Chap. 10] 



ELECTRICAL METHODS 



823 



Probably the majority of present-time treasure finders employ fixed 

 combinations of high-frequency transmitters and receivers. Arrange- 

 ment and operating principle are the same as in the low-frequency trans- 

 mitter and receiver combinations, except that an R.F. carrier is used for 



Fig. 10-134a. Single energizer, double pickup coil detector (after Theodorsen). 



Coil 



Benentor 



Smfch 



tnerqizinfCt il^ 



Ampl/fitr 



OetKhr 



Resonahnq Condenser 



Fig. 10-1346. Modification of metal detector of Fig. 10-134a (after Joyce). 



the 1000 cycles. In the Fisher Metallascope and the Barret Terrometer the 

 transmitter and receiver are arranged as on the lower right of Fig. 10-135a. 

 A circuit diagram of the Metallascope is given in Fig. 10-135a. Fig. 10-1356 

 shows a more elaborate type of the Fisher Metallascope for operation as 

 separate transmitter and receiver. In the Barret Terrometer the trans- 



