CONTENTS

RECOMMENDATION  ITU-R  M.1841     4
Compatibility between FM sound-broadcasting in the band of about 87-108 MHz and the aeronautical ground-based augmentation system in the band about 108-117.975 MHz     4
Scope     4
Annex 1  Interference mechanisms, system parameters  and compatibility assessment criteria     5
 1     Background and introduction  5
 2     Types of interference mechanisms  6
        2.1     Type A interference  6
                  2.1.1     Introduction  6
                  2.1.2     Type A1 interference  6
                  2.1.3     Type A2 interference  6
        2.2     Type B interference  6
                  2.2.1     Introduction  6
                  2.2.2     Type B1 interference  6
                  2.2.3     Type B2 interference  7
 3     Compatibility assessment parameters  7
        3.1     Introduction  7
        3.2     Characteristics of aeronautical systems  7
                  3.2.1     Designated operational coverage  7
                  3.2.2     Field strength  9
                  3.2.3     Frequencies  9
                  3.2.4     Polarization  9
        3.3     Characteristics of FM broadcasting stations  9
                  3.3.1     Maximum effective radiated power 9
                  3.3.2     Horizontal radiation pattern  9
                  3.3.3     Vertical radiation pattern  9
                  3.3.4     Spurious emission suppression  9
                  3.3.5     Frequencies  10
                  3.3.6     Polarization  10
                  3.3.7     Free-space field-strength calculation for broadcasting signals  10
        3.4     Receiver input power 10
4 Compatibility assessment criteria  11
        4.1 Standard interference thresholds  11
                  4.1.1     GBAS  11
        4.2     Interference assessment criteria – GBAS receivers  12
                  4.2.1     Type A1 interference  12
                  4.2.2     Type A2 interference  12
                  4.2.3     Type B1 interference  12
                  4.2.4     Type B2 interference  14
Appendix 1  to Annex 1  GBAS coverage and minimum field strengths     15
Annex 2  General assessment method     17
 1     Introduction  17
        1.1     Philosophy of the general assessment method  17
        1.2     GBAS  18
 2     Location and height of GBAS test points for each DOC   18
        2.1     GBAS precision approach test points  18
                  2.1.1     Fixed test points  18
                  2.1.2 Test points related to broadcasting stations  18
        2.2     GBAS positioning test points  19
                  2.2.1     Test points related to broadcasting stations that are inside each DOC   19
                  2.2.2     Test points related to broadcasting stations that are outside each DOC   19
                  2.2.3     Additional test points  20
 3     Application of general assessment method  20
        3.1     General 20
                  3.1.1     Test point selection  20
                  3.1.2     Broadcasting stations to be included in the analysis at a test point 20
                  3.1.3     Compatibility calculations  20
        3.2     Special considerations regarding compatibility assessments  21
                  3.2.1     Test point heights greater than the minimum values  21
                  3.2.2     GBAS precision approach test points  21
                  3.2.3     GBAS positioning test points  22
                  3.2.4     Calculation of GBAS field strength at test points  22
                  3.2.5     Calculation of Type A1 potential interference  22
                  3.2.6     Calculation of Type B1 potential interference  23
                  3.2.7     Calculation of Type B2 potential interference  23
                  3.2.8     Multiple interference  23
 4     Broadcasting station antenna corrections  23
        4.1     General 23
        4.2     Polarization discrimination  23
        4.3     Horizontal radiation pattern  24
        4.4     Vertical radiation pattern correction  24
                  4.4.1     v.r.p. corrections for vertical apertures of two or more wavelengths  24
                  4.4.2     v.r.p. corrections for vertical apertures of less than two wavelengths  24
                  4.4.3     v.r.p. corrections for spurious emissions in the band 108-118 MHz  25
        4.5     Combination of horizontal and vertical radiation patterns  25
Appendix 1  to Annex 2  Location of test points with maximum interference potential     25
 1     Aircraft at the same height as a broadcasting station antenna  25
 2     Aircraft at a greater height than a broadcasting station antenna  26
 3     Relationship between vertical and horizontal separation distances  26
 4     Location of maximum interference potential 26
 5     Test points for GBAS positioning service  26
 6     Test points for GBAS precision approach service  26
 7     Effect of increased test point height 26
Appendix 2  to Annex 2  Considerations regarding maximum field strength and interference potential     27
 1     Maximum field strength  27
 2     Maximum Type B1 interference potential 28
Annex 3  Detailed compatibility assessment and practical verification     29
 1     Introduction  29
 2     Matters requiring special attention  29
        2.1     Prediction of broadcasting field strengths  29
        2.2     Test point considerations  30
        2.3     Consideration of operating stations  30
 3     Multiple interference  30
 4     Detailed compatibility assessment 31
 5     Practical verification process  31
 6     Summary  31
Annex 4  Definitions     32