Патент USA US2404527код для вставки
July 23, 1946. G. PoTAPENKo l 2,404,527 ELECTRIC DISTANCE METER Filed lay 2, 1939 Genera/ar f/5 T ts I ? é T [r if l all?! c, « INVENTOR, áe/¿ÚQQ’ @7b/cent@ ' ATTORNEY. Patented July 23, 1946 UNITEDy f 2,464,527 STATES V.2,404,527 PATENT n Y " ELECTRICv DISTANCE> METER Gennady Potapenko, Pasadena, Calif. Application May 2, 1939, Serial No.‘271,300 7 Claims. (Cl.> Z50-1) l My invention relates to an electric distance me ter for measuring the distance between the meas uring apparatus and a surface capable of‘reiiect ing electromagnetic radiation of suitable frequen cy. The invention has a particularly valuable application to the problem of determiningwhile in an aircraft, the height of the aircraft above the surface of the earth. An object of the invention is to provide a meth od and an apparatus for measuring the distance between the measuring apparatus and a surface capable of reñecting electromagnetic radiation of suitable frequency. _ _ OFFICE i l ' ~ ' "Y’ 2.» tromagnetic radiation are transmitted tothe sur-' face, the distance of which-is to'be determin'ed5l and the pulses of electromagnetic radiation are received after having beenI reflected from the surface. Agmeasurement of anelectriccurren-tîkïyrv potential difference derived from the sourcefo'f transmitted radiation, or from» a separate source,` is preferably made inthe interval between trans-` mittedand received pulses by initiating the- meas urement by one pulse and counteracting»withthel second pulse the action of the first pulse. ' Since electromagnetic radiation travels with'the sub-~ stantially constant velocity ¿of approximatelyA 3><10ß- meters per second'7 the duration‘of the Another object is to provide a method andan apparatus for measuring elevation above the sur 15 measurement is an accurate measure of the- dis-’ tance travelled by the electromagnetic radiation,v face of the earth. which is substantially twice-the distance fromïthe Another object is to provide an apparatus source of radiation tothe reflecting surface. which measures an electrical quantity in the time The method and apparatus of »myï invention interval between the sending of a pulse of elec tromagnetic radiation and its return from a re 20 should be distinguished from those >previously flecting surface. employed for the measurement of distance `by pendent of the maximum amplitude of the pulses. tance given on an electrical instrument. form of my electric distance meter. I provide a short wave radio transmitter lll, pref- _ means of radio waves. Other methods have ei Another object of the invention is to provide a ther measured the elapsed time: between .trans method and apparatus for measuring the distance mission and reception of the waves directly by to a surface, in which an electrical measuring in strument is started by an electric pulse coincid 25 means of a cathode beam tube or havemodulated , the transmitter frequency linearly and have de ing with' a transmitted pulse of radio waves and termined by a beat method the. difference-"infre is stopped by an electric pulse coinciding with a quency >between waves being receivedand those reñected pulse of radio waves. being transmitted. 'I‘he latter’ method is de' Another object is to provide a method and ap paratus for measuring one of two electric pulses 30 scribed in an article by S. Matsuo, Proc. I. R.. E., vol. 26, p. 848. The apparatus of these methods only during that portion thereof when the other is bulky and requires considerable attention on of said pulses is of substantially Zero amplitude. the part of an operator. The apparatus Vof my in A further object is to provide a method and vention, on the other hand, is relativelylight, vis apparatus for producing and measuring an elec easy to operate, and requires no attention other tric current proportional to the time interval be than to read `the numerical registration of A„dise tween arrival of two electric pulses and inde . . The present embodiment of my invention is' Still another object of the invention is to pro particularly adapted to the determinationfo'f .the vide an electric distance meter which is accurate and dependable and requires a minimum of at 40 altitude of aircraft relative to the earth’s sure face, and my invention will be explained in con-` tention to operate it. nection with this use; butl it will be understood These and other apparent objects I attain in that my invention may also be employed in meas a manner which will be clear from a considera uring the distances to surfaces other than the tion of the following description taken in connec surface of the earth. ' tion with the accompanying drawing, in which: -In the disclosed embodiment of my‘invention, Fig. l is a diagrammatic illustration of one erably adapted to rgenerate alternating current Fig. 2 illustrates the relations existing between of a frequency between 10ß and 109’ cycles per two electric pulses existing in the circuit of Fig. 1 for one particular condition. 50 second. The transmitter is keyed by means of aV keying device generally designated by thenuà Fig. 3 illustrates the resultant of the pulses of meral ll to produce a »series of pulses of high Fig. 2 and that portion thereof which is measured. frequency alternating ' potential diiîerence’ be-> Fig. 4 shows an alternative form of a portion tween the >conductors I2 land-I3. For theV sake of of the circuit of Fig. l. diagrammatic illustration, Vthe keying device ‘It In the practice of my invention, pulses of elec g 2,404,527 3 4 is shown a's a relay I4, the switch of which is in serted in the conductor I2, and the coil of which is energized by a pulse generator I5 of construc tion well known in the art. The pulse generator I5 generates pulses of electric current which oc cur at regular intervals. The switch of relay I4 preferably of a length equal to one-half wave length of the radio-frequency current desired to be ñltered out. The incoming conductor 22 and the outgoing conductor 21 are both connected to the cylinder 28 and the outgoing conductor 26 is connected to the conductor 2| at a point midway between the ends of the cylinders 28 and passes out through a hole in the cylinder. Cyl inders of otherl lengths may, if_ desired, be em closes at the beginning of each pulse, conducts the radio-frequency current from the transmit ter II) to the conductor I2, and opens at the end of the pulse. The conductors I2 and I3, there 10 ployed and suitable connectionsbe'made thereto fore, have imposed a radio-frequency potential to eifect the same result, all as described in the difference which appears at .the beginning of a , „ above-mentioned article. Filters of this type are pulse, continues at substantially constant ampli "considered more desirable for very high fre tude during the pulse, and disappearsfat the end quencies than filters With lumped capacity and of the pulse. Preferably the frequency of the 15 inductance. In the embodiment illustrated in pulses is from 103 to 104 per second, although this Fig. 1,’afresistance 33 is connected between the depends upon the desired range of the distance conductors 26 and 21. meter, as hereinafter explained. It will be seen, A directional receiving antenna 3|, which may then, that within a single pulse, as it exists" at be provided with a parabolic reñector 32 to give conductors I2 and I3, there are many radio-fre 20 it directional properties, is connected to a re quency cycles, and since during a pulse the am ceiver and radio-frequency amplifier 33 through plitude of the radio-frequency variation is pref conductors 34 and 35.-> Conductors 36 and 31.are erably substantially vthe same in each cycle, a connected to the outgoing side of the receiver plot of the amplitude of the radio-frequency po 33. In series with the conductor 31 is placed the tential difference against time would be rec 25 rectifier 38 which may be of either the half-wave tangular in shape and appear similar to the rec or full-Wave type and is adapted to pass current tangles d in Fig. 2. While pulses of rectangular away from the receiver 33; and between the con shape are shown, it will be understood that pulses ductors 36 and 31, beyond vthe rectifier, is pref of-Various other suitable shapes may be employed, if desired. ‘ erably connected a ñlter 4D, preferably of the 30 concentric line type, which is similar to the fil It will be understood that the keying device ter 25 and is adapted to ñlter out the radio-fre || is shown as illustrated in Fig. l purely for quency component of the current in the conduc the sake of simplicity. A switch in the conduc tors 36 and 31, leaving in the outgoing conduc tor I2 or within the transmitter I0 may, if de tors 4| and 42 substantially only pulses of con sired, be operated by a mechanical device adapt 35 tinuous direct current ofV substantially rectangu ed to open and close it at predetermined inter lar wave shape, designated by the lettervr in Fig. vals. Or any one of the keying devices well 2. In the embodiment of Fig. l, a resistance 43 known in the art may be employed to open and is connected between the conductors 4| and 42 close the circuit from the transmitter or to pro and the conductors 21 and 4| are connected to vide “o ” and “o ” periods of the current from 40 gether. the transmitter at predetermined intervals. The In the embodiment of Fig. 1, conductors 44 and 45 are connected, respectively, to the conductors 26 and 42. A rectiñer 46 is connected in series with the conductor 44 and is adapted to pass current away from the conductor 26. An electric measuring instrument 41 preferably of relatively high resistance compared to the resistances 30 transmitter may, if desired, be modulated in a well-known manner by means of electronic de vices to eiîect this result. A directional transmitting antenna I6 is con nected by means of conductors I1 and I8 to the conductors I2 and I3, respectively, the antenna being connected with the conductors in a manner and 43, and preferably of ballistic character, is well-known in the art to provide efficient direc connected between the conductors 44 and 45 be tional transmission of short-wave radio waves DI) yond the rectifier 46, and is adapted to measure therefrom. While various arrangements known the average current in the conductors 44 and 45 in the art may be employed to provide directional or the average potential difference therebetween. transmission, a parabolic reflector 20 is shown When the conductor 42 is positive with respect herein for that purpose. to the conductor 26 current is prevented by the Conductors 2| and 22 form continuations of rectifier 46 from passing through the instrument the conductors I2 and I3, respectively. In series 41, and it is only when the ,conductor 26 is more with the conductor 2| is placed a rectiñer 23 positive than the conductor 42 that the instru which may, for example, permit current to pass ment 41 is operative. It is understood that var along the conductor 2|,away from the conductor ious‘bridge circuits and other connections of the I2. Instead of the half-wave rectiñer s_hown, I 60 electrical measuring instrument may be made to may, if desired, employed a full-wave rectiñer. accomplish similar results. A ñlter 25 is connected between the incoming As employed on an airplaneto measure the conductors 2| and 22 and outgoing conductors elevation of the airplane above thev surface of 26 and 21, and is adapted to filter out substan the earth, the antenna I6 is preferably located tially all of the radio-frequency component of 65 under one wing with the reilector 2U positioned the rectified current through conductors 2| and so as to direct the radiation downwardly. The 22, leaving in conductors 26 and 21 substantially antenna 3| is preferably located under the other only pulses of continuous direct current, of vsub wing on the opposite side of the fuselage from stantially rectangular wave shape, designated by d in Fig. 2. The filter 25 is preferably of the concentric line type such, for instance, as that described in an article lby Leeds, Proceedings of the Institute of Radio Engineers, vol. 26. pp. 576-589. A :filter of this type comprises a cylin der 28 concentric with the incoming line 2| and the antenna I 6 so as to minimize direct reception by the antenna 3| of the radiation from the an tenna I6, and the reilector 32 is so positioned as to cause the antenna 3| to receive radiation pre dominantly coming from below. It will be under stood, however, that any other `suitable arrange ment of the antenna may be employed. 2,404,527 ' 6 time Lts 4and end at time At8 Íwhereithe intervals ists In operation, the conductors I1, .IB .and 2I, 22 are subjected to pulses of high frequency electro and tata are both equal to theláintervals titz ‘and motive force. At the time t1, in Fig. 2., a pulse £3154. tromotìve force is impressed upon the conductors I1 and I8 and also upon the conductors 2| and 22. During this interval, therefore, high fre . Y* ` Y ence .exists across lthe resistance 30 proportional to the-current Id and substantially no potential > difference exists .across the resistance 43.- The quency radio waves are radiated from the an tenna tween exists tween - During the `time interval t-itza Apotential differ may begin and may continue until a later time t3. During this interval .a high frequency elec conductor 125 is therefore ypositive with respect to the conductor 42 and a potential diiïerence exists I6 toward the earth. In the interval be 10 across the instrument 41 proportional to the cur rent Id. 'In the interval tzta the current Ir through the times t3 and te no potential diiïerence the resistance »43 counteracts the effect of the between the conductors I1 and I 8 or be current Id through the resistance 3D and there eX the conductors 2| and 22. Between the «ists a potential difference between theconductors times t5 and tv another pulse .of radio-frequency electromotive force is impressed .upon the con 15 42 »and-*243 yproportional to the diiierence -Is vbe tween Ir and Id,` with the conductor 42 positive ductors I1, I8 and upon the conductors 2i, 22. with respect to the conductor 26. Since, under During the pulses between times t1 to ts and t5 these conditions, the rectifier 46 does not permit to t1 the radio-frequency potential difference be any current to pass, there is `no potential diiïerà tween the conductors 2i and `22 is rectified by the rectifier 23 and varying direct current tends 20 ence across the instrument 41 during the interval tats. During the interval 'tati no potential differ to flow through the filter 25 and the resistance ence exists across the resistance 30 anda poten 30. The filter 25 removes substantially all of the tial -difference exists across the resistance 43 pro high frequency component of the current in the portional to the current Ir, the conductor-42 be circuit, leaving substantially a continuous direct current which varies similarly to the rectangle d 25 ing positive with respect to the conductor '26. No potential diiîerence, therefore, exists across the in Fig. 2. instrument `41 during the period titi. During the The radio-frequency waves radiated from the period> tits no current flows through either ofthe antenna I6 pass downwardly to the earth’s sur resistances 30 and 43 and nopotential diñerence face from which they are reflected upwardly and are received on the antenna 3| at a time follow 30 exists vacross the instrument 41, Upon the vstart of another pulse the instrument again .registers ing their radiation from the antenna I5 by an a potential difference proportional to Id duringÍ interval depending upon the distance traveled by the interval ists and is idle 'until the succeeding the waves. The airplane makes very little prog pulse d occurs. ' ress in the short interval between radiation and In Fig, 3 is‘plctted the potential diiîerence be reception of the waves and the elapsed time in 35 tween the lconductors 26 >and 42, with those in seconds is substantially equal to two times the tervals during which measurement takes place elevation in meters of the airplane above the sur being cross-hatched. For a given frequency of face of the earth divided by BXlOS, the velocity pulses it Vwill be evident that, since the value. of of light in meters per second. The radio-fre quency waves impinging upon the antenna 3l 40 Id is constant, the reading of the instrument 41 will be proportional to IdXAt where At equals are translated by the receiver and ampliñer 33 into a radio-frequency potential difference across the conductors 33 and -31 which is rectified by the rectifier 38 and tends to produce a varying direct current through the íilter 40 and the resistance 43. The ñlter 46 removes substantially all of the radio-frequency component and leaves a contin uous direct current of amplitude Ir through the resistance 43 which varies similarly to the rec tangle r in Fig. 2. Since the effect of the current 50 Ir in the measuring circuit is opposed to that of the current Id, the current Ir is, for illustrative purposes, shown on the opposite -side of the O line in the chart of Fig. 2. The amplification of the amplifier 33 is preferably adjusted so that the potential diiierence across the resistance 43 dueto the passage of the current Ir therethrough is greater than the potential difference across the the time ’between `t1 and t2. As previously ex plained, _the time intervalnt required for the radi ation to travel to the earth’s‘surface and 'back is proportional to the elevation H of the airplane above the surface of the earth. It will be evident then that ‘the reading vof the instrument 41 will be proportional to IdXH. The instrument 41 may, therefore, lbe calibrated directly in terms of H. ' Itis important that the durationltits of each ’ pulse be at least as `long as the interval titz cor responding to the greatest distance desired to be measured, -and that the interval tats be at least as long as >the interval tits. Preferably the in-V ~ terval tats is made equal to that of tits and the duration tits of the pulse is varied .by varying the pulse frequency. The invention contemplates the possibility-.of supplying any of several different resistance 30 due to the passage of the current Id therethrough. It will be understood that it is 60 `pulse frequencies and of operating at'that fre quency .best .suited to the distance range in which not necessary that the resistances 30 and 43 be .one is interested. The »instrument «41, df course, of the same value but it is assumed here that this condition exists so that the potential differences requires :a separate calibration for each pulse fre across the respective resistances are proportional quency employed. to the currents flowing therethrough. Due to vdirect coupling between thetransmitting For a particular elevation of the airplane above and receiving antennas vit may be that a small the earth’s surface, the interval oi time elapsing current will flow through the resistance 43 co between the radiation and reception of a pulse incident-ally with the passage of the current ld ' may be tltz. The pulse d of current Id through through the resistance 130, but since it will start resistance 30 will` then, start at the time ti‘wh-ile and stop at the same times as the current Id it the pulse T of current Ir through the resistance will beevident that the only eiîect will beto 43 will not start until the time t2, and whereas counteract some of the current Id. Since the the pulse d will end at t3 the pulse r will not end »amplitude of this current due to direct coupling' until t4, the interval t1t2 being equal to the inter is constant, its eiîectupon the reading ofthe ïin- n 75 val tati. Likewise, the next pulse r will start ¿at 2,404,527 7 strument 41 will be taken account of in calibra tion of' the instrument. The circuit of Fig. 4 has only ohmic resistances An alternative form of measuring circuit is il lustrated in Fig. 4. Two vacuum tubes 50 and 5|, each with two grids, are preferably employed. Heaters 52 and 53 of the tubes 5U and 5|, respec and inter-electrode capacities which Yare small. The time constants of various parts of the circuit are therefore Very small, and by proper choice of tubes, resistances, and batteries it is possible to make the circuit operate at extremely high tively, are connected in parallel and are supplied speed so that the time interval titz can still be by a battery 54. The cathodes 55 and 56 of the recognized even though it is only of the order tubes 50 and 5|, respectively, are connected to of a small fraction of 1 microsecond. When the gether and to the negative side of a battery 51 10 circuit of Fig. 4 is 'employed the filters 25 and 40 and to the conductor 21 and 42. The anode 58 may be eliminated, if desired. While I have, in of the tube 50 is connected to the positive side cf Fig. 4, shown a particular circuit and tubes with the battery 51 through a resistance 60, and the two grids it will be understood that the same prin anode'6l of the tube 5| is preferably connected ciples may be applied to provide other vacuum to the positive side of the battery 51 through a 15 tube relay circuits employing tubes as described resistance 62 and a current measuring instrument or tubes of other well-known types. 63. One of the grids 64 of the tube 56 is con When a vacuum tube relay circuit such as that nected to a point ‘between the resistance 62 and of Fig. 4 is employed the pulse duration tits may the meter 63 while the other of the grids 65 is be made as short as desired so long as it is long connected to the conductor 26, One of the grids 20 enough to operate the relay. With this lcircuit 66 of the tube 5| is connected to the anode 58 it is not necessary that the interval tits be as long and the other of the grids 61 is connected to the as t1t'2. This will be evident from the fact that conductor 4|. A resistance 68 is preferably con current I2 starts to now at time t1 and will, by nected between the conductors 26 and 21 and an reason of the resulting bias on the grid 64, con other resistance 10 is preferably connected be 25 tinue to flow even if current Id stops ñowing and tween the conductors 4| and 42. the bias on grid 65 is removed. The current I2 The Passage of plate current I1 through the re will continue to flow until pulse r arrives at the sistance 60 places a negative bias on the grid 66 time t2. It is still necessary, however, for the of tube 5| and the passage of plate current I2 interval tate between pulses to be equal to or through the resistance 62 places a negative bias 30 greater than the interval At corresponding to the on the grid 64 of the tube 50. The resistances greatest distance desired to be measured. One 60 and 62 and the voltage of the battery 51 are possible arrangement is to make the intervals made such that the biases resulting from passage tits, tet?, etc., always substantially equal to the of the currents I1 and Iz are beyond the cut-01T interval At. This result may be automatically points of the tubes 5| and 50. The resistances 35 secured by arranging the transmitter keying relay 68 and 10\are of such Values th'at when the cur to be operated by the pulse generator to key the rents Id and Ir, respectively, pass through them, transmitter “on” and to be energized by the po the negative biases produced on the grids 65 and tential difference between the conductors 4| and 61 are suiiicient to reduce the currents in the re 42 to key the transmitter “oíî” when the pulse 1' spective tubes to substantially zero. 40 arrives at t2. But, in practice, it is preferable to The operation of the circuit is, then, as follows. operate the apparatus, as previously described, Assume that in the interval prior to t1 the tube wherein the intervals tits, tstv, etc., are independ 50 is conducting and plate current I1 is flowing. ent of At and the effect 0f the pulse coinciding The grid 66 is biased beyond cut-oir and no cur with the transmitted pulse is counteracted by rent ñows through the meter 63. At time t1 the the pulse coinciding with the pulse received after current Id starts to flow through the resistance reflection, the counteraction being eiTected in a 68, the grid 65 is biased beyond cut-oiî, and the circuit totally separated from the keying relay, current I1 ceases to flow. The bias on grid 66 as shown in Figs. 1 and 4. Under such circum then no longer exists and the tube 5| immediately the keying of the transmitter and the becomes conducting, the current I2 passing 50 stances, load on it are independent of the operation of the through the meter 63 and the resistance 62. The rest of the apparatus and the stability of the passage of the current Iz still further biases the transmitter is more easily maintained. grid 64 of the tube 56. The current I2 continues It will be seen that the apparatus disclosed is to ñow until time t2 when the passage of current adapted to function within wide limits of the in Ir through the resistance 10 biases the grid 61 to tensity of the radiation received after having such an extent that the current I2 is stopped. been reflected from the distant surface, for the During the interval tzta both tubes are non-con operation of my apparatus depends not upon the ducting. At the time t3 the bias on the grid 65 intensity of the received radiation but upon its is removed due to stopping of the current Id and time of arrival relative to the time when it was the current I1 starts flowing, biasing the grid 66. 60 sent. Another great advantage of my apparatus When the bias on the grid 61 is removed at t4 is that a definite numerical registration of dis due to stopping of the current Ir the bias on the grid 66 still prevents current from flowing through tance is continuously given without the necessity of any setting or adjustment operation to obtain the meter 63 and the tube 5|. The current I1 the measurement. continues to flow through the tube 50 until an 65 It will be understood that various changes and other pulse starts at t5 and the entire cycle is re modiñcations in the apparatus disclosed may be peated. It will be seen that current flows through made by those skilled in the art without depart the meter 63 only during the time intervals titz, ing from the spirit and scope of the invention as tsts, etc. Since the current which i-lows is con deñned in the appended claims. stant while it flows and is independent of the in 70 I claim as my invention: tensity of the radiation received on the antenna 3|, the reading of the meter 63 will vary only with the length of the time interval At, which is proportional to the height of the apparatus above the surface of the earth. 1. Distance measuring apparatus, comprising: an antenna adapted to radiate toward a sur face; means including a radio transmitter adapted to periodically energize said antenna, 75 whereby pulses of radio waves are radiated to.~ 2,404,527 9a; wardrsaid surface; an electric circuit energized by said transmitter coincidentally withsaid an tenna; a. rectifier in said circuit,v and a filter in said circuit for ñltering out radi'o-frequencycom ponents of the current in said circuit, whereby pulses of continuous direct’ current correspond ing substantially intime with said transmitted. pulses pass. through said electric circuit; means 1,0`~ said receiving means.; a rectifier in said second electric circuit, anda ñlter in said second electric circuit for filtering out radio-frequency coni ponentsof the current in- 'said circuit, whereby pulsesA of continuous directl currentl corresponding substantially‘in time with said received pulses pass through said second circuit, said receiving` means being sov adjusted that said direct current pulses in said second circuit are or greater ampli pliner for receiving said pulses of radio waves 10 tude than said direct current pulses in' said-first circuit; and an electric circuit connected> to said after having been reflected from said surface; first and second circuits> andr including measur a second electric circuit connected to said re ing means responsive to> the current iii-said ñrst ceiving means; a rectifier in said second circuit, circuit when it is greater than >the ,currentr in and a filter in said second circuit for ñltering said second circuit. , Y . out radio-frequency components of the current 4:. Distancey measuring apparatus, comprising: in said second circuit, whereby pulses of con including an antenna. and a radio-frequency am >tinuous direct current corresponding substantial ly in time with said received pulses pass through an antenna’adapted to radiate toward a surface; means including a radio transmitter adapted to periodically energize said antenna, whereby said second circuit; an electrical measuring in strument; and an electric circuit connected with 20 pulses of radio waves are radiated toward said surface; an electric circuit energized by said said instrument and with said iirst and second transmitter coincidentally with said antenna; a circuits and adapted to energize said instrument rectifier in said electric circuit, whereby pulses substantially only in response to a pulse pass of direct current corresponding substantially in ing in said first circuit corresponding substan tially in time with one of said transmitted pulses 25 time with said transmitted pulses pass through said circuit; means including an antenna and a and in the absence of any pulse passing in said radio-frequency amplifier for receiving said second circuit corresponding in time with a re pulses of radio waves after having been reflected from said surface; a second electric circuit con an antenna adapted to radiate toward a surface; 30 nected to said receiving means; a rectifier in said second electric circuit, >whereby pulses of means including a radio transmitter adapted to direct current corresponding substantially in time periodically energize said antenna, whereby with said received pulses pass through said sec pulses of radio waves are radiated toward said ond circuit; a ñlter in eachA of said circuits for surface; an electric circuit energized by said transmitter coincidentally with said antenna; a 35 iiltering out the radio-frequency components of the currents in said circuits; and an electric i rectifier in said electric circuit, and a filter in ceived pulse. 2. Distance measuring apparatus, comprising: said electric circuit for iiltering out radio frequency components of the current in said circuit, whereby pulses of continuous direct cur rent corresponding substantially in time with 40 said transmitted pulses pass through said electric circuit; means including an antenna and a radio frequency ampliñer for receiving said pulses of circuit connected to said ñrst and second cir cuits and including measuring means responsive to the current in said first circuit when it is greater than the current in said second circuit. 5. Distance measuring apparatus, comprising: an antenna adapted to radiate toward a surface; means including a radio transmitter adapted to . periodically energize said antenna, whereby radio waves after having been reliected from said surface; a second electric circuit connected 45 pulses of radio waves are radiated toward said surface; means including> an antenna and a to said receiving means; a rectifier in said second radio-frequency amplifier for receiving said electric circuit, and a ñlter in said second elec pulses of radio waves after having been re tric circuit for iiltering out radio-frequency com - flected from said surface; an electric circuit ponents of the current in said circuit, whereby pulses of continuous direct current correspond 50 energized by said transmitter coincidentally with said antenna; a second electric circuit connected ing substantially in time with said received to said receiving means; a rectiiier in each of pulses pass through said second circuit; and an said circuits, whereby pulses of direct current electric circuit connected to said ñrst and second corresponding in time substantially with said circuits and including electrical measuring transmitted and said reiiected pulses pass re 55 means responsive to said pulses of direct current spectively through said iirst and said second cir in one of said circuits during the periods when cuits; an electrical measuring instrument; and said pulses of direct current in the other of means in connection with said instrument and said circuits are not passing therethrough. with said first and second circuits for starting 3. Distance measuring apparatus, comprising: an antenna adapted to radiate toward a surface; 60 a `predetermined current through said instrument means including a radio transmitter adapted to periodically energize said antenna, whereby pulses of radio waves are radiated toward said at the Vstart of each pulse in said first circuit v and for stopping said current at the start of each pulse in said second circuit. 6. Distance ‘measuring apparatus, comprising: surface; an electric circuit energized 'by said transmitter coincidentally with said antenna; a 65 means for transmitting pulses of electromagnetic radiation to a surface; means including an elec rectiñer in said electric circuit, and a filter in tric circuit associated with said transmitting said electric circuit for filtering out radio means for producing continuous direct current ' frequency components of the current in said pulses in said circuit substantially coinciding in circuit, whereby pulses of continuous direct cur rent corresponding substantially in time with said 70 time with said transmitted pulses of electro magnetic radiation; means for receiving said transmitted pulses pass through said electric pulses of electromagnetic radiation after having circuit; means including an antenna and a radio 'been reflected from said surface; means includ frequency amplifier for receiving said pulses of ing a second electric circuit for translating saidv radio waves after having been reflected from said Surface; a second electric circuit connected to 75 received pulses into-continuous direct current 2,404,527 pulses in said second circuit substantially coin ciding in time With said received pulses; an electrical measuring instrument; and means in cluding an electric circuit connected with said instrument and with said first and second cir 12 pulses in Said circuit substantially, coinciding in time with said transmitted >pulses of electro magnetic radiation; means for receiving said pulses of electromagnetic radiation afterli’aving been reñected from said surface; .means including cuits and responsive to the direct current pulses a second electric circuit for translating said, re in said first and second circuits for energizing ceived pulses into continuous direct current said instrument only during time intervals de pulses in said second circuit substantially coin termined by the time lag between the direct ciding in time .with said received pulses;V4 and current pulses in said ñrst circuit and the direct 150.7 means, including an electrical measuring instru current pulses in said second circuit. ment and an electric 'circuit connected with said '7. Distance measuring apparatus, comprising: instrument and with said first and second cir--v means for transmitting pulses of electromagnetic cuits, for measuring the time lag between said radiation to a surface; means including an elec direct current pulses in said first circuit and tric circuit associated With said transmitting said direct current pulses in said second circuit. means for producing continuous direct current GENNADY POTAPENKO.