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2,510,299 PULSE-ECHO TESTING SYSTEM Charles W. Schramm, Nutley, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 1, 1945, Serial No. 570,885 ' 8 Claims. (Cl. 343-5) 1 2 This invention relates to testing systems and extent dependent upon the intensity of the more particularly to apparatus and systems for emitted pulse and the proximity of a resonance testing object locators. frequency of the chamber to the frequency of An object of the invention is to facilitate ad the oscillations of the transmitter pulse. Upon justment and tuning of the various elements of cessation of the impulse, the energy which has an object locator system of the type which uti been stored up in the electromagnetic ?eld within lizes the interval between transmission of a pulse the resonant chamber serves as a source of oscil of electromagnetic waves and the receipt of the lations. Some of this energy is returned by the pulse echo as re?ected from a remote body. resonant chamber over the path by which it ar Before an object locator is put into use for 10 rived to the pick-up device or dipole, which new searching or for distance-measuring purposes, it functions as a radiating transmitting element is necessary to make a routine test to insure that from which oscillation energy may be transmitted it is functioning properly. Such a test should to the radio receiver of the object locator. determine that the local radio receiver which is A strong internal electromagnetic ?eld may be to receive the echo pulse is in tune with the local 15 built up by resonance within the resonance cham transmitter from which the original pulse was ber if the chamber has, a very high oscillation emitted. It should also determine that the cir persistence or high Q, as it is usually termed. cuits both of the radio transmitter and the radio This corresponds to a condition of high selec receiver are otherwise in such adjustment that tivity in which the chamber responds effectively a reasonably good echo will be indicated from a 20 only to electromotive forces within a compara target within normal range of the apparatus. It tively narrow frequency range. As it may happen should further show that the cathode ray oscillo that the transmitter oscillation frequency drifts graph (CRO) apparatus is adjusted to give a over a relatively wide range, it is desirable to satisfactory visual indication. However, in the provide the narrow range resonance chamber case of object locators of mobile type such as 25 with a tuning device which will permit the region those on ships or airplanes, it may transpire that of its resonance response to be varied. In most at the time for testing the equipment no con applications of this apparatus it is desirable to venient target is available. Airborne object loca place the resonance chamber in close physical tors are generally unenergized until some time proximity to the radiating antenna of the object after take-oil’ of the aircraft because of the large locator and within the zone to which that an electrical drain on the plane's power supply sys tenna radiates pulse energy. This frequently re tem. An interval elapses after the power is quires that the resonance chamber be placed in turned on for warming the equipment, during the nose of the airplane or beneath a wing, or in which adjustments may be required to keep the some other location remote from the operator of receiver in tune with the transmitter. After ade the locator apparatus. It has therefore been quate frequency stability has been reached a found desirable to provide the resonance chamber check of the range capabilities is desirable. Dur with a remotely controlled motor-driven tuner ing all this time, the airplane may have traveled which causes its tuning to vary over the entire far enough, particularly if headed out to sea so expected range of frequency variation of the ra that real targets are no longer discernible. For 40 dio transmitter. The tuner should operate slowly such circumstances it has been proposed to pro enough to permit the exploration of each azi vide a so-called “phantom target" which may muth direction while the scanning devices change constitute an adjunct of the object locator or the azimuth direction, but it should operate rap may be placed at some position close to the 10 idly enough to enable the necessary tests to be cator to serve in lieu of an actual target. Such 45 made with a minimum of loss of useful search a phantom target may comprise a resonant time on the part of the object locator. chamber of conducting material having a high Two somewhat different types of cathode ray resonance persistence or high Q. An energy pick oscilloscope may be employed to portray the re up device such as a‘small dipole may be located ?ected pulse which is the received echo of the within the ?eld of the pulses transmitted from 50 pulse sent out from the radio transmitter. If the the radio transmitter and may be coupled by an scanning device is to operate over a small arc energy transfer path to the interior ?eld of the of azimuth, a type B oscilloscope, as for example, resonance chamber. During emission by the ob that disclosed in United States Patent No. 2,422, ject locator transmitter of a brief transmitted 182, issued to N. W. Bryant on June ‘17, 1947, is pulse the resonant chamber will be excited to an convenient. Such an oscilloscope indicates the 2,510,299 3 4 receipt of the echo by a luminous spot having an per second. Since the pulses or microwave trains ordinate corresponding to the distance of the emitted by the radio transmitter of the object 10 re?ecting object and an abscissa corresponding cator are ordinarily of a relatively high rate, as to the azimuth angle of the re?ecting object. If, for example, 2,000 pulses per second, the azi however, the scanning device is to operate over muthal drift or sweep of the oscilloscope cathode the entire horizon, a so-called plan position indi ray beam is su?lciently slow that it may to a cator is preferable. This differs from the type rough approximation be considered as substan B oscilloscope in that itis provided with a circu tially stationary at each of the azimuth positions. lar screen and that polar rather than orthogonal The radiated pulses occur in such rapid sequence coordinates of the luminous spot indicate the 10 that for practical purposes it may be considered distance and direction of the re?ecting object. that one is sent out for each azimuthal direction. Distance is, of course, represented by the posi Assume that the radio transmitter and the radio tion of the spot along a radius from the center receiver are properly energized, the scanning de and azimuth angle is represented by the angular vice is in operation and the resonance chamber position of that particular radius. Both the type ll of the phantom target is within the zone to which B oscilloscope and the plan position indicator are energy is radiated from the transmitter. As soon well-known devices in theart of object location. as the scanning apparatus arrives at the position A phantom target resonance chamber ener in which energy from the radio transmitter is gized by an impulse from the radio transmitter being received from the pick-up device associated will begin to return energy to the radio receiver with the resonance chamber, the electromagnetic immediately upon the cessation of the energizing _ field within the resonance chamber will begin to impulse. This will give rise on the oscilloscope build up rapidly, provided that the resonance to a luminous spot corresponding to zero distance. chamber is at that moment in tune with the in_ As the resonance-chamber continues to return coming oscillations. Since the resonance fre energy to the radio receiverI there is built up on quency of the resonance chamber is varied cycli the screen of the oscilloscope a succession of cally by the motor-driver tuner, it will attain the spots which merge into a vertical trace or spire in sought-for transmitted microwave frequency once the case of the type B oscilloscope or a radial spire while increasing in frequency and a second time in the plan position indicator. The longer the while decreasing in frequency. At these two in oscillation of the resonance chamber persists the 80 stants spires will appear on the cathode ray oscil longer is the trace or spire produced thereby. loscope associated with the object locator receiver. Accordingly, the height of such a spire is an in The traces will accordingly appear in a few sets dex of the overall effectiveness of the‘ object 10 of pairs, one pair representing each tuning cycle cator system in building up an electromagnetic of the resonant chamber and the amplitude of ?eld within the resonance chamber and receiving the traces increasing from the instant when the and indicating at the oscilloscope energy returned position of the pick-up device permits it to be from the resonance chamber. e?ective and thereafter passing through a maxi A number of factors are involved in the produc mum and ?nally back to zero at the point where tion of a spire or trace on the oscilloscope. Of the position on the take-up no longer permits it course, the radio transmitter must be active so 4° to be effective. This pattern reoccurs as long as as to emit a pulse of microwaves which the res the test is continued, but it is a moving pattern onance chamber may receive and later return to since the points at which the tuning of the reso the radio receiver. The position of the pick-up nance chamber agrees with the transmitter fre element of the resonance chamber must be within . quency bear no definite relation to the angular the zone to which energy is radiated by the trans. 45 position of the scanning device. mitting antenna. At some time when a pulse According to the present invention, the tuning of microwaves is being radiated from the radio of the resonance chamber and the scanning mo transmitter, the instantaneous resonance fre tion of the radio transmitter-antenna are so re quency of the resonance chamber must agree with lated by a mechanical coupling between the tun the frequency of the microwaves. The radio re 50 ing device and the scanning device that the pat ceiver must also be tuned at approximately the tern tends to remain stationary. This gives rise ' frequency of the microwaves which it is to re to several advantages among which are ability to ceive from the resonance chamber. From what set the mean resonance frequency of the reso has been said, it will be apparent that any im nance chamber at the transmitter frequency; provement in the adjustment of the radio trans 56 the ability to quickly determine whether or not mitter or its outgoing circuit to increase its ef the transmitter frequency is changing relative ?clency will increase the energy received by the to the tuning of the radio receiver and a simpli resonance chamber. Any improvement in the ef ?cation of the entire system required to tune the ?ciency of the energy pick-up of the resonance object locator transmitter while it is on the chamber or its connections to the chamber will 60 ground. In cases where the trace representing likewise increase the energy received by the res an actual target tends to be faint, the fixing of onance chamber and the energy which it returns the pattern tends to widen the trace-and brighten upon cessation of the energizing pulse. Any im it, thus minimizing errors. Moreover, since the provement in the tuning of the radio receiver or apparatus may be so aligned at the outset as to of its gain, or noise level. will likewise increase 65 produce a pair of traces from the phantom target the length of the visible portion ofthe trace on which are nicely centered with reference to the the oscilloscope. It is therefore possible with the azimuth zero, it is possible to check the position apparatus of this invention not only to determine of the scanning device or the “spinner," as it is if the object locator transmitter is active and called, with reference to the ?eld of the oscillo that the locator as a whole is operative, but also 70 scope. This apparatus also makes it possible to to determine what adjustments in each of the secure consistent results irrespective of the speed individual components of the entire system are of the scanning device so that a single type of helpful in improving its efficiency. apparatus may be utilized for various scanning The azimuthal scanning ordinarily takes place speeds and results may be made fairly independ at a relatively low rate, as for example, one cycle 75 cut of variations in the scanner speed. 2,510,299 5 6 In the drawing: excursion oi’ the tuner plunger I‘! from its upper Fig. 1 illustrates diagrammatically a system in most position to its lowermost position the nat cluding a radio object locator and a phantom tar ural resonance frequency of the resonance cham get associated to form a test system; ber I6 traverses the entire band of frequencies Figs. 2, 3 and 4 are graphs to aid in the explana which the radio transmitter I is capable of trans tion of the operation of the system of Fig. 1; mitting. As indicated in the drawing, the base Fig. 5 is a schematic of an embodiment of the of the motor I8 is supported by a framework invention in an airborne structure; ‘ slung from the resonance chamber I B and pro Fig. 6 is a plan view of the cam and cam fol vided with screw adjusting devices to vary the lower of Fig. 5; normal position of the motor I8 with reference to Fig. '7 is a graph explanatory of the operation the resonance chamber I6 so as to permit a man of the apparatus of Fig. 5: ual shift of the band of resonance frequencies Fig. 8 is a partial line diagram of apparatus and through which the device I6 may be tuned. a partial circuit diagram of the indicator controls Assume that the object locator has been ener of a modi?cation of the system of Fig. 5; and gized and that the key 2| is closed but that the Fig. 9 shows graphs of the performance of the output of the transmit-receive switch 6 is, con apparatus of Fig. 8. trary to the disclosure of Fig. 1, connected by an Referring to Fig. 1, the radio object locator invariable conducting circuit to the coaxial line I3 comprises a radio transmitter I for producing os so that the successive pulses received from the cillations of extremely high frequency, as, for ex 20 transmitter I by the resonance chamber and re ample, l to 30 centimeters’ wavelength in. re turned by it to the receiver 1 are of equal in sponse to short pulses of energy supplied to it by tensity. Assume further that the tuning of the the pulser 2. The output of the transmitter I may resonance chamber I6 is being varied in a gener be connectedv to a rotatable searching antenna 3 ally sinusoidal manner between the frequencies comprising a dipole 4 associated with a directive F1 and F2 as indicated in the graph ‘of Fig. 2. If' parabolic re?ector 5. The antenna dipole 4 is con the frequency of the pulse oscillations sent out by nected to the output of the transmitter I through transmitter I is at an intermediate point F3, the a transmit-receive switch 6 which may be of the varying frequency resonance chamber I6 will type disclosed and claimed in the application agree in frequency with the incoming oscillations ’ Serial No. 474,122, ?led January 30, 1943, for and will build up a strong internal ?eld and send Transmitting and receiving circuits for wave a return pulse back to receiver 1 at instants cor transmission systems, by A. L. Samuel, the func responding to T1, T2, T3, and T4. respectively. If tion of which is to e?ectively connect the trans the receiver 1 be in substantial frequency agree mitter I and the radio receiver 1 of the object ment with the transmitter I, these echo pulses re locator in alternation to the dipole 4. During an turning from resonance chamber I6 will appear energy pulse from the pulser 2 which may be of a on the screen of cathode ray oscilloscope 8 when microsecond’s duration, transmitter I produces this apparatus is a type B oscilloscope, as the oscillations for a corresponding period and im equal height spires P1, P2, P3, and P4, illustrated presses them upon switching device 6 from which in Fig. 3 of the drawing, in which the coordinates they are transferred to the dipole 4 and direc 40 or heights of the spires represent the effective tively radiated thereby. During the pulse, the de echo period or ring time of the resonance cham vice 6 serves effectively to disable the connection ber I6 and the abscissae represent position in the to radio receiver 1 to such a degree as to protect it time cycle or scanning position of the rotatable and its associated apparatus including the cath searching antenna 3. ode ray oscilloscope 8 from inordinate overloads. In the actual searching operation, instead of Upon cessation of the pulse, the device 6 returns the constant height spires of Fig. 3 of the in to its original condition and freely permits energy invariable connection which has been assumed of microwaves incoming to dipole 4 to pass to the between the transmitting circuit and the pick radio receiver 1 while maintaining the impedance up circuit I I,'there is a directive pattern, as indi presented by transmitter I too high to seriously 5.0 cated by Fig. 4. Up to the point in which the attenuate the incoming energy. The initiation of field of the energy transmitted from antenna, 4 a pulse by pulser 2 serves in a manner well effectively includes the pick-up antenna II, no known in the art to initiate a vertical or radial spires will appear on the cathode ray oscillo time sweep as the case may be in the cathode ray graph. As the directive searching antenna 3 ap oscilloscope 8. 55 proaches alignment with the ?xed directive pick The dipole 4 and the re?ector 5 of the searching up antenna, the spires increase in height to a antenna 3 may be mounted for azimuthal scan maximum when the transmission is most effective ning rotation or oscillation upon a suitable shaft and thereafter decrease. The change in height 9 driven in rotary or oscillatory motion by a of the spires from each pair to the next succeed motor I0. , ' 60 ing pair indicates the change in the strength of The phantom target may comprise a dipole the ?eld to which the pick-up antenna II is sub pick_up II associated with a directive parabolic jected as the searching antenna 4 swings in di re?ector I2 and connected to a coaxial line I3 rection toward and away from it. which extends to a circuit closer l4, shown dia Whatever the frequency of the transmitter, grammatically as of the ordinary electromagnetic 65 so long as it remains at some point intermediate relay type. When the circuit closer is closed, it the limiting frequencies F1 ~ and F2, there will connects the coaxial system I3 to a coupling loop be two effective times of energization of the res- ’ I5 projecting within a resonance chamber I6, onance chamber I6, one corresponding to that which is provided with a variable position plunger in which the tuning piston I‘! is moving upward tuner I‘! driven in vertically reciprocating manner 70 and the other corresponding to the same posi by a piston rod and crank connection operated by tion of the piston I ‘I when it is moving down a motor I8 in circuit with a winding I9 of the cir ward. The responses of the resonance chamber cult closer I4, a source 26 and a normally open I6 therefore occur in pairs, one pair for each cycle key. 2|. The resonance chamber I6 and its tuner of the movement of the tuning piston. The sepa I‘! are so designed and adjusted that during the 75 rations in time between the pulses of the same 2,510,209 7 ‘ - pair and between pulses of contiguous pairs are high speed with reference to the time cycle of the equal when the frequency of the transmitter I scanning device, in order to insure that the en-, and the mean frequency of the resonance cham tire tuning range be covered a-number of times. ber l8 coincide. If the transmitter frequency One reason for this is that in the endeavor to ob‘ changes to some other frequency, as, for exam tain optimum adjustment of the apparatus the ple. F4, pulses P1 and P2 of the ?rst pair, will longest spire is being sought and although the approach each other as will also pulses P: and P4. conditions for that spire may otherwise be satis However, pulses Pa and P3 of contiguous pairs factory, it may not appear on the CRO screen be will recede from each other, thus indicating that cause of the directive pattern of the transmission the mean' frequency of the resonance chamber I8‘ from the transmitter to the phantom target and is deviating still farther from the transmitter back to the receiving device as indicated in Fig. frequency. ,. 4. However, with a sufllcient number of tuning The fact that the individual spires of a pair are cycles, the optimum length spire will eventually closer to each other than they are to the next appear. adjacent spire of a contiguous pair is an indica 15 In order to insure that the optimum length tion that the frequency F: of the transmitter is spire will appear in the cathode ray screen and not midway between the limiting frequencies F1 that it will remain in a ?xed position, thus giv and F2. Manual adjustment of the position of ing a much-brighter trace with which the opera the motor base l8 by manipulation of the screw tor may ascertain the distance of the re?ecting adjusting devices will indicate immediately the 20 object with greater certainty, the appartus of direction of the adjustment needed to more wide Fig. 5 utilizes an interconnected tuning device ly space the spires of an individual pair. It .is and scanning device. This not only insures that accordingly possible by adjusting the apparatus the spire occur at the same identical position in until all of the spires are equally spaced to cause each scanning cycle, but also increases the ‘the mid-frequency of the band of frequencies 25 brightness of the spire since it remains ?xed in through which resonance chamber I6 is varied position on the screen. While in the apparatus to substantially coincide with the frequency of of Fig. 1, there might be as many as ?fteen tun the oscillations produced by transmitter 1. ing cycles during the progress of the cathode Fig. 5 illustrates an embodiment of the present ray beam across the CRO screen with a corre ‘invention in which the tuning of the resonance 30 sponding number of pairs of spires, in the sys chamber of the phantom target and the search tem of Fig. 5, it is preferred to have but a sin ing motion of the object locator transmitter are gle pair of spires on the screen. controlled by the same motor. In this ?gure, the The variable tuning mechanism of Fig. 5 com , apparatus is shown mounted in the nose or in a prises,a piston 81 within the chamber 24 and turret 22 of an aircraft. A shelf support 28 car 35 normally ‘biased toward one end of the chamber ries a resonance chamber 24, a vertical shaft mo by a spring 88 reacting against a collar 88 on the tor 28 and a radio transmitter 21, together with piston rod 48. The motion of the piston rod is its associated radio receiver. pulser, and cathode determined by a roller follower 4| rotatably ray oscilloscope. The resonance chamber 24 is mounted between the arms of a yoke 42 at the connected through a coupling loop 86 and coaxial 40 end of piston rod 48. The roller 41 engages the conductor 85 with a stationary pick-up 28 of half outer‘ periphery of a cam 48 carried at the upper dipole or any other suitable type positioned to end above shaft 88. A pair of lugs 88 integral receive energy from a searching transmitter di with the cam 48 carry adjusting set screws co pole transmitter 28 mounted together with its operating with a stop boss 8| projecting later parabolic reflector, 28 on the vertical shaft 88 45 ally from the upper portion of the shaft 88 to en of motor 26. The circuits from the radio trans able the precise angular position of the cam 48 mitter 21 and the radio receiver pass as in the with respect to the shaft 88 to be determined disclosure of Fig. 1. through a transmit-receive and locked. It will be seen therefore that the switch 8| to the dipole antenna 28. Although motionof the piston 81 in undergoing one tun any desired means may be used for connecting 50 ing cycle during‘a scanning cycle of the shaft the moving dipole to the stationary conductors of 88 is very much slower than that of the piston ll the radio apparatus, there is illustrated in this of Fig. 1. The two spires S1 and S: in the tun figure a. coaxial structure leading from the dipole ing cycle are indicated in Fig. 'l which shows a 28 through the shaft 88 to the rotating joint 82 screen of the cathode ray oscilloscope of Fig. 5. enclosed in the shield 88 and connected to the 55 Inasmuch as these spires S1 and Sr fall at the output terminals of the transmit-receive switch same position on the screen for each revolution 8|. As in Fig. 1, the energization of motor 26 of the scanning mechanism, it is possible by uti may be controlled by remote control switch in lizing persistence of vision techniques to obtain circuit with the motor and with the winding 84 much clearer and more distinct traces on the of a, releasing latch, release of which permits the oscilloscope, thus increasing the de?niteness of movable tuning element of the chamber 24 to be the system and facilitatlngvaccurate and quick operated. - check-ups when the object locator is in motion. During energization of the apparatus, includ It is also possible, since the positions of these ' ing the transmitter, the receiver and the motor spires may be initially ?xed with reference to a 26, shaft 88 is rotated at a constant speed to cause desired forward searching direction of the an the transmitter antenna“, 28 to scan the entire tenna 28 to use these spires as an indication - 360 degrees. By application of a blanking elec of any drift or deviation in the azimuth biases tromotive force to a grid of the CRO tube during of the oscilloscope and for correcting or adjust- ' the rearward half of the search scanning cycle, ing the biases should'occasion arise. any effect of the transmitter pulses which would 70 The tuning mechanism is provided with a latch otherwise occur during that period may be pre 88 which is impelled by a spring to snap into po vented from giving an indication on the CRO sition behind the collar 88 ‘at the moment that

device. - ' h the cam 48 and follower 4| displace the piston In the system of Fig. 1, it is desirable to vary 81 to its extreme inward position. This imme the tuning of the resonance chamber I! at fairly 78 diately stops the tuning cycle operation, leav 2,510,299 30 ing the chamber 24 tuned to a frequency outside when the contactor 66 is at its center position the range of the transmitter frequencies so as there is substantially no difference of potential effectively to electrically disconnect it from the between plates 59 and 60. As the shaft 6|, r01 system.' Closure of the testing key 2| serves to tates, the cam 62 permits contactor 68 to move simultaneously energize motor 26 and solenoid along the potentiometer 69 in such fashion as winding 94 to release the latch and permit the to impress a linearly increasing sweep voltage tuner to operate as long as the key is depressed. between plates 59 and 60. This horizontal sweep An adjusting collar 95 provided with oppo electromotive force is indicated in the upper sitely directed internal threads may be intro graph of Fig. 9. Accordingly, the beam from duced between separate aligned oppositely cathode 55 will tend to sweep in a horizontal threaded portions of tuner rod 46 to permit man direction across the face 14 of the oscilloscope ual adjustment of the length of the rod 40 when upon which the illuminated trace appears. Dur it is desired to shift the band of frequencies ing each alternate half cycle of the rotation of through which piston 31 tunes the chamber 24. the scanner shaft 6|, this operation is repeated. In the modi?cation of Fig. 8, the phantom tar 15 The vertical motion of the cathode beam oc get equipment is so correlated with the object curs ata very much more rapidrate than does locator equipment as to be operated during that the horizontal motion. To provide this vertical portion of the scanning cycle in which, while motion de?ector plates 51 and 58 are connected the object locator antenna is operating for to the terminals of a pulsating current source searching purposes, the oscilloscope is ordinarily 20 89 having a frequency which corresponds with blanked out. As shown in the ?gure, the ?xed that of the wave trains and having an intensity phantom target antenna 45 is placed at a. posi which is substantially zero at the instant of tion in the rear of the object locator antenna emission of a wave train and which increases 46. The position is such that the antenna 45 linearly with elapsed time so that the vertical and its associated re?ector 49 are entirely out 25 position of the cathode beam at any instant is of the ?eld of antenna 46 during the effective a function of the time which has elapsed since half of its scanning cycle which occurs when the emission of the wave train. The second the re?ector 48 is pointing toward the left as graph of Fig. 9 indicates the sequence of search shown in the drawing and, hence, away from the wave trains and the third graph the coincident antenna 45. This arrangement frees the trans 30 vertical sweep electromotive forces supplied by mitted scanning pulse pattern from any distor the source 89 and which persist for a substan tion which the antenna 45 and its re?ector 49 tial part of the period between wave trains. It might tend to introduce. It also improves the space condition since it enables the phantom will, therefore, be seen that the scanning oc target antenna 45 to be placed closer to the reso curs in the manner of a rapid vertical pulsation which moves slowly in a, lateral direction ac nance chamber 41 and in a generally more con complishing a horizontal traverse of the screen venient position in the airplane than out in 14 during the half cycle of rotation of the shaft front or at the side of the re?ector 48. This 6|. The intensity of the cathode ray beam from tends, moreover, to reduce the losses occurring cathode 55 is normally such that in the absence in the connections between the antenna 45 and 40 of energization of the receiver 53, the trace on the resonance chamber 41. Connected to the the screen 14 is just invisible. Whenever the re searching antenna 46, as shown diagrammati-' ceiver 53 is energized, it impresses a potential cally is a system like that of Fig. 3 including a on the cathode 55 su?icient to cause the trace transmit-receive switch 56, a radio transmitter to appear as a glowing spot if energization is 5|, a pulser 52 for exciting the transmitter, a 45 instantaneous and at one position only, or as a radio receiver 53 and a cathode ray oscilloscope line if it reoccurs at closely spaced instants. 54. The cathode ray oscilloscope is provided with Included in the circuit between cathode 55 and the usual cathode 55, intensity-control grid 56, grid 56 is a blanking source 16 associated with a vertically de?ecting plates 51 and 58 and hori potentiometer 11 and a cam-driven contactor 16 zontally de?ecting plates 59 and 66. The radio 50 provided with biasing springs not shown and receiver 53 is connected to the input or control actuated by a cam 19 also mounted on the scan circuit of the cathode ray oscilloscope over a cir ner shaft 6|. Cam 19 is so designed that dur cuit including the conventional blocking con ing the scanning half cycle it maintains con denser 92 and shunt high resistor 94, the lower tactor 18 in the position shown in Fig. 8 so that terminal of which is grounded at 96. Inordcr 55 no blanking potential is impressed by the source to provide a linear horizontal sweep electromo— 16 upon the intensity control circuit. However, tive force for the plates 59 and 60, there is as at the end of the half cycle, the follower 86 sociated with the shaft 6| of the constant speed passes suddenly from the larger radius portion motor for rotating the scanning antenna 46, a of the cam 19 to the smaller radius portion in cam 62 connected to the same shaft. A spring stantly moving contactor 18 to the left-hand driven cam follower 63 slidably mounted in a terminal of potentiometer 11 to impress upon the guideway 64 is impelled toward the cam by a grid 56 such a negative bias potential as to en compressed spring 65 placed between the collar tirely blank out the trace on the oscilloscope 66 on the follower 63 and stationary abutments screen 14 during the ensuing half cycle irrespec 61. The cam follower carries a contactor 68 en tive of the strength of the signals incoming to gaging a potentiometer 69 which is connected radio receiver 53 during that half cycle. As across the terminals of a unidirectional source 16. the shaft 6| again reaches the position at which The center of potentiometer 69 is effectively the re?ector 48 is facing forward, the blanking grounded and connected to de?ecting plate 60 potential is removed from the grid 56, thus en by means of the grounded center tap 91 of the 70 abling the searching half cycle to be repeated. potentiometer 85 which is in parallel with the Should the operator at the remote control po potentiometer 69 and the source 10. Plate 59 sition desire to make a test of the equipment he is connected by way of armature ‘H of the elec may close key 8| in series with a local source tromagnetic relay ‘l2 and the contact 13 to the 82 and the windings of electromagnetic relays 12 contactor 68. The cam 62 is so designed that 75 and 83. The effect of this operation is to actu 9,510,999 11 12 ~ ate armatures ‘II and 84 to effectively disconnect outgoing pulses and to return pulse echoes. said the contactors 88 and 18 and to connect in their target comprising an electrically resonant sys stead contactors 85 and 88 actuated by diamet temhaving a tuning device and means operated rically opposed followers 81 and 88 respectively. by said antenna-driving means for operating the The operation of the/armature ‘ll serves to trans tuning device in synchronism with the scanning fer the positive horizontal sweep electromotive operation of the antenna. , . force from the forward portion of the scanning 5. A directive radio antenna, a rotatable shaft cycle to the rearward portion since the, follower on which said antenna is mounted, a pulse trans 81 undergoes exactly the same. kind of motion mitter and a pulse receiver, means for alternately as the follower 63 but at a half cycle later in time. 10 connecting said transmitter and said receiver to Similarly, the operation of the armature 84 serves said antenna, a phantom target system compris to transfer the application‘ of the blanking po ing a tunable resonance chamber having a trans tential from source 18 to the forward half of the ducer radiator exposed to the field of said an scanning cycle, thus permitting the oscilloscope tenna, a tuner for said chamber connected to ll to be actuated by the receiver 58 only when 15 said shaft to be operated thereby and a motor the re?ector 48 is pointing rearwardly and hence connected to said shaft for maintaining it in op is in position to direct wave trains toward and eration whereby the tuning of the chamber and to receive echoes from the phantom targetres the position of the antenna are concurrently onator 41. The screen'" of the oscilloscope may varied. be calibrated to indicate when the re?ector 48 20 6. In combination, a motor, a shaft driven in is pointing directly to the rear thus providing rotary direction thereby, a directive antenna car the same sort of check with reference to the os~ ried by said shaft, a resonance chamber having cilloscope biases as is described in connection an external radiant energy transducer mounted with the operation of Fig. 5. The indication on in position to transmit energy to or receive energy the screen 14 may be in every respect identical‘ 25 from said antenna in certain of its positions, a with that on the screen shown in-Fig. 5 with the ' cam on said shaft, said resonance chamber hav advantage that there is no confusion from ac ing a movable tuner engaging said cam to vary tual targets or ‘objects in front of the equipment the tuning of the chamber with change in the since energy re?ected from surfaces in front of position of the directive antenna. ' the equipment is blanked out. It will be under 30 '1. A system for transmitting pulses of radiant stood that the details of the variable'tuning de energy and for receiving pulse echoes compris vice of the resonance chamber 41 may be iden ing a radio transmitter, a radio receiver, a di tical with those of the tuning equipment of Fig. 5. rective antenna connected to said transmitter What is claimed is: and receiver, a motor for impelling said antenna 1. A radio pulse transmitter and a pulse echo through a series of different directive positions, receiver having a common directive antenna the a tuned re?ecting system for selectively receiv directivity of which may be varied to scan a ing the energy'of a transmitted pulse and for zone in space, a testing equipment having an an reradiating an echo pulse, tuning means oper tenna positioned within the zone to receive ated by said motor, and remote controlled means connected to said tuning means and said re?ect energy from the directive antenna during scan ing system to permit disconnecting said tuning ning of the zone by the directive antenna, means for tuning the testing equipment to cause it to means from the motor and rendering said re selectively respond to received energy and a com ?eeting system ineifective at will. mon driving means for simultaneously varying 8. In combination, ascanner mounted for ro- I the directivity oi’ the directive antenna and the 45 tation about an axis to enable scanning in all tuning of the testing equipment. directions about the axis, an indicator. device connected to the scanner to receive energy there- - 2. An antenna mounted on a rotatable support, from, means for blanking operation of the indi means for continuously driving said antenna to cator device during a sector of the cycle of rota cause it to rotate, an electrical resonance cham -'ber, an electromagnetic wave pick-up device con 50 tion to limit the indications to a given sector of rotation, a test apparatus mounted‘ in the area nected to said chamber ‘and mounted in position of the blanked sector and means connected to to exchange energy with said antenna during at the blanking means and controllable at will to least a ‘portion of the revolution of the antenna. and means controlled by said antenna driving unblank the blanketed sector to permit scan 55 ning the test apparatus. said means operating at means for varying ‘the resonance frequency of the same time to blank the sector previously un said resonance chamber. - blanked and scanned. 3. A spinner antenna mounted for revolution CHARLES W. SCHRAMM. about an axis, means for causing said antenna to revolve, about said axis, means for causing 60 REFERENCES crrEn said antenna to emit recurrent pulses of a sub The following references-are of record in the stantially constant frequency, a space resonance chamber electrically coupled with said antenna file of this patent: to receive energy therefrom and means for caus _ UNITED STATES PATENTS .

ing the tuning of the chamber to vary cyclically Number Name A Date in synchronism with the rotation of said antenna 2,241,918 Muller ______-_ May 13, 1941 about its axis. v 2,306,282 Samuel ______Dec. 22, 1942 4. A radio echo measuring system comprising 2,377,902 Relson ______.._ June 12, 1945 a pulse transmitter, a pulse echo receiver, an an 2,396,112 Morgan ______V_____ Mar. 5, 1948 tenna connected to said transmitter and said re 2,402,410 Kear ______‘__ June 18, 1948 ceiver to transmit outward directed pulses and 2,480,827 Isely ______Feb. 8, 1949 inward directed pulse echoes, means for driv ing said antenna to cause it to successively scan ' FOREIGN PATENTS a series of positions in cyclic manner, a phantom Number Country Date target positioned near said antenna to receive 149,820 Great Britain _..-...- Aug. 26, 1920