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BELL SYSTEM TECHNICAL JOURNAL 



York circuits within the different frequency ranges indicated. All of 

 these curves have roughly the same mid-range slope. Incidentally, if 

 correction is made for relative transmitter power and antenna gains 

 the horizontal separation is a direct comparison of transmission effec- 

 tiveness on the different frequencies within their period of use. When 

 such a correction is applied to the curves of Fig. 2 (b) the mid-range 

 separation becomes less than 3 db, indicating that with equal trans- 

 mitter power, antenna gains and other terminal improvements the 

 average 6-A noise distribution is substantially the same for all times 

 of the day when suitable frequencies are employed to cover the diurna 

 range of transmission requirements. 



Comparison of 1930, 1932 and 1934 



As previously mentioned, short-wave transmission conditions were 



severely disturbed during the year 1930. By 1932, conditions had 



become much more favorable and 1934 was perhaps typical of a quiet 



year. In Fig. 3 (a) are included 6-A noise distribution curves for the 



10 20 -30 -20 



6-A NOISE IN DECIBELS 



Fig. 3 — Percentage distribution curves of 6-A noise measurements made during 

 1930, 1932 and 1934 on (a) all London to New York short-wave circuits and on (6) 

 all Buenos Aires to New York circuits. 



