WHEN THE SUN HAS SPOTS

New Zealand Listener, Volume 2, Issue 43, 19 April 1940, Page 12

WHEN THE SUN HAS SPOTS

The Short Wave Doesn't Go Far

ERIOUS interruptions in shortwave reception last month set radio engineers as well as astronomers looking at the sun. They saw spots, remembered that there is a close relationship between the best frequencies for long-distance radio communication over shortwave circuits and the average number of spots on the sun, and had announcers inform you at the other end of the transmitter that conditions were too bad for you to be given your usual dose of Daventry. It happened, to be exact, between 3.15 and 4.15 p.m. on March 21 and again between 11.15 and 11.55 o’clock on March 23. No one worried very much about these brief intervals, but on March 25 the trouble started again at 4 am. and lasted until 6

p.m. on March 26. This was serious, and everyone hoped that the sun would quickly get over its measles. It did, of course, and by now is brighter and merrier, above the long white cloud that is all it knows of New Zealand this summer. The "" lonized Layers " The frequencies which give the best transmission are considerably higher during periods of great sunspot activity than at times when sunspots are few. That is, for those who tune to kw/s instead of mc/s, wavelengths should be shorter. A very long way up in the atmosphere, higher even than they fight aerial battles to-day, there is what they call the ionized layers. In time of trouble on the sun, the theory goes, these become more ionized than usual, with the result that that the shorter radio waves are more effectively returned to the earth. In years of high solar activity the earth’s magnetic field is disturbed, and nearly always this disturbance affects shortwave -transmission,

It also affects telegraph communication, and telephones, for the earth potential is boosted abnormally and plays great havoc with anything going along the lines close to its surface. And that, if you see what it means, is what happened last month when New Zealand was cut off from Daventry and Daventry from Europe, and America from everywhere. All the shortwave stations, we must presume, fired off their propaganda as fast as they could during the day and night and following day, confident that no one could hear them while they made such good use of a golden opportunity to practise. Once Every Eleven Years The sun plays these nasty tricks at fairly regular intervals. Although observations have been taken for

little short of two centuries, astronomers and other interested persons say that sunspot activity reaches a peak about once in every eleven years. This year it is climbing to a new peak. It is a little late, for the last one was about 1928-29; but it is making a good job of it this time. In September of last year the sun had another try at making a nuisance of itself. There was considerable disturbance of radio communications over long distances, and in New Zealand we saw a magnificent display of Aurora Australis. The Short Ones Go Further These short waves that the sun so easily puts out of joint travel, paradoxically, much longer distances than long waves. They leave the transmitters at much shorter intervals, or higher frequencies, than long waves, make for the upper air, and coast nicely along through the ether until they get tired, or until the sun frightens them down, as it has been doing lately. Radio engineers keep an eye on this sort of thing. Each season they regularly alter their frequencies to keep pace with the change in the position of the earth in relation to the sun. Now that the importance of sunspot activity is also recognised, they periodically adjust their frequencies to suit. Now, for instance, frequencies are being raised. As the sun regains his even temper, they will be lowered again. He’s a long way off to be making so much trouble; but then, so is Hitler,