1909] 



on Researches in Radiotelegraphy . 



671 



logarithm of the ratio of the amplitudes of two successive oscillations 

 in the train. 



To obtain very sharp tuning we have therefore to employ either 

 undamped oscillations or very feebly damped oscillations in the 

 transmitter, and also a receiving circuit in which there is as little 

 dissipation of energy by resistance and other causes as possible. It 

 is then possible to cause a change of even less than one-half of one per 

 cent, or five parts in 1000 in the wave-length of the received waves 

 to cease to actuate the receiver. This means that we can distinguish 

 between two waves 1000 and 1005 or 1010 feet in length respec- 

 tively, and that our receiver may be tuned to respond to one and not 

 to the other. The persistent or undamped oscillations created by 



I ,0 



•S 50 



.§ 40 

 8 



Percentage Variation from Exact Tuning. 

 Fig. 14.— Resonance Curves. 



the arc transmitters have therefore an advantage in this respect 

 over spark transmitters, in that the damping or decrement of the 

 transmitter is less ; but it should l)e borne in mind that the damping 

 of the receiver circuit has also a large influence on the form of the 

 resonance curve, and that good isolation cannot be obtained unless 

 the receiving circuit also has a small decrement. Under favour- 

 able conditions Ave can employ a sending key, which does not interrupt 

 the production of the electric waves at the sending station, but simply 

 alters the wave-length slightly by about ^ per cent. If, then, the 

 corresponding receiving station has a feebly damped receiver, this 

 change will l)e sufficient to cut up the continuous record or telephone 

 sound at that station into Morse dots and dashes and so transmit 



