US2465925A

US2465925A - Radio control system

Info

Publication number: US2465925A
Application number: US536104A
Authority: US
Inventors: Ellison S Purington
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1944-05-18
Filing date: 1944-05-18
Publication date: 1949-03-29
Anticipated expiration: 1966-03-29

Description

March 29, 1949. E. s.I PURINGTON RADIO CONTROL SYSTEM 'Filed May 18, 1944 4 Sheets-Sheer,v l

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March 29, 1949. E. s. PuRlNGToN RADIO CONTROL SYSTEM I '4 sheets-sheet' 2 Filed May 18, '1944 TON.

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Filed May 18, 1944 `March 29, 1949. l E. s, PURiNGToN 2,465,925

RADIO CONTRGL SYS TEM Filed May 18, 1944 4 Sheets-Sheet 4 l-T 220 n/ d. `ll

osclLLAToR INVENTOR ELLISON $.'PURINGTON.

Patented Mar. 29, 1949 UNITED STATES PATENT FFICE aADlO CoN'rRoL sYs'rEM Ellison S. Purington, Gloucester, Mass.,fassignor, by mesne assignments, to Radio Corporation of America, New Yoik, N. Y., .a corporation of Application May 418. 1944, Serial No. 536,104

(Cl. 2,5 T17) 20 Claims. 1

This invention relates to a radio control system suitable for use in ultra-high frequency channels and has for an object to provide `a system of the above type adapted forradio dynamic control or for communication purposes, which is highly selective and which has characteristics such vthat it is free to a high degree from interference.

Another object is to provide a system of the above type having noveland improved details of construction and features of operation.

Various other objects and advantageswill be apparent as the nature of the invention is Vmore fully disclosed. s

The present system utilizes two channels in the ultra-high frequency range, suchas inthe range of Ll0() to 1000 megacycles, and provides for the transmission of short, timed pulses on the two channels which may be varied as to sequence `in accordance with the desired control or signal. The system utilizes a pulse transmitter which is capable of transmitting short pulses'of comparatively high power.

A radiant energy pulse is sent `from the transmitter to the receiver on one channel followed by a radiant energy pulse on the @they akanne1.. There is a frequency separationbetween'the twg channels on which energies necessary for operation are sent, and thereis a time separationV between the arrival of the two venergies at the re ceiver. The freedom from interference depends largely upon the ramount oifrequency separation of the channels and upon the amount of time separation of the energies on `the channels. .A most important factor fis theuse of transmitter energies in the form of vshort dots 4or pulses with very high peak rradiant power,and with relatively long intervals betweenthe pulses,

By the combination of pulsetype transmission, two'radiant energy channels and dilerent times of transmission of the energies onthe. two channels, an extremely high degree of security is provided.

In the present system the pulses may be from 1.0 to 50 microseconds in length. The time interval between the pulses is several times thelengtn of the pulses themselves, for example, about 5 to 20 times the length of thepulses and successive pairs of pulses are separated bya space having a duration several times the interval 'between the pulses themselves, for eXample,20 to 100 times said time interval.

The control may be` responsive to the receipt o f a single pair of pulses. Hence .thepOmplete transmission may be of extremelyshort duration, which renders its interception and interference entremely dfult- VHoweveluthe transmissions-may 'pulse from the pulse transmitter.

extend over a plurality of pairs of pulses iffie-Y sred, in which casepaccidental interference with one or more of the pairs of pulses would not affect'lthe control.

While it is Aknown to be physically possibleand practicable to produce high peak power on a narrow radio band over a short duration of time, it is not practicable to produce alcomparable'high peak powerover both a wide radio band and .over a longduration of time, as would be necessary. for successful interference purposes. Ordinary, nonpulse transmitters would not .be capable of intertering successfully with the vcontrol because sutcient power would not be available to produce a response at 'the receiver matching in intensity the On the other hand, with `a pulse transmitter it would be very unlikely thatthe interfering pulse would coincide in time with a control pulse, or vthat its rateof recurrence would correspond to that of the conltrol pulse as would be required tov produce interference on succeeding pulses. For high speed telegraphic purposes, for example, a single ldot or dash might occasionally be obliterated by interference, but for slow speed or radio control pur-poses, this amount of interference would be entirely negligible.

In accordance with the present invention, a pulse forming circuit is designed to form a sfuccessionof pairs of spaced pulses. Thepulses of each pairare separated and are used 'individually to modulate radio transmitting means operating on two different channels, the first pulse of each pair being connected to modulate the transmitter on one channeland the second pulse of each pairbeing connected to modulate the transmitter on the other channel. Selective means is provided inthe modulating circuit so that the iirst pulse of each pair may be applied to either channel at will and the secold pulse may be applied to the other channel. In this way, the pulses are radiated over the two Channels with a .frequency sequence determined by the selective'means and with a time interval determined by the original pulse forming circuit.

In a specific embodiment of the invention the pulsesin the two channels are received by separate receivers'tuned to the vrespective channels and containingtheusual detector circuits to'make the pulses'. available in an output circuit. The outputs ofthe two. receivers are.` connected to a timing comparator which is designed to be responsive Only'whee the rulsesere received with a predef termine@ time Species Inoue embodiment the timing comparator-inf 3 cludes a pulse stretching circuit which is arranged to stretch the pulse from one of the receivers so as to cause the same to overlap in time the pulse from the second receiver when the rst pulse is received a predetermined time interval before the second pulse. The combined effect of the two pulses, when they are thus caused to overlap, is utilized to actuate an output relay circuit. When only a single pulse is received or when the pulses are not received in proper time sequence to cause the same to overlap in the output circuit of the comparator no response is produced.

The effect of two overlapping pulses separately applied to the timing comparator is to produce a single pulse of a duration equal to the amount of time of overlap. This can be applied to a relay System operative on a single pulse, as for example a gaseous type electronic relay, which however requires a resetdevice such as the use of A. C. plate supply if the control operation is to 4be' repeated. While this is satisfactory for some purposes, it is in general preferable to actuate the control from the combined effect of a considerable number of recurrent pulses giving additional Security by electrical tuning to the recurrence rate.

Instead of utilizing two separate receivers the incoming radiant energy may be received in a single receiver tuned to respond to both channels. The receiver will then include suitable pulse separation means to separate the pulses received in the respective channels and to apply them to the timing comparator above outlined.

Although the novel features which are believed to be characteristic of this invention are pointed out more particularly in the claims appended hereto, the invention will be better understood by referring to the following description, taken in connection with the accompanying drawings in which certain specific embodiments thereof have been set forth for purposes of illustration.

In the drawings:

Fig. 1 is a block diagram indicating the general arrangement of a transmitter and receiver embodying the present invention;

Fig. 2 is a schematic diagram of a pulse forming circuit for use in the system of Fig. 1;

Fig. 2a is a series of curves illustrating the operation of the pulse forming circuit;

Fig. 3 is a schematic diagram of a timing comparator -circuit for use in thereceiver of Fig. 1; and

Fig. 4 is a schematic diagram of a pulse receiver utilizing a single radio receiver tuned to both channels and a pulse separating circuit actuated thereby. In the drawings, the radio transmitter and receiver circuits and the tube circuits are shown only in such detail as is necessary to an under-- standing of the present invention and it is to be understood that the circuits are otherwise of' standard and well known form and include thevarious potential sources and control elements which are well known in the art.

Fig. 1

Referring to Fig. l, the block I represents a pulse forming circuit the details of which are shown in Fig. 2 and which is adapted to produce a series of spaced pairs of pulses a and b and to separate the pulses of each pair as indicated in separate circuits terminating at terminals I I and I2 respectively and having a common ground terminal I 3. The pulse a of each pair of pulses on terminal II is assumed to precede the pulseb on terminal I2 although this sequence may be reversed if desired.

The terminals I I and I2 are connected to poles I4 and I5 respectively of a double pole double throw, reversing switch I6 the stationary contacts of which are connected by lines I'I and I8 respectively, to the input circuits of radio transmitters and 2l respectively. The radio transmitters 20 and 2l are preferably of the Shortwave pulse type' and are adapted to radiate carriers on frequencies f1 and f2 amplitude modulated respectively by the pulses a and b. The transmitters may be designed to radiate only when a pulse is received from the pulse forming circuit I0, so that the energy radiated constitutes a series of spaced pulses occurring first on the frequency f1 and then on the frequency f2 for switch position R, or vice versa for switch position L.

The pulses radiated by the transmitters 20 and 2| are received by the

receivers

22 and 23 respectively which are preferably of the superheterodyne type terminated with detectors to produce pulses in their output circuits indicated by the

terminals

24, 25, 26 and 2l. The terminal 24 of the receiver 22 is connected by a line 30 to an input terminal 3| of a timing comparator 32, the details of which are shown in Fig. 3. 'I'he terminal 26 of the receiver 23 is connected by a line 33 to an input terminal 34 of the timing comparator 32. The terminals and 21 are indicated as connected by a line 35 to ground and.

to a common input terminal 36 of the timing comparator 32.

The timing comparator 32 includes circuits to be described which are selected so that when the pulse on channel .f1 precedes the pulse on channel f2, a right relay 39 is energized and when the pulse on the channel f2 precedes the pulse on the channel f1 a left relay 38 is energized. These relays are provided with armatures 4I and 40 respectively which are adapted to close work circuits which may constitute selective control for mobile objects such as right and left steering controls or a speed control or a suitable signalling circuit, such as an automatic dot-dash receiver.

The arrangement therefore is such that the

relays

39 and 38 will be selectively actuated in accordance with the direction of closure of the switch I6 which controls the sequence of the pulses on the two channels. The switch may, of course, take the form of a push-button, key, or other suitable device which is readily operated for control or signalling purposes.

The timing comparator circuit 32 is preferably designed so that no operation results unless and until both pulses are received and unless the pulses are of sufficient duration and length and are spaced within the specied time limits. In addition, the system may be designed to respond only when the pulses on the two channels are repeated with a recurrence rate within specied limits. In this way the system is made highly selective and free from interference.

Fig. 2

Referring to Fig. 2, the pulse forming circuit is shown as comprising a master oscillator 5U of a type having high stability and designed to oscillate, for example, at 660 cycles per second. The oscillator includes a tube 5I and a frequency control circuit 52 together with the usual bias and regulating circuits, all of which are of standard construction.

The output circuit of the oscillator 5U includes ate-apt e phase Shifter 54. comprising: a condenser and e, resistor 56 connected in series. The resistor 5,8 isV connected in the input circuit of a vacuum tube ampliiier 89 including an amplifier tube 6I and an output transformer 62. The condenser 55 and resistor 56 are preferably of equal numerical impedance at the frequency of operation so that the voltage across the resistance 56` leads the input voltage to the phase shifter by 45. Hence, the voltage to the amplifier 60 leads the voltage from the oscillator circuit by 45.

The secondary of the transformer 62 is of the push-pull type, the two ends of which are connected to the input grids 5,3, 64 of a pair of mod.-

ulator tubes

65 and 65 respectively. Pulses, formed in the manner to be described, are applied to the suppressor grids 61 and 68 of the tubes 65 and 55 by a line 69. The plate ycircuit of the tube 65 is connected by a condenser 10a and a line. 1Q to the output terminal and the plate circuit of the tube 88 is connected by a condenser 1 |a anda line 1| to the output terminal I2. The two terminals are connected through resistors to a common grounded return line 12 which is connected to the terminal I3. The tubes 65 and 6.6 are normally biased by their suppressor grids to-an inoperative condition and are designed to be capable of passing current only when a voltage pulse is received from the line 69.

' The oscillator 5U is also coupled by line 88 through a phase shifter 8| consisting of a, resistance 82 and a condenser 83 to the input circuit of an amplier tube 84. The phase shifter 8|v is similar to'the phase shifter 54, but in this case the input circuit of the tube 84 is connected across the condenser of the phase shifter. Hence the voltage supplied to the tube 84 lags 45 behind tl.e voltage from the oscillating circuit. Inasrnuch as the voltage applied to the tube 6,0 leads by 45, a 90 phase difference is produced between the voltages applied to the tubes 60 and 84.

The tube 84 feeds, through an output transformer 85, a pair of rectiflers 86d and 86h having cathodes 86o and 88d' respectively connected to the two ends of the secondary 81 of the transformer and having anodes connected together by a line 88 and thence through a resistor 89 and a biasing battery 98 and a return lead` 9| to the center tap of the secondary 81. The biasing bat,- tery 98 is connected to determine the voltage .values at which current will flow through the rectiers due to the voltage impressed by the secondary 81. Rectied current ows through a tube internally from plate to cathode, thereafter' externally through secondary winding 81 and line 9| to the positive side of battery 90,y through the battery to the negative side and thence through resistor 89 to the plates 89a and 89h of the rectifying tubes. No current flows in resistor 89 except when the cathode of one of the rectifiers is negative With, respect to line 9| by an amount exceeding the voltage value of battery 98.

The positive side of resistor 89 is connected.

to the cathode 92 of a key tube 95, and the negative side of resistor 89 is connected to the grid 96 of the key tube 95. At both the positive and the negative peaks of voltage across secondary 81, the current through resistor 89 is maximum, so that the grid 9|5` off tube 95 is then highly negative with respect to the. cathode l92. As the voltage cycle progresses, the grid 96 of tube 95 comes to cathode potential, the rectifying tube vcuts oi dueto battery 90, andthe grid 96 of tube. remains at Cathode potential until the other rectiiying tube becomes conductive thereby returning the grid to a negative value.v In this manner, the grid of tube 95 is actuated by voltage pulses with a peak value which brings the grid of tube 95 to cathode potential and causes it to remain at that potential a short interval of time to form trapezoidal current pulses occurring at a rate4 of twice the frequency'of oscillator 58,.

The key tube 95 is shown as a pentode, with the cathode 92 positively biased with respect to ground by a battery |01, and with the Screen 93 and plate 9.4 positively biased with respect to the cathode by batteries. m2., lili. The positive side ci battery |83 is connected to the plate of tube 95 through a, plate. coupling resistor itt. The suppressor grid 97. of tube 9.5 is connected by line 98. to a variable tap 99 on resistor lll., one side of which is connected to the negative and grounded side of battery lill, and the other side oi which is connected to a liner |48.

In the absence of Voltage across resistors 8.9 and lill), the grid of tube 9.5. is at cathode potential, but nevertheless. no plate current flows be. cause the cathode is highly positive with respect to the suppressor. Therefore the control grid pulsesA due to rectification of voltage from second.- ary 81 are not repeated to form corresponding plate current pulses. except when the tube 95 is unblocked by a currentthrcugh resistor |98 which brings the suppressor to the vicinity of cathode potential. A circuit to be described later provides for pulsing resistor |88 recurrently in such a manner that in the embodiment shown the suppressor is. brought to the cathode potential for a sufficient time to pass two pulses, from the control grid to plate, then suppress the passage oi 20 pulses. This isrepeated recurrently in such a Way that for ex,- ample two consecutive pulses out of every twenty two impressed on the grid 98 actually produce plate current, leaving an interval bet-Ween ceIltersr of pairs of pulses 22 times. the interval between centers of the pulses themselves.

Due to the use Vof a high voltage swing from transformer secondary 81, the key tube 95 also operates as a clipper` tube so that only the peaks of the pulses. are repeated into the plate circuit, thereby forming rectangular or slightly trapezoidal shaped output pulses.

The plate 94 of tube 95 is connected through condenser yl I8. to the input grid |89 of a resistance coupled amplifier stage including pentode I l, the output of which is coupled through. condenser I4 to line 89. Positive pulses of plate current to tube 95y cause negative pulses of voltage to the grid |8901c tube negative pulses of current to the plate |12 of tube` I, and positive pulses of voltage to the line 69r and therefore to the suppressor grids 67| and 98; of tubes 65 and 68. The control grids 6.3, 64

ofthe tubes

65 and 88, however, are connected. in push-pull to the secondary of the transformer 62. Hence one of these control grids is positive with respect to the. center tap of the transformer while the other control grid is nega,- tive. When a positivepulse is applied to the suppressor grids 81, 68 from the line 89 a pulse is produced in the output circuit of the tube whose control grid is positive at that instant. The pulses supplied to the suppressor grids are timed by the phase Shifters 54 and 8| to occur on alternate half cycles of the voltage supplied to the control grid. Hence, one pulse from the line e9 is received when the control grid of the tube 65 is positive and the nextk pulse is received when the control grid of the tube 6,8 is positive, The first lpulse is thus passed through the lead 'l0 to the circuit including the output terminal and the next pulse is passed through the lead 'il to the circuit including the output terminal i2, this sequence being repeated whenever a pair or' pulses is applied from line |59. These pulses can be considered as positive pulses of current towards the plates oi'

tubes

65 and 96, and as negative voltage pulses from the output terminals to ground.

Pulse control cincuz't The lead 80 from the oscillator 59 is also connected -to an adjustable phase shifter comprising a pair of condensers |2| and a resistor |2.2 connected in series. The resistor I|222 is connected to the input circuit of an amplier tube |23, the output circuit of which is connected by means of a tapped resistor |24 to the input circuit of an amplifier |25.

The output circuit of the amplifier is connected through a condenser |26 to one cathode ||5 and one anode it of a double diode rectier tube |2'|, the other anode lll' of which is connected to a return lead |28 and the other cathode ||8 of which is connected to lead |28 by a con-- denser |29. The double rectier tube |21 and the condensers |26 and |29 constitute a portion of a countercircuit which in the embodiment described is designed to operate on a ratio of 11 to 1 Such a countercircuit is well known in the art being described in RCA Review, July 1940, A precision television synchronizing signal generator by Bedford and Smith and is accordingly not described herein in further detail. 660 cycle voltage appearing in the output circuit of the amplifier |25 charges the condenser |26 on one half cycle. When the right hand side H6, ||8 of the double rectifier |.2l is conductive the condenser |26 discharges into the condenser |29 and increases the potential of its upper plate. On the next half cycle the right hand side of the double rectier |27 becomes non-conductive so that the charge remains on the condenser |29, whereas the left hand side |5, of the double rectier becomes conductive and allows the charge to leak oir of '7 The multi-vibrator |36 is of standard construction and in the form shown includes a pair of tubes i3? and y|38 having screen and control grids which are cross connected, the respective grids being connected to a resistance network including a pair of resistors having variable taps Uli. The arrangement is such that the normal frequency of operation of the multi-vibrator |39 in the absence of synchronization will be one eleventh of B cycles, that is 60 cycles.

This free running value will be controlled to a limited degree by the setting of the taps |4| on the resistors |40.

The trigger tube |35 is connected to be pulsed when a predetermined voltage is applied tothe input circuit thereof by the condenser |29. The

output circuit of the trigger tube is connected to the oscillating circuit of the multi-vibrator |36 in such a Way that the multi-vibrator falls in step with the pulses of the trigger tube over a substantial variation in setting of the taps |4|.

In the embodiment disclosed the cathode battery |35'a of tube |35 and the condenser |29 are so chosen so that the condenser will be charged to a suiicient voltage to cause the trigger tube |35 to operate and pass current when eleven charges are received from the condenser |26. By this triggering operation, a synchronizing control voltage is impressed upon the screen |3`|s of tube |31, due to the current through tube |35. This control voltage also causes the plate to cathode branch of tube |31 to be highly conductive and discharges the condenser to or nearly to ground potential. Thereupon eleven more cycles of charge on condenser |29 again cause the trigger operation. Hence the multi-vibrator |36 is caused to operate accurately on a frequency one eleventh of that of oscillator 50, that is at 60 cycles per second. Slight adjustments of phase of the multi-vibrator oscillations can be made by adjusting the capacitance of the phase shifting condenser |2|, and by adjustment of the double resistor |49.

The multi-vibrator is designed to produce a 60 cycle alternating pulse in the plate circuit of tube |38 with spaced peaks as distinguished from a sine wave. These pulses are applied across a resistance |42 in the input circuit of a clipper tube |43 which is biased by a battery |43a to operate only at the peaks of the input pulses. The plate circuit of the clipper tube |43 includes a plate resistance |44 which lowers the plate voltage when plate current flows therein.

The plate |431) of the clipper tube |43 is connected to the input circuit of an amplier tube |45 which is normally biased to pass current and is provided with a plate resistance |45. The plate current of this tube |45, however, is reduced when the grid potential is reduced due to a reduction in plate voltage of the tube |43. This reduction in plate current through the plate resistance |45 causes an increase in the plate voltage in the form of a positive voltage pulse which is supplied by a condenser |41 and lead |48 to the resistor |05 above mentioned.

The operation of the multi-vibrator |36 and the bias of the clipper tube |43 are such that the output voltage pulses in the tube |45 are of a duration corresponding to a pair of pulses on the control grid 96 of the tube 95 and are so timed by phase adjustment that the positive bias thus supplied to the suppressor grid 91 of the tube 95 serves to produce a single pair of pulses in the output circuit of the tube 95. These pulses are supplied to the suppressor grids 6l, 68 of the tubes 65 and 68 as above described. With the multi-vibrator |36 operating at 60 cycles, a single .pair of pulses is released each 60th of a second. Since the pulses themselves are derived from a 660 cycle Wave and are separated by one half a cycle, the spacing of the centers of successive pairs of pulses is twenty two times the spacing of the individual pulses of each pair.

Operation of Fig. 2

Ythe tube 95 and serve to unblock the tube 95 during the pulse intervals.

aacute- A 'pulse is applied to the control grid A490 of 'the tube each time the voltage in the secondary '81 of the transformer 85 passes through zero. The secondary voltage is indicated by the curve E of Fig. 2A and the pulses applied to the control grid 93 and repeated as plate current are represented at a and b on the curve F. These pulses and b are continuously repeated on the control grid 96 but only appear in the output circuit of the tube 95 when they co`incide with a pulse on the suppressor grid. Hence, only pairs of pulses are produced in the output circuit of the tube 35 in dicated by the curve F. M

rThe voltages supplied to the control grid 53; 'l of the

respective tubes

65 and 33 from the master oscillator 50 are represented by the curves C and D of `Fig. 2a.. It is to be noted that these voltages are both of 660 cycles frequency but are 180 out of phase due to the push-pull connection ci the two control grids. When the pulses a and b from the output circuit of the tube III are received on the suppressor grids 61, S8 of the

tubes

65 and 63, one or the other of the tubes '35 'or 03 is rendered conductive, depending upon which of the tubes is receiving a positive bias on its control grid at that instantA Y As illustrated in Fig. 2A, the curve E is displaced 90u with respect to the curves C and D due to the phase Shifters 54 and 8|. Hence the pulses of the curve F Which occur as the curve E crosses the zero axis, coincide With the peaks of the Waves C and D. In the embodiment illustrated, the first pulse a. of the 'curve F occurs during the positive half cycle of the curve C which is assumed to be the 'curve of the grid voltage of the tube 55. Hence, the rst pulse of earch paiwill appear in the output plate circuit kof the tube S5 as indi'- catcd by the curve A or Fig. 2A and the second pulse of each 'p air will appear in the output plate circuit of the tube BB. `These pulses cause cor'- responding negative voltage pulses to occur at output terminals 'Iland l2. The phase shifter and resistors' |48 are adjusted to obtain the proper phase relationship between the curve `Gr and the curve F for causing pairs 'of pulses to be produced, y

Referring novv to Fig'. 1`, the pulses in the output circuit of the pulse forming circuit ,are shown as connected through control switch I6 to modulate transmitters 20 and 2 |l which, as previchannels. The pulse a at the terminal I alvvays occurs before thev pulse b at the terminal I2. The control switch ldetermines to which of the transmitters 20 or 2| the first pulse is to be applied. Hence the output Waves of the transmitters represent a pulse on the channel f1 f'ollpwed by a pulse on the channel f2 or vice versa, depending upon the position of the switch It.

Receiving apparatus ously pointed out, are operating on different The waves radiated from the transmitters 'zt and 2| of Fig. 1 are shown 'as received by the receivers 22 'and 23 which are tuned to the re-v spective Wave frequencies and are of standard construction to make the received pulses available in the output circuits of a detector. The detectors are 'of a ll'y'uve which will supply 'positive pulsesat terminals4` 24 and 26Hvvith respect to

ground terminals

25 and 21. These pulses are supplied to the circuitsv including input terminals and 3d of the timing comparator 32. The puise at the ternlnall either precedes or lags behind the pulse at the terminal y34 depending upon the sequence of 'the transmitted pulses.

10 Theicijrcuitfor the timing comparator 32 is Yshovvn more in detail in Fig. 3.

Fig. 3

Referring now to Fig. 3, the terminal 3| is connected by a line '|50 to a resistor |6| in the input circuit of an amplifying triode It/l. The terminalr34 is connected by a line E33 to a resistor Iti' in the input 'circuit of an amplifying triode |55. The return leads from the resistors Ibi and |64 are connected to the terminal 36. The plates u, 30| of the triodes |32 and |65 are fed through resistors |66 and |61 respectively froin a line |63 connected to a source of plate potential shown as a battery |10. For sirnplic'ity ci" construction, the triodes |62 and |55 may be' housed in a common envelope, as may other triodes of the Fig. 3. They Will be described hoivever for convenience as independent tubes.

plates

308, 309 of the tubes IBI and |84 are connected in parallel through a resistance |85 to the line |68.

The tubes |12 and |14 and associated circuits constitute in effect a pulse stretching system which operates when energized by a short negative pulse on the input grid terminal of tube |12 to produce a negative pulse of longer duration and in the same sense on the output circuit of companion tube |14. The output of one tube shown as tube |12 is capacity coupled to the input of the other tube |14 as in a multi-Vibrator, but the output of the tube |14 is directly coupled to the input of the tube |'12 as in an electrical toggle. This system has one stable equilibrium position in the absence of signals. When the condition of stable equilibrium is' momentarily upset, as by a pulse on grid 302 of tube |12 from the plate 300 of tube |32, the system does not instantaneously return to the equilibrium condition, because of the energy change in condenser |`|3 during the pulsing. As a result the plate current of output tube |14 continues to change after the pulse on tube |12 has passed. b

In the embodiment shown in the equilibrium condition tube |14 is biased to below cutoff by battery |15, While tube |12 passes current -due to the positive voltage on its grid 302 derived fromlbattery |10 through resistors |11 and |18. A positive pulse applied from terminall 3| to ground upon ampliiier |32 causes a negative pulse to be applied from the output of tube |62 uponpthe grid 302 of tube |12. In the equilibrium condition With no current flowing to or from the condenser |13 its lower plate is at ground potential and its upper plate is at the potential of the line |68 diminished by the very heavy drop through resistor |10 to the plate 303 of the cur- 'ent carrying' tube |12. When now the negative pulse is impressed upon the control grid 302 of tube |12, the plate current is momentarily diminished toward or to zero, thereby decreasing the voltage drop in resistor |19 and increasing the potential on the upper plate of condenser |13. This tends to make the upper plate of condenser |13 more positive by a charging current to the condenserfrom the plate 303 of tube |12, and this charging current, represented in the condenser as a displacement current, causes corresponding current to flow from the lower plate of condenser |13 to ground through the grid resistor 3|0. As a result, both the upper plate and lower plate of the condenser |13 are raised to a higher potential, and the grid 304 of tube |14 which is connected to the lower plate of condenser |13 is quickly raised to the potential of the cathode of tube |14 or higher. This in turn increases the current flow to the plate 305 of tube |14, thereby lowering its plate potential due to the increased drop through resistor |11. Due to the direct coupling from plate of tube |14 to ground through resistor |18, the lowering of plate voltage of tube |12 drives its grid negatively in the same sense as the original pulse. If condenser |13 were of infinite capacity, the grid 302 of tube 12 would continue to be held negative, so that the controlling pulse from tube |62 would be followed by a permanent holding pulse from tube |14. However due to the capacity of condenser |13 being nite, the potential across condenser |13 changes in accordance with the voltage and resistance in its external circuit. With the grid of tube |12 driven negatively beyond cutoff, making tube |12 currentless, condenser |13 is charged to increase its voltage toward the limiting value of battery |10. But as it approaches this value, the charging current diminishes, decreasing the current through the gridto-cathode and grid-to-ground path for tube |14, so that tube |14 commences to draw less current. As a result the potential of tube |12, until now held below cutoi after the control pulse from tube |62 has passed, approaches the cutoff point. When during the charging of condenser |13 by a current through resistor |15, the cut-ofi' point of tube |12 is reached, and it commences to pass plate current also through the resistor |16, the charging of condenser |13 is checked due to the lowering of voltage applied to the top plate of condenser |13, the grid voltage of tube |12 drops toward zero and due to the coupling from tube |14 to tube |12 the action of causing tube 12 to pass plate current is accelerated. With the charging of condenser |13 checked, the operation of the tubes is such as to cause the condenser to discharge t its equilibrium condition. During this discharge operation, the voltage on the grid 304 of tube |14 is highly negative beyond cutoil', so that equilibrium is reached with no further change in plate current of tube |14.

plates

308, 309 are l2 terminal 34 causes a corresponding unstretched negative pulse to be impressed upon the input of tube |84. By suitable choice of the resistors and the condenser |13 associated with pulse stretching tubes |12 and |14, the pulse on tube |8| may be caused to last longer than the time interval between pulses on terminals 3| and 34. Therefore in the event that terminal 5| is pulsed first and terminal 34 later, within a predetermined time limit established by the action of tubes |12 and |14, overlapping pulses will be impressed on triodes, with the cathodes connected together and` grounded by a line 3|| and with the

plates

It is possible to utilize the pulse through resistor |93 to trigger oil` a gaseous relay tube, but in the present embodiment, use is made of the fact that the pulses established in resistor |93 are of a recurrent nature.

The plate 320 of tube |95 is coupled through a condenser 322 to the anode 323 of a rectier 200, the cathode of which is connected to ground through resistor 20|, bypassed by a condenser 324, and also is connected to the grid 325 of a relay tube 202. A resistor 326 connected from the anode 323 of rectifier 200 to ground provides a D. C. return path for rectifier 200. The plate 321 of relay tube 202 is connected to the winding 39 of a relay 328, the other side of which is connected to line |88, and the cathode of relay tube 202 is positively biased by a battery 329 so that no plate current will ow unless there is current passing through resistor 20| due to action of the rectier 200. The relay 328 is provided with an armature 4| for closing an external work circuit.

The constants of the circuit associated with amplifier |95 are so chosen that it selectively integrates and amplies the pulse power derived from the plate of clipper tube -|9|. This produces a vcause operation of 'the clipper tube |95.

@interesa 'wave form withhigh proportion ofenergyfcon- 1 tent in the fundamental ratev ofpulsing which is impressed on rectifier B. This wave form is `ireci'iied, and smoothed out by the cathode con- =denser 324 of tube 200, and the D. C. component.'

"With-.in a predetermined time limit, amplifier |62 of Fig. 3 impresses a negative pulse upon pulse v`stretching circuit involving tubes |12, |14 and -resulting in a negative pulse of longer duration impressed upon the grid 306 of coincidental key tube |8I. The duration of this pulse overlaps the time interval-'at which a negative pulse is impressed upon coincidental key tube |84 due to `itl'ie later pulse received from tube |65. By the `coincidental action of tubes |'8l and |84, clipper Vtube |91 is pulsed positively so thata -pulse flows in the plate resistor |93 during the interval of overlap. This pulse is broadened, integrated and amplified by "tube |95 and rectied by tube 200 yto cause operation of the relay armature 4I.

In the alternative event that switch It of Fig. 1 is thrown for example to position L the pulse on terminal v34 precedes that on terminal 3| the circuit above described will operate to produce pulses in resistor |85 which are insufcient to For utilizing the possible control corresponding to terminal 34 being pulsed before terminal 3|, a companion circuit '203 is provided. This may be of the same general construction as that previously described, with corresponding parts ldesignated 'by like numbers but followed by the letter c. However terminal 34 is connected to drive the grid of tube |6205 'and terminal 3| is connected to `drive the grid of tube i65a. Therefore the pulse delay circuit 209 responds to a pulse on terminal '34. The output of circuit 259 includes a relay 328m with armature 4B.

In this manner, the circuit of the timing comparator of Fig, 3 provides for operation of left relay 32Bit when the switch i6 is closed to position L which pulses channel f2 before fi and it provides for closure of right 4relay 328 when the switch Il is closed to position R which pulses channel f1 before fe.

Fig. 4

In the system shown in Fig, 1 two independent ,

receivers

22 and 23 are provided which are tuned respectively to the channels f1 and f2. Fig. 4 `shows a circuit for receiving both channels on a single intermediate frequency type receiver and separating the pulses for application to the timing comparator. Referring to Fig. 4, the block 2|8) indicates a receiving circuit which is tuned broadly to receive the two channels f1 and f2 Asingle frequency local oscillator 2 and a detector 2|'2 are connected to make the two pulses available as intermediate frequency pulses in an output circuit transformer 2 I5 tuned to both intermediate frequencies in a well known manner. These pulses are supplied through the transformer 2|5 to an amplifier tube 2|S, the output circuit oi which is connected `to a well known type of frequency discriminating circuit 2|1 which includes coupled inductors 2|8 and 2|9 forming parts of a coupled. circuit system and connected at their les @mid-points through a condenser 22o. The midpoints of the inductors 2|8 and2|9 are also connected through a resistor 222 and an inductor 223 to the return lead 2'24 of the amplifier tube 2|6.

The frequency discriminating circuit 2|'l has characteristics such that one of the pulses, for example, the intermediate frequency pulse corresponding to that received on the frequency f1, may be derived from one end of the inductor 2|9 and applied by a lead 225 to an amplifier tube 226, 'whereas the intermediate frequency pulse corresponding to that received on the frequency f2 may be derived from the other end of the inductor 2 9 and applied by a lead 227 to an amplifier tube 22S. The output Circuits of the amplifier tubes 2256' and 223 are connected through selective intermediate frequency transformers 23|? and 23| respectively to rectiers 232 and 233 respectively.

Resistors

234 and 235, in circuits with the rectifier's 232 and 233, are connected respectively across

terminals

24 and 25 and across

terminals

26 and 21 which correspond to the

terminals

24, 25, 26 and 21 of Fig. 1. The pulses are thus separated 'and made individually available as positive vpulses to the timing comparator.

The operation of this embodiment is similar to that above described 'except that only a single receiver is used instead of the two receivers indicated in Fig. 1.

In the embodiment of Fig, 4 a pair of pulses on channels f1 and f2 vare received and detected in the tuner 2 it and detector 2 I2 and are applied to the amplifier Zl through a double peaked trans-- former 2|5 with transmission peaks corresponding in spacing to the two frequencies f1 and. f2. These pulses are separated by the frequency discriminator circuit 2|'| and are individually amplied in the amplifiers 225 and 22d. The amplifier outputs are rectified by the

rectiiiers

232 and 235 to produce voltage drops in the

resistors

234 and 235 in the form of voltage pulses corresponding to the received pulses. The pulse received on the frequency f1 is thus supplied to the terminals 2li and 25 and the pulse received on the frequency fz is supplied to` the terminals 2G and 2l'. These terminals are connected to the timing 'comparator 52 as shown in Fig. 1 wherein their timing is compared and the relays 328 and 3280i are selectively actuated in accordance with the pulse sequence.

It is to be understood that a plurality of channels may be used which may be pulsed in selected sequences for a multiple control. A pair of channels have been described for purposes of illustration only,

Although certain specific embodiments of the invention have been shown and described in detail, it is to be understood that the invention is not to be restricted thereto, but is only to be limited in accordance with the scope of the following claims.

What is claimed is:

l'. A radio transmitting system comprising radio transmitting means to propagate discontinuously pulsed radiant energy substantially concurrently on a plurality of different radio frequency channels, a pulse forming circuit to form a series of' discontinuous energy pulses having :i predetermined time sequence, means modulating said radio transmitting means with said pulses to seiectively propagate the individual pulses of said series on different radio frequency channels, and means controlling the sequence of said pulses on the various channels for signalling.

ases-92.5

2. A radio transmitting system comprising radio transmitting means to propagate discontinuously pulsed radiant energy on a pair of different radio frequency channels, a pulse forming circuit to form a pair of pulses in predetermined time sequence, means modulating said transmitting means with said pulses to propagate one pulse over one channel and the other pulse over: the other channel in sequence, and means con-- trolling said sequence for signalling.

3. A radio transmitting system comprising a pair of radio transmitters connected to propagate modulated carriers on different radio frequency channels, a pulse forming circuit connected to form a pair of pulses in predetermined time sequence, means modulating one of said transmitters with one of said pulses and means modulat ing the other of said transmitters with the other of said pulses, and means selecting the sequence of said pulses for signalling.

4. A pulse forming circuit for forming groups: of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator and having means converting the impressed` oscillations into a series of short spaced pulses a plurality of different frequency output circuits each connected to receive different successiveones of said pulses, means normally blocking the transfer of pulse energy to all of said output circuits, a control channel coupled to said oscillator' and having means to convert the impressed oscillations into a series of pulses spaced by a time interval corresponding to the period of several of said first pulses and each of a length to overlap at least two of said rst pulses, and means responsive to said last pulses to unblock said blocking means and release sequentially a corresponding number of said rst pulses to said output circuits.

5. A pulse forming circuit foi forming groups 1 of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator, said channel including a pulse forming rectier biased to pass current only at the peaks of the applied oscillation to form a series of short spaced pulses, a plurality of different frequency output circuits each connected to receive different successive ones of said pulses, means normally blocking the transfer of pulse energy to all of said output circuits, a control channel coupled to said oscillator and having means to convert the impressed oscillationsinto a series of pulses spaced by a time interval corresponding to the period of several of said rst pulses and each of a length to overlap at least two of said first pulses, and means responsive to said last pulses to unblock said blocking means and release sequentially a corresponding number of said first pulses to each of said output circuits.

6. A pulse forming circuit for forming groups of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator, said channel including a pulse forming rectier biased to pass current only at the peaks of the applied oscillation to form a series of short spaced pulses, a space discharge device having a control grid connected to receive said pulses, a control channel coupled to said oscillator and having means to convert the impressed oscillations into a series of pulses spaced by a time interval corresponding to the period of several of said first pulses and each of a length to overlap at least two of said rst pulses, said space discharge device having a second grid connected to receive said last pulses and being biased to pass current only when pulses are received simultaneously by both of said grids, a plurality of different frequency output circuits fed by said space discharge device, and means for elfectively coupling each of said output circuits successively to said space discharge device so that successive ones of said first pulses are applied to different ones of said output circuits in predetermined sequence.

7. A pulse forming circuit for forming groups A.of pulses, comprising a master oscillator, a pulse .forming channel coupled to be fed by said oscillator and having means converting the impressed oscillations into a series of short spaced pulses, :a plurality of different frequency output circuits each connect-ed to receive different successive ones lof said pulses, means normally blocking the trans- .fer of pulse energy to said output circuits, a con- :trol channel coupled to said oscillator, said last channel including a pulse forming oscillator operating at a frequency which is a predetermined fraction of the frequency of said master oscillator, coupling means locking said last oscillator into step with said first oscillator, pulse forming means converting the energy of said last oscillator into a series of pulses spaced by time :intervals corresponding to the period of several :off said first pulses and each of a length to over- ;l'ap at least two of said iirst pulses, and means :responsive to said last pulses to unblock said iolocking means and release a corresponding numlber of said first pulses successively to different ones of said output circuits.

8. A pulse forming circuit for forming groups of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator and having means converting the impressed oscillations into a series of short spaced pulses, a plurality of different frequency output circuits each connected to receive successively different ones of said pulses, means normally blocking the transfer of pulse energy to said output circuits, a control channel coupled to said oscillator, said last channel having a counter-circuit connected to produce pulses having a frequency which is a predetermined fraction of the frequency of said master oscillator, a second oscillator connected to :said counter-circuit to operate at the frequency .of said last pulses, a pulse forming circuit conlnected to convert the oscillations of said last oscillator into a series of pulses spaced by a time interval corresponding to the period of several of said first pulses and each of a length to overlap :at least two of said rst pulses, and means responsive to said last pulses to unblock said blocking means and release successive ones of said first pulses to different ones of each of said output circuits.

9. A pulse forming circuit for forming groups of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator and having means converting the impressed oscillations into a series of short spaced pulses, a plurality-of different frequency output circuits each connected to receive successively different ones of said pulses, means normally blocking the transfer of pulse energy to said output circuits, a control channel coupled to said oscillator, said last channel containing a counter-circuit connected to have a pulse frequency corresponding to a predetermined fraction of the frequency of said master oscillator, a multi-Vibrator connected to operate in step with said last pulse frequency, a pulse forming circuit fed by said multi-vibrator and connected to convert the oscillations thereof into a series of pulses spaced by a time interval corresponding to the period of several of said first pulses and each of a length to overlap at least two of said first pulses, and means responsive to said last pulses to unblock said blocking means and release successive ones of said first pulses to dierent ones of said output circuits.

10. A pulse forming circuit for forming pairs of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator and having means to convert the impressed oscillations into a series of short spaced pulses, a pulse circuit connected to receive said pulses, means normally blocking the transfer of energy to said pulse circuit, a control channel coupled to said oscillator and having means to convert the impressed oscillations into a series of pulses spaced by time intervals corresponding to the period of several of said iirst pulses and each of a length to overlap at leat tvvo of said first pulses, means responsive to said last pulses to unblock said blocking means and release a pair of said first pulses to said pulse circuit, an output circuit fed by said oscillator and having different radio frequency output channels selective respectively of the positive and negative half cycles of the impressed oscillations and normally blocked, and means responsive to said pulse circuit to unblock said output channels for thereby selectively transmitting thereover the individual pulses of said pair which coincide in time with the positive and negative half cycles respectively.

11. A pulse forming circuit for forming pairs of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator and having means to convert the impressed oscillations into a series of short spaced pulses, a pulse circuit connected to receive said pulses, means normally blocking the transfer of energy to said pulse circuit, a control channel coupled to said oscillator and having means to convert the impressed oscillations into a series of pulses spaced by time intervals corresponding to the period of several of said first pulses and each of a length to overlap at least two of said first pulses, means responsive to said last pulses to unblock said blocking means and release a pair of said rst pulses to said pulse circuit, an output channel coupled to be fed by said master oscillator and having a pair of space discharge devices having input circuits connected in pushpull relationship to be responsive to alternate half cycles of the impressed oscillations, individual different radio frequency output circuits fed by the respective space discharge devices, said devices being normally blocked, and means connecting said pulse circuit to unblock said devices for producing pulses in the respective output circuits thereof corresponding to the individual pulses of said pair which coincide in time with the positive and negative half cycles respectively.

12. A pulse forming circuit for forming pairs of pulses, comprising a master oscillator, a pulse output channel comprising a pair of normally blocked space discharge devices having input circuits connected in push-pull relationship and coupled to be actuated by said oscillator, individual diierent radio frequency output circuits fed by the respective devices, a pulse forming channel coupled to be fed by said oscillator and having means forming a series of short, spaced pulses corresponding to the successive half cycles of the impressed oscillations, a normally blocked 18 l space discharge device having an input circuit 'ied by said last pulses and having an output circuit connected to unblock said first devices, and a control channel also coupled to said oscillator and having a frequency converter to produce a Wave having a irequency which is a predetermined fraction of the oscillator frequency, means producing a series of short spaced pulses having a frequency corresponding to said last frequency and having a length corresponding to a pair of said first pulses, and means supplying said last pulses to unblock said last device for supplying thereby said pair oi pulses to unblock said rst devices so as to supply the individual pulses of said pair alternately to said output circuits.

A pulse forming circuit for forming groups oi' pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator and having means converting the impressed oscillations into series of short spaced pulses, a pair of different radio frequency output circuits each connected to receive diierent successive ones of said pulses, means normally blocking the transfer of pulse energy to said output circuits, a control channel coupled to said oscillator and having means to convert the impressed oscillations into a series of pulses spaced by a time interval corresponding to the period of several of said first pulses and each of a length to overlap at least two of said first pulses, phase shifting means to cause said last pulses to overlap a pair of said first pulses, and means responsive to said last pulses to unblock said blocking means and release a corresponding number of said rst pulses successively to said output circuits.

14. A pulse forming circuit for forming pairs of pulses, comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator and having means to convert the impressed oscillations into a series of short spaced pulses, a pulse circuit connected to receive said pulses, means normally blocking the transfer of energy to said pulse circuit, a control channel coupled to said oscillator and having means to convert the impressed oscillations into a series of pulses spaced by time intervals corresponding to the period of several of said iirst pulses and each of a length to overlap at least two of said rst pulses, means responsive to said last pulses to unblock said blocking means and release a pair of said first pulses to said pulse circuit, an output circuit fed by said oscillator and having different radio frequency output channels selective respectively of the positive and negative half cycles of the impressed oscillations and normally blocked, phase shifting means to cause said first pulses to coincide with the oscillator half cycles, and means responsive to said pulse circuit to unblock said output channels for thereby selectively transmitting thereover the individual pulses of said pair which coincide in time With the positive and negative half cycles respectively.

15. A pulse forming circuit comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator, said channel including a pulse forming rectifier biased to pass current only at the peaks of the applied oscillation in the form of a series of spaced pulses, a space discharge device having a control grid connected to receive said pulses, said device normally passing current and being biased to cut off in response to said pulses whereby current pulses are produced in sai-d device when the oscillator voltage passes through Zero, an output circuit fed by said oscillator and having difierent radio frequency outputchannels selective respectively of the positive and negative half cycles of the impressed oscillation and normally blocked, phase shifting means to cause said current pulses to coincide with the positive and negative half cycles in said output channels, and means responsive to said current pulses to unblock said output channels for thereby selectively transmitting thereover the individual pulses which coincide in time with the positive and negative half cycles respectively.

16. A pulse forming circuit comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator, said channel including a pulse forming rectier biased to pass current only at the peaks of the applied oscillation in the form of a series of spaced pulses, a space discharge device having a control grid connected to receive said pulses, said device normally passing current and being biased to cut off in re-I sponse to said pulses whereby current pulses are produced in said device when the oscillator voltage passes through zero, and a space discharge device having a control grid connected to receive said last pulses and biased to pass current only on the peaks of said last pulses to thereby produce short spaced current pulses, an output circuit fed by said oscillator and having different radio frequency output channels selective respectively of the positive and negative half cyclesh of the impressed oscillations and normally blocked, phase shifting means to cause said current pulses to coincide with the positive and negative half cycles in said output channels, and means responsive to lsaid current pulses to unblock said output channels for thereby selectively transmitting thereover the individual pulses which coincide in time with the positive and negative half cycles respectively.

17. A pulse forming circuit comprising a mas-- ter oscillator, a pulse forming channel coupled to be fed by said oscillator, said channel including a pulse forming rectifier biased to pass current only at the peaks of the applied oscillations in the form of a series of spaced pulses, a spacev discharge device having a control grid connected to receive said pulses, a plurality of output circuits fed by said space discharge device, and means for feeding said pulses derived from said -device successively to different ones of said output circuits.

18. A pulse forming circuit comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator having means clonverting the impressed oscillations into a series of spaced pulses, an output circuit fed by said ilu oscillator and having different radio frequency output channels selective respectively of the positive and negative half cycles of the impressed oscillations and normally blocked, and means responsive to said pulses to unblock said output channels for thereby selectively transmitting thereover the individual pulses which coincide in time with the positive and negative half cycles respectively.

19. A pulse forming circuit comprising a master oscillator, a pulse forming channel coupled to be fed by said oscillator having means converting the impressed oscillations into a series of spaced pulses, an output channel coupled to be fed by said master oscillator and having a pair of space discharge devices having input circuits connected in push-pull relationship to be responsive to alternate half cycles of the impressed oscillations, individual different radio frequency output circuits fed by the respective space discharge devices, said devices being normally blocked and means connecting said pulse circuit to unblock said devices for producing pulses in the respective output circuits thereof corresponding to the individual pulses which coincide in time with the positive and negative half cycles respectively.

20. A pulse transmission system comprising a. source of alternating current, a pair of diierent radio frequency output channels connected to be selectively fed by the positive and negative half cycles respectively fof said current, a pulse forming circuit coupled to said source and having means converting each half cycle into a short pulse, and means modulating said output channels With said pulses whereby alternate pulses are transmitted over diiTerent channels.

ELLISON S. PURINGTON.

REFERENCES CITED The following references are of record in the oi this patent:

UNITED STATES PATENTS Number Name Date 1,805,918 Meissner May 19, 1931 2,113,011 White Apr. 5, 1938 2,153,179 Fitch Apr. 4, 1939 2,211,942 White Aug. 20, 1940 2,235,768 Luck Mar. 18, 1941 2,286,377 Roberts June 16, 1942 2,352,634 Hull July 14, 1944 2,357,398 Gray Sept. 5, 1944 2,405,237 Ruhlig Aug, 6, 1946 2,405,238 Seeley Aug. 6, 1946 2,405,239 Seeley Aug. 6, 1946