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



in this case the waves passed over land for the whole distance, which 

 might be expected to produce a marked tilt in the wave front. The 

 table shows, however, that the wave front according to the observa- 

 tions is almost exactly vertical. 



Night observations 



On account of the well known shift of the apparent direction of 

 New Brunswick as observed in Washington at night, an attempt was 

 made to discover whether there was a similar shift in the angle of the 

 wave front. This was of interest since the most usual explanation 

 of the apparent shift in direction assumes the arrival at the recei^^ing 

 station of a portion of the energy by reflection from the upper atmos- 

 phere. During the observations in the autumn of 1919 with the pre- 

 liminary apparatus, experiments were carried on throughout one night, 

 while at the same time the apparent deviation in the direction of New 

 Brunswick was obser^^ed on the radio compass. No certain deviation 

 of the wave front was found, while the apparent direction of the sta- 

 tion shifted at times by as much as 30°. Observations were also made 

 every ten minutes from 5.45 p. m. to 11.45 p. m. on June 14, using 

 the final apparatus, but no certain deviation in the wave front angle 

 was observed at any time. ^ 



Comparison of the vertical and h-orizontal intensities of the wave 



The problem of the wave front angle may be attacked in another 

 way. If we are able to measure the received currents from a distant 

 station in an ordinary vertical antenna and in a ground antenna, we 

 can calculate the wave front angle since the electric intensity (volts 

 per meter) must be proportional to the projection of the wave on the 

 vertical and horizontal planes.'^ Observations have been made which 

 show that an antenna 2000 feet long in fresh water receives the signals 

 from Nauen at a wave length of 12,500 meters with the same intensity 

 as a vertical antenna having an effective height of 50 feet, the resis- 

 tance of the vertical antenna system being approximately 50 ohms 

 and the water wire approximately 100 ohms. 



Since the strength of the telephone currents is proportional to the 

 square root of the antenna watts, the field expressed in volts per meter 

 is twenty-eight times as strong in the vertical plane as in the hori- 

 zontal, which would correspond to a deviation from the vertical of 

 approximately 2°. This, it will be seen, lies within the estimated 



^ This method may perhaps be criticized on account of the unknown effects of the earth 

 currents surrounding the ground antenna. 



