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If you need the complete document, download the WordPerfect version or Adobe Acrobat version, if available. ***************************************************************** 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 ) NOTICE OF PROPOSED RULEMAKING Adopted: May 28, 1999 Released: June 11, 1999 Comment Date: [ 45 days after publication in the Federal Register ] Reply Date: [ 60 days after publication in the Federal Register ] By the Commission: Table of Contents Paragraph I. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 II. Computer Modeling versus Proofs of Performance. . . . . . . . . . .3 III. Directional Antenna Proofs of Performance . . . . . . . . . . . . .9 A. Full Proof of Performance . . . . . . . . . . . . . . . . . . . . 10 1. Number of Radials . . . . . . . . . . . . . . . . . . . . . . 10 2. Number of Points per Radial, Length of Radials. . . . . . . . 14 B. Partial Proof of Performance. . . . . . . . . . . . . . . . . . . 19 1. Number of Points Required . . . . . . . . . . . . . . . . . . 20 2. When Required . . . . . . . . . . . . . . . . . . . . . . . . 22 C. Monitoring Points . . . . . . . . . . . . . . . . . . . . . . . . 24 IV. AM Station Equipment & Measurements . . . . . . . . . . . . . . . 29 A. Base Current Ammeters . . . . . . . . . . . . . . . . . . . . . . 29 B. Antenna Monitors. . . . . . . . . . . . . . . . . . . . . . . . . 31 C. Impedance Measurements Across a Range of Frequencies. . . . . . . 34 D. Common Point Impedance Measurements . . . . . . . . . . . . . . . 36 V. Critical Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 A. Antenna Monitors for Critical Arrays. . . . . . . . . . . . . . . 38 B. Designation of Critical Arrays. . . . . . . . . . . . . . . . . . 41 VI. Conclusion . . . . . . .46 VII. Administrative Matters. . . . . . . . . . . . . . . . . . . . . . 47 Appendix A List of Commenters Appendix B . . . . . . . . . . . . .Initial Regulatory Flexibility Analysis I. Introduction 1. This Notice of Proposed Rulemaking ("Notice") is part of a broad-based streamlining initiative to overhaul Mass Media Bureau policies and licensing procedures. The Commission recently released a Report and Order that introduced substantially shorter and simpler certification-based application forms, established new broadcast application licensing procedures, and instituted electronic filing. Additionally, it has outstanding a proceeding proposing numerous changes in its technical rules that will provide greater flexibility for both AM and FM broadcasters. We propose in this Notice to eliminate some of our technical rules and relax others to materially reduce the regulatory and compliance burdens on AM broadcasters using directional antennas. There are approximately 4,790 AM radio stations presently licensed in the United States, of which about 40% operate directionally during either daytime or nighttime hours. In order to control interference between stations and assure adequate community coverage, directional AM stations must undergo extensive "proofs of performance" when initially constructed, and from time to time thereafter, to verify conformance with authorized operating parameters. The field strength measurements associated with these "proofs" and the technical exhibits which we require under our current rules impose a substantial financial burden upon these AM broadcasters, a burden not incurred by licensees in the other broadcast services. This Notice seeks to reduce our regulatory requirements to the minimum necessary to achieve our policy objectives of controlling interference and assuring adequate community coverage. 2. Five broadcast consulting engineering firms ("Joint Petitioners") initiated this proceeding by filing a joint petition for rulemaking which suggested that the use of technological advances could materially reduce or eliminate the measurement burdens imposed on AM broadcasters by the present rules. The Joint Petitioners requested a thorough examination of these rules and alternate means of directional antenna system verification. The Commission subsequently issued a Notice of Inquiry ("NOI") seeking comments as to appropriate rule changes. In response to the NOI, the Commission received 25 comments and 16 reply comments. In general, the comments and reply comments share the view that rule changes are warranted to relieve directional antenna licensees from the high cost and large amount of time currently required in verifying the proper adjustment of AM directional antenna arrays. II. Computer Modeling versus Proofs of Performance 3. The mathematical formulas for calculating the radiation characteristics of AM directional antennas are contained in 47 C.F.R.  73.150, 73.152 and 73.160. These formulas are also contained in the Bi-lateral Agreement between the United States and Canada relating to AM Broadcasting, and the Bi- lateral Agreement between the United States and Mexico relating to AM Broadcasting. The International Frequency Registration Board of the International Telecommunications Union also uses these formulas for administering the Region Agreement for Broadcast Service in Region 2. All technical parameters necessary to determine compliance with domestic and international interference standards, and with domestic community coverage requirements, for each domestic and international station are contained in the Commission's AM engineering database. These data include electrical height, distance and direction from a reference point, relative radiofrequency current amplitude and phase, for each tower in the array. Following construction of a directional antenna system and adjustment of its antenna currents and phases, the permittee must conduct a proof of performance to determine whether the radiation pattern produced by the array conforms with the predicted radiation pattern. 4. Several computer models have been developed over the years to calculate many operating characteristics of particular importance to engineers designing, installing and adjusting AM antenna systems. These models are generically referred to as "method of moments" programs, "matrix" programs, or "NEC" programs. These programs, unlike the formulas in the rules, deal with "internal" array parameters such as impedances, currents and voltages at locations within the power distribution and radiation system. These internal parameters are also used to determine the specifications for system components such as capacitors, inductors, meters, etc., and to adjust antenna systems following construction. 5. Several commenters suggest that proofs of performance may not be necessary for arrays adjusted pursuant to NEC programs. They note that the current proof of performance requirements were developed decades ago before the advent of NEC programs and modern instrumentation to monitor array performance. They contend that proofs are subject to inaccuracies inherent in field strength measurements caused by proximity effects, scattering and local electromagnetic environmental effects. They also contend that measurements may vary as a result of changes in ground conductivity due to seasonal effects and changes in land development along propagation paths. These commenters take the position that modern software and instrumentation make possible the satisfactory adjustment of directional arrays without reliance on field strength measurements. 6. About half of the commenters oppose elimination of the proofs of performance, although most of these support relaxation of the current proof requirements. Most of these commenters acknowledge that computer models such as NEC can be useful in analyzing array parameters, but retain the view that, despite their imperfections, ground-based field data provide the best indication of proper antenna system operation and that the rules should continue to rely on this core performance verification system. Some favor proofs of performance because, unlike theoretical models, field strength measurements reflect real-world conditions. Carl T. Jones Corporation, for example, "believe[s] that verification of array performance without field strength measurements will always be of questionable accuracy." Many commenters express concern that the results produced by NEC programs are extremely dependent on input parameters. Mullaney Engineering, Inc., warns that, just because a computer provides an answer, doesn't make it correct. Echoing this sentiment, Capital Cities/ ABC, Inc., refers to the "ease with which NEC can give wonderfully wrong answers." Others point out that, without field strength measurements, operators would have no independent means of verifying proper adjustment in the event of malfunction or failure of the internal monitoring instrumentation. 7. We have two fundamental concerns in adopting a methodology for array adjustments based on computer modeling programs. First, we are concerned that this methodology may not always properly limit radiation in critical directions toward other stations. There appears to be general agreement that different engineers, depending on their levels of expertise, could calculate operating parameters differently for a given antenna system. Additionally, the record reflects substantial reluctance toward abandoning field strength measurements as the most reliable method of documenting proper adjustment of AM directional antennas. Prevention of interference among AM broadcast station remains a core regulatory function of this Commission. From the record before us at this time, we cannot conclude that this function would continue to be accomplished if the requirement for proofs of performance were eliminated for stations adjusted pursuant to computer modeling programs. 8. Secondly, we are concerned about extending our AM regulations into new technical areas. Our primary regulatory interest in this area has always been restricted to AM directional antenna design and adjustment. Permits are issued only after applicants demonstrate that an array is designed to meet the Commission's basic technical requirements: adequate interference protection to other stations and adequate signal coverage to the community of license. Licenses are issued only after permittees demonstrate that their arrays have been adjusted in accordance with their permits. With the exception of certain instrumentation requirements, the Commission does not regulate the design of circuitry internal to antenna systems, nor does it regulate the methodology employed in the adjustment of antenna systems. We are concerned that adopting a methodology based on computer modeling could draw the Commission into controversial issues relating to the adequacy of adjustment programs and procedures, leading to delays in authorizing new service, rather than simply limiting our involvement to the results of antenna system adjustments. Thus, we propose not to adopt such a methodology to determine whether arrays conform to authorized radiation patterns. We seek comment in this regard. III. Directional Antenna Proofs of Performance 9. An antenna proof of performance of an AM directional array establishes whether the radiation pattern of the AM station is in compliance with the radiation pattern authorized by the station's construction permit or license. There are two kinds of proofs of performance: (1) a full proof, in which a large number of measurements of the station's signal are made to establish the shape of the radiation patterns, and (2) a partial proof, which requires a lesser number of measurements to show that the station continues to operate as it did during the last full proof. Each full proof generally consists of two sets of measurements -- nondirectional measurements and directional measurements. A minimum of 30 points along each of 8 radials is presently required for a full proof. Thus, the simplest directional antennas require 240 nondirectional measurement points and 240 directional measurement points. Complex arrays require more radials, and thus, more measurement points. Because a single radial may extend 34 km or more from the transmitter site, a significant amount of time is required to travel between measurement points, and to complete a full or partial proof. We believe that allowing measurements at fewer points and along fewer radials can sharply cut the time and cost of conducting a proof of performance, and that relaxing our proof requirements can be accomplished without affecting the technical integrity of the AM service. A. Full Proof of Performance 1. Number of Radials 10. The present rule, 47 C.F.R.  73.151, requires that a permittee use a minimum of 8 radials to demonstrate that an array conforms to its authorized pattern as follows: (a) At least three radials in the main lobe of the pattern, one toward the azimuth of maximum radiation and one to either side of this azimuth. (b) At least five additional radials distributed across the pattern to show the shape of the pattern. Radials are commonly assigned to the azimuths of pattern nulls (minimum radiation) and minor lobes. (c) Larger, more complex arrays or unique radiation patterns generally require additional radials that are specified on the construction permit or license. These may or may not include radials required by (a) or (b). Hammett & Edison and Carl T. Jones Corporation support a reduction in the number of radials required, suggesting that only radials along important azimuths should be required in addition to the main lobe azimuth. 11. Proposal. We propose to reduce the minimum number of radials required from 8 to 6 for simple directional antenna patterns and to generally require no more than 12 radials to define complex patterns. If the major lobe, minor lobes, and nulls cannot all be accounted for by the 12 radials, pattern symmetry could be used to account for the remaining minor lobes and nulls. The radials would be distributed as follows: (a) One radial in the major lobe, at the pattern maximum. (b) At least 5 additional radials, as needed to definitely establish the pattern, 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° azimuth apart. If two radials would be more than 90° apart, then an additional radial must be specified within that arc. (c) Any radials specified on the construction permit or license. Nondirectional antenna measurements would be taken along the radials used for directional measurements. 12. In addition, we propose 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 6 evenly spaced radials, in lieu of 8. 13. Based on the Commission's experience in processing AM facility applications and the comments of Hammett & Edison and Carl T. Jones Corporation, we tentatively conclude that we can reasonably rely on fewer radials, in conjunction with the 90° maximum arc restriction, to establish nondirectional and directional patterns. We tentatively conclude that using a smaller number of radials, or radials more than 90° apart, would not provide a sufficient number of points to identify distortion of a nondirectional pattern. We seek comment as to whether the proposed rule changes achieve an adequate balance between reducing proof requirements and maintaining sufficient documentation of proper array adjustment. 2. Number of Points per Radial, Length of Radials 14. The present rule, 47 C.F.R.  73.186(a)(1), generally requires that a permittee measure at least 30 points per radial at prescribed intervals to establish the directional and nondirectional field strengths along each azimuth. We agree with Hammett & Edison that an accurate measurement of an array can be accomplished with substantially fewer measurement points. At the same time, we are mindful of Independent Broadcasting Corporation's ("IBC") caution that 10 or fewer points may not be sufficient. Capital Cities/ABC, Inc., suggests that 15 points be used. 15. Proposal. We propose to reduce the number of points per radial to a minimum of 15, half the present number, as well as to shorten the minimum length of the radial from 34 to 15 km. These 15 measurement points would include the very important close-in measurement points (points at less than 3 km from the transmitter site) used to determine the inverse distance field. We propose to specify intervals between these points as follows: (1) The closest point at a distance 10 times the maximum distance between the elements of a directional array, or at a distance 5 times the vertical height of the antenna in the case of a nondirectional station, (2) Close-in measurements at 0.2 km intervals, out to a distance of 3 km (unchanged from the present requirements of 47 C.F.R.  73.186); (3) Measurements at 1 km intervals between 3 km and 5 km (3 points); (4) Measurements at 2 km intervals between 5 and 15 km (5 points); (5) Additional measurements as necessary at greater distances to achieve at least 15 points clear of potential reradiating structures; (6) Measurements at any monitoring point locations along the radial (unchanged from the present rule). 16. These intervals would provide a relatively uniform distribution of data points when plotted on the Commission's logarithmic groundwave propagation curves. We tentatively conclude that the reduced number of points and shorter radial length proposed represents the minimum, which would allow verification of the performance of the antenna system. This proposal to reduce the minimum number of measurements points per radial from 30 to 15, in conjunction with the previous proposal to reduce the minimum number of measured radials, would reduce the total number of measurement points for simple arrays by 30 points, and for more complicated arrays, by 60 or more points. Thus, in conjunction, these proposals would reduce significantly the time and expense required to obtain proof measurements. By not requiring points beyond 15 km, we would also obtain more representative field strength measurements by eliminating those measurements most subject to seasonal variations. 17. We agree with IBC that we should not modify the present measurement requirements for close-in measurements (within 3 km of the transmitter site). Although these measurement locations may sometimes be difficult to access, these close-in measurements are the most critical in determining the nondirectional inverse distance field strengths. Without an accurate assessment of the nondirectional inverse distance field, the analysis of the directional measurements becomes much less reliable. We seek comment on each aspect of this proposal. 18. For each measurement point, we propose that the applicant provide several pieces of data. These include, the date(s) of the measurements, the azimuth of the radial, the distance from the center of the array to the measurement point, the pattern being measured (day / night / critical hours), the time of the measurement, and the measured field strength value at that point. For a set of measured points along a given radial, most applicants sort this data into a table that is submitted with the application. We propose to adopt a standardized format for the submission of the data in order to facilitate electronic filing and processing. A standard electronic data format would reduce application preparation costs and, at the Commission, minimize data entry. Electronic storage of this data could also allow it to be easily retrieved by any interested party for future use, reducing trips to the Commission's Public Reference Room to view the relevant paper documents. We seek comment on the format that should be used for the compilation and submission of this data. We also request comment on whether the time of each measurement should continue to be required with these submissions. B. Partial Proof of Performance 19. A partial proof consists of measurement data taken at selected locations used in the last full proof of performance. Although fewer measurement points are used, 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 examined azimuth. 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. 1. Number of Points Required 20. Presently, 47 C.F.R.  73.154 requires that permittees make at least 10 field strength measurements within 3 to 16 kilometers from the array at radial locations used in the last complete proof of performance. If a radial contains a monitoring point, that point must be included in the measurements. 21. Proposal. We propose to reduce to 8 the required minimum number of points per radial. The proof must include any monitoring point locations, and must use radial measurement point locations established in the last full proof of performance, as is the case under the current rule. This proposal would reduce the required number of partial proof measurement points by at least 16 for simple arrays and by at least 20 or more for more complicated arrays. We believe that reducing the number of points would reduce the financial burden on AM directional licensees conducting partial proofs while still providing sufficient data to confidently verify directional array performance. 2. When Required 22. The need to conduct a partial proof of performance is triggered by an indication that the antenna system is not operating properly. See 47 C.F.R.  73.61. Indicators include monitoring point readings exceeding the limits specified on the station's license and antenna monitor readings exceeding the tolerances specified in the rules. Partial proofs are also required following replacement or modification of sampling system components mounted on the tower. See 47 C.F.R.  73.68. 23. Proposal. We propose to eliminate the requirement to conduct a partial proof of performance following replacement or modification of sampling system components mounted on the tower provided the new components are mounted in the exact location of 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. We anticipate that this proposal in many instances would eliminate the need to conduct a proof of performance and file a Form 302-AM license application. C. Monitoring Points 24. Monitoring points are specific locations on selected proof radials where licensees regularly take field strength measurements to verify that a directional array remains within the radiation limits specified in the station's authorization. They are established at the time a station's full proof of performance is conducted. A field strength limit is set for each monitoring point based upon the tolerance available 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. In many cases radiation values above these limits would result in interference to other AM stations. 25. Some commenters suggest that monitoring point requirements should be eliminated, arguing that seasonal variations in ground conductivity affect the signal strengths measured at many monitoring points. However, since 1979 the Commission has permitted the measurement of the ratio of the directional field strength as compared to the nondirectional field strength at the monitoring points. This practice effectively negates variations caused by seasonal effects or varying weather conditions, because both readings would be equally affected by conductivity changes related to weather. We concur with the several commenters who argue that monitoring point measurements remain a fundamental tool in verifying the performance of AM directional arrays independent of antenna monitor and antenna sampling system readings. As IBC points out, monitoring points give "Commission field inspectors and engineers from other stations instant access" to an array's performance without reference to the station's transmission facilities. For these reasons, we also decline T.Z.Sawyer Technical Consultants' suggestion to delete monitoring point measurements in exchange for yearly skeleton proofs taken on formerly monitored radials. Skeleton proofs were abolished in 1985 because of their limited value in showing actual antenna performance. We seek comment on these tentative conclusions. 26. Over time, it often becomes necessary to abandon a monitoring point and establish a new one. The original location may have become inaccessible due to construction or unsuitable due to changes in the local electromagnetic environment that affect the field strength at that point. 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. See 47 C.F.R.  73.158. 27. Proposal. We propose to eliminate the requirement to conduct a partial proof of performance along the radial containing the monitoring point to be changed. Instead, the applicant may simply 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. 28. We also propose to eliminate the requirement for maps and directions indicating how to reach monitoring points for applicants using GPS-determined coordinates to identify monitoring point locations. See C.F.R.  73.151(a)(3) and 73.158(a)(2)-(3). Radiotechniques Engineering Corp suggested this proposal. In order to achieve sufficient accuracy, a differential GPS receiver would be required. We would 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. We ask for comment on these proposals. IV. AM Station Equipment & Measurements A. Base Current Ammeters 29. 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). The ratio of the individual tower currents is an important parameter in the proper operation of a direction array. However, over the years antenna monitor and antenna sampling system design improvements have lessened stations' reliance on base current ammeters as a means of maintaining proper array adjustment. Some commenters have questioned the reliability of base ammeters. They are susceptible to damage from lightning. In some circumstances, these meters may also register current changes more reflective of local environmental effects than improper array performance. As a result, most commenters have urged the Commission to modify the requirement that licensees use base current ammeters to maintain proper array adjustment. 30. Proposal. We propose to delete the requirement for base current ammeters or toroidal transformers for those directional stations employing approved antenna sampling systems. Stations not using approved sampling systems have no reliable alternate on-site means of assessing antenna performance and therefore, our rules would continue to require the installation and use of base current ammeters if the Commission has not approved an alternative system. Deletion of this requirement would not, of course, prevent stations from continuing to install and monitor base current ammeters as a backup in the event of failure of their sampling system or antenna monitor. We seek comment on this proposal. B. Antenna Monitors 31. All AM directional stations are required to use an antenna monitor verified for compliance with the technical requirements in 47 C.F.R.  73.53 as a means of verifying directional array performance. This section of the rules also specifies detailed specifications that antenna monitors are required to meet. We adopted most of these specifications in 1973 and have not undertaken any updating since that time. Potomac Instruments, a manufacturer of antenna monitor systems, claims 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. 32. Proposal. We propose 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. We note that the Commission in recent years has eliminated detailed construction and operational requirements for other types of broadcast equipment, such as transmitters and metering equipment and tentatively conclude that antenna monitor rules can be relaxed in a similar manner. We believe that the elimination of these unneeded requirements will encourage the development of more dependable, less expensive, antenna monitor units. We seek comment on this proposal. 33. Greater Media, Inc.; duTreil, Lundin & Rackley; John Furr & Associates, Inc.; and Hammett & Edison request that we change our technical rule 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. See 47 C.F.R.  73.68. We ask for comments as to the accuracy and reliability of voltage sampling devices; whether they are appropriate as sampling devices for assessing array performance; and whether we should modify the rules to permit their use. C. Impedance Measurements Across a Range of Frequencies 34. Directional and nondirectional AM stations are required to take measurements of impedance across a range of frequencies. See 47 C.F.R.  73.54(c)(1) and (2). Specifically, a licensee is required to take measurements of resistance and reactance (collectively impedance) at 5 kHz intervals out to 25 kHz above and below the carrier frequency. These rules are intended ensure adequate audio quality at all audio frequencies. Several commenters suggested that this requirement should be deleted as unnecessary. 35. Proposal. We propose to delete the requirement to measure impedance across a range of frequencies. In 1984, the Commission deleted many of the audio quality requirements for FM stations, picture and video quality requirements for TV stations, and some audio quality requirements for AM stations, concluding that, with limited exceptions, competition serves as a sufficient incentive to maintain quality operations. Fifteen years later, we have no reason to believe that audio and video quality of broadcast stations has been lessened by deletion of those requirements. We tentatively conclude that retention of 47 C.F.R.  73.54(c) is not necessary because competition will serve as a sufficient incentive to maintain quality operations. We seek comment on this proposal. D. Common Point Impedance Measurements 36. AM directional stations must take impedance (resistance and reactance) measurements at the common radiofrequency input location. See 47 C.F.R.  73.54(b). The reactance at this point is adjusted by the antenna matching network to a value of zero ohms. This enables maximum power to be transferred from the transmitter to the antenna system without reflecting power back to the transmitter. Most transmitters are manufactured to feed a 50 ohm resistive load without a reactive component, and most transmission lines used by broadcasters are also 50 ohm line. Radiotechniques Engineering Corp., and Greater Media, Inc., assert that many transmitters operate best into a load with a small reactive component, and that adding a small reactive component also allows adjustment of the array impedance to equal that of the station's dummy load. 37. Proposal. Based on these practical considerations, we propose to delete the requirement that the common point reactance be adjusted to zero ohms. We seek comment as to whether a limit should be set for the maximum amount of reactance permitted. V. Critical Arrays A. Antenna Monitors for Critical Arrays 38. AM directional arrays have two radiation patterns: a theoretical pattern and a standard pattern, both calculated in accordance with the formulas set forth in 47 C.F.R.  73.150, 73.152 and 73.160. The standard pattern, which always completely encompasses the theoretical pattern, represents an upper limit of radiation that a station should not exceed under normal operating tolerances. Section 73.62(a) of the rules sets forth the normal operating tolerances for directional antennas. A licensee must hold relative amplitudes of the antenna base currents and antenna monitor currents to within 5 percent of the values shown on the license, and the relative phases to within 3 degrees of those specified on the license. Critical arrays are directional antennas which are unusually sensitive to slight variations in internal operating parameters, thus, they would be predicted to exceed their standard radiation pattern at normal operating tolerances and pose a greater potential for causing interference. Thus, licenses of stations with critical arrays specify tighter operating tolerances. 39. To monitor these tighter tolerances, 47 C.F.R.  73.69 requires stations with critical arrays to install special precision monitors. Potomac Instruments requests deletion of the requirement, and argues that the present generation of antenna monitors allows reliable operation to tolerances within that specified for many critical arrays. Potomac Instruments also notes that the very low production volume of its PM-19 precision monitor (30 in 28 years) does not justify investment in and application of newer technology in the design and construction of these monitors. 40. Proposal. We propose to discontinue specifying the use of expensive specially designed precision antenna monitors for critical arrays. Instead, we propose to simply require that the monitor installed have a digital readout graduated in increments no larger than 1/2 of the critical parameter specified in the authorization. We tentatively conclude that the rule can be relaxed to permit the use of off- the-shelf equipment without adverse impact on stations that are protected by critical arrays. We seek comment on this proposal. B. Designation of Critical Arrays 41. Several commenters suggest that staff has unevenly applied critical array classifications, and therefore, that this classification system should be discontinued. We do not believe that this is a feasible solution. There is no dispute that some directional antenna systems are inherently more unstable than others and are therefore more likely to cause objectionable interference to other AM stations, particularly during nighttime hours when skywave propagation occurs. Authorizations for such stations are conditioned to require more stringent monitoring. We acknowledge 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, the staff has not identified and designated as critical arrays all unstable arrays. We intend to change this practice by discontinuing reliance on petitions or objections as the primary method of identifying unstable arrays. Instead, we propose to apply a uniform screening process to all applications for directional facilities. 42. The staff has employed computer studies to assess array stability. The relative current amplitude and phase of each array element (tower) can be varied systematically to determine the variations that could be tolerated before the standard pattern radiation limits are exceeded in any direction. We have analyzed all licensed AM directional antennas utilizing our stability criteria and have tentatively concluded that the current criteria are too stringent and that modifications are necessary to tag only those arrays that have the highest probability of causing "real world" interference under normal operating tolerances. 43. Proposal. We propose to relax our stability criteria in two ways. First, we propose to restrict our tests for array stability to radiation pattern minima (nulls) and maxima of standard patterns in the horizontal plane only instead of testing at all azimuths and elevations. Nulls are important because they are generally located in directions where interference protection is required. Minor lobe maxima are also important, particularly with respect to nighttime skywave protection. Controlling the radiation in the directions of nulls and lobes generally assures that the radiation in all other directions will also remain under control. Also, restricting our criteria to nulls and maximas will eliminate classifying arrays as critical based on instances of theoretically excessive radiation in inconsequential directions. The studies would be restricted to the horizontal plane radiation pattern because only the horizontal plane pattern can be directly observed by means of field measurements. 44. Secondly, we propose classify an array as critical only if the standard pattern is exceeded at 10% or more of the possible parameter variation combinations. For example, a four tower array has 512 possible combinations of 1 percent current amplitude and 1 degree phase variations. The array would be designated as critical if at least 51 of these combinations would cause excessive radiation. The current test requires only one instance of excessive radiation. We believe that the proposed 10% standard will more realistically predict the likelihood of excessive radiation. We seek comments on both relaxations to the current stability test criteria. 45. Finally, based on the results of studies we have performed on the licensed AM directional patterns in our AM engineering database, we propose to exclude all two and three tower arrays from designation as critical arrays. Furthermore, we propose to categorically exclude all daytime arrays considering that objections have never been filed based on daytime interference issues related to array instability. Thus, we propose to screen only nighttime and critical-hours directional proposals. We also propose to permit licensees with facilities currently classified as critical to request staff review of their designation based on the revised criteria; however, we do not propose to review the directional facilities of any station not currently classified as critical. We seek comment on each aspect of this proposal. VI. Conclusion 46. In this Notice, we propose substantial reductions in our proof of performance requirements for AM directional antenna systems. For full proofs of performance, we propose reducing the number of measurement radials required, cutting in half the minimum number of measurement points required per radial, and shortening the length of measured radials thereby reducing by at least thirty the total number of required measurement points. We propose similar relaxation of partial proof requirements, reducing the minimum number measurement points by at least sixteen. We believe these proposals will substantially reduce the time and cost burdens associated with verifying proper operation of AM directional arrays. Additionally, we propose to delete the required use of base current ammeters and we propose to substantially reduce required technical specifications for antenna monitors. We propose to discontinue reliance on petitions and objections as a means of identifying critical arrays and propose to categorically exclude two and three tower antenna systems, as well as daytime systems, from being classified as critical arrays. Additionally, we propose to substantially relax the criteria used in classifying antenna systems as critical arrays. We also propose to discontinue requiring specially built expensive precision monitors for critical antenna systems. Comments are sought concerning these proposals and others. Although these proposals are designed to provide substantial savings for licensees of directional AM antennas, it is our tentative view that none of the proposals jeopardize the technical integrity of the AM broadcast service. 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 forty-five (45) days of the date of publication of this Notice in the Federal Register and reply comments within sixty (60) 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