RADIO EXTENSION LINKS TO TELEPHONE SYSTEM 



643 



pattern as indicated in the same sketch and such a directive pattern is 

 produced by an antenna system called the "Musa." " The name 

 "Musa" comes from the initials of the words "multiple unit steerable 

 antenna." The Musa is one of the latest developments in directive 

 antennas and possesses not only the important characteristic of a 

 very sharp directivity pattern but also is steerable so it may be altered 

 to receive a desired component, and if such desired component changes 

 its angle of arrival alteration may be made to accommodate such 

 change. 



^^'--"Z''---- IONOSPHERE --~-ri~ ----_. 



'RECEIVING POINT 



EARTH 

 (b) VERTICAL PLANE DIRECTIVE PATTERNS (NOT DRAWN TO SCALE) 



Fig. 22 — Paths of short waves over long distances as determined by the ionosphere. 



Figure 23 indicates the elements of the Musa. It consists of a row 

 of rhombic antennas lined up in the direction from which signals are 

 expected. Each rhombic antenna is connected by a transmission line 

 to a phase shifter and the outputs of the phase shifters are connected 

 to a receiver. These phase shifters may be so adjusted as to cause any 

 desirable phase additions from the separate antennas. By changing 

 the adjustments on the respective phase shifters the direction of 

 reception may be altered. In this diagram a row of antennas is shown 

 as connected through phase shifters to receiving branch A with the 

 phase shifters adjusted to produce a directive pattern as indicated in 

 the neighboring diagram marked branch A and drawn dotted. Into 

 branch A will therefore come the signals which arrive from one trans- 



