JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. Ill, MARCH 4, 1913 No. 5 



RADIOTELEGRAPHY. — The measurement of received radio- 

 telegraphic signals. L. W. Austin, U. S. Naval Radiotele- 

 graphic Laboratory. 



(A) A tester for rectifying contact detectors. The measure- 

 ment of radiotelegraphic signals at a great distance from the send- 

 ing station is complicated by the fact that the most common type 

 of detectors, the contact rectifiers, can not in general be depended 

 upon to give the same sensitiveness at all times. This type of 

 detector has a great advantage over others for quantitative work, 

 inasmuch as it can be used with a galvanometer as well as with the 

 telephone. Experience shows that the loudness of signal in the 

 telephone as measured by the shunt method is exactly propor- 

 tional to the deflection of a galvanometer placed in the same cir- 

 cuit, and in the case of nearly all tj^pes of rectifiers proportional 

 to the square of the oscillatory current. In a former article^ 

 I have described a method of calibrating the detector in terms of 

 received current in the antenna. This method, while highly satis- 

 factory in a laboratory or large station with more or less labora- 

 tory equipment, is not suited to the use of the ordinary operator 

 and quite impossible for use on shipboard since it involves neces- 

 sarily two highly sensitive galvanometers and somewhat fragile 

 thermoelements . 



In order to overcome these difficulties I have arranged a form 

 of detector tester which serves to establish the sensitiveness of 

 any rectifying detector at any given time. The principle of the 



1 Bulletin, Bureau of Standards, 7: 295. 1911. 



133 



