428 



BELL SYSTEM TECHMCAL JOLRXAL 



( ommunication have l)rouglil forlh more useful applications of the j)rinciple 

 of electrical resonance than the examples cited above. But let us now turn 

 to radio. Here the application of resonance is elemental and fundamental. 

 But not so in the beginning, however. When Marconi brought his em- 

 bryonic outfit to England in 1896 and demonstrated his best accomplish- 

 ments over the next three or four years, the problem of selectivity was 

 non-existent. Further, the type of detector then available, the Branly 



U u 



Fig. 4 — First tuned radio transmitting and receiving antennas, as proposed in Lodge's 

 British patent of 1897; tuning accomplished by inductance coils between the capacit\- 

 areas li and //'. 



metal tilings coherer or modifications thereof, was responsive to electric 

 waves varying considerably in frequency, so the need of tuning to obtain 

 sensitivity was at first not actually imperative. This detector was con- 

 nected directly in the untuned antenna circuit. Then the ambition to 

 increase the distance of reception led to a search for greater sensitivity, 

 and as a first step (1898) Marconi introduced into the receiving circuit his 

 "jigger", or oscillation transformer.-' The primary, of few turns, was in 

 the antenna circuit; the tuned secondary, wound with an eye to the reduction 

 of capacity, stepped up the voltage and applied it to the coherer. Here 

 no adjustable tuning was provided, but instead there were different jiggers 

 wound to suit the transmitted wave-lengths employed and thus secure the 

 maximum effect. 



It was foreseen in the earlv davs of radio that if it were ever to become a 



