NOTES AND COMMENTS

Radio Record, Volume I, Issue 30, 10 February 1928, Page 8

NOTES AND COMMENTS

(By

Switch

The following question has been passed on to me by "Maximum" (Wanganui); ‘Should the lead-in end of au inverted ‘I, aerial be higher than the free end? Please quote an authority for your reply." ‘The lead-in should be attached to the lower end of the aerial according to ‘500 Wireless Questions Answered"? (G. P. Kendall, B.Sc., and EK. Redpath, authors), and "The Con&Stiuction of Amateur Valve Stations’. (Alan L. M. Douglas, author). A local authority, however, after intense experimentation, considers that the higher mast should be at the lead-in end of the aerial. Many who took up radio in the natnral way have a crystal detector set somewhere in the attic, Anyone with a family, or, even with neighbours, sees times when he would be glad to have a little set all to himself and clamp on a pair of phones to keep out extraneous noises while listening to _ broadcasts that do not. interest the entourage, The weak point of the crvstal detector is its limited receiving range. That can be extended, inexpensively, by using a one-valve radio frequency amplifier. Very likely it will make the little receiver reach out five hundred miles, which is about twenty times the usual range of the simple crystal deteutor hook-up and far enough to pull in an earful any time. An English- writer in drawing a coimparison between an_ entertainment which is broadcast and one which takes place in a hall, says, "It must be borne in mind that the broadcast entertainment is brought into the homes of all sorts and conditions of people, of ali ages anti both sexes, whereas the ordinary entertainment is attended only by those who, knowing what they will see and hear, feel that they will enjoy the fare which is provided.*? In broadcasting, the listener is served with a far more diversified programme than is offered at a theatre or hall, and, it naturally follows, that few will enjox every item of such a programme, but every item will be relished by different listeners. Sonie have found it difficult to understand how a radio frequency amplifier amplifies weak siznals more in proportion than strong signals, while an audio frequency amplifier amplifies strong signals more than weak ones, ‘The secret lies in the fact that the radio frequency amplifier «mplifies the yoltage applied to the Cetector valve, and is not concerned with increasing the power output, while the audio frequency amplifier must amplify the power ayailable to actuate the diaphragm of the phones or the loudspeaker. Vibrating 4 diaphragm or cone and propagating sound waves that must run through thousands of cubic feet of air and make themselves heard bv many ears requires miuch more energy than it does to increase the grid potential of a valve. A potentiometer is a useful device in radio frequency amplification. It is known also as a stabiliser, for it helps to prevent the valve from oscillating. It resembles a rheostat in having a coil of resistance wire as its principal element, but instead of being connected im series it is shunted across the tersiinals of the ‘A\" battery. There is t variable contact in the middle of the toi] as well as the terminal contacts wt the two ends. From -this middle contact a wire leads to the grid, sometimes by way of the inductance coil. Fhe esult is that the grid is made positive and the grid circuit absorbs an appreciable amount of power. ‘The effect is similar to that of a "C" hattery used to place a biasing potential on the grid, To the average radio listener "resonance"? means very little, but in yiew of the fact that "all reception and broadcasting: depends on it, one should become well acquainted with the use of this term. Resonance, in radio, is simply a condition existing in a number of electrical circuits, which allows the action of one to cause the greatest possible response in another. When circuits are in resonance they are said to be "tuned," and one will then liave the maximum effect upon the other, When you turn the dials on your receiver you are simply bringing your set into resonance with the broadcast frequency; that is, you are tuning the circuits in the set te the same frequency to-which the circuits at the broadcast station are tuned, and, therefore, bringing your set into a condition which will allow the ‘maximum effect « lo be produced. "Rongotai" (Rongotai) writes --"Owing to their proximitv to 2YA, many local listeners with valve sets (say four or five) seem unable to get rid of a "certain amount of ‘mushiness,? even though the radio frequency valves are cut of action. Those whose sets will tune low enough (and most sets do) will find, as I have done, that a marked, improvement jin sharnness and clarity will he obtained if 2YA’s first harmonic (210 metres) is tuned in. On my set a five-valye neutrodvne,. 2YVA comes in ordinarily at about 45 degrees on the dial, but the harnionie reading is about 5 degrees. Of course, in the Jatter case it will he necessary to make use of the radio frequency amplifiers to get normal. loudspeaker strenoth, T have found this harmonic of 2VYA to give signals slightly stronger than those of 3¥YA, as received in Welling‘on?

The fundamental wavelength of an aerial is that wavelength to which it will respond when directly connected to the earth. Thus if an aerial has a fundamental wave-length of 200 metres, a transmitting station sending out waves of this length will cause electrical yibrations or oscillations to be set up in the receiving aerial, It is not generally known that @ slight A.C. hum, produced by the nearness of a wire carrying A.C. current, seems to work well as a background for DX reception. The static does not seem so sharp, and the socalled rushing of air background entirely disappears. Make sure too much A.C. hum is not introduced to your set, for that would spoil results altogether. In many cases when you buy a new condenser, templates are not furnished, and it is often a matter of extreme difficulty to mount the instrument on the panel. | A template may easily be made from a piece of cardboard, by cut. ting a hole for the shaft, then the other holes may easily be marked with an awl, . Many loudspeakers and headphones are not designed to handle high voltages, which, when applied, exerts such a strong pull on the diaphragm, that it is permanently bent into a concave form. This may be repaired by a simple remedy. ‘Take the cap off the unit and reverse the diaphragm. ‘The magnetism will draw it back into its original position. Where power operated or electrified sets have the eliminators housed in the same cabinets as the set itself, care is necessary in bringing the 110 volt leads into the set. If these run parallel to aerial or earth leads, an objectionable hum may result. The best plan is to separate the 110 volt line as far awav as possible from all the other set wiring.

An Australian listener is becoming impatient over the non-appearance _ of the promised broadcasting and reception of radio-vision as developed by Mr. Baird, the Scottish inventor. The listener writes to the Sydney ‘Wireless Weekly" :-‘*Lime rolls on, we save our pence, and polish our spectacles, and yet Mr. Baird does not produce even the most modest beginning of commer-cially-possible television. He demon- | strates ‘noises’ of red-haired heads, and publishes. blurred photographs, but when is he going to give the public. a receiver and a television service of even twenty miles range? And when he does that, what is he going to show the public that will interest them more than that which they may see at the pictures? Iask because we hear much | talk, but see no vestige of ‘performance’.’’ A moderately powered amplifier, using valves of the UX112 or UXI71 type, with plates supplied from a 150 or 180 volt source, can, in most circtumstauces, give results that will satisfy the most critical. ‘Ine main advantage to be ¢xpected through the use of high power is a gain in volume and the increased realism that comes in having, let us say, the yolume of an orchestra as it comes from the speaker, equal or exceeds that of tlie orchestra itself. However, it is obvious that the average set owner is not desirous of having a twenty or sixty piece orchestra going full tilt in bis or her living room. In a small room-and most rooms are small nowadays-this would be unpleasaut, ‘even painful. Therefore when an amiplifier is capable of giving this volume, it is seldom used for reception of the local station. A fixed condenser installed on the transinitting plant at Bellmore, New York, stands abont eight feet high, yet ouly has a capacity of 7002 mfd. Glazed porcelain insulators and high-| grade types of moulded composition insulators are best suited for aerial insulation. Spreaders should not carry parallel insulators on each wire; this reduces the insulation instead of improving it. ‘the insulators should be placed in serjes and strung at each end of the spreader rope Many rauio workers have formed the bad habit of using a sharp knife to strip off the insulation from wire. While tlis seems to accomplish the desired results more or less satisfactorily, it is a dangerous practice since the sharp blade of the knife almost invariably cuts not only the msniation but also the fine strands of the wire. In the case of solid wire. the knife often nicks this, weakening it and usually results in a break «at the most inopportune tinmie. Good practice calls for the use of a pair of pliers for scoring the insulation, which can then be removed with a pair of blunt notched pliers. A rat-tail file may be tiscd to noteh the pliers. If vou are a home-constructer and have unsightly holes in the front panel of your set, procure a piece of black heelball, obtainable from any bootmiaker, Vili the holes with this substance, making sure to put something flat at the back of the holes whilst the preparation is being pressed in. A knife may be used with adyantage for smoothing off level with the panel, after which it should be polished. The wireless press of the world is to be represented in a special section in the International Press Exhibition | next May More than 330 wireless periodicals will be represented. Radio clubs operate broadcasting stations in Sweden, in cities where a company having a monopoly on commercial broadcasting has not taken action. ‘These nineteen stations generally rebroadcast programnes from the official company’s stations, especially that at Stockholm. Germany has twenty-three broadcasting stations in twenty-one cities, all owned by the postal service. License fees from receiving sets pay expenses. A three-cornered file can be used to drili a hole in a glass panel by locking it in the church of a hand drill, and pressing lightly but firmly where the holes are desired to be made.’ A small cup of putty should be made on the glass around the intended hole. Into this cup is poured a small quantity of turpentine, this serving to Keep the point of the file well lubricated. Quite a number of listeners are surprised to find that in some cases it is possible to hear signals without an earth connection. It is possible to do this because the internal wiring of the set, the leads to the speaker, batteries, _etc.,, are acting as a counterpoise, which is simply another form of an earth. Such a counterpoise, however, is not an efficient one, and for this reason signals are, as a rule, much weaker when the earth is disconnected, and aiso tuning is likely to be affected. Further, the reception of signals without an earth, indicates that the coils in the set are picking up transmitted currents from local broadcasters (which is bad), and shows that the set should be shielded. ‘Be very caretul when soldering contacts on to lugs of transformers, condensers, or sockets, as the leat held by the lugs iy likely to unsolder the other end, and thins an open circuit will be made plich may be difficult to find. A goud idea is to immediately douse the joint with a piece of rag moistened with cold water, as this will set both the joints.

The Radio Conference in Washington has adopted the word ‘‘Mayday" as the distress call for radio telephony. It is derived from "M’aidez," which, in turn, means ‘aid’ or "help." A loop aerial 1s much less effective as a pick-up agency than an indoor aerial, and very much less effective than outdoor aerial, so that by conpling a loop aerial to an elevated aerial, the volume and range obtained from the set connected thereto is materially increased. This refers more particularly to the more distant signal strength obtainable than when the "local’? station is being tuned in. The Wurlitzer Orgen at the Arcadia Theatre, Chatswood, Sydnev, one of the sweetest toned instruments in the world, will in future be a regular item on 2BL’s Sydney programmes. In. response to numerous requests, 2BIL,’s miusical director has now decided to s¢t apart the higher class music for Tuesdays, Thursdays, and Sundays, whilst jazz and the lighter class musie will be broadcast on other days of the week. In radio, harmonics refer to the ine tidental waves mostly noticeable in undamped wave operation. These har. monics differ in length and freqnency from the trne and original operative wave of such transmitters. At times, listeners will hear the harmonics of high-power long-wave stations, while their tuners are set for much Shorter wavelengths. The telephony transmitter at Kootwyk (Holland) is provided with a beam aerial, and experiments have shown that thereby the angele of radiation has been reduced to 30 degrees. Konotwvk sends out voice. messages in French, Gere man, Tinglish, and Italian every Wede nesdayr between 14 and 15 G.M.T., aske ing for reports on strength. modulation, and constaney. ‘The call sign is PCLY, and the wavelength is 18 metres. Cuba has forty-five amateur radio broadcasting stations, and only two others. The amateurs use broadcast wavelengths, and put entertainment on the air. The hot wire ammeter is an instrtte ment used in radio transmission work, which measures current in amperes by means of a wire expanding in propottion to the heat generated by the passing current, Very few people seem to realise what a delicate piece of apparatus a fixed condenser is. Those who have taken this little device to pieces will liave found that it contains layer upon layer of very thin waxed tissue paper coated on either side with tinfoil. Naturally, it would be a verv foolish thing to lay a red-hot soldering iron on such a piece of apparatus, as the heat of the iron would melt the wax on the tissue paper, aml thus lead fo a breakdown in the dielectric of the condenser. All builders of their own sets know the difficulty in rubbing down the ehonite hought for panels to the necessary matt surface, as for some reason it is only to be bought in the polished state. The usual recommendation is to rub own with emery or crocus powder, but the resnit is usnally a scratched piece of ebonite that looks nglv. The private individual cannot get hold of the machinery that makers have for the purpose, but a really fine matt sure face ean he gained by ectting a small piece of the cream grit that monumental masons use for rubbing down lead letter inscriptions, and using that ine stead of the emery or crocus powder, A lady who had two songs to sing, seemed perfectly at ease until she vutered the studio of 2BL, Sydney, and handed her music to the accompanist. Mr. Vern Barnett, who was to accompany the lady, was suddenly startled to find that she, owing to ‘‘microphone fright,’ had forgotten come pletely the names of the pieces she had to sing, and looking feverishly at the two pieces on the piano stand, found the artist was singing some-« thing different altogether. Reconcile ing himself to his fate, Mr. Vern Bar« nett had, perforce, to vamp without music, and the result can ¢asily he imagined. If it became necessary for a Frencte man to explain in detail some intricate radio cireuit, it would be certain to take some time, judging by their means of saying ‘‘wire’ and ‘‘hase-~ board."? For the former item they say "fil de metal," and for the latter "table et peidestal."’ A shortwave wireless service haa been opened between Paris and Hanoi (French Indo-China). ‘This will assist in the relaying of messages from France to the most distant colonies, via French Indo-China, Beginners sometimes express cturiosity as to the system of allotting the call signs to the yarious Australian breadcast stations. In the Australian system the figure denotes the State or district in which the broadcasting or experimental station is located, The figure 1 is not used for some reason or other, but 2 represents New Sonth Wales, 3 Victoria, 4 Queensland, 6 South Australia, 6 West Australia, 7 ‘Tasmania, and 8 the interior as at Alice Springs. The letters following the figure are arbitrarily fixed. ‘She authorities endeayour to indicate the mame of the operating company by using two of the initial letters, except when they might be confusing, Vor instance: 2FC stands for 2--New Sonth Wales; T-Farmers; C-Company. Also 3AR means 3-Victoria; A--As« sociated; R-Radio.