Radio Broadcast - 1927, May - 61 Pages, 4.9 MB ... - VacuumTubeEra

56 RADIO BROADCAST ADVERTISERNo. 94 RADIO BROADCAST Laboratory Information Sheet \^3.V. 1927AmplionConeCabinet Model A C 12 ... $30Even the best radioset depends onthe reproducer forits quality of tone.In every test or comparison,the AmplionCone quickly demonstrateshow much thequality of reception isimproved by this fineinstrument.Especially vocalbroadcastingthe supreme test of aradio reproducer.Withan Amplion Cone, allreproduction soundsnatural and distinct.Other Amplionsfrom $12 to $135Write for Amplion literaturewhich illustrates and describesall modelsTHE AMPLIONCORPORATION OFAMERICADept. L, 280 MadisonAvenue, New York CityTHE AMPLIONCORPORATION OFCANADA, LTD.Toronto, OntarioAN EXPLANATION OF THE ACTIONTXTHEN a tube capable of amplifying a fairly* * strong signal is used to amplify a very weakone, it is evident that its power amplifying ability isnot being made use of to the fullest possible extent."Reflexing" is a system for getting more out ofa tube by making it amplify two things the incomingsignal, which is a radio-frequency current,and the detected signal, which is an audio-frequencycurrent. The accompanying diagram indicatesa simple receiver using one stage of reflexedamplification.In this receiver, the radio-frequency current entersthe receiver via the antenna and is impressedon the tube by the tuned circuit, A. It then passesthrough the tubes and into the tuned transformer,B, the output of which is impressed on a crystaldetector. The audio-frequency currents resultingfrom the detecting action of the crystal pass throughthe primary of the audio transformer, T. The voltageinduced in the secondary of this transformer isimpressed on the grid of the tube and is amplified.A pair of phones is used in the plate circuit of thetube for receiving the signal.So long as the variations of potential due to thesetwo different signals do not cause the tube to overload,neither interferes with the other. Some circuitsuse a reflex principle consisting of severalstages of radio-frequency amplification and severalstages of audio-frequency amplification. In suchsets it is advantageous to use the system due toDavid Grimes and known as the Inverse DuplexNo. 95NECESSARY CAREThe Principle of ReflexingRADIO BROADCAST Laboratory Information Sheet'"PHE storage battery has been developed to a-*remarkable degree of perfection so that it willfunction over a long period of time with only asmall amount of attention. Such attention consistsmore than anything else in keeping the batteryproperly filled with pure distilled water and correctlycharged at all times. The efficiency and thelife of the battery will decrease considerably if thesetwo points are not carefully watched. The chargingrate should be as close as possible to that recommendedby the manufacturer, this information generallybeing given on the name plate of the battery.Although the state of charge of a battery can bemeasured with some accuracy by means of a voltmeterif the proper precautions are taken, the readingsmade in this way are not generally to be reliedupon. A better method for use in testing a storagebattery is to determine the state of charge by meansof a hydrometer. The specific gravity, which iswhat the hydrometer measures, will be found toincrease the reading of the hydrometer as the batteryis charged, up to a certain point. The specificgravity reading for full charge is not the same forall batteries. For this reason, an endeavor should beNo. 96Storage BatteriesRADIO BROADCAST Laboratory Information SheetAnalysis of Voice Frequenciessystem. In this system, the tube handling the smallestamount of radio-frequency energy is made tohandle the largest amount of audio-frequency energyand, vice versa, the tube handling the greatestCrystalamount of radio energy handles the smallest amountof audio energy. In this way the point of overloadingis not reached as quickly, and it is possible toobtain high efficiency from such a receiver.May, 1927made to obtain from the manufacturer of the batteryinformation regarding the hydrometer readingwhich should be obtained using his battery when itis fully charged and when it is fully discharged.Frequently, but not always, these same data willbe found on the name plate. In the event that thisinformation cannot be obtained, it is a safe rule tocharge the battery until the hydrometer readingdoes not change during a period of one hour. Whenthis condition holds true, the battery has absorbedall the charge possible. It will generally be foundalso that, when this condition of constant specificgravity reading throughout an hour is reached,the electrolyte will also begin to gas or bubble.Care should be taken in charging the batteryto make certain that its positive terminal is connectedto the positive terminal of the source beingused for charging purposes. If the battery is chargedin the opposite direction the plates will be reversedin chemical character, and if the charging is continuedfor any great length of time, the Battery willbe destroyed. If a battery has only been chargedin the wrong direction for a short length of time itcan generally be brought back to normal by chargingin the right direction for a very long time at alow charging rate.May, 1927RELATIVE IMPORTANCE OF LOW AND HIGH FRE-QUENCIESATANY investigations have been made to de-*" termine the relative importance of the variousIrequencies that are found in the human voice.For these investigations a high-quality audioamplifying system must be employed over which itis possible to hear equally as well as by direct transmissionthrough the air.Tests have been made by the Western ElectricCompany using such an amplifying system to determinethe relative importance of different frequenciesin the voice frequency range, and the re-These curves indicate, then, that the lower frequenciesfurnish most of the energy in the voiceand that the higher frequencies are most importantfor proper articulation. If frequencies below 500cycles are eliminated the energy is reduced 60 persults of these tests are shown in the curves on thissheet. These curves were obtained by inserting inthe circuit low-pass (L.P) filters, which will onlypass low frequencies, and high-pass (H. P.) filtersdesigned to pass no frequencies below a certainpoint. First of all let us consider the curve marked1000 2000 3000 4000 5000"Articulation H. P." The curve shows that thearticulation was 40 per cent, when a high-pass filterFREQUENCYwas used that eliminated all frequencies below 2000 cent., and the articulation is only reduced 2 percycles. The articulation rises to 70 per cent, when cent. Eliminatinga high-pass filter was all frequencies above 400 cyclesused to cut off all frequencies leaves remaining 60 per cent, of the total energybelow 1400 cycles. The curve marked "Energy but the articulation is only about 5 per cent.L.P." shows that 60 per cent, of the total energy The curves on this sheet were traced from an excellentbook by K. S. Johnson entitled: Tram-in the voice remained when a low-pass filter wasused to cut off frequencies above 500 cycles. mission Circuits for Telephone Communication.