372 BELL SYSTEM TECHNICAL JOURNAL 



delay used is 400 microseconds. In samples 3 and 4 a third wave of 26 

 degrees is present. One branch was steered at this wave; the other 

 was steered at the 15-degree wave and a delay of 1000 microseconds 

 was used. 



It is of interest to compare these samples showing the manner in 

 which the MUSA branch outputs combine, with the samples in Fig. 25 

 which were obtained with a two-antenna space diversity setup. Six 

 antennas were retained in the monitoring branch but five were cut out 

 of each receiving branch, leaving one antenna to supply each branch. 

 In samples 1 and 2, antennas 1 and 6 (1000 meters apart) were re- 

 tained. In samples 3 and 4, adjacent antennas (Nos. 1 and 2) 200 

 meters apart were used. These records were obtained about 15 

 minutes later than those of Fig. 23 and show the same two waves at 

 8.5 and 20.5 degrees. No delay was used. Note that the outputs 

 combine in phase only when one wave predominates. Inserting delay 

 in either branch is, of course, not effective in improving the audio 

 combination. To do so would impair the addition when one wave is 

 predominant and would not be beneficial when both waves are 

 comparable. 



Figure 26 shows, in samples 1, 2, 3, and 4, how the delay indicator 

 tube pattern is affected by the delay adjustment. The two branches 

 were steered at the same angle, thus making both branch outputs 

 identical so that perfect delay adjustment occurs with zero delay. 

 This is the condition depicted in sample 1. In samples 2, 3, and 4 

 the delays are 340, 680, and 2700 microseconds, respectively. 



A number of tests were carried out with the cooperation of the 

 British Post Office in which twelve tones were transmitted. These 

 tones were nonharmonically related. They were separated at the 

 output of the receiver by means of filters, and commutated to appear 

 successively on an oscilloscope. The reader is referred to a paper * by 

 R. K. Potter describing this technique. Figure 27 shows a sample of 

 motion pictures made of the oscilloscope patterns. Two receiving 

 systems are compared ; the right-hand pattern shows the output of the 

 MUSA while the left shows the output of a conventional receiver con- 

 nected to a horizontal half-wave antenna. The tones trace the hori- 

 zontal lines in sequence from top (425 cycles) to bottom (2125 cycles). 

 After one pattern is executed the commutator switches from one re- 

 ceiver to the other. The twelfth tone is omitted to provide time for the 

 switching. The complete double pattern is traced in about one-sixth 

 of a second and the camera is operated at a speed which exposes each 

 frame a little longer than one-sixth of a second. 



