AUSTIN AND GRIMES: BEAT RECEPTION l^^ 



ratio. Recent experiments made on Nauen with inductances 

 varying from 2.5 mh. to 36 mh. again showed no change in sen- 

 sibiHty, provided the local oscillations were kept at the optimum 

 value. The telephone current appears to be proportional to the 

 square root of the antenna watts. 



Heterodyne, Autodyne and Sensitizing Circuit. — Commander 

 A. H. Taylor and also Mr. Israel have found that for long waves 

 the heterodyne with vacuum bulb is more sensitive than the 

 autodyne. The explanation being that with the heterodyne 

 the secondary can be set exactly on the signal wave-length, 

 while with the autodyne it must be detuned to produce the beats. 



In the Research Laboratory it has been found that there is no 

 difference in sensibility, provided the optimum coupling be- 

 tween the primary and secondary is maintained in both cases. 

 With a loose coupling as used by Commander A. H. Taylor, 

 the signal with heterodyne is stronger unless a sensitizing cir- 

 cuit is used with the autodyne. The sensitizing circuit reported 

 in 1915 (Proc. I. R. E., 4: 251. 1916) is a circuit consisting of an 

 inductance and condenser so coupled to the secondar}-^ that the 

 latter is given two free wave-lengths, one of which corresponds 

 to the wave-length of the incoming signal, while the other gives 

 the beat frequency. With the sensitizing circuit the autodyne 

 is equal to or better than the heterodyne in sensibility at any 

 coupling. Probably at the optimum main coupling the antenna 

 itself acts to a certain extent as a sensitizing circuit. 



While the sensitizing circuit has the advantage of being far 

 simpler than the heterodyne, it is found that the heterodyne is 

 less subject to interference. 



Regeneration of Spark Signals. — It has been suggested that 

 possibly the strengthening of spark signals observed with the 

 autodyne when the back coupling is closed to a point just before 

 the note is roughened by the local oscillations may be due to 

 very weak oscillations not strong enough to effect the note. 

 Experiments have, therefore, been made with weak heterodyne 

 coupling to see if the same phenomenon could be found as with 

 the autodyne. No strengthening in the spark signal was ob- 

 served until the note was roughened. 



