944 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



bination to reduce the power level at their output to one milliwatt. The 

 combination of the nine far-near pad control relays remaining operated 

 after the adjustment is finished will be translated later to measured loss 

 of the intertoll trunk in the far to near direction. After about 3 seconds 

 the far end removes the test power and pauses for a short interval. This 

 completes Step 2. Each end then prepares for Step 3. 



Steps 



For Step 3 the near end retains the far-near amplifier and the setting 

 of the far-near receiving pads and adds a near-far amplifier and a set of 

 near-far receiving pads in tandem in the input circuit to the amplifier- 

 rectifier. The far end, after the short pause, again sends one milliwatt 

 but this time it sends through the transmitting pad which was adjusted 

 in Step 1 to represent the near-to-far trunk loss. The near-far receiving 

 pads at the near end are now automatically arranged to reduce the power 

 level at their output to one milliwatt. 



In the adjustment of Step 2 the over-all loss, including the trunk in 

 the far-to-near direction, the far-near amplifier and the far-near receiv- 

 ing pads, was made db. Consequently, the net loss being measured in 

 Step 3 is simply that of the transmitting pad at the far end, which is the 

 same as the trunk loss in the near-to-far direction. Therefore the com- 

 bination of the 9 near-far pad control relays remaining operated after 

 Step 3 is finished can be translated to measured loss of the intertoll trunk 

 in the near-to-far direction. After about 3 seconds the far end will re- 

 move the test power to complete Step 3 and it will then pause for a short 

 interval before proceeding with Step 4. 



At the near end there are also two sets of check pads, not shown, which 

 are associated with the far-near and near-far receiving pads, respectively, 

 as indicated in Fig. 4. During Step 2 and Step 3 the near end makes the 

 trunk check previously described to verify the accuracy of the pad loss 

 settings and, in addition, in Step 3, rearranges its circuit in the manner 

 shown in Fig. 5 for the loop check. Thus at the near end the two sets of 

 check pads, the far-near and near-far amplifiers, and the two sets of 

 receiving pads are all connected in tandem for the loop check. 



During the short pause following Step 2 and Step 3 the far end re- 

 connects its amplifier and amplifier-rectifier as shown for Step 1 in 

 Fig. 6. If the near end is unsuccessful in the trunk check in Step 2 or 

 in either the trunk check or loop check in Step 3, it will restore the 

 circuit to the original condition at the beginning of Step 2 and will also 

 send a short spurt of test power to the far end as shown for Step 1 in 

 Fig. 6. This reoperates the measuring relay (m) at the far end momentar- 



