*Pages 1--33 from Microsoft Word - 8032.doc* Federal Communications Commission FCC 01- 60 1 Before the Federal Communications Commission Washington, D. C. 20554 In the Matter of ) ) An Inquiry Into the Commission's ) Policies and Rules Regarding AM ) MM Docket No. 93- 177 Radio Service Directional Antenna ) RM- 7594 Performance Verification ) REPORT AND ORDER AND FURTHER NOTICE OF PROPOSED RULEMAKING Adopted: February 14, 2001 Released: March 7, 2001 Comment Date: 75 days after publication in the Federal Register Reply Comment Date: 135 days after publication in the Federal Register By the Commission: Table of Contents Heading Paragraph # I. Introduction .................................................................................................................................... 1 II. Directional Antenna Proofs of Performance ..................................................................................... 3 A. Full Proof of Performance ...................................................................................................... 4 1. Number of Radials ....................................................................................................... 4 2. Number of Points per Radial, Length of Radials ........................................................... 8 3. Standard Format for Reporting Measurements ............................................................ 12 B. Partial Proof of Performance ................................................................................................ 13 1. Number of Radials Required, Number of Points per Radial ......................................... 14 2. When Required .......................................................................................................... 17 C. Monitoring Points ................................................................................................................ 19 III. AM Station Equipment & Measurements ....................................................................................... 26 A. Base Current Ammeters ....................................................................................................... 26 B. Antenna Monitors ................................................................................................................ 29 C. Impedance Measurements Across a Range of Frequencies .................................................... 32 D. Common Point Impedance Measurements ............................................................................. 34 IV. Designation of Critical Arrays ....................................................................................................... 36 1 Federal Communications Commission FCC 01- 60 2 V. Conclusion .................................................................................................................................. 42 VI. Further Notice of Proposed Rulemaking on the Use of Computer Modeling .................................... 43 to Predict Antenna Performance VII. Administrative Matters .................................................................................................................. 48 Appendix A List of Commenters Appendix B Final Regulatory Flexibility Analysis Appendix C Initial Regulatory Flexibility Analysis Appendix D Rule Changes I. Introduction 1. This Report and Order and Further Notice of Proposed Rulemaking (Report and Order) is part of a broad- based streamlining initiative to overhaul Mass Media Bureau policies and licensing procedures. In the course of this initiative, the Commission has introduced substantially shorter and simpler certification- based application forms, established new broadcast application licensing procedures, and instituted electronic filing. 1 This Report and Order reduces the regulatory burdens on AM broadcasters using directional antennas by relaxing our technical rules to the extent possible while still maintaining the integrity of the service. There are approximately 1,900 directional AM stations presently licensed in the United States. Directional AM stations use antennas which suppress radiated field in some directions and enhance it in others. In order to control interference between stations and assure adequate community coverage, directional AM stations must undergo extensive "proofs of performance" to demonstrate that the antenna system operates as authorized. The field strength measurements and technical exhibits which our current rules require as part of a “proof” impose a substantial financial burden upon these AM broadcasters, a burden not incurred by licensees in the other broadcast services. 2 This Report and Order substantially reduces this burden. 2. This proceeding began with a Notice of Inquiry in response to a joint petition for rulemaking filed by five broadcast consulting engineering firms (" Joint Petitioners") 3 , which argued that the Commission could materially reduce the measurement burdens imposed on AM broadcasters, based on certain technological advances. The Joint Petitioners requested a thorough examination of these rules and the adoption of alternate means of directional antenna system verification. The Commission subsequently issued a Notice of Proposed Rulemaking (" NPRM") 4 seeking comments on the incorporation of new techniques for AM analysis into our rules, and on our proposals to streamline existing requirements. In response to the NPRM, the Commission received 18 comments and four reply comments. 5 In general, the comments and reply comments share the view that rule changes are warranted to reduce the burdens of 1 See 1998 Biennial Regulatory Review -- Streamlining of Mass Media Applications, Rules and Processes, Report and Order in MM Docket No. 98- 43, 12 FCC Rcd 23506 (released Nov. 25, 1998); 63 Fed. Reg. 70,039 (Dec. 18, 1998). 2 Directional FM licensees incur substantially lesser incremental expenses in constructing, licensing, and maintaining their facilities. 3 The five broadcast consulting firms which filed the joint petition for rulemaking in 1991 are duTreil, Lundin & Rackley (" DLR"); Hatfield and Dawson Consulting Engineers, Inc. (" Hatfield & Dawson"); Lahm, Suffa & Cavell (" LSC"); Moffet, Larson & Johnson, Inc. (" MLJ"); and Silliman & Silliman. 4 14 FCC Rcd 9275 (1999), 64 FR 40535. 5 A list of commenters and reply commenters is in Appendix A. 2 Federal Communications Commission FCC 01- 60 3 verifying AM directional antenna patterns. This Report and Order adopts most of the streamlining initiatives proposed in the NPRM. We are confident that relaxing our proof requirements will provide meaningful relief to many AM broadcasters without jeopardizing technical standards or service to the public. However, we believe it is premature to take any action on the use of certain computer modeling methods to verify directional stations’ operating parameters. We also seek additional comments on these methods. II. Directional Antenna Proofs of Performance 3. An antenna proof of performance establishes whether the radiation pattern of an AM station is in compliance with the station's authorization. An AM station must perform a full proof to verify the pattern shape when a new directional antenna system is authorized. Partial proofs, which require fewer measurements, are occasionally necessary to show that an array continues to operate properly. For both full and partial proofs, we proposed to reduce both the number of radials and the number of measurements per radial. Nearly all commenters agreed that proof requirements could be relaxed without compromising the technical integrity of the AM service. A. Full Proof of Performance 1. Number of Radials 4. Background. Under the Commission’s rules, a permittee must measure a minimum of eight radials in a proof of performance. 6 For complex patterns, measurements are required on a sufficient number of radials to define the pattern shape completely, i. e., three radials in the main lobe, and one in each null and minor lobe. In the NPRM, we proposed to reduce the minimum number of radials required from eight to six for simple directional antenna patterns and, generally, to require no more than 12 radials to define complex patterns. The radials would be distributed as follows: (a) One radial in the major lobe, at the pattern maximum. (b) Five additional radials, and others as necessary to establish the pattern clearly. These radials will be generally at the peaks of minor lobes and at pattern nulls. This may include radials specified on the station's authorization. However, no two radials may be more than 90 q azimuth apart. If two radials would be more than 90 q apart, then an additional radial must be specified within that arc. (c) Any radials specified on the construction permit or license. 5. Nondirectional antenna measurements would be taken along the radials used for directional measurements. In addition, we proposed that those few nondirectional stations which are required to conduct a full proof (due to the proximity of reradiating structures, or other atypical circumstances) should also be permitted to employ six evenly spaced radials, in lieu of eight. 6. Most commenters support a reduction in the number of measured radials. Some suggest that the number of required radials could be reduced even further than we proposed. Hatfield & Dawson, DLR, and Sellmeyer Engineering (Sellmeyer) argue that marketplace considerations will ensure adequate 6 See 47 C. F. R. § 73.151. 3 Federal Communications Commission FCC 01- 60 4 performance, and therefore, that major lobe measurements are unnecessary. Hatfield & Dawson also suggests that, for simple patterns with a single null, “three or four radials may be used.” The Walt Disney Company (Disney) expresses similar views, stating that “[ a] two- tower ‘cardioid’ array …could be defined by two radials, and other two- tower arrays by as few as three radials.” Clear Channel Communications, Inc. (Clear Channel), DLR, and Sellmeyer agree that fewer than six radials would suffice for simple patterns. Most other commenters support our proposed minimum of six radials with a maximum span of 90 degrees between radials. According to Carl T. Jones Corporation, “complex designs may result in critical shaping of the pattern… without resulting in more than one pattern minim[ um].” 7. Discussion. We will adopt the proposed minimum of six radials, including one radial in the major lobe and a 90 q maximum span, to provide the best balance between reducing the burden of proof measurements and ensuring proper array performance. While we recognize that the null structure of simple patterns can be defined with a few radials, we believe that additional measurements are necessary to ensure that the array meets two critical Commission requirements: antenna efficiency and principal community coverage. 7 Marketplace considerations alone will not ensure that these requirements are fulfilled. As proposed, we will limit the maximum number of radials required to 12, allowing use of symmetry for complex patterns which might otherwise require more than 12 radials to define all pattern features. 2. Number of Points per Radial, Length of Radials 8. Background. A full proof establishes field strengths along each radial on the basis of 20 to 30 measured points. We proposed to reduce the number of points per radial to a minimum of 15 directional points, as well as to shorten the minimum length of the radial to 15 km. We proposed to specify intervals between these points as follows: (1) The closest point at a distance ten times the maximum distance between the elements of a directional array, or at a distance five times the vertical height of the antenna in the case of a nondirectional station; (2) Close- in measurements at intervals of approximately 0. 2 kilometer, out to a distance of three kilometers, with a minimum of seven nondirectional points (added); (3) Measurements at intervals of approximately one kilometer between three and five kilometers (three points); (4) Measurements at intervals of approximately two kilometers between five and 15 km (five points); (5) Additional measurements as necessary at greater distances to achieve at least 15 points clear of potential reradiating structures; and (6) Measurements at any monitoring point locations along the radial (unchanged from the present rule). 7 To ensure efficient use of spectrum, the Commission has long held that applicants using directional antenna patterns must fill a minimum percentage of the predicted pattern envelope. See Report and Order in MM Docket No. 96- 58, 12 FCC Rcd 12371, at paragraph 60. For AM stations, actual antenna efficiency is expressed in terms of the root- mean- square (RMS) of measured radiation values. See 47 C. F. R. § 73.151( a). 4 Federal Communications Commission FCC 01- 60 5 9. Discussion. Commenters unanimously support a reduction in the required number of points and the length of the radials. We agree with Carl T. Jones Corporation, which notes that nondirectional measurements begin closer to the antenna site than directional measurements; consequently, a proof includes more nondirectional points. 8 These additional nondirectional measurements are used to determine the inverse distance field (IDF), which is the basis for determining directional field strength. Although the NPRM tentatively rejected a reduction in the required number of close- in measurement points, we recognize that, in many cases, it is not possible for the permittee to take measurements at every specified interval within 3 kilometers of the antenna site. It has been our policy to accept fewer close- in measurements in these circumstances, provided the inverse distance field can be determined with reasonable certainty. We therefore add the stipulation that the close- in measurements include at least seven points to formalize our policy while providing some relief to the broadcaster. 10. DLR, Clear Channel, and Hatfield & Dawson favor a reduction in the number of measured points to ten and the elimination of close- in nondirectional measurements. 9 Instead of determining the nondirectional inverse distance field by graphical analysis, DLR proposes using the theoretical nondirectional field. In support of the proposal, DLR supplies a tabulation of results from 57 proofs accepted by the Commission. 10 We decline to adopt further measurement reductions. While we recognize the merit of this suggestion, our experience has shown that proper detuning of unused towers in an array may be difficult, and that unused towers can significantly distort nondirectional patterns. We continue to believe, along with the majority of commenters, that our proposed reduction in the number of required measurements will provide a sufficient basis for graphical analysis of field strength measurements. We will adopt the proposal to shorten the minimum radial length to 15 kilometers and to require a minimum of 15 points, distributed as set forth above, for full proofs. 11. Many commenters state that the distribution of measurement points should be flexible, so that the engineer may avoid areas where field strength cannot be measured reliably. NAB requests “that broadcasters be given some discretion in designating far- point measurements.” In fact, 47 C. F. R. § 73.186( a)( 1) already provides this discretion, requiring licensees to exercise good engineering judgment in selecting locations for field measurements based on the approximate intervals we establish in this Report and Order. 3. Standard Format for Reporting Measurements 12. We also sought comment on a standard format for reporting field strength measurements. Most applicants already submit field strength measurements in table format using commercial spreadsheet or database software. We proposed to adopt a standardized format for the submission of the data in order to facilitate electronic filing and processing. Electronic storage of this data could also facilitate easy retrieval by any interested party. Nearly all commenters agree that a standard data format would be useful. Potomac Instruments, Inc. presents a sample format which would be compatible with GPS receiver output. In addition, Hammett & Edison suggests that we include a field for measured ground conductivity, since 8 In a typical case, nondirectional measurements might begin at 0. 4 kilometer. Taking points at the specified intervals would give 13 close- in points, three points between three and five kilometers, and five points between five and 15 kilometers, for a total of 21 nondirectional points. If directional points are measured beyond 15 kilometers, then additional nondirectional measurements would be made at those same points. 9 DLR, Clear Channel, and Hatfield & Dawson all suggest making the graphical analysis now used optional. 10 The tabulation shows that most measured values of nondirectional radiation differ from the theoretical value by less than two dB. 5 Federal Communications Commission FCC 01- 60 6 this is the information usually sought by engineers who retrieve field strength measurements. We agree that electronic storage and retrieval of measured conductivities would be useful. Based on the comments received, we will develop a format for submission of field strength measurements and for ground conductivities derived from measurements. We will release the details of these file formats concurrently with the Public Notice releasing the new, revised version of FCC Form 302- AM to be utilized for electronic filing. In a related matter, DLR suggested deleting the requirement to include topographic maps showing each measurement point in a full proof of performance. We agree that this requirement places an unnecessary burden on the AM station. Furthermore, the size of the topographic maps makes it particularly difficult to provide them in electronic format. We will therefore modify our rules to require that licensees retain copies of the topographic maps showing measurement points, to be provided to Commission staff upon request. 11 B. Partial Proof of Performance 13. Partial proofs of performance are required after the installation of new equipment on an AM tower or where changes in the electrical environment, such as erection of a new tower nearby, could affect the radiation pattern. These proofs are conducted to verify that the array remains properly adjusted. A partial proof consists of measurements taken at selected locations used in the last full proof of performance. The field strength values measured at each point are mathematically compared to values obtained in the last full proof to yield the current value of radiation along each azimuth. 1. Number of Radials Required, Number of Points per Radial 14. Background. Permittees must now make at least ten field strength measurements between three and 16 kilometers from the array at points used in the last complete proof of performance. 12 If a radial contains a monitoring point, 13 that point must be included in the measurements. A partial proof includes measurements on all radials measured in the full proof. We proposed to reduce to eight the required minimum number of points per radial, including any monitor points. 15. Discussion. The Association of Federal Communications Consulting Engineers (AFCCE) points out that, while a full proof is “a rare event” for most AM stations, partial proofs are relatively frequent. Therefore, AFCCE states, “reducing the cost of a partial proof is more important than reducing the cost of a full proof…[ and] increases the likelihood that station management will authorize the measurements when the need is indicated.” We agree that reducing the requirements for a partial proof may expedite the process of correcting malfunctioning AM arrays. As proposed in the NPRM, we will reduce the number of points per radial from ten to eight, including any monitoring point on the radial. Further, we will incorporate commenters’ proposals to reduce the number of radials measured. We will limit the radials measured on a partial proof to those radials which include monitoring points. 14 If a directional pattern has fewer than four monitored radials, the licensee should include the nearest adjacent radials from the full proof, for a minimum of four. We believe that these changes will minimize the financial burden on directional AM stations while still providing sufficient data to verify directional array performance. 11 Maps showing measurement locations should be associated with the proof of performance application which must be available in the station’s public inspection file while the application is pending. See 47 C. F. R. § 73.3526( e)( 2). 12 See 47 C. F. R. § 73.154. 13 See paragraph 19 for definition of “monitoring point.” 14 Monitoring points are usually designated on all radials which define pattern minima. 6 Federal Communications Commission FCC 01- 60 7 16. Several commenters note that many partial proofs rely on full proof measurements which may be decades old. 15 Even when a full proof is relatively recent, changes to the area surrounding the AM station may alter propagation characteristics, or may make it impossible to locate points identified in the full proof. In such circumstances the comparison of recent directional measurements with old readings may be invalid. We agree that an alternate approach is warranted. In cases where the engineer cannot identify points from the last full proof with reasonably certainty, or where the environment around the AM station has changed, we will allow the station to select eight suitable points on each radial at which to measure both directional and nondirectional fields. The average ratio of directional to nondirectional field strength may then be used in conjunction with the measured nondirectional field to determine the directional field. 16 Occasionally, licensees performing a partial proof discover that radiation on one or more bearings exceeds the standard pattern, often from changes in the vicinity of the directional antenna which are beyond the licensee’s control. In these circumstances, we will permit the licensee to augment the standard radiation pattern based on the results of full directional and nondirectional measurements on the affected radial, including close- in points in accordance with §73.186. The inverse distance field should be determined graphically, as required in a full proof of performance. 17 2. When Required 17. Background. A licensee is required to conduct a partial proof of performance when there is some indication that the antenna system may not be operating as authorized, e. g., when monitoring point readings or antenna monitor readings exceed the limits specified on the station's license. 18 The NPRM did not propose to relax this requirement. Currently, 47 C. F. R. § 73.68 also requires a partial proof when sampling system components mounted on the tower are replaced or modified. We proposed to eliminate the latter requirement provided the new components are mounted in the same location and, where appropriate, with the same orientation, as the old components and: (1) measurements made at the monitoring points before and after installation establish that the substitution had no effect; and (2) antenna monitor values remain within the tolerances specified in the rules or on the station's authorization. If the monitoring point readings or antenna monitor values exceed authorized limits, then a partial proof would be required. 18. Discussion. All commenters who address this issue agree that a partial proof should not be mandatory when sampling system components are replaced or modified. With the provisions noted, we will delete the requirement for a partial proof in 47 C. F. R. § 73. 68. C. Monitoring Points 15 A query of our Consolidated Data Base System (CDBS) shows that approximately 80 percent of full proofs are more than ten years old. 16 This is consistent with our present policy of allowing a licensee to use the ratio of directional to nondirectional field strengths when selecting a new monitoring point. We will codify the policy in a revised rule. 17 Licensees who wish to request augmentation should file concurrently Forms 301- AM and 302- AM. Form 301- AM should include an allocation study demonstrating that no interference would result. Form 302- AM should include the results of the partial proof, along with full directional and nondirectional measurements and graphical analysis of the radial( s) to be augmented. Both forms require a filing fee. 18 See 47 C. F. R. § 73. 61. Other circumstances which necessitate a partial proof of performance include alterations to or near the AM tower (such as adding transmission lines, isocouplers or communications antennas); replacing guy wires; or changing isolation chokes for tower obstruction lighting. A partial proof is also required to verify proper adjustment of an antenna system when operation is resumed following a period of silence exceeding six months. 7 Federal Communications Commission FCC 01- 60 8 19. Background. Monitoring points are specific locations on selected proof radials where licensees regularly take field strength measurements. The measured field strength at each monitoring point may not exceed a maximum value specified on the station’s license. Monitoring point limits are based upon the difference between the radiation along the radial as determined by the proof of performance and the radiation permitted by the authorized pattern. We tentatively concluded that we should retain the requirement for monitoring points, as they provide the only indication of directional antenna performance outside the station’s transmission facilities. 20. In the NPRM, we discussed the fact that stations may need to change monitoring point locations when an original point has become inaccessible, or because changes in the local electromagnetic environment could affect field strength readings. Under the current rules, an informal application to change a monitoring point must include the results of a partial proof of performance taken on the radial containing the monitoring point to be changed. 19 We proposed to eliminate the requirement to conduct a partial proof of performance along the radial containing this monitoring point. Instead, we sought comment on allowing the applicant simply to reference the measurements taken along that radial in the last full proof of performance submitted to the Commission. The staff would assign a radiation limit for the new monitoring point using the same procedure as described above. 20 21. We also proposed to eliminate the requirement for maps and directions indicating how to reach monitoring point locations for applicants using GPS- determined coordinates to identify monitoring point coordinates. 21 In order to achieve sufficient accuracy, a differential GPS receiver would be required. 22 We proposed to specify monitoring point coordinates submitted in this manner on the station's license. Parties interested in locating these monitoring points could plot the specified coordinates onto topographical or other maps to determine the best route. 22. Commenters are divided regarding the deletion of the requirement for a partial proof on a radial when a monitoring point is changed. NAB and AFCCE support our proposal to allow licensees to select a new monitoring point from those points measured in the last full proof. According to AFCCE, “[ m] onitoring points are based on the full proof, not the partial proof. If a monitoring point needs to be changed because of construction or other factors, then the full proof data should be used.” AFCCE also suggests a uniform 20 percent tolerance on field strength readings at monitor points. Hammett & Edison agrees that a new monitoring point could be selected from the original proof points, “provided the environment… has not, itself, been subject to significant changes.” If the environment has changed, DLR, Hatfield & Dawson, and Sellmeyer Engineering support Hammett & Edison’s proposal to permit stations to submit a partial proof on the monitored radial, which may include new points if necessary. 19 See 47 C. F. R. § 73.158. 20 The field strength limit would be assigned based upon the difference between the radiation along the monitoring point radial as determined by the proof of performance and the radiation permitted by the authorized standard (or augmented) radiation pattern. 21 See 47 C. F. R. §§ 73.151( a)( 3) and 73.158( a)( 2)-( 4). In the NPRM, we proposed to continue requiring a description of the monitoring point as well as a photograph to verify that the location is free of obstructions such as overhead power lines, to identify the precise location of the monitoring point with respect to nearby landmarks, and to identify the exact placement of measurement equipment. 22 Differential GPS uses a reference signal from a ground beacon in addition to the satellite signals to reduce the coordinate error. Differential GPS has an accuracy better than ± 2 meters, while for non – differential GPS the possible error is approximately ±100 meters. USGS topographic maps have an accuracy of about ±12 meters. Some additional information about GPS may be found on the Internet at http:// www. fcc. gov/ mmb/ asd/ welcomeALT. html# GPS. 8 Federal Communications Commission FCC 01- 60 9 23. Other commenters disagree with the proposal to delete the partial proof requirement when a new monitor point is selected. Carl T. Jones, D. L. Markley & Associates, and Lawrence Behr Associates contend that it is good engineering practice to measure the entire radial when monitor point readings have changed. According to Clear Channel Communications, “the Commission should establish (or reestablish) point limits solely on the basis of full directional and nondirectional measurements along the radial.” Clear Channel also proposes a uniform 10 percent tolerance on monitor point readings. 24. Discussion. We acknowledge the concerns of commenters who note that a change at a monitoring point may reflect significant changes on the entire radial. We agree that without a partial proof, it may not be possible to distinguish local effects from changes in the radiation pattern. In view of these concerns, we are persuaded to modify our proposal. We will continue to require a partial proof on the affected radial when a monitoring point must be changed as a result of changes in field strength readings. We will allow licensees to designate a new monitor point from those points measured in the last full proof, without a partial proof on the monitored radial, when a monitoring point has become inaccessible or unsuitable for reasons unrelated to the electromagnetic environment. Licensees submitting a partial proof may refer to the last full proof of performance, or, alternatively, may measure directional and nondirectional field strengths at eight points to establish the directional field. When a directional- to-nondirectional comparison is used, the points need not be the same as those measured in the full proof. A suitable new monitor point may be chosen from the new partial proof points. Licensees may also use a partial proof based on the ratio of directional to nondirectional field strength to change the field strength limits for existing monitoring points. Any request for a change in a monitoring point location or field strength limit should be submitted to the Commission along with Form 302- AM. As AFCCE points out, our present method of determining field strength limits at monitoring points affords very little tolerance when the measured radiation is just within the standard pattern value. Present rules do not allow permittees to augment the standard pattern unless the measured radiation exceeds the standard pattern. 23 In order to allow sufficient tolerance for monitoring point limits, we will allow augmentation to 20 percent more than the measured radiation on monitored radials, regardless of whether the measured radiation exceeds the standard pattern value. We will require permittees who wish to augment to demonstrate that no interference would result. 25. Concerning identification of monitor points, most commenters favor eliminating the driving directions and the accompanying map. Few agree that coordinates determined by differential GPS alone would identify a monitoring point with sufficient accuracy on a station’s license. Hammett & Edison reports “we have often noted, during the implementation of the FCC’s tower registration program, towers with incorrect GPS- determined coordinates.” Instead of identifying the monitor point solely by GPS coordinates, Hammett & Edison suggests that we retain a brief description of the monitoring point on the AM license. Coordinates determined using differential GPS could be provided as part of the description, at the licensee’s discretion. In view of the consensus among the commenters, we will continue to require the monitor point description, and will include the description on the license. We will require licensees to provide a brief description of each monitoring point in all applications for license or for modification or re-issuance of license. Licensees may supplement this description with geographic coordinates determined by differential GPS. We will also continue to require a photograph of the monitoring point. We will delete the requirement for driving directions to monitoring points, and for maps showing the monitoring points. 23 See §73.152. Augmentation expands the standard pattern radiation envelope, normally over a limited span, to encompass anomalies in a measured pattern. 9 Federal Communications Commission FCC 01- 60 10 III. AM Station Equipment & Measurements A. Base Current Ammeters 26. Background. Licensees are currently required to install base current ammeters or toroidal transformers (current registering devices) at the power feed point of each tower, typically at the base of the tower. See 47 C. F. R. § 73. 58( b). With improvements in antenna sampling system design, fewer stations now rely on base current ammeters as a means of maintaining proper array adjustment. We therefore proposed to delete the requirement for base current ammeters or toroidal transformers for those directional stations employing approved antenna sampling systems. 24 27. Discussion. Nearly all commenters agree that the requirement for base current sampling should be deleted for stations using approved sampling systems. As Greater Media, Inc. points out, “Base current ammeters can… effectively impose a second and unnecessary set of tolerances on the adjustment of the array.” Delta Electronics, Inc., manufacturer of current sampling devices for broadcast use, suggests alternatively that the Commission require that directional AM stations “retain the capability for base current measurements” in the event that the approved sampling system or the antenna monitor malfunctions. Potomac Instruments, Inc. also cites the value of base current ammeters when antenna monitor readings shift significantly. 28. We recognize that some AM broadcasters may wish to maintain base current sampling. As we indicated in the NPRM, deletion of this requirement would not prevent stations from continuing to use base current ammeters for diagnostic purposes, or as a backup in the event of sampling system or antenna monitor failure. However, consistent with our efforts to streamline our rules, we see no need to incorporate such maintenance practices into our rules. Accordingly, as proposed in the NPRM, we will delete the requirement for base current sampling. We note, however, that stations not using approved sampling systems have no reliable alternate on- site means of assessing antenna performance. In these circumstances, our rules will continue to require stations to install and use base current ammeters if the Commission has not approved an alternative system. B. Antenna Monitors 29. Background. An antenna monitor measures the relative currents and phases of radiating elements in a directional antenna, two critical factors in defining a pattern. All AM directional stations are required to use an antenna monitor which complies with the technical requirements in 47 C. F. R. § 73. 53. 25 This rule also establishes antenna monitor specifications. We proposed to delete most of the antenna monitor construction and operational requirements of 47 C. F. R. § 73. 53, with the exception of a few provisions that would be shifted to other existing rule sections. 26 We noted that the Commission has eliminated detailed construction and operational requirements for other types of broadcast equipment, such 24 Design and Installation of Sampling Systems for Antenna Monitors In Standard Broadcast Stations With Directional Antennas, 57 FCC 2d 1085 (1976). 25 See also Public Notice to Licensees of All Standard Broadcast Stations Employing Directional Antennas, 45 FCC 2d 1062 (1974). 26 The present requirement in 47 C. F. R. § 73.53( a) that the antenna monitor be verified for compliance with the Commission’s technical requirements would be moved to 47 C. F. R. § 73.69, which deals with antenna monitors. Antenna monitor requirements for critical arrays would also be moved from 47 C. F. R. § 73.53( c) to 47 C. F. R. § 73.69. Minimum readout levels in 47 C. F. R. § 73.53( b)( 4) and (5) would be moved to 47 C. F. R. § 73.1215 (Specifications for Indicating Instruments). 10 Federal Communications Commission FCC 01- 60 11 as transmitters and metering equipment, and we tentatively concluded that the elimination of these requirements would encourage the development of more dependable and less expensive antenna monitor units. 30. Discussion. In the NPRM, we cited 1993 comments by Potomac Instruments, Inc., a manufacturer of antenna monitor systems, claiming that the present specifications in 47 C. F. R. § 73. 53 impede the development of antenna monitor systems using advanced technology and that elimination of these requirements would result in a new generation of monitor equipment. We note that a number of years have passed since this proceeding was initiated, and that further development of new instrumentation technology for AM stations may be unlikely. In its recent comments, Potomac Instruments states that it “does not believe that the elimination of 47 C. F. R. § 73. 53 would enhance the development of new and less expensive antenna monitor systems.” The manufacturer explains that the economics of the directional AM market simply do not support research and development. In view of this comment, we are persuaded not to adopt this proposal in the near term. We will leave the provisions of 47 C. F. R. § 73. 53 unchanged. 31. We also sought comment on whether to permit licensees to use voltage sampling devices to feed antenna monitors in lieu of current sampling devices such as sampling transformers and pick- up loops. We asked for comments as to the accuracy and reliability of voltage sampling devices for assessing array performance, and as to whether we should modify the rules to permit their use. Most commenters favored this proposal, but felt that it was more appropriately addressed in the context of a further NPRM, along with the issue of computer modeling and its related sampling system requirements. We will therefore seek additional comments on base voltage sampling, particularly as it relates to sampling system specifications necessary for accurate computer modeling. 27 C. Impedance Measurements Across a Range of Frequencies 32. Background. All AM stations are required to measure impedance (resistance and reactance) across the range of frequencies within 25 kHz of the carrier frequency. 28 This procedure, known as an impedance sweep, is intended to ensure adequate audio quality across the station’s operating bandwidth. In keeping with the deletion of various performance measurements for FM and TV, we proposed to delete the requirement for AM stations to perform an impedance sweep. We tentatively concluded that retention of 47 C. F. R. § 73. 54( c) is not necessary because market forces will provide sufficient incentive for stations to maintain quality technical operations. 33. Discussion. Commenters express unanimous support for eliminating the requirement to measure impedance at a range of frequencies. We will delete the requirement as proposed. D. Common Point Impedance Measurements 34. Background. Present rules require directional AM stations to take impedance measurements at the common radiofrequency input location. The rule 29 now specifies that licensees maintain a reactance of zero ohms at this point. We proposed to delete this requirement. The reactance does not affect the station’s output power, and we tentatively concluded that practical considerations should dictate the optimum common point reactance. We also sought comment as to whether a limit should be set for the maximum amount of reactance permitted. 27 See paragraphs 42 to 46, below. 28 See 47 C. F. R. § 73.54( c)( 1) and (2). 29 47 C. F. R. § 73.54( b). 11 Federal Communications Commission FCC 01- 60 12 35. Discussion. All commenters who mention common point impedance agree that it is unnecessary to maintain zero reactance. Several commenters point out that, in many circumstances, the transmitter operates more efficiently with a non- zero reactance at the common point. In response to our inquiry regarding a maximum permissible amount of reactance, Greater Media, Inc. suggests 10 ohms. Greater Media does not explain the basis of this limit, however. In the absence of a compelling reason to limit the reactive component of the common point impedance, we decline to specify a limit. As proposed in the NPRM, we will no longer require stations to adjust common point reactance to zero ohms. IV. Designation of Critical Arrays 36. AM directional antennas are not steady- state systems. Because current and phase values tend to fluctuate, our rules specify operating tolerances for these values. In most cases, maintaining current and phase variations within normal tolerance will ensure that radiated fields remain within the station’s authorized pattern. Critical arrays are directional antennas that are unusually sensitive to slight variations in internal operating parameters, i. e., they are likely to produce excessive field when antenna parameters vary. We therefore require licensees of stations with critical arrays to maintain tighter operating tolerances in order to limit potential interference. 37. Background. In the NPRM we acknowledged, as several commenters pointed out, that the staff has generally investigated an array for stability only if a petition or objection is filed against the application proposing the array. As a result, not all unstable antenna systems have been designated as critical arrays. We proposed to apply a uniform screening process to all applications for directional facilities. 38. We also proposed to relax our criteria for designating critical arrays in several ways. First, we proposed to restrict our tests for array stability to radiation pattern minima (nulls) and maxima in the horizontal plane only instead of testing at all azimuths and elevations. Second, we proposed to classify an array as critical only if the standard pattern is exceeded at 10% or more of the possible parameter variation combinations. The current test requires only one instance of excessive radiation. Finally, based on the results of studies we have performed on the licensed AM directional patterns in our AM engineering database, we proposed to exclude all two- and three- tower arrays from designation as critical arrays. We also proposed to exclude all daytime arrays which, historically, have not generated instability complaints. Finally, we proposed to permit licensees with facilities currently classified as critical to request staff review of their designation based on the revised criteria. We sought comment on each aspect of this proposal. 39. Discussion. Comments received on these issues were mixed. Some commenters suggest modifications to the criteria for designating critical arrays. The Walt Disney Company, while generally supporting our proposals, rejects the suggestion that studies be limited to pattern minima and maxima. Disney asserts that “the most sensitive areas of a pattern …are not in a null but just coming out of a null, where the signal strength rises rapidly versus azimuth.” Disney and Thomas G. Osenkowsky also disagree with our proposal to limit stability studies to the horizontal plane. Moreover, Osenkowsky opposes the categorical exclusion of two- and three- tower arrays from study. Lawrence Behr Associates maintains that daytime arrays should not be exempt from scrutiny, as we proposed. 40. We are persuaded, however, that the better course is to eliminate the critical array 12 Federal Communications Commission FCC 01- 60 13 designation. 30 Many commenters, including Hatfield & Dawson, DLR, Clear Channel, and Donald G. Everist, support this approach which is consistent with our general intent to relax AM technical requirements. We agree with several commenters, including Hatfield & Dawson and DLR, that noted that the degree of precision inherent in both our predictions of pattern shape and in our nighttime propagation model is inconsistent with the close tolerances required of critical arrays. 31 Moreover, we recognize a lack of uniformity in the Commission’s historic application of stability requirements. As Hatfield & Dawson notes, imposing stability standards on new station proposals would simply carry forward an inequity in the way we have treated potentially critical arrays in the past. To rectify this problem, we will also delete the critical array designation in all outstanding authorizations. 32 V. Conclusion 41. In this Report & Order, we have adopted substantial reductions in our proof of performance requirements for AM directional antenna systems. For both full and partial proofs of performance, we have reduced the number of measurement radials required and have cut the minimum number of measurement points required per radial. We believe these provisions will substantially reduce the time and cost burdens associated with verifying proper operation of AM directional arrays. We have removed unnecessary operating requirements in regard to base current ammeters and common point reactance. With the removal of the critical array designation, we provide substantial relief to the minority of AM stations burdened with the tight tolerances and expensive antenna monitors that this designation imposed. Although these provisions are designed to provide substantial savings for licensees of directional AM antennas, we believe that none of them jeopardize the technical integrity of the AM broadcast service. VI. Further Notice of Proposed Rulemaking on the Use of Computer Modeling to Predict Antenna Performance 42. The Joint Petitioners who initiated this proceeding in 1991 suggested that the Commission consider incorporating the use of computer modeling techniques into the proof of performance process. 33 According to the Joint Petitioners, computer modeling does not rely on the simplifying assumptions contained in our present rules, and therefore can accurately predict the relationship between pattern shape and "internal" array parameters such as impedances, currents and voltages at locations within the power 30 We believe that economic considerations in the mature AM service will discourage construction of certain types of arrays that tend to be unstable. In the event that an applicant proposes a directional antenna system which may be characterized as potentially unstable based on factors such as predicted operating impedances, RSS/ RMS ratio, or null depth, the staff may designate additional monitoring points to insure that the radiation remains within standard pattern limits. 31 AM field strength at night is subject to significant short- and long- term variation. A recent comparison of predicted and measured skywave field strengths shows that the root- mean- square error is 5. 4 dB. See Wang, J. C. H., An Objective Evaluation of Available LF/ MF Sky- wave Propagation Models, Radio Science, Vol. 34, No. 3, pp. 703- 713, May- June 1999. 32 In the NPRM we proposed to discontinue requiring the use of expensive, specially designed precision antenna monitors for critical arrays. We tentatively concluded that critical arrays could use off- the- shelf equipment without adverse impact. Eliminating the critical array designation also eliminates the need for additional performance standards for antenna monitors used by critical arrays. Accordingly, the relevant provisions of 47 C. F. R. § 73. 69 will be deleted. 33 Such computer models are generically referred to as "method of moments" programs, "matrix" programs, or "NEC" programs. NEC programs are based on the Numerical Electromagnetics Code moment method of analysis developed at the Lawrence Livermore Laboratory, Livermore, California. 13 Federal Communications Commission FCC 01- 60 14 distribution and radiation system. 34 43. About half of the comments on the Notice of Inquiry agree that arrays adjusted pursuant to moment method programs may require far fewer, if any, field strength measurements to verify that the authorized pattern shape has been achieved. Commenters in favor of computer modeling point to the uncertainties inherent in field strength measurements, which are subject to variation caused by proximity effects, scattering, seasonal changes in ground conductivity, and land development along propagation paths. Other commenters oppose elimination of the requirement for proofs of performance based primarily on field strength measurements. Most of these commenters acknowledge that computer models based on NEC or MiniNEC can be useful in analyzing array parameters, but retain the view that, despite their imperfections, field strength measurements provide the best indication that the antenna system is operating properly 44. In the NPRM, we expressed two main concerns regarding use of computer modeling: first, that reliance on modeling might not control interference adequately; and second, that we would be extending our technical regulations into new areas, contrary to the general intent of the Commission’s streamlining initiatives. We sought comment on this issue in the NPRM. Most commenters strongly support further consideration of computer modeling as a means of verifying directional antenna performance. We agree with AFCCE’s observation that “[ t] he topic is too important to ignore and too complex to address as a secondary issue.” 35 In an attempt to develop consensus on the use of computer modeling, the National Association of Broadcasters (NAB) has sponsored a series of industry forums on this topic. Representatives of large broadcasting groups, consulting engineers, and AM equipment manufacturers have participated in these discussions. NAB describes the objectives of the industry forums as follows: 1) to investigate whether computer modeling may allow further reduction in necessary field measurements; 2) to define the types of directional antenna systems for which computer modeling is straightforward; 3) to consider whether the industry should adopt uniform software for antenna modeling; and 4) to compare computer modeling to actual field measurement. 36 45. NAB filed supplemental comments on August 3, 2000 to present the industry committee’s conclusions to date. 37 The supplemental comments outline 18 criteria to define the types of directional antennas for which “accurate computer models can be produced by all AM broadcast engineers.” 38 These criteria would initially limit the number of towers in the array to six or fewer, would specify the type of sampling system which could be used, and would generally be limited to arrays clear of nearby reradiating objects. NAB and the joint commenters propose that directional AM arrays meeting these criteria could substitute computer modeling for proofs of performance based on field strength measurements. 46. We seek comments on the criteria proposed by NAB to define arrays for which computer modeling could be used in the proof process. NAB’s first eight criteria refer to characteristics of the directional antenna system, including the number of towers, the RSS- to- RMS ratio of the pattern, and certain physical dimensions of the antenna array. The next group, items 9 through 12, addresses sampling 34 These programs also aid designers in evaluating the effects of nearby potential reradiating objects. 35 See Comments of AFCCE at 3. 36 See Comments of NAB at 3. 37 Joint Written Ex Parte Filing –Supplemental Comments of Broadcasters, Broadcast Engineering Consultants, and Equipment Manufacturers. Appendix B of the Supplemental Comments lists 11 companies as joint commenters. 38 NAB’s Supplemental Comments are available on the internet via the Commission’s Electronic Comment Filing System (ECFS). The internet address is as follows: http:// www. fcc. gov/ e- file/ ecfs. html. 14 Federal Communications Commission FCC 01- 60 15 system requirements. NAB proposes use of voltage sampling instead of current sampling for towers within certain height limits. As discussed in paragraph 31 above, we request comments on the use of voltage sampling, both in conjunction with computer modeling and in arrays for which conventional proofs are done. In items 13 through 17, NAB describes structures near the directional antenna, such as towers, buildings, and power lines, which could distort the directional pattern. NAB suggests that the presence of potential reradiating structures should initially disqualify an array from proof by computer modeling. Finally, in item 18, NAB proposes acceptable ranges for the data used in the computer model. We request comments on these criteria, and on any other limitations which may be appropriate. We also seek comment on the following topics: what data should constitute a proof of performance for an array adjusted pursuant to computer modeling; what type of external monitoring may be appropriate for arrays adjusted using computer modeling; the suitability of various types of commercially available software for antenna modeling. We note that the industry committee also expected to consider software for antenna modeling, and to compare results predicted by computer modeling to actual field strength measurements. We look forward to the completion of these studies and their submission to the Commission in this proceeding. VII. Administrative Matters 47. Filing of Comments and Reply Comments. Pursuant to Sections 1.415 and 1.419 of the Commission's Rules, 47 C. F. R. §§ 1.415 and 1.419, interested parties may file comments within seventy-five (75) days of the date of publication of this Notice in the Federal Register and reply comments within one hundred and thirty- five (135) days of the date of publication of this Notice in the Federal Register. Comments filed through the ECFS can be sent as an electronic file via the Internet to . In completing the transmittal screen, commenters should include their full name, postal service mailing address, and the applicable docket or rulemaking number. Parties may also submit an electronic comment by Internet e- mail. To get filing instructions for e- mail comments, commenters should send an e- mail to ecfs@ fcc. gov, and should include the following words in the body of the message, "get form