12 



BELL SYSTEM TECHNICAL JOURNAL 



meter.^ A conventional meter would have large db divisions at one 

 end of the scale and small ones at the other. 



When a direct reading transmission measuring set is used to make 

 measurements over a wide frequency range, it is essential that the 

 response be the same at all frequencies. Variation of response of the 

 new feedback amplifier-rectifier with frequency is so small that it can 

 be calibrated with 1000-cycle current and measurements made over a 

 wide frequency range without recalibration. 



From the standpoint of efftciency, the best place for making trans- 



Fig. 9 — Projection meter as used for measuring transmission at a secondary testboard. 

 The meter is being read by the third man from the right. 



mission measurements on complete toll circuits is at the test board 

 to which all troubles are reported by the operator and where overall 

 signaling and other operating tests are made. Practically all of the 

 space in this board is taken up by jacks on which the circuits terminate 

 so that the older types of measuring set could not be provided at this 

 point. The new arrangement is ideal for application to this type of 

 board since all that is required in the board are the meter and a few 

 jacks or keys for controlling its range. This type of measuring device 

 can be applied equally well to new and existing boards of various types. 

 This feature is of particular value as the maximum efftciency of high- 

 speed measuring systems can be obtained only when all test boards 



