Radio age (Jan-Dec 1925)

RADIO AGE for March, 1925 The Magazine of the Hour 21 Event Proves that Daytime Reception Has Many Advantages, But They Are Offset by Distance Possible at Night; Darkness Stabilizes Long Waves EVER since the discovery of radio communication, many inexplicable sounds and noises have been found to cause considerable interference to the clear reception of distant signals, and especially was this noticed during the hot Summer months. During the colder months, when the nights were clear and the air was crisp and snappy, communication was established between stations several thousands of miles apart and the interfering noises, while still apparent to some degree, Were so decidedly reduced as to be practically of no consequence. Just why the hot weather reduced the signal strength as compared to the cold, or why the signals would gradually fade away at almost clock-like regularity and return again to normal strength, has been somewhat of a mystery. Various theories have been advanced for these peculiarities, but none of them has ever been actually proven, although experiments have shown that the sun has much to do with the case. Variation in Signal Strength ONE thing, however, has been conclusively proven; that is, that night reception is practically ten times as good as daylight reception. Distant reception of the broadcast wave is not expected during the daylight hours, for experience has shown that the short waves used for this work do not cover any great distance during the daylight hours, but after the sun has dropped below the horizon, conditions are entirely different. Just why these conditions apply has been explained in the following way. First, it is believed that electromagnetic waves travel through a layer of atmosphere next to the earth's surface. By FRANK D. PEARNE This layer extends from the earth to a mere matter of thirty or forty miles in height, and above this the atmosphere is of very low density and is called the heaviside layer, which is supposed to be a film of highly ionized air. This ionized layer of air has a tendency to reflect the radio wJave in about the (Kadel and Herbert) How the recorder makes a record of radio fading. Few fans know that even local stations fade. The record on the strip of paper shows how uneven some distant stations are received in New York. If the reception was consistent, a perjectly straight line would show. same way in which a light is reflected from a mirror. This, in combination with the rays of the sun, increases the conductivity and the radio wave rebounds in such a way that a receiving station located at a distance of 100 or more miles from the transmitting station will not only receive the direct wave, but also the wave which is reflected back from the heaviside layer. This wave is alternating in its nature, being first positive and then negative, these reversals taking place a million or more times in one second. If the receiving aerial is cut by both the original and the reflected wave at the same instant, and they are both at the same polarity at the same instant, then the signal will be quite strong; but if one wave happens to be at maximum and of a positive polarity, when the other is at maximum at a negative polarity, then the result of the two waves will be zero and no signal will be heard. The farther the two waves vary from the same phase, the weaker the signal will be, and the nearer they are . to the same phase, the stronger it will be. Here then, we find that we have not only the absorption of the wave energy to consider when it travels a great distance, but also the effect of the reflected wave. This theory explains to some extent why a distant station several hundreds of miles away from the transmitting station may hear a signal which is not heard by a receiver which is not so far away. It is easily seen that the height of the heaviside layer will determine the phase difference between the two waves and consequently the signal strength. Now, because the height of this layer varies considerably during the night and is practically stationary during the day,