L W4 j 



XXII. A Note on the Relation of the Audibility Factor of a 

 Shunted Telephone to the Antenna Current as used in the 

 Reception of Wireless Signals. By Balth. van dee Pol,' 

 Jim., Doct. Sc. (Utrecht) *. 



IN the measurements of the strength of wireless telegraph 

 signals, it is usual on board ship to employ a shunted 

 telephone receiver and to measure the signal strength by the 

 value of the shunt required to reduce the signal strength to 

 a point at which dots and dashes may be just differentiated. 



Such measurements have been made by Dr. L. W. Austin f 

 and by Mr. J. L. Hogan, Jun.J, to find experimentally the 

 law according to which the received antenna currents vary 

 with the wave-length and distance from the sending station. 



The above results have been criticized by Prof. A. E. H. 

 Love, F.R.S. §, who has raised doubts how far Hogan's 

 audibility factor (R+S)/S, where R is the resistance of 

 the telephone and S that of the shunt, is proportional to the 

 square or to the simple value of the antenna current I. 



Love has suggested that certain results of Austin and 

 Hogan indicate that (R-f S)/S is proportional to I 2 for large 

 values and to I for small values, in which case the theoretical 

 results of Love || and Macdonald 1[ would be in close agree- 

 ment with the corrected experimental data of Hogan. 



As long as the phenomena occurring at the contact of the 

 two substances of a crystal detector are neither qualitatively 

 nor quantitatively known, we cannot calculate the relation 

 that exists between the antenna current and the value of 

 the shunt S required to reduce the signal strength to just 

 audibility. 



Direct measurements of the antenna current at great 

 distance from the sending station cannot be made, for no 

 ammeter exists with which it is possible to measure high 

 frequency alternating currents of the order of 5 micro-amp. 

 The only way, up to the present, to find the value of the 

 receiving antenna current at great distances is to determine 

 the shunt S. Of course an experimental way must then be 

 found to compare the values of the required shunts S with 

 the actual antenna currents. 



* Communicated by Prof. J. A. Fleming, F.R.S. 



f 'Bulletin of the Bureau of Standards' (Washington), vol. vii. 

 No. 3 (1911), p. 315, and ' Journal of the Washington Academy of 

 Sciences,' Dec. 4, 1914. 



X < Electrician,' vol. lxxi. p. 720 (1913). 



$ Phil. Trans. Roy. Soc. Lond. vol. ccxv. A, p. 105 (1915). 



I] Love, see paper cited. 



% H. M. Macdonald, Proc. Roy. Soc. (ser. A), vol. xc. (1914) p. 50. 



