US1961154A - Wave signaling system - Google Patents

Description

June 5, 1934 w. A. MacDONALD WAVE SIGNALING SYSTEM Original Filed July 21, 1930 3 Sheets-Sheet l INVENTOR WA Mania/mid,

,MJM ATTORNEYS June 5, 1934.

W. A. M DONALD WAVE- SIGNALING SYSTEM Original Filed July 21, 1930 '5 Sheets-Sheet 2 l J E INVENTOR WA, Macflonapla? Y L mb/m ATTORNEYS I. zmmtum m Q x mkm m Patented June 5, 1934 UNITED STA TES PATENT o'rncs 1,961,154 wave SIGNALING sits-11 2M William A. MacDonald, Little Neck, N. Y., assignmto Hazeltine Corporation, a corporation of Delaware Original application July 21, 1930, Serial No. 469,487. Divided and this application December 12, 1931, Serial No. 580,619. In Canada June application Serial No. 469,487, filed .luly'izlst,v 1930, and issued May 23, 1933 as United States I Patent No. 1,910,399.

A primary object of the invention is to provide 'a radio receiver of the type specified embodying the features of av gang. operated multiple attenuator volume control for varying the signal intensity over a wide range of values in a substantially distortionless manner; an overall. sensitivity response characteristic varying with frequency in a manner which is under control of the designer; an overall selectivity which is also under the control of the designer but which preferably is maintained substantially constant throughout the tuning range; and an improved audio-irequency characteristic so shaped as tocompensate at least in part for the side-band. attenuation of the higher audio-frequencies caused by the selectivity characteristics of the radio-frequency tuning system. 1

Detailed objects are to provide improved coupling circuits for interconnecting the antenna 4 and first thermionic tube or for connecting successive tubes in cascade relation. The individual coupling circuits are adapted to slope the voltage amplification curve 'for a given stage-in-a desired manner whichZis under control of the designer.

Inthe radio-frequency stages the individual coupling circuits are adapted further to control automatically the variation in resonance band width with frequency over the tuning range inv accordance with a selected design. In the aggregate, the coupling circuits produce a final sensitivity-response curve of preselected slope,

and an audio-frequency characteristic of substantially constant efficiency over the essential range of frequencies iior speech and music.

A refinement consists in coupling the last radio-frequency amplifier tube to the detector by means of a coupling circuit having a higher voltage amplification ratio than the coupling systems associated with the preceding stages in order to prevent the tube preceding the detector from overloading.

Additional features oi the invention will become apparent from the subsequent detailed description:

when read in conjunction with the appended drawings. r

- tion.

25 Claims. (01. 178-44l In connection with the coupling circuits de-' scribed herein, the term eflfective or resultant coupling will be used. This will be understood as the total coupling electrostatic as well as electromagnetic existing between the portions of a circuit under consideration.

. The invention will be best understood by immediate reference to the drawings, wherein Figure 1 shows diagrammatically a complete radio broadcast receiving system inaccordance with the present invention, and Figure 2 shows a similar view of a modified circuit.

Figures-3, 4 and; show various forms of coupling circuits applicable to the present invenbased.

Referring to the drawings, the receivers com prise an antenna circuit 1, four thermionic tubes V1 to V4, inclusive, operatingas stages of radiofrequency amplification and a detectdr tube V5, all of the screen-grid -heater-element type, in-

terconnected in cascade relation by, means on coupling systems or circuits B, C, D and E, respectively with the first tube suitably coupled to the antenna circuit through coupling system or circuit A. In Figure 1, a coupling network F connects the detector output to the input of the .first audio-frequency amplifier tube Vs,the output of which is connected through the trans? former '1; to a pair of power tubes V7 and Va operating push-pull. The output circuits of the power tubes are connected in opposition through the transformer T9 to aloud speaker LS. In Figure 2,'the first audio-frequency amplifier tube v. is omitted, the detector output being coupled directlytothe power tubes through the coupling circuit E terminating in the primary winding of transformer Ta.

The radio-frequency coupling circuits A to E, inclusive, .are tunable over a range in frequency by means of the variable condensers C1 to C6, inclusive, which are gan'g operated by a uni-control device, or control member, U1 adapted to simultaneously adjust all circuits to the same resonance frequency.

Each screen grid'tube is provided with anode 2, cathode 3, grid 4, screen'grid 5, and filament 6.

The filaments 6 operate in the well-known fashion to heat the cathodes 8 to the desired operating temperature and to this end may e supplied with current from any suitable source. The filament supply circuits are omitted from the drawings for the sake of clarity, inasmuch as they are well understood in the-art andconstitute no part in the present invention.

The anodes 2 and the screen grids 5 of the radio-frequency tubes are multiplied toconductors 7 and 10. respectively, having suitable'sources connected thereto for applying the necessary operating potentials to the tube electrodes. The cathodes 3 are grounded .through the common resistance 11 which due to the fiow of space current therethrough raises the cathodes to a positive potential above ground and is equivalent to negatively biasing the grids by the same amount since the latter are grounded.

With the form of bias provided by the potential drop in resistance 11, the negative bias on 'the effect of random variations in-the mutual conductance of commercial tubes employed in the receiver. Due to the very high radio-frequency amplification employed in receivers of the type disclosed herein, it, has been found that the random variations from average of the mutual conductance of the tubes is suflicient to increase the receiver sensitivity by a factor of two or three as compared to the sensitivity obtained with the average tubes, with resultant increased tendency of the receiver toward regeneration and oscillation.

By employing the automatic bias in the form of resistance 11, if the mutual conductance of the tube is increased, this change in--tube characteristic will have little or no effect on the overall receiver sensitivity since the tendency-for an in-. crease in. plate current resultant uponthe increased mutual conductance will immediately produce an opposing effect in the form of an increased negative bias on the grid tending to reduce the mutual conductance of the tube. The net effect will be that a very slight readjustment in plate current will compensate for a rather wide variation from average in the mutual conductance of the tube with consequent stabilization in the receiver operation.

Tubes Vs-Va, inclusive, are supplied with proper operating potentials over circuits similar to those supplying tubes Vl-V4 and these circuits accordingly will not be described in any detail since the circuits are obvious from the drawings.

For the tubes carrying high-frequency current,

. the low potential point of the anode, grid and screen grid circuits are coupled.- to the corresponding cathodes through the high-frequency lay-passing condensers 12, which serve to prevent undesirable coupling effects between the input sistors 8 interposed in the battery leads extending to conductor '7. These resistors in conjunction with the associated by-passing condensers l2'serve as sections of resistance filters preventing the passage of high-frequency currents. In a similar manner the screen grid circuits are with the antenna, may have an inductance suflito respond most strongly to the lower frequencies ity coupling aids or opposes the magnetic couisolated by means of the resistors 9 interposed in the leads extending to conductor 10 cooperating with the associated by-passing condensers 12 to form filter sections. The values of the -re- 'The electrical coupling. system A comprises a pair of coupled tunable circuits interposed in cascade relation between the antenna and tube V1 for selecting and translating the desired signal with a high degree of'discrimination. The antennaand ground constitute a. pair of input terminals and the grid and cathode of tube V1 constitute a pair of output terminals, for the coupling system. The nature and magnitude of the couplings between the pair of tunable, or adjustably resonant, circuits .are such as to cause" the overall sensitivity .and selectivity to vary in a desired manner over the tunable frequency -range. Thus, to obtain substantially uniform sensitivity, i. e., constant voltage amplification as the frequency of tuning is varied, the primary coil P1 of transformer T1, included in the circuit ciently large in comparison with the antenna, capacity that the natural periodicity of the antenna circuit is lower than the lowest frequency to be received. This causes the antenna circuit within the tuning range and to discriminate against the higher frequencies, thereby offsetting wholly or in part the factors which are operative, in the well-known manner, to,cause the voltage" amplification from the primary to the tunable secondary circuit of the transformer T1 to increase with the frequency of tuning.

By properly selecting the coupling between the pling. Capacity Bl preferably comprises the inherent capacity existing between the primary and secondary turns of the transformer windings but a physical capacity may, of course, be used for this purpose. If the capacitive coupling aids the magnetic coupling, the voltage amplification will tend to increase with the frequency, whereas for the two couplings opposed the design may .be such as to cause the voltage amplification to decrease with frequency.

The resonant secondary circuit coupled to the antenna circuit comprises the secondary winding S1 of transformer T1 included in a closed series circuit with the primary winding P2 of a second transformer T2 and the variable condenser C1 for adjusting the frequency of tuning. The resonant secondary circuit S 1C1P2 is coupled through a link circuit to a second tunable circuit comprising the secondarywinding S2 of transformer T2 and the variable condenser C2 connected thereacross. The link circuit comprises the magnetic coupling existing between the'windings P2 and S2 together with the electrostatic coupling provided by condenser K1 extending between the high potential points of the two tunelectrostatic coupling increases with the fre-' quency of tuning, the resultant eifect produced in the resonant circuit S2--C2 may by proper proportioning and poling of the elements be caused to vary both the selectivity and sensitivity in a desired manner with frequency. If, for example,

it is desired to obtain a more nearly uniform resonance band width over the tuning band than ls obtainable with the usual type of resonant circuit, the pair of couplingsof the combined electrostatic and electromagneticcoupling means should be arranged to oppose each other. Under this condition, the dual coupling means produce in the resonant secondary circuit S2-C2 dualistic reactions which vary oppositely with frequency. Further, the coupling at the low-frequency end of the band should be adjusted to optimum or slightly more than optimum coupling, the adjustment being such as to provide a resonance curve having a desired band width. As the frequency of tuning increases, the opposed relations of the electrostatic and the electromagnetic couplings will cause a condition of less than optimum coupling to be obtained for the higher frequencies, thereby tending to increase the sharpness of tuning. 0n the other hand, the

natural increase with frequency of the load or effective .resistance in the resonance circuit S2-C2 due, for example, to skin effect, eddy-currents and the like, works in the opposite direc-' tion, tending to broaden the resonance curve. These two effects may by suitable design be caused to balance one another and thereby to produce effects so variable with frequency as to maintain a substantially constant degree of selectivity, of resonance band width, over the en tire frequency scale. The selectivity, or band width, is approximately the same when the system is tuned to a frequency adjacent the upper limit of the tunable range as when tuned to a frequency adjacent the lower limit of the tunable range.

Inasmuch as with the arrangement described immediately above, the effective coupling be-- tween the first and second. tunable circuits automatically decreases with increase in tuning frequency, the efficiency of energy transfer between circuits likewisedecreases in the same manner and thus tends to produce a corresponding variation in the overall voltage amplification ratio of the coupling circuit. In order to offset this efiect, the coupling between primary and secondary circuits of transformer T1 is adjusted to accentuate the. voltage ampliflcationtoward the high-frequency" end of the tuning range. In this way there is obtained an approximate balance of voltage gains in the two tuned circuits, as regards variation with tuning frequency, which results in an approximatelyflat gain characteristic as well as the above noted approach tp uniform selectivity'over the tuning range.

To attain the desired results, the capacity K1 need not necessarily be connected between the high potential points of adjacent tuned circuits,

but may be tapped to an intermediate point of either coil S1 or coil .82 or to intermediate points of both coils.

The set of curves in Figure 6 are illustrative of tuning in the well-known manner.

- 3 J the results that may by proper design be obtained with a coupling network such as circuit A of Figure 1. Figure 6 gives the results of laboratory measurements made on a circuit of the type shown in Figure 7 and although the actual measurements are for the coupling network interposed between a pair of thermionic valves, it will be apparent that the same results are obtainable when the connection is between an antenna circuit and a thermionic valve as is the case for circuit A.

Referring 'now to Figure 6, curve M1 shows the variation with the frequency of tuning of the voltage amplificationas measured from the input section of tube Vx, Figure '7, to the first tuning condenser Cx. The design wassuch as to produce the rising amplification characteristic with frequency shown in order, as explained above, to offset the effect of decrease in coupling with frequency between the first and second tuned circuits S 1-Cx and S2--C in order to provide substantially uniform overall amplification or sensitivity.

Curve M2 shows the gain characteristic or overall sensitivity for the complete network as measured from the input section of tube Vx to the input section of tube V for the condition that the electrostatic coupling Ky opposes the magnetic coupling P3S2, the relative proportioning of the and less-than optimum coupling atthe higher frequencies in order to insure substantially uniform selectivity, or at least, minimize changes in slectivity. It is apparent from curve M2 that the. overall sensitivity is practically constant through the entire tuning range.

Curve N1 is a measure of the total resonance band width at half-amplitude as measured across the first tuning condenser Cx; while curve N2 gives corresponding measurements across the second tuning condenser Cy. Curve N2 which is a measure of the overall selectivity is substantially fiat,

varying less than 20% over the tuning range.

It will be apparent from a study of the results in Figure 6 that acoupling network of the type shown in Figure 'l is admirably adapted for use in high-frequency systems since it permits the designer to control simultaneously the manner in which both sensitivity and selectivity vary with frequency.

Returning now to Figure 1, the nature of the.

requirements for voltage amplification and selectivity may be such that the coupling circuit A, as described, does not fully meet all conditions so that the alternative circuits may be found pref erable. For example, a modification that may be utilized is to arrange the primary P1 of transformer T1 instead of being of high inductance to be of low inductance, thus causing the voltage amplification to increase with the frequency of posing the capacitive coupling K1 to the magnetic coupling Pz-St' and properly proportioning the magnitudes of these coupling effects, the gain or voltage ratio of the tuning system may be ,maintained very flat, even though the effective Then by op-- coupling between the two tuned circuits decreases toward the higher frequencies.-

In Figure 2, three couplings are provided for circuit, or system, A "that become effective in greater or less degree, depending upon the frequency of tuning. .'I'he magnetic coupling Pz-Sz is substantially constantover the tuning range. The eflect produced by. capaci y K: and resistance R: in shunt therewith included in resonant circuit S2C2 is to provide an effective change in coupling between the'two tuned circuits over the tuning range, the coupling provided by these elemerits being greatest in the low frequency range.

In addition, the energy dissipating impedance means K-Rz tends to increase the power factor of the tuned circuit S?-C2, and hence of the coupling system, at the lower frequencies, thus providing wider resonance bands at such frequencies than are normally obtainable. As the frequency of tuning increases the elfective magnitude of resistance inserted in the resonance circuit.S2-Cz by the impedance K2 Rz automatically decreases, due to the by-passing effect of capacity K2. This variation in the losses or, dissipative effect, introduced by the impedance K-Rz, it will be observed, is opposed to the normal mode of variation of the resistance in the resonance circuit Sz-C2 introduced by skin efiect eddy current losses and the like, which factors ure 2, the capacity coupling K1 may or maynot be employed and may be arranged to either aid or oppose the direct capacity coupling due to the condenser K2, or may be made to aid or oppose the magnetic coupling Pz-Sz, orythe capacitive coup ings may be used exclusively, in which case the coils P2 and S2 may be positioned to'provide no magnetic coupling therebetween.

The antenna circuit contains a variable resistance R1 connected in shunt with the primary winding of the transformer T1. This resistance constitutes a volume control for adjusting the signal intensity impressed upon the receiver.- I

-Byir'1terposing the double-tuned circuit A between the antenna and the first amplifier tube, the desired signal may be chosen with such a high degree ofselectivity that the system may be rendered substantially opaque to undesired extraneous signals while at the same time selecting tin? desired signal with'minimum attenuation, thereby preventing intermodulation eifects.

Directing attention now to the first of the interstage coupling networks, the output circuit of the first radio-frequency amplifier tube V1 is in,

'stantf ally fiat voltage amplification characteristic over the tunable range. Tothis end the coils are so made that the distributed capacity between turns aifords natural periodicities within the tunable range. The transformeris further arranged to provide a small voltage step-up between primaryand secondary circuits, and also have not too high a mutual inductance between windings,

the magnetic coupling being such as to introduce the two eaks in the resonance curves adjacent the upper and lower limits of the tuning band respectively. By winding the coils P and S of high resistance wire or by connecting a resistance such as R: across the primary winding, the peaks of the resonance curve may be flattened out to such an extent that the transformer provides substantially uniform response over the tunable frequency range.

An alternative design is to provide a magnetic coupling between primary and secondary windings,,sufliciently close to introduce but a single resonance peak within the tuning range, and to properly damp this peak by means of the winding resistance or the shunt element R3 to aiford uniform voltage amplification.

The preferred design of this transformer is to construct the windings in several pies to minimize the distributed capacity between turns. These 'pies may comprise self-supporting coils held on an insulating mandrel or may be wound in slots cut in a separate form. The form may be enclosed in a metal cup to minimize the extent of 1 external field. 4 It is preferable that an iron cup be employed for this purpose since it increases the losses in the transformer circuit which, as pointed 'out above, are desirable in this instance.

A second volume control in the form of a variable resistance R4 is connected in shunt with the secondary winding of the transformer Ta, The volume control R4 is simultaneously adjust- ,able with the control R1 in the antenna circuit by means of a uni-control device U2 mechanically coupling the variable elements of these two resistances. In this way it is easily possible to secure an attenuation of 45 d. b. per control or 'a total attenuation of d. b. This form of control is especially desirable as it provides ample signal attenuation without altering the bias- .ing potentials applied to the tube electrodes and thus permits the tubes to be operated at the most favorable portions of their characteristics at all times.

Y The use of a coupling circuit B for connecting the first and second tubes, having, an untunable secondary circuit, provides several advantages,

former T3 permits the insertion of the second volume control element Rrat this point. .The volume control element R4, of necessity, introduces a certain fixed capacity to ground equivalent to about six, or more, micro-micro-farads into the secondary circuit of the transformer, so that if a tuning condenser were connected in circuit at this point the minimum capacity of this circuit would exceed that of the other resonant circuitsby the capacity of the volume control element. This would require that all of the other selecting circuits be padded up to the same minimum capacity, and would also necessitate the use of larger and more expensive variable condensers than is required with the circuit arrangement shown, since the tuning range covered by the variable condensers is determined by the ratio of the maximum to the minimum capacity. It the minimum capacity is increased, the maximum capacity must be increased in the ratio of the square of the upper and lower frequency limits in order to cover-a given tuning range. This would mean, of course, that the able frequency range.

variable capacities would have to be constructed to have a much larger maximum capacity than required with the arrangement shown.

The coupling circuit 0 connecting the output of the tube V: to the input of tube V3 may be designed to provide substantially constant voltage amplification and selectivity over the tun- The coupling transformer T4 comprises a high inductance primary winding P1 and a low inductance winding P2 of relatively few turns, both windings being magnetically coupled to the secondary winding S. The primary winding P1 is shunted by a capacity K3 such that the circuit IQP1 has-a natural periodicity lower, but not greatly, lower,'than the lowest frequency within the tuning range. The circuit Kz-Pr is thus capacitively reactive over the tuning range with the result that as the frequency of the tuning increases a smaller and smaller percentage of the total signaling current flowing in the output circuit of tube V: will flow through the winding P1, thereby in effect automatically decreasing the coupling between windings P1 and S as the frequency of tuning increases.

Winding P2 is so connected to the circuit Kr- P1 that the magnetic effects with the two primary windingsupon the secondary circuit are additive. Since the coupling between the primary winding P2 and the secondary winding S is substantially constant over the frequency range while the coupling between the windings P1 and S automatically decreases with increased frequency, the ratio of the voltage in the secondary circuit to the voltage in the primary circuit will rise with frequency, but at a rate which is under control of the designer and may be made such as to cause the amplification to remain substantially constant with frequency changes, or to rise with frequency at a desired rate.

Capacity K3 is preferably small and may in certain cases comprise the distributed capacity of the winding P1 and the anode-to-cathode capacitential end of the form supporting the secondary winding S, or it may be wound directly. over the low potential end of the secondary winding but separated therefrom by the thin sheet of insulat ing material such as varnishedcloth or celluloid.

"It is preferably to space the turns of winding P2 so that they have the same pitch as those of the secondary winding S, for in this way the distributed capacity between the two windings is reduced.

The secondary winding S is tuned to resonance by means of variablecondenser Ca and has included in the resonance circuit the condenser K4 shunted by resistance R5. The impedance K4R5 offers a higher resistance to the low frequencies than to the high frequencies. iBy proper selection of the magnitudes of K4 and R5- the amount of resistance introduced into the tuned circuit may be made to vary automatically over a wide range as the .frequency of tuning' changes, so that it is possible to broaden the width of the resonance band or to increase the power factor of the circuit at 'tlie' lower frequencies'without are coupled in cascade relation. Uniform selecmaterially affecting, or affecting only to a small degree, the power factor at the higher frequency range. In this way it is possible to secure almost any desired resonance band ratio at the two ends of the tuning range. The results of both measurements and computation indicate that when employing a secondary circuit having a power factor of about 1%, the maximum broadening effeet occurs when the resistance Rrin ohms. is

about of the same order as the capacity reactance K4 in microfarads.

The natural capacity B2 existing between the primary winding P1 and the secondary winding 8 of transformer T4 may be arranged to aid or oppose the magnetic couplings between'windings and thus intensify or diminish the magnetic coupling effects thereof as the frequency of tuning increases.

Figure 8 is illustrative of the results obtainable with coupling circuits such as network 0, the curves having the same significance as those of Figure 6. 'The curves of Figure 8 represent the results of laboratory measurements using the circuit' arrangement shown in Figure 9.

Curve Ma shows the voltage amplification as measuredfrom the input section of tube VI: to the input section of tube Vy for the condition that the dissipative impedance Ky-Ry is short circuited; while curve M4 gives the corresponding curve with the short-circuit removed, 1. e., with the impedance KyRy included in the secondary circuit as shown in Figure 9. Curves N3 and N4 give the variations with frequency of the resonance band width at half amplitude as measured across condenser 0:: for the conditions that Ky---Ry is short-circuited and is included in the secondary circuit respectively. It will be seen from these curves that by proper design a coupling circuit is obtained which provides substantially uniform sensitivity and selectivity through- 5 out the tuning range.

It will be seen from a comparison of Figures 7 and 9 and the associated curves of Figures 6 and 8 respectively that two separate and distinct types of coupling circuits have been described for securing uniform selectivity throughout the tuning range. The circuit of Figure '7 relates to a structure wherein a pair of tunable circuits tivity is secured by arranging the gain characteristic of the entire unit and the effective coupling between tunable circuits in such a way that over-optimum coupling is secured in the low-frequency range while under-optimum coupling is secured at the higher frequencies. 'In practice this results in a resonance curvefor the low-frequency range which has been artificially broad-- ened in the region of resonance byfrom 5 to 10 kilocycles on either side of the exact resonance frequency, but which follows a 'normal 1 resonance curve several channels removed from the resonance frequency. At the higher fre-' quencies of tuning the complete resonance curve is, of course, of the conventional shape.

' This point is illustratedby the. curves of Figure 10 wherein curve I shows the frequency-response' characteristic of the coupling circuit when tuned to a frequency near the upper frequency limit; while curve'H gives the results for tuning near the low-frequency limit. Due to the effect 5 of over-optimum coupling, curve Hhas' the well understood double hump in theregion of resonance which thus broadens the resonance band at its base to substantially the, same width as is obtained with curve I. The width .of-bands m H and I at resonance is, of course, designed to provide substantially uniform response with minimum attenuation over the essential band of audio-frequencies equivalent to one-half to one channel on either side of exact resonance. For wide departures from exact resonance, such as six or seven channels, the response curves do not have to be and, in fact, are not the same, as is indicated by the upper portions of curves H and I. .The curves in this region are of the conventional character, with curve H narrower in this region than curve I due to the smaller losses occurring at the lower frequencies.

Now with respect to the second method of obtaining uniform selectivity over the tuning range, accomplished by insertion of the dissipative impedance KyRy, Figure 9, in the resonance circuit, the resultant artificial widening of the resonance band at the lower frequencies is secured by actually increasing the effective power factor of the transformer which has the effect of broadening the resonance curve throughout its entire extent at such frequencies; so that if the resonance curves for the upper and lower frequency limits of tuning coincide at one channel from exact resonance, they will be of the same order of magnitude six or seven channels removed from resonance. Thus, referring to Figure 10, this resonance curve for tuning at the lower frequency will coincide with curve-I for the upper frequencies. This distinction represents a slight difference in operating characteristics between the circuits of Figures 7 and 9, although the net result will be of the same order for the'two circuits insofar as side band admission or elimination is concerned.

A double-tuned circuit D is employed in the arrangement of Fig. 1 to connect the output ciras to produce additive effects in the secondary circuit. The magnetic coupling between the'two primary windings and the secondary is so proportioned as to give a desired slope in the amplification-frequency curve of the transformer. The secondary winding S1 is tuned to resonance by means of the variable capacity Ci'connected between ground and the high potential end of the secondary, the low potential end thereof being connected through a low inductance primary winding Prof transformer T6 to ground. The

secondary circuit of transformer T5 is coupled to tunable circuit S2C5 through a link circuit comprising an electrostatic coupling by virtue' of capacity K5, extending between the high potential points of the secondary windings S1 and S2, and an electromagnetic coupling by virtue of the mutual inductance existing between windingsPs and S2 If a substantially uniform resonance band ratio is desired for the tuning range the capacity coupling K5 can be arranged to oppose the magnetic coupling, and the two couplings combined can be arranged to optimum or just over optimum coupling for the lowest frequency to be received. The magnetic coupling should predominate throughout the range. Then with the capacitive coupling opposing the magnetic the resulting coupling will decrease asthe tuning frequency increases, thereby reducing the reaction of one resonant circuit upon the other to render the tuning sharper with increase in frequency,

which effect opposes the natural tendency for the resonance curve to broaden out at the upper frequency limit, the resulting effect being such that the resonance band width is about the same throught the frequency scale.

In order ,to insure that the coupling circuit D will-provide substantially uniform voltage amp1i fication over the tuning range, it is necessary that transformer T5 be so designed that the voltage amplification for this transformer 'will increase with the frequency of tuning, as indicated in curve M1 of Figure 6, to an extent necessary to offset the decrease in efliciency of energy transfer from the firstto the second tuned circuit due to the automatic decrease in coupling therebetween.

The coupling circuit E connecting the output of tube V4 to the input of the detector tube V5 is similar in construction and operation to the coupling circuit C discussed above. It comprises the uniform gain transformer T7 having a high inductance primary winding P1 tuned by the shunt capacity K11 to a frequency below the range, and a low inductance primary P2. Both primaries are magnetically coupled in an additive sense to the resonant secondary circuit containing in series relation the tuning condenser Cs, secondary winding S, andthe fixed-capacity Kc shunted .by resistance R6 for adiusting the resonance band width.

Coupling circuit E is preferably arranged so that it has a. higher voltage gain than the circuit just preceding it, in. order that powerful local signals,of low modulation percentage will not overload the tubepreceding this circuit before the fulloutput of the power tube'is obtained. This condition is very likely to occur where the de-.

tector works directly into the power tubes. For this samereason, it isdesirable that coupling circuit E be designed for uniform gain, particularly when the tube preceding the detector tube V5 isoperating near the overload point.

The detector tube .V5' is of the screen grid type operating-as a self-biasing tube due to connection of the cathode to ground through resistance 13 which minimizes to a considerable degree the overload of the detector itself. The output of detector tube V5 is coupled by means of circuit F to the input of a first audio-frequency amplifier tube Vs. Circuit F includes a resistance coupling network comprising resistances R7 and Rs included in theanode and gridcircuits of tubes V5 and V6, respectively, the high potential terminals of the resistances being connected through a blocking condenser K7 while the low potential terminals are connected through ground and the battery supply circuit.

Interposed between the output section of tube V5 andjresistance R7 is a low-pass filter section comprising the series connected radio-frequency choke coil L1 and the shunt capacity Ks which particular filter shown is merely intended to be indicative of the method employed for shaping the audio-frequency characteristic. In some instances it may :be desirable to utilize a highpass or even a band-pass filter to attain a desired response curve.

With receiving systems as normally constructed embodying the usual types of coupling circuits for interconnecting the radio-frequency stages, the resonance band width increases with frequency of tuning due to the increase with frequency in effective resistance of the tuned circuits, producing thereby corresponding variations with frequency in the width of the side bands trans-' mitted. If the selectivity is such as to transmit at the lower frequencies of tuning a band width corresponding to the essential range of audiofrequencies, then at the higher frequencies of tuning the band width'transmitted will be so broad as to introduce extraneous signals from stations operating on other than the desired wave length. If, on the other hand, the selecting circuits are designed to transmit. the essential range of audible frequencies when the tuning is adjusted for the upper frequency limit, marked limit due to the increase in selectivity with reside band attenuation or'trimming-will occur as the. tuning is adjusted toward the low frequency frequency portion of the receiver may be designed to compensate effectively for the side-band attenuation throughout the frequency range. One method of shaping the audio-frequency characteristic in this manner is by means of the lowfrequency filter ,in coupling circuit F of Figure. 1.

Figure 11 is illustrative of what may be ac-,

.complished by way of shaping the overall frequency characteristic for a receiver of the type 'disclosed herein. Curve G1 which shows the response characteristic of the audio-frequency stages Veto Va, inclusive, is substantially flat over the essential range ofaudible frequencies extending from 11 to is. G2 shows the overall fldelity'characteristic of the receiver with the low-pass filter of coupling circuit F omitted and illustrates clearly the side band attenuation introduced due to the selecting networks at thehigher audio frequencies. response characteristic forthe audio frequency portion of the receiver including a high-passfilter in the coupling circuit F suitably designed to compensate in part for the trimming caused by the selecting networks. Curve G4 shows the final overall fidelity characteristic of the receiver with the high-pass filter included in the coupling circuitd andthus shows clearly the manner in which -.the audio-frequency characteristic has been improved. The curves of Figure 11 are not'intended tobe rigorously correct, but rather are illustrative of what may be accom-' plished by way of improving the overall receiver characteristic. It .is to be stressed again that results such as shown in Figure 11 are obtain- 'able only where, as in the present invention, the

selecting networks, are such as to provide a .tances with larger sized wire spacing the turns,

Curve Gs' shows the,

substantially uniform resonance band width throughout the tunable range.

The radio-frequency amplifier as a whole may be designed in several ways depending upon the operating conditions. Assume, for example, it is desired to employ tuned circuits having about the characteristics now commonly employed in broadcast receivers which have a power factor of about 1%, then by broadening the resonance band of the individual stages. at thelow-frequency range, while leaving .the resonance band at the high-frequency range, substantially unaffected, the ratio over the whole range will remain uniform. If the conventional number of three or four tuned circuits were to be employed, this broadening of the resonance band niightimpair the overall selectivity, but when employing coils having a 1% power factor, a larger number of tuned circuits will be employed than has heretofore been the practice, so, in this way, the desired overall selectivity can be secured.

Where a large number of tuned circuits are employed, theory and experiment indicate that the peak of the resonance curve may be quite broad while for conditions slightly off resonance the sides are very steep. This steepness oi the sides of the resonance curve (just as at the low frequency range of present commercial receiving the gain characteristic of the audio system atthe low frequency range such as by interposition of the high pass filter circuit in the detector output or by increasing the high frequency response.

The present invention may be successfully practiced when employing the conventional number of three, four or five tuned circuits. by using tuned resonant circuits of a lower power factor than 1%. This maybe accomplished by employing larger diameter coils than now commonly used and winding the secondary inducor using radio-frequency cable rather than solid wire. In this way it is possible to reduce the power factor of the tuned transformers to .5% or lower. This practice, whether employed with three or a greater number of tuned circuits, is likely to seriously impair the quality ofreproduc- -tion because of side band cutting, but as previous-- ly described, the effects may easily be compensated for by proper shaping of the audio characteristic; 1

"In many cases it is desirable to reduce the high-frequency response of the audio system, particularly above 3000 or 4000 cycles. This may be .very'conveniently accomplished in the pres- 7 cut invention by proper selection of the number and power factor of the tuned circuits so that the side-band attenuation of the radio-frequency portion of the amplifier becomes effective slope the gain characteristic so that it has about "sitivity of a receiveris high, it is preferable to. I

a 2:1 ratio; that is, it has about twice the sensi-.'

tivity at the low-frequencyv as at the high-frequency range. By sloping the curve in this way, the stability and freedom from oscillation" remains about uniform. This condition may, of course, not be desirable for all circumstances but may easily be modified as conditions warrant. Figure 2 shows a circuit designed in this manner.

In Figure 2 transformer T1 of coupling circuit A is provided with a low inductance primary winding included in the antenna circuit, thus' of the various couplings and.the design of thev dissipative circuit K2'R included in the resonant secondary circuit S2C2, is such as to provide substantially uniform voltage amplification and constant selectivity over the tunable range.

'Coupling circuit B connecting tubes V1 and V2 in cascade relation in this instance comprises,

'a uniformgain transformerT-i similar to. that of :coupling circuits C and E of Figure 1. The volume control resistor R4 is in this instance bridged across the primary circuit of transformer T4 since, for reasons explained above, it is undesirable to have this element bridging the tunable secondary circuit. The connection of control R4 across the primary circuit oftransformer T4 necessitates insulation offlall active portions of the control above ground potential, .andin this respect does not provide so desirable an arrangement as the circuit of Figure 1.

It is, of course, not essential that transformer T4 be of the uniform gain type. By, employing such a transformer, however, it is possible to de-. sign the amplification characteristic to compensate for the capacitive reactance introduced into the primary circuit. due to employment of the .tends to equalize the impedance over the entire range, thus producing uniform amplification.

The resistor R5,and shunt capacity K4, included in the resonant circuit, are selected of such values as to provide about the same or a slightly wider resonance band at the, low than at the high frequency tuning range.

The broadly tuned aperiodic transformer T3 now comprising circuit C coupling the output of tube V2 with the input to tube V; may be given' a voltage amplification slope favoring the lowfrequency over the high-frequency response in about a 2:1 ratio in order to provide a corre- -C and E of Figure 1. of uniformgain coupling circuits are available sponding overall frequency-response characteris tie for the radio-frequency amplifier.

The double-tuned circuit D of Figure 2 employs a uniform gain type of transformer T10 in the output circuit of tube V3, the gainfrequency characteristic of which maybe given a desired that preferably the natural capacity K12 betweenturns in conjunction with the anode-cathode capacity o'f tube Va is suflicient .to render. the pri- The primary winding P1 is wound to a- 1,oe1,1s4 V mary circuit resonant at a frequency slightly be low the tuning range. If necessary, of course, a separate condenser may be used to supplement 3 the natural capacity K1: in order to provide the required natural periodicity of the primary circuit. The primary P1 is coupled magnetically to the secondary winding by means of the mutual inductance between windings and also capacitively by means of condenser K12 connecting the high potential terminals of the two windings.

The primary winding due to the capacity in shunt therewith is capacitively reactive over the tuning range, and hence-has a falling impedance characteristic for increases in frequency, which efiect opposes the gain in voltage amplification with frequency, which in the absence of other factors would exist. This opposing effect is further intensified due to the automatic decrease in effective coupling between the primary and sec ondary circuits with increase in frequency resulting from the shunting effect of capacity K13.

The capacitive coupling K12 may be arranged, de-

pending upon the respective'polarities of the high potential-terminals of the primary and second-' ary windings, to either aid oroppose the magnetic coupling in the secondary circuit, the particular arrangement utilized being determined by the desired slope of the gain-frequency characteristic to be attained. In the present instance it isdesirable to have a substantially uniform frequency-gain characteristic for the transformer T 0 and accordingly the capacitive coupling K12 is arranged to aid the magnetic coupling, since otherwise the rapid decrease in impedance of the primary circuit and the automatic decrease in effective coupling between the primary and 'secondary windings would cause the voltage amplification to decrease with increase in the tuning frequency.

The resonant secondary circuit of transformer T10 ihcludes the primary winding P2 of transformer T6 which is' magnetically coupled to the secondary winding S2 thereof. The secondary winding S2 is, in turn, included in a resonant circuit 'Sz-Cs which contains the dissipative impedan'ce K14R12 proportioned to maintain an approximately constant resonance 'band width over the tuning range in the manner explained above. Thus, .the circuit-D when properly designed willhave a substantially uniform overall frequency-gain characteristic, and likewise a substantially constant'degree of selectivity over the tuning band. j

*Tlie double-tuned circuit D of Figure 2 is, of course,'an alternative arrangement to that of 'Figure '1, the transformer T5 in one instance and which could be utilized to replace such transformers, as, fon example, T4, T5 or T10. Examples of such circuitsare shown in Figures 3, 4, and 5.

Ineach of these figures I represents the input terminals and O the output Jterminals. In Figure '3 there is provided only a magnetic coupling, between the primary winding P and the secondary winding S. The primary winding of relatively high inductance and is'tuned slightly below the tuning range.

- 1,961,154 by means of the natural capacity Km between turns or by a physical condenser to a frequency The primary circuit has therefore a falling impedance characteristic over the tuning range with increase in frequency, and further. as the frequency increases there is an automatic decrease in effective coupling between the primaryand secondary circuits due to the shunting effect of capacity K11. Both of these eifects offset the inherent tendency which would otherwise exist for the amplification to increase with frequency.

In Figure 4 the primary circuit winding P is again wound to a relatively high inductance and is tuned by means of the natural capacity K18 between turns to a frequency slightly below the tuning band. In this instance, however, the primary circuit is coupled only capacitively to the secondary circuit by'means of the coupling condenser K15 connecting the high potential termi nals of the primary and secondary windings P and S respectively. As the frequency of tuning increases, the primary winding P, due toits falling impedance characteristic tends to produce an ever decreasing efiect in the secondary winding S. Opposed to this, however, is the effect of the capacitive coupling between the primary and secondary circuits, which increases with frequency, so that by properly selecting the impedance characteristic of the primary winding P and the magnitude of the coupling capacity K15,

' the frequen y-gain curve for the network may be sloped in a desired manner.

In the circuit of Figure 5 the primary winding P is of the same. general order of inductance as the secondary winding and is coupled magnetically thereto by means of mutual inductance M between windings, andcapacitively by means of condenser K16 extending between the high potential terminals of the two windings. be observed that in this instance the primary winding is not resonant at a frequency below the tuning range, and accordingly its impedance will increase with frequency, thus tending to give 'a positive slope to the gain-frequency characteristic. While the capacitive coupling Km may be arranged to either aid or oppose the magnetic coupling or may not be employed at all, in general, it will be desirable to have the capacity coupling oppose the magnetic coupling in order to provide substantially uniform amplification over the tuning band.

The high gain circuit E of Figure 2 is arranged to have a substantially flat amplification.curve..

By the proper selection of the condenser Ks and resistor R0 the selectivity characteristic is made Y either uniform or slightly broader at the low-'- frequency than at the high-frequency range.

Summing up the characteristics for the radio frequency amplifier, the overall sensitivity will have the desired 2:1 ratio favoring the low fre quencies, while the overall selectivity will be substantially uniform over the tuning range.

In Figure 2 the first stage of audio-frequency amplification shown in Fig. 1 is omitted, the circuit F serving to connect the detector output.

directly through transformer Ts to the power tubes V1 and V0 connected push-pull.

With the type of receiverg'shown in Figures 1 or 2 the sensitivity is made very high and to do this practically it is necessary to so position the parts, arrange the wiring and provide shielding sons to effectively eliminate extraneous couplings from-stage in stage and from the input to the output.

receiver.

The various tuning coils are preferably individually shielded by grounded metal cans. The amplifying tubes may be interposed between the metal cans to effectively shield the exposed portions from one another or they may be shielded by individual cans.

To eliminate common couplings in the chassisv pan, wires and-tuning condenser, etc., it has been found extremely helpful to connect, for exaniple, the low potential terminal of each transformer secondary winding directly to its own tuning Wherever possible, elements operated at low condenser rotor by means of a separate wire and brush contact rather than to ground such terminals to the chassis pan and rely on the connection from the pan to the condenser for a proper return path. It has also been found that'when employing by-pass condensers, such as for the A, B and C voltages, and also the plate by-pass .for the detector, that these connections should be made directly to the cathode of the tube under consideration rather than to ground. In this way common couplings resulting. from currents flowing in the chassis pan are eliminated.

Couplings of the nature just discussed are especially important in a design such as Figures 1 and 2, because the desired couplings between adjacent stages are small and extraneous or unknown couplings might easily vitiate the desired effects. v

I claim:

l; A high frequency electrical coupling system having input and output terminals for interconnecting successive'portions of a multi-stage thermionic radio receiver, comprising, at least one resonant circuit tunable throughout a. frequency range, and fixed -impedance means included in said coupling system producing effects so variable with frequency as to maintain the resonance band width of said coupling system substantially constant throughout said tunable frequency range.

2. A high frequency electrical coupling system having input and output terminals for interconnecting successive portions of a multi-stage thermionic radio receiver, comprising, at least one resonant circuit tunable throughout a frequency range, and fixed impedance means included in saidcoupling system producing effects so variable with frequency as to render the selectivity 'of said coupling system when timed to a frequency adjacent the upper limit of said tunable range substantially equal to the selectivity of said coupling system tuned to a frequency adjacent the lower limit ,of said tunable range.

3. A tunable high frequency electrical coupling circuit adapted to interconnect successive. portions of a multi-stage thermionic radio receiver,

comprising, a resonant secondary circuit, arid a primary circuit including a plurality of fixed impedance means so arranged and coupled to said secondary circuit as to produce eifectively in said secondary circuit dualistic reactions proportioned to maintain the selectivity of said cou- 5 pling system substantially constant throughout a tunable frequency range.

4. A tunable high frequency electrical coupling y tem adapted to interconnect successive portions of a multi-stage thermionic radio receiver,

10, comprising, a resonant secondary circuit, and a primary circuit including a plurality of fixed impedance. means so arranged and coupled to said secondary circuit as to produce effectively in said secondary circuit dualistic reactions which vary oppositely with frequency at such rate as to maintain the selectivity of said coupling system substantially constant throughout a tunable frequency range.

5. A tunable high frequency electrical coupling -system adapted to interconnect successive portions of a multi-stage thermionic radio receiver, comprising, a resonant'secondary circuit, and a primary circuit including fixed impedance means so arranged and coupled to said secondary circuit as to produce effectively in said secondary circuit dualistic reactions which vary oppositely with frequency at such rate as to automatically adjust the effective coupling between primary and secondary circuits from optimum or slightly more than optimum coupling at the low frequency end of the tuning range to less than optimum coupling at the' upper frequency limit thereof for reducing variations in selectivity otherwise present in said coupling system as the tuning is adjusted throughout the tunable frequency range. i

6. A tunable high frequency electrical coupling system adapted to interconnect successive portions of a multi-stage thermionic radio receiver, comprising, a resonant secondary circuit, and a primary circuit including fixed impedance means so arranged and coupled to "said secondary circuit as to produce eiiectively in said secondary 'circuit dualistic reactions which vary oppositely with frequency at such rate as to automatically adjust the effective coupling between primary andsecondary circuits from such a magnitude greater than optimum coupling at the low fre quency end of the tunable range to such a magnitude less than optimum-coupling at the upper frequency end of the tunable range as to maintain the selectivity of said system constant throughout the tunable frequency range. 75A high frequency electrical coupling system including at least one resonant circuit tunable throughout a frequency range, and fixed impedance means included in said resonant circuit producing eil'ects so variable with frequency as to provide approximately the same resonance band widths for said coupling system at the upper and lower frequency limits of said tunable range.

8. A high frequency electrical coupling system including at least one resonant circuit. tunable throughout a frequency range, and fixed impedance means included in said resonant circuit producing eifects so variable with frequency as to minimize changes in selectivity of said coupling system as the tuning is adjusted throughout said frequency range.

9. A high frequency electrical coupling system including at least one resonant circuit tunable throughout a frequency range, and energy dissipating impedance means decreasing in dissipative effect with increasein frequency included in said resonant circuit for reducing variations in selectivity of said coupling system throughout said timable range. I

10. A high frequency electrical coupling system including at least one resonant circuit tunable throughout a frequency range, and fixed impedance means comprising resistance shunted by capacity serially interposed in said resonant circuit for reducing variations in selectivity of said coupling system as the tuning is adjusted throughout said frequency range.

:11. In an electric signaling arrangement a tunable coupling system for coupling two portions thereof, adapted to respond to a uniform band width of frequencies over a wide tuning frequency range, said coupling jsyst'em comprising'a pair of input terminals and a pair of output terminals, an inductance element connected between said pairof input terminals, a pair of adjustablyresonant circuits coupled together by a dual coupling, a control member for simultaneously adjusting the resonance frequencies of said circuits, the first of said resonant circuits being electromagnetically coupled to said inductance element and the second of said resonant circuits being connected to said output terminals, said dual coupling being. proportioned to provide a resultant coupling which increases as the tuning frequency of said resonant circuits is decreased, whereby the band width to which said system is responsive remains substantially uniform over said tuning range.

12. A combination according toclaim 11 in which said dual coupling is a combined electrostatic and electromagnetic coupling.

13. A combination according to claim 11 in which said dual coupling is substantially less than optimum when the resonant circuits are tuned to high frequencies and becomes greater as the tuning frequency is decreased.

14. In an electric signaling arrangement, a pair of vacuum tubes each having an input circuit and an output circuit, a tunable coupling system adapted to respond to a uniform band width of frequencies over a .wide tuning range, for coupling the output of one tube to the input of the other tube, said system comprising an inductance element connected across said latter output,.a pair of adjustably resonant circuits coupled together by a dual coupling, a control member for simultaneously adjusting the resonance frequencies of said resonant circuits, the first of circuits being electromagnetically coupled to said inductance element, the second of said resonant circuits being connected to said input circuit, said dual coupling being proportioned to increase as the tuning frequency of said resonant circuits is decreased, whereby the band width to which said system is responsive remains substantially uniform over said tuning range.

15. An electric coupling systemv comprising a pair of resonant circuits tunable to the same frequency over a wide range of frequency, a control member for simultaneously tuning'said circuits. means producing a pair of'couplings between said circuits which vary with frequency in an opposite manner relatively to each other, said couplings 140 being proportioned to increase when the frequency of tuning is decreased whereby the widtl. of the frequency band transmitted by said system is maintained substantiallyuniform over the I tuning range. I

18. An electric coupling system according to claim 15 in which said pair of couplings is an electromagnetic coupling and -'an electrostatic coupling.

lLAn electric coupling system according touo said resonant 125 claim 15 in which the means producing said pair of couplings are fixed.

18. An electric coupling system comprising a pair of resonant circuits tunable to-the same frequency over a wide frequency range, a control member for simultaneously tuning said circuits, means producing an electromagnetic coupling and means producing an electrostatic cou-' pling, between said circuits, said couplings being proportioned to provide a resultant coupling between said circuits which is substantially less than optimum when said circuits are tunedto a,

high frequency and becomes greater as said circuits are tuned to lower frequencies.

19. In an electric signaling arrangement, a' tunable coupling system adapted to respond to a uniform band width of frequencies over a wide tuning frequency range, said coupling system comprising a pair of input terminals and a pair of output terminals, an inductance'connected between said pair of' input terminals shunted by such capacity that it is naturally resonant at a frequency 'lower but not greatly-lower than the lowest frequency of said tuning range, a pair of adjustably resonant circuits coupled together by a dual coupling, a control ,member for simul-v taneously adjusting the resonance frequencies of said circuits, the first of said resonant circuits being electromagnetically coupled to said inductance element and the second of said resonant circuits being connected to said output terminals, said dual coupling being proportioned to provide a resultant coupling which increases as the timing frequency of said resonant circuits is decreased, whereby the band width to which said system is responsive remains substantially uniform over said tuning range.

20. In an electric signaling arrangement, a

tunable coupling system adapted to respond to a uniform band width of frequencies over a wide V tuning frequency range, said coupling system comprising a pair of input terminals and a pair of output terminals, an inductance element connected betweensaid pair of input terminals, a pair of adjustably resonant circuits coupled together by a dual coupling, a control member for simultaneously adjusting the resonance frequencies of said circuits, the first of said resonant circuits being electromagnetically coupled to said inductance element and the second, of said resonant circuits being connected to said output terminals, said dual coupling being proportioned to provide a resultant coupling which is over-optimum at the lower frequencies of said tuning range and decreases as the tuning frequency is increased, whereby the band width to which said system is responsive remains substantially uniform over said tuning range.

21. A high frequency electrical coupling system comprising a resonant circuit, means for variably tuning said system over a-range of frequency and means for causing the power factor of said system to increase when the frequency to which said system is tuned decreases.

22. A high frequency electrical coupling system comprising a resonant circuit, means for variably tuning said system over a range in fire quency and means for introducing resistance into said circuit which effectively increases in magnitude with decreasing frequency:

23. A high frequency electrical coupling system comprising a tunable circuit, means for variably tuning said circuit over a range in frequency, means introducingresistance into said circuit and means automatically varying the effective magnitude of said resistance inversely with respect to the tuning frequency, whereby a substantially constant degree of selectivity is maintained over said frequency range.

24. A high frequencyelectrical coupling system' for translating a band of signal frequencies from an input circuit to an output circuit, said system comprising a variable tuning element for selecting the position of said frequency band over 1;; a considerable range in frequency, a resistance, the magnitude of which is dependent upon the adjustment of said tuning element and means for simultaneously varying said tuning element and the magnitude of said resistance so that when said frequency band is moved higher in the frequency-range the effective magnitude of said resistance is decreased, whereby a substantially constant band width may be maintained over said range.

25. A high frequency electrical coupling system tunable throughout a range in frequency, adapted to interconnect successive portions of a multi-stage amplifier, said'system comprising a DIBQLAiM EH1 ipsiasijwilam 14'. u'wpmzd, Little Neck, N; Y. WA"? Swuamsc sums.

" Patentdated June 5, 1934, Disclaimer filed May 29, 1935, bythe' patentee,g

.jthe assignee,Haze1tine Corporation, assenting. Enters this disclaimer to . claims 2, 8, 9,10, 21, 22, 23, and l25 'of said patent which are in the following words:'

26 A high fiequency electrical coupling system having input and output'ter- I minals for interconnecting 'successive portions of a-multi+stage thermionic radio receiver, comprising, at least one resonant circuit tunable-throughout a 'ire'quency range, and fixed impedance means included in said coupling system producing efiects sovariable with frequency as to render the selectivity of sai coupling system when timed to-a uency adjacent the upper limit of said tunable range substantially equal to thejseectivity of said coupling system .tuned to a frequency adjacent the lower-limit ofjsaid tunable range I V A j 8. Alfig frequency electrical coupling system includingat least one resonant.

circuit tunable throughout a frequency range, and fixed impedance means included in 7 said resonant circuit producing efiects so variable with fre uency as to mimr'nize.

c in selectivity of said coupling system as the timing is ad usted throughout saidfrequencyrange; r V q U 1 9. A high frequency electrical coupling system including at least one resonant circuit Vhmalie' throughout a freqlency range, and energy dissipating impedance means decreasing in dissipative e ect with increase in frequency included'in said resonant circuit or reducing variations in selectivity of said coupling system throughout said tunable range., K a

10. A high frequency electrical system including at least one resonant circuit tunablethmughout a frequency range, and fixed impedance means:cqiiiprising shuhted by capacity serially interposed in said resonant circuit for reducing variations in selectivity of said coupling system as the tuningis adjusted 'jth ioughoufl said frequency range.

"21. A High frequency-electricalcoupling'systemcom'prising a rdsonant? circuit,

. means for variablytuning said system over a range of frequency and means'i'oi'. causing the power of said system to increase when the frequency'to which'saidsystem is v tuned decreasesiv A I 22. A high frequency electrical coupling'system a resonant circuit, means for variably tuning said system over a range in frequency and means for introducing into said circuit whichefiectively increases in magnitude with d ireqeuency.

23. A high frequency electrical coupling systemcomprising a tunable circuit, means for.variabIy;tuning-said circuit over a ran '0 in frequency,- means'iintroducing resistance said circuit and means automaticafi of said redstauce inversely with respect to the tuning ire uencywh'ereby a substantially'constant degree of selectivity is maintained over said frequency range.

y varying the effective. magnitude "-25. 'A liigh frequency electrical coupling system tunable throughout a range in I uency,' adppted to interconnect successive portionsiof a multi-stage'iamphfier, systemcbm .a primary circuit and a --tun'able' resonant secondary circuit .mductively .cqup ed'to said primary. circuit and, means associated with secondary" circuit for introducing losses therein which'va as said circuit. is tuned throughout said range, to maintain substantially constant t e'sele'ctivity of said system through-,-

Oilt saidltmblfltlency rangeff une18, 1935.

, D|sc A|M|=- R 1,961,154.William A. MacDonald, Little Neck, N. Y. WAVE SIGNALING SYSTEM.

Patent dated June 5, 1934. Disclaimer filed August 20, 1935, by the patentee,

the assignee, Hazeltine Corporation, assenting. Hereby enters this disclaimer to claims 1, 3, 4, 7 15,16, and 18 of said patent which are in the following words:

1. A high frequency electrical coupling system having input and output terminals for interconnecting successive portions of a multi-stage thermionic radio receiver, comprising, at least one resonant circuit tunable throughout a'frequency range, andfixed impedance means included in said coupling system producing effects so variable with frequency as to maintain the resonance band width of said coupling system substantially constant throughout said tunable frequency range.

3. A tunable high frequency electrical coupling circuit adapted to interconnectsuccessive portions of a multi-stage thermionic radio receiver, comprising, a resonant secondary circuit, and a primary circuit "including a plurality of fixed impedance means so arranged and coupled to said secondary circuit as to produce effectively in said secondary circuit dualistic reactions proportioned to maintain the selectivity of said coupling system substantially constant throughout a tunable frequency range.

4. 1A tunable high frequency electrical coupling system adapted to lnterconnect successive portions of a multi-stage thermionic radio receiver, comprising, a resonant secondary circuit, and a primary circuit including a plurality of fixed impedance means so arranged and coupled to said secondarycircuit as to produce effectively in said secondary circuit dualistic reactions which vary oppositely with frequency at such rate as to maintain the selectivity of said coupling system substantially constant throughout a tunable frequency range.

7. A high frequency electrical coupling system including at least one resonant circuit tunable throughout afrequency range, and fixed impedance means included in said resonant circuit producing effects so variable with frequency as to provide approximately the same resonance band widths for said coupling system at the upper and lower frequency limits of said tunable range.

15. An electric coupling system comprising a'pair of resonant circuits tunable to the same frequency over a wide range of frequency, a control member for simultaneously tuning said circuits, means producing a pair of couplings between said circuits wh1cl1 vary w 1thfrequency m an opposite manner relatively to'each other, said couplings being proportioned to increase when the frequency of tuning is decreased whereby the widthof the'freguency band transmitted bys'aid system is maintained substantially uniform over the tuning range.

16. An electric coupling system according to claim 15 in which said pair of couplings is an electromagnetic coupling and an electrostatic coupling.

18. An electric coupling system comprising a pair of resonant circuits tunable to the same frequency over a wide frequency range, a control member for simultaneouslytunmg said circuits, means producing an electromagnetic coupling and means producing anelectrostatic coupling, between saidcircuits, saidcouplings being proportioned toprovide a resultant coupling between said circuits which is substantially less than optimum when said circuits are tuned to a high frequency and becomes greater as said circuits are tuned to lower frequencies.

[Ofiiaial Gazette September 10, 1935.]

Images