US2279151A - Panoramic radio receiving system - Google Patents

Description

April 7, 1942. M. WALLACE 2,279,151

' PANORAMIC RADIO RECEIVING SYSTEM Filed March 17, 1938 14 Sheets-Sheet 1 FIGJ I I o M Q INVENTOR.

o 8? MARCEL WALLACE BY V G XTERNEY Ap 7, 1942. M. WALLACE I PANoRAMIc RADIO RECEIVING SYSTEM 14 Sheets-Sh'et 2 Filed March 17, 1938 Fl C5. 7

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INVENTOR. MARCEL WALLACE 6. ATTORNEY April 9 M. WALLACE 2,279,151

PANORAMIC RADIO RECEIVING SYSTEM Filed March 17, 1938 14 Sheets-Sheet 3 IN V EN TOR.

BY 0 0 TTORNEY MAECEL WALLACE April 1942. M. WALLACE 2,279,151

PANORAMIC RADIO RECEIVING SYSTEM Filed March 17, 1938 14 Sheets-Sheet 4 30 SI 92 Wa4 m4 H.\/OLT TO INVENTOR. H 2 4 MARCEL WALLACE BY 6 d AY-TORNEY 7 April 7, 1942. M. WALLACE 2,279,151

PANORAMIC RADIO RECEIVING SYSTEM Filed March 17, 1938 l4 Sheets-Sheet 5 NORTH-SOUTH EAST- WEST Fl 6. IO

FIG. I Z 47 INVENTOR. MAIQC EL WALLACE I 06% 6 4M7 V ATTORNEY April 7, 1942. V M. WALLACE PANORAMIC RADIO RECEIVING SYSTEM l4 Sheets-Sheet 6 RECEIVER 7 CALIBRATED O SCI LLATOR C, C2 C3 A' INVENTOR.

HG 3G MARCEL WALLACE ATTORNEY AZ A' A5 FIGJB FIGSS M. WALLACE PANORAMIC RADIO RECEIVING SYSTEM 14 Sheets-Sheet 7 April 7, 1942.

Filed March 17, 1958 FIG/I7 10 T 42 AMPLIFIER L 1 ga l8 MOTOR AMPLIFIER ouTpuf 1 HIGH VOLTAGE l 27 I9 AMPLIFIER 26 25 22 L -58. i

I INVENTOR.

MARCEL WALLACE FIG. 15

I ATTORNEY M. WALLACE PANORAMIC RADIO RECEIVING SYSTEM Filed March 17. 1958 14 Sheets-Sheet 8 TO PLATE 9. 9 ac" vows 708* b FIG. 26

FIG. 25

INVENTOR.

MARCEL WALLACE April 7, 1942- M. WALLACE 2,279,151

PANORAMIC RAIQIO RECEIVING SYSTEM Filed March 17', 1938 14 Sheets-Sheet 9 II II II IN VEN TOR.

ATTORN April 7, 1942.

M. WALLACE V 2,279,151 PANORAMIC RADIO RECEIVING SYSTEM 7 Filed Mar 'ch 17, 1938 14 Sheets-Sheet 1o lira- El v 24 April 7, 1942. M. WALLACE PANORAMIC RADIO RECEIVING SYSTEM Filed March 1'7, 1938 14 Sheets-Sheet 11 TO DE T'EC TO R INVENTOR. MARCEL WALLACE ATTORNEY April 7, 1942. M. WALLACE 2,279,151

PANORAMIC RADIO RECEIVING SYSTEM Fild March 17, 1938 14 Sheets-Sheet l2 mid zed Q Waaace/ ATTORNEY 1N VEN TOR.

April 7, 1942. M. WALLACE 2.279.151

PANORAMIC RADIO RECEIVING SYSTEM g Filed March 17, 1938 14 Sheets-Sheet l4 W INVENTOR.

MA RC EL WALLACE G A okli fi Marcel Wallace, New

direct and mesne as signments, to Panoramic Radio Corporation, a corporation of New York Application March 1'7, 1938, Serial No. 196,520

r In France February 21, 1938 36 Claims.

My invention relates broadly to radio systems and more particularly to a panoramic system of radio reception.

One of the objects of my invention is to provide a signal receiving system for integrating the efiects of a multiplicity of simultaneously received signals and rendering the signals thus received visible in a manner whereby the relative characteristics of the several receiver signals may be readily compared.

Another object of my invention is to provide means in a radio receiving system for visually comparing the relative field strength of a multiplicity of transmitting stations received simultaneously in any prescribed area.

Still another object of my invention is to provide means in a radio receiving system for observing the characteristics of a multiplicity of signals simultaneously received over a predetermined and continuous band of frequencies for determining all signals operative within that band and comparing their relative strength and difference of frequency.

A further object of my invention is to provide a receiving system equipped with visual and acoustical indicating means and operative to sweep a band of frequencies adjustable at will for determining the characteristics of signals simultaneously receivable in a given area over any selected band or bands of frequencies.

A still further object of my invention is to provide a radio receiving system capable of analyzing the characteristics of. amultiplicity of signals receivable over several bands of fre'-.

quencies of adjustable width.

Another object of my invention is to provide a signal receiving system which may be readily installed on a moving vehicle, ship or aircraft for visually imparting to the observer a panoramic conception of radio signals receivable in the geographical area with respect to which the vehicle, ship or aircraft is moving for providing the observer with a sense of security as to direction of movement of the vehicle, ship or aircraft and the location thereof with respect to a plurality of signalling stations.

Still another object of my invention is to provide a radio receiving system particularly adapted for operation on aircraft which will enable an observer to visually and aurally compare the characteristics of a plurality of simultaneously received signals to provide the pilot with accurate information for guiding the aircraft toward or away from or with respect to a multiplicity of radio range beacons, broadcasting stations or other signalling stations.

A further object of my invention is to provide a receiving system particularly adaptable for operation on an aircraft in cooperation with a beam network system as set forth more fully in my Patents 1,802,688, dated April 28, 1931, for Beam network system; and 1,878,737, dated September 20, 1932, for Radio beacon system, by

which the pilot of an aircraft may be informed of signalling conditions existin'g simultaneously at any given position on the airways.

A still further object of my invention is to provide a signal receiving system which is operative to visually indicate a plurality of signals in any definite region of a predetermined band of frequencies and consequently enable an observer to determine his position in relation to the sources of emitting energy, thereby providing a sense of security and improving the confidence and morale of the pilot and aircraft passengers who are often obliged to fly under conditions of poor visibility.

Another object of my invention is to provide that type of visual indicating system for aircraft piloting which is particularly efficient in indicating differences, between parasitic signals or interfering sources of signal energy which have no function in a piloting system and the actual sources of signal energy which are to be depended upon for aircraft navigation, thus avoiding errors in piloting which have in the past resulted in grave consequences. Still another object of my invention is to provide a signal receiving system for aircraft which is effective 360 around existing radio range beacon stations, thereby increasing the usefulness of radio range beacon stations in aircraft piloting which normally provide information for pilots only in restricted paths which are the equisignal zones of the usual radio range system.

A further object of my invention is to provide (a visual indicating system for aircraft navigation in which a similitude map of the geographical area over which a plane may fly may be correlated with the characteristics of signalling energy simultaneously receivable within the area defined by the limits of the similitude map for continuously informing the pilot of the geographical position of the aircraft.

A still further object ofmy invention is to provide a system of aircraft navigation in which the usefulness of the available frequency spectrum may beconsiderably increased by reason of the complete use of the band as a continuity without the need of providing for wasteful gaps, and also by reason of the characteristics of the visual indicating system employed by my invention for effectively distinguishing and comparing the characteristics of emitted sources comprised on the whole of the band, and consequently on closely adjacent frequencies.

Another object of my invention is to provide a signal receiving system having means for periodically tuning the signal receiving system over predetermined bands of frequencies and synchronously operating the control circuits of a cathode ray oscillograph connected with the output of the signal receiving system for visually indicating the characteristics of the signalling energy simultaneously receivable over the bands of frequencies over which the receiving circuit is periodically tuned.

Still another object of my invention is to provide a panoramic radio compass system having visual indicating means operative in correlation "to the radio compass system for visually indicating the angular relation of a mobile body carrying the radio compass system, with respect to the location of a plurality of stations whose signals are simultaneously received.

A further object of my invention is to provide compare the characteristics thereof in combination with aural receiving means, terconnected between of a plurality of stations whose characteristics are visually observed.

Other and further objects of my invention reside in various combinations of circuits and instrumentalities and apparatus used in connection with the circuits of my invention, as set forth more fully in the specification hereinafter following by reference to the accompanying drawings in which: I

Figure. 1 is a diagrammatic view of one form of principles of my invention;

indication as'well as aural two sets of ima the generator illustrated in Fig. 8; Fig. 9 is a schematic view showing the arrangement of a multiplicity of beacon stations with which the panoramic receiving system of my invention is adapted to coact; Fig. 10 is a plan view one manner of coordinating means for with the screen of the oscillograph a similitude area over which a mobile body the panoramic system of my in- Fig. 11 illustrates a panoramic visual I indication of one 'of the stations visually indicated and also with means to show on the screen which one of the stations is being rendered audible; Fig. 18 shows mechanically actuated switches for operating the control circuits of the oscillograph synchronously with the operation of the periodically operated tuning means of the frequency variation of the receiver so as to obtain ges on the screen of the oscillo andthe operation of the periodically operated tuning means of the panoramic receiver; Fig. 24 illustrates a panoramic receiver in which the source of energy which operates the radio receiving system is also employed for operatin the drive means for synchronously varying the control circuits of the oscillograph and the periodically operated tuning means of the receiver; Fig. 25 illustrates another form of generator which may be employed for obtaining the control potential for the oscillograph in the panoramic receiver; Fig. 26 illustrates characteristic curves showing the changes of control potential for the oscillograph as compared to the changes in capacity in the periodically operated tuning circuit of the panoramic receiver; Fig. 27 shows characteristic curves of control potential which may be obtained by modifying the shape of the armature and/or pole'pieces shown in Fig. 25 so as to compensate for a non-linear frequency variation of the periodically tuning means of the panoramic receiver; Fig. 28 is a schematic dia-- gram showing the manner of coordinating the special form of generator illustrated in Fig. 25 with the control circuits of the oscillograph whereby the characteristics of a part of the frequency band over which the panoramic receiver is periodically tuned are visually reproduced on one axis of the oscillograph and the other part of the frequency band is reproduced on the other axis of the oscillograph; Fig. 29 shows the time correlation between the variation of frequency of the periodically tuned receiver, variation of voltage of the controlling elements showing the time when this voltage is suppressed and the moments when the connections between two of the controlling elements of the oscillograph are changed; Fig. 30 shows one method of coordinating the movement of the direction finder antenna of a radio compass receiver with the mounting of the oscillograph connected with the circuits of a radio compass receiver for correlating the angular displacement of the oscillograph screen with respect to the angular movement of the direction finder antenna; Fig. 31a. Fig. 311), Fig. 310, Fig. 31d and Fig. 31e illustrate the visual indications reproducible on the screen of the oscillograph as the angular relation of the oscillograph screen and direction finder antenna is' varied by some such correlation method as illustrated in Fig. 30; Fig. 32 illustrates a polar diagram of. either a radio range system or of a phase-reversing antenna-loop receiving system. and schematically shows the manner of visually reproducing on the oscillograph screen the signalling energy as illustrated more particularly in Figs. 31a, 31b, 31c, 31d and 31e; Fig. 33 illustrates an example of the very large number of bearings which may be taken by an observer using the panoramic system of my invention over .a predetermined course which number of bearings greatly exceedsthe possibilities obtainable in existing systems; Fig. 34 is a schematic diagram showing a panoramic radio compass embodying the system of my invention; Fig. 35 is a fragmentary view showing the characteristic curves of one station receivable on the screen of the oscillograph of the panoramic radio compass as a plane equipped with the radio compass system of Fig. 34 swings to the right or left with respect to an emitting source; Fig. 36 shows the manner in which on course or off course' signals are reproduced on the oscillograph screen of the panoramic radio compass receiver from signals of radio range,

beacons; Fig. 37 shows a multiple band panoramic receiver whereby two bands of frequencies of adjustable width appear on separate portions of the screen of the oscillograph; and Fig. 38 shows the arrangement of a series of marker beacon signals disseminated along a radio range equi-signal beam, each having different frequency characteristics so as to give continuous position indications to an observer flying along that beam and equipped with such a panoramic receiver.

My invention is directed to a panoramic radio receiving system. By the term panoramic, I refer to the ability of a radio receiver to impart a simultaneous conception of all of the signals receivable in a given area for obtaining therefrom a sense of the relative position of the receiving station with respect to the sources of all of the signal emitters. In prior radio systems, such as the finding of signalling stations, information service, aerial navigation, guiding of planes and ships, etc.. it has been necessary to be on the look-out over a wide band of frequencies in order to realize the existence of certain transmissions or for comparing these transmissions in amplitude as well'as in frequency. With the ordinary radio receivers, one must tune these receivers successively on the frequencies of each of the stations to be received. The comparison of signals thus received is difficult.

In order .to facilitate this comparison the combined use of a plurality of radio receivers has been proposed but this solution has little practical value and becomes still less so when it is necessary to receive simultaneously the signals for a large number of stations. This inconvenience is particularly grave in the case of aerial navigation when increase in weight is to be avoided. My invention accomplishes objects never heretofore obtained in the art by imparting to the observer at a receiving station equipped in accordance with my invention a sense of security with knowledge of the relative position of the receiving station with respect to all of the sources of signalling energy over a given frequency range in the vicinity of the receiving station.

My invention concerns a radio receiver for the simultaneous reception of a plurality of signals. An apparatus whose characteristic is that its instantaneous band pass which corresponds to its resonance curve, periodically moves in a continuous manner over a band of frequencies of a width adjustable according to the wish of the operator between definite tuning limits, so that the operator perceives simultaneously the signals emitted by a plurality of radio stations in the chosen band of frequencies. The radio receiver is combined with means giving for the chosen band of frequencies. over which the resonance curve of the set moves periodically, a visual representation of all the signals received at their respective amplitudes. The means of visual representation are constituted by a .cathode ray oscillograph tube combined with a source of voltage and automatic means causing an alternate sweep of the screen of this cathode ray tube in synchronism with the periodical variation of the instantaneous .band of reception of the frequency bands chosen.

According to another method of carrying out my invention the width of the band frequencies covered by the periodical sweep can be varied by means modifying the maximum electric value of the tuning element which is submitted to the periodical variation corresponding to the alternating movement of the instantaneous band of reception. 'Ifhe'invention'concerns not only a radio receiver capable of giving a. visual represen- 534, granted December tation of a multiplicity of signals but also a system oi aerial navigation characterizedby a combination of a network of radio stations whose frequency is determined by their geographic position and of a mobile body such as an aircraft carrying such a receiver, said receiver producing visual indicationsof the frequenciesreceived i6? enabling one to determine the position of the plane in relation to one or several of the transmitting stations. .Ace of the invention, the system of visual indication can be combined with a set of geographic maps of the territory over which the aircraft flies. My invention also contemplates the synchronized control of a cathode ray oscillograph with means for periodically varying the frequency range of a receiving system for simultaneously observing the signals receivable in a given area over the frequency range over which the receiver is periodically tuned. I provide especial form of circuit for predetermining the range over which the receiver is periodically tuned so that therecelver may be variably tuned over any portion of a selected frequency range or over an entire frequency range at the will of the operator.

The invention includes circuits associated with the oscillograph by which my receiver can be used as a panoramic radio compass or panoramic direction finder, by this term being understood the ability of such a receiver to give simultaneous angular indication to a plurality of stations. In one of the applications of my invention to radio compasses, I provide means for coordinatingthe movement of the direction finder antenna with an oscillograph whereby a more definite visual indication is given of the relativeposition of the moving body and the signal emitters in the area surrounding the moving body.

My invention further contemplates means for visually indicating on the oscillograph screen the relative positions of simultaneously operating emitters in the vicinity of the receiving station on both horizontal and vertical axes of the oscillograph screen and thus enlarging the vision of the observer and increasing the sense of security of the observer at the receiving station. BM invention is further characterized by the provision of means associated with the Oscillograph tube for indicating. on the oscillograph screen reverse images of the signals simultaneously emitted by the various transmitters in the vicinity of the receiving station for. enabling the observer to more accurately judge the characteristics of each of the signals which are received. With such a receiver we can use specialnetworks of transmitters which could indicate more accurately the position of the mobile body ihielationtmsuch' special transmitters for example a beam network system such as described in my United States Patents 1,802,688, granted April Beam network system; 1,878,737, granted September 20, 1932, for Radio beacon system;"2,063,-

8, 1936, for Automatic piloting system; and as set .forth in my copending application Serial No. 102,798, filed September 26, 1936. for Position indicator. By this method of reception we are enabled to use circuits of extreme selectivity such as can be obtained with crystal filters and the lik and this aifords the possibility of using a much larger number of stations within a given frequency band.

In the form of my-invention wherein a graphic representation of the characteristics of the received signals is obtained visually on both thevertical and horizontal axes of the cathode ray ording to one characteristic 7 vertical axis of the screen 0 28, 1931, for ()0 screen, I employ an arrangement on the central drive shaft extending from the motor that drives the tuning system for periodically tuning the signal receiving circuit which includes in addition to the commutator device heretofore explained in connectlon with the operation of the control circuit of the oscillograph, a sweep voltage special wave form generator and in association therewith a cam actuated mechanism for alternately reversing the connection of sets of deflecting plates with respect to the signal receiving circuit; that is, from vertical to horizontal and viceversa. The sweep volta erator reverses the direction of current supplied to the control circuit of the cathode ray oscillograph every of the rotation. The sweep voltage special wave form generator is synchronized with the rotation of the rotors so that the minimum voltage occurs at the moment when these rotors are either corresponding to minimum capacitie's ormaximum capacities of the rotating condensers. The commutator serves to periodically lay-pass the output of the generator so that for of the tuning range there is no energy impressed upon the control circuit of the oscillograph. The cam. arrangemenfcloses or opens a reversing switch for every 90 rotation of the shaft corresponding to the points of minimum and maximum voltage 0 special wave ,form generator. It can be seen that during 90 rotation, the signals received on one-half of the tuning range of the rotating condenser will be seen on one set of plates. whether vertical or horizontal, andin the next half of the tuning range on the other set of plates so that the visual representation on the screen of the oscillograph will show the stations comprised between frequencies F0 to F1 vertically disposed, and the stations comprised between F1 and F2 horizontally disposed. This results in a broad visual path over which numbers of simultaneously received frequencies may be observed either on the horizontal axis" or on the f the osciliograph. Such an arrangement also enables one frequency band to be scanned and observed on one axis of the screen of the cathode ray tube and a different frequency band scanned and the frequencies being received thereover observed on the other axis of the screen of the cathode ray tube.

In carrying out my invention, I employ various forms of tuning means in the si circuits as, for example, rotary condensers having laterally adjustable stator plates and wherein the position of the laterallyadjustable stator plates with respect to the rotor plates is selectively adjusted with respect to the periodically mevinm plates. I may also employ means for varying tlfe'transversespecial relation of the stator plates for adjusting the capacity relationship with respect to the periodically driven rotor plates. Either of these methods and 0th: r methads may be employed for controlling the frequency range over which the periodically controlled tuning system is adjustable. The system of my invention is particularly adapted for selective aural reception of any one of a'plurality ofsignals visually received with means for identifying the particular signal received. That is to say, a particular signal may be received aurally while a multiplicity of signals are being received visually and the wave forms of the emitted frequencies over the band of frequencies over which the receiving system is periodically tuned readily observed. i r

ge special wave form gen-W f the said sweep voltage I The system of my invention provides visual indicating means which quickly informs the observer as to the relative position of the receiving station with respect to the sources of signalling energy which are being simultaneously received. The indication provided on the cathode ray oscillograph screen indicates the sources of signalling energy either to the right or left of the receiving station or forward or in the rear of the receiving station. The indication is given by the form of the received signal which appears both above and below either of the axes of the screen and showing by their relative amplitudes the relative position of the receiving station with respect to the emitting sources.

My invention also contemplates'the operation of a panoramic receiver over a multiple number of bands of frequencies which may be seen simultaneously over different portions of the screen of the oscillograph, that is, the observer may be informed as to frequencies emitted in the long wave band and be simultaneously informed as to frequencies emitted in the short wave band.

The panoramic radio reception applied to \radio compasses adds to these the advantage of permitting instantaneous information as to the direction to a plurality of stations. It eliminates the necessity of tuning the radio for each station with consequent loss of time and false indications. when the stationson which observations are being made are quite near, when the most accurate information must be had, it is absolutely necessary to obtain the direction towards several stations simultaneously in order to be of real use.

Many combinations of antennas are possible. The method used is to obtain two different reception patternscontaining the'information required and applying each pattern, one on each side of the median line of the screen. These patterns can be used by either switching from one type of antenna to another type or by the use of two antennas used separately or in an additive or subtractive manner. One preferred method is the use of two directional loops forming an angle and switching them in the circuit Due to the high speed of the plane,

posed. By comparing each signal with its opposite image, produced by the other loop, the

observer notes whether these signals are equal,

in this case meaning that the loop is oriented in an equi-potential zone, or whether one is stronger than the other, thus showing the observer which of the stations are to the right or to the left. I

The same result can be obtained with the use of a combination of a non-directional antenna and a loop, used simultaneously but with means to turn the phase of the loop by 180 for'every alternating horizontal sweep.

When using the system in reference to a similitude map of the area over which a mobile body operates, either a two dimensional gradual frequency coverage of a territory or a one dimensional gradual variation maybe utilized.

In the latter case a simple distance calibrated chart can be used instead of a .two dimensional map. Assuming that a radio range beacon, such as-is used today, sends a signal directed from New York to Philadelphia and that on this beam tion proportional to distance from a predetermined point of origin. If, for example, the frequency band periodically covered is adjusted so as to reproduce on the screen four such markers, and a similitude map made to the size of the screen is used, the navigation of the aircraft is greatly simplified. It is clear that as the craft approaches one beacon, the visual indication will increase in amplitude as the other over which the craft has passed will decrease in amplitude. The passage over each marker on the territory flown may be correlated on the similitude map, on which each marker is indicated, so that as the last marker is passed and the tuning of the revertical lines, as only one distance coordinate would be used instead of two.

My invention facilitates navigation of a mobile body alongnarrow passages, sometimes long and winding, under conditions of poor visibility such as mountain passes, landing fields, etc. With such panoramic receiver continuously sweeping a band of frequencies assigned for collision prevention, an observer will be given adequate warning which can be simultaneously audible and visual of approaching danger by receipt of specially created warning signals which may come from one or a plurality of danger spots.

Another object is to avoid collisions of moving craft, between themselves, and with dangerous obstacles.

Dangerous passes or narrow passes, such as mountains, landing fields, etc., may be marked with a series of stations, preferably on two different and'adjacent frequencies so as to create an equi-potentia'l path along the route desired. In general, very low power is needed, varying between 10-100 watts when short waves are used. As the increase of field strength from a station is universely proportional to the square of the distance and when quite near approaching the cube of the distance, it can be seen that any station will give a substantial signal providing one is near enough. The power is so adjusted as to creat an equi-potential zone between, for example, Fi F2. The pilot will watch for the two signals F1 and F2 and will keep them of about equal amplitude. Stations are located in the dangerous spots, and, the pilot can see and hear at once when he approaches one of these spots and may steer away accordingly. Danger spots can be indicated always by certain frequencies which are assigned to give collision warnings. All moving craft could emit a signal on a given frequency in that band, which frequency can vary according to the position of the craft, and the power of the signal may be determined by its size and speed, enabling other craft to steer .energy is a battery l may employ for the high] voltages required by the tube elements, a small generator and the shaft of this will serve for the rotation of the tuning condensers as well as for the source of, synchronized sweep voltage.

plete disappearance of strength The weight of transformers and additional motor is thus saved.

The whole apparatus can be built very com- I ceived at that moment in that particular posii tion of the plane. As each of these beacons sends periodically two signals at a certain angle to each other, these signals periodically vary in amplitude according to which one of the two is received.

same amplitude. If the receiver is on a n zone for one of the instantly recognize this by the periodical'comthe signal. If the receiver is in an intermediary zone, the observer will be able to recognize this also by the periodical flicker oi the signal.

I am thus enabled to increase the usefulness of existing radio range beacons. Also the possibility of comparing the variation of the signal of several radio ranges at the same time has very great advantages. The observer can also recognize when a plane is crossing various beams such as markers determining approaches to cities or airports, plane passes over the silence cone of any station, by the sudden disappearance and reappearance of a very powerful signal.

With such a receiver, it becomes unnecessary to carry several receivers for various purposes, such as heretofore suggested, and it also becomes oscillator stage combined in the tube I12 following by an intermediate frequency amplifier stage comprising tube 29 followed by a detector and the first audio frequency amplifier stage including tube 32 and the final audio frequency amplifier stage including a source of alternating current with the aid of rectifiers 52 and 53.

beams, the observer will and when the are rotated by the motorls the power supply to which being controlled by a. switch 20. This motor-can be advantageously the same as the one generating the electric current usually used on board of a plane. The limits of the frequency spectrum which can be received by this apparatus can be modified on one hand with the aid of the variable condensers l and 2, each of these being connected in parallel with one of the rotating condensers 3 and 4, and on the other hand. with the aid of the variable condensers 5 and t which are connected in series respectively with each of the rotating condensers '3 and 3.

The resultant minimum capacity of a tuned circuit which includes the tuning elements H, 3 and 5, can be modified with the aid of variable condenser E for a given position of condensers 3 and 5 corresponding to minimum capacity for these condensers.

The continuous rotation of thecondensers 3 and t which are driven by the motor it gives a variation of capacity which is represented by the lines a and a of Fig. 2 for a complete revolution of the rotors. In this drawing the lines a and a are straight corresponding to a straight line capacity variation for these condensers.- This does not mean that my invention requires such condensers, for on the contrary, other forms of variation may be preferred for special uses.

In this diagram the'antenna M3 is inductively coupled with the first tuned circuit whose tuning elements are constituted by the variable condensers i, 3 and 5, this circuit being connected to the control grid it of the tube l2. The local oscillations for the conversion of the frequency are generated in the usual manner in a circuit whose tuning elements are constituted by the variable condensers 2, s and 6, this circuit being connected to the grid is of the tube 82. The width of the band of frequencies covered by the periodic sweep is made variable by means modifying the maximum to minimum capacityratio of the tuning element which is subjected to the periodical variation corresponding 7 to this periodic displacement.

The variable condensers 3 and s are provided with rotors which can turn fully 360. The two rotors which may be connected on the same shaft The maximum capacity proportional to ordinate point M, is obtained when these rotors have entered completely between the fixed plates of the stator..

The periodical displacement of the instantaneous band pass,, which is determined by the curve of resonance of the receiver, is obtained b the periodical variation of capacity of condensers 3 and 1 between a value which is pracganged together.

If the maximum capacity C of the rotating condensers 3 and 6 is equivalent to'that of each of the elements 5 and 6, which for example have their rotors completely enmeshed with the stator plates, the maximum capacity resulting for each of the groups of the series 3-5 and ti is equal to 0/2.

For any other position of the rotors of condensers 5 and 6 the maximum capacity of each group 35 and 41-5 becomes less than (1/2.

I employ various methods for adjusting the maximum capacity of the groups of elements 3-5 and L6 and consequently of the width of the frequency band periodically covered by the band pass of the set, ateach turn of the rotor blades of condensers 3 and s rotated by motor 58'. Fig. 1 illustrates one arrangement and Figs. 13 to 16 show other arrangements.

If the maximum capacity of'the variable conoscillograph tube I7 is combined with the radio a cathode ray'

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