Page:Popular Science Monthly Volume 91.djvu/329

 Popular Science Monthly

��How the Radio Inspectors Trapped a Disorderly Amateur

IUST before Secretary of the Navy 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
 * Daniels issued his order for the dis-

���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

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��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

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