330 BELL SYSTEM TECHNICAL JOURNAL 



frequency being used. The short circuit will then be removed from 

 this condenser and from the condensers representing successively lower 

 angles in Branch A until it seems probable from the recorder or cathode 

 ray oscilloscope pattern that a good signal will be received in that 

 branch. The remaining condensers in that branch are left short- 

 circuited. The short-circuits are then removed in a like manner 

 from part of the remaining range for Branch B and in the remainder 

 of the range for Branch C, the best division line being determined 

 from the cathode ray oscilloscope or recorder pattern. This procedure 

 is necessary inasmuch as branch A is used for a reference in adjusting 

 the audio frequency delay compensation and must always have a 

 satisfactory signal if that equipment is to operate. 



When using the automatic branch selector other settings of the 

 range switches are possible. One arrangement is to allow one branch 

 to stop on even numbered contacts for a part of the range and another 

 branch to stop on the remainder of the even numbered contacts. 

 The third branch may then stop on any odd numbered contact. This 

 permits two diversity branches to be set in the range of maximum 

 signal. A difference of one contact has been found sufficient to give 

 satisfactory diversity action in most cases and the recorder pattern 

 always shows that the signal is more than one contact wide. The 

 third branch is free to follow a signal in another part of the range, 

 which may grow to be the strongest at any moment. 



In order to improve the accuracy of this equipment and reduce the 

 maintenance of the monitoring cam switch an auxiliary high speed 

 cam switch is used which operates 44 times faster than the main switch, 

 closes just after each contact of the monitoring switch, and opens just 

 before each contact opens. The charging time for all condensers in 

 a given bank is thus determined by the same cam and set of contacts. 



To prevent over-running on the diversity branches from mechanical 

 inertia a special motor is used. This motor is similar to the one used 

 for automatic delay adjusting equipment. 



At times there may be only one angle at which a satisfactory signal 

 may be arriving. It is possible to get diversity action at these times 

 by setting the diversity branches on opposite sides of the average 

 angle of best reception. Provision is made for doing this with the 

 automatic equipment by allowing one bank of condensers and one 

 voltmeter relay to control all three diversity branches and then 

 mechanically off-setting the phase shifters of two branches by means 

 of adjustable couplings in the diversity cam switch drives. 



It will be seen that to obtain accurate operation of the automatic 

 angle adjusting equipment it is necessary that the charging voltage 



