WIRELESS NOTES

Nelson Evening Mail, Volume LXIV, 20 June 1931, Page 3

WIRELESS NOTES

BEST WAVE LENGTH SERVICE AREA PROBLEMS Tlie “medium” wave station, whatever its power, has a service area no greater than *2O to JO miles to 100 miles radius, whereafter fading and distortion seem inevitable. Ingenious tricks may overcome the trouble to some extent hut we are inevitably faced by limitations, says Captain P. P. Eckcrsley, M.1.E.E., in “Popular Wireless.” Increasing the power of the stations does not, alter the true service area boundary, because the point of intolerable fading occurs at a place independent of the power of the transmitting station.

AN UNRELIABLE RAY The space ray is appreciable up to very large distances. But the space ray can never he relied upon for service. True, in certain cases, wo may listen to far-away stations via the space ray for even 21) minutes at a time, hut inevitably they slowly fade away, become distorted, and so die. Later they live again. This is not service. The space ray is appreciable up to very large distances. The space ray can lie relied upon for interference! If it would stay as strong as it docs when it interferes we might rely upon it for service. As it is, its sole function is to produce awful interference on the local station.

Who lias not heard the thin piping tone of the heterodyne all through a concert? Who does not know the irritation of that harsh whispering due to the neighbouring station? Who can give one a receiver capable of “holding” a foreign medium station over a worthwhile period without its neighhour hutting in? It is a very serious state of affairs, even when the local station is interfered with clue to the ever-increasing power of neighbouring station. What is to he done? Here is some discussion upon what might be attempted.

WHAT MIGHT BE DONE Firstly, we might give better wavelengths for broadcasting. But if the same number of broadcasting stations are to exist after as bcfox*e tlie change we shall need to occupy every wavelength between 2JO to 2000 metres; It is asking a lot.

We should have to ask inter alia the removal of ship communication, aircraft communication and direction-find-ing services to other wave-bands. It is thought that the shipping might conveniently occuply lower wavelengths, because their shorter waves over water only suffer the same attenuation as a 2000-metre wave over land. (At least, in theory.) But direction-finding services are forced to use the longer waves. And aircraft are land craft when considering wireless transmission. I mean aircraft fly over land, therefore the wireless waves they emit pass over land. In sum it would be fairer to all concerned to make some readjustments, but we cannot expect broadcasting to obtain every facility it wants regardless of other wireless interests.

Secondly, wc might ask wireless receivers to concentrate moi*c upon selectivity. In my opinion the selectivity question requires; far more profound study than it has received (in the general commercial design), and we must congratulate Dr. Robinson on seeing the fundamental requirements of the modern receiver.

I speak under the possibility of correction, but I do fail to see bow it is possible to obtain greater selectivity without some sacrifice of quality. Adhering as I do to the theory of sidelmncls, and expressing my thoughts in these terms, I say that if, as we can daily appreciate, the side-bands of one station overlap those of another, the only possibility of tlie elimination of this interference is to “lop” the sidebands of one.

A RECEPTION PROBLEM

This can be done either in the transmitter or the receiver. It is preferable that the latter should do the cutting since there will always remain those so near to powerful transmitters as to be able to enjoy the benefits of the full spectrum.

Wo may then find ourselves no longer under the necessity of submitting to the autocracy of the local station. We shall have true service conditions from the distant. This could greatly enhance the pleasures of broadcasting. Broadcasting to-day suffers from the dead hand of programme monopoly. Stimulus seems to have vanished with the coming of success. More and moro people are wanting sets to listen to foreign programmes in consequence.

Night Atmosphere Governs Fading and Distortion. “As 2YA transmits in exactly the same manner during the afternoon as it does during the evening there is only one inference to be drawn—it can lie stated definitely that the trouble complained of can be attributed solely to night-time atmospheric conditions,'* says a statement made by the Radio Broadcasting Company of New Zealand Limited.

The explanation was given in reply to a cpmplaint made that there was distortion and fading of 2YA programmes in the evenings. ' An official of the company said the subject of fading and distortion was technical and involved, and an explanation in brief was difficult. It had to be remembered that the range of a broadcasting station was governed entirely by fhe medium separating the transmitter from the receiver. When a wave left the transmitting station, it travelled outward in all directions. One component hugged the surface of the ground and became gradually absorbed as the distance from the transmitter increased. Other portions of the wave continued to travel upward. The atmosphere surrounding the earth and through which the ether waves travelled might have varying conditions. In daytime the presence of the sun’s rays caused the atmosphere fo assume a condition where it was

“ionised,” or rendered more or less conducting. The waves which travelled upward from the transmitting aerial became absorbed, leaving only that portion which travelled along the ground as effective on the receiving antenna. When night fell, however, conditions changed. The lower and comparatively dense atmosphere lost the conducting properly which it had when the sun’s rays were present, but the upper, or rarilied atmosphere, still retained a certain amount of ionisation.

The upward waves, therefore, which during the daytime were absorbed, wcic not absorbed at night, but travelled onward until they reached this conducting hivor. Some were refracted and lost, hut others which struck at a somewhat more acute angle were reflected back to earth and joined with the ground wave, often out of step, as if were. The ground wave, picked up in the area which enjoyed perfect reception, was only slightly a flee tod by day or night conditions, and the range at which it lost its effectiveness depended almost entirely on the power of the station.

There are three conditions for every broadcast station: (1) An area close to the station where reception is constant both day and night; (2) a zone beyond where good daytime reception is obtained but liable to distortion at night; and (3) a zone of still greater radius where weak or no signals arc heard during the day, lmt where fairly good reception is obtained at night. These conditions are entirely beyond the control of the broadcasting station, although 'the unfortunate broadcaster usually has to take the blame. “Christchurch is in the middle zone for 2YA. In the daytime all is well. There is a straight-out wave to receive from one direction only, but at night a, receiving set is called upon to accommodate two portions of the same signals which have travelled different paths. If they arrive in their proper relationship, reception will probably be all right, but if from any cause the reflected wave becomes disturbed, tlie two portions will tend to oppose each other and distortion accompanied by fading will result.

“The only reception which can he guaranteed is that obtained within a limited radius of the local station. No matter how great may be. the power of a station, there is a distance, surprisingly limited, over which there is distortion and fading.”

Truly American A radio writer in a New York daily has no doubts about the place in the radio world which liis country holds. Ho sums up conditions very breezily thus: It’s all very well for you to point a well-manicured forefinger in the vague direction of England, Russia, or any other country where broadcasting lias been kept on a non-commercial basis; you don’t have to listen to it. . . I have heard earnest protestants declare. (“Declare”? What am I saying! They yell it into my car) that they would bo willing, delighted even, to pay a yearly tax as does the British brother for his electronic fare; that is, if by so doing they could eliminate from tlie air the annoying reminders that somebody’s collars arc “kind to your throat” and that somebody else’s mattresses “create the pause that refreshes,” and that still somebody else’s eyeglasses are “good to tlie last drop”! Wliat this ready spender overlooks is tlie fact that he hasn’t got enough money, nor have all the king’s horses and all tlie king’s men, to buy off the advertising credits on our sponsored programmes and still keep the programmes! There, isn’t any comparison between tlie kind and amount of broadcasting available to John Bull, Esq., and what we have over here. . . .

Even after.he has paid his compulsory Government tax, your Englishman lias financed (partly) no such wealth of material as that to which we are accustomed in this large country of ours, nor is his radio-reception comparable, even in his tight little isle to ours.

The United States leads tlie world in raclio-programme production. It is able to do this only because of tlie huge sums of money which it spends in the presentation of these programmes. Most of the money comes from the well-lined pockets of our big business men, who seem to have gotten the fantastic notion somewhere that your attention to their brief interpolated prayer will repay them. Last year they spent £ 13,000,000.