948 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



course, has the disadvantage that it is a one-way test and cannot be 

 used for all purposes. 



In order to provide a semi-automatic two-way test, the far-end equip- 

 ment is arranged so that a test board attendant can make a code 104 

 measurement unassisted. This measurement is carried out in 3 steps as 

 shown in the lower portion of Fig. 6. 



Step 1 



The attendant connects a test cord to the test jack of the intertoll 

 trunk and pulses forward code 104 using his test position dial or key set. 

 When the far end is ready, it returns an off-hook signal which retires 

 the test cord supervisory lamp. He then connects the other end of the 

 cord to the one milliwatt test power supply. The far end then adjusts 

 the receiving and transmitting pads in the same way as for a full auto- 

 matic test. After about 3 seconds the attendant disconnects the test 

 power and at that time observes the cord supervisory lamp ; a single flash 

 indicates that the far end was unsuccessful and is requesting a second 

 trial. If the supervisory lamp remains steadily dark he connects the 

 cord to the receive jack of his transmission measuring circuit to prepare 

 for Step 2. 



Step 2 



The far end will pause about 2 seconds after the attendant removes the 

 test power to give him time to prepare for Step 2. During this pause the 

 far end will not receive a short spurt of test power as in the case of a full 

 automatic test. Consequently, after the 2 second interval the far end 

 will return one milliwatt for 10 seconds on a semiautomatic test to give 

 the attendant time to complete a measurement. The received power is 

 read directly on the meter of the transmission measuring circuit and is 

 the loss in the far-to-near direction. When the far end removes the test 

 power, the meter reading drops back to the position of no current (in- 

 finite loss) and at that time the attendant observes the cord lamp. A 

 single flash at this time is an "add 10" signal and indicates that 10 db 

 should be added to the next measurement. A steady dark lamp indicates 

 that the next measurement should be recorded without correction. 



Step 3 



After about 2 seconds delay to give the attendant time to record the 

 first measurement, the far end again returns 1 milliwatt, this time 

 through the transmitting pad set up in Step 1 . The meter now reads the 



