data for the DOC 

Laboratories and the Table Mountain NRQZ, respectively, while figures 23 through 30 

show the measured E-field strengths for various other locations throughout the Boulder 

area. 

Figures 31 through 38 are the measured E-field strengths for a transmitter on Squaw 

Mountain operating at 533 MHz. Figures 31 and 32 illustrate the measured data for the 

DOC Laboratories and the Table Mountain NRQZ, respectively, while figures 33 through 

38 illustrate measured data for an area outside of Boulder and an area outside of Golden, 

Colorado. 

Figures 39 through 46 are the measured E-field strengths for a transmitter on Squaw 

Mountain operating at 772 MHz. Figures 39 and 40 illustrate the measured data for the 

DOC Laboratories and for the Table Mountain NRQZ, respectively, while figures 41 

through 46 illustrate measured data for an area outside of Boulder and an area outside of 

Golden, Colorado. 

The rapid variation in the measured data is due to the multiple signal (multipath) 

reflections that arrive at the receiving antenna as the measurement vehicle is in motion. 

Some other interesting features present themselves in these data. For example, for the 

case when the transmitter is located on Eldorado Mountain, the results for the Table 

Mountain NRQZ location exhibit much less variability than the other measured locations. 

This is explained by the fact that the Table Mountain NRQZ site has, virtually, a LOS 

path from the Eldorado Mountain transmitter and, hence, there are very few objects 

(excluding the ground reflection) at the Table Mountain NRQZ that would cause 

multipath effects. 

Figures 17 and 27 show results for the Eldorado Canyon route for a transmitter on 

Eldorado Mountain. Notice how the E-field strengths increase dramatically as the 

measurement vehicle emerged out of the canyon onto Highway 93. It should be noted 

that the field strengths in the canyon will most likely be higher than the measured results, 

if the Eldorado transmitter is raised to its proposed height of 115.5 m (380 ft), see Section 

5. This is because shadowing in the canyon would be less. Figures 19 and 29 show results 

for the Greenbriar loop for a transmitter on Eldorado Mountain. These figures show 

measured data for both LOS and non-LOS paths. For the LOS path (on top of Shanahan 

Hill at Shanahan Ridge Park, around Fairview High School, and Southern Hills Junior 

High), field strengths of 1 V/m and higher are observed. For the non-LOS portion of the 

loop, the field strengths drop to about 0.3 V/m. 

The effects of moving automobiles are seen in figures 47 and 48. These figures show 

measured data obtained at the intersection of Highway 93 and Highway 72, south of 

Boulder, for frequencies of 533 MHz and 772 MHz, respectively. Notice the change in 

the variation of the measured E-field when the measurement vehicle and/or other vehicles 

on the road were either in motion or were stopped. In particular, note that when the 

measurement vehicle was parked or stopped at the light, the higher frequency data (figure 

23
48) exhibit more variation in the E-field strengths than do the lower frequency data. This 

is expected since scattering from automobiles would be more pronounced for shorter 

wavelengths (i.e., higher frequencies). These differences in the field variation are also 

due to the fact that higher frequency signals experience more rapid phase variation, which 

can alter how the multipath reflections add. 

 

Propagation effects due to terrain features (LOS and non-LOS or shadowing) for a 

transmitter on Eldorado Mountain can readily be seen for the data collected for the 28th

Street route, the Broadway route, and the McCaslin loop (see figures 13 through 16 and 

figures 23 through 26). For example, on the 28th Street route (figures 13 and 23) notice 

the very strong signal strength until the intersection of 28th (Highway 36) and Broadway 

is reached. At that point the road dips into a valley and no LOS path is present (i.e., the 

road dips into a terrain shadowed region). Similar results for the Broadway route are 

observed (see figures 14 and 24). For this route we see strong signal strengths at the top 

of the Table Mountain NRQZ, but the signal decreases as the measurement vehicle drove 

off the top of Table Mountain. The field strengths stay low throughout the northern part 

of Boulder on Broadway (this part of the route is shadowed from Eldorado Mountain), 

and as the measurement vehicle approached Arapahoe Avenue, the field strengths 

increase. The trend of increasing field strengths continues as the vehicle emerged into a 

LOS situation on south Broadway. Finally, the McCaslin loop results are shown in 

figures 15, 16, 25, and 26. The variation in the E-field due to the terrain features was 

observed for this route as well. In particular, notice how the field strengths increase to 

about 1 V/m when the measurement vehicle drove through NCAR’s parking lot on the 

top of Table Mesa. 

The measured E-field strengths at both the DOC Laboratories and at the Table Mountain 

NRQZ facility are examined next. Figures 12 and 22 show the measured E-field 

strengths at the Table Mountain NRQZ for a transmitter located on Eldorado Mountain 

for frequencies of 533 MHz and 772 MHz, respectively. From these figures it is seen that 

the measured E-field strengths exceed the FCC’s regulatory requirements, which is 

unacceptable for research applications at the Table Mountain NRQZ. Figures 11 and 21 

show the E-field strengths measured at the DOC Laboratories for frequencies of 

533 MHz and 772 MHz, respectively. From these two figures, it is seen that the 

measured E-field strengths range from 0.1 V/m to as high as 1 V/m. These high field 

strengths at the Broadway site could possibly have an adverse effect on the sensitive 

measurements that are performed on a routine basis at the DOC Laboratories, as 

discussed in Section 8. 

Figures 32 and 40 show the measured E-field strengths at the Table Mountain NRQZ for 

a transmitter located on Squaw Mountain for frequencies of 533 MHz and 772 MHz, 

respectively. From these figures it is seen that the measured E-field strengths do not 

exceed the FCC limits for the Table Mountain NRQZ. 

The measured E-field strengths at the DOC Laboratories for a transmitter on Squaw 

Mountain are shown in figures 31 and 39. It is interesting to observe that data in these 

figures resemble a Rayleigh type of fading propagation channel, which is indicative of a 

non-LOS, multipath mobile environment [27, 28]. 

24
The data presented in this section are for an EIRP of 1 MW. Some of the DTV channels 

have maximum power allocations of 1.64 MW EIRP. The E-fields presented here can be 

transformed to a 1.64 MW EIRP by multiplying the results in all the figures by a factor of

1.3, resulting in even higher E-field strengths than those presented here. 

4. COMPARISON OF MEASURED AND PREDICTED E-FIELD STRENGTHS 

The data in the last section show measured E-field strengths for the two proposed DTV 

tower sites at 1 MW EIRP. The data were collected for a transmitter height of 3.66 m

(12.0 ft) on the cliff edge of Eldorado Mountain (not the proposed 116 m (380 ft) height), 

and for a transmitter height of 8.2 m (27 ft) at Squaw Mountain (not the proposed 

60.96 m (200 ft) height). In order to verify any calculated E-field strengths at the 

proposed tower locations and heights, comparisons to measured data for the lower 

antenna heights are needed. In this section, calculated E-fields obtained from the ITM 

(Longley-Rice model) are compared to the measured data in the above section. 

Using a 1 MW EIRP and the same transmitter and receiver antenna heights as were used 

in the measurements, the E-field strengths for a transmitter located on Eldorado Mountain 

were calculated using the ITM. Contour plots of E-field strengths for the Boulder–

Denver area at 533 MHz, for both a horizontally and vertically polarized transmitting 

antenna, are shown in figures 49 and 50, respectively. Figures 51 and 52 show the 

contour plots of E-field strengths for the Boulder–Denver area at 772 MHz for both a 

horizontally and vertically polarized transmitting antenna, respectively. The different 

colors on these contour plots indicate different E-field strengths. 

Using the results shown in figures 49 through 52, specific locations can be directly 

compared to the routes that the measurement vehicle drove to collect the data in the 

previous section. Figure 53 shows the calculated E-field strengths for the 28th Street 

route in Boulder for 533 MHz. These results were calculated using receiver 

latitudes/longitudes obtained from the GPS data set collected during the measurements. 

Upon comparing the measured (see figure 13) and predicted (or modeled) E-field 

strengths, excellent agreement is demonstrated. Both the measured and predicted field 

strengths are about 0.7 V/m on the LOS portion of the route (before the Highway 36 

intersection). It is also seen that both the measured and the predicted field strengths are 

about 0.02 V/m on the non-LOS path portion of the route (Highway 36 to the Table 

Mountain NRQZ). 

 

Notice, however, that the measured data have much more variability than the predicted 

field strengths. As mentioned above, the variability in the measured data is due to the 

vehicle’s motion and the motion of the local objects relative to the measurement vehicle, 

as well as the fact that the measured data contain three-dimensional multipath effects. 

Reflections reaching the receiver from all directions are indicative of a true threedimensional multipath environment. Keep in mind that the predicted E-field strengths do 

not have local scatterers (i.e., buildings, cars, people, etc.) in the model. Only the terrain 

profile is taken into account. Also, the ITM uses only profile data on the bearing from

25
the transmitter to the receiver location, referred to as the great circle path. Thus, 

multipath due to terrain features that are not in the path from the transmitter and the 

receiver will not be modeled (i.e., three-dimensional multipath effects are not modeled). 

With this noted, this comparison shows that the ITM predictions correlate very well to 

the measured data for both the LOS and non-LOS portions of this route. 

Figure 54 shows the calculated E-field strengths for the Broadway route in Boulder. 

Upon comparing the measured E-field strengths (see figure 14) and modeled results, 

excellent agreement is again demonstrated. Both the measured and predicted field 

strengths are about 0.2 V/m near the Table Mountain NRQZ. In the north Boulder part of 

the route, both the measured and predicted field strengths are about 0.02 V/m. Both 

results show that field strengths increase as the measurement vehicle climbed out of the 

shadowed region south of Arapahoe Avenue. Both results also show field strengths of 

1 V/m and higher on Highway 93. 

Figure 55 shows the calculated E-field strengths for the McCaslin loop in the Boulder 

area. Upon comparing the measured (see figures 15 and 16) and modeled results, 

excellent agreement is again demonstrated. Both the measured and predicted field 

strengths are about 1 V/m and higher for the Highway 93 portion of the route. Also 

notice that both the measured and predicted results show dips in the field strengths 

ranging from 0.01 V/m to 0.1 V/m for some of the non-LOS locations. Notice that both 

the measured and predicted results show the same behavior in the field strengths as the 

measurement vehicle drove to and from the top of the NCAR site, with the field strengths 

at the top of NCAR reaching values of 1 V/m. The observed dips in the field strengths 

seen going to and coming from the top of NCAR are caused by shadowing (non-LOS 

path) of Eldorado Mountain by Shanahan Hill (also called Shanahan Ridge) on this 

portion of the route. 

Figure 56 shows the calculated E-field strengths for the Table Mountain NRQZ. Upon 

comparing the measured (see figure 12) and modeled results, excellent agreement is 

demonstrated. Both the measured and predicted results show field strengths of about 

0.2 V/m. Most of the locations at the Table Mountain NRQZ have a LOS path to the 

Eldorado transmitter, which results in the relatively small variations in the measured field 

strengths and in the almost constant value of the modeled data. The dips seen in both 

results correspond to one location at the Table Mountain NRQZ where a non-LOS path is 

present. Both the measured and modeled field strengths for a transmitter on Eldorado 

Mountain show that all locations on the Table Mountain NRQZ exceed the FCC 

regulatory limits given in table 2. 

Figure 57 shows the calculated E-field strengths for the DOC Laboratories. Upon 

comparing the measured (see figure 11) and modeled results, excellent agreement is 

demonstrated. E-field strengths between 0.5 V/m and 1 V/m are observed. The roads on 

this site are surrounded by buildings. This is reflected in the measured data and is 

highlighted in figure 11. The decrease in field strengths seen in the measured data due to 

building blockage of the signal is not apparent in the modeled data since the ITM 

prediction model does not take buildings into account in the calculations. There are a few 

locations on the site where non-LOS paths are present due to shadowing caused by 

26
Shanahan Hill and Table Mesa. At the shadowed location (or non-LOS location) both the 

measured and modeled results give the same field strength of about 0.05 V/m. Both these 

results show that the outside field strengths at the DOC Laboratories will be close to 

0.5 V/m to 1 V/m, which can possibly jeopardize the sensitive measurements that are 

performed on the site, see Section 8. 

The Squaw Mountain transmitter location was analyzed next. Using a 1 MW EIRP with 

the same transmitter and receiver antenna heights used in the measurements, the E-field 

strengths for a transmitter located on Squaw Mountain were calculated. Contour plots of 

E-field strengths for the Boulder–Denver area for 533 MHz for both a horizontally and 

vertically polarized transmitting antenna are shown in figures 58 and 59, respectively. 

Figures 60 and 61 show the contour plots of E-field strengths for the Boulder–Denver 

area for 772 MHz for both a horizontally and vertically polarized transmitting antenna, 

respectively. Once again the different colors correspond to different E-field strengths. 

Figure 62 shows the calculated E-field strengths for the Table Mountain NRQZ for the 

transmitter located at Squaw Mountain. Upon comparing the measured E-field strengths 

(see figure 32) and modeled results, good agreement is demonstrated. Both the measured 

and predicted results show field strengths of about 1 mV/m to 3 mV/m. Both the 

measured and modeled results show that field strengths for all locations on the Table 

Mountain NRQZ are below the FCC regulatory limits, given in table 2. Thus, the 

measured and modeled data show that for Squaw Mountain, a transmitter antenna height 

of 8.2 m (26.91 ft) does not violate the Table Mountain NRQZ. Predicted field strengths 

for the actual proposed antenna heights are discussed in the next section. 

There are a few situations where the measured and modeled results do not agree very 

well. This occurs in deep shadow regions. The reason why the ITM fails to correctly 

predict the field in deep shadow regions is explained as follows. The ITM (or any 

irregular terrain model for that matter) is considered a quasi-two-dimensional model. 

This means that irregular terrain models use only the terrain profile for the bearing 

between the transmitter and receiver. Terrain features and objects that would scatter 

and/or reflect radio waves that are not on the bearing are not used in the calculation of the 

field strengths. It is possible that in a deeply shadowed location, the majority of the 

energy reaching the receiver is from scattering and reflections from objects off of the 

bearing direction (i.e., mountains, hills, buildings, cars, etc.). In such a deep fade region, 

the ITM field strength calculations are based only on a diffracted path. Thus, accounting 

for only the diffracted path and neglecting the other paths results in errors in field 

strength predictions. 

This point is illustrated in figures 63 and 64. These figures show the predicted field 

strengths for a transmitter location on Squaw Mountain for the McCaslin route and the 

Boulder-to-Golden route. By comparing these figures to the experimental results 

presented in figures 36 and 35, respectively, it is seen that for the moderate shadow 

regions the measured and modeled E-field strengths are similar. For the deep shadow 

region the two results differ. The modeled results predict lower field strengths than those 

from the measured data. 

27
For the McCaslin route, strong signal strengths are observed in the middle part of the 

route, and as the route turns back towards the Flatirons, deep shadowing regions are 

observed. For the Boulder-to-Golden route, strong signal strengths are observed on 

Indiana Avenue. However, once the route turns back to Highway 93, deep shadowing is 

observed in both results. This difference is due to the fact that the ITM does not take into 

account the full three-dimensional terrain features, and as a result, it underestimates the 

field strengths. 

Once again, this situation only occurs in deep shadow regions. Figures 53, 54, and 62 

show that for moderate shadow regions (the Table Mountain NRQZ and the Broadway 

route), the ITM predictions compare very well to the measured values, illustrating the 

accuracy of the ITM for moderate shadow regions. In any event, ITM predictions are 

conservative, since in deep shadow locations the predicted field strengths are less than 

those that were measured. 

5. PREDICTED E-FIELD STRENGTHS FOR THE PROPOSED 

TOWER HEIGHTS 

The previous section demonstrated that the ITM model can accurately (except in deep 

shadow regions, as explained above) predict field strengths for both LOS and non-LOS 

locations for a given antenna height. Therefore, this model was used with confidence to 

calculate and predict field strengths for the actual proposed antenna heights for both the 

Eldorado Mountain and Squaw Mountain sites. 

Figures 65 and 66 show contour plots of the E-field strengths for the Boulder–Denver 

area for a transmitter located at Eldorado Mountain for 533 MHz and 772 MHz, 

respectively. The results in these figures are for horizontal polarization with a transmitter 

antenna height of 116 m (379 ft), and a receiver height of 2 m (6.6 ft). Figure 67 shows 

the E-field strengths at the Table Mountain NRQZ for 533 MHz and 772 MHz. From this 

figure it is seen that for the Table Mountain NRQZ, the predicted field strengths are about 

0.2 V/m. This value, based upon transmission from Eldorado Mountain, exceeds the FCC 

regulatory limit by about an order of magnitude (or by about a factor of ten in E-field 

strength). This level of excess would thus jeopardize the research at the Table Mountain 

NRQZ. 

Figure 68 shows the E-field strengths at the DOC Laboratories for 533 MHz and 

772 MHz. From this figure it is seen that for the DOC Laboratories, the predicted field 

strengths approach 0.5 V/m to 1 V/m at various locations. These field strengths are high 

enough to affect some of the sensitive measurements performed on a routine basis at the 

DOC Laboratories, see Section 8. 

The Squaw Mountain site is analyzed next. Figures 69 and 70 show contour plots of the 

E-field strengths for the Boulder–Denver area for a transmitter located at Squaw 

Mountain for 533 MHz and 772 MHz, respectively. The results in these figures are for 

horizontal polarizations with a transmitter antenna height of 60.96 m (200 ft), and a 

receiver height of 2 m (6.56 ft). Figure 71 shows the field strengths at the Table 

28
Mountain NRQZ for 533 MHz and 772 MHz. The difference in field strengths for the 

two frequencies is due to the fact that the amplitude of the diffracted wave decreases with 

increasing frequency. From this figure it is seen that for the Table Mountain NRQZ, the 

predicted field strengths are about 0.1 mV/m to 0.2 mV/m. These field strengths are well 

within the FCC Table Mountain NRQZ regulatory limits. Thus, a transmitter can be 

located at Squaw Mountain without violating the FCC regulatory limits or jeopardizing 

the research efforts at the Table Mountain NRQZ. 

Even though the DTV frequency allocation is in the 400 MHz to 700 MHz band, there is 

the possibility that broadcasters could decide to broadcast DTV signals at their currently 

assigned NTSC frequencies [29]. This means that some DTV transmissions could be 

below 400 MHz. Since propagation loss can decrease with frequency, it is important to 

calculate field strengths that would result from broadcasting at the lower NTSC 

frequencies. Field strengths were calculated at 54 MHz (the lowest NTSC frequency) at 

the Table Mountain NRQZ and at the DOC Laboratories with the transmitter on Eldorado 

Mountain and Squaw Mountain. These results are shown in figures 67, 68, and 71. In 

figure 67, it is seen that the 54 MHz results are very similar to the 533 MHz and 772 

MHz results for a transmitter on Eldorado Mountain. The similarity in the results for all 

three frequencies is due to the fact that the Table Mountain NRQZ is LOS from Eldorado 

Mountain. For a transmitter on Eldorado Mountain, the E-field strengths for all three 

frequencies exceed the FCC limit. In figure 71 (transmitter on Squaw Mountain), it is 

seen that the 54 MHz field strengths are somewhat larger than those at the other two 

frequencies (due to diffraction effects). As seen in table 2, the FCC NRQZ limit is 

smaller for 54 MHz. The predicted E-field strengths for a transmitter on Squaw Mountain 

at 54 MHz do exceed this FCC limit. 

Here again, the data presented in this section are for an EIRP of 1 MW. Since some DTV 

broadcasters have received allocations to transmit at 1.64 MW (see table 1), predicted 

field strengths for 1.64 MW are needed. The E-field presented here can be converted to a 

1.64 MW EIRP level by multiplying the results in all the figures by a factor of 1.3, 

resulting in even higher E-field strengths than those presented here. This would result in 

even greater E-field strengths in the Boulder–Denver area, and would cause even greater 

interference at both of the DOC facilities due to a transmitter located on the Eldorado 

Mountain site. 

6. DTV E-FIELD STRENGTH REQUIREMENT 

Measured and modeled results to this point have assumed either a 2 m (6.6 ft) or 2.95 m

(9.68 ft) receiving antenna height. Designs of tower locations and power requirements 

are based on the FCC’s 9.14 m (30 ft) receiver antenna height assumption. For acceptable 

DTV reception, the FCC has recommended a minimum E-field strength of 41 dBμV/m

(0.11 mV/m) at a 9.14 m (30 ft) receiver antenna height [1]. The ITM prediction model 

can be used to determine at what locations in the Boulder–Denver area the 41 dBμV/m

field strengths for a 9.14 m (30 ft) receiving antenna height can be achieved for given 

tower locations. 

29
Figures 72 and 73 show the contour plot of the predicted field strengths for the Boulder–

Denver area for a transmitter located at Eldorado Mountain for frequencies of 533 MHz 

and 772 MHz, respectively. These results were calculated for a transmitter antenna 

height of 116 m (379 ft), a receiver height of 9.14 m (30 ft), and 1 MW EIRP. Figures 74 

and 75 show the contour plots of the predicted field strengths for the Boulder–Denver 

area for a transmitter located on Squaw Mountain for 533 MHz and 772 MHz, 

respectively. These results were calculated for a transmitter antenna height of 60.96 m

(200 ft), a receiver height of 9.14 m (30 ft), and 1 MW EIRP. 

One might ask how transmitter locations would affect DTV reception. Of interest here are 

the locations where the 41 dBμV/m (0.l1 mV/m) FCC field strength is exceeded. If 41 

dBμV/m is exceeded, DTV reception is possible according to the FCC’s assumptions. 

The data shown in figures 72 through 75 are re-plotted to illustrate where the FCC’s 

minimum field strength is met or exceeded. These new results are shown in figures 76 

through 79. In figures 76 through 79, the white areas in the plot correspond to where the 

FCC’s minimum field strength is exceeded. The blue shaded areas indicate areas with 

field strengths that are below the FCC’s minimum field strength recommendation for 

DTV reception. These blue areas indicate that DTV may not be received in these areas, 

as indicated by the FCC’s recommendation. Note that as far as the FCC’s 41 dBμV/m

(0.11 mV/m) recommendation is concerned, it is seen in figures 76 through 79 that 

Squaw Mountain covers basically the same area as a transmitter on Eldorado Mountain, 

for the purposes of DTV reception with a 9.14 m (30 ft) height fixed receiving antenna. 

Based on the results in the previous section, while the Squaw Mountain site covers the 

same area as the Eldorado Mountain site, the Squaw Mountain site does not violate the 

regulatory field strength limits protecting the Table Mountain NRQZ. The Squaw 

Mountain site would also provide additional protection to the DOC Laboratories. Note 

that if a 1.64 MW EIRP is used, the 41dBμV/m recommendation limits would extend the 

DTV coverage area. 

 

7. ANTENNA PATTERN EFFECTS 

All the predicted E-field strengths presented in this report were obtained with the 

assumption that the transmitting antenna was an omnidirectional antenna. The 

measurement data presented here were collected with antennas with moderate antenna 

patterns, i.e., a 1.9 dBi omni-azimuthal directional antenna on the Eldorado Mountain site 

and a 6.5 dBi log-periodic antenna on the Squaw Mountain site. The actual antennas that 

will be used for the proposed tower will have some type of antenna pattern associated 

with them. The ITM propagation model presented here has a capability of using any 

transmitter antenna pattern in the prediction. Unfortunately, at this time we do not have 

information on the antenna patterns. At a later date, when and if such antenna patterns 

are available, new predicted E-field strengths will be calculated. 

 

With this noted, the results in this report can still be used once the actual antenna patterns 

are known, as explained in the following. When LOS propagation conditions are present, 

the simple free-space calculation given in equation (2) can be used to determine the Efield strengths without the need to resort to the ITM prediction model. LOS situations 

30
occur for the Eldorado Mountain site for the Boulder area. For a transmitter location on 

Eldorado Mountain, many locations throughout the Boulder area (including the DOC 

Laboratories and the Table Mountain NRQZ) exhibit LOS paths. The ability of the 

simple free-space calculation given in equation (2) to predict E-field strengths in a LOS 

situation is illustrated in figures 11 and 12. These figures show the measured E-field 

strengths for a transmitter located on Eldorado Mountain for the DOC Laboratories and 

the Table Mountain NRQZ. Notice that the free-space calculation correlates very well 

with the measured data. There is some variability in the measured data, due to multipath 

effects that the free-space model cannot account for, but typical E-field strengths at both 

sites are very well accounted for with the free-space model. 

Thus, once the actual antenna patterns are known, the EIRP in any direction can be 

obtained, and equation (2) can be used to estimate the E-field strengths in the LOS 

situation. An alternative approach is to simply scale the results in this report by the 

appropriate EIRP for an antenna at a given location and a given direction. From the 

results in figure 12, it is seen that, for a transmitter on Eldorado Mountain, a reduction of 

23 dB in either the transmitter power level or in the antenna gain is needed to achieve the 

FCC NRQZ limit. 

8. EFFECTS OF BROADBAND TRANSMISSION ON 

SENSITIVE MEASUREMENTS 

Historically, the radio science programs in the former National Bureau of Standards 

(those programs are now in NIST and ITS) drove the need to establish a field site remote 

from their Washington, DC, laboratories. Boulder was chosen over several contenders 

because of the relatively quiet radio-frequency electromagnetic environment, which 

would allow for more accurate measurements and experiments; the varied geographic 

terrain, which would facilitate the study of radio propagation; and the presence of a major 

university (the University of Colorado) as well as the proximity of a large city (Denver). 

The technical mission of the Boulder labs was to develop the most accurate possible 

reference standards and calibration services to insure compatibility of the emerging radio, 

microwave, and radar technologies that the nation was then developing. Radio 

propagation research was fundamental to this work, and as higher frequencies were 

explored, the interactions between electromagnetic waves and atmospheric layers led to 

new directions of research. This work was, and continues to be, fundamental to all of the 

advances made in radio-frequency technology. NIST's research on accurate measurement 

systems, and its development of standards and calibration services for the Nation, play an 

essential role in making possible the technologies that we use daily such as wireless 

communication, high-speed digital technology, time-and-frequency synchronization, 

satellite communications, radar, and optical fiber communications links, to name only a 

few. 

Radio research projects performed outdoors often require that receivers be constructed to 

receive wideband signals. Furthermore, those receivers must often be constructed with 

high performance, low noise amplifiers (LNAs) in the so-called front-end, just after the 

receive antenna. The requirement for wide bandwidth means that such receivers integrate 

31
the total energy across a wide part of the spectrum. The LNAs used in those front ends 

are susceptible to nonlinear effects due to the integration of large amounts of energy 

across wide portions of spectrum. This effect has been documented in Reference [30]. 

Simply put, a wideband radio receiver with a sensitive amplifier in the front end will 

experience a condition known as overload in the presence of strong signals that are not 

only present at the desired frequency, but that are also substantially off-tuned from the 

center frequency. Overload of LNAs can occur in the presence of strong signals even if 

those signals are as much as a few hundred megahertz off the receiver’s center frequency 

[30]. When an LNA goes into an overload condition, its gain is greatly reduced. The 

result is loss of the desired signal or signals. 

Because of the Government’s need to be able to perform radio research in outdoor 

locations with wideband, sensitive receivers, the only practical and general technical 

solution is to limit the total power originating from local signal sources. The limitation 

must be adequate to ensure that the cumulative (integrated) amount of energy that is 

coupled into the sensitive front end amplifiers from all local signals is low enough not to 

overload the receiver front ends. This is one requirement that has caused the Federal 

Government to create and maintain the Table Mountain NRQZ. 

The grandfathered signal levels of television channels 4, 6, 7, and 9 provide an example 

of the difficulties that high signal strengths within the NRQZ produce for sensitive radio 

measurement systems. These grandfathered signal levels within the NRQZ range from

about 3 dB above the limit to as much as 13 dB above the limit. When the spectrum

survey in this report was performed, it was necessary to insert 10 dB of attenuation into 

the measurement system's front end to prevent overload by these television signals. That 

is, the sensitivity of the entire measurement system had to be degraded by 10 dB to 

prevent saturation due to these signals. This attenuation had to be inserted for all 

measurements in the television bands between 50 MHz and 88 MHz (due to strong Efields from channels 4 and 6), and also between 170 MHz and 220 MHz (due to E-fields 

from channels 7 and 9). Signal strengths below the NRQZ limits usually require no 

attenuation in the receiver system front end, and enable more sensitive and more accurate 

measurements. 

Similar measurement degradation will impair the usefulness of measurements and 

experiments in other bands, to the extent that signals in those bands exceed the NRQZ 

limits. Mobile signals that exceed the NRQZ limits may provide some technical 

opportunities for ameliorative work-arounds, but broadcast signals that are effectively 

present on a continuous basis do not allow such work-arounds. Receivers in those bands 

are permanently impaired by the incident signals, as happened for the horizontally 

polarized spectrum survey measurements described above. This integrating effect of 

several frequencies transmitting simultaneously has adverse effects on several types of

research measurement efforts that occur at both the Table Mountain NRQZ and at the 

DOC Laboratories. 

There are no Federal, state, or local laws or regulations, corresponding to the NRQZ 

restrictions, that protect the DOC Laboratories. However, the level of EM-field emissions 

from the proposed towers may be high enough on-site to compromise some experimental 

32
and metrological programs. The E-field strengths from a single station transmitting at 1 

MW EIRP from Eldorado Mountain will result in 0.5 V/m to 1 V/m over the entire site. 

To date, six stations have been given permission to operate at 1.6 MW EIRP, which, 

upon scaling the results above to the 1.6 MW EIRP level, results in an E-field-strength 

on-site of 0.6 V/m to 1.3 V/m. Furthermore, the potential tower operators are soliciting 

existing TV and FM stations to move their transmitters to the Eldorado Mountain site. 

Such a concentration of transmitters will have a more adverse effect because of the even 

broader spectral coverage. Cutting-edge physics, metrology, and radio research 

conducted at the DOC Laboratories for the benefit of industry and the Nation could be 

compromised. Some examples of programs sensitive to electromagnetic fields are given 

below. 

 

The research and antenna calibrations conducted at the NIST Open Area Test Site 

(OATS) groundscreen facility is critical for support of a very broad cross section of 

industry. Literally the entire U.S. electronics industry, including all manufacturers of 

computer and information technology, communications equipment, medical electronic 

equipment, electronic test equipment, television and other electronic entertainment 

equipment, certain appliances, industrial equipment, and many other categories, must test 

their product’s conformity to national and international standards. To be recognized, 

these tests must be traceable to NIST, and the standards themselves are developed in an 

international forum with NIST providing the technical expertise and experimental 

validation to advance the cause of U.S. industry. All tests and calibrations, and 

experimental research performed on the groundscreen are performed from 30 MHz to 

1 GHz, and the DTV bands will cover a significant portion of this band (476 MHz to 

698 MHz). The comparatively strong field strengths from the DTV towers (on Eldorado 

Mountain) will literally override the signals that NIST generates and uses in its 

calibrations and experiments. Furthermore, the broad nature of the signals is such that it 

will not be possible to shift to an adjacent null in the spectrum and obtain an approximate 

measurement. NIST research that supports ANSI, ITI, IEC/CISPR, as well as a broad 

cross section of industry, will be compromised. 

Interference problems with DTV signals are currently being experienced by commercial 

electromagnetic compatibility (EMC) laboratories where EMC measurements and 

calibrations are performed routinely at other OATS facilities, as indicated by Roland 

Gubisch [31], the vice-chair of the United States Council of EMC Laboratories (USCEL). 

USCEL was developed to aid U.S. industry with EMC standards and testing procedures. 

Gubisch indicated [31] that DTV signals have had adverse effects on an OATS in the 

Boston, Massachusetts, area. At this OATS and other sites, field strengths as low as 

0.0002 V/m (46 dBμV/m) have interfered with tests. The 0.0002 V/m is the FCC radiated 

emission limit for unintentional radiators [32]. The DTV signals act as 6 MHz wideband 

noise in the 500 MHz to 700 MHz frequency range, hindering the ability to test and 

certify electronic products on these outdoor sites. The broadband noise nature of the 

6 MHz DTV signals can be seen in the 2001 spectrum survey for the DTV Channel 32 

(578 MHz to 584 MHz) transmission, see figure A.41. In fact, Gubisch has informed 

NIST that USCEL members have experienced problems on outdoor facilities when DTV 

E-field levels are even lower than 0.0002 V/m. The broad 6 MHz signals from each 

station and the even broader spectrum saturation from strings of adjacent channels are 

33
preventing EMC test laboratories from making measurements in outdoor facilities that 

are prescribed by international standards. This is forcing commercial labs to use much 

more costly and potentially less accurate special indoor facilities such as semi-anechoic 

chambers. However, NIST as the national standards laboratory that provides the basis for 

and harmonization of all national measurements, must maintain the smallest uncertainties 

possible in its measurements. 

Other examples of the types of interference that would be experienced at the DOC 

Laboratories are as follows. In order to simulate potential effects of instrumentation of

the proposed DTV towers on Eldorado Mountain, experiments were performed in two 

different laboratories at NIST. In these experiments E-field strengths of 0.1 V/m,

0.5 V/m, and 1.0 V/m (the values that would be present at the DOC Laboratories as 

discussed above) were generated in two different research laboratories. The first 

laboratory was in the Optoelectronics Division, the Sources and Detectors Group. This 

group is developing standards and measurement systems for optical intensity noise of 

laser transmitters and optical fiber amplifiers used in optical communications systems. 

These consist of both laboratory and transfer standards. In the study, E-field strengths of 

0.1 V/m, 0.5 V/m, and 1.0 V/m were radiated onto optical noise instrumentation at 

frequencies of 400 MHz to 700 MHz. This frequency range falls within the broad 

frequency range of interest for noise studies, which presently is 100 MHz to 4.1 GHz and 

higher. For field strengths of 0.1 V/m, the noise floor of the instrumentation rose 

between 7 dBm/Hz and 10 dBm/Hz within this frequency range, a significant amount. At 

field strengths of 0.5 V/m the noise floor rose by 15 dBm/Hz to 33 dBm/Hz, a large and 

disturbing amount. At field strengths of 1 V/m the noise floor rose by 22 dBm/Hz to 

43 dBm/Hz, a significant amount. Without additional shielding of the affected 

equipment, the resultant increase in the noise floor would prevent NIST from performing 

low intensity noise measurements, in this frequency range, that are important in noise 

studies. Presently, it is not known how well additional shielding would diminish this 

problem. Such a result can only be determined experimentally. 

The second experiment was performed in the Time and Frequency Division of NIST. In 

this division, the Atomic Standards Group, Network Synchronization Group, and Time

and Frequency Service Group use GPS signals for the following: (1) to contribute the 

NIST clock (frequency standards) data to the computation of TAI (International Atomic 

Time) and UTC (Coordinated Universal Time), (2) to compare UTC as realized at NIST, 

to the frequency standards of other remote laboratories (such as the U.S. Naval 

Observatory, the National Physical Laboratory of the United Kingdom, the PhysikalischTechnische Bundesanstalt in Braunschweig, Germany, etc.), and (3) to provide time and 

frequency dissemination/calibration service to industry and research institutions. In the 

study, E-field strengths of 0.1 V/m and 0.5 V/m at 613.8 MHz and 787.7 MHz were 

incident onto the antennas for three different types of GPS receivers. The antennas were 

located on the roof of the main building at the DOC Laboratories, see figure 80. This 

figure also illustrates the LOS path that would be present from the Eldorado Mountain 

tower site. These two frequencies correspond to the first subharmonic of the GPS L2 

(1227.6 MHz) and GPS L1 (1575.42 MHz) frequencies. Due to nonlinearity effects of the 

GPS receiver’s LNA (low noise amplifier), the 613.8 MHz and 787.5 MHz signals at 0.5 

V/m saturated the front end of the GPS receiver, resulting in loss of GPS signal lock by 

34
the receiver. When the second harmonics of these frequencies were greater than 

dBm as received by the GPS antennas, the receiver could not lock on the GPS 

signal. Once the E-field strength was reduced to 0.1 V/m the receiver was able to lock on 

the GPS signal. 

−136

The above examples represent only a sample of possible and likely negative effects of 

higher levels of ambient electromagnetic fields in this frequency range on DOC 

Laboratory programs in the Boulder, Colorado, area. Other technical programs at NIST, 

as well as NOAA and ITS programs, may also be impacted. 

 

9. SUMMARY AND CONCLUSION 

In this report, we have analyzed the expected E-field strengths in the Boulder area from

two proposed terrestrial DTV transmitter locations, the Eldorado Mountain site and the 

Squaw Mountain site. The Eldorado Mountain and Squaw Mountain sites were chosen in 

this study because these two possible sites bound the propagation environment that would 

occur at both the Table Mountain NRQZ and the DOC Laboratories. The Eldorado 

Mountain site affords substantial line-of-sight coverage over the Boulder area, and the 

Squaw Mountain site affords only indirect (diffractive) coverage over the same area. The 

other possible tower sites fall between these two types of propagation conditions. The 

proposed transmitter tower heights for the two sites were obtained from either the 

landowners or public documents. 

In this analysis, measurements of the E-field strengths for a transmitter located at each of 

these sites were performed. These measured data were then compared to predicted Efield strengths obtained from the ITS ITM propagation model. The predicted field 

strengths from the two transmitter locations matched well with measured strengths from

those locations at frequencies near both ends of the existing UHF television band. This 

indicates that the ITM predictions are reliable, and can be used with confidence in 

predicting the strengths that might be received at any given location in the area (with the 

exception of very deep shadowed regions) for any given transmitter and receiver heights. 

The ITS ITM propagation model was then used to predict the E-field strengths in the 

Boulder area for the actual proposed transmitter antenna heights of two possible 

transmitter locations, Eldorado Mountain and Squaw Mountain. The E-field strengths 

were calculated based on 1.0 MW EIRP. Once the E-field strengths are obtained for 1.0 

MW EIRP, the E-field strengths can be scaled to any desired transmitter power level. 

With these predictions, we were able to determine the E-field strengths at both the DOC 

Laboratories and at the Table Mountain NRQZ. The results presented here show that at 

the Table Mountain NRQZ, the predicted E-field strengths are about 0.3 V/m for a 

transmitter on Eldorado Mountain at 1.0 MW EIRP. This number exceeds the FCC’s 

regulatory (47 CFR 73.1030) limit by about an order of magnitude. At that level, the 

research at the Table Mountain NRQZ will be compromised. The results also show that 

the E-field strengths at the DOC Laboratories for a transmitter located on Eldorado 

Mountain are about 1 V/m for 1.0 MW EIRP. These field strengths are high enough to 

possibly jeopardize the sensitive measurements done on a routine basis at the DOC 

35
Laboratories, as discussed in Section 8. On the other hand, the results presented here 

show that at the Table Mountain NRQZ, the predicted E-field strengths are about 

0.002 V/m for a transmitter located on Squaw Mountain for 1.0 MW EIRP. These field 

strengths are well within the FCC’s Table Mountain NRQZ regulatory (47 CFR 73.1030) 

limit. Thus, the results presented here indicate that a transmitter could be located at 

Squaw Mountain without violating the FCC’s regulatory limit or jeopardizing the 

research efforts at the Table Mountain NRQZ. 

As discussed above, the measured and modeled data presented in this report are for an 

EIRP of 1 MW. As indicated in table 1, some of the DTV channels have maximum

power allocations of 1.64 MW EIRP. The E-field strengths presented here can be 

transformed to a 1.64 MW EIRP by multiplying the data shown in all the figures by a 

factor of 1.3 (which would increase the E-field strengths by 30 %). This would result in 

even higher E-field strengths in the Boulder–Denver area than those presented here, and 

would cause even greater interference at both the DOC facilities due to a transmitter 

located on the Eldorado Mountain site. After scaling the results in this report to the 

current maximum EIRP levels (1.64 MW EIRP), the E-field strengths at both the Table 

Mountain NRQZ and DOC Laboratories can be determined for this maximum transmitter 

power level. The E-field strengths at the Table Mountain NRQZ would be about 0.4 V/m

for a transmitter on Eldorado Mountain with 1.64 MW EIRP, and the E-field strengths at 

the DOC Laboratories would be about 1.3 V/m for 1.64 MW EIRP. In Reference [1], 

the FCC indicates that in the future, adjustments to the allocated power levels may be 

granted under some situations, in order to allow power levels higher than 1.64 MW. The 

FNPRM [5] indicated maximum ERP of 5 MW (or 8.2 MW EIRP). If these high power 

levels are granted, the result would be even higher E-field strengths in the Boulder–

Denver area than those presented here. 

In this report we also present data from a recent spectrum survey of the Table Mountain 

NRQZ. The results of this spectrum survey indicate that at the time of the survey (late 

1998 and April 2001) the requirements of 47 CFR 73.1030 were being met by applicable 

signals at the Table Mountain NRQZ. The site therefore continues to be a useful and 

necessary location for present and future radio experiments. We also present results of a 

spectrum survey performed at the DOC Laboratories, illustrating a generally low level of

ambient electromagnetic fields. 

 

For DTV reception, the FCC specifies a minimum E-field strength of 41 dBμV/m

(0.11 mV/m) for a receiver antenna at a height of 9.14 m (30 ft). Using the ITM 

prediction model, we also predicted the coverage areas where the FCC’s minimum field 

strength for acceptable reception is met or exceeded. From the results shown here, it is 

seen that the two proposed transmitter locations (Eldorado Mountain and Squaw 

Mountain) have basically the same DTV coverage areas. However, the data in these 

results show that a transmitter on Squaw Mountain will not violate the FCC regulatory 

limits protecting the Table Mountain NRQZ. 

The models and measurements discussed in this report can aid in determining whether the 

minimum field strength requirement of 41 dBμV/m can be achieved at various locations. 

However, another very important consideration for DTV (and any digital communication 

36
system, for that matter) is multipath effects. Multipath effects result in bit error rates 

(BER), or data error, in digital systems [33-39]. These effects can and do occur with 

DTV. The multipath issue is not isolated to the outdoor propagation environment. The 

multipath effects for an indoor propagation environment (i.e., a signal propagating to a 

TV antenna inside a house) can be equal or more critical [6, 40-44]. The indoor multipath 

issue is confronted in the following manner. In laying out the recommendations for DTV 

system designs (i.e., the Advanced Television Systems Committee (ATSC) 

standardization process), receiving antennas were assumed to be located on the outside of 

homes at an antenna height of 9.14 m (30 ft). However, this may not be possible for one 

reason or another (e.g., some communities have ordinances or covenants against external 

TV antennas). As a result, receiving antennas may be placed inside homes, either on top 

of TV sets or in attics. DTV signals propagating into homes will reflect off of surfaces 

and objects in the home, resulting in substantial multipath. This indoor multipath issue 

can have an adverse effect on the quality of service for DTV systems. More detailed 

studies are needed in order to determine whether the multipath environment from the two 

proposed sites is substantially different in order to assess the ultimate location of the 

antenna towers. Such a study can help in the assessments of the DTV receiver standards, 

in order to determine whether the indoor and outdoor multipath problem will affect the 

quality of service of terrestrial DTV systems and affect terrestrial DTV proliferation in 

the marketplace. This is important because of the issue of the encumbrances on the 

analog spectrum (i.e., channels 52 through 69), which are scheduled to be returned for 

other uses at the end of the DTV transition. 

Furthermore, in a recent report [6], the ATSC Task Force has discussed the indoor DTV 

reception problem. This report includes reviews of the results of recent field tests of DTV 

reception in and around several major metropolitan areas in North and South America. 

For example, in the Washington, DC–Baltimore, Maryland, metroplex, it notes that DTV 

reception success fell from 75 % (on average) of all outdoor antenna sites with 9.14 m

(30 ft) antennas to 32 % of all indoor antenna sites. (The indoor sites were preferentially 

chosen for adequate DTV electric field strengths outdoors, at the 9.14 m antenna height.) 

A considerable portion of the report is devoted to a discussion of potential improvements 

in DTV receiver and antenna technologies that would be likely to enhance DTV reception 

with indoor (and outdoor) antennas. Short of these improvements, the report lays out two 

possible options to improve indoor reception. The first option would be to lower the 

maximum data rate. The second option would be to increase the E-field strengths to make 

indoor reception more robust, by increasing DTV transmitters’ ERPs. The ATSC report 

suggests that in order to overcome the indoor antenna problem, field strengths at the 9.14 

m (30 ft) reference height may need to be increased substantially to 97 dBμV/m. This is 

an increase of 56 dB over the FCC’s 41 dBμV/m, which is a factor of approximately 631 

in field strength. This 56 dB increase can be obtained by either substantially reducing the 

coverage area of DTV reception or by increasing the power by 56 dB, clearly an 

unrealistic scenario. Obviously, if transmitter power levels are increased to compensate 

for the indoor problem, higher E-field strengths than those presented in this report could 

occur at both the DOC Laboratories and at the Table Mountain NRQZ, as well as at other 

areas throughout Boulder. 

37
The studies in this report were carried out for two individual frequencies. In reality the 

DTV transmitter tower will have systems transmitting simultaneously over the entire 

band of frequencies shown in table 1. As discussed in this report, because of the way 

systems respond to a broad band of frequencies, a cumulative (integrated effect) amount 

of energy can couple into a system and adversely affect the sensitivity of a measurement, 

thereby potentially jeopardizing the quality of research performed at the DOC 

Laboratories. The data presented in this report illustrate that E-field strengths on the 

order of 1 V/m could be present at the DOC Laboratories. The studies presented in 

Section 8 illustrate only a few of the potential problems that may be experienced at the 

DOC laboratories. 

While the results presented in this report are for omnidirectional or omni-azimuthal 

directional antenna patterns, they will remain relevant once the actual antenna patterns 

are known. For LOS propagation, the simple free-space calculation given in equation (2) 

can be used to determine the E-field strengths without the need to resort to the ITM 

prediction model. LOS propagation conditions occur for the Eldorado Mountain site for 

the Boulder area (including the DOC Laboratories and the Table Mountain NRQZ). 

Therefore, once the actual antenna patterns are known, the EIRP in any direction can be 

obtained, and equation (2) can be used to estimate the E-field strengths in LOS situations. 

An alternative approach is to simply scale the results in this report by the appropriate 

EIRP for an antenna at a given location. With this noted, the results in this report are 

valid for estimating the E-field strengths in the Boulder–Denver area. If additional results 

are needed for a given transmitting antenna pattern at a specific location, the ITM could 

be used for such analysis at a future date. 

38
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