MARCH 4, 1921 AUSTIN: WAVE FRONT ANGLE IN RADIOTELEGRAPHY 103 



a distance of more than a quarter of a mile made this an ideal location 

 for the work. The two collector wires of the antenna were stretched 

 in a straight line by the spreader shown in figure 1 . This was con- 

 structed of wood with its joints fastened by wood dowel pins and a 

 few brass screws. The scale for determining the angle was aligned 

 with the wires by means of a transit. All the apparatus, with the 

 exception of the primary inductance and condenser, was contained 

 in a box covered with fine mesh copper screen. This box was sup- 

 ported by ropes in order to reduce the capacity between the receiving 

 set and the mast. It was also found necessary to shield the telephone 

 leads and ground the head band to the copper screen surrounding the 

 apparatus. 



At first a certain asymmetry was observed in the reading when the 

 antenna was turned through 180 degrees. This was apparently due 

 to an asymmetry in the capacity between the grounded shield and the 

 two collector wares, and was corrected by connecting a small com- 

 pensating condenser between one side of the primary and the shield. 

 This condenser also produced a much sharper minimum. Its action 

 is similar to that of the compensating condenser frequently used with 

 the ordinary radio compass. Figure 2 shows the method of coupling 

 the primary to the secondary, the magnetic field passing with some 



loss through the shield while 



. r, f i f, I, f, r; i ; r, rj f; f; rj ij r ; ^ r, ^ ( i| r; < r f| 



SHIELD 



1 1 , 



/iMPLIFIEff 



TO DETECTOR 



'n<iii'<V,<,'/,i ' ,'<',W,'>M'>i<t ' 



Fig. 2. Method of shielding circuits. 



the static field is cut off". The 

 primary and compensating con- 

 densers were supported by cords 

 in order to reduce the capacity 

 between them and the mast. 

 The antenna collectors and all 

 the instruments were thor- 

 oughly insulated. The revers- 

 ing switch in the primary in 

 figure 2 allowed the collectors 

 to be reversed without actually turning the antenna through 180 de- 

 grees. With strong signals it was necessary to turn the primary coil 

 parallel to the plane of the oncoming wave and correctly adjust the 

 compensating condenser in order to prevent the signals being heard 

 with the collectors disconnected. This precaution is of importance, 

 since any signal picked up by the instruments not only blurs the 

 minimum but displaces it. 



It was originally intended to continue the observations for several 

 months so as to make an extended series of measurements on stations 



