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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 195G 



added in the looped circuit. This reduces the input power to the ampli- 

 fier-rectifier about 0.2 db below that which causes relay (m) to release. 

 Relay (m) will remain operated and fail to pass this check if the com- 

 bined effect of increases in the milliwatt test power supply or amplifier 

 and amplifier-rectifier gains and cumulative errors in the pads exceeds 

 0.2 db gain. By means of the loop check the maintenance forces will be 

 notified whenever the measuring equipment drifts more than ±0.2 db 

 from the initially calibrated setting. 



After the loop check the receixing end restores its circuit to the 

 original connections shown in Fig. 4 and by means of relays not shown, 

 cuts out all of the receiving pad loss. Relay (m) then reoperates. The 

 circuit I'ests in this condition to await the removal of the test power at 

 the sending end. 



When the sending end removes the test power, relay (m) releases. If 

 all accuracy checks have been passed successfully, the receiving end then 

 prepares for the next phase of the test. If, however, the accuracy checks 

 failed in any respect, the receiving end restores its circuit to the original 

 condition at the start of the measurement and returns a signal to the 

 sending end to request reconnection of the test power for another trial. 



Intertoll Trunk Loss Measurement and Noise Check 



An intertoll trunk loss measurement consists of two successive one-way 

 measurements, as described above, one for each direction of transmis- 

 sion. The transmission test call is set up to one of the code 104 test lines 

 in the distant office. If the transmission measuring and noise checking 

 circuit at the far end is already engaged because another call arrived 



CONNECTION 



DURING 



MEASUREMENT 



AND 

 TRUNK CHECK 



CONNECTION 



DURING 

 LOOP CHECK 



19.9 DB 

 GAIN 



RECEIVING 

 PADS 



^VW 



19.9 DB MINUS 

 TRUNK LOSS 



TRANSMITTING 

 PADS 



V/v 



EQUALS 

 TRUNK LOSS 



TRUNK 

 CHECK PADS 



LOOP 

 CHECK PADS 



ONE MILLIWATT 



TEST 

 POWER SUPPLY 



Fig. 5 — Arrangement for loop check. 



