A SINGLE SIDEBAND MUSA RECEIVING SYSTEM 329 



only when a change in the angle of reception is required. Connected 

 to the vertical drive shafts by the horizontal shafts are the three 

 diversity cam switches and the monitoring cam switch. 



The incoming carrier in the monitoring branch D is amplified in 

 such a manner as to keep the average peak amplitude constant. It is 

 then rectified, and applied to the vertical deflection plates of a cathode 

 ray oscilloscope in the same manner as in the experimental equipment, 

 the monitoring cam switch being provided with a set of contacts and 

 resistances which act as a sweep circuit for the horizontal plates of the 

 oscilloscope. 



The rectified signal from the monitoring rectifier is also connected 

 through the auxiliary cam switch, the monitoring cam switch, a high 

 resistance, and the range setters, to three separate banks of condensers, 

 each consisting of 44 four-microfarad condensers. The condensers in 

 each bank are connected successively to the rectifier circuit once each 

 second for a short period by the cam switch so that each is charged 

 at a rate depending upon the amplitude of the received signal for a 

 particular phase shifter position. A vacuum tube voltmeter is con- 

 nected successively across each condenser of a bank. When one 

 condenser becomes charged to one-half volt or more during the 

 preceding second the vacuum tube voltmeter operates a relay. With 

 the Branch A, B, and C voltmeters this results in a relay corresponding 

 to that particular condenser being locked up and all the condensers in 

 that particular bank being discharged. The operation of the second 

 relay causes the motor of the corresponding diversity branch to start 

 and turn in the right direction so that the branch phase shifters are 

 adjusted with the least movement to the position corresponding to 

 the relay, at which point a contact in the diversity cam switch trips 

 the relay and stops the motion. 



If no further control were provided all the diversity branch circuits 

 would be set in the same position and consequently no diversity action 

 would be obtained. To prevent this the range setters, A, B, and C, 

 have been provided which are operated manually to limit the angular 

 range of operation of each diversity branch. These switches merely 

 short-circuit the condensers of a particular branch in the range which 

 it is not desired to use. Since the short-circuited condensers do not 

 acquire a charge the automatic adjusting equipment will never move 

 the phase shifters to a position corresponding to a short-circuited 

 condenser in that particular branch. 



In setting the range switches when using delay equalization it is 

 necessary to know what the condenser position is which corresponds 

 to the highest angle which it is possible to receive at the particular 



