TIA/EIA
TELECOMMUNICATIONS
SYSTEMS BULLETIN
Report on EME Evaluation for
RF Cabinet Emissions Under
FCC MPE Guidelines
TSB-92-A
October 2008
TELECOMMUNICATIONS INDUSTRY ASSOCIATION
TSB-92-A
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TABLE OF CONTENTS
1. Introduction 1
1.1. Scope 1
2. References 1
3. FCC Electromagnetic Emission Limits 1
4. Limit Case Analysis 3
4.1. Calculation of EME level based on the FCC limit of -13 dBm for each of the
transmitter harmonics (1-10). 3
4.2. Example spreadsheet calculations 3
4.3. Calculations at representative frequencies 3 MHz – 2 GHz 4
4.4. Measurement method 5
5. Transmitter Site Considerations 5
5.1. Site compliance 5
6. Summary 6
Annex A A-1
Annex B B-1
DOCUMENT REVISION HISTORY
Version / Date / DescriptionTSB-92 / July 1998 / Initial release
TSB-92A / October 2008 / Removed references to vehicular application and updated document style.
FOREWORD
This forward is not part of this Telecommunications Systems Bulletin (TSB)
This TSB is the product of work undertaken by the Electromagnetic Energy (EME) working group of the TIA TR8.17 RF Exposure subcommittee. The subcommittee addresses Radio Frequency Exposure matters. TR8.17 is a subcommittee of TIA TR8 Mobile and Personal Private Radio Standards Engineering Committee. This TSB was revised and approved for publication at the October 16, 2008 meeting of TR8.17. The motion to publish was ratified at the January 22, 2009 meeting of TR8.17.
There are two annexes, Annex A and Annex B, in this TSB and both are informative.
Patent Identification
The reader’s attention is called to the possibility that using this document might necessitate the use of one or more inventions covered by patent rights. By publication of this document no position is taken with respect to the validity of those claims or any patent rights in connection therewith. The patent holders so far identified have, we believe, filed statements of willingness to grant licenses under those rights on reasonable and nondiscriminatory terms and conditions to applicants desiring to obtain such licenses. The following patent holders and patents have been identified in accordance with the TIA intellectual property rights policy:
− None identified
TIA is not be responsible for identifying patents for which licenses might be referenced by this document or for conducting inquiries into the legal validity or scope of those patents that are brought to its attention.
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1. Introduction
1.1. Scope
This TSB establishes and documents methods and procedures of evaluation to establish compliance of fixed station cabinet emission levels with respect to the Federal Communications Commission (FCC) electromagnetic exposure (EME) limits. Specifically the EME characterization is of box level equipment only, e.g., a fixed station, control station, or similar equipment, This TSB is not a substitute for a complete transmitter site environmental assessment (EA) by means of computational methods or site measurement or a combination of these two means. A limit case analysis based on the 47 CFR part 90 certification requirements for spurious emissions limits included herein shows that certified equipment at the box level is within the FCC maximum permissible exposure (MPE) limits.
2. References
This Telecommunications System Bulletin contains only informative information.
There are references to TIA standards which contain normative elements. These references are primarily to indicate the methods of measurement contained in those documents. At the time of publication, the edition indications were valid. All standards and bulletins are subject to revision, and parties to agreements based on this document are encouraged to investigate the possibility of applying the most recent edition of the standard or bulletin indicated in Section 3. ANSI and TIA maintain registers of currently valid national standards published by them.
There are references to FCC rules. The Federal Code of Regulations (CFR) is subject to revision. The Government Printing Office (GPO) maintains a listing of the latest published titles.
3. FCC Electromagnetic Emission Limits
Controlled and general population RF Exposure Limits are shown in Table 1, below. The RF Exposure Limits shown in Table 1 are the limits adopted by the FCC. The RF exposure limits adopted by the FCC are generally based on recommendations from the National Council on Radiation Protection and Measurements (NCRP) Report No. 86 and the American National Standards Institute (ANSI/IEEE) C95.1-1992.[1]
Table 1
MAXIMUM PERMISSIBLE EXPOSURE (MPE) LIMITS[2]
(A) Limits for Occupational/Controlled Exposure
Frequency Electric Field Magnetic Field Power Density Averaging Time
Range Strength (E) Strength (H) (S)
(MHz) (V/m) (A/m) (mW/sq. cm) (minutes)
0.3-3.0 614 1.63 (100)* 6
3.0-30 1842/f 4.89/f (900/f2)* 6
30-300 61.4 0.163 1.0 6
300-1500 -- -- f/300 6
1500-100,000 -- -- 5 6
(B) Limits for General Population/Uncontrolled Exposure
Frequency Electric Field Magnetic Field Power Density Averaging Time
Range Strength (E) Strength (H) (S)
(MHz) (V/m) (A/m) (mW/sq. cm) (minutes)
0.3-1.34 614 1.63 (100)* 30
1.34-30 824/f 2.19/f (180/f2)* 30
30-300 27.5 0.073 0.2 30
300-1500 -- -- f/1500 30
1500-100,000 -- -- 1.0 30
f = frequency in MHz *Plane-wave equivalent power density
4. Limit Case Analysis
This analysis is structured to show that equipment that conforms to FCC emission limits for the carrier and its harmonics, through the tenth, will result in an equipment level EME that is compliant to the MPE limits as set forth in 47 CFR § 1.1310.
4.1. Calculation of EME level based on the FCC limit of -13 dBm for
each of the transmitter harmonics (1-10).
The limit case calculation will compute the resultant EME level, as a percent of the MPE level, of a transmitter that exhibits the maximum allowable cabinet emission limits as defined in 47 CFR § 90.210. This maximum level is a spurious emission that is attenuated by at least 43 + 10 log(P) dB, with P being the transmitter average power in watts or equivalently -13 dBm.
The cabinet emissions are considered to be emitted from a point source. As such it is necessary to define a distance at which the power density will be calculated. A distance of 20 cm is used based on the ANSI/IEEE C95.3-2002 “Recommended Practice for the Measurement of Potentially Hazardous Electromagnetic Fields – RF and Microwave” recommendation of a minimum separation distance of 20 cm between the probe and the perturbing object. This will allow controlled population to be sufficiently close to the equipment to allow direct observation or normal service interface through a terminal device or similar equipment.
4.2. Example spreadsheet calculations
Calculation method:
- Compute the power density, S, using equation 1, for each harmonic at the maximum allowable FCC radiated level (-13 dBm), at the specified distance, 20 cm, for the horizontal polarization, “where Prad is the power radiated”.
S = (Prad x 1.64)/(P x r 2) mW/cm2, r=20 cm (1)
Prad is the radiated power (mW)
R is the minimum working distance (cm)
- Compute percent of MPE for each harmonic using equation 2.
%MPE(fn) = 100 x S(fn)/MPE(fn) (2)
MPE(fn) is the allowable MPE for each transmitter harmonic , n = 1 to 10;
S(fn) is the power density for each transmitter harmonic, n = 1 to 10;
- %MPE(h) = Sum of %MPE(fn), n = 1-10.
%MPE(h) is the percent of the maximum permissible exposure in the horizontal polarization
- Repeat steps 1-3 for vertical polarization.
5. Total %MPE = %MPE(h) + %MPE(v)
4.3. Calculations at representative frequencies 3 MHz – 2 GHz
Tables showing the complete set of calculations (horizontal and vertical polarization) for each frequency and its harmonics are included in Annex A. Table 2 below shows the highest level computed for each of the various Fundamental Frequencies shown in Annex A.
Table 2
Maximum Resultant Controlled and General Population Percentage of
FCC MPE limits for each Fundamental Frequency shown in Annex A
Fundamental Frequency (MHz) / ControlledPopulation
% MPE / General
Population
% MPE
3 / 1.26E-02 / 6.30E-02
30 / 3.27E-02 / 1.64E-01
450 / 8.58E-03 / 4.29E-02
900 / 6.98E-03 / 3.49E-02
1900 / 6.54E-03 / 3.27E-02
The highest (worst case) computed level, as shown in Table 2, above at a Fundamental Frequency of 30 MHz, is more than 600 times [1/(1.64E-01/100)=609.8] below the FCC MPE limits. However, one must consider what would happen if there were some additional spurious energy that was not at the harmonic frequencies. To reach the MPE limits at the Fundamental Frequency of 30 MHz would require a total of approximately 6000 individual spurs, with each spur radiating at exactly the FCC spurious limit with equal horizontal and vertical polarized energy. In practice the spurious emissions from a cabinet will include transmitter harmonic content and spurious emissions from clocks and references that are associated with control and signal processing functions. While, industry experience has shown that the transmitter harmonic responses are the primary contributors to the spurious emissions, each transmitter design should be carefully assessed with respect to non-harmonic content.
4.4. Measurement method
The measurement method is as stated in TIA-603-C clause 2.2.12 Radiated Spurious Emissions with the following modification:
The carrier-radiated emission, terminated in a non-radiating load, must also be measured for horizontal and vertical polarization.
5. Transmitter Site Considerations
5.1. Site compliance
The analysis in this TSB indicates compliance with the FCC equipment certification requirements for equipments used at a transmitter site, in and of themselves should not exceed the RF exposure limits established by the FCC.
To assure that any transmitter site whether a base station site, a control station site or a similar transmitting facility complies with the FCC exposure limits, all site operators are reminded an RF Safety Program that includes procedures for "Evaluating Compliance with FCC-Specified Guidelines for Human Exposure to Radiofrequency Radiation" consistent with the FCC OET Bulletin Number 65 may be required. Transmitter site equipment conforming to the FCC certification requirements implies the equipment itself is within recommended MPE level limits, but does not imply that the overall transmitter site conforms to FCC MPE guidelines. Additional computations or measurements or a combination of both at each transmitter site will determine what precautions and operational procedures are necessary for each particular site to meet MPE guidelines. Proper installation of antenna distribution systems, work practices, etc. are required for a site to conform with FCC guidelines for human exposure to electromagnetic energy.
Manufacturers of FCC certified transmitter site equipment are strongly encouraged to advise all users, in their product documentation and elsewhere, that utilization of FCC certified transmitter site equipment does not in and of itself constitute complete compliance with all FCC RF safety requirements. Manufacturers should also advise all users about the need to institute appropriate RF Safety Programs to comply with FCC RF safety requirements. A suggested notice for manufacturers to include in documentation for transmitter site equipment is shown in Annex B.
All users should obtain competent advice as necessary to assure any RF Safety Program and all operations comply with all FCC RF safety requirements.
6. Summary
By itself, equipment conforming to FCC certification requirements (cabinet emissions) has a resultant electromagnetic exposure level that is several orders of magnitude below the FCC established maximum permissible exposure levels. This ensures that cabinet level emissions from individual, type accepted equipment, that is properly installed and maintained, does not constitute an EME hazard. This does not imply that a particular site where such FCC certified equipment is utilized, is in fact a non-hazardous transmitter installation. The FCC limits for cabinet RF emissions assures that unintentional cabinet emissions, at distances suitable for maintenance activities, are below the FCC MPE limits. However, the levels of intentional emission must be characterized by means of computation or measurement, to determine what precautions and work practices must be adhered to for each transmitter site.
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Annex A
Computation of Percent of Maximum Permissible Exposure
(Informative)
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Annex B
Suggested RF Safety Notification for Manufacturer’s Transmitting Site Equipment Documentation
(Informative)
Compliance with FCC RF Safety Requirements
Compliance with the spurious emissions limitations associated with the requirements for FCC transmission site certified equipment indicates the spurious emissions for this equipment, by themselves, do not exceed the FCC adopted limitations for Maximum Permissible Exposure outlined in
47 C.F.R. §1.1310.
All station owners and users are reminded that use of FCC certified transmitting equipment at a transmitting site does not assure full compliance with all FCC RF Safety requirements.
All station owners and users are reminded appropriate RF Safety Programs to assure all stations and all operations are in compliance with the necessary FCC RF Safety requirements may be needed.
All station owners and users are cautioned to engage the services of competent advisors, to assure that any RF Safety Program instituted addresses all necessary actions required by the FCC RF Safety requirements.
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[1] NCRP Report No. 86, "Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields", sections 17.4.1, 17.4.1.1, 17.4.2 and 17.4.3; copyright NCRP, 1986, Bethesda, Maryland 20814. ANSI/IEEE C95.1-1992, "IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz”, Section 4.1; copyright 1992 by the Institute of Electrical and Electronics Engineers, Inc., New York, New York 10017.
[2] See 47 CFR §1.1310.