AUTOMATIC TESTING OF INTERTOLL TRUNKS 947 



noise condition, or a 120 TPM flashing signal if the far-end has registered 

 a high noise condition. The near end is thus advised of the results of the 

 noise check at the far end. The test frame, on receipt of this signal, 

 causes the Teletypewriter to complete the record and then breaks down 

 the connection and advances to the next trunk. 



The amplifier, which precedes the amplifier-rectifier includes a net- 

 work which provides FlA noise weighting during the noise check. The 

 amplifier-rectifier is adjusted in the noise checking condition (that is, 

 when its gain is increased) so that a noise indication will be given when 

 the noise exceeds about 35 or 40 or 45 dba. Since this test is intended 

 only as a rough check to detect any abnormal noise condition, the noise 

 rejection limit used in any given office will be governed by the types of 

 intertoll trunk facilities terminating in that office. Xo correction is made 

 for the measured loss of the trunk at the time of the noise check, hence 

 the noise is checked at the receiving switchboard level. For the usual 

 types of noise the results of the noise check agree roughly with those 

 which would be obtained by an average observer using a 2-B Noise 

 Measuring Set for a similar "go-no go" type of check. 



As is evident from the previous description, each end is expected to 

 complete the various steps of its functions within allotted time intervals. 

 Timing intervals at the far end ai'e controlled by a multivibrator circuit. 

 Timing at the near end is controlled by a similar multivibrator in 

 the intertoll trunk test frame. To insure that the test circuits always 

 perform as they should and that the timing circuits are functioning 

 properl}^, checks are built into the circuits so that anything which pre- 

 vents the successful completion of a 2-way measurement on schedule 

 causes the automatic outgoing intertoll trunk test frame at the near end 

 to stop, hold the trunk busy and sound an alarm while awaiting attention 

 of the attendant. The transmission measuring and noise checking circuit 

 at the far end will, however, release itself from the test line so that it will 

 be free to handle other calls. 



Semi- Automatic Test 



One-milliwatt test power supply outlets ha\'e been provided in toll 

 offices for some time for making a one-way transmission measurement 

 freciuently referred to as a code 102 test. A test board attendant can reach 

 the one milliwatt test power supply l)y pulsing forward code 102 or bj^ 

 requesting an operator at the distant end of a manual trunk for a con- 

 nection. The test power is applied at the distant end for about 10 seconds 

 diu-ing which time the attendant measures the loss in the receiving 

 (far-to-near) direction. This is a fairly fast semi-automatic test luit. of 



