TABLE IX

PHANTOM REPEATING COILS

IMPEDANCE RATIO
LINE TO DROP 4-3
&8-7 TO 2-1 & 6-5
SUITABLE FOR 20-CYCLE
SIGNALLING
NOT SUITABLE FOR 20-CYCLE
SIGNALLING
Relay Rack Coil Rack Relay Rack Coil Rack
1:1 93-A 75-A 62-A 85-A
1:1.62 93-B 75-B 62-B 85-B
1.62:1 93-F 75-F 62-C 85-C
2.66:1 93-G 75-G 62-E 85-E
1.24:1 93-H    
2.28:1 93-J    
1:1.28    62-F  
1:2.34    62-G  

Page [ 160 ]


The 93 and 75 type coils are identical except for different mounting arrangements. The same is true of the 62 and 85 type coils. In the manufacture of the 93 and 85 type coils, a core made of many turns of fine gaged silicon-steel wire is sawed so as to introduce a gap in the magnetic circuit. This gap is filled with a compressed powdered magnetic material, which while increasing slightly the core's reluctance, gives it a high degre of magnetic stability, preventing permanent magnetization under abnormal service conditions. The two windings for the line side are wound on the core together to give the required high degree of balance, but the drop windings are wound individually. The iron core of the coil is wraped with cotton tape to protect the windings, and after the windings are put in place, the coil itself is given a wrapping of cotton tape. it is then impregnated with a moisture proof compound, placed in its case, and melted resin is poured around it until it is firmly imbedded. The leads are then brought out to the terminal punchings.

The 85 and 62 type coils are made in the same ratios as the 93 and 75 type coils, and have approximately the same electrical characteristics. Their cores are made in the same way as described above, except that the gap in the magnetic circuit is not filled with compressed iron powder. This feature makes these types of coils somewhat more stable and they are therefore especially well adapted for use in circuits on which rapidly changing direct currents are superimposed, such as those involved in high speed teletypewriter service. The same feature, however, tends to make these coils very inefficient at low frequencies and they cannot be used on circuits employing 20-cycle signalling.


 

Taken from

Principles of Electricity
applied to
Telephone and Telegraph Work

L.L. Dept. AT&T Co.
1938 Edition
(Reprinted with corrections January, 1941)