176 AUSTIN AND GRIMEJS: BEAT RECEPTION 



received current in the antenna, instead of proportional to the 

 square, as in the non-oscillating tube, the crystal, electrolytic, 

 etc. 



Recently experiments have been made which prove that the 

 linear response law holds for tubes and also for crystal detectors 

 when local oscillations are produced by a heterodyne. Dr. 

 J. M. Miller has suggested that the linear law might not hold if 

 the local oscillations were very weak, for example, if excited by a 

 heterodyne with very loose coupling, but experiment shows that 

 even here there is linear proportionality within the errors of 

 observation. 



Introduction of Resistance in the Oscillating Grid Circuit. — 

 It was discovered in 1915 that if an oscillating vacuum tube 

 (autodyne) be coupled to an antenna or loop, any amount of 

 resistance can be introduced in the secondary circuit without 

 reducing the strength of signal, provided the back coupling be 

 strengthened so as to keep the local oscillations at the same 

 strength. This resistance may amount to many thousand 

 ohms, while a small fraction of this resistance, if placed in the 

 antenna or loop circuit, will reduce the signal to silence. Re- 

 cently it has been found that the same is approximately true 

 with a plain vacuum tube, and even with a crystal detector, 

 when excited to local oscillations by a heterodyne. 



In the early experiments the phenomenon was ascribed to a 

 negative resistance action, but this is hardly possible, since the 

 grid circuit is out of tune with the signal, and of course the ex- 

 planation could hardly be applied to the heterodyne or crystal. 

 As a consequence of the above facts, it follows that with an os- 

 cillating receiving tube connected directly in a loop, the strength 

 of received signal is independent of the loop resistance. This 

 has been verified by experiment. 



Effect of Varying the Capacity-Inductance Ratio in Os- 

 cillating Receiving Tube Circuits. — As the vacuum tube is a 

 voltage operated detector of signals, it has been supposed that 

 the sensibility will be greater, the greater the inductance capacity 

 ratio in the grid circuit. It was reported in 191 7 (Proc. I. R. E. 

 5: 245. 191 7) that the sensibility was independent of this 



