ITU-R BS 411-4-1990 Fading Allowances in HF Broadcasting《高频(HF)广播的衰减允许》.pdf

1、CCIR VOLUME*X-3 90 4855232 0503737 2 m Rec. 411-4 RECOMMENDATION 41 1-4 59 FADING ALLOWANCES IN HF BROADCASTING (Question 44/10, Study Programme 44C/10) (1963-1966-1978-1986-1990) The CCIR UNANIMOUSLY RECOMMENDS that the values given in Table I below should be used for the fading factors necessary t

2、o ensure a satisfactory signal-to-interference ratio for given percentages of the time. TABLE I Ratio (dB) . (1) (2) (3) (4) Radio-frequency signal-to-interference 10 13 23 16 Wanted signai-to-atmospheric noise 6 16 22 17 Wanted signai-to-industriai noise 6 10 16 12 Column 1: the short-term fading a

3、llowance which must be made to ensure that the steady-state ratio is attained for 90% of any given hour. Column 2: the long-term fading allowance which must be made to ensure that the steady-state ratio is achieved for 90% of the hours in any one month at a particular time of-day in 90% of the cases

4、. Column 3: the sum of the values in columns (I) and (2), and is the overall variability allowance which must be made to ensure that the steady-state ratio is attained for 90% of any one hour in 90% of the hours in any month at a particular time of day and in 90% of the cases. This represents an ass

5、ured steady-state ratio for 96% of the overall time. Column 4: the square root of the sum of the squares of the values (in dB) given in columns (i) and (2), and is the overall variability allowance which must be made to ensure that the steady-state ratio is attained for 90% of the time. Note - The f

6、igures in the above Table, relating to the time availability of service, were selected on a theoretical basis and on experience derived principally from broadcasting in band 6 (MF). For HF, Study Group 6 has proposed appropriate fading allowances for a range of percentages of time and has concluded

7、in particular that the long-term fading of wanted or interfering signal depends upon the ratio of the wave frequency to the basic MUF and also upon the great-circle path geomagnetic latitude. These allowances are contained in Table III of Report 266. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services