The Effect of Direction and Distance on Reception

Radio Record, Volume II, Issue 12, 5 October 1928, Page 10

The Effect of Direction and Distance

on Reception

A Full Analysis of Factors in Reception

‘ANY and varied are the puzzles of radio, but each year reduces their number and places them in the category of facts that broadcaster and listenerin have to contend with. Variation in signal strength has eaused many and varied "comments." The phenomenon has attracted the ut tention of radio engineers ever since radio was-explanations and theories have been brought forward but cures -none. It is interesting to note in this respect one of the aims of the Autarctic expedition is the investigation of "fading." Effect of Direction. ¥ is reasonable to expect that as the receiver moves from the trans--mitter, signals will become wenker, but reference to "Our Mailbag" will show that signal strength does not weaken uniformly. One district close to 2YA will complain of poor reception, while another at a greater dixtance will "receive" perfectly. It is also noticeable that a receiver near to 2YA will receive 1YA ‘better than the stronger station. Naturally

thoughts fly to the station as the cause, but this is far from the case. It lies in the peculiarities of the atmosphere and -the surface of the ground over which the waves are to travel, NLESS the transmitting aerial is modified to produce a directional effect waves are emitted and travel in all directions. Those received come from two directions, from along the ground (the gronnd wave) and the reflected wave. For variation in signal strength reference has to be mnde to the causes lying along these routes, Ground Ray. [AV ISTIGATION shows that up to somewhere about 150 miles the Waves travel along in association with

the ground. These are little affected by fading, but their relative strengths in different directions vary considerably. The nature of the ground greatly affects the ray, especially with respect to the presence of trees, hills. metallic-ore deposits, rivers, lakes, and SO ON. Interesting research has been carried out by a well-known engineer, and his results described before the Institution of Electrical Engineers. By taking recurate rendings in several directions from 2LO (London) he was able to produce a contour map showing that in certain directions signal strength decreased more rapidly than in others. It was shown that 2LO was received best in a north-westerly direction, and least satisfactorily in a south-westerly direction. A receiver situated seventy nliles away in this latter direction would receive no better than a place 150 miles distant in the former direetion.

AN explanation was sought. It was noticed that the districts in which reception was weakest were heavily wooded. Fixperiments were conducted, und an hypothesis arrived at. It was. discovered that trees acted as aerials sud conducted some of the power to the ground.

{XPERIMENTS along these lines hive not been conducted in New Zealand, but it would be interesting to hear from some of our listeners-in in bush districts within this ‘ground ray" area, . | Reflected Rays. A PART from this direct ray, there 4% is also the reflected ray which enubles listeners-in at great distances to. receive signals. Up to a certain point the air is, as has been explained in a previous article, an insulator. This region is terminated by a "ceiling" as far as radio waves ure concerned, which has been named after its discoverer-the Heaviside layer. This atmospheric shield acts as a reflector, and directs waves back to the earth. A well-known scientific law states that when a body or ray of light (or electricity) strikes a reflector it is reflected back in such a way that the angle made by the ray to the reflector and that between the reflector and the reflected ray is the same. This explains the throwing of a beam of light by a looking-glass. The points, or rather pencil, of reflected light can be moved by merely moving the mirror on an axis. Imagine the surface of the heaviside layer moving in relation to the transmitter and some idea of the cause of fading, or rather what is considered the cause of fading, will be arrived at.

cellent DX and a. new selection of programme items. But to others, particularly those in districts where difficulty is experienced in receiving 2BL, there / will be much wailing and gnashing of.!. teeth. Already the beat note set up between one of the Jap. stations and 2BL has been responsible for much blurred reception of the latter station. IfLowever, there will also be alterations in the wave-lengths of some of the Jap. stations which might improve matters. We can only wait and listen."

KIP distances, or dead areas, occurring about 150 miles from the station are believed to be the result of this reflected ray interfering with the ground ray. At this distance the ground ray should arrive at the receiver just before the reflected ray, with the result that the positive alternation of the one is neutralised by the negative alternation of the other. At a point closer to the transmitter the time element seldom gives trouble, the two types of waves being received simultaneously. More distant stations rely solely upon the reflected waves. It has been observed that during the day, due to sunlight, the waves that go up are absorbed, and the only signals received are thus travelling direct along the ground.

HE £Sydney "Radio" says: "The news that the Japanese stations (JOAK and JOBK are shortly to increase their power to 10,000 watts each) will be received with mixed feelings by listeners-in. ‘To many it will present a further opportunity for ex-