Rain and Radio

Radio Record, Volume IV, Issue 39, 10 April 1931, Page 15

Rain and Radio

Some Curious Effects

DURING the South African Warthe first time that wireless.was ever used in warfare, by the way-it was noticed that signals were very much better after a shower of rain had fallen on the veldt. In the case of the veldt, the reason why the signals were better after: the rain than. before was because dry ground tends to absorb wireless waves and they are quickly damped. out, whereas when the ground is covered with a layer of moisture this has the

effect of preventing the waves from sinking into the ground and they’ will last longer. ve Insulator Leakage. -- THIS after-rain effect is more noticeable in the day time, when the ground wave only is received At night, when reception is accomplished mainly by reflected or refracted waves from the Heaviside Layers, this effect is not so obvious. Other factors, of course, enter into this phenomenon For example, a beneficial effect should not be so noticeable immediately after rainfall, because the aerial insulators at the transmitting and receiving stations are usually. wet, and, therefore, are not up to their usual efficiency. ‘This is because water is a conductor, so that the high-frequency currents in both aerials will tend to feak away to earth over the wet insulaOrs. When, however, a wind has dried the wet insulators, and the rain is still lying on the ground, then reception should be and usually is above normal. °"' In the case of reception during falling rain, conditions are different. The aerial insulators are usually wet, and consequently there is a definite loss of energy over the wet insulators:. More energy is, of course, lost in the high potential aerial of the transmitter than

at the receiving end, and this loss we may say will largely counterbalance any benefit gained by the passage of the waves over the wet earth, There is also the fact that when the rain is falling, a certain amount of energy is conveyed from the aerial to the ground by the conducting rain, In other words, the insulating properties of the aerial are still further reduced, and more high-frequency energy passes directly . to ‘earth without going through the receiver. Precisely what happens to wireless waves when they pass through a rainstorm is not definitely known. In the’ usual way they appear to be unaffected to any appreciable extent, yet theoretic-, ally they should be reflected by the rain slightly, somewhat in the same way as the reflecting wires of a beam station reflect wireless waves in one particular direction. This reflection must occur to a slight. extent, but as far as is known has not been remarked upon in practical working.

Absorption Hiects. ANYONE on the edge of a rainstorm might expect, however, to experience a slight increase in signal strength due to reflection, provided the oncoming waves are arriving from a suitable direction; whereas a receiving station within the area of the rainstorm may experience a slight falling-off in strength from this reflection. We may also expect the rain to absorb a certain amount of the wireless energy from the ether on the same principle that trees absorb wireless waves by acting as aerials. Then, of course, the type of rain has a great deal to do with its effect on radio.- In some parts of the world wireless reception is impossible when it» rains, owing to a continuous hiss issuing from the phones or loudspeaker. This is due to the elecirified rain energising the aerial. Charged Clouds. RAN is not the simple drop of water we used to think it was, Not so long ago rain was explained as being due to the condensation of the air by cooling, when water was formed and it rained. , Within the‘ljast few years, however, we have learnt that the raindrop is a very complicated unit, indeed, intimate- ly connected with atmospheric electricity and electrified dust. Every raindrop has a material centre which is in many eases electrically charged. This centre is in fact an ion, and this ion, it may be added, is due to the gas called radium-emanation, which is given off by the radio-active substances in the earth. The gas spreads through the atmosphere and breaks up the moleecules of air with which it collides, so forming eletrically-charged particles which we call ions. Thus falling rain may be, and often is, a widespread descent of atmospheric electricity, and .it has been found that the electrical charge on some raindrops is greater than the force of gravity; so that a rainstorm is an electrical force to be reckoned with by anything’:

passing through the air such as wireless waves, After a shower of this kind of ‘rain, the atmosphere has been cleared OF much of its electricity, the rain: has brought the ions to earth, as it were, so that we might expect the insulating properties of the air to be more efficient, therefore clear and crisp reception is likely. Speaking tentatively this may account for the clear reception sometimes noticed. after a storm, as if the air had been cleaned up. On the other hand, during such 2 rainstorm, we may expect a slight background of "atmosphere," a slight hiss’ or noisiness which muffles reception slightly. This is due to the electrical charges in the raindrops energising the aerial, So far we have only touched the fringe of the effect of weather on wireless and vice versa-Professor Houllevigue, of Paris, claims to have proved, for instance, that the mist surrounding a transmitting aerial is dispersed when the station is radiating. There is ample "scope for research in these directions by amateurs, as it is largely.a’matter of observation with an ordinary receiv-:

er

G. H.

Daly

in "Popular Wireless."

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