US2392328A - Directional radio receiver - Google Patents

Description

Jan. 8, 1946. w. P. LEAR 2,392,328

l DIRECTIONAL RADIO RECEIVER Filed Aug. 24, 1943 2 Sheets-Sheet l William 5? ear N LA l?? in H for:

INVENTOR ELM/45M ,Zn/v ATTORNEY.

Ja'n. 8, 1946. w. P. LEAR 2,392,328

DIRECTIONAL RADIO RECEIVER Filed Aug. 24, 1943 2 Sheets-Sheet 2 INVENTOR. Ul'blarn l? aan BY ./Jv ATTORNEY.

.-Qamopos. P.,

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NN, GN..

Patented Jan. 8, 1946 DIRECTIONAL RADIO RECEIVER William P. Lear, North Hollywood, Calif., assignor, by mesne assignments, to Lear, Incorporated, Grand Rapids, Mich., a corporation of Dlinois Continuation of application Serial No. 291,807, August 25, 1939. This application August 24, 1943, Serial N 499.754

(Cl. Z50-11) 14 Claims.

This invention relates to receiver arrangements for radio guidance systems for mobile craft, particularly aircraft. The present application is a continuation of my copendng application Serial No. 291,807 led August 25, 1939, and assigned to the same assignee as the present case.

The receiver arrangement of the present case is designed to operate in conjunction with a pair of non-directional radio signal transmitters arranged in spaced relation along an approach path such as an airport runway. The receiver arrangement continuously indicates to the pilot his exact relative lateral position with respect to the airport in general, and his exact position with respect to the approach path to the runway. As described in my said copending application, with the system of my invention, the pilot may approach the runway directly on the shortest route and without any trial flight since he clearly knows his orientation with respect to the airport and runway course. The two indicator needles of the receiver are in line with the center-zero index when the pilot is on-course with the runway. As he passes over the outer transmitter, the out" indicator needle reverses by 180. This serves as a marker indication to appraise him of his exact distance from the edge of the runway. As the pilot continues on-course to the runway, the second or in needle will reverse by 180 when he passes over the inner transmitter station. No separate marker beacons are thus necessary. The pilot is then ready to glide down to a landing using any suitable vertical guidance means.

Drifting from the predetermined approach course is accurately detected through the dual indicator readings, and is readily compensated for the pilot. No reliance on directional gyroscopes or other flight instruments is necessary. The results are foolproof and independent of adverse weather conditions. There are no successive receiver tuning changes or other distracting duties required of the pilot with the system of my invention. After the initial tuning operation, the dual indicator arrangement is continually effective in guiding the pilot in the manner set forth.

In a preferred form of my invention I employ two transmitter stations having the same carrier frequency. The radiation by the stations is successively switched on and off at predetermined intervals. The two stations are differentiated with either separate audio frequency tone modulations, or with one station being tone modulated and the other umnodulated. A dual automatic directional indicator system lis used aboard the mobile craft, In one form the receiver system has twoseparate rotatable directional antennae, one corresponding to each of the two eld transmitters. An automatic radio control unit is used to individually orient the two directional antennae to their null signal positions with respect to the radio transmitters".

The directional antennae are operative over a 360 range. A separate automatic control radio unit may be used for each of the rotatable loop antennae. In a preferred embodiment, I use a single automatic radio control unit connected successively to each of the two rotatable directional antennae in correspondence with the intervals of radiation of the transmitters as controlled by the audio tone modulations thereof. A composite indicator is used, having two needles, one coupled to each of the rotatable antennae. The two needles point out the actual direction towards each of the field transmitters, and appraise the pilot of his exact lateral position with respect to the airport and the approach path to the runway as will be described in more detail hereinafter.

The present invention is applicable for guiding a marine vessel into its slip, such as during fog conditions. In this case, the two radio transmitters are placed on land in line with the direction which the vessel is to enter the slip. The pilot employs the same approach equipment described in connection with the aircraft guidance and is accurately guided into the slip despite river current or zero visibility conditions. Anti-collision devices can be used for safety reasons when there is sole reliance on the radio guidance in docking the vessel.

It is therefore among the objects of the present invention to provide a radio receiver arrangement for indicating to the pilot his exact relative position with respect to two spaced transmitter stations; to provide such a system including two directional antenna, means for orienting the antenna with respect to received radio signals, a directional control unit, a composite indicator having needles operatively associated with each antenna, and means selectively operable in response to the received radio signals for intermittently connecting each antenna and its orienting means to the directional control unit; to provide a dual radio directional guidance system for giving substantially continuous bearing indications on each of a pair of spaced radio transmitters; and to' provide a novel radio instrument approach system employing a plurality of rotatable directional antenna automatically controlled from a unitary directional control receiver.

These and further objects of my present inthrofugh connection leads |36.

vention Will become apparent from the following description and accompanying drawings.

In the drawings:

Fig. 1 is a diagrammatic arrangement of a cornplete receiver system incorporating the principle of the present invention.

Fig. 2 illustrates one form of the dualY indicator mechanism, being partly in section.

Fig. 3 is a schematic electrical diagram of a preferred circuit arrangement for the automatic directional receiver equipment corresponding to |22' connect the Winding 0f loop antenna |20' torelay armatures |24 -and |25.

Relay armatures |25 and |21 are employed for selectively connetcing the control motorfdriv'e arrangement for the loop antennae tothe receiver. Relay` solenoid is arranged to actuate relay leads 23" for connection to the front contacts of armatures |324 to |21 when energized by currentsfrom the automatic directional receiver system connected thereto through leads |29. The position of loop antenna systemZ is controlled by reversible motor |3Il connected to loopy shaft I2| through electromagnetic clutch |32 and gearing |33, |34. Motor |3|is connected inipara'llel with magnetic clutch V|32 and in turn to thev back contacts of relayarmaturesil26,` |21 by leads |35.

The motor control system of rotatable loop antenna i20" comprises motor |3|" connected toA shaft |2| through electromagnetic clutch Y|32" andg'ears |33', |734. Motor 13|' and clutch |32" are connected across front contacts of relay armatures |26, l'lthrough leads |35\. Relay armatures |125, |21 are connected to the motorro-v lay ,system of the automatic directional unit The preferred constructionofY the rotatable loop antennae |20,

|20 Vand their associated electromotive d-rives isv preferably inl raccordance with the disclosure of` myPatent No. 2,308,521 4issued January "19, 1943 entitledV Automatic radio direction indicator. The automatic radio directional receiver sche-e' matically illustrated in Fig. 1 is preferably similar to-thatdisclosed in my said patent modified to perform the radio guidance operationV inV connection with the two loopsystems. Relay armatures |24 through |21 are normally attracted to theA upper or front contact position shown through norm'al continuous energization of relay solenoid|30. With the relay armatures in the upper position, loop antenna |20 is in circuit connection with the automatic radio directional circuit through leads |28, land its associated motor and clutch |31', |32. i5 also connected theretoY through-leads |36.

'he'receiver system normally operates in this position as an automatic directional receiver indicating the bearing onany radio station tuned in by the receiverunit. Ai loop position ltransnfiitterY unit |40 is employed to .transmit the angular position yof loop antenna |25 to remotely located meter |45. A direct current vSelsynv telemetering arrangement incorporating a batteri/14| and three-Wire cable |42 is used in the embodiment of Fig. l. Needle 2 of meter |55 is associated with rotatable antenna |20' and indicates its angular position on the scale of meter |45.

When the automatic receiver is to be used for instrument approach in conjunction with spaced field transmitter stations such as indicated in Figs. 1, 4 and 5, of my copending application Serial No. 291,807, the directional receiver circuit is tuned to the predetermined frequency of the transmitters. In this case, directional antenna |20 will be movedto point so that its null signal position corresponds to the direction towards the unmodulated transmitter station and out indicator needle 2 of Vmeter |45 will thus point towards the unmodulated station. The'automatic angular orientation of loop |20 through control motor |31' is effected during the transmission interval of the unmodulated station, within onethird of a second in the prefered case.

During the transmission of the in station, the predetermined audio frequen-cymodulation of the radio frequency carrier Wave at such station will cause relay |30 to be deenergized in a manner toV beV described, and.' relayarmatures 5.12.4...to` |21 `will drop to the back contact position. Thus,

a bearing ronthe tone modulated station. D. lC.`

Selsyn transmitter' |40'. is energized by battery |4| and connected to meter |45 through cable |42. Loop antenna- |20 is automatically moved. so that its null signal positionraccurately. corresponds to the direction towards'I the tone modulated station;

needle 2; The-Zero indexv 0 corresponds to the airis of thel aircraft. After adjustment of the tun-4 ing of the directional receiver to the common car' rier frequency of' both transmitting stations, in?Y strument approach guidance as described in connection with' Fig. 1 of my said copending application.V Serial No. 291,807 is effected. The altere* nately radiating transmittingor field stations causer relay soleno'd |30 to correspondingly switch rotatable antennav system' |20 and alternately system |20 'out of andV into vcircuit relation with the automatic directional receiver. The arrangement is such as to successively move the respective antennae'and their associated` needles on indicator r| to point out, preferably to within 1' of arc,rthe direction towards the respective eld stations.

The preferred automatic directional receiver, commento both'rotatable loop antenna systems,

is shown inblock diagram in'Fig'. 1 nand Vcerro-.

I of indicator' radio frequency receiver |53 are demodulated and impressed upon audio frequency amplifier |55. During the transmission interval of the unmodulated transmitter, no separate tone or audio frequency relay signal is derived and relay solenoid |30 remains normally energized attracting relay armatures |24 through |21 as indicated in Fig. 1. However, during the transmission interval of the radio transmitter modulated by a relay tone, say of 75 cycles, a. corresponding 1.5 cycle note will appear at the output of audio frequencyamplifier |55l The 75 cycle tone is impressed upon relay filter |58 which prevents the passage of other frequency signals and passes the predetermined relay frequency of 75 cycles in the present The output of lter V|58 is connected to relay rectifier |59, the output of which is connected to solenoid |30. A preferred arrangement for the actuation of solenoid |30 is such that the solenoid is normally energized connecting loop antenna system to the directional receiver. Upon reception of a radio signal bearing a substantial 75 cycle (or other predetermined frequency) signal relay is arranged to be deenergized and switch the directional receiver from directional antenna system |20' to directional antenna system |20. It is to be understood that the relaying action wherein the predetermined (75 cycle) note causes energization of relay |30 instead of deenergization thereof may equally well be employed. Detailed circuit diagram Fig. 3 illustrates the arrangement for effecting the herein described operation of relay solenoid |30 by the 75 cycle signal.

The loop winding relay armatures |24, |25 are coupled to the loop radio frequency amplifier |60 through radio frequency transformer IGI, |62 by transmission cable |28 which is preferably of low impedance. A variable condenser |63 in shunt with the secondary winding |62 is used to tune-in 4the desired radio station. vAll the tuning controls such as condensers |54 and I 63 are preferably mechanically ganged together to provide the unitary tuning control. It is to be understood that a plurality of receiving bands may be employed to permit operation of the receiver system over a wide range of radio transmission frequencies. If a particular frequency is used for effecting the instrument approach to an airport, a rapid switch over means to bring the receiver to that frequency may be provided, as will be understood by those skilled in the art.`

In describing theoperation of the automatic directional receiver section, which lies to the right of broken lines |38, reception by one of the loop antennae is assumed. With the position of relay armatures4 |24 through |21 shown in Fig. 1, loop antenna |20 and its associated control motor circuit are connected to the automatic receiver. In accordance with the automatic receiver used in the system of the present invention and described in detail in my Patent No. 2,308,521, a loop control signal is provided dependent upon the received loop antenna signal, to operate the motor drive for the loop antenna and rotate it to its null position with respect to the oncoming radio signals. The normal or stable position of the loop antenna is at the null or electrical neutral position with respect to the oncoming radio signals from the associated transmitted station, giving an exact angular indication of the direction to the transmitter of the radio signals. In the present case, the unmodulated transmitter is assumed to be radiating for controlling the orientation of loop antenna |20' and needle 2. When the modulated transmitter station is transmitting, loop antenna |20 instead is connected to the system, resulting in a similar electrical action.

When the angular position of the loop antenna |20' is changed from null during approach maneuvers, the radio signal is picked-up by the loop and impressed upon amplifier |60. The magnitude and phase of this signal depends upon the amount of the off-null angular position of the loop and the direction of the transmitter to the right or' left thereof, respectively. A local generator |54 of an audio frequency current, preferably of the order of one hundred cycles, is used to modulate the radio signals derived from Vthe loop antenna and producea resultant toneV modulated radio signal. I prefer to use a tone signal of 102.5 cycles as indicated in the drawings, but a different frequency may instead be used so long as it is different than the signal for relay |30. Loop signal modulator |65 schematically designates the modulation stage, preferably a balanced modulator, for combining the loop signal of |60 with the tone signal of |64.

The resultant tone modulated radio signal at |60 has a magnitude and phase dependent upon the olf-null position of receiving loop antenna. The tone modulated signal is then suitably combined with the non-directionally received signal from antenna |50 by a coupling means, such as coupling coil |66 linked with secondary winding |52 of the input transformer to radio frequency receiver |53, The nature of the radio signal impressed upon the input of amplifier 53 is described in more detail, in connection with Fig. 3 of my said Patent No. 2,308,521. The superposition of the non-directional radio signals with the locally modulated loop signals provides a resultant radio signal with the 102.5 cycle tone component having a magnitude and relative phase dependent upon the off-null position of the loop antenna with respect to the oncoming wave. Radio frequency receiver |53 may be a tuned radio frequency circuit or a superheterodyne circuit. The receiver unit |53 contains a demodulator or detector for the audio frequency components of the amplified radio signals. The audio frequency signals at the output of unit |53 comprise modulations of the original radio wave plus the 102.5 cycle tone or control signal obtained when the loop antenna is olf null.

An audio frequency amplifier |55 is connected to the output of receiver-detector unit |53. Ampliner |55 supplies audio unit |56 with suiiicient energy for operating headphones oonnectable to jack |51 at the output thereof. The output of audio frequency amplifier |55 is also connected to a separate control signal amplifier |61 through a suitable phase shifting net-Work |68 and 102.5 cycle pass lter |09. The 102.5 cycle tone signal is thus filtered out from the output of audio frequency amplifier |55 and amplified a substantial degree for use as a control signal to operate the relay control tube system indicated at |10. The relay control tube system is energized by both the control signal from amplifier |61 as well as the correspondingly amplified tone signal obtained directly from generator |64 and intermediate tone amplifier |1|. Details of the operation and interrelation of the respective control signals and the relay control tube system |10 are described in further detail in connection with Figures 4 and 4a of my Patent No. 2,308,521.

Control relays indicated at |12 comprise solenoids |13 and |14 connected to the relay control -|2|'- and associated gearing.

either relay |13 or |14` is determined upon thetube system,|1|l.A Solenoidsz|13and |15 areselectively energized Vfrom control system- |10 -in laccordance with the angular position to the right or left ofthe loopconnected, yWithrespect to the direction of the oncoming radio waves. When relay |13 isenergized, it attracts its armature |15 to-` close the electrical circuit through ground -in-y cluding its front contact, batteryY |11, Vand the loop motor. When antennav is connected to the system, motor |3 is thus energized. Motors |3| and -|3|f are connected in a predetermined manner to operate-in the direction to rotate loop antennae |20 and |20" respectively towards their null signal position through their shafts '|2| `and Energization l of direction of the angular deviation of the connected loop antenna (|20) from its null position with respect tothe-radiating station. so-that thev contact position, deenergizing and stopping thel associated motor. Electromagnetic clutches |32 and |32 are electrically' shunted across l their motor. energization circuits to immediately disconnect theassociated motor from` the loop antenna-insuring a rapid stop-of the loop rotation at the time of motor deenergization, and eliminatingY the. possibility of overshooting or overdriving bythe motor dueto its mechanical inertia; The frictional forces of the gearing and-the bearings of` theloops are generally suiicient to quickly stop the, loop rotation.

In practice I have constructed systems in accordance-with the present invention Whichautomatically operate the loopsand therefore the associatedbea-ringindicators at a rate of 180 and more per second.-v The accuracy :of the lresultant bearing may readily be made within 1 of arc, i, e. theA actual directional indicationV on each radio transmitter beingcorrect to-within 1 or less.V The-bearing indications arefon a 360"` dial andamove` -to the stationary bearing position through the shorter angular path. I prefer a rate of indication of about 125 per second for the one-thirdv of a second transmitterl radiation periods.

When theloop antenna reaches, cris substantially at, its null signal-position a zero or substantially zero magnitude radio frequency signal isyimpressed upon radio frequency amplier |60 for modulation at |65 by the generated .tone signal from. |65.v The magnitude of the control signalfrom amplier accordingly is-also zero, or

substantially `zero atthat time, and control relays |12v are in the deenergized position shown. The

loop accordingly remainsstationary when it is at ergized by the oncoming radio signal from thel transmitter, and impress it'fupon amplifier |60 witha magnitude and phase relation correspond- F escasas Y ing to the altereddirection thereof, Should the` deflection ofthe aircraft cause the loop toreceive a signal of phase corresponding to that whichv energizes solenoid |13, the abovedescribed operation. of-the loop motorie repeated to bring the-loop to the new null signal position. Should, however; the aircraft turn so that the loop-is deviated in theA opposite angular direction,- the phase of the control signal impressed upon relay control tube system Y|10 will be different by 180"n and energize solenoid |14 instead.

When solenoid |14 is energized, its armature |16 is attracted to the .front contact to electrically` complete the connected loop motor circuit'including its-associated clutch, ground, andbattery |11. Electromagnetic clutch |32' is, thereupon immediately engaged and motor |3|' is -rotated in the direction oppositeto that corresponding'to itsv energization by solenoid |13 when loop system |20' is in connection with the receiverv aS shown in Fig. 1. Motors |3| and |3| arege versible in the Apresent case, kand are not neces sarily a direct current type. Relay armatures |15 and |16 are arranged so that the directiony of current flow throughthe connected motorie selectivelyreversed to cause the motor to rotatev its.` associated, loop Vtowardsits null signal posi1 tion in the shorter path of rotation. Thus, when solenoid |14 :is energized, the motor will rotatein a direction opposite to that due` to energizetion ofrelay |13. Y.

An important feature ofthe preferred automaticdirectional receiver resides in the fact that, for any bearing, the loop antennae arel at their electrically neutral and geometric null positions, and remain stationary for the duration of the bearing. Furthermore, no sense or directional ambiguity occurs, and the null positionwhich the loop assumes is4 accurate for `any bearing on the transmitters. Pointer 2 of indicator |45moves in. exact correspondence-with loop antenna |20' and is arranged to point to the center zero posi` tion 0 shown on the dial, when the open planeof loop |20' is perpendicular to the longitudinal axis of the aircraft. Similarly, pointer orneedlemovesin exact correspondence with loop an tenna |20, pointing to: center zerowhen the` plane of loop |20 is 'perpendicular to the flight direction.

The accuracy of indication is independent ofl the position -of indicator needles I and 2 since any reading thereof corresponds to fan electrical null position of loop antennae* |20 and |20", and'no balancingrof electrical :parameters orsignal components are required to maintain the readings. The interpretation of the readings; is readilyapparent to thepilot, andhe eflectsan instrument approach asidescribed in connection with Fig.V 1

of vmy said copending application Serial No.`

rent Vloop positiontransmitter of thesecond loopA system. Three-pole double-throw switch vr| is used to connect leads |83 with cable |83 as shown indotted during the double indicator instrument telemetering manner.

Aapproach operation of the system so that both needles and 2 of meter |45 are independently controlled.

Indicator needle I is connected to central spindle |86 pivoted in end bearing |81. Magnetic core |88, shown in dotted, is secured tospindle |86 and arranged to magnetically coact with the interior of annular winding |8| in the usual Indicator needle 2 is coupled to the end of tube |90 concentric about spindle |86. Tube |90 is rotatable on diagrammatically indicated bearing |9| for independent rotation with respect to spindle |86 of needle Magnetic core |92, shown dotted, is mechanically secured with rotatable tube |90, and is magnetically coactable with annular winding |82. Indicator needles and 2 are coaxial and independently controlled to assume the angular positions of the two loop antenna systems during the instrument approach maneuvers described. A casing |93, having a ange |94, fitted within the open end of housing |80, encloses indicator needles l and 2 and contains the scale for the indications. A transparent window |95, such as glass, is tted into the top end of enclosure |93.

When the dual receiver system is to be used for taking fnormal directional bearings on only one transmitter station and not for the described twostation instrument approach maneuvering, threepole switch |85 is thrown to the position drawn in solid lines in Fig. 2 connecting annular windings |8| and |82 in parallel. Both indicator needles and 2 then act in unison, one above the other, and each assumes the same angular position on the scale of meter |45. For ordinary automatic directional operation, both sections of the meter are connected in parallel with one of the loop position transmitters and give the same reading.

Accordingly, when the dual indicator of Fig. 2 is in circuit with a dual receiver system in accordance with the present invention, three-wire cable |84 connects to the position transmitter of the loop antenna normally in circuit with the receiver, and three-wire cable |83' to the loop position transmitter of the other antenna. For example, if used in the receiver system of Fig. 1, cable |84' would correspond to cable |42', connecting t position transmitter |40 of loop antenna system normally connected to the re-A ceiver through relay armatures |24 to |21; and cable |83' would correspond Ito cable |42 connecting to position transmitter |40 of antenna system |20. Three-pole switch |85 is operated to the solid position for both needles of indicator |45 to give a single reading when the automatic directional system is used for radio guidance in general, and is connected to the dotted position when the pilot is ready for instrument approach to a runway having stations corresponding to T1 and T2 of Fig. l of my copending application SerialNo. 291,807 when both needles become independently operative in the manner described.

Fig. 3 is a detailed schematic electrical diagram, partially in block form, of a commercial form of the automatic receiver system constructed in accordance with the principles of my present invention. Relay system |24 through |21 selectively connects the two loop antennae systern |20 and |20' to the receiver as shown in Fig. l. Fig. 3 is a specific electrical showing of the system shown generally in Fig. 1, and represents a preferred embodiment thereof though not limited thereto.

Signals from the rotatable loop antenna in circuit with loop transmission cable |28 are impressed upon primary winding |61 of the loop radio frequency input transformer, secondary winding |92 of which is shunted by tuning condenser |63 and connected to the control grid of radio frequency amplifier pentode 200 for ampliication and introduction to the control grids of balanced modulator stage |55. The gain of loop amplifier 200 is manually controllable by rheostat 20E connecting the cathode thereof to ground. The anode of amplifier 200 is energized through a shunt radio frequency choke coil 202 connected to the B supply.

The output of loop amplifier 200 is coupled to the control grids of tubes 203, 203 of modulator 55 through coupling condensers 204. The cathodes of tubes 203, 203 are tied together and connected to ground through by-pass condenser 205 and biasing resistance 205. An audio frequency osciliator |54 comprising two triodes 201, 201 is arranged to generate an audio or tone frequency currentl of a relatively low frequency. The control grids of triodes 201, 201' are coupled to the anodes thereof by condensers 208, 208. Cathcdes of the oscillator triodes are tied together and connected to ground through biasing resistor 209.

Resistors |98 and |98 are coupled between the grid electrodes of triodes 201,201' and ground. Intermediate taps on the resistors |98 and |98' couple a portion of the available alternating current tone energy from oscillator |64 to the grids of modulator triodes 203, 203 through coupling resistances |06 of about one megohm each and through coupling condensers |91, |91'. Further resistances |99, |99 normally connect grid coupling condensers |01, |91 to ground to stabilize the 4grid circuits of tubes 203, 203.

The actual frequency of the tone current generated by oscillator |04 as used in the system is optional, and may for example lie anywhere in the audio frequency spectrum, or even higher. Practically, however, the tone frequency should be chosen so as to emciently pass through the respective radio frequency circuits as side-bands, and the audio frequency circuits as well, be audible to the pilot when present and differ from the relaying tone from the eld transmitters. It is also desirable to prevent interference with theintelligibility of the aural messages of the ,radio signals. An important consideration is to minimize any effect due to the sound modulations of the radio wave upon the control circuit. I have found that a control signal in excess of 200 to 300 cycles contains sound modulation components after filtering out for control purposes.

Modulation kicks occur when the sound frequencies of the radio signals coincide with the control frequency, and interfere with the stability of the directional indications. A tone frequency of the order of 100 cycles is suciently high to efiiciently pass through the radio and audio frequency channels of the system, sufciently low to not interfere with the intelligibility of the audio frequency modulations of the radio signal, and is not effected by modulation kicks. A practical tone frequency in this range I found to be a tone of 102.5 cycles, as indicated in the figures. This frequency is satisfactory when the loop relaying frequency of the tone modulated transmitting station is '15 cycles. The field transmitter tone should differ sufficiently from the receiver control frequency, 102.5 cycles in the present case, to be properly filtered out of the audio output circuit. Thus 75 or less cycles, or

Yshunted there-across.

150 or more cycles per `second are satisfactory for. the tone modulated transmitting station when 102.5 cycles are used in the receiver.

Control grid electrodes of modulator triodes '203,V 203' accordingly simultaneously receive the audio frequency tone signal from oscillator |64 and the radio frequency signal picked up by the connected directional antenna. The output of modulator stage |65, obtained through the anodes of tubes 203, 203', is connected to opposite sides of radio frequency winding |66 coupled to secondary winding |52 of the non-directional antenna circuit. The anode supply for modulator tubes 203, 203 is obtained through a center tap on winding |66 connected to the common B supply as indicated.

The frequency of the loop modulated signals is the sum and difference of the received radio signals and the low frequency oscillator tone signal. directional radio frequency signals with the tone modulated loop signals upon winding |52 produces a resultant signalv upon the control grid of radio frequency amplifier 2|0. The non-directional signal'from, antenna |50 serves as a reference signal or :sense determinator, so that the right or left sense of the loop antenna signals is established for further control action on the orientation of the loop antennae. Thus proper functioning of the automatic directional receiver is assured, quickly bringing the connected lcop antenna back to 'its null signal position to give accurate bearing indications on the fieldstation transmitting. Y

The signals impressed upon the control gi'idlz` of radio frequency pentode 2|0 are amplified and The simultaneous induction of the nonshown in block'diagram form.4 The anode indicated at 236 .of 'outputstage of intermediate 'frequency amplifier 235 is connected to transformer 231, the primary and secondary windings of which are respectively shunted by adjustable condensers 238 and 239 and tuned to the intermediate frequency. An audio frequency detector stage 240 has its control grid connected to the output of intermediate frequency transformer 231 for demodulating the signals and produce corresponding audio frequency currents across cathV ode resistor A245 connected to ground.

Both the radiosignal tone modulations as well as the local control signal if present, produce a corresponding .audio frequency signal across resistor 245 vby the detectoraction.V The anode ,of detector r240 is connected to the common B supply as indicated. Condenser 246, between the i cathode of detector 240 and ground,Y by-passes Y audio frequency signal modulations von the radio transmitted through voutput radio frequency transformer 2|| havingv its secondary winding tuned to resonance by variable condenser 2|2 The output of transformer 2H is coupled to intermediate grid electrode 2|5 lof the radio frequency mixer stage 220 vthrough coupling condenser 2|6. Radio frequency mixer stage 220 is shown as a hexode wherein grid electrode 2|1 adjacent to the cathode is energized by a signal emanating from a local beat frequency oscillator 22| operated in the usual manner for superheterodyne reception. The anode and screen grid operating potential for stage 220 isv supplied through respective resistors 222, 223.

The output of radio frequency mixer stage 220 comprises primary-Winding 225 of a step-down intermediate frequency transformer shunted by adjustable condenser 221 for resonating the coil-Y 'attheintermediate frequency, such as 455 kilocycles. Transformer 225, 226 is .a step-down transformer sol that a long low impedance transmission line 230 may be used to permit placing the intermediate frequency `and audio frequencyV amplifier equipment remote from the radio frequency section including directional and nondirectional radio signal amplifiers, and loop Vmodulatcrstage. Transmission cable 230 is an electricallyshielded low impedance cable terminatingin a correspondingly low impedance primary rWinding 23| "of step-up intermediate frequency transformer 23|, 232. Secondary winding 232 of `the terminating transformer isshunted by a resonating adjustable condenser233 to tune the transformer to the intermediate-.frequency used. The output of step-up intermediate frequency transformer 23|, 232 isconne'cted to the grid electrode indicated at 234 of the input stage of two-:stage intermediate frequency amplifier 235 carrier lwave and the control or tone signalampliiied together therewith, are impressed upon two-stage amplifier 260 for further amplification to an appreciable signal level. AThe outputcf amplifier 260 is coupled to the aural amplifier indicated at 21,0, ito the output of which earphones 215 areconnected. The pilot .adjusts the aural level of the ,signals by a separate manual control in aural unit 210. The output of Vaudio frequency amplifier 260 is also coupled to - amplifier stages 280 and 290 for selecting and further amplifying .the 102.5 cycle loop ymotor contro signal and impressing it upon relay control system |10, and also Ato pass filter 350 for controlling the selective connection of loop systems |20 and |20' to the receiver, through transmitted relaying signals. f

The output of audio frequency amplifier V260 is coupled to the control -grid 20|v of amplifier stage Y280 vby coupling .condenser 26| and phase .shifting net-work 262,

263. Resistor 265 is 'shunted across phase shifting network 262, 263

connecting the control vgrid of stage 280 to ground. The relative impedance of resistor 262 and condenser263 `is chosen to suitably shift the phase of the 102.5 cycle control signal to be impressed upon `control grid 28| to' compensate for anymisphasing thereof caused in the circuits prior to that point.v Such phasing is made to cause the Yphase relation cf the ignalarri ing at the input of tube relay control system |10 to iba-substantially in-phase or 180 out-of-phase with the .correspondingly impressed tone signal `from amplifier I 1|.

The control signal impressed upon controlgrid electrode 28| of pentode amplifier stage 280 is amplified in a conventional manner. The output of amplifier 280 is impressed upon control grid 29| of a further amplifier stage 29D through coupling condenser 282. A tuned filter 285, 288 is .used to filter out other signals or modulations than the 102.5 cycles, and most efficiently pass this signal frequency. Other filter arrangements than the shunt ,choke coil 285 and condenser 283 maybe used. Amplifier stage 290 comprises a triode tube, the anode circuit of which includes primary winding 292 of audio frequency coupling transformer 235. Secondary winding 233 of transformer 295 is shown schematically coupled to the input of the relay contro1 system |10. The output of 102.5 cycle amplifier |I| is impressed upon relay control system |10. Fig. 4 of my said Patent No. 2,308,521 illustrates a preferred circuit arrangement for the relay control tube system |10.

Variations in the level of the received radio signals are compensated for by an automatic level control. A further arrangement of the system maintains constant the anode or B voltage 'supe ply for critical parts of the circuit despite varia tions in the supply voltage thereto, to insure uniform sensitivity and operation 'of the loop motor controls and associated electronic relay system. A voltage regulator tube 350 is connected between a particular point 305 and ground, to maintain a predetermined and uniform operating voltage supu ply for the critical part of the electronic control arrangement which includes the anodes of oscillator |64 through lead 304, the amplifier l| through lead 301 and electronic relay system |13 through lead 306.

An automatic level or volume control arrange ment is provided through rectifier 3m fed by an intermediate frequency signal tapped from intermediate frequency output anode 235 through coupling condenser 3|| to anode 3|2 thereof. Delayed automatic volume control (D. A. V. C.) action is obtained by providing a positive biasing voltage raising the potential of cathode 343 to delay the biasing control action till the received radio signals reach a predetermined level. Anode 3|f2 of rectifier 3I0 is connected to the control grids of the respective radio frequency, intermediate frequency and audio frequency stages of the circuit to establish a substantially fiat and uniform amplification response ofthe signals through the system.

Coupling resistances 3|5, SI5, 3|?, 3|8 are used in this level control circuit, and control grid 236 of the intermediate frequency amplifier is connected thereto by direct connection 3|9 through f secondary winding 232. The second stage of the intermediate frequency amplifier 235 is prefera ably also controlled by the level control circuit described. The inclusion of at least the first audio frequency amplifier stage 250 in the signal control circuit from rectifier 3|0 results in a very fiat overall response despite wide signal level changes in the received radio Waves.

A manual switch 323 is provided at the cathode of the first radio frequency amplification stage 2|0 to disconnect the automatic volume control effected thereto through resistor SI5, for manually controlling the bias through variable resister 322 in the cathode circuit. This manual volume control is useful for communication or reception of radio range signals. A further switch 325 is provided for continuous wave beat frequency oscillator 330 to connect it to audio frequency detector stage 245 for heterodyning continuous waves. Continuous Wave oscillator 330 is used for audibly perceiving continuous wave transmission and serves as a signal station finder for such stations. The normal connection o switch 325 to ground contact 325 is schematically indicated for rendering oscillator 330 ineffective as a heterodyning means, which connection is used for phone reception. By ungrounding switch 325,

oscillator 330 becomes eiective for heterodyne reception of continuous waves.

A direct current millemeter 353 is connected between the output of automatic volume control stage 310 and ground, through series resistance 345. Meter 330 serves as a' measure of the automatic level biasing current and indicates the relative signal strengths of received radio signals. Meter 340 thus serves as arelative distance or millemeter. Flight toward a station increases the signal strength and therefore the indication on meter 340. Flight away from a station correspondingly decreases its indications.

The audio frequency output of amplifier 260 is connected to a highly selective filter 350 by leads 345 to segregate the radio relayY tonef'l cycles V in the present embodiment, from other audio frequency signals which may be present. Pass filter 350 is selected to pass efficiently the chosen relaying frequency. The actual construction of pass filter 350 is optional, and I have illustrated one form which it may assume in practice. A resonant shunt path comprising inductance 35| and capacitance 352 tuned to the frequency to be passed, comprises the initial section thereof. A series inductance 353 connects shunt path 35|, 352 to a further shunt path 354, 355. The output of filter 350 contains series inductance 356.

Filter 350 is specifically designed to reject the 102.5 motor control frequency which orients the loop antennae. The invention is not limited to any particular frequency for either the loop motor control or the relay switching control. The output of filter 350 is coupled to a rectifier arnplifer stage 350 through coupling condenser 351. The '75 cycles signal is impressed upon detector anode 358 having shunt resistor 359 to ground across which the rectied component isbuilt up. The cathode of stage 350 is positively biased with respect to ground by battery 33|. Control grid 333 of the triode section of tube 360 is coupled to diode anode 358 through resistor 362. A by pass condenser 36d connects grid 333 to ground.

Relay solenoid 35 is connected between anode 366 and the B supply for stage 350. Normal anode circuit current passes through solenoid 355 when no relaying tone signal is impressed upon stage 360 from filter 350. This current is suiicient to energize the solenoid 365 and attract armature 310 against contact 339 as shown in dotted. In this `position, relay contact 369 isconnected with armature 310, and energization of relay solenoid |30 is maintained through local source 313. Relay armatures |24 through |21 ac cordingly are normally against their front contact position as shown in Fig. 1, connecting loop antenna system |20 to the directional receiver circuit.

When the tone modulated transmitter station is operating and the audio frequency tone modulation thereof is present in the receiver, the relaying tone, namely the 75 cycles frequency signal, passes through lter 350, is rectified by stage 350 and causes a substantial negative bias upon control grid 363 thereof. The negative bias chokes off the normal anode current owing through solenoid 365, and permits spring 312 to draw armature 310 from contact 359 again-St. backstop 31| as shown in solid in Fig. 3, opening the circuit between battery 3T3 and solenoid |30. When the 75 'cycle relaying signal is received, switch-over relay |30 is accordingly deenergized in the described embodiment. When relay solenoid |30 Y needle.

disconnecting loop system |20 vfrom the directional receiver andV connecting loop system |20 thereto.

The switch-over or relaying action by solenoid |30 occurs when the tone modulated field station is radiating. The altomatic loop orientation by the directional receiver is made eiective on loop antenna system |20 for the duration of transmission of the tone modulated station. Loop antenna |20 is quickly moved to its null signal position with respect to the tone modulated station by stable action, bringing the local 102.5 cycle signal below the value to cause operation of loop motor |3I. Indicator needle of indicator M5 (Fig.' 1) corresponds to loop an-tenna |20 and to the tone modulated station as previously described. Needle I remains at the position which l antenna |20 assumes after antenna system |20 is unswitched from the directional receiver, upon cessation of the tone modulated signal and transmission of the unmodulated signal.

In accordance with the operation of the receiver system described, when the tonemodulated station ceases transmitting and the unmodulated station starts transmitting, loop antenna system |20 is disconnected from the receiver circuit and remains stationary while the other antenna system |20 is placed under the control of the directional receiver. Signals from 4'the unmodulated station orient loop |20 to point thereto. Needles I and 2 remain. stationary during the quiescent periods of the transmitters. Since approach maneuvers take place at a speed in the range of 80'to 120 miles per hour,'a switching rate of about one-third of a second for -the field transmitters is preferred. I have found during extensive experimentation that a rate of switching less than onehalf of a second gives indications by the needles l and 2 which effectively indicate the pilots lat- 'eral position with respect to the two landing eld stations. l

The broaderprinciples of my present invention lare not dependent upon the specific automatic receiver unit disclosed for operating the dual indicator system. However, the success of the invention depends upon the use of a rapidly operating and accurate automatic directionindica'ting receiver unit such as I have hereinabove dis- .cing accuracy in directional positioning of the loop antenna and its corresponding indicator Such rate of operation results in completion of bearings on the transmitters well within the preferred one-third of a second period Yof transmission of 'the stations.

Although specific embodiment of the invention has been shown and described to illustrate the application of the principles thereof, it

Will be obvious that the invention may be other- Wise embodied without departing from such principles.

What is claimed is:

1. Avradio directional receiving system comprising tworrotatable directional antennae; a single receiver unit, common to both of said antennae, for automatically orienting a connected sponsive to "successively received radio signals for correspondingly successively connecting Vsaid kdirectional antennae tosaid single receiver unit for individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said relay means for giving directional bearings on a single transmitted radiolsignal.

2. A radio directional receiving system comprising two rotatable directional antennae; a single'receiver unit, common to both of said 'antennae, for automatically orienting a connected one of said directional antennae toa stable bearing position with respect to correspondingly received radio signals; an indicator electrically connected with each of. said directional antennae for pointing out their angular orientation, said indicators being coaxially arranged; relay means' responsive to successively received radio signals for correspondingly successively connecting said directional antennae to said single receiver unit for individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said relay means for giving directional bearings on a single transmitted radio signal; and switching means for disconnecting the associated indicator from the normally unconnected directional antenna and connecting it with the indicator of said normally connected antenna, whereby both indicators give identical Adirectional readings corresponding to the orientation of said connected directional antenna.

3. A radio directional receiving system comprising two rotatable directional antennae; a single receiver unit, common to both of said an'- tennae, for automatically orienting a connected one of said directional antennae to a stable bearing position with respect to correspondingly received radio signals; a dual position indicator having a pair of indicating elements each connected to one of said directional antennae for pointing out their angular orientation; and Y a device responsive to successively received radio signals for correspondingly successively connecting said directional antennae to said receiver unit for individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said device for giving directional bearings on a single transmitted radio signal.

fl. A radio directional receivingV system comp rlsing two rotatable-directional antennae; a slngle receiver unit, common to both of said antennae, for automaticallyV orienting va connected one of said directional antennae to a stableA bearv Y ifn'g' position with respect to kcorrespondingly rehizeiyeolV radio signals; an indicator connected with eac-hof said directional antennae for pointing out their angular orientation; and relay means' re'- one of said directional antennae to astable bearing position with respect to correspondingly re- Y ceived radio signals; two position transmitters each connected to one of said antennae for telemetering its angular orientation; a pair of position indicators each connected to one of said position transmitters; and relay means respons1ve to successively received radio signals for correspondingly successively connecting saidV directional antennae to said receiver unit for individual orientation to obtain directional bearings `on the separately transmitted radio signals,vone ofsaid directional'antenna normally being in connection'with said receiver unit during'inaction of said relay means for giving directional bearings on asingle transmitted radio signal.

5. A'radio directional rec'eivingsystem comprising two rotatable directional antennae; a single receiver unit, common to both of said antennae, for automatically orienting a connected one of said directional antennae to a stable bearing position with respect to correspondingly received radio signals; two position transmitters each connected to one of said antennae for telev metering its angular orientation; a dual position indicator having a pair of coaxial indicating elements each electrically connected to one of said position transmitters; relay means responsive to successively received radio signals for corresponding successively connecting said directional antennae to said receiver unitfor individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said relay means for giving directional bearings on a single transmitted radio signal; and switch means for connecting both of said indicating elements in parallel to the position transmitter connected to the antenna normally connected to said receiver unit, whereby both indicating elements give identical directional readings corresponding to the orientation of said connected directional antenna.

6. A radio directional receiving system comprising two rotatable directional antennae; a single receiver unit, common to both of said antennae, for automatically orienting a connected one of said directional antennae to a staple bearing position with respect to correspondingly received radio signals; an indicator connected with each of said directional antennae for pointing out their angular orientation; and a device responsive to successively received radio signals for correspondingly successively connecting said directional antennae to said receiver unit for individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said device for giving directional bearings on a single transmitted radio signal; said device including a solenoid connected to said unit, a first set of contacts connected to one of said antennae and its orienting means, a second set of contacts connected to the other antenna and its orienting means, and movable armatures connected to said unit and operatively associated with said solenoid.

7. A radio directional receiving system comprising two rotatable directional antennae; a single receiver unit, common to both of said antenna, for automatically orienting a connected one of said directional antennae to a staple bearing position with respect to correspondingly received radio signals; an indicator electrically connected with each of said directional antennae for pointing out their angular orientation; a device responsive to successively received radio signals for correspondingly successively connecting said directional antennae to said receiver unit for individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said device for giving directional bearings on a single transmitted radio signal; said device including a solenoid connected to said unit, a first set of contacts connected to one of said antennae and its orienting means, a second set of contacts connected to the other antenna and its orienting means, and movable armatures connected to said unit and operatively associated with said solenoid; said solenoid normally being energized to 4 retain its armatures in engagement with one set of contacts to normally connect said one antenna to said unit. v

8. A radio directional receiving system comprising two rotatable directional antennae; a single receiver unit, common to both of said antennae, for automatically orienting a connected one of said directional antennae to a staple bearing position with respect to correspondingly received radio signals; an indicator electrically connected with each of said directional antennae for pointing out their angular orientation, said indicators being coaxially arranged; a device responsive to successively received radio signals for correspondingly successivelyV connecting said directional antennae to said receiver unit for individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said device for giving directional bearings on a single transmitted radio signal; said device including a solenoid connected to said unit, a l'irst set of contacts connected to one of said antennae and its orienting means, a second set of contacts connected to the other antennae and its orienting means, and movable armatures connected to said unit and operatively associated with said solenoid; said solenoid normally being energized to retain its armatures in engagement with one set of contacts to normally connect said one antenna to said unit; and switching means for disconnecting the associated indicator from the normally unconnected directional antenna and connecting said associated indicator with the indicator of said normally connected antenna, whereby both indicators give identical directional readings corresponding to the orientation of said connected directional antenna.

9. A radio directional receiving system comprising two rotatable directional antennae; a single receiver unit, common to both of said antennae, for automatically orienting a connected one of said directional antennae to a stable bearing position with respect to correspondingly received radio signals; a dual position indicator having a pair of indicating elements each connected to one of said directional antennae for pointing out their angular orientation; relay means responsive to successivly received radio signals for correspondingly successively connecting said directional antennae to said receiver unit for individual orientation to obtain directional bearings on the separately transmitted radio signals, one of said directional antenna normally being in connection with said receiver unit during inaction of said relay means for giving directional bearings on a single transmitted radio signal; said relay means including a solenoid connected to said unit, a rst set of contacts connected to one of said antennae and its orienting means, and movable armatures connected to said unit and operatively associated with said solenoid; said solenoid normally being energized to retain its armatures in engagement with one set of contacts to normally connect said one antenna to saii unit.

l0. In a radio guidance system incorporating two spaced and successively radiating transmitters having the same carrier frequency with the signals of one transmitter being tone modulated, two rotatable directional antennae; a receiver unit for automatically orienting a connected one of said directional antennae to a stable bearing position with respect to correspondingly received radio signals,V said receiver unit being tunedjto the common carrier frequency of the two successively radiating signal; transmitters; an indicator connected with each of said directional antennae for pointing` out their angular orientation; one of said directional antennae normally beingl in connection with said, receiver unit duringv receptionA by said unit of unmodulated. signals from one of the transmitters for giving. directional bearings on a single transmitted radio. signal; and selectively operable means eiective upton reception by said units of tone modulated signals from the other transmitter to connect, the. other antenna to said unit for obtainingindividual bearing indications on each of the transmitters;

11;. In a radio guidance system incorporatingtwo.. spaced and successively radiating` transmit.- ters having the same carrier frequency with the signals of one. transmitter being tone modulated, tv vo rotatable directional antennae; a receiver.. unit for automatically o rienting a connected one of saidv directional antennae to a stable bearing position with respect to correspondingly received radio. signals, said receiver unit beingY tuned to thecommoncarrier frequency of the. two successively. radiating signaltransmitters; an indicator connected with each of said directional antennae. for oointing out their angular orientation; one) Qff-Safldrcicnal. entennanormally beingin con--` nection with said receiver unit. during reception.. by said unit of unmodulated signals from one of the transmitters for giving: directional bearings on a single,Y transmitted radio signal; a. device llcllldiligi asoloncidoonnected tosaidunitiarst.

rnittersJV andI selectively operable means. effective..

iipolrreoeption; by saidf units...of. tone modulated; signals from the other transmitter.. to. eiect de;- eocigiaaiion.orSaidsolenoid.toconnecttne other. antenna toV said unit for. obtaining.individual;v bearing indications onA each of the transmitters.

l2t In; a4 radio.Y guidance system. incorporating two spaced andl successively radiating. transmit; tershaving the same` carrier frequency with. the

` signalsof one transmitter. being. tone modulated,

two rotatable directional antennae; a. receiver.

unit for automatically orienting a. connectedlone.

or. saidfdirectionalantennae to estable bearing.

- position Withrespectto correspondingly received radio signals, said receiverunitbeing tuned toA the common carrierA frequency of the. two suc-v cessively radiating,y signal transmitters; an?v indi.- c ator connected with each of said, directional an-v tennae for pointing out their angular; orientation; one of saidv directional antenna; normallybeing. inconnectioniwith said receiver. unitduring.

reeentionfby. said unitv of unmodulatedlsignals..

from.v one of` the transmitters for giving directional bearings ona single transmitted radio, signal; a deviceY including aY solenoid connected tofsaid unit, a rstlset of contacts connected-to.. one. of said antennaeandits;orienting..means, ay second set of contacts connected; to the. other ane torinaVv and'. its orienting meanaandz movable; ar.. matures. CQlIieCtEd 11.0 Seid urlt.. andoperatively,

noid to... connect theother antennatoesaidaunitforf obtaining. individual: bearing; indications on: Yeacn` ortho transmitters" 1-3., In; a radio guidancesystemincorporating.. two. spaced; and successively radiating: transmit-.

.. ters having the samej carrier frequency: withrthe:

signals of. one transmit-.terzbeilistone..` modulated. two-rotatable directional antenna.; a, receiver unit'. fork automatically.` orientingga connected Yonejo saidI directionalantennaefto astable bearing; p.o,.. sition with respect. to corr.esoondingly.-ireceivedJ radio signals.. said receiver unit being; tuned. to.. the, common. carrier frequency` of the'tvvof suc.,- cessi-voir radieting;signaltransmitters'; admiro.- Siticn; indicatoru having. a pair. or. indicating .ele-- monts cach. electrically comicotod,v tori-nie.L of said. dircciiferial-w antennae; for pointing out; their anfgular. orientation; oncof Said directionalantenna normally being inl connection. withv said receiverI unit duringv reception by. s aid unit of. unmodulated -l Signals from one of; the transmitters for giving.; directional` bearings on. a. Single. transmitted. radio' Signal; c device including ai Solenoid con.- ncctcdto, said unit., a.. rstsotroi contacts. oon-- ncctcdy to one of Saidv antennae and itsforienting;

1 .mcanaelid movable armatures comicctcdtcsaid;

unit. and. operatively associated; with: So1enoid... said solenoid: normally: being energized to retain its. armatures engagement with.. cnc-sot of; oon..-

tacts to normally.` connect said; one antenna to;v

scid` unit during; reception: by scid, unitl or. uri.- modulated signals. from one of the transmitters; selectivelyoperable tone` pass filterl means. eiec.- tivcfupon rocclctionbrsaidnunt oitonemodulatcw Signals fromthe. other trcnsmittcrto effect de:

enereizcticnfoifscid solenoid tofoonnect the.otiier.'

enterica. tc. said; for obtaining individual.. bearing. indications.. cricachf` oir the. transmitters.

14.2111@ radio guidance system incorporating; two; spacedV anigsuccessivclr radiating. transniitry ters having the. same carrier frequency'withzthe'. signals of one transmitter beingtonemodulated, two rotatable directional-, .antennaep a receiver unit. for-automatically. orientingr4 agconnectedi onev of said directional antennaeto a stable 'bearing- Position With rcsnectzto correspondinglyreceived?. radio f signals.. Said receiver.' unit. beine. tuned .Y to;l the: common cerner frequency off the; two. suc..- ccSSi/clv..radiating..sienalitrarismitters; twonosiz-J tion transmitters. eachV connected to.v one.. of. said:A

energized to retain its armatures in engagement with one set of contacts to normally connect said one antenna to said unit during reception by said unit of unmodulated signals from one of the transmitters; selectively operable tone pass lter means effective upon reception by said unit of tone modulated signals from the other transmitter to eiect deenergization of said solenoid to connect the other antenna to said unit for obtaining individual bearing indications on each of 10 the transmitters; and switching means for disconnecting the associated indicating element from the normally unconnected directional antenna and connecting said associated indicating element with the indicating element of said normally connected antenna, whereby both indicating elements give identical directional readings corresponding to the orientation of said connected directional antenna.

WILLIAM P. LEAR.

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