824 



ELECTRICAL METHODS 



[Chap. 10 



mitter is behind the operator and emits an approximately vertical field. 

 The receiver, equipped with a sensitive galvanometer, is forward and so 

 adjusted that either a maximum- or medium-size scale deflection is ob- 



3f S 30 5 X 6 30 



Fig. 10-135a. Circuit of Fisher Metallascope, with combined transmitter and 

 receiver (after Chapel). {R2, 5 ohms, 1 W.; R^, 2 ohms, 1 W.; 1, milliammeter (0-1); 

 2, R.F. choke, 1500 turns No. 34ECC; 3, 1 megohm; 3A, 3 megohms; 4, 0.1 megohm; 

 5, 0.0005 mfd., fixed; 6, 0.006 mfd., fixed; 7, 0.001 mfd., fixed; 8, to 0.0005 mfd., 

 trimmer adjuster; 8A, 0.00025 mfd., fixed; 9, push-pull switches; 10, phonetip 

 jacks.) 



-lZ"3e"^ 6 JO i JO 6 so e JO 7 30_^ 



Fig. 10-1356. Circuit of Fisher Metallascope, separate transmitter, and receiver 

 (after Chapel). R^, 5 ohms, 1 W.; R^, 2 ohms, 1 W.; 1, milliammeter; 2, R.F. choke, 

 1500 turns. No. 34ECC; 3, 1 meg. resistor; 3A, 3 meg. resistor; 4, 0.1 meg. resistor; 5, 

 0.0005 mfd., 1 W., fixed; 6, 0.006 mfd., 1 W., fixed; 7, 0.001 mfd., 1 W., fixed; 8, to 

 0.0005 mfd. trimmer adjuster; 8A, 0.00025 mfd., 1 W., fixed; 9, push-pull switches; 

 10, tip jacks for phones.) 



tained on barren ground. A decrease in scale deflection then indicates the 

 presence of a metallic body. The depth penetration of the high-frequency 

 treasure finders, for a medium-size metal chest, is probably not in excess 

 of 6 to 7 feet. 



