A SINGLE SIDEBAND MUSA, RECEIVING SYSTEM 331 



should be large as compared with the final voltage on any condenser 

 and that the final voltage must be the sum of a number of charges. 

 The time necessary for a condenser to reach the final voltage can be 

 varied from 8 to 45 seconds or longer and successive movements of a 

 diversity branch phase shifter drive will not be oftener than this. 

 Once the motor has started, however, it will move the phase shifter 

 shaft through an angle of 180°, the maximum which would ever be 

 necessary, in 6 seconds. 



Recorder 



In order properly to set the phase shifters manually or to set the 

 range adjusters of the automatic angle adjusting equipment it is 

 necessary to know the phase shifter positions corresponding to the 

 angles at which signals are arriving. The angle monitoring cathode 

 ray oscilloscope shows how the signal amplitude vs. phase shifter 

 position varies from second to second. By using a retentive screen 

 on the oscilloscope it is possible to see the traces for the previous few 

 seconds at the same time as the most recent trace. The traces, 

 however, normally vary appreciably in position of maximum amplitude 

 and it is somewhat difficult to form an opinion from looking at the 

 oscilloscope as to just where to set the diversity branches. By in- 

 tegrating the value of received signal over a number of seconds a 

 better conception can be obtained. 



In addition to the cathode ray oscilloscope it also seemed desirable 

 to have a record available to the operator of the variation of signal 

 intensity with phase shifter position as it changes from minute to 

 minute so that he would not continuously have to observe the oscillo- 

 scope to determine whether the range adjusting switches were set 

 properly. This required one more variable to be considered than the 

 ordinary recorder is designed to register and it was consequently 

 necessary to devise a new type of device. 



The scheme of recording operates in a somewhat similar manner to 

 the automatic angle adjusting equipment. A set of 44 condensers is 

 charged by the incoming signal through the monitoring switch. Each 

 condenser corresponds to a particular position of the phase shifters 

 and consequently with a particular vertical angle of arrival at a 

 particular frequency. A vacuum tube voltmeter is successively con- 

 nected to the condensers until one is found which has acquired a 

 predetermined potential in the order of two volts. A relay in the 

 plate circuit of the voltmeter then operates, causing only that par- 

 ticular condenser to be discharged and making a record on a paper strip. 



The recorder consists of a mechanism for driving a paper strip 5" 

 wide at a constant speed over a drum having a spiral wire on its 



