598 



EXPLORATION GEOPHYSICS 



A schematic wiring diagram for high and low frequency apparatus is 

 shown in Figure 374. When the high frequency coil is used, the detector 

 is of the oscillating type in order to provide a heterodyne signal for 

 audibility and increased sensitivity. For low frequency work, the detector 



t—OP PO- 

 LO- 



Hh 



rOC GO- 



: ijsmpm 



Fig. 374. — Wiring diagram for electromagnetic direction-finding apparatus. 



tube functions merely as an audio-frequency amplifying tube. If desired, 

 pentode tubes can be employed in the amplifying stages for greater 

 amplification. 



OIRECTION- 

 FINOING 

 COIL 



Fig. 375. — Field surrounding a simple conductor in a homo- 

 geneous medium. (A.I.M.E. Geophysical Prospecting, Tech- 

 nical Paper 134, 1928.) 



Applicability of Directional Coils: Field Surrounding a Simple 

 Conductor in a Homogeneous Medium. — The field surrounding a small 

 diameter conductor in a homogeneous medium will travel outward from 

 it in the form of concentric circles or envelopes, as depicted in Figure 



