That Eleven Year Cycle

Radio Record, Volume V, Issue 13, 9 October 1931, Page 9

That Eleven Year Cycle

by

COSMOS

In this article "Cosmos" tellg you in progressive sequence, the substance of considerable observation and research. He reviews the factors governing radio reception, and goes on to point out how good radio seasons have been dependent upon solar activity manifesting itself in eleven-year cycles.-Ed.

HE science, of radio has made such: enormous ‘advances in the past decade that it is now: in many respects well nigh perfect. There are many critics who aver that the modern electric radio is too powerful, but they are in the same class as the critic who can find nothing powerful

enough, and no radio nearly as good (by his way of it) as the great set he built himself so many years ago. Properly and intelligently handled a good electric radio will convert those feeble voltage impulses

that reach an aerial into a true and faithful rendering of just what they represent. If the output is marred by static or distortion, it is simply that science has so far been unable to design a set that will differentiate between those impulses that are meant to reach the aerial, and those that are not.’ A good strong signal has a strength of about ten micro-volts per meter when it reaches the aerial, and if a set is amplifying this signal to give room volume, it stands to reason that .a static discharge of the same intensity will have the same volume as the wanted signal. If the static were

‘persistent 1t would be ruinous to entertain--ment. In this case the ratio of static, or atmospherics, to wanted signal is 1-1. If the atmospherics had a strength of three microvolts per meter and were conflicting with a wanted signal of ten microvolts per meter, the ratio would be 3-10 and the atmospherics would be heard only as a background. Static in these latitudes is more of a seasonal disturbance than a chronic one, and providing that the aerial can pick up a signal strength of ten microvolts per

meter atmospherics will seldom mar a programme. At this point we must give consideration to the vagaries of radio waves in transmission. Consider fig. la. Here we see that transmission is accomplished by two fundamental circuits known as the sky wave and the ground wave. The sky wave may be likened to a ball that bounces along, and the gtound wave to a ball that is thrown. Many and varied are the phenémena that affect the sky wave, and while it is this sky wave component that gives us distant reception, it is also it that brings us distortion in its many guises. Above the Earth, at a variable distance, there is a refracting or reflecting layer, which since 1902 has been called the Kenelly-Heaviside Layer, after the investigators who almosi simultaneously founded its theory. Kenelly an American, and Heaviside an Englishman. The distance that a sky wave will reach from a transmitter before it becomes too attenuated to be of use is governed by the percentage of absorption that takes place at each contact with the Layer and with the Earth. The amount of absorption that takes place at each contact with : the Earth is governed by the particular class of terrain at the spot of incidence, being much less when the Earth is wet, as it is then a good reflector of radio waves. As regards the Heaviside Layer the amount of absorption that takes place is more or less proportionate to the number of bounces that the wave must make between it and the Earth before it reaches its destination.

This in turn is governed by the height that the wave must go before it reaches an electronic density sufficient to reflect it back to earth, and it will be seen that the higher the wave goes before reaching its turning point the fewer will be the number of rebounds it will have to make before it reaches its destination. .

In table 2 is shown the approximate heights at which the electronic density is sufficient to turn waves about ten metres long back to earth. © With longer wavelengths corresponding to lower frequencies, the height at which the electronic density would be sufficient to turn the waves back to earth would be much less, and herein we find the reason for the great distances spanned by short waves, taking comparatively few strides to encompass the earth. It must not be supposed that the Heaviside layer remains stationary for any length of time. Heising tells us that layer is constantly on the move, rising and falling rhythmically about every quarter of an hour. Rising at a speed of something like six miles per minute and falling much more quickly, probably at 20 miles per minute. At this juncture it is well to consider the reason for the very decided attenuation that daylight and even moonlight has upon the sky wave component. We know that the ionised Heaviside layer is highest and least intense on a winter’s night, lowest and most intense on a summer’s day; higher and less intense on a winter day than on a summer day, that its height and intensity thus varies from night to day, from no moon to full moon, from season to season and from sunspot cycle to sunspot cycle. . The science of physics and chemistry tells us that when a diffuse gas is subjected to ultra-violet radiations some of its atoms lose

electrons, which may either attach tnemselves to other complete atoms or remain as free electrons. The gas will then contain free electrons, positive ions or atoms which have lost an electron, and negative. ions or atoms which have gained an electron, and in this state of electrons, positive ions and negative ions and gas is said to be ionised. Applying this knowledge to the ionised Heaviside layer we find that the layer is ionised more or less effectively according to the intensity of the ultra-violet rays to which it is subjected, most of which emanate from

the sun, but undoubtedly the ionisation is to some extent due to emanations which possibly reach the layer after speeding through space from greater suns than ours. In a_ completely ionised state the Heaviside layer

acts toward radio waves in the broadcast spectrum in much the same way as a short circuit affects an electric transmission line, and it is now that we can visualise why it is that distant radio reception, via the sky wave component, is almost directly influenced by the intensity of the light through which the waves make their way. On a winter day the intensity of light is only about one-fourth of its corresponding summer value, which accounts for the greater signal strength in winter and at night. To return to earth and the ground wave component as illustrated in table 1a, we find that reception via this path is practically independent . of light and darkness, and that the signal strength at any distance from a transmitter is mainly governed by the class of country over which the waves have to travel. Referring to table 3, which gives the distances accepted as standard in the United States for true service range, we see that the distance is not all directly proportional to the power, radiated, but is governed by the law of inverse (Concluded on page 10.4

TABLE &% Winter Day ...cccee..cce+-- 100 miles Summer Day eosooo eo Ceo 200-350 miles Winter Night ....c0c0ce. 175-250 miles Summer Night ....cceccee 250-400 miles Spring and Autumn ...... 150-225 miles These figures are from Marshall, U.S., for waves of about ten metres. It is not intended that they represent the approximate turning point of broadcast frequencies, as the figures are not even proportionate, due to the varying factors that affect different frequencies,

TABLE 3, Watts power. Miles. 5 *"eceee 1 500 coooee 10 50,000 eoeroe 100

squares, which law also governs the intensity: of light at various distances from its source. But there is another limiting factor to really satisfactory service, and that is "fading." A line may be drawn with considerable accuracy around a transmitter that will show the point in any direction at which fading will commence. The factors which control this fading distance are practically independent of the power of the transmitter, and they are the class of country over which the waves are propagated and the wavelength of the waves themselves. Table 4 shows the distance «" the fading ring from a transmitter wer various classes of country and on various wavelengths. From a study of this table it is seen that the Ionger the wavelength the greater the true service range or distance between the transmitter and the locality where fading commences, irrespective of the class of intervening country, and also, for any given wavelength the distance between the transmitter and the fading ring is governed by the class of intervening country, being greatly reduced over rough country. It is seen that a 200-metre station will give satisfactory reception over only ten miles of mountainous country, against fifty miles over flat country. Likewise that a 400-metre station has a true service range of over twice as far. The Ground Wave. REFERRING to figs. 1a and 1b, we see that the ground wave component has a more direct and therefore a shorter path than its less direct companion the sky wave. The varying distances covered by tle waves traversing each of these two jauths cause a swing: ing phase difference between the ground wave and the sky wave, such that when as in la the two components are in phase, the signal strength is twice its normal value, and as in 1b where the two components are in phase opposition, they neutralise each other completely, and the signa! strength is zero. _ The intense fading or hashing which 4s very noticeable at distances as shown in table 4 is largely due to this cause, and it becomes less pronounced as the distance from the first fading ring is increased, due to the attenuation of the ground wave. While the sky wave gives satisfactory signal strength over great distances, the quality of reception is all too often’ marred by distortion. Indeed it is far more often present than not, and very few long-dis-tance signals arrive as clear and erisn as they left the transmitter. The more perfect a radio set is from a tonal standpoint the more obyious the (istorted signals are in its output. Many home-built radio sets suffer so mueh from inherent distortion that their owners are immune to distortion, and they are so used to the tone of their own sets that true tone quality sounds strange to them. A Cause of Distortion. AN accepted cause of distortion ‘s known as the differential sideband theory. A radio phone signal is comprised of a narrow band of frequencies which may be classed as the carrier frequency and two sidebands. the frequency of one being above, and that of the other below, the carrier frequency. |

Due to the refractive index being influenced by the frequency, it stands to reason that any two signals of different frequencies will, after refraction from the heaviside layer be in slightly different phase relation to each other to what they were previously, and as the Heaviside layer is constantly on the move, and varying in density, it is readily conceivable that the signals must often arrive distorted and mushy.

As long ago as 1826 a German astronomer, Heinrich Schwabe, found .by long and patient observation that the number of sunspots on the sun varied from year to year in a cycle of a little over eleven years. In recent times it has been observed that distant radio reception is strongly influenced by the sunspot cycle of Herr Schwabe, as shown for recent years in fig. 5. In those years of maximum sunspots radio

via the sky wave has been poor, and in the years when the sunspots were at a. minimum it showed a marked improvement. Sunspot Cycles. CIENTISTS now believe that the sunspot cycles are caused by the gravitational ‘pull of the planets on the sun, which pull reaches its maximum at periods closely corresponding to those pf maximum sunspot activity, due to the additive attraction of the planets as they line up each eleven years or so. It is believed that this gravitational pull of the planets affects the sun in much the same way as the moon affects the earth and her tides; the sun b»ing in a molten state, the pull causes its fiery surface to open up and release flaming vortices that reach out into space for many times the diameter of our world. It is to be expected that such unusual activity will affect rhe radiations of ultra-violet, and light and heat waves that reach the Harth (they, all travel at the same speed of 186,000 miles per second), and indeed records prove the theory. Years of Maximum Aetivity. REFERRING again to figure five we see that the years 1905, 1917 and 1928 were the years of maximum activity in the solar regions, and we know that those years brought hot summers and droughts in many parts. Like wise, as would be expected, the u!traviolet radiations reaching the Harth in those years were more intense, and ‘although 1905 was before the era of broadcasting as we know it, the years 1917 and 1928 were noticeably poor for

long distance reception, ... On the other hand, about 1928 when the sui spot cycle was at its ebb some remarke able ‘long-distance reception was obtained on what are now considered really obsolete sets. We are now nearing the next ebb period in the sunspot cycle, and what do we find-the summers are becoming colder, the seasons less defied, and the whole Earth is probably darker than it was about 1928. The ionizing ultra-violet radiations are less in tense, and radio reception is improving perceptibly. Probably in 1934-35 the long-distance records of 1923 will be eclipsed generally. Further evidence to prove this theory is visible on the stumps of recently felled trees. It is occasionally ob} served that every eleventh ring or, thereabouts is wider, showing that the tree made greater growth in that year, due to greater heat, and possibly in some measure to the stimulating impetus of the ultra-violet radiations it was subjected to. Summary. N summing up our observations, the following facts seem to stand out in relief :- That the sky wave component does not give really satisfactory service, and that only those listeners living within the first fading ring of a transmitter get really satisfactory reception. That the longer the wavelength of a transmitter and the greater its power the greater is the number of listeners who derive true service 480m that transmitter.

(Continued from page 10.)

\ That, seeing that we cannot control the sunspot cycle, the seasons, and, in short, all those phenomena that make signal strength at a given distance so variable, will it not become feasible to forecast signal strength over given distances, and to increase the output of the transmitter when conditions are adverse or decrease it under favour-

able conditions, aS the case may ve, and so aim at constant signal strength? To give rein to the imagination, it seems that the broadcast transmitter of the future may be so controlled, and transmit on both higher power and on higher wavelength than at present. Probably radio as we know it is not radio as we will know it.

From figures by P. P. Eckersley, chief engineer B.B.C. Wenstrom and Serigs figures compiled under U.S. conditions were within | per cent. of Eckersley’s data.

Class of Country. 200 Flat ceec.re 50 Hilly ..2.080 24 Mountainous . 10 TABLE 4, Wave-length-Metres. 300 400 80 120 37 62 17 26 aATilacd. 500 1200 160 4890 75 260 34 110 1500 620 330 160