US2287514A - Electric translating circuit - Google Patents

Description

June 23, 1942. R, B. DOME ELECTRIC TRANSLATING CIRCUIT Filed March 11, 1941 L0 LL 9% Pa 3. 3

Frequency Ratio 3 Z Y I .4 .5 Frequency Ratio ZR:

Fig.5.

Inventor: Robert B. Dome,

by His Attorrwey.

so Frequency Cycles Per Second Patented June 23, 1942 ELECTRIC TRAN SLATING CIRCUIT Robert B. Dome; Bridgeport, Conn., assignor to General Electric Company, a corporation of New York Application March 11, 1941, Serial No. 382,701 Claims. (Cl. 179-1715) My invention relates to signal transmission systems, and more particularly to systems for transmitting signals having frequencies extending over wide frequency bands with minimum distortion.

It is frequently desirable to transmit such signals from a source to a utilization device therefor, when the source and the utilization device have different impedances. As an example, it

is often desired to transmit signals from a modulating electron discharge device to a modulated carrier wave. amplifier. As is well known, for the transfer of maximum energy from a source "to a utilization device, the two should 'have the 1 same impedance. Usually, however, the impedance of a modulating electron discharge device differs from the impedance of the associated modulated carrier wave amplifier, with the result that less thanthe maximum possible amount of energy is. transferred from the modulating device to "the amplifier, and, which is worse in many situations, the transmission time of signals passing between the modulating discharge device and the amplifier varies widely at different signal frequencies, resulting in undesirable distortion.

Although transformers may be used to provide impedance matching in some cases, many situations arise where satisfactory transformers either cannot be constructedor are difficult to produce,

as when the frequency band to be transmitted is extremely broad.

It is an object of my invention to provide improved means for transmitting signals having frequencies extending over a wide band between circuits of different impedance, while maintaining the signal transmission time substantially constant over the frequency band.

It is a further object of my invention to provide such an improved transmitting means in which the ratio of inputto output voltageis substantially constant over the frequency band.

It is highly advantageous to utilize such transmitting means in television apparatus for transferring video signals between circuits having substantially different impedance. Such video signals may have frequencies extending over a band of frequencies as much as four or more megacycles wide, for which transformers cannot be constructed and, if the phase shift between input and output of the transmitting means does not change substantially linearly with respect to frequency over the band, serious distortion may be produced. .Such a transmitting means is, in particular, useful for transferring video signals from a detector circuit, which usually is of low impedance, to a following amplifier circuit, which usually is of high input impedance, or from a video modulator to a power amplifier.

The addition to a'modulating electron discharge device, of means for insuring that the time of transmission of lpw frequency signals 'to the accompanying modulated amplifier is constant, tends to lower the impedance of the modulating electron discharge device,,so that an even greater difference exists between the impedance of such a modulating electron discharge device,

compensated for low frequency signals, and the input impedance of an accompanying modulated amplifier. i

It is accordingly a further object of my invention to provide suitable means for transferring video signals from such a modulating electron discharge device, compensated for low frequency signals, to an accompanying carrier wave amplifier, while maintaining the signal transmission time and the ratio of input to output voltage through the transfer means substantially constant over the band of frequencies.

- The features of my inventionwhich I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and manner of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. '1 illustrates one embodiment of my invention, Figs. 2 and 3 include curves representing certain characteristics of my invention, Fig. 4 is another embodiment of my invention, and Fig. 5 includes curves representing further characteristics of the device of Fig. l. y

In Fig. 1 a balanced power amplifier, including electron discharge devices 10 and H, is supplied with'radio frequency oscillations from a source, not shown, and transmits the amplified oscillations to antenna l2. the devices l0 and l I is supplied from a source I3 of potential through a modulating inductance I 4, the potential across which is modulated by an electron dischargedevice [5 in response to signals from a second source, not shown, from which the device] 5 is energized. Such apparatus is useful for the transmission of signals, such, as

' the oscillations amplified through the devices I0 and H are high frequency carrier oscillations. The balanced power amplifier including the devices l0 and II is of usual constructionv The Operating potential for input circuit includes an input transformer l6, energized from the source, not shown, and whose secondary is connected between thecontrol electrodes l1 and I8 of the discharge devices l and II. The cathodes of these two devices are connected to ground, and through a resistance IS in shunt to a condenser 20 to the central point of the secondary of transformer IS. The output circuit of the discharge devices I0 and H includes an inductance 2| connected between the anodes 22 and 23 of the discharge devices. A condenser 24 isconnected in shunt to the inductance 2! to form a circuit tuned to the fr quency of oscillations impressed on the discharge devices I0 and H through the transformer l6.

Neutralization is provided in this power amplifier by two condensers 25 and 26, the first being connected between the anode 22 and control electrode [8, and the second being connected between the anode 23 and the control electrode I]. An inductance 21, connected between the antenna l2 and the ground, is coupled to the inductance 2| to transfer oscillations amplified through the power amplifier to the antenna 12 for radiation therefrom.

The source l3, as mentioned above, supplies operating potential for the discharge devices Illv 'and H, its negative terminal being grounded and ductance H in response to signals from discharge device IS, the cathode '29 of the device I! is connected to ground, and the anode 30 thereof is connected to apoint between the inductances l4 and 23. Signal voltages from the'second source mentioned above are impressed between the control electrode 3| of the' discharge device l5 and ground. I

When no signal is applied to the control elecat low frequencies may be satisfactorily compensated by the provision of a series combination of resistance 32 and condenser 33 in shunt to the equal to one half the reactance of the inductance M. In order to make the/circuit whol y resistive at this lowest modulated frequency, the value of resistance 32 is made equal to half the-reactance I of the inductance H or equal to the reactance of the condenser 33 at this lowest signal frequency to be transmitted. The choice of such a value forresistance 32 results in the highest permissible value it can have, and still have zero transmission time of signals at the lowest frequency. That is, if a higher value of resistance were used, no value of capacitance could be found for condenser 33 which would yield zero transmission time. I

While lower values of resistance may be used and still obtain zero transmission time by proper choice of values for condenser 33, this again is undesirable because the lower resistance absorbs more modulator power and thereby reduces its available power for the power amplifier. If for some compelling reason it is desirable to use a lower value of resistance, the condenser 33- ductance L of inductance l4 divided by, two times the square of the resistance'R of resistor 32, or

trade 3|, a constant potential is supplied from the source I3 to the discharge devices i0 and H, and the intensity ofradiation from the antenna I2 is constant. When signals fromthe second source are applied to the control electrode 3|, current flowing through the cathode 29 and anode 30 of the discharge device l5 varies in response thereto, so that the potential across in-- ductance ll varies, and consequently the potenthrough the discharge devices I0 and II varies in response to the signals, and the intensity of radiation from the antenna l2 varies likewise.

In order to limit to a small value the amount of signal current passing through the inductance choice of'a high value for the inductance II, the

transmission time of low frequency signal components through the discharge device l5 to the power amplifier may be undesirably greater than the tra ponents therethrough. .This variation of trans- 'mission time with variation of signal'frequency mission time of "higher, frequency com- In Fig. 5, curve 34 illustrates the relation, when resistance 32 and condenser 33 are not connected in circuit, between the transmission time of signals through the discharge device I! to the power amplifier, plotted as ordinate, and the signal frequency,plotted as abscissa. Curve 35 illustrates the relation between the same factors, when the resistance 32 and condenser 33, properly adjusted, are added to the apparatus. The

of the discharge device I! may be 900 ohms, the

inductance ll may be 132 henrys, the condenser 33, 0.107 microfarads, and the resistance 32;

24,900 ohms. The transmitter whose components have these values has a characteristic represented by curve 35. r

. It is well known that it is desirable, for the maximum transfer of, power from a source to a load, to make theresistance of the source equal 'to the resistance of the load. Provision of such equality of resistance has. also been considered desirable as an aid in providing constant transmission time of oscillations at all frequencies between such a source and load. Unequal phase shift, or transmission time, at different frequencies can be readily compensated for in such an the capacity of the associated a limit frequencypf the signals to..be transmitted.

- arrangement where theresistance of the source "The load resistance of the power amplifier is and the resistance of the lcadare equal.

The stray capacity to ground of a modulated amplifier,,such as a power amplifier including the discharge devices i and H, is usually different from the stray capacity to ground of a modulating electron discharge device, such as the device l and its associated circuits, and the associated resistances are also different. In general, it is found that in a circuit of this kind a low resistance is associated with a high capacity, and that a high resistance is associated with a low capacity. The reactance, and the impedance, of such a modulating discharge device and the associated modulated amplifier are generally difierent, making it diillcult, if not impossible, to adjust the respective resistances of the modulated amplifier and the modulating discharge-device to suitable values to obtain constant signal transmission time therebetween at all frequencies, while still keeping the modulation capability of the modulating discharge device high enough to modulate fully the power amplifier. If sumcient capacity be added to the modulated power amplifier, or to the modulator, whichever is the lower, to make the input and output capacitances equal in order to make it possible to adjust the apparatus for substantially constant signal transmission time at all frequencies, the ratio of ,signal voltage at the power amplifier to signal voltage at the modulating discharge device becomes too low at the upper frequencies of the signal. Such dificulties are overcome in accordance with my invention by the provision of theinductance 28 connected from the central point of the inductance 25 to a point between the anode 3d and the inductance id, and the adjustment of the values of certain circuit constants.

The stray capacity to' ground, associated with the modulating electron discharge device i5 and its associated circuits, is represented by a condenser 36, shown in dotted lines. The stray capacity to ground associated with .the inductance it, including the shunt resistance 32 and condenser 33, is represented by a second condenser 37, also shown indotted lines. These stray capacities 3d and 3'4 are effective between the anode 30 and ground. I j

The modulated power amplifier including the discharge devices l8 and it also has various stray capacities associated with it, which are-repre- This stray capacity 38 includes the anode to cathode, and anode to control electrodecapacity of each of the discharge devices it and ii, the neutralizing condensers 25 and 28, the stray and the devices are operating within theirratsented by a condenser 3d, shown in dotted-lines.

capacity of the inductance H to ground, and

denser 26 to ground.

In a particular device, which is described as an example, the electron discharge devices W and Ii may be type 83$ transmitting tubes. The capacity 38 in this device has a value of 25.6

micromicrofarads. It is desired to transmit telethe resistance component of the load impedance,

wiring and conue by adjusting the coupling between inductances' 1i and 21, until the resistance of the amplifier is of suitable value, equal to the reactance of the stray capacity'at the upper limit frequency. By such adjustment of the anode potential of the amplifier, instead of using a shunt resistance, power loss in the shunt resistance is avoided, while no less power is radiated from the antenna l2.

To determine the necessary anode potential for the amplifier it is necessary only to know the maximum rated anode current for the discharge device, and to avoid operating the amplifier above its rated anode power dissipation. Forthe 834 type device, the maximum rated anode current is 100 milliamperes. A simple calculation according to Ohms law indicates that a voltage of 312 volts across .a load resistance of 1560 ohms produces a current of 200 milliamperes, which is the maximum rated current for two such discharge devices in parallel. It is, therefore, desirable to adjust the anode potential supply for thedischarge devices I0 and- H to 312 volts. The power supplied from the source l3 to the power amplifier is, therefore, 62.4 watts,

ings.

In this particular apparatus two type '845 transmitting tubes in parallel are used, as the modulating electron discharge device it. Because .of the fact that two 845 type tubes can supply only 60 watts of power to the power amplifier, when the resistance of the power amplifier is 1560 ohms, the input to the devices in and H must be reduced to 60 watts, thereby making the required anode potential 306 volts for devices IO and H; and the total anode current 196 milliamperes. The load resistance of the amplifier is thus unchanged, being still 1560 ohms. The radio frequency output from the power amplifler undersuch conditions is about 36.6 watts.

Using such discharge devices in the particular apparatus, the sum of capacities 36 ands! is the inequality of the stray capacities of the modvoltage ratio constant.

represented by the power amplifier :including 1 electron discharge devices Hi and H, is-"made at least as low as the reactance of the'strav ulating discharge device and the modulated power amplifier, so as to make it appear even more impossible to make the transmission The provisionof the inductance 28 in accordance with my invention makes it possible to tolerate such widely unequal stray capacities, and still provide equal'transmission time and voltage ratios at signal frequencies up to the upper fre-,

quencylimits be transmitted!" The eifective capacity 38 of the power amplifier at' the-up'per resistance of the discharge device I! is adjustedto a value equal to the reactance of the sum of time. and

stray capacities 36 and II. at the upper frequency limit of the signals to be transmitted. Since, in the particular arrangement described, the sum of the stray capacities 36 and 31 is l micromicrofarads, as pointed out above, the reactance of these stray capacities 38 and 31 at the upper freapplied to the power amplifier, is substantially quency limit of four megacycles is 850 ohms. In

accordance with my invention, the equivalent anode resistance of the discharge device I! is made 850 ohms. That is, the equivalent anode resistance of the discharge device I! is'made equal to the reactance of all stray capacity associated with it at the upper frequency limit of desired signals, as is also done for devices III I and IL This may be readily done for the modulating amplifier by providing a controlled amount of negative, or degenerative, feedback in the modulator, as by the insertion of-an adjustable cathode resistance 39, which as is well known I by those skilled in the art, may be adjusted to change the dynamic plate resistance of the amplifler.

It is worthy of particular note that, in the adjustment and arrangement of any sort of apparatus according to my invention, the inductance 28 is utilized to separate the apparatus into two sections, in each of which the circuit resistance is made equal to the reactance of all circuit capacities at the highest frequency which it is desired to transmit.

In apparatus so adjusted, constant transmission time of oscillations of any frequency. up to a high limit frequency, and a constant ratio of voltage in the two circuit sections, may be assured by provision of the inductance 2|! with a value of reactance at the high limit frequency equalto half the sum of the resistances of the two sections of the apparatus on the two sides of the inductance 28.

In the particular apparatus, described above by way of example, the actual value of the inductance 28 is 48 microhenries. Its reactance at the upper limit frequency of four megacycles is 1205 ohms,-being equal to the average of the resistance associated with device l5 and the resistance associated with devices "I and II mission time'of signals from device It to the power amplifier, and the ratio of voltage supplied through theidischarge device I! to the voltage If it be considered that the stray capacities 3i and 31 are effective between the resistance in the modulating discharge device circuit and the inductance 28, the impedance Z5, with the stray capacities 36 and 31 in shunt thereto, may be represented by the symbol Z0, and may be ex- The following equations express the circuit rela-.

"tions as set forth above: I

fo =w (3) in which R1 is the effective resistancein ohms of all apparatus, including discharge device I 5, connected to the input side of reactance 28; R:

is the effective resistance in ohms of all appara-- tus, including the power amplifier, connected to the output side of inductance 28; C1 is the total stray capacity in farads, represented by condensers 36 and 31, of all apparatus connected to the input side of inductance 28; C2 is the total stray capacity in farads, represented by condenser 3B, of the apparatus including thepower amplifier; L is the value of the inductance 28 expressed in henries; and in is the limiting high frequency in cycles per second, up to which it is desired to transmit signals without distortion. Having adjusted the various components of the apparatus to particular values in conformity with .these relations, it may be shown that the trans- 75 the ratio of signal frequency f to the upper limit pressed as follows:

2+ a (6) The impedance across which the signal voltage appears, as it is transmitted through the discharge device l5, may be represented by the symbol Z, and may be expressed as follows: Z=RI+Z6 (7) The ratio of the voltage ea across C1 to the effective signal voltage e1 impressed across the impedance Z by the discharge device I! is as follows:

61-Z Z+R1 v Now let a: represent the voltage applied across the impedance Z4 of the power amplifier, and the ratio of e: to ea ls:

Z Z.+Z. (9)

To obtain the ratio of-the output voltage ez, appearing across the power amplifier, I to the input voltage 81 to the apparatus, applied through the discharge device It, Equations 8 and 9 maybe'multiplied, obtaining the following equation:

63 ZAZG 1 R1+Z.)(z1+zo Equation 10 is the general network equation for apparatus to which my invention may be applied, In order to determine what results may be' expected by the use of the particular values set forth hereinbefore for the components represented by the symbols R1, R2, C1, C2, and L, Equations 1, 2, and 8 may be substituted into Equation 10, eliminating the symbols L, C1, and C2 to obtain the following equation:

ELM-1h. T T I 61 R2 |[2( f J 5T (3 --.;T,)] (l l) Assigning an arbitrary value of unity to lo and in. R: l the relation between the voltage ratio ea/ei, and

also an arbitrary constant value less than unity frequency in, may be readily plotted as a graph. The curve 40 in Fig. 2 represents this relation in which the voltage ratioxez/ei is plotted as ordinate, and the frequency ratio f/fo as abscissa. Inspection shows that a substantially uniform voltage ratio exists for signals transmitted through a circuit adjusted in accordance with my invention up to a frequency ratio substantially greater than unity.

By comparison of the real and imaginary parts of the expression of voltage ratio in Equation 10, the phase relation between voltages e2 and e1 may be obtained, as follows:

f. i =t -l iLiLjT- 2 1 f l. Againassigning an arbitrary value of unity to fo,'the relation betweenthe phase angle o and the ratio of signal frequency I to the upper limit frequency f may be readily plotted. -In Fig. 3 the curve 4| represents such a relation, in which the phase angle expressed in radians, is plotted as ordinate; and the ratio of signal frequency f to upper limit frequency ft is plotted as abscissa; Inspection shows that a substantially uniformly increasing phase angle exists between the'input voltage e1 and the output voltage (22 in apparatus arranged according to-my invention, as the signal frequency increases through the band of frequencies within which undistorted signals are to be transmitted.v

To, obtain the transmission time t of a signal passing from the input to the output of a device arranged according to my invention, the following relation may be used:

The curve 42 of Fig. 3 represents the relation between transmission time T, determined by Equation 13 and expressed in seconds, plotted as ordinate (an arbitrary value of unity being again cycles, Equation 13-. may besolved to find that the transmission time from input to output of a device adjusted-in accordance with my invention device as described above. The load circuit, whose resistance and reactance may not easily be made equal to the resistance and reactance of the power amplifier circuit, may be considered as being represented by the discharge devices III and II, and their associated circuits, in v Fig. 1. In other words, any suitable type of signal utilization circuit maybe substituted for the carrier wave amplifier including discharge devices HI and H.

Then to adjust the device in accordance with my invention, the resistance 32 and condenser 33 with suitable values are added in shunt to the inductance l4. Next the resistance is made I substantially equal, at the upper limit frequency of 'amplified'signals, to the capacitive reactance in the power amplifier circuit including the discharge device l5. The same equality is provided in the utilization circuitincluding the discharge devices l0 and H, and finally the reactance of the inductance 28 at the upper limit frequency i of amplified signals is made equal to half the sum of the resistances in'the power amplifier circuit and in the utilization circuit.

In Fig. 4 there is illustrated a portion of a television receiver which may be arranged according to my invention. In the figure a diode rectifier 50, acting as a second detector, is energized through a transformer 5| from a source, not shown, of intermediate frequency oscillations. These intermediate frequency oscillationsmay be modulated in intensity in accordance with video signals to be detected. A circuit is provided through which rectified current from the device may flow. This circuit includes the device 50, the'secondary of the transformer 5|, aninductance 52, and a resistance 53, in order. A condenser 51, whose reactance is low at the frequency of the intermediate frequency oscillations transmitted through the transformer 5!, but whose reactance is substantial at the frequency of'video signals to. be detected by the device 50, is connected in shunt to the inductance 52 and the resistance 53 to ,by-pass intermediate frequency oscillations therearound. The resistance 53, across which the detected video signals appear, is connected between the control electrode and the cathode 55 of an electron discharge amplifying device 56 for amplification of video unityto theupper limit frequency ft, it beas- I sumed th'atthe upper limit frequency ft is 4'mega- I is very nearly equal to 0.06 microsecond for sig-'- nalsof any frequency up to 4 megacycles. Further, the maximum transmission time for a signal of any frequency differs from the minimum circuitassociated with the power amplifier device. The requisite steps ,in applying myinven tion to such a power amplifier are the same as those-followed in adjusting such a modulating signals before their use.

crderto-adjust thisv circuit including the second. detector 50 and the input to the amplitying device 5.6 in accordance with my invention, three steps are necessary. The first step is to determine the total circuit resistance which is effectiveat theinput side of the inductance. 52. This resistance is composed-almost entirely of the internal resistance of the diode rectifier 50.

*I-Iaving determined this total circuit resistance,

the reactance of condenser 51 (which is regarded asincluding all stray capacity) is made equal to this resistance at the upper limit frequency,

may be equally well appacity or the discharge. device 55 between the controlelectrodeg fl and cathode 55. This total circuit capacity is represented in the drawing 'of signals which it is desired to transmit to the amplifying device 56. This is done in accordance with Equation 1, given previously.

The second step requires the determination of the total circuit capacity. efiective atthe' output side of the inductance 52. That is, the circuit capacity effectivelyin shunt to the resistance 53 is determined. This circuit capacity is almost entirely stray capacity, primarily internal ca by a condenser, shown in dotted lines, con- .tion by following four steps. it is necessary to separate the apparatus into capacity.

' nected in shunt to resistance 53. The value of resistance 53- is made equal to the reactance of the condenser 58 at the upper limit frequency of signals to be transmitted. This step is in conformance with the requirements of Equation 7 2, given above.

The third .step requisite to the adjustment, of

the device in accordance'with my invention is thereof. This step is in conformance with Equation 3, given above.

Having adjusted the circuit in accordance with Equations 1, 2, and 3, the result to be expected from the circuit may be determined by inspection of the curves 40, ,and 42 in Figs. 2 and 3, as explained above in connection with the device of Fig. 1.

In general, my invention may be utilized with any apparatus for transmitting oscillations, such, for example, as video signal transmitting devices like those illustrated in the drawing, or other apparatus, such as two transmission lines of unequal surge impedance. Such apparatus may be arranged in accordance with my inven- In the flrst'step,

two sections by placing an inductance therebetween, each of the two sections being capable of being represented electrically by'a resistance and a capacity in shunt to each other.

The next step, after separating the two sections by the inductance, is to determine for one of the sections, so formed, the total value of circuit resistance, and the total value of circuit The reactance of the capacity at the upper limit frequency to be transmitted is calculated. Itis then preferred that the resistance be adjusted, if' convenient, until it is equal to this reactance. If it is inconvenient to adjust the resistance, the capacity may be adjusted to provide the desired equality. it usually being easy' to add more capacity to the circuit to make the reactance at the upper limit frequency equal to the resistance. In any case, the reactance and resistance are made equal at the upper frequency limit.

In the third step the same process is carried 1 out in making the resistance of the other section such sections of the device, for signals of any frequency .up to the upper limit frequency.

ave shown and described a particular embodiment of my invention, it will be obvious While 1 h to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a transmission path for oscillations having frequencies extending over a band of frequencies having an upper limit frequency, an inductance separating said path into two sections, each of said sections having substantially equal effective resistance and capacitive reactance at said upper limit frequency, and said inductance having a reactance at said upper limit frequency substantially equal to half the sum of said-resistances. I

2. Apparatus for transmitting between two circuits oscillations having frequencies extending over a band of frequencies having an upper limit frequency with uniform gain at all frequencies in said band, and each of said circuits having resistance and capacity, the capacitive reactance and resistance in each of said circuits being equal at said upper limit frequency, and an inductance connected between said circuits having reactance at said upper limit frequency substantially equal to the average of said two resistances.

3. In a system for transmitting oscillations between a source and a load with uniform gain over a range of frequencies and withthe same transmission time at all frequencies in said range, said source including an inductance, a resistor in series with a capacitance across said inductance proportioned to produce zero transmission time at a low frequency in said range, the capacitive reactance and resistance of both said load and said source including said inductance, resistor, and capacity being equal at a high frequency in said range, and an inductance between said source and load having reactance at said high frequency equal to the average of said resistances.

4. In a system for modulating oscillations from a source upon a carrier wave in a carrier wave amplifier, said source including. an inductance connected to supply operating current to said amplifier, said oscillations from said source having frequencies in a predetermined range and being impressed across said inductance to vary such operating current, a resistor in series with a capacitance connectedacross said inductance and proportioned to produce zero transmission time of said oscillations at a low frequency in said range, the capacitive reactance and resistance of both said amplifier and said source including said inductance, resistor, and capacitance being equal at a high frequency in said range, and asecond inductance connected between said source and said amplifier having reactance at said high frequency equal to the .average of said resistances.

5. A signal transmission system for transmitting signals between a source and a load with uniform gain over a range of frequencies, said source including an inductance whichtends to increase transmission time of signals at a low frequency in said range, and means to reduce the product of the capacitance and the signal transmission time at said low frequency comprising a resistance in series with a capacitance connected across said inductance, the resistance and the capacitive'reactance of said capacitance being equal at said low frequency to half the reactance of said inductance.

6. In a system for transmitting oscillations between a source and a load with the same transmission time at all frequencies in a'range of fre- 7.In a system for transmitting oscillations extending over a range, said system comprising an electron discharge amplifier having an output circuit including an inductance, a load circuit in .shunt to saidinductance, said inductance acting to increase transmission time of oscillations from said amplifier to said load at a low frequency in said range, and means to reduce transmission time of said oscillations at said-low frequency compfising a resistance in series with a capacian electron discharge device having iterminals acrosswhich signals from said source may be' impressed, said source andsaid-device respectively havingresistance and capacity between said terminals, whereby signals transmitted therebetween are subject to distortion at- .a. predetertance connected across said inductance, saidre- I .sistance and the capacitive reactance of said casource and said amplifier, the reactance of both pacitance each being equal to half the reactance of said inductance at said low frequency.

8. In a systemfor modulating oscillations from a source upon a carrier wave in a carrier wave amplifier, said source including an inductance connected to supply operating current to said resistance and reactance such that oscillations transmitted therebetween are subject to distortion at apredetermined high. frequency,--' and means for minimizing such distortion comprising a second inductance connected between said said amplifier and said source including said first inductance. being capacitive at said. high freamplifier, said source and said amplifier having ducing equality between quency and equal to the respective resistance,

and the reactance of said second inductance. at

: said high frequency being made equal to the average of said resistances.

9. A signal transmission system comprising a source of signals having frequencies extending over a range, said source having output terminals,

capacitive reactancetending tohe unequal to the resistance at a high frequency in said range both in said source and in said load circuit whereby signals transmitted therebetween-are subject to distortion at said high 'frequency,=means prothe resistance and capacitive reactance at said high: frequency respectively in said source and said load circuit, and means for transmitting-signals from said source to said load circuit with distortion at said high frequency comprising an inductance having a. reactance at said high frequency sub-- stantially equal to the averageot the resistances of said source and said load circuit.

, hes-Em B. norm

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