US1642389A - Voltage amplifier - Google Patents

Description

- Sept. 13, 1927.

T. E. SHEA VOLTAGE AMPLIFIER 2 Sheets-Sheep J,

five/War.- 77/770Ihyf, Shea i Filed Oct. 18, 1925 S t. I

ep 1.927 T. E. SHEA VOLTAGE AMPLIFIER Filed 001' 18, 1923 2 Sheets-Sheet 2 Hya.

:4 Frequency in Kilocycles hve/vfah' 7/77? by X of/zy f. Jhed in its electrical action a Patented Sept. 13, 1927.

UNITED STATES 1,642,389 PATENT OFFICE.

TIIOTHY E. SHEA, OF RUTHERFORD, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, or vnew YORK,

N. Y., A CORPORATION OF NEW YORK.

VOLTAGE AMPLIFIER.

Application fled October 18, 1923. Serial No. 669,219.

This invention relates to the production of high voltages of certain selected frequencies by means of uniform or artificial resonating lines. Artificial lines ma be defined as recurrent series of identica sections each section having lumped impedance eflfectively in series with the line and lumped admittance effectively in shunt across the line.

Such an artificial line tends to simulate uniform line of distributed constants, the total series impedance of the uniform line being equalto the total series impedance of the artificial line and the total shunt admittance of the uniform line being equal to the total shunt admittance of the artificial line at all frequencies. The electrical angle subtended by a uniform line of distributed constants is hyperbolic radians where Z and Y are the total series impedance and the total shunt admittance of the line. The correction factor which must be applied to the electrical angle of a uniform l1ne in order to obtain the electrical angle subtended by the artificial line is:

2m where m is the number of recurrent sections in the artificial line. For the derivation of this expression reference is made to Kennelly, Artificial Electric Lines, copyright 1917, and particularly to Equation No. 244, Chapter VI. Y

When a voltage is applied through a very small impedance at one. end of a uniform line the voltage produced atthe remote end, if the remote end is terminated in an infinite impedance will be V,=V sech 6 (3) the applied voltage and V is the voltage at the remote end. The relationship expressed by Equation 3 is well known, (see for example Fleming, the Propagation of Electric Currents in Telephone and Telegraph Conductors, Chapter III, Equation 34) and in its derivation it is customary to assume that the Whole E. M. F. of the source is applied to the line terminals regardless of the current strength. In other where V, is

the line, and may be made of the 9 (n being any odd integer) the voltage at the far end of the line will be very large with respect to the applied voltage. There thus results a large voltage amplification which will be limited only by the efiective resistance and conductance of the line but if these are reasonably small the amplification may be made large.

The artificial line will simulate a smooth line in producing such voltage amplifications except that the calculated frequencies at which the voltage amplifications occur must be corrected by applying to the electrical angle of the smooth line the correction factor given in Equation r The correction factor may be controlled by m, the number of recurrent sections in order dethe proper number of secsired by using tions.

In order that in either uniform or sectional lines it is necessary that in certain frequency ranges the series impedance be substantially inductive reactance and the shunt admittance be substantially capacitative susceptance, or vice versa, that the series impedance be substantially capacitative reactance and the shunt admittance be substantially inductive susceptance. The angle subtended by the smooth line and the artificial line will then be respectively where X is the total series reactance and 13 the total shunt susceptance, and

Heretofore, so far as known, no use has been made of voltages produced at the distant end of a uniform or sectional artificial line because (1) the power output is small, (2) the introduction of the impedance of ordinary translating circuits, to which the voltages would ,have to be transferred,

quencies by means of causes the disappearance of the resonance phenomena themselves, and (3) the impedance of the voltage source has not been properly designed and related to the line. In particular it may be pointed out that in the prior practical application of sectional networks, of thetype under discussion as filters, it has been the usual custom to terminate the network in an impedance equal to the surge impedance of the network. Because of this the phenomenon of high voltage production at certain selected frequencies is avoided.

It is herein proposed to utilize the high voltages which ma be set up by the methods hereinbefore described by employing them to control vacuum tube repeater circuits of practically infinite input impedance and since such circuits are controlled almost entirely by voltage variations rather than power variations it becomes possible to utihas what have heretofore been considered negligibly small amounts of power. It is known how to make vacuum tube input circuits of impedances of the order of 1,000,000 ohms and upward for almost any frequency over a wide range of frequencies. These values are suiiiciently high to be considered practicall infinite inasmuch as they disturb, to a neg igible extent only, the resonance phenomena herein considered. Lower impedances may be made use of under certain conditions consequently the invention is not limited to any precise value of input impedance.

The impedance of the input circuit or voltage source through which voltages to be amplified are applied to the network may be made to have negligible efiect.

(1) By making the impedance of the portion of the circuit through which the voltages are impressed on the network, small in comparison with the impedance of the network,

(2) By incorporating the impedance of the voltage-providing circuit in the structure of the line,

(3) By the insertion of an annullin impedance in series with the voltage providing circuit, or

(at) By translating the voltages to be' areplified through a circuit so designed that its ougput impedance may be treated by (1),

9. or 3 An tibject of the invention, therefore, broadly stated, is to produce greatly amplifled voltages of a selected frequency or reuniform electrical lines or artificial lines.

In further describing the invention reference will be made to the accompanying drawings wherein Fig. 1 is a diagram of a uniform line which is used in explaining the theory of the invention; Fig. 2 is a diagram illustrating the selectivity of such a line as Fig. 1 for certain voltages; Figs. 3 and 4 are diagrams of a T-network or line and a inetwork or line respectively; Figs. 5 an 6 are diagrams of typical sectional lines with formula applicable to the design thereof; Figs. 5, 5", 6 and 6 are graphs explanatory of Figs. 5 and 6; Fig. 7 is a circuit diagram of a system for producing a selected series of carrier Waves; Fig. 7 a modified form of Fig. 7 and Fig. 8 a diagram illustrating the selective action of such a circuit as"that of Fig.7.

A consideration of the general theory of this invention and of the effect of series resistance and shunt conductance upon the voltages which will be set up at the distant end of the line will make clear the basic principles of operation of systems embodying the invention.

With reference to Fig. 1 the uniform line 10 has a series impedance for unit length 11 of Z :7'+ jwL ohms or a total series impedance of where Z is the length of sistance per unit length, L is the inductance per unit length, R is the total resistance, and L is the total inductance. The shunt admittance per unit length 11 is Yzg-l-joG or a total shunt admittance of where g is the shunt conductance per unit length, C is the shunt capacity per unit length, and G and C. are the total shunt conductance and capacity respectively.

A source of voltage 12 of value c is con nected across the input terminals BE and a vacuum tube repeater across the output terminals DF. We will assume that the gridfilarnent im edance of the repeater is only negligibly t itierent from infinity.

Then

the line 1' is the relln'm z. 1 secht) (6) T representing the ratio of voltage, V at the "far end of the line to the voltage, Vnfq, impressed upon the near or input end.

=sech w (53%; 1), (8)

where 9, and 8,, are the real and the imaginary parts of 9. Further,

emi..=. a=a.+ie.=

' sponds to an where a=th6 electrical angle per unit length of the line, and a, and 11 are the real and imaginary parts of a If wJm=%- n being any odd integer, then i n1! 1 1 .1211 T-Sh[;*(-Q;+'Q;) 4'] approximately. ut since sech (9 +jng)= Fjcsch 6, the size of T is approximately determined by 21 i T-csch 4 (11) But since each 6 approaches when 6 is small we have approximately,

From the foregoing it appears that for large values of Q and Q,, T becomes very great.

The behavior of T for large values of Q- and Q. for a line such asshown in Fig. 1, is shown in Fig. 2 in which the ratio T for each peak value of voltage has a definite finite value given by Equation (12). Tilt and G are constant the several peaks will be of equal amplitude. If Q and Q are constant the successive peak voltages will diminish in a ratio inversely proportional to the frequency.

Consider the action of artificial lines having lumped shunt impedances and lumped series impedances such as'shown in Figs. 3 or 4, these being" representative of symmetrical lines having the two generally used types of termination commonly known as mid-series and mid-shunt terminations.

The electrical angle a of such lines per section is where Z is the series impedance and Y is the shunt admittance of each section.

For a line having m sections angle factor is electrical,

in which 9' and 6' are the real and imaginary parts respectively of 9.

If. Z be and jwL, and Y condensive, having components g and jmC,

=2m sinh' ur lljg H06 1) (16) and ' 1 T=sech 2m smh w /LO +31) 1) (17) By comparing Equation (17 with Equation 8) we see that these two equations are identical if it be assumedthat The approximation in Equation (18) holds when 9 does not exceed .5 to 1.0 radians from which it follows that the number of sections should be chosen so that the highest of the desired resonance frequencies correangle of less than one radian per section. Formula (12), therefore holds true within certain limits for inductive-condensive lumped lines such as shown in Figs. 3 and & wherein Z and Z are in the form of inductance .and capacity, respectively, and the correction factor of Equation (2) may be employed where the disparity is appreciable to determine the actual frequencies of resonance." v

The foregoing mathematical analysis shows that voltages of certain frequencies may be greatly. amplified by means of uniform or sectional lines.

- \Vith uniform lines the maximum amplifications will occur at frequencies harmonical ly related.

Lines of lumped constants may be designed so that the frequencies of maximum amplification are in approximately harmonic relationship through a considerable range.

inductive, having components 1' The frequencies may depart from harmonic relationship if the design is appro priate for such departure. Although the principal emphasis in this specification is laid upon amplification of voltages of harmonically or nearly harmonically related frequencies it is contemplated that the principles herein set forth may be applied in designing modified arran ements to select and amplify voltages of requencies in a great variety of relations.

In Fig. 5 is shown a typical line 20 adapted, in accordance with the present invention, to select and amplify certain odd harmonic voltages. The line comprises lumped series inductances L and lumped shunt capacities C Under Fig. 5 are given the formula: applical le to the line 20. In Figs. 5 and 5" are graphs of the quantities 9, Z and Y and a graph indicating the resonance frequencies which comprise a fundamental and an indefinitely extended series of odd multiples thereof.

In Fig. 6 is shown another typical line 21 in which the lumped series inductance of adjacent sections have a mutual series aiding inductance M. The formulm applicable to this line are shown in Fig. 6 and in Figs. '6 and 6 are graphs of the quantities 9, Z and Y and a graph indicating-the selected frequencies. In connection with the graph of selected frequencies it is noted that the ratio controls the asymptotic limit of 9'.

In theory any number of resonance frequencies from one to infinity may be had by varying the ratio {C By reference to Figs. 7 and 8 the solution of a'practical problem may be illustrated. Let it be required to produce frequencies of 1,000 cycles, 3,000 cycles, 5,000 cycles etc, for application to a carrier suppression modulator. Let it be assumed that the source denoted by E in Fig. 7 is adapted to generate a voltage wave containing components of the desired frequencies and of such reactance as to properly form the end section of a line 20 similar to the line 20 of Fig. 5. A thermionic repeater 22 of very high input i1npedance terminates the line. The output circuit of the repeater 22 is coupled to a modulator 23 of the carrier suppression type which is supplied with oscillations of a frequency of 31,000 cycles per second from a source 24 for translating the selected wave frequencies to new values.

Let the surge impedance of the line 20 be 1,000 chins and let it have ten sections. Neglecting resistance the iterative impedance IT Z.,= 6 1,000 ohms. Since H mo {L 0 n (20) For the fundamental frequency H 76 ow 1 2 2 fo1 1 2 Therefore,

1 .l a /no. ,7OE 4OOOO .025 10 (21) 8o Whence L,:.025 henries.

C =.025 microfarads Now assume Q 50 and Q zinfinity, whence H I 2 T=sech 9=sech /8994? -csch H 64.

The value of T for 3,000 cycles, etc., may be similarly obtained in accordance .with the comments following equation (12). If r and g are constant T zT and the output current of the modulator 23 Will have an amplitude varying with frequency as indicated in Fig. 8. The voltages of 20, 28, 30, 32, 3% and 36 kiloeycles appear in the output circuit in greatly amplified form and may be selected by any suitable or known system of tuned circuits or other electrical networks and used, for example, to set up carrier waves in a carrier telegraph system. It is apparent that carrier waves may thus be produced for supplying waves constituting (1) a full harmonic system, (2) an odd harmonic system, (3) a non-harmonic equally spaced system or 1) a non-harmonic but unequally spaced system;

In Fig. 7 is shown a modified form of vacuum relay input circuit in which a high resistance 24 is connected across the gridfilament circuit in series with a source 25 for negatively polarizing the grid of the relay. The resistance 24 may have a value of the order of 1,000,000 ohms or more which makes the input impedance a sufficiently close approximation to the theoretically desirable infinite impedance.

Another use of the present invention is 120 in systems of radio or other frequency amplification where large amplifications are difficult to attain. By making use of the present invention for greatly increasing the voltage at a selected frequency or frequencies and applying the voltage thus increased to an electron discharge amplifier a large stable amplification can be attained. One or more stages of a multistage repeater may thus be replaced by a circuit in accordance with the present invention with advantages in selectivity and amplification.

The invention may be used in an case where frequencies which a line can e de signed to amplify are to be selected and other frequencies attenuated or extinguished. The translating element or relay constitutesthe high terminal impedance.

It is to be noted that the lines employed in carrying out this invention resemble certain types of filters described for example, in Campbell Patent No. 1,227,113, May 22, 1917. The selective phenomena, however, with which the present invention deals are present both in the transmitting and in the non-transmitting ranges of such filters as ordinarily used but principally in the transmitting range. Furthermore the terminations which such filters require and which are employed in practice would destroy the resonance phenomena upon which this invention depends.

The principles and mode of application of the invention having been described, the features believed to be novel are set forth in the appended claims.

What is claimed is:

. 1. A systemfor selectively amplifying a plurality of voltage waves comprising in combination, a wave source adapted to generate a plurality of waves of different frequencies, a space discharge amplifier including a control electrode, and an artificial line of recurrent structure composed of substantially non-dissipative reactances connected between said source and the control electrode and cathode of said amplifier, the reactances of said line being roportioned to produce resonances at the requencies of the waves generated by said source, and the impedance of said source being negligibly small in comparison with the surge impedance of said line, whereby the effect of the line resonances is strongly intensified.

2. A system for the selective transmission of Waves of harmonically spaced frequencies comprising in combination, a wave source adapted to produce a plurality of waves of harmonically related frequencies, a space discharge amplifier including a control electrode, and an artificial line of recurrent structure composed of substantially non-dissipative reactances connected at one end to said source and at the other end to the control electrode of the cathode of said amplifier, each section of said line comprising an inductance in series with the line and a capacity in shunt to the line, and the impedance of said wave source being negligibly small in comparison with the surge impedance of said line, whereby the effect of the line resonances is strongly intensified.

3. A line of recurrent sections of reactive elements having a source of voltage of a plurality of frequencies connected to one end and the input terminals of a space discharge relay connected to the other end, the impedance of said relay between its input terminals being more than one hundred times the surge impedance of the line, and the impedance of said voltage source being less than one hundredth part of the surge impedance of the line.

4. A system for selectively amplifying voltages of harmonically spaced frequencies comprising a low impedance source of harmonically related waves, a space discharge amplifier, and an artificial line having a plurality of recurrent sections of reactive elements, said line being connected at one end to the control electrode and cathode of said amplifier and being connected at the other end to said source, and further being so terminated at said source as to incorporate the reactive portion of the impedance of the wave source as an element of the line whereby the line is substantially short-circuited by said source.

In witness whereof, I hereunto subscribe .my name this-16th day of October A. 1).,

TIMOTHY E. SHEA.

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