Radio Broadcast (May-Oct 1922)

How to Begin to Enjoy Radio By CAPTAIN LEON H. RICHMOND, SIGNAL CORPS, U. S. A. Editor, Technical Training Literature, Office Chief Signal Officer Captain Richmond, who was Professor of Physics at Western iMaryland College before the war, was commissioned in the Signal Corps at the outbreak of the war. After passing through various instruction camps, he was assigned to the Royal Navy (British) Flying Field at Crsnwall, England, where he worked with Lt. Commander J. M. Robinson (British Navy) in developing a radio direction finder and other radio apparatus for airplanes. Upon the completion of this duty, and after a short time at an American flying field, he was assigned to duty at the .Army Signal School. Langres, France, where he was in charge of the Radio Department at the signing of the Armistice. For the last year and a half, Captain Richmond has been on duty in the Office of the Chief Signal Officer at Washington. — The Editor. II WHENEVER it is desired to receive a certain transmitting station, the radio receiving set must be iuned to that station. This is done by turning the knob or knobs on the receiving set. It is the purpose of this article to tell just what is done when these knobs are turned, i. e. why turning the knobs tunes the set. OSCILLATING CURRENTS A RAD 10 wave is produced by an electric current which moves first in one direction along a wire, then moves in the opposite direction. Such a current is called an alternating current, the word alternating describing the change in direction of the current. When the alternations of current (changes of direction) take place thousands of times per second, the term oscillating current is used to describe it. Radio waves used in present da\ radio communication are produced b\" electric currents which oscillate with a frequenc\ of between 10,000 and 6,000,000 times per second. This oscillating current sets up radio waves of the same frequencw (See first article of this series for relation between frequency and wavelength.) The radio wave, coming to your receiving set, sets up in it oscillating currents. IF THE RECEIVING SET IS TUNED to that frequency (wavelength). CONDITIONS FOR OSCILLATIONS (fREE) ABETTER understanding of tuning can be had if we compare it with something with which we are all familiar. Let us first consider what happens when a weight is put on a spring balance. If set in motion, the weight will move up and down, that is, it moves alternately in one direction and then in the other, without any outside aid. A little thought about it will show that there are two factors which cause this up and down motion. The weight is one factor, the spring is the other. When started in downward motion, the weight keeps moving beyond the position where the two will finally come to rest, but as soon as it gets beyond the point of rest, the spring begins pulling back. The further the motion from the point of rest, the m.ore the spring pulls until finally the weight stops moving down and starts moving up, being pulled back b\' the spring. We can get the same effect in another way. It would be well to do this experiment to fix the idea firml\' in \ our mind. Take the blade of a hack saw or some similar object and fasten it in a vice allowing some of it to project. By some means fasten a weight to the projecting end. Pull the end to one side and let it go. It will vibrate back and forth. Again the weight keeps it moving be\"ond the point of rest and the springiness of the hack saw blade pulls it back toward the point of rest. Try this experiment with a hack saw blade, a kitchen steel knife, or a spatula. The condition under which an\" s\ stem will oscillate is clearl\' set forth in the above experiment. To state it again, it is that there must be present something which will keep the system moving be\ond the point of rest, and there must also be present something that will pull the sx stem back toward the point of rest, the pull becoming stronger the farther the displacement from the point of rest. When