ELECTRICAL TESTS AS'I) THEIR .II'I'LICITIOXS 



373 



ina<k'. till" vtlmity of prop;>Kati()n is approximately 54,700 miles per 

 sccoiul. The average dilTerenre in frequencies between peaks on the 

 curve is al>out SSO c\cles. AjipKinR lliese tinures in the aliove formula* 

 gives the distance out to the irregularity as 70 miles. In this case 

 the ninth and tenth loailing coils were missing, which gave a very 

 close ciieck to the compniefi 70 mile figure. A great deal of use is 



Fig. 18 



made of measurements of this kind in locating trouliles which alTect 

 telephone repeater operation and in directing the work of liiieinen in 

 clearing these troubles. 



A further use which can be made of a bridge similar to the one just 

 descriited is in the location of impedance unlialance conditions which 

 tend to increase crosstalk and noise between circuits. This is a 

 fairly recent development and a description of it will be included in a 

 paper to be published later. 



(4) 7V5/5 of Balance of Apparatus. Certain t\pcs of equipment 

 assfx-iated with telephone circuits are made up of apparatus which has 

 to be closely balanced with respect to the various parts in order that 

 the equipment when connected to telephone circuits will not cause 

 unbalances in these circuits. Any unbalances introduced in this 

 way will increase noise and crosstalk in the same manner as impedance 

 unbalances in the line circuits themselves. Cord circuits, phantom 

 repeating coils, compf)site sets, etc., are examples of the types of 

 equipment in which unbalances in the apparatus may affect noise and 



