CHAPTER 4

SPECTRUM AVAILABILITY

Introduction

National policies can address the problem of increased demand for spectrum in a number of ways. One way is to place greater reliance on market-based forces to guide spectrum apportionment. NTIA in its NTIA Spectrum Policy Study and elsewhere has examined the use of market-based forces to guide spectrum apportionment. NTIA is mindful that when spectrum is commercially non-viable or when spectrum is required for public interests (public safety, national defense, education, etc.), market forces may not be the ideal spectrum management approach to satisfy increased demand for spectrum. Because of the nature of some frequency bands and radio service allocations, the existing practice of long-range spectrum planning where spectrum is re-allocated may be an alternative approach to satisfy increased spectrum demands.

In the NTIA Requirements Study, an estimate of additional spectrum included spectrum in the HF band needed for amateur, broadcasting, aeronautical mobile, maritime mobile, and mobile radio services. These HF spectrum requirements were developed based on projected service needs and effect of new technology. Because propagation characteristics make the HF band unique, this spectrum availability study was accomplished for the five radio services simultaneously since spectrum requirements satisfaction in the HF band affects each other as well as the other existing radio services. NTIA estimated the additional spectrum requirement for these services to be approximately an additional 3,088 kHz for the five radio services. Having identified the future spectrum requirements for HF frequencies, the next step in the NTIA strategic planning process is to identify the availability of HF spectrum that could satisfy those requirements.

The intent of this chapter is to identify the available candidate HF spectrum to satisfy the shortfall for those services identified as needing additional spectrum in Chapter 2. NTIA believes that the HF spectrum is sufficiently flexible enough to accommodate most, if not all, requirements for additional HF spectrum. Note that the discussion contained herein is strictly for planning purposes and identifies possible long-range planning options to satisfy the additional HF spectrum requirements.

Long-Range Planning Options for Increased Spectrum Availability

Additional spectrum cannot be produced or discovered. We can only use the spectrum that current technology permits, and we must use it as efficiently as practicable. When spectrum demands exceed available allocations, there is a limited number of long-range planning options possible to satisfy the demand for spectrum access. For the purposes of this study, four general long-range planning options for additional HF spectrum access are discussed in the following paragraphs.

Option 1. Make More Efficient Use of Current Allocations. The HF block allocation system for the HF band has worked generally well since the 1920's; however, since the early 1950's, use of the HF band has been contentious among various Administrations. Increased flexibility can be accomplished in the HF band by lessening arbitrary boundaries to accommodate other radio services and employing adaptive technology, automatic link establishment, and single-sideband technologies. These methods are possible for the HF band in the form of increased spectrum sharing. As was noted in the NTIA Requirements Study, new systems and services trying to gain access to HF radio frequencies often must contend with entrenched users with long histories of serving the public and private needs and who have large investments in equipment. Mandating use of spectrum-efficient technologies in the United States would greatly improve HF spectrum availability, although this would be expensive to some users.

Option 2. Reaccommodate Incumbent Spectrum Users. Under certain circumstances, it may be possible to reaccommodate spectrum users from one frequency band to another, or within the same frequency band, in order to clear the band or a portion of it for another radio service. This was also accomplished as a result of recent WRC's when existing HF users were reaccommodated in other portions of the HF spectrum in favor of new radio services. Presently, in the United States, hundreds of microwave facilities must be relocated to other frequency bands which have already been rechannelized or to alternative facilities to accommodate the new personal communications service (PCS) devices.

Option 3. Use Other (non-spectrum) Technologies. The relative advantages of spectrum-dependent systems and wireline(1) systems are changing. Long-haul microwave systems are being converted to employ optical fiber cable to take advantage of fiber's higher capacity. The introduction of market-place forces has the potential to drive users to substitute non-spectrum using technologies for spectrum using technologies. However, in the HF band, it does not appear feasible to use wireline systems due to the expenses involved for long-distance communications and the mobile nature of the requirements associated with many HF users.

Option 4. Use Higher Frequencies. To satisfy long-distance radiocommunications requirements, users either employ HF, satellite systems, or fiber/cable. Some HF users have partially or completely transitioned their operations from HF to satellite communications with many still maintaining HF systems for backup or as a cheaper alternative. Aeronautical mobile and maritime mobile users frequently maintain both. International broadcasters are reluctant to migrate to higher frequencies because their target audiences have only HF receivers and cannot afford the purchase of a more expensive receiver at a higher frequency band. Unique uses of the HF band mitigate against complete dependence on higher frequency bands. International broadcasters are investigating the use of satellite-sound broadcasting for reaching selected audiences. Although aeronautical mobile and maritime mobile users are increasingly employing satellites for long-distance communications, they will still have HF spectrum requirements until the transition is complete.

Of the four long-range planning options discussed above, Options 1 and 2 appear the most feasible to satisfy HF spectrum requirements in the United States though there may be regulatory difficulties nationally and internationally. More spectrum can be made available by increasing the flexibility of allocation boundaries to increase use to other services. Sharing, in this sense, is possible among users or radio services rather than among licensees in a particular allocated service and removing some "exclusive" designation of allocations to allow for shared government and non-government use. Increased sharing among users or radio services can broaden radio service use and open up a separate or adjacent block(s) of spectrum. The most likely radio service candidate to share with in the HF region appears to be the fixed service and to a lesser extent, fixed and mobile service bands.

As was noted in the NTIA Requirements Study, the availability of alternative technologies may bring a decrease in HF crowding. Communications satellites and greatly improved optical fiber undersea cables have taken over the majority of overseas circuits. Inexpensive very small aperture terminals and improved wired telecommunications infrastructure in many foreign countries are also reducing the past heavy dependence on HF circuits. Automatic link establishment (ALE) techniques and HF data link technology being developed to support civilian aviation have recently made HF communications more reliable and useful. Although HF fixed use may decrease, it will remain very important for emergency use within the United States and for backup communications between the United States and foreign countries.

Appendix A shows the HF portion of the National Table of Frequency Allocations along with the size of the sub-band and the numbers of Federal and non-Federal assignments. An assignment does not necessarily correlate to the number of transmitters—one assignment can have tens or hundreds of transmitters associated with it. Nonetheless, it serves as a relative baseline for evaluation in a particular band.

In finding spectrum available for the various radio services identified in Chapter 2, the table in Appendix A was used to locate blocks of spectrum with the least amount of usage (i.e., assignments or licenses), and doing it with the least amount of reorganization to the National Table of Frequency Allocations. However, this did not preclude selecting blocks that were distributed throughout the HF band vice concentrating in a particular area. No attempt was made to determine real-time spectrum occupancy.

Spectrum Availability for the Aeronautical Mobile (R) Service

The NTIA Requirements Study found that an additional 108 kHz(2) in the HF band will be needed for aeronautical mobile (R) operations within the next 10 years. The four HF bands below were identified as candidates to satisfy this spectrum requirement and, because of airborne safety aspects, aeronautical mobile (R) operations require exclusive frequency band allocations. A change to the ITU Radio Regulations by a competent future WRC will be necessary satisfy this spectrum requirement.

9900-9925 kHz. The 9900-9925 kHz band is the lower 25 kHz portion of the 9900-9995 kHz band, allocated to the fixed service. There are approximately 26 Federal and 4 non-Federal assignments in this 25 kHz-wide band; however, 10 of the Federal assignments support the aeronautical mobile (R) service. It appears feasible that the band 9900-9925 kHz could be re-allocated for the aeronautical mobile (R) service.

12205-12230 kHz. This band is the upper 25 kHz portion of the 12050-12230 kHz band allocated in the United States for the fixed service. There are approximately 146 assignments (120 Federal and 26 non-Federal) in this 25 kHz block of spectrum that would have to be reaccommodated.

19655-19680 kHz. The 19655-19680 kHz band is the upper 25 kHz portion of the 18900-19680 kHz band allocated to the fixed service. This 25 kHz band contains about 25 Federal assignments. It appears feasible that the band 19655-19680 kHz could be re-allocated for the aeronautical mobile (R) service.

19800-19830 kHz. To satisfy the remaining mobile spectrum requirement, 30 kHz (19800-19830 kHz) could be re-allocated from the 19800-19990 kHz band which is allocated for the fixed service. In this 30 kHz band, there are approximately 2 Federal and 12 non-Federal assignments and it appears that the 30 kHz band, 19800-19830 kHz, could be re-allocated to the aeronautical mobile (R) service.

Spectrum Availability for the Aeronautical Mobile (OR) Service

The NTIA Requirements Study noted that to support aeronautical mobile (OR) service operations within the next 10 years an additional 30 kHz was needed in the HF band. The two bands below were candidates that could satisfy this spectrum requirement: the first band is adjacent to an existing aeronautical mobile (OR) allocation and the second is adjacent to an aeronautical mobile (R) band. Because of the nature of aeronautical mobile operations, sharing frequency allocations with other radio services is not always feasible and changes to both the National Table of Frequency Allocations and the ITU Radio Regulations will be necessary to satisfy this spectrum requirement.

4750-4765 kHz. Fifteen kilohertz could be re-allocated from the lower portion of 4750-4850 kHz band that is currently allocated for the fixed and mobile services.(3) The 4750-4765 kHz band is adjacent to an aeronautical mobile (OR) band and has about 63 assignments: 47 Federal and 16 non-Federal. Of the 47 Federal assignments, only 40 would have to be reaccommodated because 7 assignments presently support the aeronautical mobile (OR) service.

11400-11415 kHz. The 11400-11415 kHz is the lower portion of the fixed service allocated band: 11400-11650 kHz. There are approximately 64 Federal (seven of which support the aeronautical mobile (OR) service) and 16 non-Federal assignments in this 15 kHz of spectrum space and it appears feasible that these assignments could be reaccommodated in the 11415-11650 kHz band.

Spectrum Availability for the Mobile Service

A requirement for 100 kHz of additional HF spectrum for the mobile service used in support of aeronautical operations was identified in the NTIA Requirements Study. The five HF bands described below were identified as candidates to satisfy this spectrum requirement. All five bands are presently allocated to the fixed and mobile service. Because of the relatively small number of assignments that need to be reaccommodated, it appears that the bands below could be allocated exclusively to the mobile service except aeronautical mobile (R).(4) To support this additional spectrum requirement for the mobile service, a change to the National Table of Frequency Allocations would be needed.(5)

4635-4650 kHz. The mobile service could be allocated 15 kHz for exclusive use from the upper portion of the 4438-4650 kHz band. This band is presently allocated to the fixed and mobile services and is 212 kHz wide. In the 4635-4650 kHz band, there are approximately 29 Federal and 99 non-Federal assignments that support radio services other than the mobile service that would need to be reaccommodated.

5730-5750 kHz. Twenty kilohertz appears available in the lower end of the 5730-5950 kHz band to satisfy a portion of the mobile service spectrum requirements. This band is allocated to the fixed and mobile services. The 5730-5750 kHz band could be exclusively allocated to the mobile service and the approximately 69 Federal and 15 non-Federal assignments that support radio services other than the mobile service would need to be reaccommodated.

6765-6790 kHz. This band is the lower 25 kHz portion of the 6765-7000 kHz band that is allocated for the fixed service (primary) and mobile service (secondary). Exclusive allocation of the 6765-6790 kHz band to the mobile service could be accomplished and approximately 440 non-mobile assignments would have to be reaccommodated: 90 Federal and 350 non-Federal.

11155-11175 kHz. Twenty kilohertz appears available at the upper end of the 10150-11175 kHz band to satisfy a portion of the mobile service spectrum requirement. This band is allocated for fixed (primary) and mobile(6) (secondary) services and could be exclusively allocated to the mobile service. In this 20 kHz, there are approximately 10 Federal and 16 non-Federal assignments that support radio services other than the mobile service. It appears feasible that these 26 assignments could be reaccommodated.

23350-23365 kHz. To satisfy the remaining mobile service spectrum requirement, 15 kHz (23350-23365 kHz) from the 23350-24890 kHz band could be re-allocated from this fixed (non-government) and fixed and mobile(7) (government) allocated band. Exclusive allocation of the 23350-23365 kHz band to the mobile service could be accomplished. There are about 13 Federal and 7 non-Federal non-mobile assignments in this band that would need to be reaccommodated.

Spectrum Availability for the Maritime Mobile Service

The NTIA Requirements Study found that an additional 30-60 kHz in the HF band will be needed for maritime mobile operations within the next 10 years. The three HF bands below were identified as candidates to satisfy this spectrum requirement; however, to preserve the balance of spectrum accessible to the aeronautical mobile (OR) service and to maximize the band flexibility, we believe that the three bands could be allocated on a primary basis to the maritime mobile and on a secondary basis to the aeronautical mobile (OR) service.(8) To satisfy these additional spectrum requirements, changes to the National Table of Frequency Allocations would be needed as well as changes to the ITU Radio Regulations.

4438-4453 kHz. Fifteen kilohertz could be re-allocated from the lower portion of the 4438-4650 kHz band so that the 4438-4453 kHz band is allocated to the maritime mobile and aeronautical mobile (OR) services. This band is currently allocated to the fixed and mobile services. The 4438-4453 kHz band contains approximately 444 non-maritime mobile assignments: 93 Federal and 351 non-Federal.

16335-16360 kHz. This band is part of the larger 15600-16360 kHz band, which is currently allocated to the fixed service. The 16335-16360 kHz band has approximately 106 non-maritime mobile assignments: 98 Federal and 8 non-Federal assignments. It appears feasible that this band could be allocated to the maritime mobile and aeronautical mobile (OR) services and that the affected non-mobile assignments could be moved into the remaining 735 kHz of the 15600-16335 kHz band.

22855-22873 kHz. To satisfy the remaining maritime mobile spectrum requirement, 18 kHz (22855-22873 kHz) from the 22855-23000 kHz band could be re-allocated. Presently, this band is allocated for the fixed service and could be re-allocated for maritime mobile and aeronautical (OR) mobile services. There are approximately 18 non-maritime mobile assignments in this band (8 Federal and 10 non-Federal) and it appears that these affected assignments could be reaccommodated.

Spectrum Availability for the Amateur Service

In the NTIA Requirements Study, NTIA noted that the amateur services expressed spectrum requirements of approximately 900 kHz of additional HF spectrum. The amateur requests for international reallocations would be appropriate issues for FCC private sector advisory committees addressing U.S. preparations for future WRC's. The additional allocation near 5 MHz will require technical studies to determine the availability of these bands to support amateur use. The expansion and upgrading of amateur allocations in the 10 MHz, 14 MHz, 18 MHz, and 24 MHz appear acceptable; however, this will depend on future decrease of requirements for the aeronautical mobile (R) or the fixed services internationally. The alignment of the amateur bands at 3.5 and 7 MHz worldwide will require the inclusion of these proposals in U.S. preparations for future WRC's.

3500-3800 kHz. The amateur service indicated a 300 kHz requirement of a common, worldwide exclusive amateur allocation in the 3500-4000 kHz band. In the United States the 3500-4000 kHz band is allocated for the amateur service; however, in other regions of the world, the amateur service shares portions of this band with fixed and mobile services. The 3500-3800 kHz band is a good candidate for a common, worldwide exclusive amateur allocation at the 3.5 MHz band.

4945-4995 kHz. A new amateur service requirement for 50 kHz of shared use around 5000 kHz appears possible at 4945-4995 kHz. This band is allocated to the fixed and mobile services. In this 50 kHz, there are approximately 150 Federal and 50 non-Federal assignments.

6900-7200 kHz. The amateur's requirement for 300 kHz band aligned worldwide at the 6900-7200 kHz band needs to be addressed at U.S. preparations for future WRC's. This requirement is to reduce inter-regional sharing and interference from HF broadcasting in the 7100-7300 kHz band; however, the 7100-7300 kHz band is presently allocated in the United States and in Region 2 to the amateur service. In Regions 1 and 3, this band is allocated to the broadcasting service. The 7000-7100 kHz band is allocated worldwide to the amateur and amateur-satellite services. From 6765-7000 kHz, the worldwide allocations are for fixed (primary) and mobile (secondary) services. In the United States, there are approximately 775 Federal and 101 non-Federal assignments in the 6900-7200 kHz band.

10100-10350 kHz. The amateur service requirement for the 10100-10350 kHz band is for a new worldwide allocation where the amateur service is primary. Internationally, this band is allocated on a primary basis for the fixed service, to the amateur service on a secondary basis at 10100-10150 kHz, and to the mobile service on a secondary basis at 10150-10300 kHz. The 10100-10350 kHz band in the United States has two allocations: the 10100-10150 kHz band is allocated exclusively for the amateur service and the 10150-10350 band is allocated for the fixed (primary) and mobile (secondary) services. The 10150-10300 kHz band is a large portion of spectrum that the amateur service could possibly share this band in order to satisfy another radio service's additional spectrum requirements. There are a total of approximately 659 U.S. assignments that would be impacted in this band: 599 Federal and 60 non-Federal.

14350-14400 kHz. In this band, the amateur service requirement is for 50 kHz of primary, exclusive worldwide amateur allocation. Worldwide, this band is allocated for the fixed and mobile services. In the United States, the 14350-14990 kHz band is allocated to the fixed service on a primary basis to the Government and non-Government and on a secondary basis to the mobile service for Government operations. There are approximately 140 Federal and 45 non-Federal assignments in this band.

18168-18318 kHz. The amateur service requirement for expansion of the 18068-18168 kHz amateur band by 150 kHz appears feasible into the next higher band. This adjacent higher band is the 18168-18780 kHz band that is allocated in the United States and Regions 1, 2, and 3 for the fixed service as primary and for the mobile service on a secondary basis. In the 18168-18318 kHz band, there are approximately 216 Federal and 42 non-Federal assignments.

24740-24890 kHz. To satisfy the 150 kHz additional requirement for the 24890-24990 kHz amateur band, expansion would have to be into the fixed and mobile allocated band below the amateur band. The band above it is allocated to the standard frequency and time signal service. There are approximately 207 Federal and 21 non-Federal assignments in the 24740-24890 kHz band.

29700-30000 kHz. The amateur service requirement is for re-allocation of the 29700-30000 kHz band for the amateur-satellite service (space-to-Earth). The Republic of South Africa has also proposed to re-allocate this band nationally for this purpose. Presently, this band in the United States is allocated exclusively for non-government land mobile service use at 29700-29800 kHz and for the fixed service at the 29800-29890 kHz and 29910-30000 kHz bands. Additionally, the 29890-29910 kHz band is allocated for exclusive fixed and mobile government use. There are approximately 260 assignments in this 29700-30000 kHz band: 22 Federal and 238 non-Federal.

Spectrum Availability for the Broadcasting Service

Recent radio conferences have resulted in the expansion of broadcasting service allocations in the HF band. The WARC-59 ended with having a total of 2,150 kHz HF spectrum allocated to the broadcasting service in Region 2 (525 kHz below 10 MHz and 1,625 kHz above 10 MHz). At the WARC-79, the broadcasting service obtained 780 kHz more allocated spectrum in Region 2 (125 kHz more below 10 MHz and 655 kHz more above 10 MHz). Though an additional 790 kHz of HF spectrum was allocated to the broadcasting service at the WARC-92, two significant limitations were placed on the use of these new frequencies. First, they cannot come into operation until April 1, 2007, and second, the WARC-92 prohibited their use until a process for planning the HF broadcasting spectrum has been completed. Expansion of the broadcasting service allocations in Region 2 has generally been at the expense of the fixed service.

As compared to the broadcasting service, the HF spectrum requirements of the other radio services were small and it appears feasible to re-allocate small portions of other frequency bands to accommodate their smaller spectrum requirements. However, the broadcasting service spectrum requirement of about 1,900 kHz is relatively large and is one of the five radio services expressing spectrum requirements that total about 3,088 kHz in the HF band. No spectrum requirements were expressed for the radio astronomy, fixed, fixed/mobile, and standard frequency/time signal services and, thus, the spectrum allocated to these services is the only spectrum available to satisfy the expressed HF spectrum requirements.

It is difficult to identify blocks of HF spectrum as possible candidates for satisfying the broadcasting service requirements because broadcasting does not share well with other services,(9) with the resultant hardships of reaccommodation of current users to other HF spectrum or, possibly, to a non-spectrum dependent medium. No spectrum is available in HF bands allocated to the radio astronomy and the standard frequency/time signal services due to the nature of the radio service and small amount of spectrum allocated. The only possible spectrum available for any sharing or re-allocation is from spectrum allocated to the fixed and fixed/mobile services. The broadcasting requirement comprises about 16 percent of the combined spectrum that these two services have allocated. Looking at the distribution of U.S. assignments throughout the HF band, it appears there are many blocks of U.S. fixed and fixed/mobile allocated bands that could be re-allocated to the broadcasting service. Further, the additional allocations for the broadcasting service identified below would be appropriate issues for advisory committees addressing U.S. preparations for future WRC's.

9200-9400 kHz. This 200 kHz block of spectrum is a portion of the 9040-9400 kHz band that is allocated for the fixed service. Also, it is adjacent to the 9400-9500 kHz band allocated for the broadcasting service at the WARC-92 and could complement the broadcasting service expansion from 100 kHz to 300 kHz in this portion of the HF spectrum. There are approximately 465 Federal and 59 non-Federal assignments in this band.

10150-10300 kHz. This 150 kHz block of spectrum is part of the 10150-11175 kHz band allocated worldwide for the fixed (primary) and mobile (secondary) services. There are approximately 659 U.S. assignments in this band: 599 Federal and 60 non-Federal. It should be noted that this band was previously identified to satisfy some amateur service spectrum requirements for expansion of the amateur service. It appears feasible that both the broadcasting service and amateur service could share this band where the broadcasting service is primary and the amateur service is secondary.

11500-11600 kHz. This 100 kHz block of spectrum would complement the 50 kHz at 11600-11650 kHz allocated at WARC-92 for the broadcasting service. This block of spectrum is allocated to the fixed service and contains about 223 Federal and 8 non-Federal assignments.

14350-14450 kHz. The 14350-14450 kHz band is a portion of a band allocated worldwide for the fixed service (primary) and mobile (secondary) service. In the United States, this band has approximately 284 Federal and 52 non-Federal assignments.

15800-16000 kHz. This 200 kHz of spectrum would complement 100 kHz of spectrum at 15800-16000 kHz allocated by the WARC-92 for the broadcasting service. Worldwide, this block of spectrum is allocated to the fixed service. There are approximately 247 Federal and 49 non-Federal assignments in the United States.

17410-17480 kHz. Allocation of this 70 kHz band to the broadcasting service would give the entire 17410-17550 kHz band to the broadcasting service since the 17480-17550 kHz band was re-allocated to the broadcasting service by WARC-92. This band is allocated to the fixed service worldwide. In the United States there are approximately 162 assignments in this band: 123 Federal and 39 non-Federal.

18168-18268 kHz. This 100 kHz is a portion of the 18168-18780 kHz band that is 612 kHz wide with allocation in the United States and worldwide to the fixed service (primary) and mobile (secondary). In the United States, there are approximately 230 Federal and 35 non-Federal assignments in this band.

19020-19680 kHz. The 19020-19680 kHz band is a portion of the 18900-19680 kHz band, a 780 kHz-wide band, allocated in the United States for the fixed service. The 19020-19680 kHz band, in the United States, has approximately 558 assignments: 487 Federal and 71 non-Federal. This band is also allocated worldwide to the fixed service and is adjacent to the 18900-19020 kHz band allocated by the WARC-92 for the broadcasting service.

19825-19925 kHz. This band has about 29 Federal and 12 non-Federal assignments in the United States and is allocated in the United States for the fixed service.

21850-21924 kHz. In the United States, this band is allocated to the fixed service; however, worldwide, this band has two allocations: fixed service for the 21850-21870 kHz band and aeronautical fixed service at 21870-21924 kHz. In this band, there are approximately 111 assignments in the United States: 79 Federal and 32 non-Federal.

22855-22905 kHz. This band in the United States is allocated for the fixed service. There are approximately 73 assignments in this band: 44 Federal and 29 non-Federal.

Summary of Long-Range Planning Options

For the purposes of spectrum planning, the following frequency bands could be considered for satisfying future HF spectrum requirements. In finding spectrum available to satisfy the various services identified in Chapter 2, information from Appendix A was used to identify bands with low usage (i.e., number of assignments or licenses), good distribution throughout the HF band, and requiring the least amount of revision of the National Table of Frequency Allocations.

Chapter 4 Footnotes:

(1)In this discussion, the term "wireline" is applied to systems that use electromagnetic transmissions, but are inter-connected by wire, fiber optic cable, or other non-radiating media.

(2)Markey, supra note 14.

(3)Mobile services except aeronautical mobile (R).

(4)Only the fixed assignments need to be reaccommodated. The aeronautical mobile (R) service is excluded because of its need for exclusive allocations.

(5)Mobile service, in this discussion, refers to the mobile services except aeronautical mobile (R).

(6)Except aeronautical mobile (R).

(7)Except for aeronautical services.

(8)In the amateur and broadcasting services discussions to follow, about 50 kHz of spectrum accessible to the aeronautical mobile (OR) service is affected.

(9)Broadcasting shares HF bands with the amateur service with some success, but could not share with a commercial or government service.

(10)Markey, supra note 14.