Transatlantic Radio Telephone Transmission ' 



By I,LOYD ESPENSCHIED, C. N. ANDERSON 

 i.iul AUSTIN BAILEY 



.S\Mii'sis: i 111, juiHT j;ivi> .in.iKx's o( i>l>s(Tv.iii(ins iil Iohk-w.ivc trans- 

 mission across the Atlantii' over a |HTio<l of aliotit two years. The principiil 

 conchisions which the data seem to justify are as follows: 



1. S<jlar radiation is shown to Ik- the conlrolling factor in flelermininR 

 the iliiirnal and season.d variations in signal field. Transmission from 

 east to west and west to east e.\hil>it similar characteristics. 



2. Transmissiim in the region l>or<leringon thedlvisioii between the illumi- 

 nated and the <larkeni'j| hemispheres is characterizetl by increaseil attenu- 

 ation. This manifests itself in the sunset and sunrise dips, the decrease 

 in the persistence of high night-time values in sununer anil the decrease 

 in daylight values during the winter. 



^. Definite correlation has been found between abnormal radio trans- 

 mission and disturluinces in the earth's magnetic fiekl. The effect is to 

 decrease greatly the night-time field strength and to increase slightly the 

 daylight values. 



4. The limit of the high-night-time value of signal field strength for 

 transatlantic distance is essentially that given by the Inverse Distance 

 Law. The normal daylight field strengths obtained in these tests can Iw 

 ajiroxiniated by a formula of the same form as those earlier proposed but 

 with somewhat different constants. 



5. The major source of long wave static, as rcceivefl in both England and 

 the I'nited Slates, is indicated to be of tropical origin. 



6. In general, the static noise is lower at the higher frequencies. M 

 night the decrease with increase in frequencv is exiwncntial. In day-time 

 the decrease with increase in frequency is bnear in the range of 15 to 40 

 kilcx-ycles. The difference between day antl night static is, therefore, 

 apparently due largely to daylight attenuation. 



7. The effect of the static noise in interfering with signal transmission, 

 as shown by the diurnal variations in the signal-to-noise ratio, is found 

 to be generally similar on lx)th sides of the Atlantic. 



8. Experiments in both the I'nited States and England with directional 

 receiving antennas of the wave antenna ty|)e show an average improve- 

 ment in the signal-to-static ratio of about 5 as compared with loop reception. 



IT will Ix^ recalled th.it something over two years ago, experiments 

 in one-way radio telephone transmission were conducted from 

 the I'nited States to England.- In respect to the clarity and uni- 

 formity of the reception obtained in Flurope, the results represented a 

 distinct advance in the art over the transatlantic tests of 1915. 

 However, they were carried out during the winter, which is most 

 favorable to radio transmission, and it was realized that an extensive 

 favorable to radio transmission, and it was realized that extensive 

 study of the transmission obtainable during less favorable times 

 would Ik; ret|uired before the development of a transatlantic radio 

 telephf)ne service could Ix; undertaken upon a sound engineering basis. 



' Presented before the Institute of Radio Engineers, May 6, 1925. 



' "Transatlantic Radio Telephony," .Arnold and Espens»hicd, Journal of A. I.E. E., 

 .August, 1923. .See also, "Power .Amplifiers in Transatlantic Telephony," Oswald 

 and Schelleng, presented before the Institute of Radio Engineers, May 7, 1924. 



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