OVERSEAS RADIO EXTENSION 253 



Transmission Results 



We now come to a consideration of these transoceanic links which 

 is perhaps the most important one from the standpoint of the service 

 given and of the engineering development required. It is that of the 

 general transmission effectiveness and of the continuity of service 

 which is given. So far as the radiotelephone circuits operating out 

 of the United States are concerned, this phase of the subject is pretty 

 well summarized by the charts given in Fig. 7. These show from top 

 to bottom the continuity of tivo-ivay transmission which has been 

 obtained over the past year, (1) on the long-wave transatlantic circuit, 

 (2) on one of the short-wave transatlantic circuits, and (3) on the 

 short-wave circuit which operates with Buenos Aires. The last named 

 circuit has been in operation only since the spring of this year. 



The black areas show in each case the hours of the day during which 

 the circuit was commercially usable. The white gaps indicate periods 

 during which no operation was attempted and for which there are no 

 data. The dotted-in lines show the periods during which the circuit 

 was found to be commercially unusable, i.e., the lost time periods. 



The following points are to be noted: 



1. The long-wave circuit, shown at the top, is poorest during the 



summer months. This is because of atmospheric disturbances 

 due to lightning. Throughout the year shown, the long-wave 

 circuit was available for service about 80 per cent of the time 



2. The North Atlantic short-wave circuit, center figure, was fairly 



good last summer but suffered much lost time during the spring 

 months of 1930. The poor behavior during the spring is ap- 

 parently due to unusually high solar activity. Such related 

 phenomena as aurora disturbances in the earth's magnetic field, 

 and earth currents have been affected similarly. For the year 

 shown this short-wave circuit was commercially available about 

 64 per cent of the operating time. Similar experience was had 

 on the other two transatlantic short-wave telephone circuits, 

 one of which was operated over a longer period of the day than 

 that shown. 



3. The combination of the North Atlantic of the long-wave and 



short-wave circuits gives a much improved result as compared 

 with either one alone. As is indicated in the diagrams, last 

 summer when the long wave circuits suffered from "static," 

 the short-wave transmission was fairly good; conversely, this 

 last winter and spring when the short-wave transmission suf- 

 fered severely from magnetic storm effects, the long-wave cir- 

 cuit was the mainstay of the service. 



