INTERTOLL TRUNK NET LOSS MAINTENANCE 969 



curves for distribution grades from 0.38 db to 3 db are shown on the 

 template. The smallest envelope having not over 8 per cent of the grand 

 total of measurements outside of the envelope represents the approxi- 

 mate distribution grade. In the example, this is the 1 db curve, for which 

 22 points or 4.1 per cent of the total fall outside of the curve. Using a 

 cut-out template corresponding to the distribution grade, a trace is 

 placed on the stroke sheet, as shown on Fig. 6. 



In cases where the small number of measurements or the character 

 of the dispersion makes it difficult to fit the data with any of the en- 

 velope curves of the template, RMS methods of determining the distri- 

 bution grade and bias afford a better estimate. In the example on Fig. 

 6, the bias is thus found to be —0.18 db and the distribution grade is 

 found to be 1.14 db. 



When the automatic transmission test and control circuit described 

 in the companion paper is used for measuring net losses, the bias and dis- 

 tribution grade can be determined more quickly and easily. This circuit 

 measures the transmission in terms of deviations from the specified loss 

 and records these by a teletypewriter. In addition, registers indicate the 

 total number of measurements and the number of deviations falling in 

 the ^'2 db bands shown on the stroke chart. The final strokes for each 

 band can thus be placed on the chart directly without the need for 

 stroking each measurement. From this point on, the analysis and the 

 final tracing of the envelope curve which is selected are the same as in 

 the case illustrated by Fig. 6. 



EFFECTIVENESS OF OVER-ALL TRUNK TESTS AND ANALYSES 



Simple Layouts 



With simple trunk layouts particularly those involving one voice- 

 frequency or carrier link, plant forces have been able to use over-all 

 trunk measurements and analyses as a direct aid in maintenance. Early 

 field trials of the stroke chart method were made at two operating tele- 

 phone company offices. The testers made up stroke sheets from their 

 routine measurements and interpreted the results to find clues as to 

 what to investigate. Stroke sheets made at successive routine testing 

 periods also showed them what improvements they were obtaining in 

 the operation of the trunks. 



Both offices started with distribution grades of about 1.8 db and with 

 biases of about ^^ db. The trunk plant was then given a thorough cleanup 

 and realignment more rigorous than that called for in the maintenance 

 practices at the time. Similar rigorous circuit order tests were followed 



