US2401481A

US2401481A - High-frequency signal generator

Info

Publication number: US2401481A
Application number: US358981A
Authority: US
Inventors: Daniel E Harnett
Original assignee: Hazeltine Research Inc
Current assignee: Hazeltine Research Inc
Priority date: 1940-09-30
Filing date: 1940-09-30
Publication date: 1946-06-04
Anticipated expiration: 1963-06-04
Also published as: GB578151A

Description

June 4, 94., D. E. HARNETT y HIGH-FREQUENCY SIGNAL GENERATOR Filed sept. 5o, 2 she/etssheet 1 llllll INVENTOR HARNETT DANIEL E ATTORNEY AAAAAAAA "gli PowER AMPLIFIER PowER AmPLlFlER ZSheets-SheetZ jlo MODULATION Sl GNAL GENERATOR MODULATOR MODULATION SIGNAL GENER ATOR MODULATOR FIG. 2.

MODULATOR FIGB.

MODULATR HIGH-FREQUENCY SIGNAL GENERATOR uMODULAR-0R il l l l l C l 0` (L .Fame 4, i946.

E EJ

OSCILLATON GENERATOR OSCILLATION GENERATOR GENERATOR GENERATOR GENERATOR mvENToR DANIEL E HARNETT ATTORNEY (f) OSCILLATION GENERATOR 4. I

OSCILLATION OSGILLATION OSCILLATION v ture which affect the oscillator.

Patented Juiced, 1946 i omen @el E.

a im; Tuchalioe, N. Y., assigner, by

mesme assients, to Haseltin essai-cli, Enc.,

hicago, mi., a corporation of than ,application September 3G, ledit/Seriali No. 358,981

This invention relates to highirequency signal generators for generating stabilized oscillations at any one of a plurality of predetermined high frequencies and, while the invention is of general application, it is particularly' suitable for use as a carrier-frequency generator in a carriersignal transmitter adapted to transmit carrier signals having any one of a plurality of different carrier frequencies.

Itis frequently desirable to provide a high-fre'- quency signal generator or oscillator for generating stabilized high-frequency oscillations at any one of a plurality of predetermined high frequencies. For instance. such an oscillator is useful in a carrier-signal transmitter adapted to transmit carrier signals of any one of a plurality of different carrier frequencies. If a tunable high-frequency oscillator is used in such a transmitter, it is generally found that the frequency of the generated carrier signal tends to drift; for instance, such a drift or change in frequency may be caused by variations in humidity or tempera- Crystal-controlled oscillators have been used in order to eliminate such diillculties, but if the transmitter is to be used on a large number of different channels,

d Claims. (El. 25d-36) vantages of the prior art arrangements mentioned above.

It is another object of the invention to provide a simplied crystal-controlled high-frequency signal generator for generating signals of any desired one of a plurality of predetermined high frequencies. y

In accordance with the invention, a high-frequency signal generator for generating any desired one of a plurality of predetermined signals comprises a first crystal-controlled oscillator for generating oscillations of 'a predetermined frequency, and a second crystal-controlled oscillator for generating oscillations of a predetermined frequency and comprising a fundamental component and a plurality of harmonic components. Means are provided for selecting any one of predetermined ones of :the above-mentioned generated components, together with means for heterodyning the selected component with the firstthe circuit for such an oscillator becomes verycomplicated and very costly due to the large number of crystals and switching elements required. Other expedients have, therefore, been suggested to overcome these difculties. Thus, it has been proposed to provide a tunable low-frequency oscillator, the stability of a low-frequency oscillator being relatively much better than that of a high-frequency oscillator, and to heterodyne the output of the low-frequency oscillator with the output of a high-frequency crystal-controlled oscillator to provide a source of relatively stable high-frequency oscillations adjustable over a range of frequencies. Such a system, however, also usually has the disadvantages that the frequency drift thereof is greater than is tolerable under certain conditions of operation and that a frequency error is introduced in determining the correct adjustment of the tunable low-frequency oscillator for each high-frequency signal to be generated. It is very desirable, therefore, to provide a highfrequency signal generator which is not subject to one or more of the disad vantages enumerated above.

It is, therefore, an object of the present invention to provide an improved high-frequency signal generator for generating signals of any one of a plurality of predetermined high frequencies which is not subject to one or more of the disadnamed oscillations, to develop a desiredoutput In accordance with a preferred embodiment of the invention, the signals generated are equally and closely spaced relative to the mean frequency of the band of frequencies including the desired output signal and the said first crystal-controlled oscillatorgenerates oscillations of a relatively high frequency, while the said second crystalcontrolled oscillator generates oscillations of a relatively lowffrequency.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Fig. l of the drawings is a circuit diagram, partly schematic, of a Icomplete carrier-signal transmitter for operating on any one of a plurality of dlerent'channels which includes av highfrequency signal generator in accordance with the invention; while Figs. 2 and 3 are schematic diagrams of diiferent embodiments of the invention.

Referring now more particularly to Fig. 1 of the drawings, the circuit thereof represents a conventional carrier-signal transmitter comprising; in cascade, a carrier-signal generator 8 and carrier-signal ampliier 9, the details of which are described hereinafter, a modulator illv to which is also coupled a modulation-signal generator Il, a power amplifier I2 and an antenna circuit I3, I3.' The operation of the transmitter, neglecting the details of operation of units 8 and 9 comprisdenser 50.

3 ing the present invention, will be readily,r understood by those skilled in the art, rendering a de tailed description thereof unnecessary. In brief,

however, modulation signals are generated in unit and are applied to the modulator' l0 where they are caused to modulate carrier-frequency oscillations of a selected frequency supplied by units 8 and 9, the modulated-carrier signal so produced being thereafter amplified in the ampliiier I2 and supplied to the antenna circuit I3, I3 for transmission.

Coming now to the portion of the system of Fig. 1 comprising'the present invention, the highfrequency signal generator s includes a first crystal-controlled oscillator including tube 20 for generating oscillations of any one of a plurality of predetermined relatively high frequencies. The oscillator is of the tuned grid-tuned plate type and includes a parallel-resonant circuit including a condenser 2| and an inductance 22 coupled between the oscillator-anode element of fthe tube and -ground through a condenser 23 and also an inductance 24 connected between the first signal-input electrode of tube 20 and ground through a resistor 25, the series-connected inductance 24 andresistor 25 being adapted to have included in parallel therewith by means oi' a switch 3| any one of a plurality of frequencycontrolling crystals Ai-Aio, inclusive. A suitable bias is provided for the tube 20 by means of a cathode resistor 32 by-passed by a condenser 33. The output circuit of the oscillator tube.20 includes a band-pass selector circuit comprising a. transformer 34, 35 tuned by condensers 36, 31, respectively, a damping resistor 38 being coupled across the secondary winding 35'to broaden and flatten its response characteristic so that it is effective to pass any of the predetermined oscillations generated by the oscillator tube 20 with approximately uniform response.

A second crystal-controlled oscillator including a vacuum tube 40 is provided for generating oscillations of a predetermined relatively low frequency and of a wave form rich in harmonic components, for example, a square wave form, this oscillator also being of the tuned grid-tuned plate type. This oscillator comprises a seriesconnected inductance 4| and resistor 42, which is shunted by a frequency-controlling crystal 43, connected between the first signal-input electrode of tube 40 and ground and a parallel-resonant circuit, comprising an inductance 44 andV a condenser 45 coupled between the oscillatoranode element and groundc through a by-pass condenser 46. A cathode-biasing resistor 41 bypassed by a condenser 48 is provided for vacuum tube 40, while the output circuit thereof includes in series an inductance 49 andal by-pass con- As stated above, the circuit of the oscillator 40 is so proportioned that oscillations are generated comprising a fundamental component and a plurality of harmonic components o'f substantial amplitude. This is accomplished by operating the anode of tube 40 at a relatively low voltage so as to obtain anode-circuit limiting of the tube current, in whichcase the generated oscillations are of substantially square wave form. Although such an output signal is rich in harmonics, the intensity of the harmonics may be a discontinuous function of theY order ofthe harmonics and the inductance 49 is provided for differentiating the oscillations. l

The generator 8 also includes means for selecting any one of a predetermined number of the above-mentioned fundamental and harmonic components generated in oscillator tube specically for selecting consecutive ones of the coml ponente. 'This means comprises a tube 52 having Van output circuit including an inductance 53 adapted to be tuned by any one of condensers B1-B1o, inclusive, selected by means of a switch 59. The output signal from oscillator 40 is supplied to the signal-input electrode of tube l2 through a coupling condenser 60 and a grid-leak resistor 6I. The oscillator 40, together with the selector 52, may, therefore, be considered as a crystal-controlled oscillation generator for generating oscillations `oi! any of a plurality of predetermined frequencies.

In order to heterodyne the selected component derived from oscillator 40 by means of tube 52 and its associated selectorl circuits and the oscillations developed by oscillator 20,*there is provided a modulator including tubes 63, 64 having a balanced input circuit including inductances 65 and 66 respectively in series with the cathodes oi' tubes 63 and64. The signal components of oscillator 40, which are selected through the circuits associated with vacuum tube 52, are applied to the modulator by means of an inductance lator 63, 64 is of the unbalanced type and includes a tuned circuit comprising a parallelconnected inductance 'III and condenser' 1|, inductance 1|) being inductively coupled to an inductance 12 connected to the input terminalsl of unit 9, the inductance 12 being tuned by a condenser 13 and damped by a resistor 14. The input circuit of modulator 63, 64 is thus untuned with respect to the signals provided from the low-frequencyv oscillator 40 and is relatively broadly fixed-tuned with respect to the range of signal frequencies provided by oscillator 20. Such a circuit avoids the necessity for switching in the input and output circuits of the modulator comprising tubes 63 and `64. y

In order further to select the modulation signal developed in modulator 63, 64, there is provided a selector system including an amplifier tube 16 having input electrodes connected across the secondary winding of

transformer

10, 12 through a cathode-biasing resistor 11 shunted by a condenser 18, any one of a plurality of selector circuits C1-C1o', inclusive, being adapted to be coupled into the output circuit of tube 'I6 by means of a switch 80. Each of the tuned circuits Ci-Cm, in-v clusive, is individually adapted to pass a band of frequencies comprising the signals generated by modulator 63, 64 when a corresponding one of the condensers Bi-Bm, inclusive, is connected into circuit to tune inductance 53 and the crystals A1A1o, inclusive, are successively switched into circuit to tune inductance 24. The anode of tube 16 is coupled to the input circuit of modulator l0 by a coupling condenser 3|. Suitable operating potentials for the

tubes

20, 40, 52, 63, 64, and 16 are supplied from the sources +Sc and +B in a conventional manner, as indicated.

'Ihe system preferably includes a dial arrangement 82 adapted to be unicontrolled with switch 3| and having thereon digits from zero to nine.

inclusive, to indicate the particular one of the crystals Ai-Aio, inclusive, which is coupled into the circuit of tube by switch 3i. Also, there

dials

82 and 83 are disposed adjacent to one another and, since there are ten selectable frequencies generated by each of the oscillators 2t and et, forming a decade system, the two associated digits thereon indicate numerically the particular channel to which the transmitter is tuned.

In considering the operation of the high-frequency generator 8, 9 of Fig. l, it will be assumed that crystals Ai-Ani inclusive, are adapted to tune the crystal-controlledl oscillator 20 in'equal frequency steps each equal to the desired frequency separation of the resultant carrier signals. `Furthermore, it will be assumed that oscillator dil is adapted to generate oscillations such that, with the cooperation of selective circuits formed by inductance 53 and .condensers Br-Bio, inclusive,

fundamental and harmonic components of such oscillations which are Selected vary in steps which are multiples of the over-all range of oscillator 2li, in this case thesteps. being ten times those of oscillator 2%, that' is, ten times the desired frequency separation of the resultant carrier signals.

Furthermore, it is assumed that the selector circuit lil, li, i2, 'i3 in the output circuit of modulator 53, Gt is effective to pass components corresponding to only the .sum frequencies of the ilrst and second crystal-controlled oscillations.

It is thus seen that tube 2i) operates in a conventional manner to develop sustained sinusoidal oscillations at a frequency determined by the particular one of the crystals Ai-Aio, inclusive, which is coupled into its circuit. Similarly, tube et generates oscillations, the frequency of which is determined by the crystal 43, the feed-back coupling being sumciently great and the anode voltagel being sufllciently low that the oscillations are of substantially square wave form. The simial input to tube 52 comprises the square-wave oscillations generated by tube i0 differentiated by inductance t9 into oscillations of double-impulse wave form which are applied to the signal-input electrode of tube 52 through the coupling condenser 60 and grid-leak resistor 6l so that the positive peaks of m lustrated, the frequency of the oscillations of oscilthe differentiated signal pulses are stabilized at the zero grid-voltage level, while thenegative pulses of the .wave are in the cutoff region of the grid voltage-plate current characteristic of tube 52, The output of tube 52 under these conditions consists of narrow current pulses which include harmonics which progressively decrease in amplitude with the order of the harmonic. The selector circuits in the output circuit of tube 52 have a common inductance 53 so that, when the various condensers Bi-Bw, inclusive, are successively switched thereacross, the L/C ratios of the resulting selector circuits progressively increase with frequency, thus compensating ior the progressive decrease in amplitude of the harmonic components with increase in their order. While the oscillator 2t has been described as a. multicrystal sinusoidal oscillator and the oscillator t@ as a single-crystal multiharmonic oscillator, it will be understood by those skilled inthe art that either oi the oscillators 20 and it may be'of either of these types, depending on the frequency requirements. However, usually vthe frequency relations are such that one ci the oscillators is a relatively high-frequency oscillator for which the multicrystal oscillator is most suitable. Furthermore, it will be understood that the number of harmonic .components which can b'e usefully separated in the output circuit of an oscillator of the type of oscillator 40 is limited bythe limitations of conventional selector circuits. Under the conditions assumed above, it will be seen that, with the switches in the positions illator 26 is determined by crystal Aa and the irequency component of the output of oscillator 40 which is selected is determined by the condenser Bz. Therefore, the carrier signal developed by the modulator 63, 66 has a frequency which is the heterodyne sum of these frequencies, that is, the twelfth channel signal, as indicated by the dials 82, e3 unicontrolled with the selector switches befand 3i, respectively. At the same time, the switch Bil is operated to connect the selector circuit Ca in the output circuit of amplifier l5, this circuit being effective to pass all carrier signals generated by selection of condenser Baby switch 5S, with which switch il'is unicontrolled, and by the selection of any of the crystals Ai-Am, inclusive, associated with oscillator 26. It is, therefore, seen that the transmitter illustrated is adapted to operate on any of adjacent channels while only eleven crystals are required in the circuit; that is, the high-frequency generator of the invention is effective to generate any one of a plurality of signals which are equally and closely spaced relative to the mean frequency of the band including the desiredl output signals.

It is thus apparent that by utilizing the principles of the invention, any desired frequency range can be covered in steps of any desiredfrequency separation by providing a first crystalcontrolled oscillator, such as oscillator 2t, f0r

generating oscillations of predetermined frequencies having frequency spacings equal to those of the signals to be generated and by providing a second frequency-controlled oscillation generator, such as oscillator tu, for generating oscillations comprising a fundamental component and harmonic components. the fundamental frequency thereof beingk equal to the product of the desired frequency spacing of adjacent channels and the number oi' oscillation frequencies developed by therst oscillator.

The principle of the embodiment of the invention illustrated and described in Fig; 1 may be generally defined in terms of certain elementary or basic factors which are usually the known characteristics of any system to be designed and which will aid in such design. If it is assumed that the system is required to cover n adjacent channels having a, frequency separation s and a lowest carrier frequency c. the following rela-A tions apply:

Let m=number or frequencies developed by the first oscillator, for example, oscillator t;

, lI=lowest order harmonic of oscillator dii utilized when oscillator 2e is tuned by a single crystal.

by the selectivity of the selector 1o, 'ima/ts in the output of modulator 63, 6d, that is, the lowest frequency spacing of the sum and difference fre, quency components in the output of modulator 63. 64 that can be satisfactorily separated. If is .fe-HfcfI-gfl Where flmfl) nents selected from the output of the second oscillator are the successive harmonics from H/m to H/m+ 2:5-1)

. The number of harmonic filters required for tube 52=n/m. The relative-tolerance limits for the selector circuits including condensers Bi-Bip, inelusive, equals mA, where A is a constant depending on the power factor of the selector circuits. The value of H/m is approximate and actually the next higher integer will generally be selected as the lowest order harmonic. Furthermore, in some cases, it may be desirable, arbitrarily. to select the lowest order harmonic 'at some higher value,

While applicant does Inot intend' to be limited to any particular circuit values, the arrangement of -Fig. 1 has been found to be of particular utility in providing an oscillation source for a transmitter adapted to operate over the frequency spectrum of -28 megacycles and including one hundred channels each having a separation fn of 80 kilocycles, the lowest carrier frequency fc being 20.04 megacycles. In such an embodiment. ten crystals .were provided for the first oscillator (m=l0) to develop output oscillations In Fig. 2 there is illustrated in schematic form a complete carrier-signal transmitter which includes an embodiment cf the signaly generator of the invention generally similar to that of Fig. 1 and similar circuit elements have identical reference numerals. In order'to generate a carrierfrequency signal to be supplied to the modulator i0 of the transmitter of Fig. 2, there are provided three crystal-controlled

oscillation generators

8l, 82, and 83 and modulators 8l and 85. Only the portions of the oscillation generators necessary to an understanding of the invention are shown in the drawings. Oscillation generator 8|, the circuit of which may be of any conventional type. for instance, of the same type as oscillator 20 of Fig. 1, is provided with frequencycontrolling crystals D1, Da, Da, D4, individually adapted to be connected into the circuit of the oscillator by means of switch 88 in the manner described above with reference to oscillator 20. Oscillation generators82 and 83 may be of the same tiype as the oscillation generator including tubes I0 and 52 of Fig. 1, the oscillation generators being adapted to have their output frequency determined by condensers Ei-Es, and Fi-Fs, respectively, adapted to be connected into the circuit.4 of their respective oscillators by means of switches 81 and 88, respectively. The output circuit of modulator 84 is tuned to select the sum heterodyne signal derivedfrom oscillators 82 and 88 and apply it to the input terminals of modulator 85. The oscillations generated by oscillation generator 8| are also applied to input terminals of modulator 85 and the sum heterodyne components are selected in the output circuit thereof as an input signal for modulator l0. The remaining portion of the system is the same as that of Fig. 1

therefrom of 7.64, 17.72, 17.80, 17.88, 17.96, 18.04.

18.12, 18.20, 18.28, and 18.86 megacycles. Correspondingly, the second oscillator corresponding to oscillator 40 wasprovided with a crystal resonant at a fundamental frequency mf. of 800 kilocycles, while the selector included in the output circuit of tube l2 was provided with ten condensers eectlve to select the 2.4, 3.2, 4.0, 4.8, 5.6, 6.4, 7.2, 8.0, 8.8, and 0.6 megacycle components f of the second oscillator, comprisingthe third (H/m) to twelfth (H/m+1z/m'-1) harmonics of the frequency-determining crystal, In this embodiment of the invention, it was found expedient to utilise crystals in the first or high-frequency oscillator 28 of the low-temperature coemcient A' cut type oscillating in Yshear in theVthird-harmonic mechanical mode. Such crystals are read- `ily obtainable with a temperature coemcient of 2 cycles per megacycle per degree C. in the temperature range of 20 to 55 degrees C. Ihis corresponds to a stability of about 0.01 percent. Also, a crystal of the A cut type, but oscillating-in the fundamental mechanical mode, is preferred for use in the second or low-frequency oscillator Il. The following tube types were utilized in th transmitter referred to: y Tube 20 Type 6K8 Tubes 63, 64--- Type 6J5G` Tube 40 Type 6K8 Tube 52---'.--.----... Type esKrG'r In considering thev operation of the circuit of Fig. 2, it will be seen that the' elements 8i-85, inclusive. perform the same function as

elements

8 and 8 of Fig. 1; that is, they cooperate to produce a carrier-signal input to modulator i0. Also, it will be seen that the carrier signals so developed are such that the transmitter may be operated in one of adjacent channels. In order to effect this type of operation, the crystals Di-Di, inclusive, are so chosen that individually they condition oscillation generator 8l to provide output signals of relatively high frequency which are spaced by the desired frequency spacing of the carrier signals to be developed by the transmitter. Condensers Ei-Es, inclusive, are so chosen that they condition oscillation generator 82 to generate output signals of a relatively lntermediate frequency and having a frequency spacing of one-fifth of the over-all frequency spectrum to be covered by the transmitter, while condensers Fi-Fs, inclusive, are so chosen that the output signals of oscillation generator 83 are of a relatively low frequency and lhave a frequency spacing of one-fifth of the frequency spacing of the signals developed by oscillation generator 82. As used herein the terms relatively high," Arelatively intermediate, and relatively low" are intended to distinguish between the mean frequency of the oscillators to which the terms refer even in case the bands of frequencies covered :by the oscillators may be. in part, coextenslve or overlapping. If the circuit is proportioned as stated above and if the switches 86, 81, and v88 are in the positions shown, a carrier-frequency signal corresponding to the lowest channel in the frequency range to be covered by -the transmitter will be generated and of Fig. 1.

e carrier-frequency signals corresponding to the succeeding four channels will be obtained by operating switch 86 through each of its successive positions. Thereafter; if .switch 88 is operated to its second position, the operation of switch 86 through each ofl its four positions is effective to condition the transmitter to generate the next succeeding four carrier signals required, etc.

It will be understood that any of oscillators 8|,

32, and $3 may be of either of thetypes'shown.

consecutive harmonics thereof, specifically, the

harmonic components from 2-I l, inclusive. Os-

and that each of the oscillators may be adapted to provide any required number of output `signals in accordance with the requirements of any yparticular installation. l

A preferred modled arrangement of they embodiment of Fig. 2 is adapted to cover the frequency range of -28 megacycles in 100 channelsof 80 kilocycles band width. In this arrangement, a single crystal is provided for oscillation generator ai which is effective to provide output oscillations of 17.4 megacycles. Also, in this arrangement, each

lof oscillation generators

82 and 83 is adapted to provide ten dierent output signais, the oscillation generator 82 comprising an SOO-kilocycle crystal-controlled oscillator and the cillation generator 8 3' comprises an 880-kilocycle crystal-controlled oscillator and condensers Fi'-F1s, inclusive, are so proportioned that condensers being adapted to be switched by switched by switch 88 to select the third to the twelfth harmonic thereof.

In this arrangement, therefore, and with the switches in the position shown, the output signal of oscillation generator 8i is 17.4 megacycles, that of oscillation generator 82 is 2.a megacycles, and that of oscillation generator t3 is .24 megacycle. The signal output of oscillation generators t2 and @Si is, therefore, heterodyned in modulator oli to provide an output signal of 2.64 niegacycles, which signal is heterodyned in modulator a5 with the output signal of 17.4 megacycles from oscillation generator 83 to provide an output signal of 20.04 megacycles which is the frequency required for the first channel.` The remaining higher frequency signals may be developed -by operating the switches 8l and 8B' in the sequence described above. If desired, these switches may be unicontrolled with a decade dial mechanism, such as that included in the system In Fig. 3 there is illustrated still another embodiment of the invention.- which is generally .similar to that of Fig. 2 and similar circuit elements have similar reference numerals with the addition of a prime. The circuit of Fig. 3 differs from that of Fig. 2, however, in the number of harmonic frequencies generated by each of the oscillation generators which are utilized and in the manner of combining the diierent signal outputs thereof to provide the desired output signals. The oscillation generator ci has only a single-frequency-determining crystal Di', while oscillation generator d2 includes ten condensens E12-E10', inclusive, for selecting ten consecutive harmonics thereof and oscillation generator 33 has nineteen condensers Fil-F19', inclusive, for

selecting nineteen consecutive harmonics thereof. In this arrangement, however, the output circuit oi modulator B' is adapted to select the difi@ ference heterodyne signa1 from oscillators Si and 82', while the output' circuit of modulator 85' is proportiond to select the sum heterodyne signal from the modulator stl and oscillator 83.

the second to twentieth harmonics thereof are selected as an output signal for oscillation generator 83'. In order to select desired harmonics of the oscillators 82 and 83', there is provided a switch 90 having a series often stationary contacts connected to condensers Elf-E10', inclusive, a series of nineteen movable contactscoupled to condensers F1'-Fie', inclusive, and a contact member 9i being operable to connect pairs of corresponding elements of the oscillation generators 82' and 83' into their respective oscillator circuits. The switch 90 also includes an operating handle orlmob 93 to operate the contact member 9i and a handle or knob 94 for operating the movable contacts connected to vthe condensers Fi'-F19', inclusive. With the switches in the position shown, the transmitter of Fig, 1 is conditioned to operate on the lowest channel of the range and may be conditioned for operating on the succeeding nine channels by operating lever 93 to the left successively to connect corresponding pairs of condensers into the circuits of oscillators 82 and 83', thereby selecting the successive harmonics of both oscillators, "progressively increasing the frequency of the output of modulator 85' in steps of 80 kilocycles. In order to condition the transmitter for operation on the succeeding channel, the switch contact member Si is returned to the position shown and handle 9G is moved one position tothe right, thereby effectively adding to the frequency of the oscillator 8l the difference between the third harmonic of oscillator 83' and the second har- The transmitter may monic of oscillator 82'.l then be conditioned for operation onthe succeeding nine channels by moving handle 93 to the left and may similarly be conditioned to operate on the remaining channels by similar operations of the switch 90. It will be understood- '82', 83 and 82', 83 of Figs. 2 and 3 comprises a crystal-controlled oscillator for, generating osl cillations of a predetermined frequencyy including a fundamental component and a plurality of harmonic components. Furthermore, it is seen that any of the oscillation generators of Figs. 2 and 3, except oscillation generator 8i', is a crys-y tal-controlled oscillation generator for generating oscillations of a plurality of frequencies.

While therev have been described what are at 4 present considered to be the preferred embodi- Assumns, as before, that it is desired to provide ing from the invention,` and it is, therefore, aimed l1 in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A high-frequency signal generator for generating any one of `a plurality of signals which are closely spaced relative to the mean frequency of the band of frequencies including the desired output signals comprising, a first oscillator for generating oscillations of any of a plurality of predetermined relatively high frequencies and including a plurality of frequencydetermining crystals each resonant at one of its oscillation frequencies, a second crystal-controlled oscillator for generating oscillations of a predetermined relatively low frequency and comprising a fundamental component and a plurality 'of harmonic components having a frequency spacing greater than the frequency spacing of said predetermined relatively high frequencies, means for selecting any predetermined one of said high-frequency oscillations and any one of predetermined ones of said components. and means for heterodyning said selected component with said selected oscillations to develop a desired output signal, each of said predetermined harmonic components being so related in frequency to said selected oscillations that the sum and difference heterodyne components can be readily separated.

2. A high-frequency signal generator for generating any desired one of a plurality of predetermined equally-spaced signals comprising, a first oscillator for generating any of a plurality of oscillations of predetermined relatively high frequency, a second crystal-controlled oscillator for generating oscillations of ay predetermined relatively low frequency comprising -a fundamental component and a plurality of harmonic' components having a frequency spacing greater than the frequency spacing of said predetermined relatively high frequencies, means for selecting any predetermined one of said high-frequency oscillationsand any one of predetermined consecutlve ones of said components, and means for heterodyning'said selected component with said selected oscillations to develop a desired output signal, each of said predetermined harmonic components being so related in frequency to said selected oscillations that the sum and difference heterodyne components can be readily separated.

3. A high-frequency signal generator for generating any one of a plurality of predetermined equally-spaced signals comprising, a rst relatively high-frequency crystal-controlled oscillation generator for generating any of a plurality 12 of oscillations of predetermined frequencies having a frequency spacing equal to that of the signals to be generated, a second crystal-controlled oscillation generator for generating oscillations of a relatively' intermediate predetermined frequency and comprising a generator for generating oscillations having a fundamental component and a plurality of harmonic components having frequency spacings equal to the product of the frequency spacing of said first-mentioned generator and the number of said first plurality of oscillations, a third crystal-controlled oscillation generator for generating oscillations of a relatively .low predetermined frequency and comprising a fundamental component and a plurality of harmonic components having frequency spacings equal to the product of said second frequency spacing and the number of said plurality of harmonic components to .be selected, means for adjusting said first oscillation generator to generate a predetermined one of said oscillations. means for selecting from each of said second and third oscillation generators predetermined harmonic com-v ponents, means for heterodyning the harmonic components selected from said second and third oscillation generators to provide modulation components, and means for heterodyning said modulation components and the oscillations produced by said first oscillation generator to provide a de. sired outputy signal.

4. A high-frequency signal generator for generating any one of a plurality of predetermined equally-spaced signals comprising, a Afirst relatively high-frequency crystal-controlled oscillation generator for generating any one of a P111- rality of oscillations of predetermined frequencies having frequency spacings equal to that of thel signals to be generated, a second crystal-controlled oscillation generator for generating oscillationsA of a relatively low predetermined frequency, and comprising a fundamental component and a plurality of harmonic components having frequency spacings equal to the product of the frequency spacing of said first-mentioned generator and the number of said first plurality of oscillations, means for adjusting said first oscillation generator to generate a predetermined one of said oscillations, means for selecting from said second oscillation generator a predetermined one of said harmonic components, and means for heterodyning the harmonic component selected from said second oscillation generator and the oscillations produced by said first oscillation generator to develop a desired output signal.

' DANIEL E. HARNETI'.