US1672995A - Electric-current transmission - Google Patents

Description

' June 12, 1,928.

D. F. WHITING ELzcrRIc CURRENT TnmsmssIon Fi led llay 28, 192s {Sheets-Sheet '1 lnven/orx Dana/d E Whlling. by r June 12,1928. 1,672,995 D. F. .WHITING zwcmc 0mm TRANSMISSION Fil'ed lay 28, 192:5 2 Sheets-Sheet 2 Q Miles gaih V I Cycles persecond I 1 1 1 1 1 l 1 Q 200 I 100 600 800 I000 I200 I400 I600 /800 2000 2200 2100 2000 800 .7000

Cycles per second I l l I l l ll I l 200 1m @00- $00 AW #00 I009 QM Z000 2200 100 2500 300 transformer to raise the I Patented dune 12, 1928 Y UNITED STATES PATENT,

ojrricsl] V DONALD I. WRITING, 01' NEW YORK, N. Y., ASSIGNOB WC mun, moonronn'rnn, or saw You, N. Y., a oonromnox or You.

nnc'rmc-ctmnm'r TBANBIISSION. V Application fled Kay 88, 1923. Serial .10. 641,840.

r This invention relates to transmitting electric currents, especially to repeating telephone currents, and aims to accomplish such repeating efliciently and without undue distortion. i

In accordance with the invention the transmission characteristics of an electron tube repeater or the like are controlled preferably by providing inductance effectively in series in the input circuit of the repeater and so arranging a condenser in the repeater input circuit as to provide capacity effectivel across the input circuit, the inductance ten ing toresonate with the tube capacity and the capacity between the winding turns of the gain frequency curve of the repeater at the higher frequencies to be transmitted, and the capacity of the condenser cooperatin Y with the inductance to give the desired Snipe of this part of the curve. For instance, in case the adjustment of "the inductance to raise thispart of the curveto the desired do for one gain setting of the repeater ten sto cause an unduly large rise for another gain settin of the repeater, the condenser may be use to ,prevent such undue rise. The different settingsof the repeater may be obtainecf l i y employing between-the incoming line and the input terminals of the amplifier a. device having a variable ratio of input voltage to output voltage, as for example, an input transformer having taps on its secondary winding; and the condenser may be so arranged as to provide capacity connected effectively across the secondary;

winding of the transformer by adjustment of the transformer from one gain setting to another, as for instance from a hi her to a lower gain setting. This action 0 the condensermay serve to compensa e forvaria tions in the. effect of the tube capacity upon the repeater gain as the gain setting is changedi effective y in series in the input circuit of the repeater to resonate with the tube ca-' pacity or not. A Fig. 1 of the accompanying drawingsis a circuit diagram of one embodiment of the invention; Figs. 2 and 3 are curves for facilit'ating explanation of theinvention; Figs. 4, 5, 61nd are circuit diagrams'illustrating modifications of the form of the invention shown in Fig. 1; and Fig. is an elevation at one type f structure whlch m yem dy whether -.inductance is inserted transformer is made su an effective leakage inductance of approxithe transformer and compensating condenser 1, 4, 5 or 6.

of I a In. ig. 1, currents such for exam le as speech frequency currents are repeate from a line 11- to a line 12 by means of an electron tube amplifier 13. The line 11 is preferably terminated by a resistance 14 '0 apmately the value of inductance 17, this leakage inductance may serve the purpose of the inductance 17 The secondary winding 19 of the in ut transformer has p conductors 1 to 9, tie tap conductor 1 bei g connected to the cathode of the tube 13, t e control electrode or lgrid of which may be connected to any of t e tap conductors by means of an ciently great to give adjustable contact 20 at the end of 's'conductor 21 leading from the grid (all after the fashion disclosed and. claimed in t Mathes Patent No. 1,495,422, issued May 27, 1924). A condenser 25 is preferably con- .nected between the tap conductor 9 and the grid, for reasons appearing hereinafter, and

"an output transformer 31 is preferably incable,

ter posed between the tube 13 and the line 12. he curves of F i 2 are observed gain frequency curves, 0 the repeater for different settings of the contact 20, all of these curves having been taken with the inductance 17 and condenser 25 out of circuit, and

all of these curves except the cur've9 for tap 9 having been taken with the condenser'18 in circuit, Curves 2,13, 4, 5, 6, 7, 8 and 9 correspond to the taps of the same numbers, respectively. The ordinates of the curves give the gain in terms of miles of standard "The curves of Fig. 3 are corresponding observed gain frequency curves of the repeater with the inductance 17 and the condensers 18 and 25 in-circuit, the capacity of the condenser25having been maintained at a constantvalue of mmf. The induc nee- 17 was 13 milhenries, the capacitg 18 as M nt, smiths tube 13 was type 1 l -B an I \Vestern Electric vacuum tube. The impedances of line 11, resistance 14 and line 12 were 900 ohms, 900 ohms and 700 ohms respectively, the impedance ratio of the step up transformer 16 was 909:600,000 for the highest gain setting and the ratio of transformer 31 was 6,000:7GO. Curves 2, 3, 1, 5, 6, 7",8 and 9' correspond to taps 2, 3, 1, 5, 6. 7, 3 and 9 respectively.

Considering now the action of the repeater of Fig. 1 in its highest gain setting but with the inductance 17 and the capacities 18 and 25 out of circuit, the effective input impedance of the tube 13 is high relative to the impedance of the secondary winding of transformer 16 at low frequencies, but at the higher frequencies of the voice range the capacity between the tube electrodes and the capacity within the coil itself have an appreciable effect. For these reasons the transformer presents an inductive reaetance to the line in the lower part of the voice range of frequencies and a capacitive reactance in the upper part of the voice frequency range. If no compensation for the effects of these reactances is provided, the repeater may give a' desired gain in the middle portion of this frequency range and yet the transmission may fall off considerably at the upper and lower parts of the range as instaneed in the curve 9 of Fig. 2, with resulting distortion of the speech signals. This would also re sultin poortransmission of ringing currents which in practice usually have a low frequency, as for example, 135 cycles per second. Therefore, as disclosed in the patents of W. L. Casper, Nos. 1,530,648 and 1,530,649 issued March2et, 1925, there is provided in series with the primary winding 15 the inductance 17 having such a valuethat this inductance (and the leakage inductance of the transformer where the leakage inductance is of a material value) will resonate with the capacitive reactance described above at a frequcncy in the neighborhood of the upper part of the voice frequency range and thereby, as indicated by curve 9' of Fig. 3, prevent the transmission from materially falling off at the higher speech frequencies and further, as disclosed in the patent of P. H. Pierce, No. 1,530,613, issued March 24, 1925, the condenser 18 is provided to annul the inductive reactance of the transformer at frequencies in the lower art of the voice range, the action of this con enser being to increase the gain of the repeater at the lower frequencies of the voice range, as indicated by a comparison of the curves 9 and 9 of Fig. 2, so that the gain frequenc characteristic of the repeater will'not fa ofi unduly at these low frequencies (although at still lower, frequencies the gain will of course be diminished, instead of increased, by the cone denser 18).-

gain setting of the repeater of Fig. 1 when the inductance 17 and the capacity 25 are not in circuit, it appears that as the contact.

quencies of the speech frequency range to be lowered less than the gain at lower frequencies is reduced as indicated by comparison of curves 9, 8 and 7, and that after this movement of contact 20 has progressed pasttap 7 the gain at the higher frequencies of the voice range becomes greater than the gain at lower frequencies, as instanced in curves 6, 5, 4, 3 and 2, this latter effect being due apparently to the approach toward the higher speech frequencies of the frequency of resonance of the leakage inductance of the transformer with the input capacity of the tube and the capacity between the winding turns of the transformer. .Thus, while speech transmission may be practically distortionless when the contact 20 is on tap 7, the repeater may distort considerably at other gain settings.

As noted above, the distortion for the highest gain setting may be overcome by inserting inductance 17 in circuit, as indicated by curve 9- of Fig. 2, the resonance condition which makes curve 9- horizontal practically throughout the length of the curve being analogous to that which makes curve 7 horizontal throughout its length. However, after the insertion of inductance 17 the distortion for low gain settings will probably be even worse than before, the excess of the gain at high frequencies over the gain at low frequencies being increased. To reduce the distortion for low gain settings, the con denser 25 is connected in circuit. If the capacity of condenser 25 remains constant, as the contact 20 is moved from high voltage to low voltage taps the apparent capacitive reaetance of this condenser as seen from the primar Winding of the transformer varies inversely as the square of the ratio of the number of secondary turns across which the condenser is connected to the number of turns in the primary-winding of the transformer; and this variation of apparent capacitive reactance tends to compensate-for the variation of the apparent input capacitive reactance ofthe tube as seen from the primary winding of the transformer, this latter apparent capacitive reactance varying inversely as the square of the ratio of the number of secondary turns across which it is connected to the number of primary turns of the transformer. If the capacity of condenser 25 is not to be varied, this condenser should have a capacity somewhat greater than the input capacity of the. tube 13, rather than equal to the in- 7 put capacity of the tube as might/be expected Considering now the effect of changing the on first thought for if the two capacities are equal, then when the contact engages the middle of the secondary winding of the transformer there will be substantially no current through the conductor 21 the drop across condenser 25 being practical equal to that across the input capacity of t e tube since the negative grid potential from battery C insures. that the'resistance of the tube is of the order of infinity), and the two capacities will in effect he in series across the secondary winding, so that their combined reuctance presented to the'secondar winding will be twice the reactance whic the input'capacity of the tube presents-to the secondary winding in the highest gain setting of the repeater.

However, the capacity of condenser 25 may be varled as the setting of contact 20 is changed, where it is desired to reduce distortion to a minimum for the various gain settings. Moreover, a close approach to distortionless transmission for the various-gain settings may be obtained with automatic variation of the capacity of the compensating condenser in response to movement of the gain settlng contact, one 'means for accomplishing this being indicated in Fig, 4 wherein the parts are the same as in Fig. 1 except that a contact 20 and a condenser 25 connected by a shaft have replaced-the contact .20 and condenser 25. The condenser 25 comprises a fixed semi-circular plate 36 connected to the grid of the tube by a con-' ductor 37, and also comprises a plate 38 attached to and movable with the shaft'35 which moves contact 20 over the tap conductors 1 to 9. The condenser 25 may have its plates so shaped, or may be otherwise so designed, as to have the requisite amount of capacity to perform its compensatin function with a high degree of accuracy 1n each operative position of contact 20. As shown in Fig. 4, the voltage between any two adj acent taps may be the same, and the outline of plate 38 is an approximately Archimedean spiral, so that as contact 20 is moved counterclockwise from the position shown the rate of decrease of the capacity of condenser 25 with the angular displacement of contact 20 increases from a minimum, slow- -ly for some time but always more and more rapidly until the contact 20" and the plate '38 have moved through 180. When the contact 20 is moved from tap 9 to tap 5 theapparent impedance of the input capacity of the tube as seen from the primary win ing of the transformer increases in the ratio of 1 to 4, and in order to compensate for this 1 increase the apparent impedance of the condenser 25 as seen fromthe, rimary winding of the transformer when t e contact 20 is on tap 5' should be approximatel four thirds or the apparent impedance t at the input ca acity of the tube would have were it seen our the primary winding of the transformer with the contact 20 on tap 9.

That is, when contact 20 is on ta 5, the impedance of condenser 25should be equal to one third of the impedance of the input capacity of the tube, which means that the capacity of the condenser should then be equal to three times the input capacity of the tube. As the contact 20 approaches very close to the zero gain setting, the value of the capacity of condenser 25' should 'of course closely approach the value of the input capacity of the tube, since the apparent input capacity of the tube as seen fr m the primary winding of the transformer is negli- 'gibly small for such a setting of contact 20.

Instead of connecting an automatically variedcompensating condenser between tap 9 and the grid of the tube, an automatically varied compensating condenser may be connected across the grid and filament of the tube as shown at 25 in Fig. 5, which is otherwise like Fig. 4 except that the con-- deanspiral, and as contact 20 is moved counterclockwise through 180, from the position shown, the capacity of condenser 25 increases from zero to a maximum, the rate of increase with angular displacement, being relatively slow at firstand increasing throughout the 180 displacement. hen the contact 20 is on tap 5 the capacity of condenser 25 should be approximately three times the input capacity of the tube, as explain'ed for the circuit of Fig. 4; but when the contact 20 is in the lower gain settings the capacity of condenser 25 should be large, and the capacity necessary will depend upon how low a voltage it is desired to tap from the transformer, or in other words how low a gain it is desired toobtain at the lowest gain setting of the repeater. V

The requisite capacity of the compensating condenser may be reduced by employing a condenser arrangement. such as is shown in 6, which is otherwise like Figs. 4 and 5. In Fig. 6 a compensating condenser 25 comprises a fixed plate 45 connected to the filament of tube 13,'and also comprises a plate 46 connected to tap 9 by a conductor 47, the plate 46 being rotatable by the shaft 35 which engages a v gain adjusting contact 20 with taps 2 to The outline of plate 46 is approximately an Archimedean spiral,

and as contact 20 is rotated counter-clockwise through from the position shown,

the capacity ofcondenser 25 increases from zero' to a maximum, the rate of increase Fig. 7 is like Fig.5 except that instead of the condenser 25 of Fig. 5, a separate condenser unit 25 is employed for each position of a gain adjusting contact 20, whichcorresponds to the gain adjusting contact 20 of Fig. 5, the contact 520 connecting one pole of the appropriate condenser unit to whichever one of the taps 2 to 9 happens to be in engagement with the contact. The condensers 25 have different values,'the requisite value of the particular one of these condensers which is in use for any given gain setting of the repeater being the same as the requisite value of the condenser 25 of Fig. 5 for the same gain setting.

In circuits such as those of Figs. 1 and 4: to 7, it is desirable to avoid the introduc tion of excessive capacities due to leads and switching means, and Fig. 8 shows a struc-- The trans-.

ture which attains this end. former 16 and a housing 51 therefor are mounted on a base 50. The housing carries a condenser 25 which comprises upper and lower nonconducting plates 55 and 56, respectively, connected by upright members 57. On the plate 55 are mounted fixed con.- tacts such as contacts 1 to 9, only one of 'these contacts, 5 being shown; Short tap conductors from the transformer 16 lead 'to these contacts such as 5, one of these tap conductors being indicated at 58. A confact 20 may be rotated by a shaft to engage the various contacts such as 5, the shaft having hearings in the plates 55 and 56. Fixed condenser plates of conducting material are mounted. on the members 57, and condenser plates 61 of conducting material are mounted on shaft 35' to rotate therewith, the plates 60 and 61 being so shaped or related that the rotation of shaft 35 varies the capacity of the condenser 25 in the desired manner, as for instance in the manner in which the capacity of the condenser 25*, 25 or 25 is varied by rotation of shaft 35. The transformer and condenser of Fig. 8 may be connected in any circuits for which they are suited. For instance, they may be arranged former 16 and the condenser 25, 25 or 25 are arranged in those circuits.

The straps interconnecting the several fixed plates 60 and movable plates (51 of condenser 25 have been omitted in Fig. 8 for the sake of clarity, and the interconnections betweenfixed and movable plates 60 and (31 and the contact brush 20 and contacts 1 and 9 where they may occur have also been omitted for the-same reason and because of the differences in the connections of Figs. 4, 5 and 6.

' Although the invention has been described I in circuits ofv .the types shown in Figs. 4 to 6 as the trans mission of currents in the voice frequency range, it is not restricted to transmission of such frequencies, for its principles are applicable also to the transmission of'currents of other frequencies. It may be realized in various embodiments differing from the specific forms depicted, without depart ing from the scope of the appended claims.

The invention claimed is:

1. A repeating circuit comprising an electron tube, an input transformer therefor having an inductance effectively in series with a winding of said transformer for resonating with the input capacity of the tube and the capacity between the winding turns of the transformer at a frequency in the neighborhood of a frequency to be repeated, and a condenser providing a capacity effectively across the secondary winding of said transformer of such magnitude as to materially lower the gain of the repeater circuit at the frequency of said resonance.

2. A circuit for repeating currents of a frequency range adequate for speech transmission comprising a space discharge amplifying device having input electrodes, an input transformer for said device having a winding provided with taps for connection to one of said input electrodes whereby different gain settings for said circuit may be obtained, inductance effectively in series with a winding of said transformer and of such value as to decrease the distorting ef-.

fect of said circuit on the higher. frequencies to be transmitted for the higher gain said transformer of such value as to decrease.

the distorting effect of said circuit on the higher frequencies to be'transmitted at the lower gain settings of said circuit.

3. A circuit for repeating currents of a frequency range adequate for speech transmission, said circuit comprising an electron tube, an input transformer therefor having an inductance effectively in series with a winding of said transformer for resonating with the input capacity of the tube and the capacity between the winding turns of the transformer at a frequency in the neigh borhood of the upper frequencies of the voice range. and a condenser providing a capacity effectively across the. secondary winding of said transformer for controlling the gain of said circuit at frequencies at least as high as a frequency in the neighborhood of the upper frequencies of the voice range.

4. A repeaterfor currents of a frequency range adequate for speech transmission, said repeater comprising an electron tube having input electrodes, an input transformer for said tuhe having a winding provided with taps for connection to one of said'electrodes,

' a condenser for providing capacity effecgain 0 tively across said winding, and means for varying the connection of said electrode to sai taps and for insuring that the value of capacity which is provided effectively across said wlnding by said condenser is simultaneouslg so varied as to equalize the repeater anges due to the variation of the connection of said electrode to said taps, over the upper part of the frequency range to be transmitte a 5. In'combination, an electron tube having input electrodes, an input transformer therefor having a windingprovided with taps'for connect-ion to one of said electrodes,

a condenser for providing capacity efl'ectively across said -winding, -and means for input capacity of said tu e across-saidwindvarying the connection of said electrode to said taps and for simultaneousl ,so va ing said effective capacity provi ed by sa1d condenser as to compensate for the variation of the. value of capacity provided b the input capacity of said tube effective y across said winding.

6. 'A circuit comprising an electron tube having an electrode, an nput transformer therefor having a winding provided with taps, means for adjustabl connecting said electrode to said taps, an a condenser between said electrode and a fixed oneof said such value as to compensate for "ariations of the effective 'capacit provided by the ing, as the. connection of said electrode to said .taps isvaried. 7.' A circuit comprising an electron tube having two input electrodes, an input transformer for said tube, said transformer having a winding provided with taps, means connecting one of said electrodes to one end of said winding, a condenser connected between the other of said electrodes and the other end of said winding, and means for adjust-ably connecting said other electrode to said taps to vary the gain setting of sand circuit, and for simultaneously varying the capacity of said condenser, "said condenser being designed with respect ,to said means so that its variation in capacity for a given change in said gain setting is pro rtioned.

to compensate for the 'varation 1n t e apparent input capacitive reactance of said tube 'with the change in gain setting tending to cause distortion in said circuit.

8. A circuit comprising havin an electrode, an input transformer there orhaving a winding provided with vtaps, meansf for adjustably connecting said electrode to said taps, a variable condenser connection of said electrodeto said taps in such manner as to decrease the potential of said electrode at a constant rate. I

9. In a circuit for repeating currents havinga wide frequency range, an electric space discharge tube having input electrodes with an effective input capacity therebetween, an

input transformer for said tube, said trans-- former having tap conductors, a contact, means movable :to engage said contact with said taps to vary the gain of said circuit, I

a variable condenser in circuit withsaid transformer and sa1d tube and mounted III immediate proximity to said transformer,

said condenser having its maximum'capacity of the order of said effective input capacity of said tube, and means operable by said first mentioned means to vary the capacity of said condenser as the setting of said contact is changed, said condenser being designed with respect to said movable means so that its variation in capacity for a given change in gain setting is proportioned to compensate for the variation in apparent input capacitive reactance of said tube due to said change in gain setting whichtends tocause distortion in the repeated currents of certain frequencies.

an electron tube In witness whereof, I hereunto. subscribe as my name this 25th day of May, A. D., 1923.

DONALD WHITING.

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