WIRELESS NEWS.

Press, Volume LIX, Issue 17815, 14 July 1923, Page 11

WIRELESS NEWS.

TELEPHONY RECEPTION. HOW TO TUNE-IN RADIO CONCERTS. (SPECIAI.LT VIIUITM FOB "the miss.") (By "Electra.") There is absolutely no excuse whatever for the interference caused by receiving valves when one is trying to receive telephony. In some cases, I am sorry to state, it is being done deliberately, but in the majority of cases I think the fault can be laid at tha door of the inexperienced experimenter. Even those who have just started in "the game" cannot very well plead ignorance, since there is always some experienced experimenter who will be pleased to show the beginner how tt. tune telephony; and until one has acquired the necessary information, there should be no trying to receive broadoast. You will " only help to add to the bedlam that, is going on, on short waves, at the prese-it time. Another cause of the trouble is, I feel sure, the use of prohibited circuits, for instance, tho primary and tickler, and one-coil circuits using regeneration. The use of these circuits in inexperienced hands is absolutely forbidden, and such cases should be reported to the radio inspector of the district. It is my intention in this article to give some instruction on the adjustment of a set for the reception of telephony, and my suggestions are primarily addressed to those sunateuis whose sets employ reaction (either magnetic or. capacity) to boost up the incoming signals. If the instructions are caretullv followed, the best results with a minimum of interference will be ensured. Oscillating Receivers. The reception of wireless speech and music calls for very careful adjustment, if one is not to be a nuisance to any wireless neighbours; for it must be Remembered that valve receivers of the reaction type are in themselves tratosmifctera of small power. The waves radiated from the receiving aerial, although very weak, are capable of travelling several miles, and consequently will affect all valve receivers in that radius. Valve receivers act as transmitters only when the set is "oscillating"—that is, when the reactance coil is so tightly coupled to the inductance that the valve generates oscillations which are passed into the aerial. When the set is in this condition it is impossible to receive telephony at its, best, although it is as well to let the set oscillate while searching for the carrier wave of the station transmitting telephony; bub only while searching for it. As soon as it w found, stop your set from oscillating. A Simple Test. The beat way to find out if the set is oscillating is to tighten the coupling between the reactance and inductance coils, at the same time tapping the aerial terminal with the finger. If the set is oscillating, a loud elicit will be heard in the telephones each time tho terminal is tapped. If capacity' reaction is used, rotate the reaction oondenser until clicks are heard in the 'phones, when the aerial terminal is tapped. One or two taps of the terminal is all that is required—and don't (as a well-known local experimenter puts it) "think it is a typewriter." Condenser and Coupling Adjustments. Haying got the receiver into an oscillating condition, telephony, can now be tuned in, an*d the necessary adjustments made which .will give the speech and musio at its best. By means of the aeria] tuning condenser arid inductance tapping switch, esareh for the carrier wave, which will' come in with aloud howl. Now rotate the condenser until the howl dies out, and" it will be found that ajstill further rotation of the condenser will bring the howl in again. The dead spot between the two howls is the correct position. If telephony is going on it will be very distorted and indistinct, because the set is oscillating. To correct this, loosen the coupling between inductance and reaction until the set just stops oscillating, then finally tune the station by : means of the aerial tuning condenser. The telephony will now be very distinct, and if the foregoing instructions, which are very simple, bare been pro-' perly carried out, there will be no trace of distortion. In addition to getting the telephony at ita best, one has the satisfaction of knowing that one is interfering with other "listenersin." The old saying, "Do-unto othera, etc," can very well be applied here. Pilament and "B-Battery" Adjustments. There are other factors which make for the correct reception of telephony.The filament and high tension current must be adjusted to their best values, and it will be necessary to experiment a little with the filament resistance until the best point is found, always remembering to keep tie valve filament as dull as possible, consistent with good signals, luere is a current proportion of high tension to low tension for telephony, and to find this proportion make the following test. Get the set into an oscillating condition, then loosen reaction until oscillations just cease. This point can be found as previously stated, by tapping the aerial terminal while reaction as being loosened. Note the position of reactance and inductance (or reaction oondenser if this is used) when the oscillations cease. Now tighten the reaction and notice if oscillations commence exactly at the spot where they stopped. If this is the case, the proportion of hightension to low-tension is correct, and the set is in its most sensitive condition for receiving telephony. If, however, there is an overlap of the points where oscillations cease and where they commence—that is, if tney do not cease and commence at exactly the same spot—it is necessary to adjust the "B-Battery" supply until the two points coincide. If the aerial tuning oondenser has a greater capacity than .0005 it will be found an advantage to connect a small threeplate variable condenser across the larger one so as to act as a vernier. This small condenser permits of muoh sharper tuning than is possiWa with the larger capacity aJone. Always bear in mind that if your set is oscillating yon cannot be receiving pure telephony, and,. furthermore, yon are in- all probability causing serious interference to everybody for several miles around. As soon as yon have picked up the dead spot between the two howls of the carrier wave, get off the oscillation point and enjoy the transmission which you have tuned in. Vernier tuning condensers, vernier filament rheostats, adjustable "B Battery,'' and shielded panels are all a great help when receiving telephony or C.W. signals. If you are still in doubt as to the tuning of telephony, get hold of on© of the "old hands" and I am sure he will be only too pleased to be able to "put you- wise." Englishman First to Invent the "Super" Circuit. Major Edwin H. Armstrong, of Columbia University, contrary to the an- ' nouncement made public, was apparently not the first to discover the principle of super-regeneration in radio receiving. That nonour, judging; from facts unearthed by Lloyd Jacquett, of the New York "Evening ' Mail," belongs to John Brno© Bolitho, an Bnjjiahmaiiii Patents oorering the ap-

plication of this radio principle were; awarled him in the United States A; year befor© the Armstrong circuit was made publio,»and his English patent* were granted as early as Fundamentally, arid in many important essentials, it corresponds with Ann- v strong's far-fanwd oircuit. Yet to-day Armstrong is a world %*»?. "} ™)° realm of science, and Bohtho is unknown. The Englishman was ahead of his time, and did not fully, realise or appreciato the value of, his discovery. < Armstrong's ultimate achiev'ement. was an improvement over Bohthc»b idea. It was more practicable at a more auspicious moment at tne very height of the radio erase. Questions. H.J.G., Timaru.-The circuit for will be forwarded to *w..ißvjta» course. -This oircuit ia considered a very eftkienlj and sensitive one, l»*f cannot say if it is as gpod.orjetter than the Armstrong regenerative, «* I have never compared the known of anyone who has done so. *or a beginner it is one I would reoonv meno. • . , . t±^. J.F., Linwood.—Your aerial is quite suitable, but why not.make it a twowire 70ft longP There is no need to have insulated wire for an aerial. A suitable circuit will be forwarded" to you very shortly. _.«■•' /m "Crystal," Timaru.—(li Yes. (2) On no account use the gas-pipe as an earth. For one thing, the joints ara not electricaDy good and explosion may ensue. In the matter of your "earth, two or three copper . plates buried! about 10ft apart, preferably below or 1 near the aerial, ana at least 4ft below tho surfaoe. Failing this, copper cables (stranded) buried about Sft below the aerial; or it can bo made fan or umbrella shape. Piping 2 inches in! diameter, and about 6ft long, let into tlie soil vertically, with the earth well j packed around it. will make a goods "earth." Do not drive the pipe into tho soil, as it tends to make bad contact with the former. (3) \LW tima signals at 10.30 a.m. every day. The! distance you will be able to cover depends on the power of the transmitting station. You should be able to pick up all New Zealand stations, including V.L.C.. and boats within a radius or about 300 miles. L.8., Riccarton.—-Please forward further particulars of tho tKanaiornier you, require, such as the ampprequired on the output side, or the size of the rectifier you intend using. Is the circuit you require to use two valves, one R P. and the other as the detector P The best solution to use is pure bicarbonate of soda. G.W., Sainsbury.—(l) I have neve* used Myers' tubes myself but have l always heard them spoken of as a firstclass valve by all -who have used them. (2) It will deperid upon the numbor of valves used in the receiving . circuit. On the type of set you wish to make, excellent results should be obtained. This is a question that no definite 4m- , swer can be given to. This applies to both aerials. (3) It is not absolutely necessary to have the grid condenser and leak variable, but ithelps to make the set more adaptable to the use of different types of valves, etc. (4) Noj approximately 3000 to 35,000 metres. (.5) Not in the least. (6) A .loosecoupler is considered better for waves up to about 2500 metres. (7) Yea. (8) Re coils—is the type you honeycomb or spider-web coils P" I would recommend the former in your case. In reference to the cdrouit, I do not'consider it or the transfonnera at all - satisfactory. I would advise you, to procure a small book called "Radio Frequency Amplifiers and How to Make them," by John M. Avery. This-book sells at one and ninepenoe, and if you cannot procure it I will forward some to you upon receipt of one and elevenpence. I will forward you a circuit very similar to the one described inthe iabowe book, but morte (suSRaWe for \ your: purpose. Myers' tubes can be used throughout. Will be pleased- to hear from you again. Questions wilt be answered in this ootamn on jfoattere.. Concerning -wireless. address' all letters to "Electra," care The Editor, "The Press," and "post in time to reaaa this office- before noon on Monday. Name and ' address must be given, and one side of tha paper only Written upon. If a circuit'id -' required, please enclose stamped addressed envelope. <