US2334189A

US2334189A - Relay system and associated circuits therefor

Info

Publication number: US2334189A
Application number: US338862A
Authority: US
Inventors: Hallan E Goldstine
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1940-06-05
Filing date: 1940-06-05
Publication date: 1943-11-16
Anticipated expiration: 1960-11-16
Also published as: GB547510A

Description

Nov. 16, 1943.

H. E. GOLDSTINE RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June 5, 1940 6 Sheets-Sheet l (Ittorneg Nov. 16, 1943. H. E. GOLDSTINE RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June 5, 1940 6 Sheets-Sheet 2 ll 55% \WGERMQ EEGQS 010114115 aazdsifiii i attorneg m I Mm wstibws wwhs Nov. 16, 1943.

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Cmomeg Nov- 16, 1943- H. E. GOLDSTINE I RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June 5, 1940 6 Sheets-Sheet 4 gmw *2 Q "2 '1 it n v &'

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RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June 5, 1940 6 Sheets-Sheet 5 7'0 0/) SYSTEM 70 flurammc FBEOI/EIC) comma 00/7 3nnentor flaZknE Gamma Nov. 16, 1943.

H. E. GOLDSTINE RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June 5, 1940 e Sheets-Sheet e 3nvze n tor (Ittorneg flazzmzt G5 w)? Patented Nov. 16, 1943 UNITED ,1 PATENT 7 lassifies RELAY SYSTEM AND Assoonirsn amounts THEREFOR I HallanE Goltistine;Tort Jeifer'son, N}: assign z [or to Radio Co'ffiii'ration of Am rica',a corpora- .7 non etnelaware Aiimieatitn June 5. 1940, Serial Noi eaasea f This invention relates generally to laying system. More'partielilally, the inven= tion relates to such features as 1) the frequency modulator circuit, (2) the repeater'station for receiving a frequency modulated signal on one carrier'i'reqlienoy and relaying or retransmitting this frequency modulator signal. on another -car'-'- rier frequency, and (3) the antitcainatic frequency control circuit employing cavity or concentric line resonators.

The following is adetailed diseussion 0f the invention accompanied by drawings, wherein Fig. 1 shows very generally a eofnplete radioi relay system in which the present; invention may beemployed; Fig. 2 shows .the'ireiiuency modulatorsystem oi the inventioneiiiployed in a repeater station of the system; of f Fig. 1 --fOr converting video signals into frequencymodulated high irequeneey signals; Figs. 3a-and Blitakeh together show apparatus employed atone of the repeater Patent "2}239,724,' granted April 29; 1941.

aeeemmodate the full band snectrum of high definition television. This; antenna consists of two separate and independent radiator systems, I and 2; the former fersound andthe latterfor vision transmission, both radiators being sum ported on a eofnmongcelumh located an appre= ciable distance aboveg-rounmhsually on the top of-awtall building 1 Thewantenha system of the transmitter Stati'on Ais of thez'type' installed at the top of the Empire State Building in New York; New York; aridis describedquite adequately in the opend ing "apDIiEQtiOr-I 0f N118 E; Lsihdenblamiserial N0.

2081573-fl1d May-..18, 1938;"1'1OW United States The antennas on statlonsB, G and D are of the uni directional type, there :helng useda pairofah or relay stations of the system of Fig. '1' for.

ignals of the orderoi si x' inet rs andless; and may he" used for the'transmission of television signals; although it will be underst od that it may also beus'd totrahsmit' telegraph si nals or any etherty'pe of radio signal. The system includes a transmitting station 'A', lurality or intermediate re eater or relaystations .3 amp, and a receiving station D, suitably spacedaflart along the line of transmission. litepeater station's B and C are designed terepeat the signals from station A to station D. The-arrows indicate the directions of the sighals'between the =respe'c tive stations. Although onlytwo repeater stations have been shown, it shouldiloe understood:

that this nuinheris illustrative of any number of repeater stations whiehmay be located atq frequent intervals along the line "of transmis-i sion, for relaying and amplifying signals.

The antenna system indicated at the transmitting station A of Fig.-;1- is shown to beer the voiimidirectional--tyfie, havifig constant character istics over a frequency bane sufiieieiitiv wiaeto tennas at' fihe% intermediate istatibnsB and C, one forireeeivirig thewsignalsifrom :the nearest transmittingiantenha'anti the other for repeat= ving andifieradiating tlie signals to the neiit. re-

pater-orirelaystation along "the line of trans= mission; Sineewthe transmission range 'of the ultra short waves at which this system is designed i rte junction deiienels' substantially upon the airsl-ifie, or visual distance; a factor propore.

tio'nal to the lieight above the. earths surface, it is proposedttoiloeate all stations at points having as g'featrlieightwas'possible; such asflon moun tair'isj tall huildings, radio .iinasts,, tc. The re= ,eeivingi antennafifi at repeaterwstation B consists of :afiair of" dipole. arrays placed. one behind theJUthrli ands'hitably phasd relative to' each otherifieeiprovidingaa unidirectional efieot. This 1 antenna isdsigned to receive the signals transmittedfriiinstation-YA. Referene is hereby made to Garter, United States Patent No. 2,-183,784;"granted Deeei'nbertw; 193.9,ior a shit ibledeshrihtibmbf antenna 1 The reradiating i or transmitting antenna! or station B is of the rhetal parahohe'typewhich has at its focus a dipole or at plurality or dipole antennas arranged in mesa-me straight line; These dipole antennas niaya be oi the folded type which has. been found to he more-leffeetive than thesingleidifidleand is oreierably of the general-form described in the eoperitiing implication" of Philips; Carter Serial Ila-"155,385, filed J uly 24, 1937', he? United states Patent 2383,9145; gr83nted-=May 2l5,' 19 12. At "re:- peater station C thererar'e shown a r'eceivingam tenna '5, "andia reradiating Ur-transmit-ti-ng an- 1 teiina; Gybothof the parabolic type employing folded dipole sahtenhas "as'described in :ECjIlflBC-Y tion with antennafl of station B. 'Antenr'iais'ii anti 6: are,of course effective in difierent direc tions, the receiving antenna being positioned (.to receive the signals from station B while the tower. The antenna 1 at receiving-station D comprises a parabolic -reflector having at its focus one or more dipoles, preferably folded up dipoles, l0

' this antenna being, of course, directed to receive the signals from antenna 6 of the adjacent repeater station. The antennas of stations. A'to D, inclusive, have been described as being of particular types, mainly by way of example, since it is apparent that other types of antennas can be used to achieve the desired results.

In the operation of the system'of Fig. 1, television signals emanating from broadcasting station A are amplitude modulated and radiated at afrequency of 45.25 megacycles and received on an antenna 3 at stationB, from which the signals pass to a television receiver thereat-to providea video component, theband width of which may besubstantially of the order of 4 megacycles The video output of this television receiver at station Bisrused to control a trans mitter with multi stages of frequency tripling,

described more in detail later in connection with Fig. 2. The output of station B radiated from antenna 4"is'a frequencymodulated wave of the order of 500 megacycles; (in one particular embodiment tried out. in practice the output was about474 megacycles'witha band frequency deviation of plusand minus about 3.5 megacycles).

\ At repeater station Cthe receiving antennai receives the 500. megacycle afrequency. modulated signal. radiated by. antenna 4 of. station B, and

x converts the signal bymeansof apparatus described later in more detail ;in connection-with 40 Figs. 3a and 3b to a 100zmegacycle signal for more efficient amplification. This 100.megacycle, signal is then amplified and converted to an output-frequency. modulated signal having a'mean frequency. different than'the incoming frequency, 4;")

' let us sayafrequency of'.512.6 megacycleawhich is thentransmitted byantennafi towardthe next. adjacent station, in this case receiver. sta-, tion D. At theifinal receiving station;.,-D in the radio link,v therfrequency modulated signal 59 of 512.5 megaoyclesis received on antenna 7. and converted to a lower frequency 'signalwhich is then amplifiedand amplitude'limited before it is passedlon to a detector which transforms the frequency modulated signals to amplitude modu- 5.5 latedzsignals. From the foregoing, itv will be seen that the amplitude modulated signal transmitted by the T broadcasting transmitter at station A at one frequency is received at station B and converted to a 'frequency modulatedsignal 60 of a different frequency which is then radiated todstation C wherethis frequencymodulated signal ischanged to a frequency modulated signal having-another and different carrier frequency,- after whichthe last converted signal is .trans- 35 mitted to station .13 where it may be converted to-an amplitude 'modulated signal forlocal use or for use in affecting another broadcasting station to send out. the television signals over one or more additional stations.

' Fig. 2 illustrates the frequency modulated cir-" cuit .employed at station B for producing a desired frequency modulated. signal from the :am-

'plitude modulated waves received'at this station. The'system of'Fig. 2 .comprises a master; 75,

oscillator 8, a frequency modulator circuit 9, a

first tripler stage II] for tripling the frequency impressed thereon, an amplifier stage II for amplifying the output of the first tripler stage, and a second tripler stage [2 for tripling the frequency in the output of amplifier ll,'alsoa final amplifier stage l3 of the inductive output electron discharge'device type, and an automatic frequency control circuit I4 for stabilizing the frequency of the master oscillator 8. Although stages 9, l0, II and I2 are each shown as comprisinga pair of electron discharge devices arranged in push-pull, it should be understood that if desired the two vacuum tube electrode structures of each of these stages may be included withina single evacuated envelope. As an illustration, the push-pull electrode structures of stages 9 and I0 may each be constituted bya single electron discharge device tube of the RCA 832 type, while the amplifier stage II may be I constituted by a single electron discharge deviceof the RCA 829 type. The second tripler stage l2 may be constructed in accordance with the teaching described in the copending ap-, plication of Orville E. Dow; (Serial No. 302,655,

filed November 3, 1939, now United States Pat.-

ent 2,253,849, granted Aug. 26, 1941, while the amplifier stage I3 may be of the type described in the copending application of Fred H. Kroger, Serial No. 296,045, filed September 22, 1939. In the operation of the circuit of Fig. 2,'the video component of .the signal received at stationB is applied in parallel to the two control grids of the. electrode structures of the frequencyv modulator-9, which functions to modulate the output of the master oscillator 8.. The master oscillatonas an example, may. generate oscillations of a frequency of the order of, 52.67 megacycles. The. output from the master oscillator is passed onto the frequencymodulator stage 9 and the frequency modulated waves then impressed upon the jfiISt tripler stage III, which provides an out- 7 put of,'let us'say, .158'megacycles, this last outputbeing amplifiedin stage II and then passed on to the second tripler stage I2 from which there is. obtained, let us say, an output of 4'74 megacycles with a band frequency deviationof approximately plus and minus four megacycles,

which .last output is passed on to the amplifier stage l3 from which energy isderived for radiation by the antenna 4. It should be noted that the frequency modulator is capacity coupled to.

the master oscillator 8 by means of condensers C1 and C2, although it should be understoodthat, if desired, inductive coupling may be employed by the'useof suitable transformers between the master oscillator and the frequency modulator.

The condenser C3 in the frequency modulatorv stage 9 is of very small value compared to the to .the

modulation but fairly large compared radio frequency. v

The amplifier stage-J3 consists of an electron discharge device circuit comprising a vacuum tube structure, generally of the, so-called inductive output type consisting of an evacuated glass envelope. E containing'within it anfindirectly heated cathode K, a filament or'heater F, a gridv G, ringlike accelerator electrodes M,- M, a collector electrode R, and a suppressors. The heater 1 may be supplied with energy from a suitable alternating current source ihrough choke coils (not' shown) Connected tothe grid Gis a connection extending to-the outputof the tripler stage I2.

The collector electrodeR forgathering the elec- 2 trons traversing the length of the glass envelope supply 2B.

E is shown to be cup-shaped in formalthough', if desired, it may be hemispherical, conical or of other'suitab-le shape." Centrally located within the interior of collector R'there is'provided a rod-like suppressor electrode S for gathering secondary electrons which may emanate from',R. The suppressor S may take any suitable formaccording to the design of "the'collector R. Accelerator electrodes M, M are narrow 'in-width and are maintained 'at a suitable positive potential relative to the cathode. Surrounding the-exterior of the glass envelope E and located intermediate the two accelerator electrodes M, M there is pro vided a tank circuit [5 (hour-glasstype) in the form of a surface of revolution gwhose central surface is perpendicular tothe electron beam emanating from-cathode K. This tank circuit is symmetrically arranged around the glass envelope E and is provided with a gapa, b. Theconfiguration of this tank circuit l5, as-shown in the drawings, is the cross section of a surface of revolution through the axis of revolution in the plane of the drawings and approximates two equal sectors'with their vertices toward the glass envelope E. The dimension of the tank circuit I5, as measured from the center of the glass envelope to the arc of the sector, is approximately one-quarterof the length of the communication wave corresponding to the resonant frequency, provided that the gap at, h is not supplied with capacitor discs to change the frequency to a value less than the natural frequency of the resonator. This tank circuit is a high Q, low loss circuit and is preferably made of a high electrically conducting material such as copper. For focusing the electron beam there are provided a plurality of magnetic lenses (not shown) in series relation and surrounding the glass envelope, the magneticfield being provided by a strap of iron I6 which is placed adjacent the sides of one .of the sectors of the tank [5 andthen completed through an iron core H, in turn 'surrounded by an electromagnetic field .coiforsol'enoid l8 excited byv a directzcurrentsource. of A suitable output coupling coil 2| derives energy from the tank circuitand supplies this energy to the dipole antenna 22 ofithe antcnna system 4. Themanner in which the amplifier circuit l3 functions isnow well understood and is described quite adequately in. the Kroger copending application Serial No. 296,045, supra, to which reference is herein made.

In order to stabilize the frequency of the mas-'- ter oscillator 8, there is provided an automatic frequency control .(AFC) circuit I I which iscoupied between the master oscillatorB and the out put of the second tripler stage 12. AFC circuit it comprises a pair of

rectifientubes

23 and 24 supplied with radio frequency energy from the tuned

circuits

25 and 26, .the latter in turn being coupled to the tripler stage l2 by means oftconnection 21. The tuned circuits 25 and have intersecting resonance curvesat the mean or assigned carried frequency of the output of the sec;

ond tripler, stage [2, with maxima at frequencies lying either side ofthe, output'frequency of the tripler l2, these, tuned circuits applying the potential fluctuations to the anodes of the two

detector tubes

23 and 24 so that output current balanced amplifier circuit comprising vacuum tubes 28 and 29in whose anodeicircuits is connected a polar relay 3ll, the latter in turn controlling the directlon of rotation of the reversible motor 3| whose shaft 32'is shown in dotted lines connected tothe condenser 33for controllingthe frequency of (the master oscillator 8. It'should benoted that the outputs of

tubes

28 and 29 are in opposition to each other and it will thus be obvious that with equal current. flow through both tubes28 and 29 the polar relay 30 will have its armature in mid position, without causing the motor to rotate oneway or the other. Any fre quency change in the output of the tripler I2, produced let us say by the change in the frequency of the master oscillator 8, will cause one of the two

resonant circuits

25, 26 to become more strongly energized than the other, as a consequence of which there will be a greater fiow of current through one of the

tubes

28 or 29, depending upon which cf the tubes23 and: 24 is more strongly excited with departure of frequency from the assigned carrier frequency. The net response in the polar relay 30 will-beproportional to the difference between the assigned carrier wave in the output of the tripler stage 12 and the wave impressed by the tripler l2 upon the tuned circuits 25 and 2B. A departure from the desired mid band frequency will thus unbalance the direct current voltages in ,the outputs of

tubes

28 and 29, and will cause thepolar relay 3!) to affect the motor 3| to rotate in one direction or the other, depending upon whether the frequency is higher or lower than the desired mid band frequency in the output of the tripler stage. The rotation of the motor 3| will be in such direction as to cause *the condenser 33 tochange its value such that the master oscillator 8 returnsto .a frequency where the signal in the output of the secondtripler I2 is again at mid band assigned frequency. l V

- Figs. 3a and 3b considered together, illustrate the apparatus at the repeater station C of Fig. 1, and includes a receiving antenna 5, a receiver 34 for converting the received incoming signal which is of the orderof 500 megacycles to an intermediate frequency of megacycles, a frequency converter inductive output electron discharge device 35, an amplifier 36' also of the inductive output electron discharge device type, a local oscillator circuit consisting very generally of a master oscillator 31, a first frequency tripler stage 38, an amplifier stage 39, a second frequency tripler stage 40, and an amplifierof 'the inductive output electron discharge .device type 4!. There is' also provided an automatic frequency control (AFC) circuit 42 for stabilizing the frequency of the master oscillator 31; The

receiver 34, which is shown. conventionally in box form, includes an ultra high frequency converter unit for converting the incoming signal waves of the order of 500 megacycles to anintter mediate frequency of about 100 megacycles, and also intermediate frequency amplifierapparatus for this 100 megacycle band. The ultra high frequency converter unit of the receiver 34 is shown in Fig. 4, which will be. described later. The automatic frequency control circuit 42 is shown in more detail in Fig. 5, which isalso to be described in greater detail later.

In the'operation of Figs. 3a and 3b, the in coming signals received on antenna 5 are converted to an intermediate frequency of about 100 megacycles by the receiver of Fig. 4 and passed on to the output circuit 43 which is designed-to pass a wide band of frequencies on both sides of the mid band intermediate. frequency. Output circuit 43 is shown coupled through a concentric line connectingfcircuit 44 to the grid of the inductive output vacuum tubeiconverter 35 to whose cathode circuit there is inductively coupled the amplified output of th local oscillator. Converter tube 35 is generally of the type described above in connection with the amplifier I3 of Fig. 2, and a more detailed description thereof is to be found in the copencling Kroger application, supra. The cathode circuitfor the converter tube 35 includes a coaxial line 45, the inner conductor of which is coupled to one leg of the heater while the outer conductor is coupled to the other leg of the heater. By means movable along the jlength of the coaxial line 41 to the mid frequency of the band pass.

of the arrangement shown, the cathode circuit 3 comprises, in effect, a parallel tuned circuit tuned to the 412 megacycle frequency and towhich is coupled the loop extending-to the output of the inductive output vacuum tube 4| of the local oscillator circuit. Since the amplifier 4| is designed to amplify oscillations of the order of 412.5 megacycles, .in the manner described in more detail hereinafter, the converter functions to provide in its output circuit a mid band frequency of the order of 512.5 megacycles; which is then passed on throu h a coaxial line affair 41 to an inductive output type of amplifier 36 Where the signal having a mid band frequency of 512.5 megacycles is amplified and then passed on to the antenna system 6 for radiation to the next adjacent station.

It should be notedthat energy is derived from the output of the converter circuit by inductive coupling tothe coaxial line 4'! over a metallic strip 48 which extends within the tank circuit of the converter tube 35 but is insulated therefrom. The outer conductor of the coaxial line line 41 is grounded, insulated from th tank circuit of converter 35, and has its ends adjacent this tank circuit provided with flange-like metallic strips -49- which extendon opposite sides of the aperture in the tank circuit. 'It should be noted thatthe tank circuit is here maintained at a positive potential relative to ground and that one or more accelerator. electrodes of the electron discharge deviceis coupled 'to the tank circuit through a resistor. This arrangement is merelyfor simplicity of design, since it will-be obvious that if desired the ring-like accelerator electrodes can be provided with a positive potential while the tank circuit is left free or grounded.

In view ofthe fact that the outer conductor of the coaxial line 41 is grounded, and the tank: circuit maintained at a positive potential, it is necessary to isolate the inner and outer conductors of the coaxial line 41 from' the tankcircuit and this is done in themanner shown in the drawing by means of the .fiange 48 and 49." The aux+ iliary pot or coaxial line 50 is, in effect, a tunable inductance arrangement which; tunes the output circuit for the converter and is provided with a slidableconnection 5| movable. along the inner and outer conductorsof the coaxial line 50 for adjusting the inductance of the circuit.-. .In effect, that portion of the tank circuit of: the converter which is labeled 52 constitutes'a loop made up of a metallic flange 53 and connected at one end to the arc of the tank. The tank-circuit comprises the primary of a transformer, whose secondary circuit consists of the loop 52,. the flange 48, the coaxial line 41 and the coaxial line tuning inductance 5U. The coaxial line 5|] then servesto tune the secondary since it .is

ductor of. the line '41. The coarse tuning-of the v output circuit of the converter is first effected by moving the position of the coaxial line inductance 50 suchthatthe secondary circuitis tuned The variable condenser 54 serves as a micrometer adjustment to tune the secondary. The area of theloop 52,- of course, must be adjusted to first obtain the desiredband pass and then for uniform response in the band pass the output circuit of the converter is adjusted by means of the slider 5| while maintaining constant the position of the line50. One advantage of the particular output arrangement just described is that the feed line to the next adjacent stage is mainmained fixed at all times and need not be moved. In this connection, attention isinvited to copending application Serial No. 346,106, filed July 18, 1940,.jointly by myself and Orville E. Dow, for a description of a similar coupling circuit.

The amplifier 36 is energized from the coaxial line 41. over the loop 55 which is inductively coupled to the loop 56 comprising suitable connections. between the grid and the cathode of this amplifier stage. Here again it will be noted that the tank of the amplifier 36 is shown main! tained at a positive potential while the output circuitfor the amplifier 36 is substantially similar to the output, circuit for the converter 35, and possesses thesame relative advantages. The grid of the amplifier 35 as well as the grid of the converter tube 35 are maintained at suitable negative values relative to the cathode.

Stages

31, 38, 39 and14|l of the local oscillator circuit are similar in arrangement to stages 8, III, II and |2, respectively, of Fig. 2, and are designated in the same manner. The master oscillator 31 is designed to generate oscillations of the order of 45.83 megacycles, these oscillations in turn being-tripled in frequency by the stage 38 to 137.5 megacycles. then amplified in stage 39 and the frequency again tripled by stage 40 to 412.5 megacycles, this last frequency being impressed upon the grid of the inductive output amplifier 4| and the amplified oscillations derived therefrom by loop 51 applied .over line. 58. and coupling loop 46 to the tuned cathode circuit of the converter tube 35, wherethe oscillations from the local oscillator are. beat with the intermediate frequency of megacycles to provide a sum frequency, the latter being passed on from the converter to the amplifier 36 in the manner described hereinabove.

Amplifier 4| is-alsoof the type previously de-, I

scribed above in connectionwith the'amplifier l3 of Fig. 2, and is described in greater detailin the ,copending Kroger application, supra.

From the foregoing, it will'be seen that an'incoming-frequency modulated signal of one carrier frequency is received by the repeater station of Figs. 3a and3band changed at this station to a frequency modulated signal of another carrier frequency. The incoming received frequency is first changed from the order of 500 megacycles to l00r-megacycles for most efficient amplification and thenthe frequency of 100 megacycle component' increased to a different frequency, for example 512.5 megacycles, which is thenradiated.

.The ultra high frequency converter unit employed in the receiver 34 of Fig. 3a for changing the incoming frequency of the order of 500 mega- The output of stage 38 is figure illustratesia system very tgenerally'of the type described in copending application 8erial No. 222,104, filed July 30, 1938, by KG. McLean, now United States-Patent 2,236,004., granted March 25, 19,41, Vand, if desired, may comprise thev identical converter unit arrangement shown in this copending applicatiomi Referring to'Fig.:4 in more detail, there is shown, conventionally, a": detector III) to whose grid is fed the incoming signal energy arriving from the antenna and to whose cathode is supplied oscillatory energy:- irom a local high frequency oscillator I22. Both the detector IIII andthe oscillator [22? have, re spectively associated therewith, concentric line. resonator circuits I III, I02, each having an outer conductor andan inner conductor. The inner conductor of resonator lfll carries a multi-fingered contact section Hi4 which provides contact to movable piston [05 on which is mounted the tuning capacitor plate I05. The concentric line I 02 has for its: inner conductor a pair of tubular conductors H6 and I placed end to.v end and coaxially arranged with respect to the outer conductor. The tubular conductors H4 and U8 have their adjacent ends spaced. apart andprovided with capacity plates I23 which are adiust-- able with respect to one another for tuning purposes. The tubular conductor H4 is also provided with a multi-fingered contact section as shown, and a movable piston. on whichis mounted one of the capacitor plates 103. The: output I09 of the detector 0 receives the'beat irequency (100 megacycles) of the incoming signal wave and the-local oscillator frequency and extends to an intermediate frequency amplifier circuit, not shown. The intermediate frequency coil I08 is tuned by a copper slug. which is adiustable in position inside the coil iorm. An inspection of the detector unit H0 will show that there is included in each-leg of the filament or heater thereof a filter :unit comprising choke coils I26 and low pass ifilter condensers t2t.v The filament and the anode circuit of oscillator I22 are also similarly provided with filter elements I25 and I 21, generally of the same type shown in connection with the detector unit. The filter elements of the detector unit I I0 and the oscillator unit I22 are divided into shielded compartments and the vacuum tubes per so are also shielded both from the shielded elements and the filter units and from the associated concentric line tuned circuits. The cathode of the detector H0 is connected to the oscillator concentric line through a bias resistor and condenser combina* tion I I3 and H2. The. oscillator I 22,- it shouldbe observed, comprises a vacuum tube whose anode is grounded "to the shield or outer conductor-of the concentric. line through a'by-pass condenser I2 I and-whose gridelectrcde is coupled through a coupling condenser II! to the plate. Hi3 ofz the lit)? the usual pair; of; rectifier or diode tubes coupled to'ofi tuned circuits whose resonant characteristics intersect at the assigned mid band intermediate frequencya When metal vane II-Iv is rotated in response to an unbalance in the discriminator circu-it caused by the departure of frequencyfrom the desired frequency, such that the vane is parallel with the. axis of the inner conductors I16 and H4, it-will be seenthat con-,

siderable flux aboutthe tube I'M-is interrupted, and the inductance of, H4 is reduced, thus raising the oscillator frequemzy. One the'other hand, whengvane H1 is. rotated 90 from this position relatively little flux is interrupted and the frequency lowered Afriction clutch is preferably used between the motor 134 and the vane [[1, .so that the vane may be set at the centerzof its tuning range by a. suitable panel control knob, thelatter also serving to indicate the position or the vane. I

Fig. 5 illustrates the preferred form of automatic frequency control circuit designated by box. 42in Fig, 3b, and comprises a pair of Vacuum tube detectors-V I and 1,51' associated respectively with concentric line resonator circuits 152 and [53. Resonatorcircuits [52. and IE5 have intersecting resonance, curves with maxima at irequencies lying either side of the assigned operating frequency of 51125 megacycles in the outputof the amplifier 3 6 of Fig. 3a. Energy from. the output of the amplifier 36 of Fig. 3a. is fed through transmission. line TL which is capacitiveIy coupled to bothconcentric line resonators. I52 and I53, andtthe rectified outputs on the, cathodes of the rectifier'tubes [50 and tilt are applied in push-pull to the balanced vacuum tube amplifiers [54' and [5.5. Theanodes of both amplifier tubes are connected through leads I756 to the opposite terminals of. the windingof sensiti've polar'relay [51. Tubes l54 and I55 areprovi'd'ed with screen grids supplied with a, positive potential through .a voltage regulator tube 158, and with suppressor grids which are connected to their cathodes, as shown. A reversibletmotor inner conductor N6 of the associated concentric line resonator 102, the latter tunc'tioning as a frequency controlling element; A resistor H8 connects the grid of theoscill'atortoground, I

In order to. compensate rordriitmg either of the oscillator I22 of Fig. 4 or the"v signal freiquency received over the antennaxi, there. ispm'e vided an. automatic tuning device comprising: a. reversible telechron motor I34 which drives. a metal vane H'I located below the inner, conductor Ilfiof the; concentric line I02. Controitvoltage for the automatic frequency control motor-13.41 is obtained from a discriminator circuit in. the:

I59 controlled by polar relay I51 functions to vary the position of the condenser in the master oscillator circuit. over a flexible shaft [60. In view of the sensitivc nature of polar relay [51 there are provided two ruggedauxiliary motor relays LEI" and I62 between the motor- 159 and the polar relay. I51 in orderto protect this polar relay. The circuitvfor operating the motor either in one direction or the other will be obvious from a mere inspectionjof the contact arrangement shown in the drawings, it

being understood, of course, that the polar relay I51 will moveits armature one way or the other depending'upon whether amplifier tube l54or;

I draws more current than the other. Normally, when thereis no drift from the assigned mid band frequency, the outputs of both amplifiers l5land I55 will be the same and balanced; as a consequence-of which the polar relay I51 will be in the position shown in the drawing with the armature midway between its opposed contacts. Whenever a drift in the. frequency occurs, the-rectifiers I50 and [5| will draw difierent currents and influence their respective amplifier tubes I55: andv I54, respectively, to operate the polar'relay I51 such that the motor I59 will rotate itsshaft 1-60 to vary the tuning of master oscillator in a manner torestore the frequency to the desired value.

output of the ultra high frequency converter unit. Thisoiscri-minatorcircuit may' comprise at the termination thereof nearest said resonator circuits for matching the impedance of said feeder, and means for tuning out the capacity across said resistor.

5. In a radio system, means for producing energy which is frequency modulated including an oscillator, an automatic frequency control cir-,- cuit for said oscillator comprising two concentric line resonator circuits having intersecting resonance curves with maxima lying either side of the mean operating frequency, a coaxial line feeder having its inner conductor capacitively coupled to the inner conductors of said two resonator circuits in electrically parallel relation for supplying said two resonator circuits with said frequency modulated energy, means for connecting the outer conductors of concentric line resonator circuits and said coaxial line together and to ground, a resistor connected between ground and the termination of said feeder nearest said resonator circuits, and a variable inductance element in parallel to said resistor for turning out the capacity across said resistor.-

6. A system in accordance with claim 5, characterized in this that said variable inductance element is a coaxial line, the inner conductor of which is connected at one end to that ter minal of the resistor which is connected to said feeder, the other end of said last inner conductor being directly connected to the outer conductor.

7. In combination, an oscillator having a frequency controlling element, a frequency stabilizing circuit comprising two concentric line resonators having intersecting resonance curves with maxima lying either side of the mean operating frequency, means for supplying frequency modulated energy of said mean operating 'frequency to said two resonators in cophasal relation, a rectifier connected to each resonator for obtaining a direct current component therefrom, a first relay, a balanced amplifier circuit coupled to said rectifiers and responsive to an unbalance in the outputs of saidrectifiers to operate said relay, a pair of contacts on said relay, second and third relays connected to said contacts and alternatively operable in response to the closures of said contacts, a reversible motor connected to said second and third relays and responsive tothe operation thereof for varying said frequency controlling element in a direction to lessen said unbalance.

8. A frequency stabilizing system comprising two resonator circuits having intersecting resonance curves with maxima lying either side of the mean operating frequency, a-

feeder for supplying said two resonator circuits cophasally with said frequency modulated ener y, rectifiers for said two resonator circuits, the

outputs of said rectifiers being coupled to a circuit responsive to the difference voltage, a resistor-connected to said feeder at the termina means for turning out the capacity across said resistor.

1 9. A frequency stabilizing system comprising two resonator circuits having intersecting resonance curves with maxima lying either side of the mean operating frequency, a feeder for supplying said two resonator circuits cophasally with said frequency modulated energy, rectifiers for said two resonator circuits, the outputs of said rectifiers being coupled to a circuit responsive to the difference voltage, a resistor connected to said feeder at the termination thereof nearest said resonator circuits for matching the impedance of said feeder, and a variable inductance element in parallel to said resistor for tuning out the capacity thereacross.

10. A frequency stabilizing system comprising two resonator circuits having intersecting resonance curves with maxima lying either side of the mean operating frequency, a feeder for supplying said two resonator circuits cophasally with said frequency modulated energy, rectifiers for said two resonator circuits, the outputs of said rectifiers being coupled to a circuit responsive to the difference voltage, and a resistor connected to said feeder at the termination thereof nearest said resonator circuits for matching the impedance of said feeder.

11. In combination, an oscillator having a frequency controlling element, a frequency stabilizing circuit comprising a pair of resonators having intersecting resonance curves with maxima lying either side of the mean operating frequency, means for supplying frequency modulated energy of said mean operating frequency to said two resonators in cophasal relation, a

rectifier connected to each resonator for obtaining a, direct current component therefrom, a

first relay, a balanced amplifier circuit coupled to said rectifiers and responsive to an unbalance in the outputs of said rectifiers to operate said relay, a pair of contacts on said relay, second and third relays connected to said contacts and alternatively operable in response to the closures of said contacts, a reversible motor connected to said second and third relays and responsive to the operation thereof for varying said frequency controlling element in a direction to lessen said unbalance.

HALLAN E. GOLDSTINE.