Radio broadcast .. (1922-30)

284 Radio Broadcast little the basic theories of radio are known to the general public. . . . AND WHY HE COULDN'T GET IT BUT to get back to the subject in handwhy couldn't the operator get Los Angeles? .Why can't you always increase the distance by increasing the sensitiveness of your set? The fact is, there is a limit. It can't be done. To explain this clearly, let us consider a form of receiving set such as the super-heterodyne which can be arranged to provide an unlimited amount of radio-frequency amplification. What is there to prevent, for instance, the carrying of this amplification as far as we wish? If the radio wave, even from the weakest transmitter, actually does go on and on, why can't we merely add radio frequency and receive farther and farther? The answer is simple, and depends upon a single factor of fundamental importance to radio reception — static. THE "STATIC LEVEL" NOW, static is, as we are accustomed to think of it, a crashing sound in the receivers resembling thunder crashes during an electrical storm. It is extremely bad in the summer time and practically absent in winter. However, under this heading of static can be classed, for the sake of convenience, all types of radio-frequency noises: local interference from induction, elevator clicks, buzzes, etc. "In the winter, on a seemingly perfect night for radio reception, when, perhaps, not a particle of electrical disturbance can be heard in the ordinary regenerative set, still there is static present, as will be readily learned if one starts to experiment with sensitive receivers. // is' the quantity of this radiofrequency noise that exists which is the limiting factor in our distance reception. In other words, no matter how low the "static level" drops, if we amplify sufficiently we can .bring it back to a roaring series of crashes and clicks in the phones. And unless the signal which it is desired to receive is present with greater intensity than the static, it cannot be heard. It is an impressive sight to look out over a body of still water and see a submarine sink slowly below the level of a smooth sea. This is the finest analogy to a radio wave and the static level that I know of. The signal goes on and on, always diminishing in value until it reaches the point where it sinks below the surface of the static level; and, as in the case of the submarine, which cannot be seen below the surface of the water, no matter how powerful the field glasses employed, so will a radio signal disappear below the static level and be lost to the listener no matter how sensitive the receiver. This could well be called the threshold value of the transmitting station's wave. "Threshold value," a term used in physics, indicates (as applied to a radio signal) the critical value above which the signal is audible and below which it disappears. There is always an infinite amount of small electrical disturbance present in a city. Its intensity depends upon conditions and locations in which receiving work is done. In some locations this static interference is so bad that it makes long-distance work out of the question, regardless of the type of set used. Naturally, the man who buys the finest receiving set obtainable expects the finest kind of reception, and it is sometimes hard to explain to him that he cannot get results in spite of the apparatus he uses. Without knowing the cause of the trouble, he immediately puts the blame on the equipment and the dealer's judgment, or capabilities. I know of many in c DISTtlMCE FIG. I The distance from the Pacific to the Atlantic Coast is represented by the line AC. X Y indicates the strength of a broadcast signal sent from the Pacific Coast. It can be heard in New York (C), with sensitive enough apparatus, because, at that point its strength is still greater than the static strength. But at B (somewhere out on the Atlantic Ocean), the strength of static and signal are equal stances where radio enthusiasts who are trying to solve this static problem have spent hundreds of dollars shifting from set to set. They vainly hope to find a " good set," as they would call it, when, as a matter of fact, it is their receiving conditions, not the sets, that are fundamentally wrong. "DEAD SPOTS" ANOTHER problem frequently encountered is that of "dead spots." It is an undeniable fact that there are many places, not only in the city (although the complaints