RADIO NOTES

Dominion, Volume 24, Issue 65, 10 December 1930, Page 16

RADIO NOTES

By

"ETHER "

Radio and Rum Running.

A man said to be known internationally as a “radio wizard” and “wanted” by France and England for infraction of radio laws, was among the persons apprehended. by the' Brooklyn (U.S.A.) police when they raided a rum-runners’ wireless station at Coney Island on September 27. The transmitting apparatus, valued at £3,000, was used for regular communication with rum-running vessels outside the 12-mile radius. Watch Your Watch.

I wonder how many people have had their watches ruined by experimenting with moving-coil loud speakers (remarks “Free Grid” in the “Wireless World”). Mine camo to disaster recently when examining the magnet system of one of the “permanent” type of moving-coil loud speakers. Being on my wrist it came well within the influence of the magnetic field, and is now hopelessly magnetised, so much so, in fact, that it not only loses, which is the customary symptom of a magnetised watch, but refuses to go altogether, so strong was the magnetising force. The remedy, of course, is to place it for a time in a strong alternating current field, this having a demagnetising effect, and this I intend doing. Query Comer.

“Mains Supply” wants to know the best way to control‘the voltage output from an eliminator. There arc two ways of doing this. One method drops the voltage by placing a resistance in series with the plate supply to the valve in question. The drop iu volts in this case is proportional to the current drawn. One milliamp passing through a resistance of 100,000 ohms drops 100 volts. This method is all right where fairly large currents are passed. The second method is to use a potentiometer and tap off the required voltage somewhere along the potentiometer. The potentiometer is placed across the eliminator supply terminals. Provided the resistance of the potentiometer is about 50,000 ohms only a small 'current will flow through it when no current is tapped off.. Tappings may be made to various portions of the potentiometer. The highest voltages will be toward the positive end of the potentiometer. This method is very useful for breaking down a high voltage supply, using the first method for fine Icontrol subsequently. Potentiometer control is particularly useful when it is required to tap off only small currents. In the case of anode bend rectifiers only a fifth of a milliamp is required. A very high resistance would be required to drop only a few volts by the first method, resulting in poor regulation.

“Wairarapa” says: Is it better to use transformer coupling or resistance coupling in the audio end of a receiver? Transformers have been so perfected they give, even responses down to frequencies below 50 cycles, Moreover, they give a voltage step-up themselves of three or four-times. On the whole this method of coupling has much to recommend it. Resistance coupling is best used only after an anode bend detector in whiph position transformer coupling, is not so satisfactory. HOW A SET WORKS Detector and Amplifiers The electrical variations representing speech or music have frequencies ranging between 25 and 8,000 or 10,000 cycles a .second, and these are conveyed across the space intervening between the transmitting station and the receiver by means of a radio-frequency wave, that is, by a “carrier wave” whose frequency is greater than 30,000 cycles a second or so, For a wavelength of 300 metres the radio-frequency involved is one million cycles a second or 1,000 kilocycles a second, the frequency being inversely proportional to the wavelength.. The amplitude or strength of the high-fre-Swave is varied or modulated m ince with the wave shapes representing the matter broadcast (says S. O. Pearson in the “Wireless World”). Every receiver possesses a detector or rectifier which performs the essential function of separating out the low-fre-quency electrical variations from the radio-frequency or carrier-frequency oscillations. Without this separation it would be impossible to operate any electro-mechanical reproducing device. The detector thus really forms the nucleus of every receiver, and one of the first points in designing a receiver is the attainment of efficient and satisfactory rectification. The efficiency and general performance of a valve detector depend to a very largo extent on the value or amplitude of the high-frequency voltage applied to its grid circuit. In general the voltage developed across the tuned circuit associated directly with the aerial is too small to enable the rectifier valve to function properly if the latter is connected directly to the tuned aerial circuit. Only when the station being received is powerful and moderately close is satisfactory rectification under these conditions attainable. , x .. ■For the reception of distant stations which produce extremely feeble oscillations in the aerial tuning circuits one or more valves are employed between the aerial tuning circuit and the detector valve in such a way as to produce highfrequency voltage oscillations of greatly increased amplitude at the grid of the detector; the high-frequency oscillations are virtually amplified before being applied to the grid circuit of the detector, but it will be realised presently that the energy represented by these oscillations of increased amplitude is drawn from a local source of supply .such as a hightension battery. The so-called amplified oscillations are really a new set in a separate 'circuit quite distinct from those in the aerial circuit, but are controlled by the aerial oscillations through the medium of the amplifying valves in such a way as to have the same form and frequency.

TESTS OF RANGE

What a Set Should Do

TRANS-TASMAN RECEPTION

So many queries come in as to what can be and what cannot be received in the Wellington district that a few notes on the subject will be of interest. The receiver used for these tests consisted of one high-frequency screen-grid stage, -rid detector, and transformer-coupled audio stage. Headphones were used, although many of the statiohs received were loud enough for a cone speaker. The aerial was by no means good. it consisted of fifty feet of wire suspended about five feet above the roof of a onestoried house. The earth was to the water mains. . . „. . Almost any morning 3ZC in Christchurch, on 250 metres, can be heard emitting its ration of monotonous matutinal recipes. This station is unmistakable as it is about the only one with a woman announcer. Incidentally her voice is particularly clear. Even in bad static she can be understood easily, which is more than can be done with the gruff voice of a man under similar conditions. Station 2ZM 260 metres, generally comes in well in the evenings, but it is subject to. fading. While other small fry, such as 4ZL (246 metres, and —YB (463 metres) are fairly consistent ether shakers in the vicinity of Wellington.. A simple set of this type, besides picking all the “A” class stations m New Zealand as a matter of course, is capable of reaching out across the Tasman. Such stations as 2FG (4dl metres), 2BL (353 metres), 2UE (293 metres) and 3AR (484 metres), may be heard almost any ’night when static permits. On good nights, in fact, several of these stations can be made to work a modest loudspeaker. After about eleven o’clock or possibly a little later, the Japanese stations come on the scene. These stations are so regular they cannot be considered any special test of a receiver s sensitivity. A test of this nature is best made among the smaller fry of Australia, such as 2HD (288 metres) or 2DB (255 metres). A set of the type used in these tests can pick many of the smaller stations in Australia on good nights. On some, occasions over two dozen stations have been logged altogether, while the faint murmurings of a number of others may be heard. The trouble in many cases is the unusual shyness on the part of stations to announce their names. Earlier in the evening it is possible with a good aerial and a more sensitive receiver to hear stations in the United States, such as Chicago and others. . ■ Those who cannot find sufficient cash to purchase a multi-valve, factory-built set can embark upon the construction of a humble three-valve receiver with the confident expectation of interesting results on both headphones and the loudspeaker. MAINS UNITS Trouble With Short-wave Sets I have no hesitation in saying that the source of nearly all the. troubles that crop up when a mains unit is used with a short-wave set is the detector. It is child’s play to make the “notemags, work from the cheapest eliminator, but when we get to the detector we generally run right into a nest of troubles (writes “W.L.S.” in “Popular Wireless”). Unfortunate though it may seem, the trouble generally comes from the detector and not the mains unit. If the H.F. choke is doubtful, if the by-pass condenser is not above reproach, and particularly if no trouble has been taken at all to provide a really efficient by-pass for H.F. before it gets too far round the detector anode circuit, then it stands to reason that the slightest modulation in the H.T. supply, whether ripple from D.C. mains or 50-eycle stuff from imperfectly-smooth-ed A.C. mains/ will cause plenty of trouble. Therefore see that your by-passing scheme is efficient. This means not only that its' physical 1 position on the baseboard is. correct. Remember, above all things, that in the region of 20 metres one good long loop in the wiring may have half the inductance of the tuning coil! . - Ths, if you are. using an ordinary series-fed circuit you should be able to trace the following short, direct wires: from detector anode to one side of the reaction coil; from the other side to an H.F. choke and also to one side of the reaction condenser (the other side of which goes to L.T. negative); from the other side of the choke to one end of the transformer primary; from the other end of the primary straight down through a 2 mfd. condenser to L.T. negative, and also through 10,000 or 20,000 ohm resistance to H.T. positive. Using Extra Smoothing. If you can find all this there should not be much wrong with the “set” part of the business. Now for the eliminator. If it is a really good, mains unit it should work straight away with one of the appropriate H.T. tappings taken to the detector H.T. terminal mentioned above. If it is of the cheap kind without enough smoothing, take the detector H.T. lead out through an externally-con-nected 20 or 30 henry choke, and connect the “set” side of this choke straight down to earth through a 2 mfd. or 4 mfd. condenser. If there is still a trace of hum, do not be afraid of using 8 mfd. It is cheaper than buying high-tension batteries any- - y > Need for a Good Earth. I honestly fail to see how anyone can be troubled with hum now, providing he has a moderately good earth on the set. That, too, is a point missed by a number of people who have found that they can work a short-waver quite well off batteries without an earth. The next trouble that may arise is that the set will continually be slithering in and out of oscillation (at least, we hope it slithers —some of them will go in and out with ear-shattering explosions). This is, of course, due to slight but persistent variations in the mains voltage, and is, unfortunately, common to a great number of supplies, including mine. This phenomenon is capable qf causing much annoyance, but, luckily, there is a simple remedy. Simply connect, a neon lamp across the detector positive and negative H.T.

IMPORTANT CENTRE

' Listening at Sydney, LA PEROUSE STATION Overlooking Botany Bay, on the heights of La Perouse, at Sydney, stands the most important and largest wireless receiving station in the southern hemisphere. Of the most modern design, the equipment incorporates the latest ideas in commercial receiving apparatus. From a network of stations throughout the world, traffic is received there. Messages from ships’ stations in the Pacific and Indian Oceans, and from the coastal radio stations on the south-west-ern seaboard of Australia. A wireless telephony service is also maintained between La Perouse and the trawlers operating off the Australian coast. La Perouse is also the terminal of the wireless telephony service between Australia and Great Britain and twenty-two European countries, and will be the Sydney switching terminal for the wireless telephone service from Great Britain and Europe to New Zealand. The latest news of the world is also received there from the Rugby highpower station, while reception is effected of broadcast programmes transmitted from English, American and Continental high-power broadcasting stations. Short-Wave Range. The enormous ranges at present attained by short-wave working is demonstrated by the reception at La Perouse of experimental communications from shortwave stations in Britain and Europe, the United States, Canada, Africa, Asia and the Dutch East Indies. , . La Perouse maintains communication with all the short-wave stations in the Pacific, including Rabaul, Suva, Noumea and San Francisco. Effective communication is also kept up with ships’ sta-' tions equipped with short-wave apparatus crossing the, Pacific and Indian O< The S 'system of centralising wireless activities, developed by Mr. E. T. Fisk, Managing Director of Amalgamated Wireless, has resulted in the establishment of three large centres—the transmitting centre at Pennant Hills, Sydney, the receiving centre at La Perouse, and the control centre at Amalgamated Wireless headquarters in the city of Sydney. Under the old system it would have been necessary to have a separate site for each of the nine commercial services at present operated by the firm from Sydney. Operators are stationed at only La Perouse and headquarters, the staff at Pennant Hills transmitting station comprising radio engineers alone. The operating efficiency of all the services has been greatly improved by the system of centralisation, apart from the economy both in equipment and personne The visitor at La Perouse receiving station sees only a small building and a few masts, but the opetrator inside the building sees one of the wonders of modern science—a receiving station with gigantic electrical “ears,” able to detect the smallest vibration, and to read, instantly, its message, whether it has travelled one or ten thousand miles. With headphones to his ears, each operator sits before a typewriter, with a Morse key at the side. This is a simple, unpretentious-looking instrument, but a depression of the key actuates a transmitter at Pennant Hills, some 16 miles away. While listening to a .message from a ship, the operator can, simultaneously, send a message to it, or to another vessel by the Pennant Hills marine transm Another operator is in touch with far away Noumea. Others are exchanging traffic with ships, with New Guinea, or with coastal radio stations. Others again are listening-in to the latest Press news from Engla'nd and the Continent, or are receiving messages from experimental short-wave stations in Europe, America and the East. Day and night messages are flashed from all parts of the globe, to be picked up by the ever-watching operators in Sydney. The touch, of a. keyboard, the depression of a switch, immediately phts the transmission of messages into action. Altogether nine services are operated from the La Perouse station. Messages from Rabaul, the Fiji stations, and the Beam stations at Braybrook, Melbourne, received at La Perouse, are automatically relayed to SydPrinciples and Experiments.

The electro-magnetic principles discovered by Oersted and Faraday a, century ago, the experiments of Joseph Henry, and the discoveries of that great “electric king,” Lord Kelvin, the mathematical predictions of that brilliant physicist, James Clark Maxwell, and the laboratory work of Henrich Hertz m 1886, verifying Maxwell’s deductions, were milestones in the evolution of wireless telegraphy, even though many of these scientists were not at the time, aware of the uses to which their discoveries were to be applied. Branley, Lodge and Pop off, noted scientists, were also instrumental in advancing experimental wireless. It remained for Marconi, however; then a youth of 21, in 18&5, to devise a practical scheme of communication without the use of wires. A stroke of genius resulted in a new science which was destined to have a greater effect on human activities than any invention, except probably printing, of the preceding 19 centuries. Australia to-day is in the forefront of wireless progress. HEAVISIDE LAYER Messages to Mars

A good deal of controversy has been created by some theories put forward by Dr A. S. Eave, of McGill University, Montreal, at a meeting of the Royal Society of Canada, relating to the problem of the Heaviside Layer (says Dr. Roberts in “Popular Wireless’). The Heaviside Layer is now believed to exist at a height of from 200 to 400 miles above the surface of the earth (varying in its position and properties at different times and in different con ditl°lt8 lms since been discovered that there are at least two further electrical layers, estimated to lie at distances respectively of about 150 miles and 75 miles above the earth’s surface. The Heaviside Layer formed a very convenient peg upon which to hang the theory of the zig-zag transmission of radio waves around the curved surface of the earth. It seems, if Dr. Eave s theory is correct, that our views on the question of long-distance radio transmission will have to be considerably modified, as it would seem fairly certain that for practical purposes the radio waves would not be able to penetrate even the first electrical layer, and so could not be affected to any appreciable extent by the Heaviside Layer, which is at a much greater distance. It has been said that the presence of these electrified layers in the upper atmosphere must be an absolute bar to any possibility of transmitting radio signals to another planet (Mars,' of course), but I do not think that this is quite a proper view to take, for it must surely depend upon the wave-length and nature of the waves. \ Inasmuch as light waves and heat waves (which are closely related to radio waves) pass freely through these electrified layers, whatever they may be, it is certainly not inconceivable that some type of radio waves may be found which may not be absorbed by the electrical layers. At any rate, considering only the types of radio waves with which we are familiar at present, it seems that these are almost completely reflected or absorbed by the electrical regions in the upper atmosphere and therefore unable to be projected into inter-planetary space.