US 2566876 A Description (OCR text may contain errors) Sept. 4, 1951 R. B. DOME PHASE SHIFT SYSTEM Filed April 17, 1946 Mg FigJ. 2 Sheets-Sheet 1 Fig. 2. g PHASE 35 I SHIFTINS 25 NETMIORK MODULATOR I 27 29 R BAND MIKE PUSH PULL PASS ND FILTER AMQHFIER 22 I I l l Z3 mm; mm T NKTWORK I. 28 32 3o cARmER qa'nmss FREQUENCY SHIFTING GENEEATOR DEVICE II N F1 3. 5 Ill 30 2- 6- O 37 3 I m 2 2 so A w a a 100 51' 50 F g l u I J Q2 1 u 1 0 no 1000 m0 moon 0 I00 200 man 2000 500a FREQUENCY (c.P.s.) FREQUENCY (GP-51) lnventof-z Robert B. Dome, His Attorney. p 4, 1951 R. B. DOME 2,566,876 PHASE SHIFT SYSTEM Filed April 17, 1946 2 Sheets-Sheet 2 F: .7 as .6 g I Fig.8. K PHASE 35 SHlFTlNO fli-Tvlf fl monumnn 27 1' m5 Pusn Z5 MAKER gag; 51:5, ,gzrg- Z8 N am 5' I I I I T 22 H 24 Pnl mss 34 42 43 s'mFTms MOWLATOR NETWGRK 30 ".Afi DEVI E Fag s rzrf v 33 GENERATOR FREQUENCY I6,000 45 27 FREQUENCY 15000 84pm ns'om 7 0 mm mm K '01; 0,131,027 lagoon Inventor: Robert E Dofne, His Attorney. Patented Sept. 4, 1951 PHASE SHIFT SYSTEM Robert B. Dome, General Electric New York W". mm. admin-t CQ lIl L'a corporation Application April 11, 1946, Serial NO. 6m 18 Clalnu. (Cl. 331-) My invention relates to electrical phase shift systems and it has for its object to provide new and improved means for obtaining from a single source of voltage two resultant voltages which are constant in amplitude, but which difler in phase by a substantially constant phase angle. There has long been felt the desirability of a system which can convert a voltage from a given source, for example a voltagevarying over the audio frequencyrange, into two new voltages of the same frequency but with a phase angle difference between the two derived voltages held substantially constant over a wide range of frequencies. Thus, each derived voltage would have an amplitude characteristic linearly variable with the input amplitude and the ratio of the amplitude of either of the derived voltages to the amplitude of the input voltage should be independent of frequency. Such a phase shift system is extremely useful, for example, as in a single side band telephone system in which the output voltage at the final side band frequencies is obtained directly without the usual necessity for double or triple modulation methods and without the necessity for very sharp cut-oil band pass filters. Accordingly, it is another object of my invention to provide a new an improved single side band transmission system. It is still another object of my invention to provide a new and improved wide band phase shifting system in which the phases of voltages of different frequencies are shifted with respect to their source in two independent channels and the phase angle in each channel is shifted according to the logarithm of the product of a numerical constant times the frequency. constant times the frequency of the input voltage. The features of my invention which I desire to protect herein will be pointed out with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following descripton taken in connection with the accompanying drawing in which Fig. 1 is a circuit diagram of one channel of a phase shifting system embodying my invention; Fig. 2 is a modification of the system of Fig. 1 including an additional network; Fig. 3 illustrates still another modification of the circuit of Fig. 1; Fig. 4 is a block diagram of a single side band transmitter utilizin the phase shifting system of Fig. 1; Figs. 5 and 6 are curves illustrating, respectively, the phase shift and the difference angle between the output voltages of the system of Fig. 4; Fig. '1 is a modification of the system of Fig. 3; and Fig. 8 includes a block diagram of a single side band transmitting system in which the phase shifting system of my invention is combined with electric wave filters and graphs illustrating the operational characteristics It is still another object of my invention to I provide a new and improved phase shifting system which employs dissipative impedance elements. One of the features of my invention consists in shifting the phase of the two derived voltages with respect to the source in two independent channels by choosing suitable circuit constants in the two channels so that the phase diflerence of the derived voltages at any frequency is maintained substantially constant at as the input voltage is varied over a wide range of frequencies. Another feature of my invention consists in employing filter sections of a semi-lattice form so that the change in phase is obtained without any distortion in the amplitudes of the resultant voltages. Furthermore, the phase angle in any one channel is shifted progressively according to the logarithm of the product of a numerical of this system. I Referring to Fig. 1, I have shown a source I of voltage which may be, for example, a source of audio frequency voltages having an outputterminal 2 connected to the control electrode 3 of an electron discharge device 4. The opposite terminal of the source I may be grounded and the discharge device I has a cathode 5 connected to ground through a resistor 6. The anode I of the device I is connected through the resistor I to the positive terminal of a source of anode voltage illustrated here as the battery 9. The negative terminal of the battery 9 lsillustrated as grounded. The. circuit thus far described is a conventional phase inverter circuit. If the resistors 5 and I have equal ohmic values, voltages of equal amplitude, but displaced in phase by are available with respect to ground at the anode and cathode, respectively, of the electron discharge device 4. A phase-shifting network is connected across the anode and cathode terminals of the device 4 and comprises a capacitor Ill connected in series with a resistor ll. Preferably. the capacitor is connected to the anode so that it likewise functions to block the flow of unidirectional currents. A voltage shifted in phase with respect to the source I may then be obtained by connection between conductor l2, connected to the junction of the elements It and II, and ground. II If the potential across resistor I is designated as ea and that across resistor 8 as es, the current through the elements l0, llis where the subscripts correspond to the impedance elements concerned. Hence Therefore, as the frequency of source 1 varies, the amplitude being kept constant, an is constant in From Equation 5, it is apparent thatthe phase The output terminal 12 is connectedto another phase shift network similar, to that employed in connection with electron discharge device 4. Like elementsof the two networks are denoted by' similar reference numerals, the numerals being primed for the second network. In this second network, the values of Rh and C are set. to give a different frequency are than do the elements the logarithm of theapplied frequency. 7 If this same phase shifting process is-continued produces an increase in phase angle of approxi- -mately 73.5. The deviation of 1.1" refers to amplitude but variable in phase according to Equation 2. In order to generalize Equation 2, let a ia -i Substituting (3) in (2), 22 swamfi 1 r slope of the frequency curve is such that doubling the frequency at any point in the linear range deviations from this 73.5". Explained less mathematically, it will be seen that at very low frequencies the impedance of condenser 10 is very high and practically the entire transmission takes'place through resistance ll. Since the time constant determined by capacity l0 and resistance II is higher than that of'condenser l0 and resistance ii oscillations of these frequencies are also passed practically entirely by resistance I I. At a next higher part of the total frequency range condenser l0 passes the oscillations increasingly more freely than resistance I producing a phase shift finally attaining one hundred and eighty degrees. This occurs at a frequency lower than any corresponding shift produced by the output circuit of tube 4 because of the higher time constant of that circuit with the result that these phase shifted oscillations are transmitted almost entirely through resistance II to the output terminals. At, a still higher frequency condenser l0 passes the Oscillations more freely than resistance H with the result that a further one hundred and eighty degree phase shift takes place. Thus as the frequency increases from the low end of the range to the high end the phase of the oscillations at the output terminals gradually shifts through three hundred and sixty degrees. As previously pointed out, the circuit of Fig. 1 illustrates only one channel of a phase shifting network. If a second channel consisting of a network of, for example, six stages identical in all respects to the channel illustrated in part in Fig. 1 is set up, and if a slightly different value of m0 is employed for the first stage or circuit of the channel and each stage of the network with its RuCin product is equal successively to 5.3 times the RuCm product of'the next succeedim stage, another phase angle curve will result which again increases 73.5 for each doubling of frequency. At any frequency, however, there is maintained, within 12.2% a fixed phase angle -'diiference with the output voltage of the first channel. By suitably choosing the correct value of too for the second channel, the phase angle differences between the output voltage of the two fv'ersus frequency curve may be obtained for any 10,000 cycles 900, and until a total of, for example, six phase shifting I networks have been passed through and if the ratio of one RuCm product toithe next succeeding one is approximately 5.3, then it will be foundthat very good phase linearity to within 1315 available over a range in frequencies .of 500:1. Thus, the circuit may be operated with this phase linearity to translate frequenciesvarying over "the range of 3045.000 cycles. 3 earity with variations of :l.l is available over Phase angle lin-' a range of frequencies of 60:1, such as the range from 100 cycles to 6000 cycles. The value of 1.1 refers to maximum deviations from a straight line in. the range specified. Furthermore, the ' one-channel, I have found that a most convenient relation is one in which the phase angle progres- Ru and Cm with such a circuit and element sively shifts according to the logarithm of the values, I have found that there is a value of RnCm' which yields a substantially linear zone 7 in which the total phase angle varies linearlywithk frequency. Thus, for example, if at 10 cycles the Y "phase angle shift through a channel comprising six networks is selected to be 300, at 100 cycles the shift may be 500, at 1000 cycles 700, at 1080 at'l= In other words, there are 200 diiferencein shift for a change, in frequency of 10 to 1. In the second channel, the phase shift angle at 10 cycles may ,be made equal to 210;-at 100 cycles, 410; at 1000 cycles, 610; and at 10,000 cycles, 810". Th'us,' in this channel also the phase angle shifts progressively according to the logarithm of the frequency. v The angle advances 200 for frequency changes of 10 to 1. It is to be noted, however, that, at any frequency, the phase angle difference between the two channels is In the circuit of Fig. 2 I have illustrated another resistance-capacitance network which does not require the isolation tube I, shown in Fig. 1 aseae'ie a capacitance it connected in parallel therewith. The output voltage of the composite phase shifting system is obtained between the terminal l1 and ground. In this circuit the product of resistance H and capacitance II is made equal to the product of resistance It and capacitance It, as well as the product of resistance It and capacitance it. Therefore, Ou=aC1a where a is a constant and. consequently, X with the addition of the elements l3-Ii having the relationship set forth above, a total phase .shift of 360 is provided when the input frequency changes from zerofrequency to infinite frequency. This condition holds, provided, Furthermore, the derived voltage has constant amplitude over the entire frequency range, that is, the output voltage is a constant fraction of the input voltage of the network regardless of frequency. If, again, it can be shown that the phase shift o for any input frequency I is obtained by the equation, ffo(f'fo') (f'fo)'' fuf In this equation; 3 is an arbitrary factor, the choice of which is dependent upon the desired curve for the quantity 4. The relationship between the quantities s and a is given by the equa- -tion I have found that, if the quantity s lies between 3 and 5, a fairly straight line for the variation of with the logarithm of the frequency is obtained. The absolute value of the output voltage so is given by the following equation: where e is the input voltage. Since s lies between 3 and 5, as expressed above, it will be seen from the relation (I that a lies between 1/5 and 1/7. Then from the equation given above it will be seen that R1: is from live to seven times larger than Ru. Since the time constants CmRn equals the time constants CuRu the time constant determined by resistance II and capacity is much smaller than that determinedbycepacity ll-andrelistance II. a Thus we have in this-circuit of Fig. 2 exactly the same situation that we have in Fig. 1 in that at the lower frequencies the first one hundred and eighty degree phaseshift is produced by elements II and I3 and at higher frequencies a further one hundred and eighty degree phase shift is produced by elements I I and I4. Thus at the lowest frequencies in the range condensers Ill and. II have practically infinite impedance and the oscillations are transmitted entirely by resistance l3. At higher frequencies condenser III passes the oscillations more freely than resistance l3 and the first one hundred and eighty degree phase shift takes place in the voltage between the output terminals. On a further increase in frequency the impedance of condenser Ill becomes low relative to that of resistance II and the latter controls the transmission through this branch. At still higher frequencies the impedance of condenser l4 gradualhr reduces and this condenser finally passes oscillations more freely than' resistance ll thereby producing a further one hundred and eighty degree phase shift. 'Thus as the frequency varies from the low end of the range to the high end a complete three hundred and sixty degree phase shift takes place in the voltage at the output terminals. Fig. 3 shows a circuit arrangement similar to that illustrated in Fig.2 and which likewise is arranged to produce a total phase shift of 360 when the input frequency is varied from zero frequency to infinite-frequency. In this circuit, instead of using an electron discharge device to obtain the two 180 displaced source voltagw, I have shown here a transformer It for accomplishing this result. The signal source I isconnected to the primary winding iii of the transformer, while the secondary winding 20 is provided with a centertap 2| which is connected to iu n CHR13= IB lS R" 40.12 5 f a 1-4a. In Fig. 4 I have shown a block diagram of a single side band transmitter utilizing the principle of the phase shifting circuits disclosed in Figs. 1-3. In this transmitter a. source of audio voltages, which is illustrated as a microphone 22, is connected through a band pass filter 23 to a. push-pull device 24. The push-pull device may take the form of either the electron discharge device. 4 of the'transformer l8 and is arranged to provide voltages across the output terminals 25, 26 which have a phase difference of 180. The terminals 25, 2i are each connected to networks 21, 28. The network 21 preferably comprises a phase shifting channel which may consist of the impedance elements III, II, l3-I6. The network 28 comprises a second phase-shifting channel of similar impedance elements which is arranged so that the phase difference between the two channels can be maintained substantially constant at over a wide range of frequencies. The output voltages of the networks 21, 28 are supplied assume respectively to balanced modulators II, 80. A carrier frequency generator 3| is directly connected by means of conductor 32 to modulator 29 to supply carrier frequency thereto to be modulated by the output of the network 21. The output voltage of the generator 3| is likewise supplied through a 90 phase shifting device 33 to the modulator 30.' The outputs of the two modulators 29, 30 are supplied to a mixer and ampliiler circuit 34 to produce a single side band radio frequency. This output frequency may be supplied to an antenna 35 or any other suitable transmitting device. In order to find the proper values for In in the two networks 21, 28 which are to yield a phase angle difference of 90", let it be assumed that F is the geometric mean frequency between the upper and lower frequency limits of good phase, angl difference. This frequency F0 is not critical, but a value of 700 cycles per second is a practical mean frequency. Having decided upon the mean frequency of the system. it is merely necessary to define the two phase shift networks 'so that one has a phase angle of 18045 at 700 cycles per second and the other a phase angle of 180+45 at 700 cycles per second. If the value of In of the first network is to be determined, then tanfo=2,l26 f=2,126 F0. Therefore, the proper valueof In for the phase network 21 is 1488 cycles per second. By reciprocal relationships, the value of In of the second network 28 may be found to be cycles per second. With these values of In for the two networks, the values of the resistance and capacitance required may easily be calculated. The phase shift curves for the two networks 21, 2B, calculated in the manner described, are shown in Fig. in which the phase angle in degrees is plotted as ordinate and the logarithm of the frequency in cycles per second is plotted as abscissa. The curve 36 corresponds to the phase shift curve of the network 21 having a frequency j =1488 cycles per second, while the curve 31 corresponds to the phase shift curve for the network 28 having a frequency fu=329 cycles per second. The difference angle for the phase shifts in the two networks is shown plotted in Fig. 6 in which the value of (pa-p1, that is, the difference between the phase shift angle of curves 31 and 36 at a given frequency is plotted as abscissa and the logarithm of frequency in cycles per second is plotted as ordinate. It is seen that this difference angle is maintained substantially at 90 over a range of frequency varying from 130 cycles per second to 3600 cycles per second. When the transmitter of Fig. 4 is modulated with audio signals, a single side band carrier wave is obtained without the requirement of auxiliary filters to aid in reducing the unwanted side band. Furthermore, I have found that the weaker side band is maintained at a value which is less than 5% of the stronger side band when the deviation from a 90 phase shift is less than 6. As a result, it is quite evident that, from a study .of the curves of Figs. 5 and 6, most satisfactory operation of the single side band is obtained by the use of my improved phase-shifting system. In the circuit of Fig. 7, I have illustrated an extension of the circuits of Figs. 1-3 which provides a wider range of frequencies over which the phase angle variation varies linearly with the logarithm of the applied frequency. In the circult of Fig. 7, the capacitance "is connected across the resistance II and the resistance 39 is connected in series with capacitance H. A network 40 is provided to replace the elements l5. l8 of Fig. 2. The total network of Fig. 7 has a total phase shift of 540 as the input frequency is varied from zero frequency to infinite frequency. This additional phase shift is obtained by the use of the capacitor and resistance 39. The impedance of the network is so constructed to maintain constant the voltage output over the entire frequency range. The elements I, II. II and II of this circuit operate in the same manner as the corresponding elements of Figs. 2 and 3 to produce the first three hundred and sixty degrees of phase shift. In'this circuit the elements 38 and 39 are added to produce a further phase shift of one hundred and eighty degrees making a total phase shift of five hundred and forty degrees. Thus at the lowest frequencies condenser ID has high impedance and the oscillations are passed by resistance l3 having the phase of the lower winding of the transformer. At a higher frequency the impedance of condenser l0 becomes low and it passes the oscillations through resistance II which becomes increasingly effective as the reactance of condenser l0 reduces. This produces the first one hundred and eighty degrees of phase shift. At a still higher frequency condenser ll passes the oscillations through resistance 39 more readily than resistance ll thereby producing the next one hundred and eighty degrees of phase shift. Finally at the highest frequencies condenser 38 passes oscillations more freely than resistance 39 thereby again producing a one hundred and eighty degree phase shift making a total of five hundred and forty degrees. Obviously the system may be still further extended to produce additional shift of phase. It will thus be observed that the principle of Figs. 1, 2, 3 and 7 is the same, each phase shift of one hundred and'eighty degrees being brought about by a single RC circuit, or combination, having a resistance arm and a capacity arm to one of which voltage of one phase is applied and to the other of which voltage of opposite phase is applied. By utilizing a plurality of these RC combinations having time constants corresponding' to different parts of the frequency range the respective one hundred and eighty degrees shift are made cumulative so as to produce a shift in phase from the low end of the frequency range to the higher equal to the product of one hundred and eighty and the number of RC combinations employed. The principal difference between the system of Fig, 1 and that of Figs-2, 3 and 7 is that in Fig. 1 the different RC combinations are in separate stages whereas in Figs. 2, 3 and 7 all of the RC combinations are in the same stage. The principle of operation is the same in all of the figures. In the block diagram of Fig. 8, I have shown another transmitting system of the single side band type which employs conventional filters and which likewise permits the utilization of audio frequencies which approach zero frequency. In this circuit the source of audio frequency, indicated as the microphone 22, is connected through a high pass filter ll to a push-pull device 21. The device ad is similar to that described in connection with the system of Fig. 4 and is arranged to provide outputvoltages which are displaced in phase by 180. The output voltages of the device 24 are supplied to the networks 21, 28 which are constructed in a manner similar to that described in connection with Fig. 4. A carrier frequency generator 3| is directly connected to a modulator 28 where the carrier frequency is modulated by the output of the network 21. The voltage of the generator Si is shifted in phase by 90 by th phase-shifting device 33 and supplied to the balanced'modulator 80 where it is combined with the output of the network 28. The outputs of the two balanced modulators 28, 30 are combined in a mixer 84 and filtered in a band by 90, it is apparent that networks embodying my invention may be employed to produce two outputs with substantially constant mutual phase angle displacement of any desired amount, be that amount 90, 120, or 11. It will be apparent also, that, while I have described the use of two voltages displaced by 90 1 phase angle in a single side band transmitter. pass fllter 42 which may be, for example, of the quartz crystal type. The voltages translated by the filter 42 are amplified by an amplifier l3 and supplied to an antenna (r other type of radiating element 85. One of the deficiencies oi the conventional single side band transmitter employing a band pass filter is that the filters employed usually remove audio frequencies below about 600 cycles per second. By the use of my improved phase shifting system, however, an output radiation may be obtained which contains single side band components corresponding to an audio frequency range varying from 2'7 to 8000 cycles per second, instead of being limited to a range of 600 to 8000 cycles per second. This is illustrated by the curves contained in Fig. 8 in which curve 44 illustrates the normal audio frequency range which may be transmitted by a microphone of high quality. The curv 45 illustrates the frequency curv at the output of the high pass filter 4| which may be designed to have a cutoff frequency of 27 cycles per second. The networks 21, 28 are designed to provide 90 phase angle difference over the band from 2'! to 600 cycles per second. Assuming that the suppressed carrier frequency is 100 kilocycles per second, curve 46 illustrates the range of frequencies which are present at the output of the mixer 84. It will be observed that one side band is suppressed in the region of 27-600 cycles per second spaced from the carrier. The characteristic of band pass crystal filter 42 is denoted by the curve 41. The composite characteristic of the system is therefore denoted by the curve 48 which shows that the signal radiated contains single side band components corresponding to an audio frequency range of 2'7 to 8000 cycles per second. Th additional range from 27 to 600 cycles per second adds considerably to the naturalness of speech and the low frequency notes of music. From th foregoing, it is apparent that my improved phase-shifting system permits a shifting of the output voltage relativ to the input voltage through a phase angle which is substantially linearly proportional to the logarithm of the input frequency. Atthe same time, the amplitude of the output voltage with respect to the input is independent of frequency. Two such networks may be employed to obtain two voltages displaced 90 for single side band generation as described previously. In addition, by the choosing of suitable sets of circuit components, it is possible to obtain three voltages of 120 displacement, rather than the 90 displacement described. Such voltages may be useful in operating a three-phase motor, for example, from a sin le phase source of frequencies. Thus, while I have described systems in which the output voltagesare displaced such voltages may be utilized for other purposes, such as for application to the deflection plates of an electrostatic type of cathode ray tube to obtain a circular trace so that the pattern will remain circular for wide changes in input frequency. One of the advantages of my improved phaseshifting system is that it does not employ inductances in the filter circuits required with their attendant and inevitable series resistance and shunt capacitance. In this way, this system is relatively free from any objectionable pick up of unwanted signals from stray magnetic fields. At the same time, the system is relatively low in cost, size, and weight. v While I have shown and described a particular embodiment of my invention, many modifications will occur to those skilled in the art and I therefore aim in the appended claims to cover all such modifications as fall within the true spirit and sco e of my invention. What I claim as new and desire to secure by Letters Patent of the United States is: 1. A single side band transmitter comprising a source of audio frequency voltage, means for pro-' ducing two audio frequency voltages displaced in phase by 180", a pair of independent channels, each comprising a plurality of resistances and capacitances, means supplying said two voltages to each of said channels to shift the phase thereof, the value of the resistances and capacitances in said two channels being such that the difference of the phase shift angles in said two channels is maintained substantially constant at a value of as the frequency of said audio voltage is varied from a value close to zero to an intermediate frequency in the audio range, a source of rad o frequency voltage. means for modulating said radio frequency voltage with the output of a first of said channels, means for shifting the phase of said radio frequency voltage by 90, means for modulating said shifted radio frequency voltage with the output of the other of said channels, and means for mixing said two modulated radio frequency voltages to produce a radio frequency voltage having a single side band for frequencies below said intermediate frequency and two side bands for frequencies above said intermediate frequency, and means to suppress the narrower of said two side bands. 2. A wide band phase shifting system comprising a pair of input terminals, means for producing at said terminals voltages balanced with respect to ground, a pair of resistances connected in series between said terminals, a first capacitance connected in series with a first of said resistances and a second capacitance connected in shunt to the second of said resistances, said resistances having a common point, and a third resistance and a third capacitance connected in parallel between said point and ground, the products of corresponding of said resistances and capacitances being equal. 3. A wide band phase shifting system com prising a pair of input terminals across which voltages balanced with respect to ground are provided, a pair of resistances connected in series 11 between said terminals, a first capacitance 01 being connected in series with a first of said resistances R1 and a second capacitance being connected in shunt with the second of said resistances R2, said resistances having acommon point, and a third resistance R: and a third capacitance C: being connected in parallel between said point and ground, R1 being equal' to an: where a is a constant, and Re being equal to the productsof clRl, C2Rc, CsR: all being equal. sistance-capacitance combination corresponding to a, respective portion-of the total frequency 4.. A single side band transmitter comprising a source of audio frequency voltage, means for producing two audio frequency voltages displaced f in phase by 180', a pair of independent channels, each consisting of a plurality of resistances and capacitances, means for supplying said two volt- 1 ages to each of said channels to shift the phase thereof, the value of the resistances and capacitances in said two channels being such that the difference of, the phase shift angles in said two range and each capacitance having higher impedance to the oscillations of the lower frequency in the respective portion than the resistance of the' same combination, and each resistance having higher impedance than the corresponding capacity to oscillations of higher frequency in o the respective portions, and the time constants of the different combinations being diilferent and so related that the phase shifts in the different portions are cumulative and produce a total phase shift over the total frequency range that is sub-'- stantially linear with the logarithm of frequency. -7. In combination, a phase shift network comprising two capacities and two resistances, and a pair of'output terminals, said network having two input arms one including one of said capacities and the otherfincluding one of said resistances, means to convert single phase oscillations to oscillations of opposite phase balanced channels is maintained substantially constant by a predetermined value as the frequency of said audio voltage is varied over a wide range offrequencies, a source of radio frequency voltage, means for modulating said radio frequency voltage with the output of a first of said channels, means for shifting the phase of said'radio fre-- quency voltage by said difference angle, means for modulating said shifted radio frequency voltage with the output of the other of said two J channels, and means for mixing said two modu- I ponent. having a resistance element and a capacity element, means to pass oscillations of one phase from said converting means through one ele ment of each combination to the other of said output terminals and to pass oscillations of opposite phase through the other element of each combination to said other output terminal, the impedance of the different elements of each combination being so related that oscillations of the lower frequencies in the respective range are with respect toone of said output terminals and 0, apply said; opposite phase oscillations to said input arms,'-'whereby at low frequency said one resistance passes said oscillations freely to said othero'utput terminal whereas at a higher frequency said one capacity passes said oscillations more freely than said one resistance to said other output terminal thereby to produce a shift of phase" at said output terminals, said other resistance being included in said network at a point to impede the flow tosaid other output terminal of oscillations in the higher frequency part of the range passed freely by said one condenser and said other capacity being included in said network at a point to pass oscillations to said output terminals the flow of which is impeded by said other resistance, said other resistance and other capacitance determining a time constant different from the time constant determined by said one resistance and one capacitance and being proportioned to produce a phase shift varying linearly with the logarithm of frequency over said range. 8; In combination, a phase shift network adapted tohave applied thereto alternating voltages having freque'ncies extending over'a wide range, means to convert said voltage to balanced voltages of o osite phase, and means to derive from said balanced voltages an output voltage varying in phase from a predetermined phase relation to said applied voltage at a median fre-- quencydetermined by the constants of the nettransmitted more readilyby the resistance andthose of higherfrequency in the respectiverange more readily bythe capacity whereby each combination produces a one. hundred .and eighty deare cumulative over the total ranges. 6. The combination, in a phase shiftnetwork, a pair of output terminals, means toproduce oscillations with respect to one of said output termi capacitance combinations each comprising a'resistance element and a capacity element, means on; gree phase shift of oscillations between said terminals and the different combinations having different time constants whereby said phase shifts of said frequency. work in-either direction by an extent greater thann'inety degrees, and means including in said last, means to maintain the phase relation betweenj's'aid output and applied voltages substan- -que.ncies=in said wire range. tiallyi 'linear' with ;;the logarithm of the" freadapted: to have applied thereto alternating voltfageshaving' frequencies extending over a wide range, means.- to convert said voltage to balanced voltages of opposite-phase,'and means to derive ,f romsaid balanced voltages an output voltage 'vai'ying'in'phase from a predetermined phase re- ,lation-to said applied voltage at a median frenals or opposite phase, at least two resistance-L to transmit said oscillations of one phase'through one element of eachzcombination and'to transmit said oscillations of opposite phase through the other element of each combinatii'in, each f uency determined by the constants of the netwforkiinuei'ther direction to an extent greater v [thanninety-degrees, means included in said last lm e'ansitjo -maintain the phase relation between 'said output and applied voltages substantially linear with, the logarithm of the frequencies in ,said .widerange, and means to maintain a con- :QQIn combination, a phase shift network 13 stant amplitude relation between said output and applied voltages. 10. In combination, a phase shift network adapted to have applied thereto alternating voltages having frequencies extending over a wide range, means to convert said voltage to balanced voltages of opposite phase, and means to'derive from sad balanced voltages an output voltage varying in phase from a predetermined phase relation in. said applied voltage at a median frequency determined by the constants of the network in either direction to an extent greater than ninety degrees, said last means comprisinga plurality of resistance capacitance combinations connected to produce said phase shift, each resistance capacitance combination having a fixed time constant, and the time constants of the different resistance capacitance combinations being related to maintain the phase relationship between the output and applied voltage substantially linear with the logarithm of the frequen-' cies in said range. V 11. The combination, a plurality of phase shift networks in cascade. each comprising means to produce balanced voltages of opposite phase and means to derive therefrom a voltage variable in phase in either direction from a fixed phase relation corresponding to a median frequency determined by the time constant of the respective network, the time constant of each network being different from the time constant of the preceding of frequency over said range of frequencies. - 15. A phase shift network connected between a pair of input terminals and a pair of output terminals, said input terminals having impressed between them a signal voltage having frequencies extending over a wide range, said network comprising a plurality of electron discharge devices, each having an input electrode and a pair of output electrodes and having an operating circuit connection in which the voltage applied to the input electrode is reproduced with opposite phase on one of said output electrodes, a series combination of resistance and capacity connected between said output electrodes of each device, the. point between said resistance and capacity being connected-to the control electrode of the next discharge device, and the point between the last resistance and capacity being connected to one 7 of said output terminals, the diii'erent series connetwork by anamount such that the output voltage of the last network has a phase relation with respect to the input voltage of the first network varying linearly with the logarithm of the frequency over the range of frequencies applied to the first network. 12. The combination, a plurality of phase shift networks in cascade, each network comprising means to produce balanced voltages of opposite phase and means to derive therefrom a voltage variable in either direction from a fixed phase relation corresponding to a median frequency determined by the time constant of the network, the time constants of the different networks being different and said networks having resistance and capacitance proportioned to produce substantial linearity between the logarithm of frequency and the phase shift produced. 13. The combination, a plurality of phase shift networks in cascade, each comprising means to produce balanced voltages of opposite phase and means to derive therefrom a voltage variable in either direction from a fixed phase relation corresponding to a median frequency determined by the time constant of the network the time constant of each network in the cascade having a ratio of substantially 5.3 to the time constant of a different network in the cascade. 14. A phase shift network connected between a pair of input terminals and a pair of output terminals. said input terminals having impressed between them a signal voltage having frequencies extending over a wide range, said network comprising a plurality of electron discharge devices, each having an input electrode and a pair of output electrodes an having an operating circuit connection in which the voltage applied to the input electrode is reproduced with opposite phase on one of said output electrodes, a series combination of resistance and capacity connected between said output electrodes of each device, ' the point between said resistance and capacity being connected to the control electrode of the next discharge device, and the point between the nected resistance capacitance combinations having different time constants, the time constant of each resistance capacitance combination other than the first being greater than the time con-s stant of the preceding resistance capacitance combination in the cascade connection by a ratio of substantialy 5.3. 16. In combination, a network having a pair of output terminals, and having a pair of input terminals to which may be applied voltages oi opposite phase with respect to the voltage at one of said output terminals, a connection between the other output terminal and each of said input terminals, impedance elements in each of said connections so proportioned relative to each other that as the frequency increases said oscillations are passed more freely first by one, then the other, then again by said one of said connections whereby a phase shift of three hundred and sixty degrees occurs in oscillations between said output terminals. 17. The combination, in a phase shift network, having a pair of output terminals, and a pair of input terminals to which input terminals may be applied oscillations with respect to one of said output terminals having opposite phase and a wide range of frequencies, a connection from the other output terminal to one of said input terminals comprising a resistance and a capacitance in series, a connection from said other output terminal to the other of said input terminals comprising resistance and capacity, in parallel, the impedance of the series connected resistance and capacity being lower to frequencies in the intermediate portion of the frequency range than the impedance of the parallel combination and said parallel combination having impedance lower than said series combination at frequencies at respective portions of the frequency range beyond said intermediate portion. 18. In combination, a phase shift network having a pair of output terminals, means to produce two oscillatory voltages with respect to one of said output terminals having opposite phase, two branch paths to the other output terminal. means to supply one of said voltagm through one of said paths and the other through the other path to said other of said output terminal, and impedanees in said paths so proportioned that each path has lower impedance than the other at alternate portions of the frequency range. ROBERT B. DOME. file of this patent: Number 16 UNITED STATES PATENTS Name Date Green July 2, 1929 Usselman July 28, 1936 Shepherd May 22, 1945 Stodola Apr. 9, 1946 Patent Citations
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