US1755114A

US1755114A - Unicontrol signaling system

Info

Publication number: US1755114A
Application number: US20484A
Authority: US
Inventors: Louis A Hazeltine
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1925-04-03
Filing date: 1925-04-03
Publication date: 1930-04-15
Anticipated expiration: 1947-04-15
Also published as: NL18770C; DE534456C; GB250162A; AT118870B; FR599767A

Description

April ls, 1930.. I L. HAZELTINE 1,755,114

' UNICONTRCL SIGNALING SYSTEM Filed April s, 1925. r 2 Sheets-Sheet 1 INVENTOR ATTORNEYS April 15, 1930. L. A. HAZELTINE UNICONTROL SIGNALING SYSTEM Filed April 3, 1925 2 Sheets-Sheet 2 Angular adjmsfmenl (fl/lsp/acemenfj fic,

- [NVENTOR W ATTORNEYS Patented Apr. 15,

UNITED STATES PATENT OFFICE LOUIS A. EAZELTINE, OI HOBO KEN, NEW JERSEY, ASSIGNOR' '10 HAZEL'I'INE B- POBA'IION, OF JERSEY CITY, NEW JERSEY, A CORPORATION 01 DELAWARE UNICON'IBOL SIGNALING SYSTEM Application filed April 3, 1925. Serial No. 20,484.

This invention relates to radio amplifiers and radio receivers.

The circuit arrangement for reception of radio signals which hasproduced excellent 5 results because of its sensitivity and selectivity is that employing tuned radio-frequency amplification in several stages, with elimination or neutralization of coupling between stages, as describedin my United States Let- 1 ters Patents No. 1,489,228, No. 1,533,858, No. 1,577,421 and N 0. 1,648,808. While receivers of this type have met with almost universal approval from users, it has been recognized that it would be highly desirable to reduce the means for tuning to a single control, and further to obviate the need of an external antenna.

Telephone transmitting stations employ undamped carrier currents, the oscillations of which have no decrement, so that the incoming signals can be received in closely coupled and sharply tuned circuits. The employment of undamped carrier currents permitting the use of closely coupled and sharply tuned circuits has previously necessitated an individual control for each of the several stages. This multiplicity of controls is due to the fact that manufacturers have been unable, in practical construction, to produce coils and condensers with substantially no variation in electrical characteristicsa condition which must be met if a single control is to be employed for tuning a plurality of circuits exactly. Where a common control was formerlyprovided to vary simultaneously the tuning of all the circuits of a radio receiver, the mentioned manufacturing variations introduced wide inequalities, with resultant detuning in the respective stages throughout at least a portion of the intended operating range, or effective frequency band, because no means ware/provided to adjust all stages ,once and for all to have identical electrical characteristics over the entire operating range. The inevitable result of this detuning was a serious impairment both of amplification and selectivity.

There have been proposed so-called master-control radio-frequency receivers in which a single control is provided for the purpose of roughly tuning, simultaneously, each of several clrcuits, a number of separate con-. trols being provided to tune the individual circuits to exact resonance, thereby overcoming the mentioned detuning which results from inequalities in the-elements of -those circults. This system, of course defeats its own purpose, since there are actually at least as many controls as there are circuits to be tuned.

Furthermore, receivers are frequently used with antennas improperly erected by those unfamiliar with the preferred characteristics of such structures, so that such antennas Vary widely in their constants, and consequently the tuning of the circuit immediate- 1y associated with the antenna system is affected within wide limits.

One of the main advantages of this invention resides in its application to a multistage radio-frequency amplifier wherein a single control may be employed, as distinguished from the previously discussed master-control together with supplemental controls for the individual stages.

Another feature of the invention resides in the provision of a complete antenna system entirely supported by a cabinet.

Referring to the drawings:

Fig. 1 shows a plan view of a radio receiver embodying this invention, with the tain parts broken away to disclose the in-.

terior arrangement of parts;

Fig. 1 shows a side elevational view of this receiver with a side wall removed;

Fig. 1" shows a form of electrostatic scree utilized in the preferred embodiment of this invention;

Fig. 1 shows the complete circuit diagram of the receiver illustrated in the figures above;

Fig. 2 shows a calibration curve of a variable condenser; and

Figs. 2 and 2 show two views of a referred constructionfor the variable con ensers, including the two adjustable features; Fig. 2 being a sectional view taken along line 2 of Fig. 2".

Referrin to Figs. 1, 1 and 1, there is shown a ra '0 receiver cabinet with an

upper compartment

5, 6, 7 and 8 within which are mounted coils T T,, T,, a multi-unit condenser with units C1, C, and (3,, vacuum tubes V V,, V,, V an audio-frequency transformer AF, and all necessary batteries enclosed in a metal container. It will be noted that'the mentioned coils, in order to minimize undesirable magnetic coupling between them, are mounted in a row at one side of the compartment with their axes inclined at an angle of approximately to their common line of centers. The shaft of the multi-unit condenser is mounted in bearings supported at the front and rear of the compartment and is arranged to be rotated by a control or pointer 26 which moves over a scale 27 on the panel or front of the cabinet. At 25 there are shown rheostats for controlling the heating current of the vacuum tubes. The interior of the mentioned compartment may be lined with an electrostatic screen in the form of zig-zag wires, such as 9, indicated in Fig. 1", and similar wire screens 9 indicated by dotted lines in Fig. 1 may be employed to rtially shield the stages from each other. Etch section of the screens should referably be connected at one point to the ow-potential side of the filament circuit. This system of screens, together with the batteries and their container appearing in the upper right hand corner of Fig. 1', may, due to the resulting large conducting surface, serve as a counterpoise in the antenna system. In this way the conductin surface is made large and the resistance of t is portion of the antenna system reduced. At the lower portion of the cabinet there is mounted a metal sheet 1, serving as an antenna, which is connected to the first tuning coil T by means of a metal rod 2. In the space betweenthe metal sheet 1 and the upper compartment, there may be supported in any convenient manner a loud-speaker mechanism 4 and an amplifying horn 3.

The above-described arran ement of counterpoise and antenna provi es an antenna 111 of very low radio-frequency resistance and of fairly high capacity relative to the linear dimensions, although the effective height is low. The low resistance and moderate capacity of the antenna make desirable cation and one stage of audio-frequency amplification, provided it is desired to receive well only those stations which are near enough not to have pronounced fading, orto be affected seriously by atmosphericdisturbances. While, as has been stated, the preferred embodiment includes a self-contained antenna, the value of this invention resulting in extreme simplicity of control may be had with antenna and ground exterior to the cabinet, if there be provided in the antenna circuit a condenser of such capacity that small changes in capacity resulting from changes in antennas are negligible as compared with the resultant capacity of the condensers; or if such antenna condenser be arranged to be adjusted once for all with the particular antenna employed.

A convenient and compact form of tuning condenser is that having circular moving plates. This form of condenser gives within its working range a straight line relation between capacity and angular adjustment,-

or displacement, as illustrated in Fig. 2". To carry out the purpose of this invention, it is necessary that the condenser plates be rigidly and accurately plane and parallel, so that the calibration curve, Fig. 2, will be identical in shape for all condensers. This curve should preferably be a straight line. However, there will still exist the robability of differences in the various tuna le oscillatory circuits, due to differences in the fixed capacities of the wiring and of the coils, etc.; and there may also be variations in the clearances of the plates of the different condensers that will cause their rates of change of ca acity to differ slightly from one another. 0 compensate for the first condition a supplemental or auxiliary adjustable plate 10, shown in Figs. 2 and 2, electrically connected to the moving plates, but not moving with them, is placed adjacent to one of the outer stationary plates and is adjusted relatively to that plate, when the receiver is first assembled, so as to tune both radio-frequency amplifier input circuits and the detector input circuit to the same maximum resonant frequency when the main variable condenser units are set for minimum capacity.

While for the purpose of this invention ad justable plate 10 can be supported in any convenient manner, for it may, for example, be mounted as illustrated in Fig. 2". The construction there represented provides a threaded journal 13 surrounding the condenser shaft 12. On the inner end of this journal there is an integral collar 15 against which a nut 14 forces the condenser plate 10. Another nut 17 holds the journal tightly to the insulating plate 16 and serves to lock the assembly after the proper adjustment has been made.

To com ensate for the differences in the rates of c ange of capacity of the various condenser units, or in the rates of change of resonant frequenc of the oscillatory circuits ,in which the con enser units are connected,

the outside stationary plate 11, Fig. 2", is arranged to be moved axlall This latter adjustment is made when t e receiver is first assembled so as. to tune all three radiofrequency input circuits to the same minimum resonant frequency when the main vari able condensers are set for maximum capacity. This adjustment may affect slightly the initial adjustment of plate 10 which may now have to be readjusted. The final result of these adjustments is that all of the tuned circuits will be in resonance with one another for every setting of the tuning condensers, because the calibration curves are straight lines (or else are exactly similar) and, having been made to coincide at two points, coin cide throughout. In other words, the slopes of the capacity-displacement curves of the several condenser units will be identical. When all the tuning condenser units are provided with these adjustable features, it is, possible to engrave a wave-length or frequency scale 27 on the panel, prior to assembly, and to permanently adjust all condenser units to suit this scale.

The adjustment 'of plate 11,-Figs. 2 and 2, will also compensate for accidental differences in the self-inductance of the tuning coils. Mechanical forms of adjustment other than those indicated in Figs. 2 and 2 are, of course, possible, but, in general, they should be such as to determine or vary, first, the fixed or minimum value of the tuning capacity (or maximum resonant frequency), and second, the rate of change of capacity (or resonant frequency) with given displacement of the tuning control.

It is possible to use other shapes of condenser plates than that giving the straightline-capacity calibration curve of Fig. 2, as, for example, condenser plates so shaped that when the condenser is connected across a suitable inductance, they will produce a straightline-frequency curve; but such calibration curves must agree with one another in the respect that their ordinates when plotted from some particular axis for each are pro- J portional throughout.

The apparatus previously described may be connected in a circuit arran ement similar to that shown in Fig. 1. nthis figure there are shown two sta es of tuned radiofrequency amplification including the vacuum tubes V and V a detector tube V and an audio-frequency amplifier including the tube V A greater or less number of stages of radio-frequency or of audio-frequency amplification may be used, if desired, without departing from the spirit of this inven tion. The first tuned circuit of this diagram includes the electrostatic capacity of the antenna system above referred to which is not present in the tuned circuit of V, or the cirof V These two capacities will, in part,

balance each other, the difference being taken care of bythe factory adjustments of the variable condensers, as previously described. A neutralizing "condenser (J connected between the grid circuit of vacuum tube V and the secondary winding of transformer T tother with a second neutralizing condenser 5: connected between the grid circuit of vacuum tube V and the secondary winding of transformer T function to eliminate undesirable inherent capacity couplings, and hence to prevent regeneration and a corresponding tendency towards oscillations.

The presence of regeneration control is incompatible with the unitary tuning control of aplurality ofsuccessive tuned stages in a vacuum tube amplifying system because any appreciable variation in the regeneration adj ustments necessitates a corresponding variation in the tuning control of those stages only in which the regeneration occurs. The degree of regeneration and the corres onding tendency towards oscillations is argely determined by naturally variable factors, such as the condition of batteries, i. e., the internal resistance thereof, the settings of the filament rheostats and the characteristics of the vacuum tubes, because these and other factors influence the effectiveness of the coupling between the output and input circuits of the tube or tubes. It therefore follows that in order to render unnecessary the detuning of any of the stages for oscillation control and to attain efiicient simultaneous tuning of the several successive circuits everyreasonable precaution should be taken to prevent regeneration. To this end an embodiment of the present invention is herein described as including means for neutralizing or eliminating substantially all undesired capacity coupling, electromagnetic coupling and other forms of undesired coupling, whereby regeneration is substantially prevented. It is unnecessary to describe further the functions of the various circuits since they are fully disclosed in my mentioned patents. It will be understood, however, that the tuning of the circuits of V V and V is simultaneously and uniformly accomplished since the condenser units C1, C and C of these circuits are controlled by the common rotatable shaft 12.

I claim:

1. In a wave signaling system, the combination of an inductance coil, a variable condenser connected thereto, said coil and condenser together comprising a tuned circuit, and two independent adjusting means for said condenser, the adjustment of one of which determines the maximum resonant freuency of said circuit, and the ad ustment of t e other of which determines the rate of change of resonant frequency of said circuit.

a wave signalin system includinga tuned multi-stage amp ifier each stage 'of which includes an oscillatory circuit comprising a coil and a variable condenser, said condenser having aplurality of adjustingmeans, a plurality of said circuits being simultaneously tunable by a common control, the method of renderin said circuits in resonnance with each other throughout their intended operating frequenc range, which comprises adjusting one 0 said means to bring said circuits into substantial resonance at a certain frequency, and adj ustlng a second of said means to determine the rate of change of resonant frequency when the frequency is variedcby said tuning control common to said cicuits.

3. In a wave signaling system including a tuned multi-stage amplifier each stage of which includes an oscillatory circuit comprising a coil and a variable condenser, said condenser having a plurality of adjusting means, a plurality of said circuits being simultaneously tunable by a common control, the

method of rendering said circuits in tune with each other throughout their intended operating frequency range which comprises adjusting one of said means to bring said circuits into substantial tune at a certain maximum resonant frequency and adjusting a second of said means to bring said circuits into substantial resonance at a certain minimum resonant frequency, whereby the adjustment of said tuning control simultaneously varies the resonant frequency of said circuits While the same are rendered substantially in tune with each other throughout the intended operating frequency range.

4. In a wave signaling system, the combination of an inductance coil, a variable condenser connected thereto, said coil and condenser together comprising a tuning circuit, and adjusting means for said condenser whereby the maximum resonant frequency of said circuit and the rate of change of resonancefrequency of said circuit may be substantially independently adjusted.

5. In combination with a radio-frequency signaling system wherein a plurality of tuned oscillatory circuits are simultaneously adjusted by a unitary control, a variable condenser connected in each oscillatory circuit to tune the same by variation of its electrostatic capacity, said condenser being characterized in that it includes three separate adjusting means, the first of which determines a minimum capacity value, the second of which determines a maximum capacity value, and the third of which effects a variation according to a predetermined manner in the values of electrostatic capacity between said minimum and maximum capacity values.

6. In a radio-frequency signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain frequency range by a unitary control, means supplemental to said control for adjusting the rate of charge of resonant frequency of at least" one'of said circuits.

7'. In a wave signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain frequency range by a unitary frequenc -control, adjusting means connected in eac of said oscillatory circuits whereby the rate of change of resonant frequency of each of said circuits may be individually adjusted.

8. In a wave signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain frequency range by a unitary frequency-control, a plurality of adjusting means connected in each of said oscillatory circuits whereby the maximum resonant frequency of each of said circuits and the rate of chan of resonant frequency of each of said circuits may be individually adjusted.

9. In a tuned radio-frequency amplifier having a plurality of oscillatory circuits simultaneously tunable over a certain frequency range by a unitary control, means supplemental to said control for individually adjusting the rate of change of resonant frequency of certain of said circuits whereby said oscillatory circuits may be maintained substantially 1n resonance with each other when tuned over said frequency range by said unitary control.

10. In a wave signaling system, the combination of an inductance coil, a tuning condenser having means for varying the capacity thereof, said coil and condenser being connected together to comprisean oscillatory circuit, and frequency-adjusting means for said circuit whereby the maximum resonant frequency of said circuit and the rate of change of resonant frequency of said circuit may be adjusted supplementally of said means for varying the capacity of said condenser.

11. In a radio-frequency signaling system wherein a plurality of oscillatory circuits are intended to be simultaneously tunable over the same frequency range by a unitary frequency-control," means supplemental to said control for adjusting the slope of the frequenc -displacement characteristic of said unitary requency-control for certain of said .cies as there are means ity of substantially independent means associated with a certain one of said circuits and supplemental to said control to adjust said certain circuit at as many different frequenrovided so that more than one of said circuits are resonant with each other thruout said frequency range.

13. In a wave signaling system, the combination of an inductance coil, a tuning condenser having means for varying the capacity thereof, said coil and condenser being connected together to comprise a tuning circuit, and adjusting means for said circuit whereby the maximum resonant frequency of the circuit and the rate of chan e of resonant frequency of the circuit may e adjusted supplementally of said means for varying the capacity of said condenser.

14. In a wave signaling system, the combination of an inductance coil, a tuning condenser having means for varying the capacity thereof, said coil and condenser being connected together to comprise a tuning circuit,

and adjusting means for said condenser,

whereby the maximum resonant frequency of said circuit and the rate of change of resonant frequency of said circuit may be adjusted independently of said means for varying the capacity of said condenser.

15. In a radio-frequency signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain resonant frequency range by a unitary control, said frequency range having maximum and minimum limits, two separate means in each oscillatory circuit other than said unitary control for determining, respectively, one point at or near the maximum limit of said frequency range and another point at or near the minimum limit of said frequency range,

at which points all of said circuits may be individually adjusted by said means to-be in resonance with each other when tuned simultaneously by said unitary control.

16. In a multi-stage radio-frequency amplifier, the combination in each stage of an inductance coil and a tuning condenser connected thereto, said condenser including capacity-varying means, each coil and condenser together comprising an oscillatory circuit which is adjustably resonant over a certain frequency range by variation of the capacity of said condenser, and. a plurality of means other than said capacity-varying means connected in each oscillatory circuit by which all of said circuits may be accurately adjusted individually to be in resonance with each other at at least two different frequencies in said frequency range when tuned simultaneously by said capacity varying means.

17 In a radio-frequency signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain frequency range by a unitary control, two separate means in each oscillatory circuit meother at at least said two different frequencies within said frequency range. 18. In a wavesignaling system wherein a plurality of oscillatory circuits are intended to be simultaneously tunable over a certain frequency range by adjustment of a unitary control, the method of bringing said oscillatory circuits into substantial resonance with each other thruout said frequency range which comprises individually adjusting to resonance certain of said circuits at a frequency near one limit of said range and then individually adjusting the same circuits to resonance at a frequency near the other limit thereof.

19. In a wave signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain frequency denser in each of said circuits for tuning the same by adjustment of the position of said control, means connected in certain of said circuits for bringing all of said oscillatory circuits into resonance with each other at a plurality of frequencies within said range, comprising one adjustable electrical means for bringing-said circuits into resonance at one of the frequencies within said range when said unitary control is at acertain first position, and another adjustable electrical means for bringing said circuits into resonance at another frequency within said range when said unitary control is at a certain second position.

20..In a radio-frequency signaling system wherein a plurality of oscillatory circuits are simultaneously tunable by a unitary control,

a variable condenser connected in one of said oscillatory circuits to tune the same by variation of its electrostatic capacity, said condenserbeing characterized. in that it includes three adjusting means, the first of which operates in the usual manner to vary the electrostatic capacity of said condenser between certain minimum and maximum limits thereof, the second of which determines the said minimum limit thereof, and the third of which determines the rate of change of capacity resulting from variation of the firstmentloned adjusting means.

21. In a multi-stage radio-frequency amplifier, a vacuum tube in each stage having an input circuit and an output circuit, each input circuit including a coil and a variable condenser unit to tune said circuit to frequencies within an intended operating freuency range, undesired coup ing between said stages whereby a tendency toward oscillation is produced, means for limiting sa d tendency whereby detuning of any of said stages for oscillation control 1s rendered unnecessary, a plurality of ad usting means for at least one of said condenser units, each means of said plurality having its predominant effect at a different frequency, whereby all of'isaid input circuits may be caused to have substantially identical electrical characteristics thruout said operating frequency range, and a single manual control mechanically interconnecting said condenser units for tuning all of said input circuits simultaneously over said operating frequency range.

22. In a multi-stage radio-frequency amplifier, a vacuuin tube in each stage having an input circuit and an output circuit, each input circuit including a coil and a variable condenser unit to tune said circuit to frequencies within an intended operating frequency range, undesired coupling between the input and output circuits of certain of sa1d stages whereby a tendency'towards oscillation is produced, means for limiting said tendency whereby detuning of any of said stages for oscillation control is rendered unnecessary, a plurality of frequency-adjustin means for at least one of said input circuits, one of said frequency-adjusting means comprising a minimum-capacity adjustment for one of said condenser units and another of said frequency-adjusting means comprising a se arate adjustment for the rate of change 0 frequency of one of said input circuits, whereby all of said input circuits may be caused to have substantially identical electrical characteristics'thruout said operating frequency range, and a single manual control mechanically interconnecting said condenser units for tuning all of said input circuits simultaneously over said operating frequency range.

23. In a multi-stage radio-frequency amplifier, a vacuum tube in each stage having an input circuit and an output circuit, each input circuit including a coil and a variable condenser unit to tune said circuit to frequencies within an intended operating frequency range, undesired coupling between the input and output circuits of at least one stage whereby a tendency towards oscillation is produced, means for limiting said tendency whereby detuning of any of said stages for oscillation control is rendered unnecessary, and a single manual control for tuning all of said input circuits simultaneously, certain of said condenser units being provided with a plurality of substantially independent adusting means supplemental to said single manual control and so arranged with respect thereto that the capacity value of each of said certain condenser units may be separatelv and independently adjusted at a plurality of different frequencies, whereby all of said input circuits may be caused to have substantially identical electrical characteristics thruout said operating frequency range.

24. In a radio-frequency amplifying system including a plurality of vacuum tubes, each vacuum tube having an input circuit and an output circuit, at least one of said circuits of each tube being sharply tuned over an operating frequency range by means including a variable condenser unit, undesired coupling between the input and output cirsuits of at least one tube whereby a tendency towards oscillation is produced, means for limiting said tendency whereby detuning of any of said circuits for oscillation control is rendered unnecessary, and a single manual control for tuning simultaneously all of the circuits which include said condenser units, certain of said condenser units being provided with a plurality of substantially independent adjusting means supplemental to said single manual control and so arranged with respect thereto that the capacity value of each of said certain condenser units may be separately and independently adjusted at a plurality of different frequencies, whereby all of the circuits which include said condenser units may be caused to have substantially identical electrical characteristics thruout said operating frequency range.

25. In a multi-stage radio-frequency amplifier, a Vacuum tube in each stage having an input circuit and an output circuit, each input circuit including inductance and capacity, one of which is variable to tune said circuit to frequencies within an intended operating frequency range, undesired coupling between the input and out at circuits of certain of said stages where y a tendency towards oscillation is produced, means for limiting said tendency whereby detuning of any of said circuits for oscillation control is ren- 4 dered unnecessary, a unitary control common to said input circuits for simultaneously adjusting the resonant frequency thereof within said operating frequency range, and supplemental adjusting means connected in certain of said input circuits whereby the maximum resonant frequency of each of said certain input circuits and the rate of change of resontant frequency of each of said certain input circuits may be individually adjusted so that all of said input circuits may have' substantially identical electrical characteristics thruout said operating frequency range.

26. In a radio-frequency signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain frequency range by movement of a unitary control, adjust-ing means supplemental to said plurality of oscillatory circuits are simultaneously tunable. over a certain frequency range by the movement of a. unitary frequency control, adjusting means connected in each of said oscillatory circuits for individually adjusting independently of the movement of said frequency control the rate of change of resonant frequency of each of said circuits.

28. In a tuned radio-frequency amplifier having a plurality of oscillatory circuits simultaneously tunable over a certain frequency range by the movement of a unitary control, adjusting means supplemental to said control for individually adjusting independently of the movement of said control the rate of change of resonant frequency of certain of said circuits, whereby said oscillatory circuits may be maintained substantially in resonance with each other when tuned over said frequency range by said unitary control.

29. In a radio-frequency signaling system wherein a plurality of oscillatory circuits are simultaneously tunable over a certain fre quency range by a unitary control, means supplemental to said control for adjusting the maximum resonant frequency and the rate of change of resonant frequency of at least one of said circuits.

30. In a tuned radio-frequency amplifier having a plurality of oscillatory circuits simultaneously tunable over a certain frequency range by a unitary control, means supplemental to said control for individually adjusting the maximum resonant frequency and the rate of change of resonant frequency of certain of said circuits, whereby said oscillatory circuits may be maintained substantially in resonance with each other when tuned over said frequency range by said unitary control.

31. In a radio-frequency signaling system intended to have a plurality of electrically similar oscillatory circuits, each said circuit being intended to be tunable over the same frequency range by movement of a frequency control, a plurality of, substantially independent means associated with a certain one of said circuits and supplemental to said frequency control to adjust said certain circuit at as many different frequencies as there are means provided, so that adjustment of said plurality of circuits from one of said different frequencies to another of said difi'erent frequencies requires the same extent of movement of all of said frequency controls.

In testimony whereo I aflix m signature.

LOUIS A. HAZ LTINE.

LDISOLAIMEZR 1,755,114.Louis A. Hazeltine, Hoboken, N. J. UNICONTROL SIGNALING SYSTEM.

" Patent dated April 15, 1930. Disclaimer filed-January 18, 1936, by the patentee, the assignee, Hazelt'ine Corporation, assenting.

Hereby enters this disclaimer to claims 10 29 of said patent.

[Oficial Gazette February 18, 1936.]

, 12, 13, 14, 16, 17, 19, 21.23, '24, and