NEW TRANSMISSION MEASURING SYSTEMS 



11 



of its excellent performance the 1000-cycle generator shown in Fig. 5 

 will be used generally in the toll plant for 1000-cycle testing. 



Figure 7 shows several positions of the transmission test board now 

 widely used for measuring toll telephone circuits. Introduced in 1926, 

 it preceded the development of the reverse feedback amplifier-rectifier 

 and the transmission measuring set used in this board is therefore of 

 the comparison type in which the results are read fron calibrated 

 dials. Testing power is provided by a variable frequency oscillator 

 from which frequencies in the voice range can be obtained. The size 

 of this equipment precluded its being installed in test boards which 

 contain the circuit terminals so that trunks between the measuring 



Fig. 8 — New amplifier rectifier for general use in toll transmission maintenance. 



equipment and these terminals are necessary. In large offices a num- 

 ber of these transmission test boards have been provided. 



Figure 8 shows the new reverse feedback amplifier-rectifier used 

 with the latest toll transmission measuring system. This simple panel, 

 which is about one-fourth the size of the measuring set employed in 

 the test board shown in Fig. 7, contains everything required at the 

 receiving end of a circuit excepting the meter and the keys for changing 

 the measuring range. With its associated meter and keys, it is less 

 than one-half as expensive as corresponding elements in the trans- 

 mission testboards. It can be used with the variable frequency 

 oscillator shown in Fig. 7 or with the 1000-cycle machine shown in 

 Fig. 5. 



The meters used with this amplifier-rectifier have a specially de- 

 signed magnetic circuit which gives an evenly spaced scale on the 



