288 BELL SYSTEM TECHNICAL JOURNAL 



and the fluxmeter. The 2000 and 4000 ohm resistances in this circuit insure distor- 

 tionless input voltage to the rectifier. The fluxmeter is damped by an 80 ohm shunt. 

 The needle, which was initially at zero, will therefore move, its deflection being pro- 

 portional to I idt. 



Time in Seconds— 10-14: 



Switch G is closed by the cam on the revolving disc N and locks relay A . 



Contact 1 of relay A is opened and opens the rectifier fluxmeter circuit, thereby 

 iiringing the fluxmeter needle to a stop. 



Contact 3 of relay A is closed and makes the battery X charge the 10 /z/ condenser 

 through the 50,000 ohm resistance. 



Time in Seconds — 11-14: 



The cam Z presses the needle point down on the scale OS. Now, one of three 

 things will happen. 



1. Static has decreased since the last period, so that the needle point will make 

 contact with the metal strip OP and close the following circuit: Battery X, needle of 

 fluxmeter, winding of relay C, switch H and switch G to battery A'. Relay C is 

 therefore closed and its closed contact 2, together with contact 3 of the open relay D 

 will start the gain control motor. After approximately half a turn of the gain control 

 or motor shaft Y the needle point is lifted from OP by the rotation of the cam Z, but 

 relay C stays closed due to the fact that it is self-locking through its contact 1, so that 

 the shaft Y continues turning until the switch E is opened by the disc T. This opens 

 the self-locking circuit of relay C. Relay C therefore opens and the gain control 

 motor stops after the shaft Y has made exactly one complete turn and increased the 

 gain of the set one step (4 Transmission Units or 1.58 times). Notice that the opening 

 of the needle point contact does not break any current, due to the use of self-locking 

 relays. This preserves the needle point contact. 



2. Static has not changed since the last period. The needle point will now touch 

 the insulating strip PQ and nothing else will happen, i.e., the gain of the set remains 

 unchanged. 



3. Static has increased since the last period so that the needle point now will make 

 contact with the metal strip QS and close relay D and as in case 1 the motor will start 

 and turn the shaft Y one turn, but this time in the opposite direction, i.e., the gain 

 of the set is decreased one step. 



Time in Seconds — 14: 



Switch G is opened again by the revolving disc N and opens relay A. Contact 2 

 of relay A is closed and will discharge the 10 m/ condenser through the fluxmeter, 

 thereby bringing the needle back to zero. (Notice that the time constant of this dis- 

 charge circuit is 10000 x 10xlO-« = l/10 seconds.) 



Time in Seconds — 15: 



A new period has started. 



The purpose of the switches M and H is to stop the motor when the gain control 

 switch arm has reached the end of the scale. 



The recorder is of such recent development that no comprehen- 

 sive data are yet available. 



Fig. 4 shows part of an actual record of static received on a set 

 tuned to 57.5 — 59.5 kilocycles. The ordinates represent the attenua- 

 tion of the gain control of the set and it is to be remembered that the 

 gain of the rest of the set is constant. The curve shows that the 

 static power on the morning of October 30 changed more than 10,000 

 times. The point B on the curve gives the effect of inducing a local 



