RADIO AND ITS RECEIVERS

Sun (Auckland), Volume I, Issue 197, 9 November 1927, Page 16

RADIO AND ITS RECEIVERS

Conducted for THE SUN by

C. M. Taylor,

B.Sc., M.I.R.E.

The writer ■wishes to correct a statement in last week’s notes, that Mr. A. Hintz and Mr. G. Salt were to be heard during the children’s hour from station IYA. The source of the information was the “Radio Record,” and that being the official organ of the Broadcasting Company, it was taken that these gentlemen would be heard; but unfortunately the children are going to miss the cream of what was promised.

A new radio shop has opened in lower Queen Street. The proprietor is not new to listeners, though his location is. Mr. Roy Keith is too wellknown to need any further introduction.

The writer heard a carious fault in a local set the other evening. Only faint disturbed music could b° got from the speaker, but when the speaker was taken away, and completely disconnected from the set, good loudspeaker reception of IYA was got from the set alone. The sot was ,a sixvalve shielded model and the only thing wrong was a badly soldered joint to the condenser tuning the detector grid. This accounted for the faulty reception on the speaker, as the set was good when this repair was made; but this could not possibly account for the “self-contained speaker.” The reason is probably the fact that the set is completely mounted on a metal chassis of iron, and with the transformers bolted to it, a magnetic leak was evidently set up in one of the audio stages, which set the chassis in vibration. The transformers themselves were bolted quite tightly, so that it could not com© from a loose combination. With the advent of Summer Time the Australian stations are two and 11half hours later, and here is an apportunity for the New Zealand Company to make itself very popular by increasing its service to take the place of the stations which formerly held a large share in our entertainment. * * * One hears many opinions on the suggested new Anglican station. Fears of confusion seem paramount, also fears that each religious body will want a similar station and so add to the congestion in the ether. If the new stations come it will all be for the progress of radio, but steps should b© taken to keep the stations well apart in actual distance. For example, the first new station to go up might be placed somewhere out at Papakura, and the next one out at Whitford. ♦ * * The relay of the Melbourne Cup wa» a striking success and it is interesting to note that the short wave transmission was received in a short-wav© adapter plugged into a six-valve seC the results being superior in this r© spect to those received on a standard short-wave set. * * • BATTERIES FOR DAY’S OUTING When one goes to the beach fot weeks at a time, the commercial set is usually taken and reinstalled in lts» temporary home, the work of removaJ and reinstallation being only a small item; but when one goes for the day only lots of the ordinary types of sets

would be quite portable if it were not for the batteries. Local reception is all that is wanted and the batteries are the main drawback. B batterie© can be got in small units, which giv© quite a good life. The A battery the main trouble, but if dull emitter valves are used the small C batteries make excellent A batteries, and ar« quite cheap. If kept for this dayout purpose only, they will be found a good proposition. COMPETITIONS IN RADIO That enterprising station, 3LO, Melbourne, has announced two new competitions—one an exhibition of homemade sets, and the other a sort of Radio Tattersall, in which listeners merely send in their names and licence numbers, and a draw is made. The prizes in the first case are three for each class of set, crystal, valve, multivalve, short-wave and components. In the second case the prize is a trip to Tasmania for two persons during the

Christmas holidays, December 20 to January 4. No wonder radio is popular in Victoria. SHORT-WAVE IMPROVEMENTS Short-wave enthusiasts will be interested to know that extensive improvements are being made to station PCJJ. The station is closed for two months for complete overhaul, and replacements are being made with larger and more powerful apparatus. The station power has been variously rated, the latest reports being -10 k.w. output, and the station, with the new apparatus and its increased power, is to be on the air probably early in December, so that next winter should see better relays coming from the Old World. ATMOSPHERICS Science has not yet been able to banish these bogeys from our radio, and many theories have been advanced to explain the cause of static. Probably a variety of factors contribute to this annoying interference with radio

communication. Thunderstorms undoubtedly play their part, and electrical discharges in the atmosphere are certainly one of the chief causes of the trouble in summer. An interesting suggestion which has been made to account for some of the trouble is that it is sometimes caused by meteorites entering the earth’s atmosphere. Meteorites are masses of material, usually of metal, of varying sizes, which wander at high speeds through space. Occasionally one will strike i the earth’s atmosphere, and the l'ricj tion caused generates intense lieat, file ; meteorite becoming visible as a shooting star. It is estimated that many thousands strike the atmosphere every year, and the larger ones cause some electrical disturbances, giving static in reception. This theory is interesting, but it does not indicate whether the meteorite visitation is greater during the summer to account for the greater increased disturbances obtained during that period of the year. FILAMENT PROTECTION When bright emitter valves were used, the insertion of a flash lamp globe in the negative B battery lead was adequate protection, as those valves took up to and over half an ampere each. To-da3 r , with the modern valves, few take over .25 amps., and many very much less, and as the average globe will pass as much as .5 amp. for a short time, the valves have not the same protection. If the globe is cracked, however, with a file nick, or a touch from a red-hot iron, the globe returns to its efficiency as a fuse,

as a cracked globe will blow when a current of the order of 50 milliamps is passed. NEW POWER OSCILLATOR The writer has been asked several times lately for a circuit of a lowpower oseillator, which can be modulated at audio frequency, and to be used for test work on capacity bridges, balancing of radio frequency circuits, and such work. The one used in his workshop is that largely employed by many of the big American factories, and has the virtue of simplicity and cheapness—and, if made with good components, sharpness. The components actually used are 3in low-loss ebonite former 3in long, .0005 general radio vernier motion condenser, IPM2 U.X. base Mullard valve, Yaxley 30ohm rheostat, 2 meg. Mullard leak, .00025 aero vox condenser and clips, 1 small single pole single throw-switch. The coil is space wound with 54 turns of 18-gauge enamel wire, and a tapping taken off in the centre. The switch is mounted to short-circuit the grid leak. When the switch is open the

action of the grid condenser and leak | is to reduce the frequency of the oscillations. With the above valves, a nice clear note is got, and when the switch I is closed the oscillator can be used | as a heterrodyne wave-meter or as a j generator of high frequency oscillations. INVENTOR SEES AHEAD ! In the New York • Times,” Dr. Lee 'De Forest writes an interesting article I on the future of radio. For the greater part the research laboratories of the world are working on three main proj blems, battery eliminators, improved loud speakers and mono-control receivers. He states that although the number of eliminators on the market at present is legion, few if any of these are entirely satisfactory. With the advent of the universal need for high frequency detector and power ampere voltages, the problem of B supply is far from solved. The choice of valves used in the receiving set may upset the voltages supplied to the other valves in the set. In this respect the use of a soft valve in a set may completely upset the whole supply. Again, the desirability of using several valves the filaments of which cannot properly be connected in series, renders the elimination of the A battery a difficult problem. This difficulty is more or less overcome by the use of raw A.C. on the filaments or the use of special heater elements distinct from the electron emitter cathode. Dr. De Forest considers that with the number of clever engineers engaged on this subject the battery will eventually be eliminated. He admits also that the perfect loud speaker does not yet exist, and suggests that the perfect fundamental principle of operation has yet to be found. So that with bad quality, of jazz music to start with, badly located pick-up arrangements, more or less distortion and overloading at the transmitter, plus what we get in the receiver and amplifier, added to the sorry approximations of the loud speaker, the radio audience is still held a long way from Utopia. Dr. De Forest does not think that the radio engineers are progressing as fast as they should in loud speaker designs. With regard to the single dial control, he points out that when we are working within a fraction of a kilocycle, a few inches more or less of wire, a few drops more of insulating compound will introduce variations impossible to foresee. In some cases, where a separate vernier condenser has been added to gauged condensers off each * stage in a single dialled set, it has been possible to bring the volume up over 100 per cent. ELIMINATION OF STATIC

Hundreds, and perhaps thousands, of devices have been produced with this end in view. When these have been thoroughly tested, however, while some have had some slight merit, none have proved cure-alls.

The various devices can be classified into directional reception devices, audio-frequency tuning devices, signallimiting devices and balanced circuits. The directional reception, particularly in the long,-wave signalling, is the most effective means of combating static we have at present. This principle is used in the Beverage aerial, which in some cases is several miles long. Audiofrequency tuning can be used on code work on account of the difference in tone between static and the signal, but being a device which works on the prominence of a certain tone it is useless in telephony. Limiting devices may have some use on weak static and strong signals, but when strong static is cut out the set is practically dead. Dr. Austen, of the Bureau of Standards, thinks that at present the only

j solution is to make the signal so much stronger than the static that it may be i avoided by using an insensitive receiver. NEW APPARATUS Trickle charges, which are perhaps the nearest solution to the A batter> problem at present, are employing the new dry plate rectifying unit. The makers of the well-known France charger have introduced a new modei employing this dry rectifier. It is made with three ratios of charging—f, and 1J amperes. The whole is encased in an attractive crackle finished metal box and has this big advantage that it may be left on while the set is being used. A new model Stewart Warner matched-unit receiver is out. This receiver has discarded the conventional grid leak and condenser method of rectification and is using the anode bench method. The model is produced in a standard and de luxe type. The Crosley is using a unique method in giving a variety of models to the buyer. The “Bandbox.” a shielded six-valve set. is the basic standard of the range of eight models, and it fits into various different designs of cabinets. The ElO Federal has undergone several slight changes, which make for simplification without detracting from its performance, one change being one B battery lead for all valves except the power valve. THE SUN has had one of these new models to try and it is up to Federal standard. The Osram G.E.C. bulletin announces three new Osram valves, the D.E.H. 610, D.E.L. 610, D.E.P. 610. These valves complete the Osram series of two, four and six-volt valves; that series which every British valve maker now produces. The feature of this new series is the length of filament used, giving greater emission of electrons at a lower impedence and at low temperature. CHILDREN’S SESSIONS Now that children’s sessions are being run at greater length, and with no small success, it might be interesting to both children and parents to know who are the uncles and aunts, and on which evenings they are on the air. On Tuesday evenings “Uncle Leo,” the Rev. Lionel Fletcher, has charge of the children’s hour. On Wednesday it is “Uncle Tom,” Mr. Garland; on Thursday, “Uncle Joe,” Mr. J. M. Clarke; on Friday, “Nod,” Mr. J. Culford Bell, the announcer, who formerly was heard as “Tom Thumb”; and on Saturday, “Cinderella,” Miss R. Palmer, the children’s organiser. The musical items given by the children themselves during the last week have been of a high standard, and it is thought that in many cases they should be reserved for the regular programme later in the even- i ing. U.S.A. BROADCASTING STATIONS Many of the American broadcasting stations within range have recently altered their wave-lengths. The following list has been brought up to date, according to our latest information:— ECDKA.—East Pittsburgh, Pa., 309 metres, variable high power. KFAB.—Lincoln. Neb.. 342 metres. 1.000 watts. KFl.—Los Angeles, Calif.. 468.5 metres. 5.000 watts. KFKX.— Hastings. Neb.. 2SB metres. 5.000 watts. KFOA.—Seattle. Wash.. 454 metres. L.OuO watts. VVCBD. —Zion. 344.6 metres, 5,000 watts. WCCO.—Minn.. 416.4 metres. 5.000 watts.

WBBM.— Chicago. 111.. 255.4 rnitm. 10.000 watts WEAF. —New York. 491.5 metres*, 5,000 VVEBH.—Chicago. 370 metres, 2.000 WEMC.—Berrien Springs. Mict., 315.1 metres, 4.000 watts. KFNF. Shenandoah. lowa. 4CL2 metres. 1.000 watts. KRQB. —Fort Worth. Texas, 50LI metres, 1,000 watts. WGHP. —Detroit. 270 metres, 1.500 watts. WGY.—Schenectady. N.Y.. 379.5 metres, 5.000 watts. WHT-—Deerfield. 238 metres. 3.500 watts.