US2449819A - Multiplex radio communication - Google Patents

Description

W p n Filed May 29, 1944 E. S. PURINGTQN MULTIPLEX RADIO COMMUNICATION s Sheets-Sheet 2 INVENTOR ELLISON S. PURINGTON.

RNEY

-limit after the first pulse.

Fatented Sept. 23, mt

uuirsn STATES PATENT OFFICE MULTIPLEX RADIO COMMUNICATION Delaware Application May 29, 1944, Serial No. 537,799

21 Claims. (Cl. 250-9) This invention relates to a radio control system of the type Prop gating timed pulses over a pair of radio frequency channels and has for an object to provide a system for selectively actuating a plurality of controls over a single pair of channels.

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

In a. copending application entitled "Radio control system, Ser. No. 536,104, filed May 18, 1944, I have disclosed a radio control system comprising two radio channels which are pulsed in succession with a control means to select the pulse sequence and pulse intervals for signalling or control purposes, and a receiver including relays which are selectively actuated in accordance with the pulse sequence and intervals. In that application, proper operation required the second pulse to be received within a definite time That method provided for dual control, such as for example, the right or the left deflection of a remote mechanism in accordance with the selected pulse sequences and intervals.

In the present'invention, I provide for a large number of controls by the general method of pulsing two radio communication channels in succession. The term channel, as employed herein, comprises the necessary apparatus and includes the transmission media for wave transmission by a selected carrier frequency. or by a separate transmission line, whereby the transmission of two pulses or pulse series may be segregated in transmission. However, it is a feature of my present invention that the second pulse must arrive at the receiver at a time between upper and lower time limits after the first pulse in order that control may be exercised. Multiplex operation is therefore established by selection of the amount of transmission delay between the pulses on the two channels. As employed herein, the term pulse-interval" means the time interval between pulses on the two channels, and the term pulse sequence means the order in which the pulses are transmitted over the two channels.

In one embodiment the present system provides for six possible control operations, but this is merely for illustration and no definite limit is to be assigned to the number of channels that may be provided. Moreover, although I have shown work circuits in the form of electro-magnetic relays, it will be understood that direct 5 electronic work circuits may be substituted. It is within the scope of my present invention that the various channels may for example correspond to diflerent shades of facsimile picture values, or to diiierent keys of a Teletype circuit, or any arrangement where a considerable number of different operations are required.

Although the novel features which are characteristic of this invention are pointed out more particularly in the claims appended hereto, the nature of the invention will be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which a specific embodiment has been set forth for purposes of illus 2o tration.

In the drawings: Fig. 1 is a schematic diagram of a transmitting apparatus embodying my invention;

'Fig. 2 is a schematic diagram illustrating a. receiving apparatus therefor; and

Fig. 3 is a schematic diagram of a selector circuit of the receiver.

Fig. 1

with reference to the transmitter of Fig. 1, the essential parts comprise a pulse forming circuit III, a time delay network 30, pulse amplifiers 69. 18, a bank of push button switches 50 to 55 for controlling three time delay selector relays 56 to il, a radio channel reversing relay 59, and dual channel pulse type transmitters 90, 9|.

For forming the pulses a so-called howling or blocking oscillator is used. It is well known that any type of negative grid oscillator with excessive feed back. and excessively high grid leak can be arranged to self modulate. The oscillator shown is of the electronic coupled type, with an oscillatory circuit l'l comprising a condenser l2 and an inductance l3 with one end of each connected to ground by a line 23 and the other ends coupled to the grid ll of a space discharge tube 15 through a blocking condenser IS. A grid leak comprising a fixed resistance H in series with an adjustable resistance I8 is connected from 50 grid of tube l! to the ground line 23. The cathode of tube I is connected to a tap 28 on the inductance I3. Voltage is supplied to the plate 19 of the tube l5from a source 28, shown as a battery, througha resistor 2|. A lay-pass condenser 22 is connected between the plate l9 and the ground lead 23 to aid in establishing a proper D.'C. voltage from plate to ground.

This oscillator is set to burst into violent oscillation. Thereupon high biasing voltage builds up acrossresistors I1 and i8 and the oscillations are quenched. By using a very high frequency oscillator this operation of starting and blocking can be made to occur in a very short space of and shunt condensers 49 with mutual inductance betweenadjacent inductors. The design of such a line to pass with suitable fidelity a. given pulse is well known to those skilled in the art and will I those of the terminating resistors 46 and. By

time. For example with suitable choice of conj stants oscillation pulses can be produced at 100 pulses per'secondwith each pulse of about 100 microseconds duration.

:These oscillation pulses are impressed upon by a lead- 21 to the tap 28 on the inductance 'l3 and having a cathode 29 positively biased by a bat- High frequency components are deleted from this pulse by condensive paths to, ground comprising a bypass condenser. 35,.and a bypass condenser 36 shunted by a resistor 31, both coupled to the plate through a blocking condenser 38. The resistor 31 and condenser 39 areconnected in the input circuit'of a space dlscharge'tube 39, operating as a clipper tube.

' It will be understood that condensers 35 and a negative voltage pulse is'produced across the plate resistor 33' as indicated by the curve 34.

. not be here described. It is of course important that the line be suitably terminated so that the output wave form will represent the input wave form to a suitable degree.

At suitable points, tappedresistors 55 and 86 are connected across the artificial line, the values of these resistors being high in comparison with proper design, a pulse can be made to occur across resistor 65, centered, for example, 50 microsec- I onds after the middle of the pulse at the'entrance of the artificial line across resistor 46. Similarly pulses'acro ss resistors 66 and 41 may occur, for

example, '100'and 150 microseconds respectively afterthe initial pulse across the resistor 43.

A tap 61 on the resistor 48 is connected to the control grid 68 of. an. amplifier tube 69 havin a plate Ill connected'through a resistor H to the I I 7 source 28. The'cathode 12 of the tube 69 is connected to the lead '13 which is connected tolthe negative side of source 28 and is grounded.

The pulse across resistor 46, after attenuation by the use of ,atap 6! is thus impressed upon 36 may be represented in part by the internal 1 capacitances of the tubes and circuit wiring.

' Condenser 38 and resistor 31 serve to couple the pulses onto the clipper tube 39 and are chosen I with very short time constants so that a sharp negative pulse and a sharp positive pulse are produced in the resistor 31 corresponding to the leading and following edges of the pulse in the resistor 33 as indicated by the curve 34a.

The cathode 48 of the tube 39 is biased positively by a battery 41', so that tube 39 passes current only during a small portion of the positive pulse, thereby producing a very narrow rectangular or trapezoidal current pulse in its output circuit. The plate 42 of the tube 39 is connected to the source 28 through a resistor 43 in which a corresponding negative voltage pulse is produced.

This method of pulse sharpening can for example convert pulses of the order of 100 microseconds duration to pulses of the order of 10 microseconds duration. With this type of pulse forming circuit, the rate of pulsing is readily controlled and adjusted by variable resistor Hi. It is not required that this pulse rate be highly stable. In fact, there may be advantages in making the pulse rate vary and this can be accomplished by causing variations in the value of resistance l8 by mechanical or other methods such as a "wobbling device I8.

The output pulses of the pulse former III which are produced in resistor 43 are transferred through a blocking condenser 44 and are impressed as negative pulses by a line 45 upon the time delay network 38, across the input of which is connected a. tapped resistor 46, and across the output of which is connected a resistor 41. This time delay network is here shown as an artificial transmission line using a plurality of recurrent low pass units including series inductances 48 the grid of the amplifier tube 69. pulse to 691s negative and the outputpulse across the resistor His a positive voltage pulse. I

Selector relays 58, 51'and 58 are provided for connecting tap 14 of resistor 85, or tap 15 of resistor 68, or the 'ungrounded end of resistor 41 to a lead 16 connected to the grid 11 of an amplifier tube 18, having a plate 19 connected through a resistor 88 to the source 28 and having a cathode 81 connected to'the ground lead 13. Relays 58, 51, 58 selectively close circuits to supply vol-j age from one of the three resistors 65, 6'6 and 41 to the grid of amplifier tube 18. A resistor 83. of high impedance in comparison with resistor 41, is connected from grid 11 to ground so that the grid circuit of the tube I8 is not opened when the relays 56, 51 and 58 are all open. The taps on resistors 65, 66 and 46 are so chosen that the magnitude of the pulses on tubes 69 and I8 is approximately the same. Since these pulses are negative, and they may be made of suificient magnitude to cause cut off of the tubes 69 and I8, the output pulse across resistor may be of substantially the same wave shape as the immediately preceding pulse across resistor II.

A relay 59 of the balanced armature type is connected to actuate a double pole double throw switch 83. The switch 83 includes movable contact blades 84 and 85 connected respectively through blocking condensers 86 and 81 to the plates 19 and 10 of the tubes 18 and 69, and fixed contacts 88 and 89 connected respectively to input circuits of transmitters 90 and 9| which are of standard type to radiate waves on channels ,f1 and is modulated by the pulses from the tubes 18 and 69. The transmitters are shown as having input resistors 92 and 93, and as connected to radiators 94 and 95 respectively for radiating waves on selected frequencies f1 and is.

The relay 59 is provided with windings I08 and Illl. The winding l88 is connected to one side of key operated contacts 58, 5|, and 52 and the winding IN is connected to one side of key operated contacts 53, 54 and 55. The other sides of contacts 50 and 53 are connected through winding I04 of relay 58 to ground. The other sides of contacts 5| and 54 are connected through winding I85 of relay 5! to ground. The other The input winding I06 of relay 50 to ground. The return of windings I and IN is connected to the source 20.

For simplicity, the radio transmitter is shown as two separate transmitters, one operative at frequency f1, and the other at frequency In. With the relay contacts positioned as shown, the initial pulse from the amplifier 00 is transmitted on channel is, and the following pulse from the amplifier I8 is transmitted on channel f1. Push button switches 50-55 serve to select the channel which is to be pulsed first, and to determine the interval between the two pulses. Each push button corresponds to a definite control operation.

Preferably neither transmitter is to be pulsed except when it is desired to operate a control. When no control switch is closed, the relay 50 will be in neutral, and no pulses will be delivered to either transmitter. In the illustration shown, switch 52 is closed for the purpose of establishing a definite control operation, causing current to flow from the positive end of battery 20 through the winding 100 of relay 59, and through the winding lflli'oe'irelay 58 to the negative side oi battery 20, thereby causing channel is to be pulsed from the amplifier 69 and the channel 11 to be pulsed from the amplifier I0. Since the amplifier I0 is fed from the resistor 65 there will be 50 microseconds delay between centers of the pulses.

With the switch closed instead of the switch 52 the tube I8 would be pulsed from the resistor 55 with I00 microseconds delay and with the switch 50 closed the tube I8 would-be pulsed from the resistor 01 with 150 microseconds delay. With the switches 55, 50 or 53 closed the same respective delays would be introduced but the winding IOI would be energized to reverse the switch 83 so that the first pulse from the tube 69 would be fed to the channel it by the transmitter 90 and the later pulse would be fed to the channel I: by the transmitter 9|.

Six possible combinations of time delays are provided by the system shown, but it is obvious that the number of possible combinations may be increased greatly by using lines of greater length, or by increasing the number of taps in the line shown.

The radio transmitters 90, 9I may be of any standard design for pulse transmission. Here are shown two independent units corresponding to channels A and f2, respectively, provided with individual radiators 90 and 95. However, a single transmitter operating on two frequencies with a single antenna may be used as disclosed in my copending application Serial No. 543,918, filed July 7, 1944, or in a system of the general type disclosed in U. S. Patent 1,601,109, granted to E. L. Chafiee on September 28, 1926.

Fig. 2

such as of the superheterodyne type.

The output resistors III; and III are connected to control grids '8 and H9 of pulse inverting amplifying triodes I20, I2I having cathodes I22, I23 positively biased by batteries I20, I25 and having anodes I20a, 'I2Ia, connected through output resistors I26, I21 to plate batteries I28 and I29 respectively. The tubes are biased to 6 accept positive pulses and negative pulses are delivered from the resistors I25 and I2'I. The anodes I20a, IIIa are connected through blocking condensers I00 and "I to two artificial transmission lines I00 and I00. having input termination resistors I05, I00 and output termination resistors I01. I00. The lines I00 and I00 may be similar to the line 00 above described and designed to introduce similar delay periods. Across the lines I00, I00 at suitable points are bridged tapped resistors I00 to I02 and I00 to I05 respectively having taps I'00a to I0'5a respectively so adjusted that substantially the same amount of pulse energy is available at the taps as at the output termination resistors I01, I00. The resistors-I00, I00 are connected at the input end of the lines I00, I00. The resistors III, I00 are connected at points corresponding to the resistor 55 of Fig. 1, the resistors I02, I05 are connected at points corresponding to the resistor 05 of Fig. 1, and the terminal resistors I01, I00 correspond to the resistor 01 oi Fig. 1 so that corresponding delays are introduced by the intervening portions of the artificial lines.

Three coincidental selective relay systems I50 (shown in detail in Fig. 3) are provided with input terminals I H connected by a line I52 to the tap I00a on resistor I00 and with input terminals I53 connected by a line I50 to the tap I00a on the resistor I00. The three relay systems are provided with input terminals I55 which are connected respectively by lines I55, I51 and I50 to taps IOIa and I02a on resistors MI and I02 and to the terminating resistor I01, and with input terminals I50 which are connected respectively by lines I'5I, I52 and I50 to taps H011 and I05a on resistors I00 and I05 and to the terminating resistor I00. The relay systems I50 are also provided with ground terminals I50. Each system I50 is designed to be selectively operative in responseto coincidental pulses at terminals I5I and I55 or terminals I 50 and I50. Since the pulse from the receiver I I0 is delayed by the line I33 and the pulse from the receiver III is delayed by the line I00 the first relay system I50 is responsive to pulses having a 50 microsecond spacing, the second relay system I50 to pulses having microseconds spacing, the third relay system I 50 to pulses having microseconds spacing, and each relay system is selective to a reversal in pulse sequence. For the case shown in Fig. 1, the time interval for example is 50 microseconds, with channel is actuated first, so that the pulse from radio receiver III (channel is) will arrive at the terminal I50 of the first relay system I50 coincidentally with the arrival of the pulse from radio receiver IIO, (channel ii) at its terminal I50 and the corresponding relay will operate. on the other hand, for this unit, there will be 100 microseconds interval between the two pulses arriving at its terminals I5l and I55 and the second relay will not operate. A similar selection is made by the other relay systems I50 for pulses having 100 microsecond spacing and 150 microsecond spacing respectively, giving six selections corresponding to the six key switches 50 to 55 of Fig. 1.

Fig. 3 I

Fig. 3 shows the unit I50 in detail. with input terminals I5I. I50, I55 and I60 corresponding to like numbered terminals of Fig. 2. This unit is powered from a battery I10 for filaments (not shown) and cathode bias purposes, and a battery "I for plate supply. An output relay I12 is of the balanced type and is provided with output terminals I13 and I14. The conditions are shown with pulses on terminals I5I and I55 non-coincidental as for example being 100 microseconds apart, but with the pulses on terminals 153 and 160 coincidental.

A pair of space discharge tubes 200, 20I have input circuits connected across resistors 202, 203, which are connected between terminals I53, I respectively and ground terminal I60 to carry the respective input pulses. The anodes 200a and 20Ia of the tubes 200, 20I are connected to the source I'll through plate resistor 200 and line 205. The plates 200a, 20Ia are also connected through a resistor 206 to the control grid 201g of a space discharge tube 201 having a grid resistor 200 and a grounded cathode bias resistor 203 with a bypass condenser 2l0. A resistor 209a is connected from the cathode of tube 201 to the line 205. The anode 201a of the tube 201 is connected to the line 205 through a plate resistor 2I I.

The anode 201a is connected by a line 2I2 and blocking condenser 2I3 to the input circuit of a space discharge tube 2 having a resistor 2I5 and condenser 2I6 connected between grid and grounded cathode, and having an anode 2 Ila connected to the line 205 through a plate resistor 2 I1 and connected to ground through a condenser The anode 2I|a of tube 2 is connected through blocking condenser 2l9 and line 220 to the control grid 22Ig of a space discharge tube 22 I. A resistor 2 I So is connected between the line 220 and ground. The cathode of the tube 22I is connected by a line 222 to the positive side of battery I10 and its anode is connected through a plate resistor 223 to the'plate supply line 205.

The tube 22I is resistance coupled by the plate resistor 223 and a condenser 224 to the anode of a rectifier tube 226. The cathode of the rectifier tube 226 is connected to ground through a cathode resistor 221, shunted by a bypass condenser 220, which is connected across the input circuit of a space discharge tube 229. A resistor 230 is connected from the anode of the rectifier tube 226 to ground for D. C. return purposes. The anode of the tube 229 is connected to one end of winding 23I of the relay I12, and the other end of the winding is connected to line 205.

The tubes and circuits above described constitute one channel of the unit between the input terminals I53, I60 and the winding 23I of the relay I12. A similar channel connects the input terminals II, I55 and a second winding 33I of the relay I12. To avoid duplicating the description, the parts of the second channel have been given the same reference characters as the corresponding parts of the first channeL'but increased by I00 and it is to be understood that the above description also applies thereto. It will be understood that cathode biasing resistors 209 and 2091:, and bypass condenser 2I0 pertain to both channels, as also do certain other parts, but in the main channels are independent.

Tubes 200 and NI are key tubes for pulses impressed on terminals I53 and I60, and tubes 300. l

and 30I are key tubes for pulses impressed on terminals I5I and I55. Tube 201 is a clipper tube actuated from the conjoint outputs of tubes 200 and 20I, and tube 301 is a clipper tube actuated from the conjoint output of tubes 300 and 30I. Tubes 2 and 3" are selective integrator tubes, tubes 22I and 32I are rectifier driver tubes, tubes 226 and 226 are rectifier tubes. and tubes 223 and .ing tubes drive the grids negative.

329 are relay tubes for actuating the windings 23I and "I of relay I12.

Each of the key tubes 200, 20I, 300, 30I may be thought of as a resistor having a value of, say, 10,000 ohms when the grid is at cathode poten tial, but as a resistor of infilnite impedance when the grid is sufiiciently negative. The voltage of the grid of tube 201 with respect to ground will have a low positive value when no voltage exists across resistor 202 or 203, a higher value when either terminal I63 or I60 is highly negative and the other is at cathode potential, and a very substantially higher value when both terminals I63 and I60 are highly negative. Bleeder resistor 209a is connected to make the cathodes of tubes 201, 301 suitably positively biased with respect to ground. Adjustments are such that no current passes through resistor 2 unless both of the tubes 200 and 20I are of very high impedance. Cutofl for tube 201 may occur for example when the two tubes 200, 20I in parallel have an impedance of, say, 50,000 ohms, with full current flowing only when the parallel impedance is infinite. No current therefore will fiow through resistor 2 unless both terminals I53 and I 60 are at the same time highly negative with respect to ground. Thus with overlapping negative pulses on terminals I53 and I60, a current pulse will pass through resistor 2H for the duration of the time of overlap, but with pulses on terminals I5I, I55 which occur microseconds apart without overlap there will becorresponding pulses through the resistor 300 but not of sufiicient amplitude to produce a pulse through the resistor 3I I. Therefore of the six sets of inputs for units I50 of Fig. 2, only terminals I53 and I60 of one unit will be coincidentally pulsed to produce pulses in the clipper tube output resistor 2 I I.

The output pulses of tubes 201, 301, whenever such exist, are negative pulses, and these are applied to the amplifiers 2I4 and 3 which serve as pulse integrators, or as selective amplifiers. The cathodes of these integrator tubes are at ground potential, and the pulses from the preced- The values of the condensers 2 I3, 2I6, 2 l8 and 2I9 and resistors 2II, 2I5, 2-I1, 2I9a are suitably chosen so that pulses of current through resistor 2 are efliciently amplified, broadened, and integrate-d to produce a very high value of the fundamental alternating voltage across resistor 2I9a. This choice of values can be readily made by those skilled in the art. Preferably the circuit will be designed for maximum efficiency of production of A. C. voltage across resistor 2 I 9a at pulse rates corresponding to those of the transmitter, say 100 pulses per second for the illustrative case considered.

Rectifier driver tubes HI and 32I operate with cathodes positively biased to utilize the positive and negative swing of voltage across their grid resistors. These driver tubes for simplicity are shown as resistance coupled to the plates of rectifiers 226, 326. through cathode resistors 221 and 321, bypassed by condenser 228, 328 'to relay tubes 229, 329. Relay tubes 229, 329 are positively cathode biased by battery I10 so that with no rectified voltage across the input circuits, little or no plate current-flows through the relay 23I, 33I. When sufficient rectified voltage is developed, the relay coil will be energized to close the circuit from ground to relay terminal I13 or I14 according to the channel pulsed.

In the operation of this circuit, when termi- The rectifier outputs are fed more nals I53 and I60 are simultaneously pulsed negative to cutoif, a pulse is produced acros resistor Ill. These pulses will be recurrent due to the rate of recurrence of the pulse on terminals I53, I60, and are integrated, broadened and eiilciently amplified at the pulse rate to actuate the grid of tube 22lwith alternating current of the pulse rate. Tube 221 amplifies the A. C. input and the amplified output is rectified to produce direct current through the input resistor 22'! of tube 229, causing current through the relay winding and closure of the relay contact I13 as above described.

It will be understood that a specific embodiment oi the invention has been set forth for purposes of illustration. While I have specifically indicated operation by radio channels and electrical delay lines, it is obvious to those skilled in the art that the method is applicable to other channels suchas by sound transmission.

What is claimed is: a

1. The method of signalling which compris propagating a pair of radiant energy pulses over dififerent communication channels at predetermined spaced time intervals, selecting the time period between said pulses and selecting the pulse sequence for signalling, receiving said pulses at a remote point, selecting the received pulses in accordance with their timing and sequence, and utilizing the selected received pulses for signal reception. i

2. The method of signalling over a pair of radio frequency communication channels which comprises producing a series of pairs of pulses with controlled timing between pulses and between pairs, radiating one pulse ofeach pair over one of said radio frequency channels and radiating the other pulse oi. each pair over the other of said radio frequency'channels, selecting the timing between pulses and selecting the pulse sequence on the two channels for signalling, receiving said pulses at a remote point, selecting the received pulses in accordance with their timpulses. a pair of radio frequency transmitters,

a circuit for deriving pulses, a delay circuit con- 7 nectedto receive said derived pulses and to progressively delay the' same, a pair of radio'transmitters, modulating circuits therefor, a plurality of selectors selectively connecting said modulating circuits to difl'erent parts of said delay circuit to propagate said derived and delayed pulses in difi'erent selected time intervals, re-

ceiving means for receiving both of said propagated pulses, a delay'circuit connected to introduce a time delay into the first propagated pulse received to cause the twopropagated pulses to coincide in time, and signal means actuated by the conjoint efifect of said coincidental pulses.

7. A multiplex signalling system comprising a circuit for deriving pulses, a delay circuit connected to receive said derived pulses and to progressively delay the same, a pair of radio transmitters, modulating circuits therefor, a plurality of selectors for selectively connecting said modulating circuits to diflerent parts of said delay circuit to propagate said derived and delayed pulses in diflerent selected time sequences, receiving means connected to receive both of said propagated pulses, a plurality of selector channels fed by said receiving means, said channels having difierent pulse delay circuits corresponding to the different delays introduced at the .transmitter by said selectors and designed to make the two propagated pulses coincidental in one channel only, and signal means actuated by ing and sequence, and utilizing the selected received pulses for signal reception.

3. A multiplex signalling system comprising means producing a pair of pulses having predetermined time separation, a pair of radio frequency communication channels, means for propagating said pulses over different ones of said radio frequency channels, means for selecting the timing of said pulses and for selecting said pulse sequence for signalling, receiving means receptive of both of said pulses, mean selective of the received pulse sequence and timing, and signal utilizing means selectively actuated by said last means.

4. A multiplex signalling system comprising a pair of radio frequency signalling channels, means producing a series of pairs of pulses having predetermined time intervals between pulses and between pairs of pulses, means propagating one pulse of each pair over one of said radio frequency channels, means propagating the other pulse of each pair over the second of said radio frequency channels, means selecting the timing of the pulses of each pair and for selecting said interval for signalling, receiving means receptive of both of said selected propagated pulses, means selective of the received pulse interval and timing, and signal means selectively actuated by said last means.

5. A multiplex signalling system comprising a the conjoint eflect of said coincidental pulses. 8. A pulse transmitter comprising a pulse forming circuit, a delay circuit connected to receive pulses from said circuit and to progressively delay the same, a pair of radio transmitting means to propagate waves on two communication channels, and means for selectively modulating each of said transmitting means from difierent parts of said delay circuit to introduce a nected to receive said pulses and provide delayed predetermined time delay between pulses propagated on the two channels.

9. A pulse transmitter comprising a circuit for deriving pulses, a delay circuit connected to receive said derived pulses, and to progressively delay the same, a pair of radio transmitting means to propagate waves on two communication channels, means for modulating one of said transmitting means by said derived pulse direct from said pulse forming circuit, means for modulating the other of said transmitters by said delayed pulse after traversing selected portions of said delay circuit, and means" for selecting said delay circuit portion for introducing different predetermined time delays between pulses.

10. A pulse transmitter comprising a circuit for deriving pulses, a delay circuit connected to receive said derived pulses and to progressively delay the same, radio transmitting means to propagate waves on two channels, means for modulating one of said transmitting means by said derived pulse direct from said pulse forming cirsuit, means for modulating the other of said transmitters by said delayed pulse after traversing selected portions of said delay circuit, means for selecting said delay circuit portion for introducing different predetermined time delays between said derived and said delayed pulses, and reversing means connected to said pulse deriving and delay circuits to select the sequence and intervals of said pulses to the respective trans-' mitters.

11. A pulse receiver for receiving and selecting from a plurality of radio frequency channels a plurality of pulses having different time intervals, comprising receiving means to receive a pair of pulses over different ones of said radio frequency channels, a plurality of circuits connected to be fed by said received pulses, said circuits each having difierent pulse delay networks connected to delay one of said received pulses so that both of the received pulses are made coincidental in each of said circuits, and signal means connected to said circuits to be actuated by the conjoint effect of said coincidental pulses.

12. A pulse receiver for receiving and selecting from a plurality of radio frequency channels a plurality of pulses having diflerent time intervals, comprising receiving means to receive a pair of said pulses over different ones of said radio frequency channels and to segregate said received pulses, a pair of delay circuits connected to be fed by the respective received segregated pulses, a plurality of circuits connected to difierent points on said delay cincuits, said points being selected to make the pulses coincidental in each of said circuits, and signal means connected to said circuits to be actuated by the conjoint effect of said coincidental pulses.

13. A pulse selector circuit comprising a pair of space discharge tubes each connected to be fed by different series of pulses having different occurrence time intervals, a key space discharge device connected to be fed by the outputs of said pair of tubes and biased to respond only to the conjoint action of such of said differently occurring pulses of said different pulse series as are received simultaneously in both of said pair of tubes, an integrator space discharge tube circuit connected to said key tube and responsive to repeated pulsings of said key tube, a rectifier fed by said integrator tube circuit, and a relay actuated by said rectifier in synchronism with simultaneous occurrence of pulses in said different pulse series.

14. A pulse selector circuit comprising a pair of space discharge tubes each connected to be fed by different series of pulses having diflerent occurrence time intervals, a key space discharge device connected to be fed by the outputs of said pair of tubes and biased to respond only to the conjoint action of such of said difierently occurring pulses of said difierent pulse series as are received simultaneously in both of said pair of tubes, an integrator space discharge tube circuit connected to said key tube and responsive to repeated pulsings of said key tube, an amplifier tube fed by said integrator tube circuit, a rectifier fed by said amplifier tube, a power tube fed by said rectifier and a relay fed by said power tube, said relay being actuated by said power tube in synchronism with simultaneous occurrence of pulses in said different pulse series.

15. The method of signalling which comprises propagating and receiving one of a pair of differently timed energy pulses over one channel, propagating and receiving the other of the pair of n y pulses over a second channel, and difl'erently utilizing the received pulses in accordance with the time interval by which the pulse received over the first channel precedes that received over the second channel.

16. The method of signalling which comprises propagating and receiving the tw pulses of a pair of energy pulses over two sepa ate channels, selectively choosing the time interval between the pulses, selectively choosing the sequence of pulse propagation on the two channels, and selecting said received pulses for signal reception in accordance with their sequence of occurrence and the time interval between the two received pulses on the two channels.

17. The method of signalling which comprises propagating and receiving a first recurrent series of energy pulses on one communication channel and propagatin and receivin a second differently timed recurrent series of ener y pulses on another communication channel with the same rate of pulse recurrence on both channels, and selecting said received recurrent series of pulses for signal reception in accordance with the time interval between the most nearly simultaneous pulses of the two received recurrent series of pulses.

18. The method of selective signalling which comprises propagating and receiving a recurrent series of energy pulses on one communication channel and propagating and receiving a second differently timed recurrent series of energy pulses on another communication channel with the same rate of pulse recurrence on both channels, selecting said received pulses in accordance with the time interval between the two most nearly simultaneous pulses of the two series, selecting the communication channel on which the series made up of the first of said most nearly simultaneous pulses is transmitted, and selecting the received pulses for signal reception both in accordance with the said selections of pulses by time interval and selected communication channel.

19. A signalling system comprising a pulse forming circuit for forming an energy pulse, a

transmission line pulse delaying circuit with a plurality of input, intermediate and output terminations providing different amounts of time delay, means for applying pulses to said line circuit from said pulse forming circuit, a two communication channel pulse transmitter, and means for applying relatively delayed pulses to the two communication channels of said transmitter from two of said plurality of terminations of said line.

21. A signal receiving system comprising a two communication channel receiver, two transmission line delay circuits, provided with at least two terminations, means for feeding one line circuit from one communication channel of said receiver, and means for feeding the other line circuit from the other communication channel of said receiver, a utilization circuit responsive only to coincidental signals from two inputs, means for feeding one of said inputs from a termination of one of the two line circuits, and means for feeding the other of said inputs from a termination of the other of said two line circuits.

ELLISON S. PURINGTON.

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

Number UNITED STATES PATENTS Name Date Shoemaker Jan. 6, 1903 Raymond-Barker May 11, 1915 Carson July 8, 1919 Mathes June 16, 1925 Mathes Feb. 23, 1926 Clement Dec. 6, 1927 Symonds May 14, 1929 Hammond, Jr July 28, 1931 Number Number Name Date Goshaw Nov. 6, 1934 Lemmon Sept. 1, 1936 Blumlein Sept. 12, 1939 Peterson Sept. 3, 1940 Fitch Feb. 4, 1941 Reeves Dec. 16, 1941 Reeves Feb. 3, 1942 Guanella et a1. Mar. 2, 1943 Beatty Sept. 7, 1943 FOREIGN PATENTS Country Date Great Britain Oct. 9, 1941 OTHER REFERENCES Wireless World, April 1944, Morse by Pulses, by R. C. Whithead, pp. 102-105, inclusive.

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