Radio mirror (Jan-Oct 1923)

— Jul,, 7. 1923 RADIO DIGEST 11 First Steps for Beginners in Radio Chapter VIII — The Regenerative Detector By Thomas W. Benson, A. M. I. R. E. DEGI.NN'ERS will find the accompanying " series by Mr. Benson very helpful in learning the rudiments of the popular science of Radiotelephony. The articles yet to appear are: Chapter IX— Radio Frequency Amplification. Chapter X— Audio Frequency Amplification. Chapter XI— How Super Regeneration Is Accomplished. Chapter XII— Reflex Circuit Operation. Chapter XIII— About Headsets and Loud Speakers. Chapter XIV— Batteries Used in Radiophony. REGENERATION is possible only by reason of the fact that the energy or current flowing: in the plate circuit of a tube is many times greater than the controlling current in the grid circuit. Obviously it should be possible to take a small part of this energy and feed it back into the grid circuit and thus cause a still greater change in the plate current. It Fig. 35 — Conventional Type of Single Tuned Regenerative Circuit Using Tickler Feed Back should be remembered that it is the extent of the change in the plate current that determines the strength of the signals in the head phones or loud speaker. Regeneration It simply remains then to arrange some means of transferring energy from the find a second coil connected between the plate and the positive B battery. This coil is placed in inductive relation to the inductance in the aerial circuit, the two coils usually taking the form of a variocoupler, the stator in the aerial circuit, the rotor in the plate circuit. The func reduced till the speech clears up and the signals are the loudest. Direction of Windings To obtain maximum results with this circuit, two things are essential. The winding on the tickler must be in such a direction that the current induced in the '«KiwmJ Figure 38 — Capacitive Feed Back as Applied in a Modified Reinartz Circuit tion of the coil in the plate circuit is to transfer energy by means of its inductive properties back into the grid circuit. The action of the arrangement is as follows: Consider the tube lighted and a signal striking the aerial circuit. The tube functioning as described under tube detectors acts to vary the plate current. The plate current flowing through the "tickler," as it is termed, induces a current in the aerial circuit to cause greater electrostatic charges to reach the grid and hence greater changes in the plate current with an increase of signal strength. The adjustment of the tickler is rather critical; when the coupling is too close, too much energy reaches the grid and the whole circuit oscillates, acting as a Radio "(transmitter. In fact, the device will transmit speech for a half mile or so if a telephone transmitter is connected in the ground lead to modulate the waves emitted from the aerial. Loose Coupling Between Coils. On the other hand, with too loose a coupling between the coils the maximum effect upon the plate current will not be obtained and the loudness of the signals decreased. The proper point of operation is just before the oscillating point. The Figure 36 — The True Ultra Audion Circuit and Two Modifications that Employ Capacitive Feed Back plate to the grid circuit to convert the regular tube detector into a regenerative detector. There are a number of methods of accomplishing this, but these can all be divided into three classes, inductive, capacitive or resistive. The first two methods are in more general use and we shall circuit is then just balanced, a hollow purring sound being heard in the receivers. An incoming signal just unbalances the circuit so to speak and trips it into oscillation, but the oscillations stop immediaately upon the removal of the disturbing medium. Figure 37— Tickler Feed Back as Applied to Two Circuit Tuners and a Method of Obtaining Regeneration. (Not Advised.) 5rst consider their application to single | However, when receiving Radiophone circuit tuners. broadcasts, it will usually be found that Considering the simpler form of single the sound is distorted when the regenera circuit tuner as shown in Figure 35, we | tion is pushed this far, so the coupling is Delicate Soldering Both the manufacturers' and amateurs' problems on all fine work are readily solved by the instrument constructed for this particular purpose. THE POST SOLDERING IRON Platinum Heating Unit — Interchangeable Tips {Large and Small) -Universal Current 6^ ONE-HALF ACTUAL SIZE Awarded Certificate of Excellency, N. Y. Evening Mail Radio Institute From your Dealer, or write POST ELECTRIC COMPANY (Dept. 509), 30 E. 42nd St, New York aerial circuit will be in the same direction as the current from the received waves. Should the set not function when first connected, the leads to the tickler creased, when the clicks come closer together, till finally they are just inaudible. At this point the grid leak is of proper value. Having laid down the theory of the regenerative circuit, possible variations come rapidly to mind. Thus the two windings may be honeycomb coils, or spider web coils. A variometer with the stator in the aerial circuit and the rotor in the plate circuit will serve the same purpose. It will be found that the filament brilliancy and plate voltage have a decided effect upon the operation of the circuit and should both be varied till best results are obtained. A vernier rheostat is well worth the extra cost, and a potentiometer shunted across the A battery as shown by the dotted lines will enable one to control the plate voltage to a nicety. It will be noted that a fixed condenser is connected across the phones and B battery. This functions to bypass the Radio frequency currents that flow in the plate circuit to obtain regeneration and will make the set more stable. The Ultraudion circuit devised by Deforest was possibly the first form of the wwvwwvw Figure 39— Three Circuit Tuner Using Tuned Plate Feed Back can be reversed. The other factor is the grid leak value. This should be variable and carefully adjusted. Too low a value will cause the tube to block, that is, give clicks in the receiver which may have quite a time interval between them. The leak should then be in capacity feed back type of regenerative circuit and is shown in Figure 36 in its original form. Its action is based on the presence of the capacity across the phones being in both the grid and plate circuits. (Continued on page 14) THE LARGEST RADIO STORE IN AMERICA BUILD YOUR OWN SET THE LARGEST RADIO STORE IN AMERICA ACCORDING TO OUR INSTRUCTIONS RESULTS GUARANTEED— PANELS ON ALL SETS DRILLED— READY TO MOUNT Complete Parts for Knocked-Down Receiving Set $17.95 Beg. Our CONSISTING OF Price Price 2 Variometers $10.00 $3.90 1 Variocoupler 5.00 1.75 3 BakeUte Dials 3.00 .75 Bemler BakeUte Socket. 1.00 Howard Bheostat .... 1. 10 Cunningham C-300 Detector Tube .... 5.00 Mahogany Cabinet .... 4.50 Genuine Formica Panel 2.25 8 Binding Posts 80 Switch Lever .50 12 Switch Points .40 Freshman Grid Leak and Condenser Combined.. I.OO Complete Drawing for Assembly and Wiring 1.00 .45 .80 4.45 2.75 1.75 .40 .25 .20 .75 .50 Regular Price $30.85 (17 QE Our Price »«»-» 1.85 .40 Complete Parts for Flewelling Circuit $12.45 Beg. 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