Radio broadcast .. (1922-30)

What Causes Fading? By CAPT. P. P. ECKERSLEY Chief Engineer, British Broadcasting Co. HE phenomenon of "fading" has been known to wireless engineers for some time, but the advent of broadcasting has brought the subject into great prominence. There may be those, fortunately situated in relation to one of the broadcasting stations, who .have never experienced fading; so. at the risk of redund ancy, 1 will try to explain first what 1 mean by the term. You are listening to a station 1 50 miles away when all at once the signals go dead, or weak. You fly to the regenerative control, but everything you do has no effect, when suddenly without warning the sound bursts out again. The number of people who have conscientiously soldered, tightened and tuned, and scratched their bewildered heads, must be legion, as the number who write in, having satisfied themselves that their end is all right, and complain of the variability of the transmissions, is certainly considerable. As a matter of fact, the transmissions by the British Broadcasting Co., are not variable, and except where light and shade are desirable in musical items, radiation and modulation are maintained sensibly constant. The cause of the variability lies, therefore, between the transmitting station and the receiving station. The question is, then, what is there to influence the attenuation of the waves so markedly and so variably? Why in certain places does London fade while other stations do not? Why is fading noticeable only at night, and why should night time signals be stronger than day time signals in certain places and not in other places? Why should 2 LO be audible only a quarter of an hour after sunset in Salamanca, Spain, and why The phenomenon of "fading" becomes more noticeable as the cold. weather, with its long-range reception, approaches. Broadcasting from a given station may be remarkably loud one minute and almost inaudible the next. Adjustment of the receiver will not overcome this trouble and it is very naturally the subject of much discussion and conjecture. In this short article, reprinted from The Wireless World and Radio Review, London, the author explains in simple language one of the generally accepted theories. — THE EDITOR. should the Shetlands get us pretty uniformly, while people in the Victoria district (no! London, not B. C.) experience fading effects which are never noticed, say, in Hampstead? The answer is easy as far as I am concerned, and it simply is, / don'i knoic ! But a general theory exists which 1 will give you, and which probably forms a basis on which to build the explanations of minor variabilities. First of all, wireless waves travel through the ether, which is the assumed medium for the transmission of all electro-magnet ic waves. This medium is not in any sense of the word matter, inasmuch as matter is ponderable and can be analyzed, weighed, felt, and experienced by the human senses as it were. The ether is perfectly nonconducting to electricity, and to our senses it is nothing. But floating about in the ether are minute particles which in various permutations and combinations form matter — air, water, earth, and so on. Now, if matter is conductive to electricity, it impedes the progress of electromagnetic waves traveling through the ether which holds matter. Thus, if the air which is suspended in the all-pervading ether is conductive, it impedes wireless waves. It may come as a surprise to many to know that air can be conductive; it is not usually necessary to suspend the filament terminals of your set in a vacuum, but air can become quite conductive, and especially does it become so under the influence of sunlight. What happens is that the little particles called molecules in the air are made lively by the sunlight and split up into electrified units, which make possible the conduction of electricity. Thus, in the accompanying diagram I have drawn a rough sketch of the world, with the