ill BELL SYSTEM TECUXICAL JOURNAL 



troubles whirli tend to change the normal impedance characteristics. 

 The omission of loading coils or the reversal of one loading coil wind- 

 ing, the installation of intermediate apparatus or of emergency cable, 

 etc., cause impedance irregularities which are very detrimental to 

 telei)hone repeater operation. The effect of these irregularities on an 

 aliernatiiig current is to reflect some of the current back towards 

 the sending end, this reflected current either adding to or subtracting 



1800 r 



1600 t 



Fig. 17 



from the current entering the line. This effect can be observed in 

 impedance measurements by peaks and hollows in the eff'ective 

 resistance and inductance curves. 



I'ig. 18 shows two resistance ciu\es of measurements made on a 

 loaded No. 104 copper circuit (No. 12 N. B. S.), Curve .4 being for a 

 condition where two consecutive loading coils were missing and 

 Cur\e B for the condition after these coils were connected back in 

 the circuit. The small irregularity in Curve B was due principally 

 to the irregularity introduced by the use of a 1,500 ohm termination 

 when making the ineasurement. The distance in miles from the end 

 of the circuit at which the measurements were made to the irregu- 

 larity caused In- the missing loading coils is given fairly accurately 

 b\' the fdrmula: 



where 1' i> ilie velociiy of the measuring current in miles per second 

 for the panic iilar l\|)e of circuii tested and (/a— /i) the average differ- 

 ence in fre(iuencies between successive peaks of Curve A. For the 

 type of circuii on which the measurements shown on Fig. 18 were 



