MEASUREMENT OF TELEGRAPH TRANSMISSION 



151 



in the received teletypewriter characters from their proper positions 

 are measured in terms of condenser voltages. Indications are afforded 

 of the average distortion and the peak value of the total distortion, 

 the latter being the sum of the bias, characteristic and fortuitous 

 effects. 



SIGNAL 



IN 



LOOP 



DISTRIBUTOR 

 SEGMENTS 



-dh I — ®^ 



JM METER 



TO LOOP 



?= 



REFC.E 



Fig. 4 — Explanatory sketch of start-stop telegraph transmission 

 measuring set. 



The general features of this set will be described in the following. 

 In Fig. 4 a condenser-charging circuit is shown with a distributor for 

 the purpose of timing the charging intervals in the measurement of 

 distortion occurring at transition B. Assume the distributor brush 

 to be traveling in the direction of the arrow after being released by the 

 mark-to-space transition at A by means of arrangements not shown. 

 This same transition causes the relay armature to move to the spacing 

 contact {S) and the condenser to begin to charge from the constant 

 current supply, but as soon as the brush touches the grounded segment 

 the condenser is discharged completely. After leaving the grounded 

 segment the brush travels over an open segment and during this 

 time the condenser accumulates a charge. At transition B, the arma- 

 ture of the relay moves to its marking contact {M) and the voltage 

 of the condenser is compared with the reference voltage (REFC. E) 

 which has been previously adjusted to such a value that if there is no 

 distortion the condenser voltage and the reference voltage will be 

 equal. However, if transition B does not occur at the proper time, 

 because of distortion, the condenser voltage will differ from the 

 reference voltage and a momentary current will flow through the 

 indicating meter {M) in proportion to the amount of distortion. 



