418 BELL SYSTEM TECHNICAL JOURNAL 



some future time, of a MUSA transmitting system. That horizontal 

 steering of transmitting directivity may be decidedly important is 

 strongly suggested by observations made on transmissions from Dav- 

 entry in which significant effects upon flutter fading have been found 

 to be associated with the orientation of the directional transmitting 

 antennas. 



Acknowledgment 



The experiments described in this paper necessarily involved the 

 coordinated effort of many individuals, in both the British Post Ofiice 

 and the Bell System, and their help has been appreciated. Mr. E. 

 Bruce had charge of the design of the rhombic antennas and trans- 

 mission lines, and Messrs. L. R. Lowry and W. M. Sharpless had im- 

 portant parts in the various phases of the work. 



The authors are particularly indebted to Mr. R. K. Potter who 

 contributed much through his keen interest throughout the entire 

 work. 



Appendix I 



Broad-Band Characteristic of the MUSA 



The frequency characteristic of the MUSA may be calculated 



from (3). Frequency and angle appear only in the form 2Tra{v — cos 5) 



where a is inversely proportional to frequency. By writing the 



equation 



Iv - cos 5] = ^^-^ — ^— [u - COS (5 -f A5)] 



we express the angular shift, from 5 to (5 + A5), of a given point on 

 the directional pattern as the frequency is varied from/ to (/ + A/). 

 This equation may be rewritten as 



. , A/ V — cos 8 



1 + - 



/ u - cos (5 + A6) ■ 



As an example consider A/ — 200 kilocycles, / = 10 megacycles, 

 5 = 30 degrees, and i; — 1.05. Then A8 = — 0.4 degree. For lower 

 values of 8, A5 becomes still smaller. 



The frequency characteristic expressed in terms of percentage band 

 and angular shift given by the above equation is independent of the 

 size of the MUSA. It relates to the over-all length of the system, how- 

 ever, by the fact that for greater lengths a given angular shift has more 

 effect. 



