THE WIRELESS WORLD

Otago Daily Times, Issue 22391, 12 October 1934, Page 2

THE WIRELESS WORLD

By Magna Vox.

NEWS AND NOTES I | I I

Items of local interest are - invited by “Magna Vos" for publication in this column It is necessary that such matter should reach this office by Tuesday of each week for insertion on the following Friday, 2BL, Sydney.—Bs6 K. 0., 358 metres. 2FC, Sydney.—66s K.C., 422 metres. 3AR. Melbourne.—62o K.C., 492 metres 3LO. Melbourne.—B3o K.C., 371 metres. SCL, Adelaide.—73o K.C., 395 metres. 4QG, Brisbane.—76o K.C., 385 metres. IVA, Auckland.—6so K.C., 461.3 metres. 2YA, Wellington.—s7o K.C., 526 metres. SYA, Christchurch.—72o K.C., 416.4 metres. 4YA Dunedin.—79o K.C.. 379.5 metres. 4YO, Dunedin.—ll4o K.C., 261 metres. ANSWERS’ TO CORRESPONDENTS, “ Charger," Oamaru.—A trickle charger is a unit which has a very low charging rate, and which is therefore suitable tor the continuous charging of accumulators when not in use. The one you mention is a very satisfactory charger, and with four hours’ use of the set and 20 hours charging each day your accumulator should be kept up to the mark all the time. “Six-valve," Waipiata.— (1) The noise could be caused by many faults, such as ; (a) Too high a coupling resistor in the grid circuit of the output tube (the resistance may have been correct when the set was built, but gone up in value since); (b) a faulty grid leak or grid condenser if they are used; (o) a loose connection; (d) a faulty valve. - (2) You can attach a pick-up by connecting one side of it to the chassis or earth and the other to the grid of your detector valve. (3) PI to grid; P2 to C-Sl to plate; S2 to high tension. J. B. N., Dunedin.—Distortion refers to the unuaturalness of the sound emanating from the speaker. Associated with sound, it is logical to look for the cause in the sound or audio section of the receiver, and it so happens that the majority <p£ cases of distortion find their source in the audio frequency amplifier. A notable exception is the case of muffled or “ drunimy ” tones, when the radio frequency system may be suspected, and further tests made accordingly. IYA’S POWERFUL PLANT. It is understood that with the advent of lYA’s new and powerful transmitter there will be some reforms and modifications in the programmes. With the more powerful “ voice " of the new plant there should be no further need for the repetition of sporting results for the benefit of the country listener, who may, at the critical moment, have found the first announcement of a result drowned in a burst of static. There is likely, too, to be some minor rearrangement in programmes for the same reason. In the past the tendency would seem, where interests conflicted, to favour the, country listener rather than the city dweller; but this wag only fair, in view of the other sources of entertainment that are available in the main centres. With the new powerful IYA this position will be modified to some extent. The first of the changes announced is the arrangement for an improved old-time dance session on one Saturday in each month from each station. The service will be inaugurated by 2YA next Saturday, and will be followed by IYA on the first Saturday in November.

BROADCASTS ON SHORT WAVE. Owners of short-wave sets should shortly have the opportunity of picking up some interesting transmissions from Daveutry. For example, in the near future the Daventry short-wave transmitters will broadcast a series of talks entitled “Meet the Detective,” in which famous exponents of sleuth fiction will describe how their tales were evolved and how the principal actors first took shape in the minds of their creators. The list includes “ Sapper," who will deal with Bulldog Drummond: A. E. W. Mason (Hanaud); Baroness Orczy (“The Scarlet Pimpernel ”); Freeman Wills Crofts (Inspector French); Austin Freeman (Dr Thorndyke) ; and Andrew Soutar (Phineas Spinet). These talks will, of course, be electrically recorded. Mr C. Madden, the Empire production chief, has other series in view, including “ Living Dangerously ■’ and “Nightmare. Also there are to be “ gossip ’’ hours and other touches calculated to bring an informality to the Empire programmes, "■ FAMOUS STATION TO BE SOLD. Poldhu, the most famous wireless station in the world, on the edge of the wild Cornish coast, not far from the Lizard, is to disappear. Marconi’s Wireless Telegraph Company, Ltd., has given orders for its saie, lock, stock, and barrel, and on the spot whore some of the greatest advances in wireless have been made it is probable that seaside bungalows will appear. It was from Poldhu that the first wireless signal was sent across the Atlantic. That was in December, 1001. The following year experiments from Poldhu carried out by Marconi while travelling in the liner Philadelphia established the then surprising fact that wireless stations have a range approximately three times greater by night than by day, for he discovered that he could pick upPoldhu’s signals only at 700 miles | in daylight, but up to 2000 miles after ! nightfall. Later that year a regular ser- I vice was opened with Canada, via Glace | Bay, and in 1903 wireless communication I between England and the United States j was established through Poldhu and Cape ! Cod by an exchange of messages between ; King Edward and President Theodore I Roosevelt. In 1912 Poldhu received the ; tragic message from the Titanic which ; told the world that the biggest ship j that had ever put to sea was sinking | fast. In July, 1920, the first telephonic ! call to a ship at sea was made from | Poldhu. It was to the Victorian, then j on its way to Montreal with delegates to i the Empire Press Congress. I

PROGRAMMES BY WIRES. On more than one occasion it lias been suggested that the lines used for telephones nnd tor the distribution of electrical energy should be also used for conveying broadcasting programmes. A recent revival of the subject has created a feeling of uncertainty in the minds of some who foresee the possibility of dispensing with what is at present understood by a wireless receiver. At first sight it would seem that programmes could be easily made available in this way, and that only simple receiving apparatus would be necessary, but a consideration of the practical problems of such a scheme, at least ag they are known at this date, shows that if a receiver of the present type is not necessary something equally complicated, and therefore equally expensive, would be necessary if a reasonably wide choice of programmes is required. The problems of supplying programmes to listeners by means of wire channels are in many respects similar to those of establishing and operating a telephone system. If o pair of wires is supplied with a programme listeners at any point in the circuit would bo able to hear the programme with equipment no more complicated than a loud speaker or a pair of headphones connected to the line, with some simple means for controlling volume also in the circuit. With only one listener plugged in, the system would resemble that of a telephone exchange and a subscriber having his own line. With two or more users the general scheme would be similar to that of a “party” telephone line. If more than one programme was wanted, as many additional pairs of wires as programmes could be used, the receiving l means being connected to the required pair, but that would soon lead to complications and expense in the wiring. Some economy of wire could be effected by making use of what are known as “ phantom ” circuits, which means, for example, that three wires could supply two programmes, or four wires three programmes. The carrying capacity of the lines may be increased by superimposing upon them, in addition to the ordinary speech frequencies, one or more modulated carrier wave systems. While for many practical telephone purposes this system is excellent, it is not entirely suitable for the supply of broadcasting programmes to private houses by means of wire lines. A high-frequency carrier wave has to be generated at the sending station. The wave has to be modulated with the speech and music and fed to the line. At the receiver this wave or series of waves has to be selected from others of a like nature, and then treated as if it were a wave picked up by means of an ordinary aerial, the only difference being that its wavelength would probably lie between 10,000 and 30,000 metres. Because of the ease with which high frequencies escape from wire lines

the number of channels that arc available for practical communication of this kind are few. Besides that, the channels would be very close, and because they were supplying signals of approximately equal strength filters and selection means of high ability would be required. This, plus the necessity for providing detecting or demodulating arrangements and amplifiers, would by no means result in a simplification of the apparatus at the receiving point. Power lines have been and are used for carrying telephone messages, but, unless there have been farreaching developments, it is not likely that they or any other system will ever become popular as a means of supplying broadcast programmes to homes because of the limitations in the choice of programmes.

WAVE FORMS. Although it is apparently a simple type of sound, a noise such as the report of a revolver is harder to deal with faithfully than many musical notes. The wave form of a sound such as this has a very steep front and a relatively Hat top, so lhat, instead of the wave following a fairly smooth and periodic curve, it resembles more a series of rectangles or squares. Although they do not appear to have any particular curve associated with them, it can 'be shown mathematically that such a form can be analysed into a multitude of frequencies extending from zero to infinity. The component frequencies cover a wide band and include a greater number of individual frequencies than a more musical sound. For instance, a noise may include a fundamental of 50 cycles per second, plus all the odd harmonics; that is, vibrations of 150, 250, 350 cycles, and so on up to frequencies in excess of 20,000. Such a sound, therefore, applied to a broadcasting system is a very severe test of the microphone, the rest of the transmitting equipment, the receiver, and the loudspeaker, not only for their ability to respond quickly to a sudden change of curi’ent, but also for their ability to deal with a wide range of frequencies, because unless the higher harmonics are present, the characteristic form and sound of the wave arc lost. Uunfortnnatcly, no system can handle successfully every frequency from zero to infinity, nor even every frequency which is audible to the majority of people. Further, every electrical circuit has a property which is equivalent to inertia in mechanical devices. A mechanism such as a flywheel requires considerable effort to set it in motion quickly, and likewise requires considerable effort to bring it to rest quickly. This is because every mass desires, as far as possible, to remain in its original state, whether that state be one of rest or one of motion. In a similar manner any electrical circuit, and more particularly one in which coils aud ! chokes are included, does its best to keep j constant the value of the current flowing therein. It offers considerable opposition to a rapid increase and also to a rapid decrease. This pi’Operty of circuits is known as inductance, and in some cases it is of great value. Most of the sounds that have to be handled by a broadcasting system are of a Complex form. Their complication is largely due to the fact that, in addition to the fundamental frequency, there are always a certain number of overtones or harmonics present. It ie these overtones or harmonica which give the speech Or music its distinctive quality and enable a listener t 6 distinguish between the same note sung by a soprano or other singer or sounded by a flute, piano, violin, or other instruments. Tims, a note which has a fre-' quency of 250 cycles per second may have associated with it in varying qualities harmonic frequencies of 512, 1024, 2048, 4096, 8192, or more cycles per second. The combination of frequencies such as these results _jn a wave from which, instead of being relatively smooth from crest to /crest, has a number of intermediate peaks and troughs, the magnitude of these peaks and troughs, as well ns their disposition, being governed by the number and strength of the harmonics or overtones that are included with the fundamental note. Besides these variations in form, there are always large changes in the average magnitude or volume of the transmission. No item, whether it be speech, song, or a combination of instruments, maintains a constant volume for anything but a small fraction of a second. Abrupt changes are always present, and form an essential part of the reproduction. For exahiple, in speech, words beginning with letters such as '*p.” “t,” or “k" cause sudden changes in volume, while the report of a gun, the clapping_ of hands, and other noises produce similar results. These types of sound which rise abruptly to their maximum value aud fall perhaps equally papidly again are known technically as “ transients." As the name implies. the sound _or wave is something which is of fleeting nature without any lasting or sustained characteristic.

HERE AND THERE. The announcement that the new IYA broadcasting station would be Opened at the end Of this year haa been reaffirmed by Mr E. C. Hands, manager of the New Zealand Broadcasting Board. *** V It is estimated that B stations in New South Wales alone received £17,000 for broadcasting political speeches during the recent Federal elections. Of this the Labour Party paid about £9OOO. Most of the B stations now charge £2O per halfhour for “ time on the air.” * sis # An internal system of wireless communication is about to be established in Brazil, the Government of which has given the Marconi Company (England) the contract for the manufacture and installation of nine transmitting and receiving stations. These will provide a network of new telephone and telegraph services, which will link up all the States and principal centres of the country. Three stations will be erected on a common site at Rio de Janeiro to work with different cities.

France promises to be a wireless joyland. A new law has come jtito force which compels manufacturers to fit antiinterference devices to all electrical apparatus capable of distorting wireless reception. The list of apparatus specified as requiring these gadgets include vacuum cleaners, refrigerators, washing machines, electric heaters, lifts, printing machinery, all type 8 of electric motors, and even wireless sets.

The Australian Broadcasting Commission sent two of its officials to' England to study radio there. The Sydney programme director writes that 8.8. C. programmes are dull, that Australian people would not stand them, and that the talent is usually not above Australian standard. That is complacent enough, but the conductor of the Wireless Chorus at Sydney affirms that it is equal to that of the 8.8. C. 1 Next we will be told that the Sydney Orchestra is equal to the 8.8. C. combination.

Many strange things arrive at Broadcasting House, London, but a long parcel delivered there recently must be the queerest of all. It was formally received and signed for as “one babbling brook.” It was designed for the Effects Department, but when heard on the radio it sounds like a genuine little stream trickling merrily through the countryside. The contrivance is six feet long ajjd was made by a carpenter ! There is another particular “ eli'ectthe screams of seagulls—which have been heard so often that they were believed to be genuine noises recorded on a gramophone record. But gulls are too awkward to record, so the 8.8. C. mep take«two little strips of wood, like pieces from a bundle of firewood, tie them together at each end and stretch a piece of elastic in between. When they blow through the strips it vibrates the elastic and produces that realistic seagull noise.

A group of expert navigators intends to make a trip around the world in a small boat to explore isolated, rarely visited islands and conduct scientific research. After 20 years of planning and mapping out, this trip has now ripened towards realisation. The expedition, which is under the leadership of Captain 0. A. Schumann, of Houston, Texas, expects to finance the undertaking by producing advertising materials. For instance, it will be possible to take photographs of natives enjoying beverages, cereals, and various other food products, using soaps and cosmetics, being entertained by radio, etc. It is expected that radio communication will be carried on both directly and by relay over amateur stations.