US2114036A - Frequency stabilization system - Google Patents

Frequency stabilization system Download PDF

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Publication number
US2114036A
US2114036A US106126A US10612636A US2114036A US 2114036 A US2114036 A US 2114036A US 106126 A US106126 A US 106126A US 10612636 A US10612636 A US 10612636A US 2114036 A US2114036 A US 2114036A
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United States
Prior art keywords
frequency
oscillator
circuit
variations
feedback
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US106126A
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English (en)
Inventor
John W Smith
Gorden N Thayer
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AT&T Corp
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Bell Telephone Laboratories Inc
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Priority to NL54603D priority Critical patent/NL54603C/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US106126A priority patent/US2114036A/en
Priority to GB26621/37A priority patent/GB498186A/en
Application granted granted Critical
Publication of US2114036A publication Critical patent/US2114036A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C3/00—Angle modulation
    • H03C3/02—Details
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C3/00—Angle modulation
    • H03C3/02—Details
    • H03C3/08—Modifications of modulator to linearise modulation, e.g. by feedback, and clearly applicable to more than one type of modulator
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C3/00—Angle modulation
    • H03C3/02—Details
    • H03C3/09—Modifications of modulator for regulating the mean frequency
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C5/00—Amplitude modulation and angle modulation produced simultaneously or at will by the same modulating signal

Definitions

  • the principal object of the invention is to efg fect the stabilization of the carrier frequency -in very high .frequency communication systems.
  • another object is to stabilize the mean frequency of the carrier wave in frequency modulation systems, and a third lobject isto eliminate or reduce unwanted frequency modulations in amplitude modulation systems.
  • a further object is the elimination of distortion producing frequency .variations in frequency modulated systems.
  • modulation of the carrier wave may be-eifected by varying either its ampli tude or its frequency in proportion to the strength m of the modulating signal.
  • Athat tho-carrier frequency bestabilized at a constant preassigned frequency and in the case of frequency modulation it is desirable that the mean frequency of the 2s .carrier be held constant.
  • the carrier wave lgenerator is preferably an oscillator of a type such that the frequency generated vcan be varied readily through a wide range under the w influence of an applied signal voltage.
  • Fixed frequency oscillators such as piezoelectric crystal controlled oscillators are not suited for this purpose and other available types are subject to' slow variations which. at very high frequencies, may amount to avery large number -of cycles. By the'present invention these slow drifts of a frequency modulated oscillator are substantially prevented while at the same time the desired frequency variations in accordance withthe modi-4 40 ulatingsignalare retained.
  • the varying control j current is fed back to thefrequency modulating le. device ci'.7 in eifect. to the moduiatingsignsl in. put circuit.
  • the control current preferably re produces all of the signal variations togetherwith A,
  • the whole of the gg detected signal and the accompanying undesired variations are fed back to exercise the stabilizing control.
  • the feedback or control is 40 not impressed on the signal input circuit, but on .an auxiliary frequency control means through which it exerts a quick acting compensating control of the' frequency.
  • the stabiiizins system of the invention 45 also acts as a detector for frequency modulated waves. it may be operated as a receiver vin conjunction with the transmitter. therebyproviding s two-way transmitting and receiving equipment in vwhich frequency stabilization of the transmitt'er is accomplished with a minimum of ap- Other features of the invention relate to limiting the range of operation of the frequency stabilisation equipment and indicating the operative 66 condition; toV switching arrangements whereby in Fig. y6 constitute a more detailed schematic representation of such a station; and
  • Fig. 5 shows the response curves of filters used in the system.
  • the system shown schematically in Fig. 1 comprises, essentially, a high frequency transmitter arranged for operation either with frequency modulation or with amplitude modulation and provided with feedback circuits for the stabilization of the mean radiated frequency.
  • the system includes switching and circuit arrangements whereby part of the feedback circuit may be utilized for the detection and reception of incdming signals and a guard circuit for limiting the operation of the feedback control.
  • the transmitter portion of the system and its stabilizing circuits will be described rst.
  • the carrier wave generator comprises a triod'e tube' i to the grid and plate of Vwhich are connected Lecher wires 2 and 2 forming an oscillation circuit.
  • the oscillation generator is of the negative grid type, in which case, even at extremely .high frequencies, the frequency of 'the oscillations is determined mainly by the reactances' of the oscillation circuit.
  • Plate current is supplied to the oscillator tube from battery l and a suitable negative bias is applied to the grid f by battery 4.- Alternatively the negative grid bias may be furnished by the fall of potential due to the plate current in choke coils 5 and l' inserted in the iament leads.
  • Condenser O connected across the ends ⁇ of the Lecher wires forms a short circuit for the high frequency currents and high frequency 'chokes 'i4 and 1 serve further ⁇ to isolate the oscillation circuit ⁇ frolnthe current supply circuits.
  • An antenna consisting of Adjustment or control of the carrier frequency is effected by a variable condenser comprising vilxed plates i5 and Il connected respectively to -the plate and grid of the oscillator tube and movable plate Il symmetricallydisposed with respect to the fixed plates.
  • Plate Il is mounted on the moving element of a polarized electromagnetic :ging device I4.' the details oithe condenser its driving means v.being shown more fully in Fig. 2.
  • The-motion of the' plate I1 isrestrained by a spring Il whichmakes the displacement substantially proportional to the ourrent delivered to thedevlce.
  • Microphone I0 is connected through a signal amplifier Il and a two-way switch. l! 'eitherfto the-terminals of device I4 or to a transformer. i3, the secondary of which is included in the oscillator plate circuit.
  • switch i2 When switch i2 is -moved to the right the microphone is connected to the actuating winding of device Il.
  • Amplified speech currents from Vlmicrophone l0 ⁇ will then produce synchronous displacements of condenser plate I1' proportional to the current intensity, thereby changing the natural Iperiod of the oscillator tuned circuit and effecting a variation of the carrier frequency substantially proportional to the signal.
  • the microphone is connected to transformer I3, by operating switch I2 to the left, the amplified speech voltage is superimposed on the steady plate voltage of the oscillator thereby producing amplitude modulation of the carrier wave. 4
  • the feedback circuit includes an antenna consisting of a receiving doublet I8, i9 so placed as to receive waves radiated from antenna 8, 8'.
  • a transmission line 20 couples doublet i9, i9' tov generated oscillations being multiplied to a sultable high value by means of a harmonic generator 24.
  • the intermediate frequency amplifier preferably consists of a large'y number of stages, as shown in greater detail in Fig. 3, toproduce a strong feedback effect.
  • the portion of the feedback path following the intermediate frequency ampliile'rin includes la detector-converter circuit wherein is developed a control voltage corresponding in' magnitude and sign to the variations of the frequency ofthe carrier oscillations from a preassigned fixedv value.
  • filters may be high-pass and low-pass types respectively so proportioned that their attenuation characteristics cross in theranges 'of increasing attenuation adjacent the cut-ot frequencies.
  • it will generally be more convenient to use simple resonant circuits tuned respectively to frequencies above and below the desired reference fre- 'fiers 2l and, the outputl voltages of filters 21 and will vary in amplitude in opposite ,senses as the oscillation frequency varies and will be equal at the frequencyedetermined by the intersection offthefllter characteristics.
  • Rectification 40 The feedback circuit divides into two vpaths at Y ananas l of these voltagesby rectifiers 28 and I!
  • variable low frequency voltages in y resistances 29 and II corresponding to the frequency variations of .the carrier.
  • a differential voltage kis obtained therein which is directly proportional to the frequency vdeviation from the assigned carrier amplifiers 26 and-Il.
  • Volume limitera of known types may also be used. for example, the tubes of amplifiers fl and Il may be operated at a point above plate current saturation so that'the outputs are held substantially constant.
  • the differential control voltage derived from the detector-converter F circuit is applied to a push-pull direct current amplifier, l2, through an equalizer or filter network Il.
  • the output terminals of the direct current amplier are connected to the actuating winding of control device I4, 4the connection being so poledy as to bring about the proper frequency compensating action.
  • the purpose of'equalizer network ll. is to insure that the control currents are maintained in the proper phase relation at all frequencies in the operating range. Usually this networkl may be omitted since the phase variation in the feedback loop is generally negligibly small.
  • a frequency-modulated wave is thus obtained from which frequency that relay Il .is operated and the variations representing signal distortion are eliminated and which is stabilized about a fixed mean frequency.
  • the elimination of the undesired frequency drifts is eected in a manner analogous to the elimination of non-linear distortion in the stabilized feedback amplifiers described in the lar-v modulatiomwhether electrical orv mechanical, and
  • the signal voltage is impressed on the plate of the oscillator vacuum tube through transformer il.
  • the feedback circuit in this case does not reproduce the amplitude' variations of the carrier, because of the amplitude control of amplifiers 28 and 3ft, but does produce control currents corresponding to frequency variations of thecarrier. These will, in general, include variations due to oscillator instability and also vunwanted frequency modulations produced by and corresponding to the modulating signal voltage.'
  • the control currents are fed back to control device i4, as in the case of frequency modulation,- and act thereon to produce a compensatingadjustinent of the oscillator frequency. Since there is no' degenerative feedback to ⁇ tl1e signal input circuit a less powerful signal input maybe used.
  • the whole of the feedback loop be capable of transmitting freely all of the signal'I frequencies, for example the voice' feedback and the several advantageous operating characteristics mentioned above are not obtained.
  • a guard circuit is provided winch interrupts the plate current supply to ampllner Si, 32, when the frequency approaches these limits.
  • Ihe guard circuit branches from the output of intermediate frequency amplifier 25 and includes amplifier Il, band-pass filter 41, detector load resistance B0, direct current ampliner ii and relay Il, the back contact of which controls the plate current supply to tubes 8l and 3 2.
  • the pass-band of filter 41 lies between the resonance frequencies of filters 21, and 34. as indicated by curve u of Fig. 5. When the oscillations lie.
  • the-stabilizing control were permitted to operate before the frequency has reached a value within the operating range of the converter lters, its action would be reversed and the operation would tend to drive the oscillation frequency towards either a zero or an innitely large value. If the filters could be. made to have continuously rising characteristics, this could not happen.y Such filters, however. are difficult and costly to construct for operation at radio fre'- quencies. Wide frequency variations may also occur when the oscillator plate voltage is applied after the cathode hasbeen fully heated. In this case the frequency reaches approximately its normal value very rapidly.
  • the guard circuit also serves to provide auto- I matic volume control for the ampliers of the feedback path.
  • a resistance 48 shunted by acondenser of low capacity is inserted in series with rectifier Il and the output of filter 41.
  • the rectified current develops a negative voltage in this resistor which is transmitted by conductor 52 to the several amplifiers 25, 28, 33 and demodulator 2
  • the capacity in shunt toresistance 49 should be large enough to act as a by-pass for the carrier frequency currents, but not large enough to reduce the signal frequency variations of the rectified voltage.
  • TheY rapidity of the control may be adjusted by,suitable resistance-capacity nlters which may be included l within the amplifiers.V For demodulator 2
  • is connected'y by switches 42 and Il to the output of'thedetector-converter, the amplier output being coupled to a telephone receiver M.
  • the transmitting oscillator may be disabled by interrupting itsV plate Acurrent supply by means of transmit-re- Iceive switch j".
  • switch l2 is arranged to connect amplifier Il iii-.parallel with the input of guard circuit amplifier 5
  • a two-way communication channel can be established. Switching from the transmitting condition to the receiving condition is effected by the operation of the single switch 45. Changing from frequencymodulation to amplitude modulation is effected ation of switches I2, l2, and". i t
  • the carrier oscillator was designed to operate at a frequency of 300 megacycles per second.
  • the heterodyne frequency furnished by harmonic generator 24 was ,295 megacycles, the intermediate-frequency of the feedbackcurrents being ve million cycles per second.
  • Filters 21 and Il ' were designed to have -their characteristics cross at this frequency and to have their resonances separated by about 400,000 cycles.
  • the degreeof stability obtained was thus substantially that of the crystal oscillator 22, since any variations of the control point of filters 21 and 34 could affect only the relatively low intermediate frequency and could affect that by the operonly to a very small extent. ,l
  • Fig. 2 shows the circuits of the carrier wave oscillator and constructional features of the tuning control device I4.
  • Fig. 3 shows the circuits of the heterodyne generator comprising oscillator 22 and harmonic producer 2l and of demodulator 2l and intermediate frequency amplifier 2l.
  • Fig. 4 shows the remaining portion of the feedback circuit and the guard circuit.
  • the tuning control ldevice I4 - is of the electromagnetic moving coil type.
  • the movable condenser plate i1 is attached rigidly to the supporting frame l5 of the moving coil, its plane coinciding with the coil axis.
  • Fixed plates Il and Il are disposed symmetrically with respect to plate Il and parallel thereto with about 50 per cent .overlap for 'the normal position of the coil. VMotion of the coil along 'its axis thus varies thecapacity4 between plates l5 and I0 substantially proportionally to the displacement of thecoil.
  • Springs I8 act as the coil restraint and also serve to hold it centrally in the magnet air-gap.
  • Resonance of the moving system may be prevented by applying mechanical damping thereto, for example, by covering the surfaces of springs 'Il 'with dissipative material, such as felt, or with a thin coating of lead.
  • the damping should not be great enough to prevent yresponse of the device at any frequency in the signal range.
  • electrical damping may -be provided by a suitable ,resistance 54 connected acrossy the moving coil terminals.
  • the power for all of the vacuum tubes and 'for magnet winding I8 is supplied by full-wave rectiner s1, sa. Fig. s, and an associated smoathingm- :sol
  • v 'Harmonic generator M comprises three frequency multiplying-.stages each using screen-grid pentode tubes with indirectly heated cathodes.
  • the output circuitof oscillator 22 is so arranged that a harmonic of the generated frequency is supplied to the input of the harmonic generator, thereby securing additional frequency multiplication.
  • Demodulator 2i also uses ⁇ a screen-grid pentode tube with indirectly heated cathode, the posing said varying strength currents upon the Iincoming oscillations being impressed on the conoscillationsv from said signal source to countertrol grid and the heterodyne oscillations on the actthe frequency modulation of the carrier wave. suppressor grid between the screen and the anode. 2.
  • Intermediate frequency amplifier 25 comprises a carrier wave generator, means for modulating 5 live pentode stages coupled together and to the the frequency of said generator in accordance demodulator by double tuned circuit broad-band with signal currents, a source of signal currents, a filters. signal input circuit coupling said source and said The output of amplifier 25 is fed into buffer modulating means, a feedback path coupling the amplifiers 26 and 33 in the plate circuits of which output lof said generator and said signal input 10 are connected the converter filters 21 and 34.
  • said, feedbackvpath including means for These filters consist of simple anti-resonant cirreproducing from the carrier wave currents havcuits tuned to different frequencies and proporing strength variations corresponding to the tioned to provide response characteristics inter-i frequency modulations thereof, and means forsecting in the manner shown by curves 52 and impressing said varying strength currentsv upon 15 53.
  • the rectiflers shown, at 28 and 35 inl Fig. 1 said input circuit, the transmission characterisare constituted by the space paths between auxiltic of said lfeedback path and its connection to lary' anodes 62 and 63 and the cathodes of tubes said input circuit being such that the fed back 40 and 4I, which are of the diode-triode type. currents are in substantially opposite phase re- Theswitches 42 and I3 of Fig. 1 are combined lation to the signal currents from said source and 20 in a two-way double throw switch 61. The' outare approximately equal thereto in magnitude.
  • Rectifier I8 is a carrier wave oscillator comprising a tuned circonstituted by the space paths between auxiliary cuit which determines the frequency of the gen- 30 anodes 65 and 66 of amplifier tube 5i which is a erated waves, a variable tuning element in said double diode-triode. Electrodes 66 and 66' are tuned clrcuit,'means determining a substantialconnected together through a condenser., the outly fixed frequency, means for automatically adput of filter 41 being'connected to anode 66.
  • a 60 bias is supplied to the tubes of amplier 26 and 6.
  • through lead 12 and filter 13, the a carrier wave oscillator comprising a tuned cirtime constant of which is large enough to percuit which determines the frequency of the genmit only slow variations to be transmitted.
  • lli erated waves a' variable tuning element in said 66 'steady initial grid bias for all of these tubes is tuned circuit.
  • means determining e substantially 55 provided by the fall of potentialin resistance 16 fixed frequency means foil varying said tuning which is connected in series with resistance 15 element 'in accordance with signals, means for between the negative terminal of the power supdetecting departures of the oscillator from the ply rectifier and the cathodes.
  • the indicator xed frequency. scid detecting means beine re- 39, meter or lamp, is included inan auxiliary cirsponsive to slow departures of frequency and to so cuit connected to the front contact of .relay 60 departures at signal rates. and means for autoliei plate curmatlcally adjusting said tuning element in rerather than directly in the amp rent circuit as m Fig, 1, sponse to said departures of both kinds.
  • a carrier wave oscillator comprising y a carrier' wave generator, a, source of signal oscuit which determines the frequency of the genr impressing oscillations from erated waves, a variable reactance element in said cillations, means fo y said source upon said generator whereby the fretuned circuiti means determining ai Substantially ting means for apprisncy of the generated carrier wave is modu- Xed frequency.
  • afrequency stabilized oscillator system comprising an oscillator generator, frequency correcting means therefor, means determining a substantially fixed frequency, and means for automatically adjusting said correcting means in l response to departures of the generated frequency from said fixed frequency, an auxiliary transmission path coupled to the output of said generator and responsive to impressed oscillations in a limited range of frequencies centered about said fixed frequency, and current responsive means in the output of said path for disabling said corrective means when the frequency of the generated oscillations lies outside said limited range.

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US106126A 1936-10-17 1936-10-17 Frequency stabilization system Expired - Lifetime US2114036A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
NL54603D NL54603C (zh) 1936-10-17
US106126A US2114036A (en) 1936-10-17 1936-10-17 Frequency stabilization system
GB26621/37A GB498186A (en) 1936-10-17 1937-10-01 Frequency stabilization systems

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Cited By (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2425614A (en) * 1943-09-16 1947-08-12 Rca Corp Controlled carrier amplitude communication system
US2426193A (en) * 1943-06-17 1947-08-26 Rca Corp Radio transmitter automatic volume control
US2435010A (en) * 1944-11-27 1948-01-27 Gen Railway Signal Co Continuously checked communication system
US2438801A (en) * 1942-02-27 1948-03-30 Rca Corp Monitoring and measuring apparatus for frequency modulated signals
US2447492A (en) * 1944-04-15 1948-08-24 Rca Corp Timing modulation
US2462856A (en) * 1942-05-19 1949-03-01 Sperry Corp Transmitter and/or receiver circuits
US2475779A (en) * 1941-05-14 1949-07-12 Rca Corp Wave length modulator and control means
US2477039A (en) * 1944-01-05 1949-07-26 Hartford Nat Bank & Trust Co Transceiver circuit arrangement
US2482914A (en) * 1945-06-27 1949-09-27 Rca Corp Signaling
US2503243A (en) * 1945-12-11 1950-04-11 Cohen Albert Electrodynamic relay
US2510461A (en) * 1946-04-09 1950-06-06 Raytheon Mfg Co Multistation microwave communication system
US2518931A (en) * 1950-08-15 Wave-guide
US2543248A (en) * 1942-11-12 1951-02-27 Hartford Nat Bank & Trust Co Device for the medical treatment of persons with high-frequency energy
US2555391A (en) * 1946-03-04 1951-06-05 Arthur A Glass Radio oscillator control
US2582668A (en) * 1948-03-10 1952-01-15 Hartford Nat Bank & Trust Co Device for synchronizing the frequency of an oscillator to a control oscillation
US2604585A (en) * 1948-04-10 1952-07-22 Louis W Parker Frequency stabilized transmitter
US2609463A (en) * 1948-10-26 1952-09-02 Fauthal A Hassan Electric actuating device
US2610270A (en) * 1949-09-03 1952-09-09 Curtiss R Schafer Chopper
US2617015A (en) * 1945-01-23 1952-11-04 Everard M Williams Panoramic system
DE741721C (de) * 1940-10-22 1953-05-04 Siemens & Halske A G Berlin Un Einrichtung zur Demodulation frequenzmodulierter Schwingungen
US2656458A (en) * 1951-10-01 1953-10-20 Joseph M Johnston Compressional wave telemetering device
US2684438A (en) * 1950-08-15 1954-07-20 Murray G Crosby Relay feedback system
US2730712A (en) * 1949-10-20 1956-01-10 Marconi Wireless Telegraph Co Frequency modulated radar system
US2741679A (en) * 1952-11-12 1956-04-10 Joseph F Keithley Circuit interrupter
US2750565A (en) * 1952-09-13 1956-06-12 Raytheon Mfg Co Altimeter modulators
US2752499A (en) * 1953-11-02 1956-06-26 Rca Corp Ultrahigh frequency sweep generator
US2756337A (en) * 1952-03-12 1956-07-24 Hazeltine Research Inc Frequency-control system
US2762922A (en) * 1953-02-19 1956-09-11 Pye Ltd Automatic frequency control
US2839684A (en) * 1954-05-06 1958-06-17 Cgs Lab Inc Automatic frequency control
US3087124A (en) * 1958-05-29 1963-04-23 Raytheon Co Feedback system for reed modulated magnetrons
US3096768A (en) * 1960-05-27 1963-07-09 Tron Inc Fa Electrotherapy system

Cited By (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2518931A (en) * 1950-08-15 Wave-guide
DE741721C (de) * 1940-10-22 1953-05-04 Siemens & Halske A G Berlin Un Einrichtung zur Demodulation frequenzmodulierter Schwingungen
US2475779A (en) * 1941-05-14 1949-07-12 Rca Corp Wave length modulator and control means
US2438801A (en) * 1942-02-27 1948-03-30 Rca Corp Monitoring and measuring apparatus for frequency modulated signals
US2462856A (en) * 1942-05-19 1949-03-01 Sperry Corp Transmitter and/or receiver circuits
US2543248A (en) * 1942-11-12 1951-02-27 Hartford Nat Bank & Trust Co Device for the medical treatment of persons with high-frequency energy
US2426193A (en) * 1943-06-17 1947-08-26 Rca Corp Radio transmitter automatic volume control
US2425614A (en) * 1943-09-16 1947-08-12 Rca Corp Controlled carrier amplitude communication system
US2477039A (en) * 1944-01-05 1949-07-26 Hartford Nat Bank & Trust Co Transceiver circuit arrangement
US2447492A (en) * 1944-04-15 1948-08-24 Rca Corp Timing modulation
US2435010A (en) * 1944-11-27 1948-01-27 Gen Railway Signal Co Continuously checked communication system
US2617015A (en) * 1945-01-23 1952-11-04 Everard M Williams Panoramic system
US2482914A (en) * 1945-06-27 1949-09-27 Rca Corp Signaling
US2503243A (en) * 1945-12-11 1950-04-11 Cohen Albert Electrodynamic relay
US2555391A (en) * 1946-03-04 1951-06-05 Arthur A Glass Radio oscillator control
US2510461A (en) * 1946-04-09 1950-06-06 Raytheon Mfg Co Multistation microwave communication system
US2582668A (en) * 1948-03-10 1952-01-15 Hartford Nat Bank & Trust Co Device for synchronizing the frequency of an oscillator to a control oscillation
US2604585A (en) * 1948-04-10 1952-07-22 Louis W Parker Frequency stabilized transmitter
US2609463A (en) * 1948-10-26 1952-09-02 Fauthal A Hassan Electric actuating device
US2610270A (en) * 1949-09-03 1952-09-09 Curtiss R Schafer Chopper
US2730712A (en) * 1949-10-20 1956-01-10 Marconi Wireless Telegraph Co Frequency modulated radar system
US2684438A (en) * 1950-08-15 1954-07-20 Murray G Crosby Relay feedback system
US2656458A (en) * 1951-10-01 1953-10-20 Joseph M Johnston Compressional wave telemetering device
US2756337A (en) * 1952-03-12 1956-07-24 Hazeltine Research Inc Frequency-control system
US2750565A (en) * 1952-09-13 1956-06-12 Raytheon Mfg Co Altimeter modulators
US2741679A (en) * 1952-11-12 1956-04-10 Joseph F Keithley Circuit interrupter
US2762922A (en) * 1953-02-19 1956-09-11 Pye Ltd Automatic frequency control
US2752499A (en) * 1953-11-02 1956-06-26 Rca Corp Ultrahigh frequency sweep generator
US2839684A (en) * 1954-05-06 1958-06-17 Cgs Lab Inc Automatic frequency control
US3087124A (en) * 1958-05-29 1963-04-23 Raytheon Co Feedback system for reed modulated magnetrons
US3096768A (en) * 1960-05-27 1963-07-09 Tron Inc Fa Electrotherapy system

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Publication number Publication date
NL54603C (zh)
GB498186A (en) 1939-01-04

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