Popular Science Monthly 



How the Radio Inspectors Trapped 

 a Disorderly Amateur 



IUST before Secretary of the Navy 

 ** Daniels issued his order for the dis- 

 mantling of all unofficial wireless stations, 

 the Government radio inspectors about 

 New York found it necessary to track a 

 disorderly amateur who continued to send 



An automobile was used to carry 

 about a simple loop direction-finder 



out false "S O S" signals. Their method 

 of running down this amateur is of especial 

 interest now that we are at war. 



The false distress signals were sent out 

 every night or so. Luckily the wavelength 

 was short and ships at sea did not hear 

 them. But the Herald wireless station 

 and the Brooklyn Navy Yard did. Recog- 

 nizing the signals to be the work of an 

 amateur, they immediately reported to the 

 authorities, and Louis L. Krumm, chief 

 radio inspector of the Department of 

 Commerce, started on his track. He first 

 acted upon a hint from the Herald operator 

 who explained that he could hear the sig- 

 nals more loudly on his own apparatus in 

 Brooklyn than on the sensitive instruments 

 in the Herald station in Manhattan. 



This at once confined the search to 

 Brooklyn. To locate the transgressor ex- 

 actly, a small directive-loop receiving set 

 was "hitched up" in an automobile which 

 was run about the Brooklyn streets. The 

 wire loop was about four square feet in 

 area, and could be turned about to face 

 in any direction. The circuit of this 

 loop was closed by the ordinary condenser 

 and coupler secondary of an audion receiv- 

 ing outfit (see illustration at right). 



Starting from a given point in Brooklyn, 

 the inspectors found that when the plane 

 of the loop was turned in a certain direction 

 the "S O S" signals were heard most 

 plainly. This meant that the amateur's 



313 



station lay somewhere along that direction ; 

 for, as every amateur should know, when 

 a wireless wave passes through a wire 

 loop end-on, the electromagnetic lines of 

 force will induce a certain current in one 

 vertical wire of the loop, and a different 

 electric current in the other vertical wire, 

 the resultant current flowing around the 

 loop being equal to the difference in these 

 two induced currents. The reason why 

 the two induced currents are different is 

 shown in the diagram on the follow- 

 ing page. At A the lines of force pass 

 through the loop end-on, and the intensity 

 of the lines of force cutting the vertical 

 wire nearer the sending station S is less 

 than that of the lines cutting the other 

 vertical wire, causing a corresponding dif- 

 ference in the two currents. Obviously, 

 the resulting current flowing in the loop is 

 a maximum and the signals are heard the 

 loudest when the loop is pointing directly 

 towards the sending station, as the loop 

 at A is doing. At C, on the other hand, 

 the two vertical wires are equally distant 

 from the station S. The same current is 

 induced in the two wires, since the same 

 intensity of the lines of force are cutting 

 them. The induced currents, on "bucking" 

 each other, are simply neutralized and no 

 resultant current will affect the audion 

 detector coupled to the loop. 



Now that the radio inspectors knew 

 one line of direction to the amateur's 



With the regular audion equipment, a wire 

 loop was used instead of an aerial ground 



station, they immediately proceeded at 

 right angles to this line of direction; as 

 from A to B in diagram. At B they de- 

 termined a new line of direction to the 

 culprit by again turning the loop around 



