8 AUSTIN: SLIPPING CONTACT DETECTOR 



antenna. Unless extraordinary precautions for good insulation 

 are taken about 50,000 seems to be the most advisable limit. 



RADIO-TELEGRAPHY. The slipping contact rectifying detector. 

 L. W. Austin. Naval Wireless Telegraphic Laboratory. 



In 1908 I described 1 a detector for electrical waves in which a 

 bit of tellurium was pressed against an aluminum shaft in rota- 

 tion. In connection with these experiments, it was found that 

 any slipping contact if sufficiently light gave audible responses 

 in the telephone when connected in the usual position of the detec- 

 tor. 



Later experiments showed that this form of detector was very 

 sensitive and extremely simple in use, requiring little adjustment, 

 no stopping condenser and no external E. M. F., full sensitiveness 

 being obtained with the detector simply placed in series with the 

 secondary inductance of the receiving circuit, and a pair of tele- 

 phones of from 600 to 1000 ohms resistance. The best results 

 have been obtained by the use of a slowly rotating disk of highly 

 polished copper or nickel driven by a spring motor, against which 

 a bit of fine copper wire is lightly pressed. 



The one difficulty which has stood in the way of the practical 

 usefulness of this device was the obtaining of a proper surface on 

 which the light sliding point could move, there being a tendency 

 under most circumstances for the point to jump, thus breaking 

 up the signal and making it difficult to distinguish the dashes 

 from the dots. With the introduction of high spark frequency 

 this difficulty has been to a large extent overcome, the wave trains 

 following each other closely enough so that the dashes as heard 

 in the telephone are invariably continuous if the adjustment is 

 correct. When the signals are strong the musical note of the 

 spark is reproduced in the telephone. Unfortunately, however, 

 when they begin to weaken, the irregularities of the contact break 

 up the musical note and it degenerates into a rustling sound 

 which does not serve to distinguish one station from another. 

 In sensitiveness this detector considerably surpasses any of those 



Electrical World, 48: 924. 1906. Phys. Rev., 24: 509. 1907. 



