2024-24105. Rules for FM Terrestrial Digital Audio Broadcasting Systems

IBOC Station's F(50,10) field strength at the upper or lower first-adjacent station's analog 60 dBµ F(50,50) contour	Maximum permissible FM digital ERP for the respective (upper or lower) sideband
51.2 dBµ and above	−17 dBc.
50.7 dBµ to 51.1 dBµ	−16 dBc.
50.3 dBµ to 50.6 dBµ	−15 dBc.
49.6 dBµ to 50.2 dBµ	−14 dBc.
49.5 dBµ or less	−13 dBc.

( print page 84100)

If, in a subsequent Order, the Commission modifies the formula used to determine the maximum permissible digital power level, it will adjust this table at that time.

15. Interference Mitigation and Remediation. The Commission found that the interference mitigation and remediation procedures set forth in the 2010 MB DAB Order are sufficient to remedy any reports of inter-station interference as a result of asymmetric sideband operation, given that reduction of power on one sideband necessarily reduces the potential for interference and therefore makes such interference less likely. The Commission reserved further consideration of modified interference mitigation and remediation procedures in the FM digital power increase context, and anticipates addressing such concerns in a future Report and Order in this proceeding.

16. Pending Proceedings. The Commission adopted the proposal that any licensees with asymmetric sideband operation under experimental authorizations that are compliant with the rules adopted in this First R&O may file Schedule 335-FM notification at any time after the effective date of the rules adopted in this First R&O and before the existing experimental authority expires. NPRM, 38 FCC Rcd at 7171, para. 30. No commenter opposed this proposal. Therefore, after the rules adopted in this First R&O take effect and the changes to Schedule 335-FM are approved by the Office of Management and Budget and there is an announcement of such approval published in the Federal Register , any station currently employing asymmetric sideband operation under experimental authorization that is compliant with the rules adopted in this First R&O may transition to non-experimental asymmetric sideband operation by notifying the Commission through Schedule 335-FM at any time prior to expiration of the experimental authorization. Although the Commission does not require that stations currently operating with power greater than −14 dBc under existing special temporary authorization file Schedule 335-FM, it encourages such stations to update their records in LMS using Schedule 335-FM in order that their sideband power levels are properly reflected in LMS. Any station seeking a power increase above −14 dBc in the future must request authority to do so using Schedule 335-FM.

Procedural Matters

Final Regulatory Flexibility Analysis

17. As required by the Regulatory Flexibility Act of 1980, as amended (RFA) an Initial Regulatory Flexibility Analysis (IRFA) was incorporated in the Modifying Rules for FM Terrestrial Digital Audio Broadcasting Systems, (NPRM), released on August 1, 2023. Modifying Rules for FM Terrestrial Digital Audio Broadcasting Systems, Notice of Proposed Rulemaking, 38 FCC Rcd 7158 (2023). The Federal Communications Commission (Commission) sought written public comment on the proposals in the NPRM, including comment on the IRFA. No comments were filed addressing the IRFA. This Final Regulatory Flexibility Analysis (FRFA) conforms to the RFA. 5 U.S.C. 604.

A. Need For, and Objectives of, the Report and Order

18. In the First Report and Order, the Commission found that it is in the public interest to allow FM broadcast stations transmitting a hybrid analog-digital signal to operate with different digital effective radiated power (ERP) on the upper and lower digital sidebands, upon notification to the Commission on FCC Form 2100, Schedule 335-FM. This replaces the current procedure whereby a digital FM station must apply for an experimental authorization to operate with different digital ERP on the upper and lower digital sidebands (asymmetric sideband operation); this experimental authority must be renewed annually.

19. The FM digital radio system inserts redundant digital sidebands above and below a station's existing analog signal. The Commission's existing rules assume that digital power is the same on both digital sidebands, i.e., symmetric sideband operation. The advantage to asymmetric sideband operation is that it allows a digital FM station to operate with lower power on the digital sideband closer to a first-adjacent-channel analog FM station, thus reducing the potential for interference to that station, while enabling the digital FM station to increase power to the digital sideband where there is no or only a very distant analog FM station to protect from interference. For example, a Class A digital FM station on Channel 251 might have a Class A analog FM station on Channel 250 within 75 kilometers of the digital station, while being several hundred kilometers from the nearest analog FM station on Channel 252. In such a situation, the digital FM station would reduce digital ERP on the lower digital sideband, protecting the analog station on Channel 250, while increasing power and, therefore, signal coverage on the upper digital sideband where there is no adjacent channel station to protect. The total digital ERP transmitted over the two digital sidebands would be the same as it would be if both sidebands were transmitting at the same digital ERP (symmetric sideband operation), thus there would be no increase in the total digital energy emitted by the digital FM station.

20. The Commission in the First Report and Order adopted its proposal to allow digital FM stations wishing to use asymmetric sideband operation to do so by notifying the Commission using FCC Form 2100, Schedule 335-FM, and modified that schedule by including fields to report the digital ERP being transmitted on each digital sideband, as well as the total digital ERP. It made an exception, however, for digital FM stations operating on Channels 296-300 (107.1-107.9 MHz), at the top of the FM broadcast band, which must continue to seek experimental authorization for asymmetric sideband operation. This was deemed necessary to protect users in the lower frequencies of the Aeronautical Radio Navigation Spectrum (ARNS) from possible interference resulting from higher power on an upper digital sideband. The Commission further concludes that a station permanently discontinuing asymmetric operation need not disclose its reasons for doing so. It also implemented the proposal that any FM licensees operating facilities under experimental or special temporary authorizations that are compliant with the rules adopted in this proceeding may transition to asymmetric sideband operation by filing Schedule 335-FM notifications after the effective date of the rules adopted in the First Report and Order. Commenters generally supported the Commission's proposal to allow asymmetric sideband operation upon simple notice to the Commission, though some raised concerns regarding notifications, interference remediation, and the transition to asymmetric sideband operation. The Commission observed that adopting rules simplifying the process of initiating asymmetric sideband operation is likely to reduce inter-station interference rather than exacerbate it, and thus concluded that existing interference mitigation and remediation procedures are sufficient at the present time, but also concluded that Form 2100, Schedule 335-FM should be amended to provide fields for the notifying station to indicate the ( print page 84101) digital ERP transmitted on each digital sideband, as well as the total digital ERP.

21. This minor administrative change will help streamline processing of these requests and will further the Commission's efforts to transition all broadcast filings to the Bureau's Licensing and Management System (LMS).

B. Summary of Significant Issues Raised by Public Comments in Response to the IRFA

22. There were no comments filed that specifically addressed the proposed rules and policies presented in the IRFA.

C. Response to Comments by the Chief Counsel for Advocacy of the Small Business Administration

23. Pursuant to the Small Business Jobs Act of 2010, which amended the RFA, the Commission is required to respond to any comments filed by the Chief Counsel for Advocacy of the Small Business Administration (SBA), and to provide a detailed statement of any change made to the proposed rules as a result of those comments. 5 U.S.C. 604(a)(3). The Chief Counsel did not file any comments in response to the proposed rules in this proceeding.

D. Description and Estimate of the Number of Small Entities to Which the Rules Apply

24. The RFA directs the agencies to provide a description of and, where feasible, an estimate of the number of small entities that may be affected by the rules adopted herein. 5 U.S.C. 604(a)(4). The RFA generally defines the term “small entity” as having the same meaning as the terms “small business,” “small organization,” and “small government jurisdiction.” 5 U.S.C. 601(6). In addition, the term “small business” has the same meaning as the term “small business concern” under the Small Business Act. 5 U.S.C. 601(3). A small business concern is one which: (1) is independently owned and operated; (2) is not dominant in its field of operation; and (3) satisfies any additional criteria established by the SBA. 15 U.S.C. 632.

25. Radio Stations. This industry is comprised of “establishments primarily engaged in broadcasting aural programs by radio to the public.” U.S. Census Bureau, 2017 NAICS Definition, “515112 Radio Stations.” Programming may originate in their own studio, from an affiliated network, or from external sources. The SBA small business size standard for this industry classifies firms having $47 million or less in annual receipts as small. U.S. Census Bureau data for 2017 show that 2,963 firms operated in this industry during that year. Of this number, 1,879 firms operated with revenue of less than $25 million per year. Based on this data and the SBA's small business size standard, we estimate a majority of such entities are small entities.

26. The Commission estimates that as of June 30, 2024, there were 4,413 licensed commercial AM radio stations and 6,620 licensed commercial FM radio stations, for a combined total of 11,033 commercial radio stations. Broadcast Station Totals as of June 30, 2024, Public Notice, DA 24-644 (rel. July 3, 2024) (July 2024 Broadcast Station Totals PN), https://docs.fcc.gov/​public/​attachments/​DA-24-644A1.pdf. Of this total, 11,032 stations (or 99.99%) had revenues of $47 million or less in 2023, according to Commission staff review of the BIA Kelsey Inc. Media Access Pro Database (BIA) on July 3, 2024, and therefore these licensees qualify as small entities under the SBA definition. In addition, the Commission estimates that as of June 30, 2024, there were 4,356 licensed noncommercial (NCE) FM radio stations, 1,965 low power FM (LPFM) stations, and 8,906 FM translators and boosters. The Commission however does not compile, and otherwise does not have access to financial information for these radio stations that would permit it to determine how many of these stations qualify as small entities under the SBA small business size standard. Nevertheless, given the SBA's large annual receipts threshold for this industry and the nature of radio station licensees, the Commission presumes that all of these entities qualify as small entities under the above SBA small business size standard.

27. We note, however, that in assessing whether a business concern qualifies as “small” under the above definition, business (control) affiliations must be included. The Commission's estimate, therefore, likely overstates the number of small entities that might be affected by its action, because the revenue figure on which it is based does not include or aggregate revenues from affiliated companies. In addition, another element of the definition of “small business” requires that an entity not be dominant in its field of operation. The Commission is unable at this time to define or quantify the criteria that would establish whether a specific radio or television broadcast station is dominant in its field of operation. Accordingly, the estimate of small businesses to which the rules may apply does not exclude any radio or television station from the definition of a small business on this basis and is therefore possibly over-inclusive. An additional element of the definition of “small business” is that the entity must be independently owned and operated. Because it is difficult to assess these criteria in the context of media entities, the estimate of small businesses to which the rules may apply does not exclude any radio or television station from the definition of a small business on this basis and similarly may be over-inclusive.

E. Description of Projected Reporting, Recordkeeping, and Other Compliance Requirements for Small Entities

28. The First Report and Order adopts procedures that will create new reporting, recordkeeping, and compliance obligations for small digital FM stations that operate with asymmetric power on the digital sidebands. Specifically, it replaces the current requirement that digital FM stations request experimental or special temporary authorization for asymmetric sideband operation with a new, simplified notification procedure on existing FCC Form 2100, Schedule 335-FM. This form will be modified to collect the total digital ERP and the digital ERP on each of the upper and lower digital sidebands used by a digital FM station. Form 2100, Schedule 335-FM, will now be the means by which a small, digital FM station will report (or request authority in the case of an increase of total digital ERP above −14 dBc) the following actions: the initiation of hybrid digital operation; the initiation of asymmetric sideband operation at any power level, as well as the permanent discontinuance of asymmetric sideband operation; an increase of total digital ERP above −14 dBc; or a decrease in total digital ERP from a level above −14 dBc to a level below −14 dBc. Form 2100, Schedule 335-FM will also be amended to provide a digital FM station proposing to increase total digital ERP above −14 dBc to certify that it complies with the power levels set forth in table 1 to amended § 73.404(f) (regulating In Band On Channel Digital Audio Broadcast Operations), which is based on the current formula used to calculate acceptable power levels, but adapted to calculate those levels on a per-sideband basis. As is currently required, a station choosing to increase total digital ERP to a level between −14 dBc and −10 dBc must still attach to its Schedule 335-FM submission an exhibit demonstrating that the proposed FM digital ERP is permitted for each digital sideband, using newly adopted table 1 to 73.404(f). However, the ( print page 84102) Commission will continue to require that small and other entities request experimental authorization for a digital FM station on Channels 296-300 seeking to engage in asymmetric sideband operation to avoid any potential issues regarding interference with the ARNS.

29. Requiring small and other entities to use FCC Form 2100, Schedule 335-FM for the provision of the digital ERP is minimally burdensome, as this form will collect the same or similar information the notifying FM station would use to request asymmetric sideband operation and is less burdensome than preparing an application for experimental authorization and renewing such authorization annually. Small entities will likely use the same processes and professional staff to comply with the FCC Form 2100, Schedule 335-FM requirements. Accordingly, although there is not sufficient evidence quantifying the compliance cost of the adopted rule changes, the Commission anticipates the approaches it has taken to implement the requirements will have minimal cost implications and should significantly reduce compliance requirements for small entities that may have smaller staff and fewer resources.

F. Steps Taken To Minimize Significant Economic Impact on Small Entities and Significant Alternatives Considered

30. The RFA requires an agency to provide, “a description of the steps the agency has taken to minimize the significant economic impact on small entities . . . including a statement of the factual, policy, and legal reasons for selecting the alternative adopted in the final rule and why each one of the other significant alternatives to the rule considered by the agency which affect the impact on small entities was rejected.” 5 U.S.C. 604(a)(6).

31. In the First Report and Order, the Commission considered a number of alternatives that will minimize the impact of the revised rules. Specifically, the Commission adopted measures to simplify the implementation of asymmetric sideband operation for digital FM stations, by notification through Form 2100, Schedule 335-FM rather than application for experimental authorization and annual renewal. The Commission sought to weigh the impact of these measures on small and other entities against the public interest benefits gained from them and has determined that the benefits outweigh the costs. As some commenters have observed, the burden of filing an experimental application and annual renewals has likely discouraged many digital FM stations from implementing asymmetric sideband operation, and has therefore impeded the implementation of such operation and its corresponding benefits, including expanded signal coverage and interference protection. The Commission concludes that these benefits outweigh the burdens imposed by the current procedures, and justify the simplified process adopted in the First Report and Order.

32. The Commission also observes that adopting rules simplifying the process of initiating asymmetric sideband operation is likely to reduce inter-station interference rather than exacerbate it, and thus concludes that existing interference notification and remediation procedures are sufficient at the present time, but also concludes that Form 2100, Schedule 335-FM should be amended to provide space for the notifying station to indicate the digital ERP transmitted on each digital sideband, as well as the total digital ERP. While the provision of these items of information are a minimal additional burden, they consist of information that is readily available to the broadcaster and will assist other FM stations in evaluating interference complaints.

33. The use of Form 2100, Schedule 335-FM will simplify required station submissions, and harmonizes such submissions with the recent transition of the Media Bureau's application filing system to LMS. The Commission also considered whether a station permanently discontinuing asymmetric sideband operation should be required to include a short statement disclosing its reasons for doing so when notifying the Commission, and determined such information was not necessary based on commenter input. This decision will eliminate an added burden to certain stations, as well as allow them to preserve the confidentiality of their business decision making. The Commission further concludes that digital FM stations currently using asymmetric sideband operation under experimental or special temporary authorizations shall be able to continue operation upon notification using Form 2100, Schedule 335-FM, provided such notification is submitted before the experimental authorization or STA expires. This option has been determined to be the least burdensome alternative, as compared to other options such as filing a one-time application with annual renewal. Finally, to avoid any potential issues regarding interference with the ARNS, the Commission will continue to require experimental authorization for a digital FM station on Channels 296-300 seeking to engage in asymmetric sideband operation. This will impact relatively few digital FM stations, and has been deemed necessary to protect ARNS users pending the results of testing by aviation industry stakeholders and the broadcast industry proponents of the new procedures.

G. Report to Congress

34. The Commission will send a copy of the First Report and Order, including this FRFA, in a report to Congress pursuant to the Congressional Review Act, 5 U.S.C. 801(a)(1)(A). In addition, the Commission will send a copy of the First Report and Order, including this FRFA, to the Chief Counsel for Advocacy of the SBA. A copy of the First Report and Order and FRFA (or summaries thereof) will also be published in the Federal Register .

35. Paperwork Reduction Act Analysis. This First Report and Order may contain new or modified information collection requirements subject to the Paperwork Reduction Act of 1995 (PRA). Public Law 104-13, 109 Stat 163 (1995) (codified at 44 U.S.C. 3501-3520). All such new or modified information collections will be submitted to the Office of Management and Budget (OMB) for review under section 3507(d) of the PRA. 44 U.S.C. 3507(d). OMB, the general public, and other Federal agencies are invited to comment on any new or modified information collection requirements contained in this proceeding. In addition, we note that pursuant to the Small Business Paperwork Relief Act of 2002, Public Law 107-198, 116 Stat 729 (2002) (codified at 44 U.S.C. 3506(c)(4)), the Commission previously sought specific comment on how it might further reduce the information collection burden for small business concerns with fewer than 25 employees. We have assessed the effects of the required collection of information on these small entities.

36. Congressional Review Act. The Commission has determined, and the Administrator of the Office of Information and Regulatory Affairs, Office of Management and Budget, concurs, that this rule is non-major under the Congressional Review Act, 5 U.S.C. 804(2). The Commission will send a copy of this First Report and Order to Congress and the Government Accountability Office pursuant to the Congressional Review Act, 5 U.S.C. 801(a)(1)(A).

Ordering Clauses

37. Accordingly, it is ordered that, pursuant to the authority contained in sections 1, 4(i), 4(j), 301, 302a, 303, 307, 308, 309, 316, 319, and 324 of the ( print page 84103) Communications Act of 1934, as amended, 47 U.S.C. 151, 154(i), 154(j), 301, 302a, 303, 307, 308, 309, 316, 319, and 324 the foregoing First Report and Order is adopted, and the Commission's rules are hereby amended as set forth herein.

38. It is further ordered that the First Report and Order and the amendments to the Commission's rules shall be effective 30 days after publication of a summary in the Federal Register , except that the amendments to §§ 73.404 and 73.406, which may contain new or modified information collection requirements, will not become effective until OMB completes review of any information collection requirements that the Media Bureau determines is required under the Paperwork Reduction Act. The Commission directs the Media Bureau to announce the effective date of the rule changes to §§ 73.404 and 73.406 by subsequent Public Notice.

39. It is further ordered that the Office of the Managing Director, Performance and Program Management, shall send a copy of the First Report and Order in a report to Congress and the Government Accountability Office pursuant to the Congressional Review Act, 5 U.S.C. 801(a)(1)(A).

40. It is further ordered that the Commission's Office of the Secretary shall send a copy of this First Report and Order, including the Final Regulatory Flexibility Analysis, to the Chief Counsel for Advocacy of the Small Business Administration.

List of Subjects in 47 CFR Part 73

• Communications equipment
• Radio
• Reporting and recordkeeping requirements

Federal Communications Commission.

Marlene Dortch,

Secretary.

Final Rules

For the reasons discussed in this preamble, the Federal Communications Commission amends 47 CFR part 73 to read as follows:

PART 73—RADIO BROADCAST SERVICES

1. The authority citation for part 73 continues to read as follows:

Authority: 47 U.S.C. 154, 155, 301, 303, 307, 309, 310, 334, 336, 339.

2. In § 73.310, revise paragraphs (a) and (b) to read as follows:

§ 73.310

FM technical definitions.

(a) Frequency modulation. The following definitions pertain to frequency modulation, as defined in § 73.310(a)(17).

(1) Antenna height above average terrain (HAAT). HAAT is calculated by: determining the average of the antenna heights above the terrain from 3 to 16 kilometers (2 to 10 miles) from the antenna for the eight directions evenly spaced for each 45° of azimuth starting with True North (a different antenna height will be determined in each direction from the antenna): and computing the average of these separate heights. In some cases less than eight directions may be used. ( See § 73.313(d).) Where circular or elliptical polarization is used, the antenna height above average terrain must be based upon the height of the radiation of the antenna that transmits the horizontal component of radiation.

(2) Antenna power gain. The square of the ratio of the root-mean-square (RMS) free space field strength produced at 1 kilometer in the horizontal plane in millivolts per meter for 1 kW antenna input power to 221.4 mV/m. This ratio is expressed in decibels (dB). If specified for a particular direction, antenna power gain is based on that field strength in the direction only.

(3) Auxiliary facility. An auxiliary facility is an antenna separate from the main facility's antenna, permanently installed on the same tower or at a different location, from which a station may broadcast for short periods without prior Commission authorization or notice to the Commission while the main facility is not in operation ( e.g., where tower work necessitates turning off the main antenna or where lightning has caused damage to the main antenna or transmission system) ( See § 73.1675).

(4) Center frequency. The term “center frequency” means:

(i) The average frequency of the emitted wave when modulated by a sinusoidal signal.

(ii) The frequency of the emitted wave without modulation.

(5) Composite antenna pattern. The composite antenna pattern is a relative field horizontal plane pattern for 360 degrees of azimuth, for which the value at a particular azimuth is the greater of the horizontally polarized or vertically polarized component relative field values. The composite antenna pattern is normalized to a maximum of unity (1.000) relative field.

(6) Composite baseband signal. A signal which is composed of all program and other communications signals that frequency modulates the FM carrier.

(7) Effective radiated power. The term “effective radiated power” means the product of the antenna power (transmitter output power less transmission line loss) times:

(i) The antenna power gain, or

(ii) the antenna field gain squared. Where circular or elliptical polarization is employed, the term effective radiated power is applied separately to the horizontal and vertical components of radiation. For allocation purposes, the effective radiated power authorized is the horizontally polarized component of radiation only.

(8) Equivalent isotropically radiated power (EIRP). The term “equivalent isotropically radiated power (also known as “effective radiated power above isotropic) means the product of the antenna input power and the antenna gain in a given direction relative to an isotropic antenna.

(9) FM Blanketing. Blanketing is that form of interference to the reception of other broadcast stations which is caused by the presence of an FM broadcast signal of 115 dBµ (562 mV/m) or greater signal strength in the area adjacent to the antenna of the transmitting station. The 115 dBµ contour is referred to as the blanketing contour and the area within this contour is referred to as the blanketing area.

(10) FM broadcast band. The band of frequencies extending from 88 to 108 MHz, which includes those assigned to noncommercial educational broadcasting.

(11) FM broadcast channel. A band of frequencies 200 kHz wide and designated by its center frequency. Channels for FM broadcast stations begin at 88.1 MHz and continue in successive steps of 200 kHz to and including 107.9 MHz.

(12) FM broadcast station. A station employing frequency modulation in the FM broadcast band and licensed primarily for the transmission of radiotelephone emissions intended to be received by the general public.

(13) Field strength. The electric field strength in the horizontal plane.

(14) Free space field strength. The field strength that would exist at a point in the absence of waves reflected from the earth or other reflecting objects.

(15) Frequency departure. The amount of variation of a carrier frequency or center frequency from its assigned value.

(16) Frequency deviation. The peak difference between modulated wave and the carrier frequency.

(17) Frequency modulation. A system of modulation where the instantaneous radio frequency varies in proportion to the instantaneous amplitude of the modulating signal (amplitude of modulating signal to be measured after pre-emphasis, if used) and the ( print page 84104) instantaneous radio frequency is independent of the frequency of the modulating signal.

(18) Frequency swing. The peak difference between the maximum and the minimum values of the instantaneous frequency of the carrier wave during modulation.

(19) Multiplex transmission. The term “multiplex transmission” means the simultaneous transmission of two or more signals within a single channel. Multiplex transmission as applied to FM broadcast stations means the transmission of facsimile or other signals in addition to the regular broadcast signals.

(20) Percentage modulation. The ratio of the actual frequency deviation to the frequency deviation defined as 100% modulation, expressed in percentage. For FM broadcast stations, a frequency deviation of ±75kHz is defined as 100% modulation.

(b) Stereophonic sound broadcasting. The following definitions pertain to stereophonic sound broadcasting, as defined in § 73.310(b)(8).

(1) Cross-talk. An undesired signal occurring in one channel caused by an electrical signal in another channel.

(2) FM stereophonic broadcast. The transmission of a stereophonic program by a single FM broadcast station utilizing the main channel and a stereophonic subchannel.

(3) Left (or right) signal. The electrical output of a microphone or combination of microphones placed so as to convey the intensity, time, and location of sounds originating predominately to the listener's left (or right) of the center of the performing area.

(4) Left (or right) stereophonic channel. The left (or right) signal as electrically reproduced in reception of FM stereophonic broadcasts.

(5) Main channel. The band of frequencies from 50 to 15,000 Hz which frequency-modulate the main carrier.

(6) Pilot subcarrier. A subcarrier that serves as a control signal for use in the reception of FM stereophonic sound broadcasts.

(7) Stereophonic separation. The ratio of the electrical signal caused in sound channel A to the signal caused in sound channel B by the transmission of only a channel B signal. Channels A and B may be any two channels of a stereophonic sound broadcast transmission system.

(8) Stereophonic sound. The audio information carried by plurality of channels arranged to afford the listener a sense of the spatial distribution of sound sources. Stereophonic sound broadcasting includes, but is not limited to, biphonic (two channel), triphonic (three channel) and quadrophonic (four channel) program services.

(9) Stereophonic sound subcarrier. A subcarrier within the FM broadcast baseband used for transmitting signals for stereophonic sound reception of the main broadcast program service.

(10) Stereophonic sound subchannel. The band of frequencies from 23 kHz to 99 kHz containing sound subcarriers and their associated sidebands.

3. In § 73.402, add paragraph (i) to read as follows:

§ 73.402

Definitions.

* * * * *

(i) Asymmetric sideband operation. For digital FM stations, the use of different power levels on the upper and lower digital sidebands in a hybrid or extended hybrid DAB system.

4. Delayed indefinitely, in § 73.404, add paragraphs (e) and (f) to read as follows:

§ 73.404

IBOC DAB operation.

* * * * *

(e) Except stations operating on Channels 296-300 (107.1-107.9 MHz), FM stations may transmit hybrid IBOC signals with asymmetric power on the digital sidebands, as defined in § 73.402(i). Stations operating on Channels 296-300 (107.1-107.9 MHz) may seek an experimental authorization to transmit hybrid IBOC signals with asymmetric power on the digital sidebands.

(f) All FM stations transmitting hybrid IBOC signals may operate with total digital effective radiated power of up to −14 dBc. No station may operate its digital carriers with a total effective radiated power in excess of −10 dBc. A station planning to operate with a total digital effective radiated power in excess of −14 dBc must certify compliance with table 1 to this paragraph (f) by calculating the F(50,10) signal strength of its analog signal at the first adjacent station's F(50,50) 60 dBµ contour. Compliance with this table must be established for the upper and lower IBOC digital sidebands separately. All calculations must be made using the standard FCC contour prediction methodology.

Table 1 to Paragraph (f) —Maximum Permissible FM Digital ERP per Sideband

IBOC station's F(50,10) field strength at the upper or lower first-adjacent station's analog 60 dBµ F(50,50) contour	Maximum permissible FM digital ERP for the respective (upper or lower) sideband
51.2 dBµ and above	−17 dBc.
50.7 dBµ to 51.1 dBµ	−16 dBc.
50.3 dBµ to 50.6 dBµ	−15 dBc.
49.6 dBµ to 50.2 dBµ	−14 dBc.
49.5 dBµ or less	−13 dBc.