THE WIRELESS WORLD

Otago Daily Times, Issue 22717, 1 November 1935, Page 3

THE WIRELESS WORLD

NEWS AND NOTES

By Magna Vox

Items of local interest are invited by "Magna Vox" for publication m this column. It is necessary that such matter should reach this office by luesdayot each week for insertion on the following Friday. 2BL, Sydney.—74o K.C., 405 metres. 2FC. Sydney.—6lo'K.C., 492 metres. SAB. Melbourne. —680 K.C., 476 metres. 3LO, Melbourne.—77o K.C.. 360 metres. SCL, Adelaide.—7Bo K.C., 411 metres. 4QG, Brisbane.—Boo K.C., 311 metres. IYA, Auckland.—66o K.C., 461.3 metres. 2YA Wellington.—s7o K.C., 526 metres. 3YA, Chrlstchurch.—72o K.C.. 416.4 metres. 4YA, Dunedln.—79o K.C, 378.5 metres. 4YO. Dunedln.—ll4o K.C, 261 metres. ANSWERS TO CORRESPONDENTS. "Experimenter," Middlemarch.—lt is really permissible. So use as lona an aerial as can be worked without affecting the tuning of the set. There is no danger of straining the set in any way by doing this. Height is even move important than length, and if you can raise the end of your aerial, still better results can be looked for. From the log you have forwarded, however, I should say that you are just about getting the best possible results from your machine, as there seems to be very little you cannot tune in. D. F. M., Dunedin.—(l) It would seem that one of the valves is responsible for your trouble. Perhaps some of the internal supports have come loose, and move about as the receiver warms up. You might be able to trace the trouble by tapping each valve with your finger nail to find whether one of them is noisy. (2) Such a fault may or may .not show up on a tester, but otherwise if the set works all right, I do not think you would do any harm by leaving it there. Probably the valves have been in the set for some time. "Ohoke" Temuka.—(l) I am not particularly keen on using transformers a» chokes. It is, however, possible to do it by connecting the B plus terminal to the G terminal. The plate of the valves is then connected to the P of the transformer, and the B supply to the C minus terminal. Try connecting the two windings in series the other way round, and use the connection which gives the best results. (2) I do not know. Can the agent from whom you bought the set ten you? If not, I am afraid you will have some difficulty in getting the information (3) New Zealand Express Co., Crawford street. (4) For obvious reasons I cannot, in this column, enter into any controversy on the merits og demerits cu the sets you mention. (s)' Out of the question. COMING ATTRACTIONS. The Broadcasting Board has arranged for a further group of well-known artiste to tour the main stations. Miss istella Power, Australian soprano, who has recently returned from the United States, and who has been broadcasting over the Australian network, will give five re citals from IYA early in December, while Miss Imelda Fama, pianist, and sißter of the well-known Tano Fama, will arrive here in mid-January. Another notable engagement is that of Mr Roland Foster, examiner for Trinity College of• Music, London, who is to give two piano recitals in January. Mr George Ellwood, one ot New Zealand's greatest 'cellists, will broadcast from IYA on November 22, 23, and 27. WAR "EFFECTS" BANNED. There will be no more "dramatised" presentations of war news by 2FC. Ins commission has issued instructions to its staff that news from the theatre of war must be confined to fte spoken word, and that no attempt ft to bo made to colour what is already' a dreadful business. FROM THE HEIGHTS. The first of a series of broadcasts from high spots of the British Isles was heard in transmission 1 last Friday, when a speaker ascended to the top of the Royal Albert Hall, London, and gave his impressions to listeners. The height of the Albert Hall is 120 feet. Among other high spots which may be visited are the following:—Blackpool Tower; the Churcn of St. Mary Redcliffe. Bristol; Canterbury Cathedral; Edinburgh Castle: the -8.8. C. transmitter at Moorside Edge; the National Museum of Wales, Cardiff: Greenwich Observatory; Birmingham Town Hall; York Minster; the Norman Tower, Windsor Castle; Eddystone Lighthouse. The broadcast from the top of Blackpool Tower will be given to-morrow. A UNIQUE RECORD. Brisbane claims the unique record of having the oldest and youngest amateur radio operators in the British Empire. They are Mr Philip Hardgvave, aged 78, of station VK4PH, and Miss Madeline M'Kenzie, aged 12, of station VK4GK. Mr Hardgrave, a retired solicitor., qualified for his amateur's, proficiency certificate two years ago, obtaining 04 per cent, marks for operating and 75 per cent, in the technical teste. His enthusiasm knows no bounds, for he keeps his own card index of every amateur station in Australia and also New Zealand. Miss M'Kenzie gained her certificate a few months ago, her marks in thc> operating section being 08 per cent, for sending and 96 per cent, for receiving. Her father has been a keen amateur for 15 years; the whole family, indeed, is "radio conscious,". for Mrs M'Kenzie and two sons, aged 10 and 8 years respectively, can all read Morse. A MYSTERIOUS ADVERTISEMENT. An advertisement appeared in some New Zealand papers urging listeners to tune in to a Sydney, B station at stated times. Many conjectures have been made regarding the subject of the broadeast, some of these being Christian science lectures or propaganda for New Zealand B stations which lias been banned in New Zealand. Neither of these was correct, as the broadcast at the hour indicated was a sponsored session eulogising South Australian wines. THE DAY OF THE LOUDSPEAKERS. Hitler has stated that he conquered Germany with loudspeakers. This contention seems to have been reflected in the exhibits at the recent German radio show. Thanks to the demand for highpower amplifiers for political purposes, apparatus of this kind was more in evidence at Berlin than in London. German amplifiers up to about 20 watts are of the class " A " type, while those above employ modified quiescent" systems. Methods of suppressing harmonic distortion appear to be more, widely .used. Perhaps the most progressive amplifier seen at Berlin was a Philips model, which automatically changes itself over from class "A" to class "B" when a given signal strength is exceeded. Thus it seems that Berlin is leading in the field of amplification development. NOISES AND THEIR CAUSES. There is generally a certain amount of "noise" associated with the reception of broadcast programmes. Some of it is within the direct control of the designer or operator of the receiver, as, for example, imperfections which may be duo to faulty connections or the use of parts which are defective or of inferior quality. Noise due to power supply disturbances and interference is more or less under control, if not at the receiver, at any rate at the source of the interference. Naturally, occurring static disturbances are beyond control, although their effects can be lessened, except in extreme cases, by increasing the powers of transmitters. But even if every precaution is taken to eliminate disturbances due to the causes abovementioned, there still remains the type of noise which may be best described as a "hiss," and which is most apparent when the receiver is brought to its most sensitive state. This type of disturbance is of consequence at the present time when sensitivity is one of the primary qualities of a receiver and a high degree of amplification is expected and obtained from practically every set. The hissing, rushing noise which is almost invariably present in a receiver which has a high gain is considered to be due primarily to two causes, known respectivelv as "thermal agitation and "shot effect." The first is put down to the uneven movement of electrons in a conductor which is carrying a current. The condition may be approximately likened to that of water flowing along a pipe. If the pipe has a roughened internal surface that part of the stream which is in proximity thereto is diverted from its path and thrown towards other

sections of the stream, so that the uniformly smooth flow is disturbed. It might be imagined that the flow of electrons which form a current along a wire may also be subject to disturbances, the result of which is to create email irregular series of pulses in the output. "Shot effect" occurs within the valves. Theoretically, electrons are emitted from the hot cathode of the valve in an even stream, the density of which depends upon the properties of the cathode, the plate, voltage, and other characteristics of the valve. In practice, however, the emission is not perfectly even, and is subject to small local variations which cause the plate current to vary slightly but irregularly both sides of ite mean value. The process here may be compared to the boiling of water. For example, a saucepan of water which is boiling vigorously may, in equal periods of time, produce equal volumes of steam, but it will be noticed that from instant to instant the number of bubbles rising to the surface of the water varies. The emission of electrons from a hot cathode is*, so to speak, a boiling out process, and, like the boiling of water, i fi not per; fectly even for every minute fraction of a second. The difficulty is that the two effects just mentioned occur in every circuit and valve in a receiver. In the late'r stages the strength of the signal is usually such that it completely overrides these small variations and imperfections, but in the early stages, e.g., the aerial circuit or the frequency changing stage of a superheterodyne receiver, the disturbances due to thermal agitation and shot effect are relatively great compared to a weak signal. The signal variations and the noise variations become inextricably mixed in the early stages, and in succeeding stages the noise is amplified at the same rate as the signal. Thus in the output the hies level may be comparable with the signal. With the demand for sensitive receivers, particularly those which are designed to pick up the relatively weak impulses from oversea short-wave stations, this inherent noise has become a matter of considerable importance to the designers of valves and associated circuits. In a superheterodyne receiver the frequency changing valve is a comparatively prolific source of this type of trouble, and it is for this reason that much research has been carried out in the production of valves which will perform the frequency changing function with a minimum of added disturbance and circuit arrangements which will result in the frignnl at that stage being comparatively high, and, therefore, less affected.