US2510139A - Radio control system - Google Patents

Description

June 6, 1950 E. s. PURINGTON RADIO CONTROL SYSTEM :s sheets-sheet 1 @www Original Filed May 18; 1944 IN VEN TOR.

ATTORNEY.

June 6, 1950 E. s. PURINGTON RADIO CONTROL SYSTEM Original Filed May 18, 1944 3 Sheets-Sheet 2 Y INVENTOR. Ella/0)? Jl Pari/zgza/z BY M NN ON..

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ATTORNEY June 6, 1950 E. s. PURINGTON v2,510,139

RADIO CONTROL SYSTEM' Original Filed May 18, 1944 3 Sheets-Sheet 3 ATTORNEK Patented June 6, 1950 UNITED STATES PATENT OFFICE RADIO CONTROL SYSTEM Delaware Original application May 18, 1944, Serial No. 536,104, now Patent No. 2,465,925, dated March 1945, Serial No. 602,235

11 Claims. (Cl. Z50-20) This application is a division of my copending U. S. application Serial No. 536,104 filed May 18, 1944 entitled Radio control system, now Patent No. 2,465,925 granted March 29, 1949, assigned to the same assignee as the instant appli cation.

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 for radio dynamic control or for communication purposes, which is highly selective and which has characteristics such that it is free to a high degree from interference.

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

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

The present system utilizes two channels in the ultra-high frequency range, such as in the range of 400 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 other channel. There is a frequency separation between the two channels on which energies necessary for operation are sent, and there is a time separation between the arrival of the two energies at the receiver. 'Ihe freedom from interference depends largely upon the amount of frequency separation of the channels and upon the amount of time separation of the energies on the channels. A most important factor is the use of transmitter energies in the form of short dots or pulses with very high peak radiant power, and with relatively long intervals between the pulses.

By the combination of pulse type transmission, two radiant energy channels and different times of transmission of the energies on the two channels, an extremely high degree of security is provided.

In the present system the pulses may be from to 50 microseconds in length. The time interf val between the pulses is several times the length of the pulses themselves, for example, about 5 to 20 times the length of the pulses and successive pairs of pulses are separated by a space having a duration several times the interval between the Divided and this application June 29,

pulses themselves, for example, 20 to 100 times said time interval.

The control may be responsive to the receipt of a single pair of pulses. Hence the complete transmission may be of extremely short duration, which renders its interception and freedom from interference signals extremely diicult. However, the transmissions may extend over a plurality of pairs of pulses if desired, in which case, accidental interference with one or more of the pairs of pulses would not affect the control.

While it is known to be physically possible and practicable to produce high peak power on a narrow radio band over a short duration of time, it is not practicable to produce a comparable high peak power over both a wide radio band and over a long duration of time, as would be necessary for successfully overcoming strong interference signals. Ordinary, non-pulse transmitters would not be capable of interfering successfully with the control because suilicient power would not be available to produce a response at the receiver matching in intensity the pulse from the pulse transmitter. On the other hand, with a pulse transmitter it would be very unlikely that the interfering pulse would coincide in time with a control pulse, or that its rate of recurrence would correspond to that of the control pulse as would be required to produce interference on succeeding pulses. For high speed telegraphic purposes, for example, a single dot or dash might occasionally be obliterated by interference, but for slow speed or radio control purposes, this amount of interference would be entirely negligible.

In accordance with the present invention, a pulse forming circuit is designed to form a succession of pairs of spaced pulses. The pulses of each pair are separated and are used individually to modulate radio transmitting means operating on two different channels, the rst pulse of each pair being connected to modulate the transmitter on one channel and the second pulse of each pair being connected to modulate the transmitter on the other channel. Selective means is provided in the modulating circuit so that the iirst pulse of each pair may be applied to either channel at will and the second 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 pulses in the two channels are received by separate receivers tuned to the respective channels and containing the usual detector circuits to make the pulses available in an output circuit. The outputs of the two receivers are connected to a timing comparator which is designed to be respon sive only when the pulses are received with a predetermined) time spacing.

In one embodiment the timing comparator includes 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 firsty pulse is received a predetermined time interval before the second pulse. The' combinedeffect of the two pulses, when they are thus caused to overlap, is utilized to actuate an'v output relay circuit. When only a single pulse isv 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 eflectof two overlapping pulsesseparately applied to the timing comparator is to produce a single pulse of a duration equal to the amount of time of` overlap. This caribe applied.. to a relay system operative. on. a` single pulse, as for. examplea gaseous typeelectronic. relay, whichihowever requires a resetdevice such as the use of' A. C. plate supply if. the control. operation isy to be repeated. While this is. satisfactory for some purposes,.it is in general. preferable to. actuate the control from the combinedeffect of a considerable number of. recurrent pulses giving additional security by electrical tuning tothe recurrence rate.

Instead. of utilizing two separate receivers the incoming radiant energy may bereceived in a singie 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 applythem to the timing comparator above outlined.

Although the novel features which are believed tobe characteristic of this invention are pointed out more particularly in the claims appended hereto,.the invention will be better4 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 purposesof illustration.

In the drawings:v

FigureV l is a block diagram indicating the general arrangement of atransmitter and receiver embodying the present invention;

Figure 2 is a schematic diagram. of a timing comparator circuit for use in the receiver of Fig. 1; and

FigureA 3 is a' schematic diagram of 'a pulse receiver. utilizing a single radio receiver 4 tuned t'o both channels and a pulse separatingcircuit actu'- ated thereby;

In the drawings, the radio transmitter. and receiver circuits andthe tube circuits arev shown only in such detail as is' necessary to an understanding of the present invention and it is to be understood that the circuits are otherwise of standard and'well known form andA include the various potential sources and control elements which arev` well knownin the art.

FIGURE l.n

Referring to Fig. l, the block irepresents a pulse forming circuit the details of which arenot herev shown and which is adapted to produce a, series of spacedpairs of pulses a. and b and: to separate thepulses of each pair as indicated in separate circuits' terminatingv atr terminals` H and 4 l2 respectively and having a common ground terminal I3. The pulse a of each pair of pulses on terminal il is assumed to precede the pulse b on terminal l2 although this sequence may be reversed if desired; y

The terminals H andl i2 areconnected to poles i4 and i5 respectively of a double pole double throw, reversing switch i6 the stationary contacts of which'are connected by lines il and i8 respectively, to the input circuits of radio transmitters 2u" andi 2li respectively. The radio transmitters Zit and 2l are preferably of the Shortwave pulse type and are adapted to radiate carriers on frequencies f1 andfz amplitude modulated respectively by tlie pulses a and b. The transmitters may be designed to radiate only when a pulse is received from the pulse forming circuit il, so that the energy radiated constitutes a series of spaced pulsesroccurring 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 Zilla'nd 2i" are receivedb'y'the receivers 22' and2'3 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 21. The terminal' 24T of the receiver 22 is connected by a line 30 to an input terminal 3i of. a timing' comparator 32., the details ofV which are shown in Fig. 3. The terminal 2e of the receiver 23 is connected by a line 33 to an input' terminal 34 ofthe timing comparator er. The terminals 25 and 21 are indicated as connected by a line 35 to ground and. to a common inputv 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 fz, a right relay 39" is energized and when the pulse on the channel f2 precedes the pulse on the channel" fi a left relay 38 is ener'giz'edl These relays. are provided with armatures!!! and all respectively which are adapted' to close work circuits which may constitute selective' control for mobile objectssuch as right andI left steering controls or a speed' control or a suitable signalling circuit, such as an automaticl dot-dash receiver.

They arrangement therefore isl such thatk the relays 39 and 38 will be selectivelyactuated in accordance with the direction ofy closure of the switch It whichk 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 isA readily operated for control or signalling purposes.

The timingcomparator circuitV 32 is preferably designed so-thatno operation results unless and until both pulses are received and unless the pulses are of 'suicient duration and-l` length and are spacedl within the specified time limits; In addition, the systemv may be designed torespond only when the pulseso'n the twofchannels are re Deat'ed' with a recurrence.- rat'ef within speci-fied limits. In thisway the system is madef highly selective" and free from interference-1.

Receiving' apparatus The waves-radiated from the transmitters 20 and 2| of Fig. 1 are showny as received by the receivers. 22r and 23 which are. tuned tothe respective wave4 frequencies andare of. standard construction to make the` received pulsesavailable inlthe output circuits oa detector. The detectorsare. of atype which will supply positivepulses atVV terminals 24'f and 2`6` with. respect'. to. ground terminals 25 and 21. These pulses are supplied to the circuits including input terminals 3| and 34 of the timing comparator 32. The pulse at the terminal 3| either precedes or lags behind the pulse at the terminal 34 depending upon the sequence of the transmitted pulses. The circuit for the timing comparator 32 is shown more in detail in Fig. 2.

FIGURE 2 Referring now to Fig. 2, the terminal 3| is connected by a line |60 to a resistor |6| in the input circuit of an amplifying triode |62. The terminal 34 is connected by a line |63 to a resistor |64 in the input circuit oi an amplilying triode |65. The return leads from the resistors |6| and |64 are connected to the terminal 36. The plates 300, 30| of the triodes |62 and |65 are fed through resistors |66 and |67 respectively from a line |68 connected to a source of plate potential shown as a battery |10. For

simplicity of construction, the triodes |62 and |65 may be housed in a common envelope, as may other triodes of the Fig. 2. They will be described however ior convenience as independent tubes.

The pulse output of the tube |62 is fed through a condenser |1| to the control grid 302 of a tube |12. The plate 303 of tube |12 is connected through a condenser |13 to the control grid 304 of a tube |14. The cathodes of the tubes |12 and |14 are connected to ground through a biasing battery |15. The plates 303, 305 of the tubes |12 and 14 are connected to the line |68 through resistors |16 and |11 respectively. The plate 305 of the tube |14 is also connected through a resistor |18 with the control grid 302 of the tube |12 and through a resistor |19 and a condenser |80 to the control grid 305 of a key tube |8I. The output circuit of the amplifier tube |65 is connected by a line |82 through a resistor |83 to Y the control grid 301 of an amplier tube |84. The plates 30B, 309 of the tubes |8| and |84 are connected in parallel through a resistance |85 to the line |68.

The tubes |12 and |14 and associated circuits constitute in eiect a multivibrator circuit 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 |62, the system does not instantaneously return to the equilibrium condition, because of the energy change in condenser |13 during the pulsing. As a result the plate current of output tube |14 continues to change after the pulse on tube |12 has passed.

In the embodiment shownin the equilibrium condition tube |14 is biased to .belowcutoi by battery |15, while tube |12 passes current-due to the positive voltage on its grid 302 derived from battery through resistors |11 and |18. Al positive pulse. applied from' terminalV 3| to ground upon amplier |62 causes a negative pulse to be applied from the output of tube |62 upon the 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 or the line |68 diminished by the very heavy di'op through resistor |16 to the plate 303 oi the current carrying tube |12. When now the negative pulse is impressed upon the control grid 362 oi tube |12, the plate current is momentarliy diminished toward or to zero, thereby decreasing the voltage drop in resistor |16 and increasing the potential on the upper plate o condenser |13. rliiis tends to make the upper plate of condenser |13 more positive by a charging current to the condenser lrom tile plate 303 of tube |12, and this charging current, represented in the condenser as a displacement current, causes corresponding cuii'ent to flow from the lower plate ol condenser |13 to ground through the grid resistor 3|0. As

20j a result, both the upper plate and lower plate quickly raised to the potential of the cathode 0I'. tube |14 or higher.

current flow to the plate 305 oi' tube |14, thereby lowering its plate potential due to the increased drop tlnough resistor |11. Due to the direct coupling irorn plate oi' tube |14 to ground through resistor |18, the lowering oi' plate voltage ol' tube |12 drives its grid negatively in the saine sense as the original pulse. 1i" 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. I-lowevei' due to the capacity of condenser |l3 being finite, the potential across condenser |13 changes in accordance with the voltage and resistance in its external circuit. With the grid ol' tube |12 driven negatively beyond cutolii, making tube H2 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 grid-to-cathode and grid-to-ground path for tube |14, so that tube |14 commences to draw less current. As a result the potential or tube |12, until now held below cutoi after the control pulse from tube |62 has passed, appioaches the cutoff point. When during the charging of condenser |13 by a current through resistor |16, the cut-off point of tube |12 is reached, and 1t commences to pass plate current also through the resistor H6, the charging of condenser |13 is checked due to the lowering of voltage applied to the top plate oi 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 to its equilibrium condition. During this discharge operation, the voltage on the grid 364 of tube |14 is highly negative beyond cutoff, so that equilibrium is reached with no fui-ther 1 change in plate current of Atube |14. A .v

By this action, the negative pulse impressed for a short time by the tube |62 upon the grid of tube |12 causes an extended positive'pulse to appear on the grid of tube |14, and an extended negative pulse to be impressed from the plate of 4 tube |14' onto the grid 306 of tube |8|.

The alternating current output of the amplifyingrtube .I5..is .transmitted though .lineY |32;- andlresistor.. |33 .toithe control gridiil'ini ,triade tubelii/i. .Consequently;through.thetaction of. tubes |52, .|12 .and 1.113,3, positive .pulseapplied to terminal 3| ,causes anegative. pulse with...the

sance startingtime, but..of longer-.duration tobe.,

impressed .upon the .inputoftube I8|. Also by. the action of .tube |55,.a `4positive..pulse applied. to terminal 3.4 `.causes a ..corresponding.un. stretched negative. pulse to .be impressed .upon the inputf tubel. .By suitable-choice .of the resistors `and .the condenser .|13 .associated with pulse.stretchingtubes .|12 and H4, the .pulseon tube 8| .maybe `caused .to `last .longer than vthe time .interval .between pulses .on .terminals 3| and-.34.v ...Therefore in the .eventthat terminal 3,5 is pulsed .rstand yterminaluild later, withina predetermined time limit established by .the acf.

tion of tubes `|72 and .114,.overlapping pulseswill be :impressed on .the two tubes-|8| and |841.. If

however vterminal 34 .is .pulsedrst .then the pulse. on tube. .|84 willfhave passed .before ithepulse onY tube |8| starts,.and there will beno overlap .of

these pulses.

.The tubes|8|y and. |84 .arecoincidental key tubes, and in '.the embodiment. shown theyare triodes, with .the .cathodes connected together and grounded Abya Aline I3| .and Ywith the plates 3G87, .339 connected together .and Yfed Afrom Ythe line .lvthrough theresistor |85. The .plates 3&3, 339l are vdirect coupled through resistor |96 to the grid 3| 2 of-a clipper tube 13| lhavingl its cathodetbiased positive with. respect to ground bya battery 3l3 andits vplate 3|@ fed-from the line |68 .through a resistor |33. The grid 3|2 of tube-.|9| Vis positively 4biased .byY the direct current .flowing through resistors |85- and |90 and'- through .the grid resistoriii to-ground,-but the Y cathode .battery 3| 3.*.biases/'the cathode of tube |9| toa .muchlhigher/ potential than its-grid; so that as a net result, tube-|9| isbiased considerably .beyond cutoff.r so that YVnormally. no -plate current ,.ilows through .resistor f l 93.

'Circuitconditionsare sovadjusted that -no -current: passes through resistor |93 until Ithe -grids l of.both-tubes IBI and-|84 are very* considerably negative. .Inthe absence ofapulse ontube I-Bi Y.

for example, cutoi -of -tube--|3ll by a negative pulse will cause achange of `plateY current through resistor |85,-but.no-effectlin resistor M33. Onlywhen thepulseson tubes 48| Vand B84 Jare coincidentalwill-there be a pulse through resistor S3.v`

It Yis possible v to 'utilize the Ipulse through 'resistor |93 :to trigger-oia-gaseous relayY tube, butY in the .present embodiment,-use isvmade of the fact thatthe pulses established in resistor-|93l are. of .a recurrent nature.l

The plate v3M `of clipper tube- ISI is connected through condenser |94 to the grid 3|@ of amplifyingtriode |35, which in turn is connected toY ground .by a resistor 3|? and condenser 3%3 yin parallel. The cathode of the triodev amplier |35. is grounded by line 3|9 and its plate '32@ is connected to line Y|558 through a .plate resistor 32|. The plate 32E) of tube |95 is coupled through acondenser332v to the-anode of a rectier23i3, thecathodeof whichis connected to ground through. resistor V20|, bypassed by a .condenser 32d, and also is connected to the grid 325 of a relay tube 2&2. A resistor 325 conm nected from the anode .323 of rectifier 29|! to ground provides a D. C. return .path for rectier. 234). The vplate 32T of relay tube 2in? is connected to the winding 39 of a relay 328, the wher side 0f which isenaectd to Vvlire les,

The constants of the circuitassociated-withr-A amplifier |95 are so chosen that it selectively integrates and amp'lies'theA pulse power derived v.from-the-plate of clipper tube 49|'.This produces a wave-i`ormwith high properti'onwofr energy content vin the fundamental rates offpuls ingmhich yis impressed on-rectier 28|):- `'lliis cathode condenserl 3 2d ot tube -2 il Q, andthe 131C; component vof @the rectifiedvv current raisesmthe grid o-fsrelay tube A2532 to-cathode potential Gaus--V ing-plate current to owand attract therelay armaturev 4 In` the operation of `Figure-2, -thus` far discussed, when uponclosure `for-example of switch-lfi-'toV position R a-'positive pulse is impressed `upon-terminal-3|--with-respect -to-egroundterminal-35',

within a predetermined time limit, amplifier I 32.,-of-Fig. -2 impressesanegative pulse upon pulse stretching-circuit involving tubes 112, |14" and resul-tingin a negative pulse Yof longer durationaimpressed uponthe grid -3U6 of 'coinciden'-r tal key tube-HSI; Theduration of 'thispulse overlaps the time interval at -whichanegative` pulse-isl-impressed uponcoincidental key tube |BAdue-tothelaterpulsereceived' from tube |35.

.By-the coinciden-tal action vof tubes` i8! and |84- clipper tube--|9|-is pulsed "positively so that a pulse flows in -the plate Yresistor |33 during the interval-of over-lap. rIhis--pulsem-is broadened, integrated and amplified by'tube '|95` and rec- .1'. tiedby tube -20!lto`cause operationiof the relay I.

armature-4tl In the 4alternative `event that -Aswitch I6 v,of Figfl `is thrown for-example to position L-the pulse ori-terminal 34- precedesthat on terminal 3| the circuit above described will roperate-z to' produce-pulsesinresistor |85 which areinsuli-- cient to cause operation oflthe clipper ytube |95.'

For-utilizing the possible control corresponding to terminal 34 beingv lpulsed before terminal 3|,"i

a-companion-circuit 239 -is provided. This `may' be of the-same -generalconstruction as that pre- Viously-described; with corresponding parts 'des-1 ignatedby like numbers'but followed'by the letj ter a; -lEIoweverv terminal-31| is connected -to ldrive thegrid of tube `||i2a andterminal 3|' is connected to drivethe'gridof tube '-|5a. 'Ihere-v fore the-pulse delay circuit12|9 responds Vto a pulse on terminal' Bil.Y The output of' circuit 299 includes Va lrelay 328er with armature 40.

In this-manner, Athe circuit ofthe timing comparatoro'Fig. A2 provides Ikfor 'operation of left relay 328a when the switch I6' is closed to position-L which pulses `channel fzjbefore f1 and'it provides vfor closure'of right relay5323 whenthe e switch |1 is closed to position `R, .whichv pulses.

channel vJrbefore f2.

.FIGURE 3.,.

In the system shown in'Fig. 1 two independ- Ient receivers' 22'Y and 23 vare *provided :which are tuned-respectively-fto the* channels f1 and f2. Eig. 3 shows-a circuit-for receivingboth channels'pn a nsingle .intermediate Y frequency type receiver and .separating thefpulses for application tothe =timing comparatorr- Referring 1to l3. the

assi0,139l

block 210 indicates a receiving circuit which is tuned broadly to receive the two channels ,f1 and fz. A single frequency local oscillator 211 and a detector 212 are connected to make the two pulses available as intermediate frequency pulses in an output circuit transformer 215 tuned to both intermediate frequencies in a well known manner. These pulses are supplied through the transformer 215 to an amplier tube 216, the output circuit of which is connected to a well known type of frequency discriminating circuit 211 which includes coupled inductors 218 and 219 forming parts of a coupled circuit system and connected at their midpoints through a condenser 220. The midpoints of the inductors 218 and 219 are also connected through a resistor 222 and an inductor 223 to the return lead 224 of the amplifier tube 216.

The frequency discriminating circuit 211 has characteristics such that oneof the pulses, for example, the intermediate frequency pulse corresponding to that received on the frequentiy f1, may be derived from one end of the inductor 219 and applied by a lead 225 to an amplifier tube 226, Whereas the intermediate frequency pulse corresponding to that received on the frequency fz may be derived from the other end Hof the inductor 219 and applied by a lead 221 to an amplier tube 228. The output circuits of the amplifier tubes 226 and 228 are connected through selective intermediate frequency transformers 230 and 231 respectively to rectiers 232 and 233 respectively. Resistors 234 and 235, in circuits with the rectifiers 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 pulses to the timing comparator. l

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. l. l

In the embodiment of Fig'. 3 a pair of lpulses on channels f1 and f2 are received and detected in the tuner 2111 and detector 212 and are applied to the amplifier 216 through a double peaked transformer 215 with transmission peaks corresponding in spacing to the two frequencies f1 and f2. These pulses are separated by the frequency discriminator circuit 211 and are individually amplified in the amplifiers 226 and 228. The amplifier outputs are rectified by the rectifiers 232 and 233 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 24 and25 and the pulse received on the frequency f2 is supplied to the terminals 26 and 21. These terminals are connected to the timing comparator 32 as shown in Fig. 1 wherein their timing is compared and the relays 328 and 328a 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 beA l0 limited in accordance with the scope of the following claims.

I claim as my invention: 1. A system responsive to a pair of pulses received in predetermined sequence over individual channels, comprising multivibrator circuit means responsive to the first received pulse of the pair being received on one channel to stretch the duration of said first pulse an amount to cause the same to overlap in time the later received pulse and non-responsive to the rst received pulse being received on the other channel, whereby the pulses are made coincidental in time only on reception of the first pulse on said one channel, and a key circuit responsive to the combined effect of said coincidental pulses.

2. A system responsive to a pair of pulses received in predetermined sequence over individual channels, comprising multivibrator circuit means responsive to the first received pulse of' the pair being received on one channel to stretch the duration of said first pulse an amount to cause the same to overlap in time thelater received pulse and non-responsive to the first received pulse being received on the other channel, whereby the pulses are made coincidental in time only on reception of the first pulse on said one channel, a pair of space discharge devices having input circuits responsive to said coincidental `pulses and biased to pass space current except when blocked by said coincidental pulses, and

an output circuit responsive to the simultaneous C blocking of said devices.

3. A system responsive to a pair of pulses received in predetermined sequence over individual channels, comprising'multivibrator circuit means responsive to the iirst received pulse of the pair being received on one channel to stretch the duration of said first pulse an amount to cause the same to overlap in time the later received pulse and non-responsive to the first received pulse being received on the other channel, whereby the pulses are made coincidental iny time only on reception of the first pulse on said one channel, a pair of space discharge devices having input circuits responsive to said coincidental pulses and biased to pass spacelcurrent except when blocked by said coincidental pulses, a plate resistor carrying the space cur- Arent of said devices and connected to cause a substantial increase in plate voltage when no space current fiows, and an output circuit responsive to said substantial increase in voltage.

4. In a radio pulse receiver for receiving and separating a pair of pulses received on different radio frequency channels, a receiving circuit receptive of both of said channels and including means terminating ina detector connected to make both pulses available at different frequencies, a frequency discriminating circuit comprising a pair of tuned circuits including mutually coupled inductances connected together at their mid points, one of said tuned circuits being coupled to be fed by said detector and individual output circuits connected to opposite potential points of the other of said tuned circuits.

5. In a radio pulse receiver for receiving and separating a pair of pulses received on different radio frequency channels, a receiving circuit receptive of both of said channels and including means terminating in a detector connected to make both pulses available at different frequencies, a frequency discriminating circuit comprising a pair of tuned circuits including mutually coupled inductances connected together at their ine sneciive. cnennels anni i li ecineied levi .lesi

11 midxneiniei cneoi seid inneilsclr pledv t'obe fed by 'snaid detect a output circuits connected to cppo, points of vthe other `oi"`said tunfed'ci o nuity c'rcuits'e'ach includinga sfiace dischae 5 "1f-1ery havingwanmoutput"circuiha rectifier o #coupled to een en'enointeneinnoone a'resistor connected to carry rectified c nt fer-developing e noieniiel didn enfe'seniine seid pulse! A receiving system responsive to the sednenees. of endif di niilses on different channels, ceinnrisine indio reeeivine cineifiiieiuneli teli-- ceive ene resneciive cnenneis' endieiniineiinein detector ineens inekine ine -nnlse's' efvelileiele ni diierent frequenciesg a comparator rl'ifavingi afbar, of .channels connected io receive seid nillses ficln said detector means, `said channels 4having se; to the other of said chann s and to said niiiltif'y nnence discninnneiine ineens -ie'sncneive in ille viieveier and ,Responsive io coincidence' lel .seid sednencecf snidnvises end i.esneciivelvreencn;` sive to reverse pulse sequences, and means lactuatedrby the-respectiveche'ufneiels.

A vreceiving system responsive .to the svequence vof apair of pulses ondiffernfchannls, comprising lradio receiving circuitswtu'nedlto ref ooive che respeciive channels ind tezminnting in detector means making the pulses availalle at different `freqliencies, a comparator havingva pair of channels connected to receive saidU pulses from said detector means, said channels having sequence discriminating means responsive tothe sequence of seid pulses yend resneciivelv responsive to reverse pulse sequences, said last means l including ineens in `enen cnennei ic exiendine innere: period of? one of seid pulses -enninonni'c'cnre- 351cv iinv oninni oi ...seid second innlnviblc spending ,to inelee loeivveen niilsesso inni-ine siielclies inediireiien ci seidoinei nnlse re:

annel,` an

two pulses eine censedio cveilnn iniiinein One celved over seid einer cliennei Aev seid ,precie channel oi ih e r.other eicconiiney io their see teinnned iinie d 'en ienveiclnn inter ei seid quenco, oircnlis respcnsive only fic ine ooino.- ionir o f nnlses d over seid ,one clinnnel dental eiect of A both pulses v coynnectemd inY said 4 0 and a second key circit connected tonsaid one channels, end relev ineens resnonsive io seid cliennel and iolsnidseeond innliivinneiernndrelesicncni-issp e to o ci of d einer' :dj A receiving s vsieni responsive to the see etneionednd send onefnnlsefvvnerelov Aseidseccnid qucnce p f a pairnoi pulses on 4different channels, key circuit is actuated by the first received vpulse ccinnfisine .indie receiving circuits innen ic re* vno .ci snidneirloeine vec eived onseid seed, d ceive ine nesnec channels end-ienninniine in nel end eine jsecond eceived n nise of end deieeicr ineens .inelsine ine pulses eveileilole ei beingreoeivedonsnidnesecnenneiend no diffelenii.frediien cies.` e rceinnereicr having e, nels nte,d ,bv,ine si reeei .dinilse of seidfnd of channelsconnected to receive said pulses `from receiyedonsaid ifrstgh'anlnel.

' i ciel" ineensy seid channels eeen nen/ine o0 Eloi-ISDN S,- i?URiNQTQlS- V.de ievone nnlse en evnonni io nieliefche pulses., coincideniel vvnen in corresponding EEFEEENQES CFF 011131,19@ an@ beingfSP-@Q/ely AT BSPOSY@ 1101??? `The :following reierencesare of V,record in the verse nnlse -sednences end .circuits responsive me of .ihispainm Onlvie iheeoinciden-.inleiecii'of bein nuls neciedfioloeeocoeceo weones in ,cneiesoeoeivo 5@ UNH-ED STATES PATENT-S channels, Number Name lDate 9 nreceivine svsieni resnensiveioilie sednence 14573303 rCnlniiis Febl'161926 of .e neinofnnlsescndinevent-fchnnnels,cdinrnisr ,979,484 N eviv 6; 193,4 ine indio reeevinecircniis inned ic receive ine ,so 2,211,942 Ave-20,1194@ respective channels end terminating r in-,d eieeioic 2,266,401 Reeves- 4 Dee- 1G, .1941 means .Ina-king thepulses Lavailable iat different 2,269,041 Schu'ssler Jan. 6, 1942 frequencies, alicoinparator having a pair ofchan- 2,3794-'748 Roberts vJuly 3, 11945 nels eonnecied io receive :sind n nlses frein seid 2,405,237 'Ril-mig `4 Aile-6,1946 detector mearissaid channelsreach havingrmeans ,65 2,418,127 vLabin Apr. 1; .1947

ce delev one ynulseen? amount to yineke the pulses coincidental when in ,ecrnesponding sequence nd being respectively iesponsive to reverse n duendes, eircnits nesponsive only io the o omoif deniel eiieeilei looinipnises ,conneeied in be nc-f :19,

nonnen endend-1e

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