Radio Review

Evening Star, Issue 19758, 7 January 1928, Page 17

Radio Review

Flashes from Everywhere.

IS LIGHTNING A.C. or D.C.? “ Is lightning alternating current or direct current?” This question was recently asked by a radio enthusiast who was anxious to determine the question, but was unable to find out for himself. and could find no one who could give a satisfactory answer. Per' haps the following from an American magazine may prove of interest to tho enthusiast as well as to many others:—* “ From the fact that lightning can be heard in a radio receiver, it would appear, off-hand, that the discharge must be of an oscillating Or alternating current nature, since radio, a priori, is an alternating current science, in Professor Humphrey's 1 Tho Physics ot the Air, 1 in the chapter on lightning, tho matter is discussed in considerable detail. Experimental evidence is given of the direct current nature of the lightning discharge, as well as a mathematical analysis showing tho impossibility of' producing oscillations in the alternating current sense by means of such a discharge. Briefly, the experimental evidences of the existence of direct current only are ns follows :—(1) Lightning striking a telegraph line has often been known to operate the instruments along the line. Where the discharge of an alternating current nature, it would not operate the instruments if of a high frequency, and if of a low frequency would merely cause them to buzz. (2) Direct current electric lighting circuits using overhead distribution wires have, at 'times, had the polarity of their dynamos reversed as a result, of lightning striking tho wires. , Only a direct current impulse could reverse tho field polarity of a dynamo, (if) Oscillographic records of lightning discharge currents indicate that all the energy is on one side of the zero line, thus showing no reversal of the current, “ In discussing the subject mathematically, Professor Humphreys anaylsek' the electrical circuit, composed of the condenser, formed by the under surface of the cloud and the surface of the earth, and the conductor, formed by the ionised path of the discharge. it can bo shown that if the resistance of an electric path relative to tho inductance and capacity of tne path is above certain critical values, the discharge of electricity a ag that path is iion-ojcillatory; that is, it s a unidirectional discharge. It can also be shown mathematically that the resistance of tho ionised path over which tho lightning discharge travels is generally higher than this critical value, so that tho discharge must be uuiclii actional._ There are other considerations which seem to bear out this contention.

A NEW VALVE. A new receiving valve labelled UX-222, known ns a four element valve, because it has a filament, plate, and two grids, has been introduced by the Radio * Corporation of America (writes “Grid,” in the ‘ Listener In’). The valve is designed for use as a radio frequency amplifier in dry battery operated circuits, and according to radio engineers it is a valve of great promise in the experimental and development field. The standard valve has but one grid. The new amplifier has two grids placed concentrically with each other and with tho filament element. This arrangement constitutes a distinct departure from the conventional radio valve construction. The “ control grid ” element, which corresponds to the “regular” grid in receiving valves of the typo now in general use, is connected to a terminal cemented to the top of the glass envelope. The other grid clement is known as the “ screen grid,” and is attached to a terminal in tho standard base in tho conventional manner.

Dr Alfred N. Goldsmith, chief broadcast engineer, commenting on the several applications of tho new device, said; “The four-element valve, which is still iu tho experimental stage, has been designed primarily for high voltage amplification in radio _ frequency circuits. It has , several distinct applications, two of which are as iqllows; First, when the 1 regular ’ grid is connected to the coupling or tuning coil and the proper ‘ C ’ and ‘ B ’ voltages applied, tho valve becomes automatically neutralised, preventing what is known ns 1 feed-back,’ or the unstabilising influence found in conventional valve applicatioii. With the unbalancing influence thus removed, the receiver becomes very stable. Construction and operation aro simplified. Thus the customary howls often caused by self-oscillation are entirely avoided. “The seepnd application in radio frequency circuits is made with a reversal of the grid connections,” lie added. “ When so used it is known as a 1 spaco-chargc-grid ’ valve. Its use in this manner affords a very high voltage amplification or effective signal gain, tho amount of which depends upon the coils with which it is used and various other details. In each application the valve must bo entirely shielded by a metal jacket, with the ‘ regular' or control grid passing out through a small hole in the top of tho shield. Other provisions are that tho control grid and plate wires from tho valve be kept well separated. The metal shield must also bo connected to either the positive or negative ‘A ’ battery terminal on tho valve socket.”

“ As to why we hear lightning crashes' on tho radio set. that is easily explained. Radio listeners living in districts where the house-lighting power is direct current know that if a light is turned on or off in tho room with tho radio set a click is heard in the ’phones or on tho loud speaker, in this case the sudden stopping or starting of the current causes rapid building up or dying down of the lines of force around tho lighting circuit wires, and those moving magnetic lines induce currents in some part of the radio receiver. In the case of the lightning discharge we have, successively, a rapid rise and fall of electric and magnetic fields, since here Iby current both starts and stops with groat suddenness. Thus, although the c; irgo does nob reverse in direction, tho very rapid motion of the lines of force causes a momentary current to be induced in the radio antenna*. Thus we get the crash in the receivers or loud speaker. It is the very suddenness of the disturbance which makes it so loud. “ The duration of tho average single flash is about .0002 of a second, according to Professor Humphreys.”

In tho first application of the UX-222, where automatic neutralisation is secured, the control grid must bo used with a “ C ” battery bias of from minus 1 to minus 1.3 volts. This is secured easily by adjustment of a potentiometer placed in the negative lead ol tho “ A ” circuit near tho valve socket. Tho middle terminal ol the potentiometer is connected to the control grid through tho grid tuning coil. In addition the screen grid must bo connected to or biased by a 15-volt positive battery. This may be secured by connecting to tho 45-volt terminal of tho valve plate battery. The recommended valve plate potential in this case is 135 .volts. In the second application to radio frequency circuits, where it is used as a space-chargc-grid valve, the outer or screen grid becomes the control grid, which is biased with a “C” battery from zero to 1.5 volts negative. ’The space-charge grid, or former control grid, then functions in another capacity and must ho biased about 22.5 volts positive by connecting to the valve plate battery at that voltage tap. The recommended plate potential is 135 to 180 volts, the latter voltage being used if the valve is used with ' resistance coupling in the plate circuit instead of tiie coupling by means of the conventional coil system. The resistances adapted for this use are between 100,000 and 250,000 ohms, or one-tenth to onequarter megohm. In regard to the amplification secured when properly connected to receive the broadcast waves the UX-222, if employed for self-neutralisation, will increase the signal voltage about thirty to forty times, as compared with a five to seven voltage multiplication secured with the conventional general purpose receiving valve. On the other hand, when employed as a space-charge-grid valve, tho received signal voltage may be increased by more than 15U times per stage. The UX-222 requires but 0.132 amperes of filament current at a filament voltage of 3.3. Thus it may be easily operated from three dry cells connected in series, or two groups of throe cells connected in series, and finally tho groups connected in multiple. The output voltage of such a cell group will be 4.5 volts; therefore a rheostat of from nine to ten ohms, which is provided with three terminals similar to _ a potentiometer, can bo connected with its full resistance in series with the “A” battery negative and valve socket negative terminals This will furnish the valve with 3.3 volts for its operation, and at the same time make it possible to use the drop in voltage across the resistance to bias the valve grid by connecting the centre or variable tap of the resistance to the grid input coil of the valve. The general application of the UX-222 in the radio industry is still a matter of reflection by engineers, as models of tho valve have only recently been circulated among tho licensed manufacturers of the RCA lor consideration individually by engineers and designers of the companies. The shortcomings of the conventional three-ele-ment receiving valve aro perhaps most greatly manifest in what is called interelectrode capacity, or the capacity between the electrodes themselves, plus the capacity between the more or less parallel connection wires that make contact with the circuit through the base of the valve. This capacity allows some of tho energy of tho plate circuit to be fed into tho grid circuit, tending to unbalance the circuit and create a state of oscillation. Such conditions are detrimental to the relaying action of the valve, and may greatly distort the incoming signal. The detrimental effect of self-capacity is said to be absent in the UX-222, because of the introduction of tho fourth element, the screen grid. When “properly biased on all grid elements, the valve will not only operate totally without oscillation, but will also multiply the signal being received from four to five times ns much as the general purpose amplifier, the 201-A.

MICROPHONE FRIGHT. It is surprising that people who have spent a lifetime on the stage should suffer with “nerves” when they face the microphone. In fact, it is the experience of broadcasters that many prominent artists are utter disappointments for broadcasting, and simply because they get “microphone fright.” Rupert Hazell, who made such a remarkable “hit” at 3LO, said that when he faced the little “ black perforated contraption ” he wanted to say “everybody happy,” as he always did, but felt so horribly unhappy himself that he could not get the words out. However, he made up for it as he gained his “air leg,’’ and wound up by being perhaps the greatest radio comedian 3LO has ever had. Madame Elsa Stralia, who has.sung over and over again to royalty of all nations, showed decided signs of “nerves” in facing the microphone, even after she had been broadcasting for months, and Stephanie Deste, who, as “Wanda” in. ‘ Rose Marie,’ faced huge audiences nightly without a sign of nerves, became “mike stricken” until the ordeal of speaking into the little “patch ot black infinity” had become familiar. f The late Lee White was strangely nervous when broadcasting, and never really got used to what she always regarded as an ordeal, although it was impossible to detect the slightest sign of nervousness in listening to her remarkable broadcast performances. One speaker at 3LO, who was a prominent orator, became absolutely tongue-tied before the microphone, and his talk had to he abandoned, and Mr Lawson, when Premier of Victoria, experienced a spasm of nervousness the first time ho broadcast. The Prime Minister (Mr Bruce), however, is very placid and cairn with “mike, and they are now quite old friends. AERIAL DON’TS. Perhaps tho following aerial don’ts will help one to gain better reception with his radio Don’t neglect to. include a lightning arrester in the aerial circuit. Don’t forget that the insulation of tho aerial is one of the most important points if efficiency is desired. Don’t use insulators that are unnecessarily heavy. . Don’t use any common piece or rope to support the ends of the aerial. Don’t omit to make some provision for the contraction of the aerial ropes that will take place in wet weather. Don’t forget that soot on an insulator makes an excellent conductor and that the efficiency of the set Will suffer as a consequence. Don’t try to econoihise by using a thin wire for the aerial. Don’t omit to clean the insulators occasionally, especially if the installation is near the sea or in a smoky atmosphere. ~ Don’t forget that the earth connection is an important adjunct to tho aerial. Don’t use very light supporting masts; they bend. Don’t use iron wire for the aerial. Don’t allow the lead-in to be too near the house.

‘RADIO HANDBOOK.’ A copy of Scott’s ‘ Radio Handbook ’ has been received. In this, the fourth edition, tho author goes fully into the intricacies of radio, but everything is explained in uon-tcchnicul terms. A wealth of information is given in the handbook, which embraces _ a _ great number of radio topics. Circuit diagrams are included.

Don’t run the aerial wire parallel to any other wires or metallic conductors. Don’t use knotty wood for the mast. Don’t omit to stay the mast.

•• Henry" will be pleased to answer any questions through this column relating to the fascinating hobby. Each correspondent must sign hla name and address (not necessarily for publication). Newsy items will be welcomed.

ON SHORT WAVES

FOR NON-LISTENERS. Every day (including Sundays) a concert, consisting of vocal, instrumental, news, orchestral, and other items is put on the air from one or mors of the New Zealand stations, and in addition there are many amateurs who transmit some quite good programmes. If an item from a particular station does not altogether please, he can (within the range of his set) tune in another. The programmes of concerts to bo broadcast from each station are published in the ‘ Evening Star,’ with the time of each item, so that anyone is enabled—within reason, of course—to prepare a composite programme of desired items.

Taken all round, the programmes broadcast in New Zealand are of quite a high standard, and many pleasant hours may bo spent listening in. In view of these facts it would pay nonlisteners to install radio receiving sets in their homes. It must be remembered. however, that before any wireless apparatus can bo put to use a license must bo obtained. The annual license fee is 30s.

The essentials of a receiving set are ' ; —(l) The aerial, a means of intercepting the waves as they pass through the ether: (2) the tuner, a device for causing the aerial to be in harmony with the incoming waves; G, a rectifier, which is for rectifying the incoming oscillations; (4) the phones or loud speaker, a means of making those rectified oscillations audible. If it is desirable to install a readymade set, any dealer will gladly furnish all information with regard to x erecting of an aerial, and will also explain the functioning of the set it is intended to buy. It would also be desirable to spend a few shillings and become the possessor of a book or two explaining the workings of radio. To operate a bought set no experience is needed. It is just a matter of turning on the battery current and adjusting a few knobs, and, swish, there is the station.

The enthusiast who wishes to build a set of his own would do well to let an experienced friend help him. Now, then, non-listeners, what about it? Just think the matter over, and I am sure you would like to be in the ranks of the vast arhiy of radio enthusiasts. Listening in is really more fascinating than you would think. There is a distinct thrill in chasing up a distant station.

If ever you get into difficulties with a set and cannot find anyone who can put your receiver to rights, just drop a line to the writer, and he will bo only too pleased to give what assistance he can.

What do the words “ short wave reception ” conjure up in the minds of listeners? The average enthusiast’s impression of long-distance work on short waves is connected with cold, _ early hours, and the unpleasant sensation of rising out of bed in obedience to a harsh alarm clock. This is not necessarily the case. Certainly short wave broadcasting is often heard early in the morning, but, on tho other hand, many of the stations are working in the daytime. i For tho listeners who arc anxious l 'to hoar England it will bo consolatibm to learn that some of the stations there can bo received without an all-night vigil. Short wave enthusiasts, however, would do well to persevere at the Morse code. The best way of learning is, when the letters are memorised, to keep listening to some Morse station working faster than one can read. Ho should not be discouraged if he finds ho can only rend one letter in every word. In time ho will find himself almost unconsciously receiving more and more of every transmission to which he listens. When he is “ Morse perfect ” he may anticipate bearing nearly every active country in the world. Short wave reception is, therefore, well worth any trouble that may have been spent in preparation. HERE AND THERE. Every Monday morning between 7 and 9 o’clock (New Zealand summer time) 3LO, Melbourne, transmits a special Empire programme on a wave length of 32 metros. Generally the volume on three tubes is excellent, and the music exceptionally pure, hut last Monday an unsteadiness was reported. We had something good from RFN last _ Sunday night. “Tho Russian station was in great form.'' said one listener. Orchestral music was more in evidence than usual. Well, 3YA saw the New Year in all right, but surely those in charge at Christchurch did not expect us to listen to the stuff they put out. The bunging of crackers and the din of pipe music, along with yelling and shouting and other unintelligible noises seemed to combine in one mighty assault against tho ears of the listeners. The ringing in of the New Year by tho full peal of the Cathedral bells looked all right on tho advertised pro. gramme, hut was most disappointing, over the wireless at any rate. Could not the microphone have been placed nearer the bells and further away from the racket in the street?

Now, on the other hand, 2YA broadcast the watch night service from St. Andrew’s Church, and recaption of tins was excellent.

Auckland, I believe, also saw the New Year in, but 4YA shut down after his night concert, and was heard no more. Surely ho could have given us something. Even a short quarter-hour programme and a broadcast of the Town Hall chimes at midnight, followed by a “ happy New Year all ” would have been welcomed.

While on the subject of Nov/ Year programmes it may be mentioned that the Americans gave 1928 a hearty welcome On Sunday night (Saturday in America) all the stations I have heard ot made quite a feature of the New Year broadcast.

SCL, Adelaide, has started a children’s session at midday. From the large amount of letters received it may he judged that this session is almost as popular as the evening one. Originally the midday children’s hour was instituted for the benefit of sick children. ■ Volume from the Australians is ■‘nothing to write home about ” To-night 3LO is to broadcast the ih Gatano Revue from the Tivoli Theatre. Broadcasting has been introduced in Salvador. •

A little less picture, theatre orchestra relaying would be welcomed fiom the New Zealand stations. A number of listeners wait till the relaying ceases before tuning in the night programme. When I wrote these lines Christchurch was relaying from some theatre or other, and every now and then the sound _of laughter almost drowned tho music, ns well as grating on one’s ears.

The best arrangement for the wiring of a soft detector tube is to connect tho filament side of tho _ secondary circuit to the negative terminal of the detector tube socket. When a hard tube such as the UV-201 A is used as a detector, the filament wire from

the secondary circuit should be connected to the positive socket terminal. Remember this point as well as the resistance of the rheostat when you change from ono tube to the other. Step by step scientists are completing the conquest of the radio waves that are shorter than one metre. The cathode-ray oscillograph has been used successfully to detect and examine waves down to .30 centimetres long, a trifle over Ift. This means a frequency of one billion cycles a second.