Radio Broadcast (May-Oct 1922)

8o RADIO BROADCAST picked up than the first method. This is because the energy lost in the tuner in the first method is saved by the second method. One advantage of the first method, however, hes in the fact that, with the same capacity, a greater range of wave lengths can be received than by the second method. The following data concerning coil antenna is given as a guide for making one. This data does not follow, in some respects, the formulae that have been developed by radio engineers for the design of these antennae. However, FIG. 4 coil antennae made according to these descriptions have given good results. To receive 360 meters. Coil made as in Figure i . Frame four feet square. Ten turns of wire. Spacing 3 inches. Tuner to be shunted across the coil as shown in Figure 4. To receive 600 meters. Coil made as in Figure i. Frame four feet square. Ten turns of wire. Spacing one-fifth of an inch. Condenser only to be shunted across coil as in Figure 5. To receive 3,000 meters. Coil made as in Figure 1 . Frame six feet square. Fifty turns of wire. Spacing seven-sixteenths of an inch. Condenser to be shunted across the coil as in Figure 5. These examples ought to enable one to make a coil antenna with some assurance of success. The following simple rules apply: A longer wave length requires more turns if the size of loop and spacing is unchanged. Conversely shorter wave lengths require fewer turns. For the same wave length and spacing, increasing the size of the loop diminishes the number of turns required. The converse of this is true. For the same wave length and dimension of coil, decreasing the spacing decreases the number of turns required. This factor makes a very considerable difference in the number of turns. The converse of this is true. Ordinary No. 18 bell wire is a satisfactory wire to use. RADIO COMPASS A RADIO wave consists of electromagnetic and electrostatic lines of force. These sweep the coil antenna and afi'ect it. Considering only the electrostatic lines of force, it is seen that their efi'ect upon the coil is as follows : (The efl^ect of the electromagnetic lines of force is the same, as can be shown by a diff^erent process of reasoning). At any given instant the electrostatic lines of force have different intensities at different distances from the source of the waves. Also at any given instant the electrostatic lines of force have the same intensity at the same distance from the source of the waves. Electrostatic lines oi force set up potentials in an object which they sweep. If in the same conductor one part is at one potential and another part at a different potential, a current will flow. Suppose the coil antenna is directed toward the sending station. One end of it is nearer that station than the other end. Hence the two ends are at different distances from the sending station, at any instant the two ends are swept by electrostatic lines of force of different intensity, which consequently sets up a different potential in the two ends of the coil. This difference of potential will cause a current to flow, thus enabling the signal to be heard. On the other A FIG. 5 hand if the coil is broad side to the sending station, the two ends are equidistant from it; they will be swept by electrostatic lines of force of the same intensity; there will be no difference of potential established; no current will flow and no signal will be heard. Thus it is seen that when the coil is directed toward the sending station, full strength signals will be heard and when it is at right angles (broadside) to the sending station no signals will be heard. At intermediate positions the strength of the signals will vary from zero to