US2256083A - Automatic frequency control system for braking-field oscillators - Google Patents

Description

Sept. 1,6, 1941- R.v w. GEORGE 2,256,083

AUTOMATIC FREQUENCY CONTROL SYSTEM FOR BRAKING-FIELD OSCILLATORS Filed April l5, 1959 3 Sheets-Sheet l AAA.. .Alim -v v n... vvvv vv L`,Wolff/M4 T 7 g 116 Wg/00 TUBE PHASE ADJusrER COU/L ING BAR/am us5/v osC/M701?- DETECTOR INVENTOR.

I ,QA Hu/.GEORGE BY ATTORNEY.

Sept. l

R; W. GEORGE AUTOMATIC FREQUENCY CONTROL SYSTEM FOR BRAKENG-FIELD OSClI-.ILATORS DIFFERENT/.4L DETECTOR DE TECTOR v PHASE AoJusrER Filed April l5, 1959 3 Sheets-Sheet 2 NA m E N |H||,

4H ES? f 35 ....E V "Il" qc, 5% v l||||||||||| LL Si Q ATTORNEY.

Sept. 16, 1941. R, w. GEORGE 2,256,083

AUTOMATIC FREQUENCY CONTROL SYSTEM FOR BRAKING-FIELD OSClLLTORS Filed April l5, 1939 3 SheehS-Shet 5 BAR/(HA l/SEN asc/mme IZQ 3 acAMpL/F/ER 4 Z L /NTEpMEo/ATE FREQUENCY Dgff/OZAL l AMPL/F/ER g U5 ULTRA H/GH /NTEnMEU/ATE FREQUENCY FREQUENCY D/SQETRE/TTOL AUD/0 asc/Mrap AMPM/VER OUTPUT E19, 4 1 u l/ TRANS ULTRA f//GU FREQ.

asc/wrok DIFFERENT/AL oETEcToR A HI +Ep A ac AMpL/F/ER .5

. ELECT/MAGNET v o/FFEEENT/AL l NEAR U50. TUBE UETECTUR -l- L Y g INVENTOR.

- ATTORNEY.

UNITED; stares are `mrroiulrrio FREQUENCY ooNTnoL sys- TEM Foa Baarnse-rieti) osciLLA'roits Ralph W. George, Riverhead, N; Y., assigner to Radio Corporation of America, a corporation of Delaware 'y @ENCE A Application April 15, 1939, Serial No. 268,014

1 Claim. (Cl. Z50-Bil) The present invention concerns an ultra high bodying the principles of rthe present invention; frequency oscillator system, such as a braking Fig. 5a shows schematically an electromechanield or Barkhausen-Kurz type, whose frequency cal circuit arrangement whichv can be used for can be automatically controlled by varying the some of thecircuits of Fig. 4; andrFigp5b shows voltages of the oscillator or by the tuning of the a modified circuit which can be used for electrooscillator circuit. According to the invention, a magnetic control of the oscillator. The same diiferential detector operates at a suitable inreferencennumerals appearing throughout the termediate frequency and sets up a plus or minus figures of the drawings designate the same or voltage which is amplified suitably and made to equivalent parts.

control the grid or plate voltage, or the tuning lo Therterm Barkhausen is herein used broadly of the ultra high frequency oscillator in a manas being descriptive of any typeof electron disner to compensate for a change in the intercharge device using a grid which is maintained mediate frequency. Where it is desired to conata high positive .potential anda plate or anode trol a receiver, it is proposed to make the ultra at. a much lower potential with Yrespect to the high frequency oscillator follow the transmitter l5 cathode, whereby oscillations of electrons about frequency. Where it is desired to control a the gridmay or may not bemade to'occur, detransmitting ultra. high frequency oscillator, it pending upon the adjustment of the circuit conis proposed to combine a relatively weakultra stants and voltages.

high frequency of known stable frequency such Referring to Fig.. 1 ofthedrawings, there is as a harmonic of a local stable oscillator, or 2O shown an ultra short radio wave fr'equelly-IlflOll-l crystal controlled oscillator with the transmitulation receiver having a differential detector and ter frequency to produce a suitable intermediate a direct current amplier stage which gives a voltfrequency which through the diiferential detecage output carrying plus or minus with theintertor produces suitable controlling means which mediate frequency. More specifically, the circuit are applied to the ultra high frequency transmit- 0f Fig- 1 ShOWS 2, receiving antenna Of the die ting oscillator. pole type which is coupled by means of a trans- It is known that ultra high frequency oscillators mission line to the Lecher wire system 2 conare especially subject to slight and uncontrollable nected in turn to the grid 3 and anode 4 0f a variations in their circuit conditions, etc., which Barkhausen oscillator-detector 5,. The Lecher cause frequency variations, and it is also known 30 Wle SyStBm SShllllted by a COIldGIlSer 6 and an to use crystals as frequency stabilizing elements. additional tunable condenser l, the latter being Direct crystal control of the frequency of the osutilized for tuning the resonant period of the oscillator through many stages of frequency multicillator detector circuit. Condenser 9 serves to plication, however, is complicated and expensive, ground the plate orranode 4 of the Brarkhausen and therefore not well suited for reception purdetector 5 for radio frequency potential. Batposes and most transmission purposes. teries B4 and B5 provide suitable pOlaIiZiIlg D0- The present invention is a means of obtaintentials to the plate ll and grid 3, respeCtiVQly, ing automatic frequency control with a moderate of the vacuum tube 5. The grid 3 is maintained amount of apparatus, which has an advantage at a high positive potential by a battery B5; and that it will keep a receiver in tune with a transthe P12308 4 al? an extremely 10W POStVe 0I' nega'- mitter over a long period of time and without tive potential with respect to the cathode Il).

attention. v The intermediate frequency which is produced Another advantage 0f the invention is that the by combiningthe signal and oscillator frequenfrequency control achieved requires only a very cies in detector 5 is taken from the grid side of small amount of power from the stable oscil- 3 the Lecher wire system2`and is coupled through later, when applied@ frequency @enum of e, transformer Il to intermediate lfrequency amplitransmitter oscillator. iierv l2, the output of which vis passed to the A further and important advantage of the ingrid of the coupling tube I3. A condenser lill) is vention is that constant frequency or tuning is used to tune the primary coil of transformer Il maintained regardless of any ordinary voltage 50 to the desired intermediate frequency. The outchanges to any of the component parts. put of the coupling tube I3 is passed to a phase A description of the invention follows in conadjustment circuit I4, the latter 0f which may junction with drawings, wherein Figs. l to 4, be enclosed in a shield. Although not shown in inclusive, illustrate four different' embodiments the drawings, it should be understood that all of an ultra high frequency oscillator system em- 53 radio frequency circuits are properly shielded in conventional manner. The phase adjuster I4 may take Vthe form' of an artificial line. The signal energy derived from the phase adjuster'is resonated in parallel tuned circuit I5, in turn coupled'to parallel tuned circuit I6, the latter being connected between the grids of balanced modulator detectors I1 and I 8. The detectors I'I andA [8f comprise a differential detector circuit whose purpose will be given later. Ther same signal energy applied to the grid of the coupling anode current of one tube I'I or I8 of the 'Y Vdifferential detector will increase While that of theother tube I8 or I 'I Will decrease, with tube I3 is also applied through connection I9 to Vthe .grid of the phase shiftrlr transformer cou:

pling tube 20, from whose anode cophasal signal potentials are fed to the cathodes of the differential detectors II and I8,- asshown. It will thus be appreciated that a diierential signal is applied to the grids of the detectors I I and I8 while a cophasal signalis appliedto thecathodes of these detector tubes. This portion of the frequency modulation receiver comprising the stages I 2 to. 20 is Yvery similar to and` adequately de,.- .sripeu inf my. United, ,States .Patent No. 2.03.5345, erantedJMareh 3,1; 1.936. particularly Fig. 2, te

' `which reference is hereinmadefor amore d etailed description thereof. Coupled across the anodes ofv the differential detector' I'I and I8 there isprovided a direct current amplifier stage 27| whichapplies apcontrol voltage tothe plate 4 of the BarkhausenV oscillator detector tube 5.over

- connection 22. which includes inl series therewith bat-terr B3. and part of battery B4. The battery 3.3.?. Supplies plate power to the direct current amplifier 2l 'while the battery B is used Yto reduce the plate voltagev of the direct current amplifier 2l to a, value more suitable for use in circuit with the plate ofv the Barkhausen, oscillator 5. The battery- B I serves to apply. positive polarizing potentials to fthe` mid point ofthe potentiometer resistor RI, R2, the resistors o f whichare serially connected. Withrespect to each other and in shunt to the 'output of the differential detector I'I, I 8.

` 'l suitable audio frequency output circuit, 34 is shownl coupled Athrough an audio output transformer 23, tofthe anodes of the differential detector I1, I8.V Connections suitable for receiving amplitude orffrequency modulation areobtained byemploying a reversing switch 2,4 yin one section of the primary winding of the audio frequency transformer, as shown, Element 25 comprises a suitable head phone Vor other signal utilization means. A suitable low, pass (audio frequency) Viilterpas.. shown, serves tofpass only loW frequency variations of the. direct current control voltage tothe rst heterodyne oscillator.

In thev operation of Fig. l, the receiver functionssubstantially. identically with the frequency modulationkreceiver described in my above'men- Y tioned United States Patent No.-2,035,7,45 .withV the following differences. 'The anode current of` the two vacuumtubes I ,1. and i8, Of thediieren` ,3.

tial Cli'aeotor is passed through the potentiometer branches Rl and. R2, respectively, before being connected with the detector plate supply Bl. The voltages across. the resistances RI andv R2r are egual and-opposite as long asthe signal intermediate frequeney'is et vthe mid band 0f the detector, ,asV isalsothe case When-no signal is present.' Normally, the resultant voltage Ec acrossthe grid land cathode of the direct current amplifier 2ll iszero, and. thevoltageacross the anode impedance ,R3-isconstant,v andthe plate voltage of the Barlgliausen-oscillator is constant.

the result that the Voltage Ec impressed on the direct current amplifier 2| Will be changed, in turn producing a change in the voltage across R3 which is impressed on the plate 4 of the Barkhausen oscillator 5. The polarity of the poten tial Ec is so chosen that the resulting voltage'on the plate of the Barkhausen oscillator 5 will change the frequency of the oscillator in a direction to bring the intermediate frequency back to the mid'band of the differential detector.

Fig. 2 shows a modification of Fig. 1 in that the automatic frequency controlling voltage from the differential detector is applied both tothe grid 3 and to the plate 4 of the Barkhausen oscillatordetector 5, although it will be appreciated that if desired this controlling voltage may be applied only to the grid of the Barkhausen detector. In Fig. 2, there is also provided a dilerential direct current amnlier Comprising vacuum tubes 25, 2.1 for producing differential Changes in the plete and grid voltages of theBarkhausen oscillator' 5, The circuitl arrangement Vhere used for supplying the differential voltage Ec to the differential v'clip-v rect current amplifier eliminates the Vnecessity for the lowf pass filter of Fig. 1. 1nv operation, onehalf the voltage across `resistor R3 appears as positiveand negative (or negative and positive) increments of voltage in series with the grid and plate voltage, supplies for the'braking field oscillation detector 5. -Sinee the plate voltcase tif the potential of only one' ofthe electrode elements of the Barkhausen oscillator is varied for frequency'control. IV have foundthat the frequency of the Barkhausen oscillator 5 can be maintained practically constant with varying power supply, if the plate and grid thereof are arranged to take suitable proportional amounts of the power voltage change and both in the same direction, Whether this change is in a positive ora negative direction. ,Y

Itis contemplated, inzaccordance with the invention, that anyone or all of the factors controlling the frequency of an ultra high frequency oscillator may be used inthe automatic control of the frequency including any other electrodes and the emission control of thecathode; For inling voltage is applied to a, special grid 28 placed between the cathode I0 and grid 3 of the tube 5 Y detector or its equivalent.

However, when. the intermediate frequencyV changes,V due to f an undesired change in the ieeilener of 'the'eilsheeeee eseilleier, the

and drawing no current.

It is 21150 contemplated in accordance with the invention, that electro-mechanical means may be used to control the tuning and/or voltages of an ultra high frequency oscillator from a differential shown conventionally, in box form, means designated A for converting the outputV of the diiferential detector to suitable electrical values which are utilized by other means B in applying. frequency control to either a transmitting oscillator y or to the receiving ultra high frequency oscillating detector. The means B may apply electrical control through a mechanically driven voltage control system, or it may apply tuning lcontrol i by means of a mechanical, system, or it may appily magnetic control in either a mechanical, or

In Fig. 4, there is electrical manner. Fig. a. shows an arrangement for vachieving the results set forth in Fig. 4. In Fig. 5a, the differential direct current amplifier is replaced by a sensitive differential relay 55, the relay tubes 5l are normally at plate current cut-off by means of bias battery 52, A change of frequency causes relay 50 to short circuit the bias on one of the tubes 5I which causes plate current to flow in that tube, thus operating the electromechanical device 54 as follows. The rotating shaft 56 is driven continuously by motor 55 through the flexible coupling 51. Normally, the shaft rotates without touching either side of the groove in the wheel 58, in which case the frequency controlling condenser 59 is not moved. When plate current flows in one of the relay tubes 5|, the armature 58 is pulled up or down accordingly, thus engaging one side of the groove in 58 and causing the condenser 59 to be rotated in the proper direction to correct the frequency change.

It is further contemplated that the automatic control feature of the invention for use with a Barkhausen or other type ultra high frequency oscillator may be applied to the oscillator by the method of varying a suitable magnetic field placed in the region of the elements of the tube; such magnetic eld can be varied in amplitude and/or in its relative position by the means B in Fig. 4. Thus, mechanical control of a magnetic eld may be had in Fig. 5a, for instance, by attaching a magnet to the shaft of 58 in place of condenser 58 so that the position of the eld, or its strength, is changed by rotation of the shaft. If magnetic control is really desired (which might be the case in magnetron type oscillators), it might be preferable to use direct current amplifier stages fed by the differential detector, in order to control the current in an electromagnet suitably placed near the oscillator tube. Such an arrangement in simple form is shown in Fig. 5b, the operation of which will be evident from an inspection of the drawings.

If desired, the principles of the invention may be applied to an ultra high frequency transmitter, wherein the Barkhausen oscillating detector of Figs. 1 and 2 is replaced by a suitable oscillating detector of known stable frequency which is designed to have its frequency controlled, or by a Barkhausen oscillator of improved frequency stability; or it may be an ordinary rectifying detector in which the transmitter frequency and a known stable frequency such as the harmonic of a crystal controlled oscillator may be combined to produce the intermediate frequency. Also, the control voltages or currents of the differential detector would be utilized to control the frequency of the transmitting oscillator which might be of the Barkhausen type which is controlled in the embodiments described, or any known oscillator subject to frequency control.

What is claimed is:

In an ultra short wave frequency-modulation receiver, a multi-electrode Barkhausen oscillator coupled to a receiving antenna for beating with the received signal to produce an intermediate frequency, an intermediate frequency amplifier, a detector coupled to the output of said intermediate frequency amplifier, a direct current amplifier and a low pass audio frequency filter coupled to the output of said detector, and a cir-- cuit from said direct current amplifier to an electrode of said oscillator for maintaining the frequency thereof at a steady value differing from that of the incoming wave by a predetermined amount, whereby only low frequency variations of the direct current voltage are passed to said oscillator.

RALPH W. GEORGE.

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