CONTENTS

RECOMMENDATION  ITU-R  P.533-9     2
Method for the prediction of the performance of HF circuits^,      2
Scope     2
Annex 1     3
1 Introduction  5
2 Location of control points  5
3 Basic and operational maximum usable frequencies  6
        3.1 Basic maximum usable frequencies  7
        3.2 E-layer critical frequency (foE) 7
        3.3 E-layer basic MUF  7
        3.4 F2-layer characteristics  7
        3.5 F2-layer basic MUF  7
                  3.5.1 Lowest-order mode  7
                  3.5.2 Higher-order modes (paths up to 9 000 km) 8
        3.6 Within the month probability of ionospheric propagation support 8
        3.7 The path operational MUF  9
4 E-layer maximum screening frequency ( f_s) 9
5 Median sky-wave field strength  10
        5.1 Elevation angle  10
        5.2 Paths up to 7 000 km   11
                  5.2.1 Modes considered  11
                  5.2.2 Field strength determination  12
        5.3     Paths longer than 9 000 km   18
        5.4 Paths between 7 000 and 9 000 km   20
6 Median available receiver power 20
7 Monthly median signal-to-noise ratio (S/N) 21
8 Sky-wave field strength, available receiver signal power and S/Ns for other percentages of time     21
9 Lowest usable frequency (LUF) 22
10 Basic circuit reliability (BCR) 22
       10.1 The reliability of analogue modulated systems  22
       10.2 The reliability of digitally modulated systems, taking account of the time and frequency spreading of the received signal     22
                  10.2.1 System parameters  23
                  10.2.2 Time delay  23
                  10.2.3 Reliability prediction procedure  23
       10.3 Equatorial scattering  24
Appendix 1 to Annex 1  A model for equatorial scattering of HF signals     25