WIRELESS NEWS.

Press, Volume LX, Issue 18266, 27 December 1924, Page 6

WIRELESS NEWS.

REFLEX SETS.

SOME POPULAR FEARS AND

MISTAKES,

(uticiallt wwrrxx to» "thi TMSO (By "Electro.") The growing popularity and rapidly extending use of tho reflex type of radio circuit hare given rise to certain unfounded criticisms by would-be > experts. One of the erroneous statements * that using a tube ttrLce, once for radiofrequency amplification and again for andio frequency kills the tube. It may be authoritatively and unqualifiediv stated that the life of a vacuum tube is not shortened nor m aiiv way impaired when need in a properly designed reflex circuit. As Jamos &, (Suilfield. Associate of the American "Tnstitnto of Electrical Engineers, • has recently pointed out, it is incorrect to assume that reflexing a tube exhauste the thorium coating on tho filament. The onlv wav to destroy the thorium coating on tho filament is by excessive }i batterv voltage and excessive filament current,. Iteflexing the tubes docs not do it. High plate voltage ami undue filament voltago would, or rourso. drive the thorium out of tho filament and impair anv tube, but reflexing the tube has notliing to do with the life of it. The way in which they are operated, and not the type of circuits thev are used in, is the chief j factor in the length of their useful service. Tubes and Tubes. Any tube to amplify properly must have copious electron emission, duo to the peculiar properties of the tube. The thorium coating on the filament can often lie restored by burning the tube at rated filament voltage for one and a-half times the period that the tube was burned in, making it do double duty. The plato voltage is not applied to the tube when restoring the thorium. I<oss of electron emission is caused only by evaporation of the thorium on the filament. In a vacuum tube a layer of thorium atoms is formed on the surface of the filament. This layer is of high electron emissivity. As fast as atoms of thorium evaporate from the surface there is a movement of atoms inside the body of the material, which places another atom in the same surface layer in the same position occupied by the evaporated atom, thus restoring the equilibrium of the thorium inside the filament, a In other words the ability of tubes to amplify is onlv impaired by the exhaustion of the thorium caused by two filament current and excessive battery voltage. The life of the tube is terminated by the evaporation and not by the exhaustion of the thorium* JEu Economical Prtadple. The reflex principle is so economical aptl efficient that it can't be "kept -down." In fact, it is becoming so popular that this coming year will undoubtedly be a "reflex year" in radio. Certain makers of neutrodyne and superheterodyne sets are recognising this and are already reflexing their sets. The advantages of reflex are obvious. In sets using the same tube for both radio and audio frequency amplification makes the receiver more sensitive; that is, it brings in the distant stations. It iB the radio telescope which reduces distance. The andio amplification builds up the sounds so that they may be reproduced by a loud speaker; it is the radio magnifying glasg that gives the voice waves their volume. By reflexing the amplified radio waves through the same tube for further amplification at audio 1 frequency, very marked economy of tabes is secured. Reflexing savea both initial cost of tubes and their upkeep. It reduces A and B battery upkeep, and also makes it possible to dispense with extra controls which would be required if the reflex principles were not employed. The reflex circuit is one of the highest developments of radio to-day. It brings in distant stations loud and clear, providing amplification without distortion. Reflex is one of radio's most dependable and efficient circuits, and there is every indication that it will bo the dominant type of circuit in the near future.

' TIDES AND WAVE LENGTH VARIATION. The special amateur radio station IMO, installed at Wiscasset, U.S.A., by the American Eadio Belay League for the purpose of communicating with the schooner Bowdoin, carrying Captain Donald B. MacMillan home from the Arctic, had not been in operation more than twenty-four hours before mysterious changes became noticeable in the wave length of the transmitter. "When the sending set was tuned to a wave length of 165 metres there would be a variation of eight metres in a few hours; when it was tuned to the short wave of 80 metres there would be a variation of about throe metres in approximately the same time. This phen-

omouon continued despite all efforts to keep tho oscillator ehaxply tuned, and amateurs with whom the station was in communication persistently asked -why th« sending waves wuro bciny changed.

Tha adjustments of the station were tone over very carefully several times, and a wave metttr was employed frequently to clieck the oscillations. Finally in occurred to Traffic Manager Schnell that since the antenna and counterpoise had been suspended from the dock over the water the tide might, have something to do with it* Whereupon he decided to take his readings with the wave meter at the ebb and flow of the tide, and compare them. He discovered that in every case the wave length increased with the rise of tlw tide and decreased with the fall. Now, in order to keep the transmitter at a constant wave he made regular adjustments to correspond as far as possible with the tide's movements. He declared the tide changed tliß capacity of tho station's counterpoise.

DO RADIO SETS GO OUT OF DATE ?

How many times have people said that they like to listen to radio programmes, but will not buy a set because it may be out of in a few weeks ? It is probablo that almost everyone has at one time or another heard this said by some person who should be a radio enthusiast, but fears the rapid progress of tie industry, as ho calls it, will antiquate his set. Just how this idea is obtained bv some people is a mystery, as tho only radical improvements in the game have been the development of new receiving sets and tho improvements of broadcasting stations. This improvement of receiving sets, however, lias not —at least not yet, and it doeß not seem on ita way to do so—antiquated any receivers that were in use before the beginning of the broadcasting. Receiving sets used in amateur stations before tho general public took up this interesting pastime are still in use. and bid fair to outdo most of the receivers that are supposed to be so new and superior to all that have £one before.

During the last six years the circuit arrangements of the standard sr.ta have not changed one iota. There have been a lot of "new circuits" devised by experts, but every one of these can be traced down to the old stand-bys. Tho neutrodyne is a now circuit and has done mnch to popularise radio, but the standard sets that all the old-timers know have done more than their share in this work, and doubtless will do a great deal more. Apart from the above reasons for the claim that sets do not become out of date and thereby make it necessary to buy new ones, there is one that outshadows all the rest in importance. This is the fact that nntil the present method of transmitting is changed any receiver now in use will always be able to receive signals from stations that are transmitting. Tlhe distance reception of these sets will also remain the same. HERE AND THERE. Th« direct cause of comparatively poor results obtained by some of the receiving sets ifl the aerial system. Some are improperly placed, others have poor and unsoldered joints, quite a lot are poorly insulated, while others are of a length far from suitable. A flame brought near a battery while it is charging will result in an explosion, which sometimes is fatal. If it is necessary to look in a battery, do so with the aid of an electric torch or move the battery where mora light can be had. A new metallic grid leak has come upon the market. The importance of the proper grid leak in a circuit is 6neh> that it is often the determining factor in satisfactory reception. The problem of making a leak which would have all the qualities that a good leak 6honld have was not an easy one, but it has been mastered.