US2425315A - Pulse communication system - Google Patents

Description

Aug. 12, 1947. J'. B. ATwooD ETAL PULSE COMMUNICATION SYSTEM Filed Feb. 17, 1944 2 Sheets-Sheet l .Hip

llg. l2, 1947. J. B. ATwooD ETAL PULSE COMMUNICATION SYSTEM Filed FebQl?, 1944 2 sheets-sheet 2 M S Ria Y Of E TNW m mfg@ mi?? MM) PHY a a,

Patented Aug. 12, 1947 UNITE STTES PULSE COMMUNICATION SYSTEM Application February 17, 1944, Serial No. 522,758

30 Claims. (Cl. Z50- 15) This invention relates generally to a radio relaying system, and more particularly to such a system employing pulses of high frequency energy which are short compared to the time intervals between them for transmitting the radio signals.

An object of the present invention is to enable the eicient reception and retransmission of modulated pulses of high frequency energy in a radio relaying system.

Another object is to provide a repeater station for use in a radio relay system, which receives and retransmits pulses of high frequency energy and which overcomes the eects of extraneous feed back between receiving and transmitting antennas.

A further object is to provide a repeater station for use in a pulse communication radio relay system which introduces a delay between the received and retransmitted pulses and utilizes the received pulses to block the receiving channel in the intervals between received pulses during which intervals the delayed pulses are retransmitted.

A still further object is to provide a system for generating pulses and for modulating the width of the generated pulses in accordance with signal modulation,

A still further object is to provide a system for converting width modulated pulses to phase modulated pulses.

The following is a more detailed description of the invention accompanied by a drawing, wherein:

Fig. 1 illustrates a preferred form of repeater station in accordance with the invention for use in a pulse communication radio relay system, and

Fig. 2 is av circuit diagram of the coupling tubes, delay networks and receiver channel blocking device of Fig. 1.

Referring to Fig. 1, there is shown a repeater station which is illustrative of any one or more similar intermediate stations located between terminal transmitter and receiver stations of a radio relaying system for carrying on communication by means of pulses of high frequency energy. The terminal transmitter station is not shown since it may comprise any known type of station for radiating relatively short duration pulses of carrier frequency. The pulse rate or phasing of these pulses may be modulated in accordance with the signal modulations. The terminal receiver station which is also not shown may comprise any known type of station for receiving these modulated pulses. By way of eX- ample only, and not by way of limitation, reference may be had to Peterson copending application Serial No. 431,617, filed February 20, 1942, for details of one type of pulse transmitter and receiver which can be employed at the `terminals, and to Dow copending application Serial No. 482,578, led April 10, 1943, for another type of transmitter which can be employed as a transmitting terminal.

Broadly stated, the repeater or relay station of Fig. 1 comprises receiving and transmitting antennas, labeled as such, and circuits for delaying the received pulses prior to reradiating similar pulses containing the signal modulation. A blocking device is employed for rendering the receiver channel of the repeater station insensitive during the periodbetween incoming pulses,

i and the delayed pulses are retransmitted during the time the channel is insensitive. In this Way it is impossible for the retransmitted pulses to be fed back over the ether to the receiving antenna and then through the circuits in the output of the receiver to produce undesired singing. By modulating the amount of delay of the pulses at the repeater station, it is possible for the attendant at the repeater station to break in on the circuit and send a, message along the chain of stations toward the terminal receiver. Circuits are provided, as will appear hereinafter, for removing noise from the incoming signals. There is also provided a local monitor at the repeater station for enabling the attendant to listen to the incoming signals. A pulse selective circuit followed by a limiter serves to eliminate undesired interference in the local monitor.

In Fig. 1, the graphical representation of the different outputs from the various circuit stages is given immediately above the connections in which these outputs appear, in order to aid in an understanding of the following description.

Let us assume that the pulses of high frequency energy originating at the terminal transmitter have an average pulse rate (unmodulated condition) of twenty kilocycles and that the vpulse repetition rate or pulse frequency is modulated in accordance with the signals to be transmitted in a range between plus three kilocycles and minus three kilocycles. The modulation may be either speech or keyed tone, .and the highest modulation frequency should be considerably lower than the pulse repetition rate. The pulses will then Vary in rate between seventeen kilocycles and twentythree kilocycles and will be received on the receiving antenna and amplified in radio frequency amplifier 90. A frequency converter 9| having in circuit therewith a local heterodyne oscillator 93 will change the carrier frequency of the incoming pulses to a lower or intermediate frequency which is amplified in 92. The inter mediate frequency amplifier 92 preferably comprises several stages of screen grid tubes. The pulses of intermediate frequency energy are then rectified by rectifier 94 whose output contains noise ripples. The rectied pulses then are applied to a clipper 95 which removes a portion of the rectified pulse between the top and bottom to thereby provide a clean pulse having the noise ripples removed. In other words, the clipper is a top and bottom limiter which removes noise and variations above and below certain limits. In practice, the clipper may consist of a Ypair of threshold devices in cascade and whose grid biases are so vadjusted that it is possible to utilize any desired portion between the top and bottom of the incoming pulses. The clipped pulses are inverted relative to the rectified output from 94 (i. e., in a negative direction), and these negative pulses then impressed upon a coupling tube structure which has two outputs, one of which goes to the pulse rate rselective circuit |0| of the local monitor .circuit and the other of which goes to another coupling tube structure |02. The output pulses from |00 which are applied to apparatus |02 are of positive polarity.

Coupling tube stages |00 and |02 each include a pair of electrode structures, aswill appear in more detail from a description of Fig. 2.

Coupling tube stage |02 has two outputs, one being applied to an adjustable delay circuit |93 for controlling the timing of the retransmitted pulse, and the other to an independently adjustable delay circuit |04. The outputs from |02, it should be noted, are inverted relative to the -positive character of the pulses applied to the input of this'same stage. Delay circuit |03 includes a diiferentiator for producing sharp peaked impulses from the slopes ,or wave fronts of the applied pulses and also an arrangement for enabling only the positive peak to pass therethrough having a desired time delay. This positive peak is Obtained from the trailing edge of the negative output pulse from a trigger circuit.

The positive peak impulse from delay circuit |03 serves to control a pulse generator |05 which is normally inactive and responds to the positive peak impulse to produce a pulse which is delayed relative to the corresponding pulse received on the receiving antenna. Putting it in other words, pulse generator |05 is a circuit which requires a tripping pulse to render it active and whose time constants are such that it restores itself to the stable state a short time after it has been tripped. Several such pulse generators are known in the art. One type is generally referred to as an electronic trigger circuit having one degree of electrical stability. Such a trigger may comprise two evacuated electron discharge devices whose grids and anodes are coupled together` in regenerative manner. Another type is the blocking oscillator normally biased to the anode current cut-off condition. The output from pulse generator |05 comprises a series of pulses corresponding to the series of pulses received on the receiving antenna but delayed by a desired time interval, and these delayed pulses, after amplification in multi-stage power amplifier |06, serve to control the generation of high frequency pulses from a pulse rcontrolled generator |01. The output of generator |01 is radiated from transmitting antenna. The

high frequency generator may be any suitable type, such for example as a magnetron, or the kind shown in Peterson copending application Serial No. 431,617, supra.

From the foregoing, it will be appreciated that delay network |03 affords a possibility of adjustment or modulation of the amount of delay of the outgoing signal pulses limited to an interval between incoming pulses. For enabling the attendant at the repeater station to break in and transmit messages, there is provided a local modulation circuit, either speech or keyed tone, which is impressed on audio amplifier |08, in turn controlling the amount of delay of delay network |03. The repeater station attendant can thus superimpose his own message (as a variable pulse rate) on the repeated signals whenever it is desired to communicate between the repeater station and any one or more subsequent stations in the direction of the receiving terminal.

The output from adjustable delay circuit Hit is a series of pulses of negative direction, and these pulses control blocking device |09 to block the receiving channel at the intermediate frequency amplifier stages 92 during the interval between received pulses, The delay circuit |04 assures the fact that the incoming pulses are passed by the receiving channel (through the intermediate frequency amplifier stage) without cutting off parts of the received pulses, before the blocking device |09 functions to block the receiving channel. Otherwise, that is, in the absence of delay |04, the receiver channel might be blocked off before the end of a pulse is completely received. Blocking device |09 assures the fact that the receiver is insensitive for a desired interval between received pulses. In the preferred form of the invention, the blocking device functions to reduce the voltage on the screen grid electrodes of the intermediate frequency amplifiers 92, as will appear later from the description of Fig. 2. It should be noted that the output pulses from blocking device |09 are in a negative direction.

The delay circuit |03 is so adjusted that the signals are retransmitted over the transmitting antenna during the interval between received pulses, at which time the receiving channel is blocked off. Otherwise, the retransmitted pulse might be picked up by the receiving antenna and cause singing or undesired feed back.

The local monitor circuit comprises a pulse rate selective circuit |0| which reshapes or converts the pulses applied thereto by coupling tube structure |00 to a substantially sine wave form. In practice, the selective circuit itil may comprise two coupled parallel tuned circuits each properly damped so that the overall circuit gives a :dat top or uniform response over the range from seventeen kilocycles to twenty-three kilocycles. Although the output from pulse rate selective circuit |94 is of sine wave form, modulated between seventeen kilocycles and twenty-three kilocycles, there are also present slight amplitude variations which are removed by limiter H9. Limiter |0 preferably comprises two screen grid vacuum tubes in cascade. The screen grids of these limiters are supplied with a low positive polarizing potential to assure a flat anode current output. The output from the limiter H0 is a sine wave modulated between seventeen kilocycles and twenty-three kilocycles and is applied to a balanced discriminator and detector circuit which converts the pulse yrate or frequency modulation to amplitude modulation. The audio modulation from the rectiers coupled to the output of the discriminator is then passed on to a low pass lter 2 which removes the components above three kilocycles. This filtered audio modulation is then amplied in audio amplier ||3 and heard in acoustic transducer H4 or recorded in any other suitable utilization device.

Fig. 2 shows the detailed circuits of the coupling tube structures 00, |02y the delay networks |03, and the blocking device v| 09. The same parts of Figs. 1 and 2 are labeled with the same reference numerals. The coupling tubes and |02 each comprise a pair of separate three-electrode structures Within a single evacuated envelope.

In the operation of the circuits of Fig. 2, the application of a negative pulse -from the output of clipper S to lead I0 will produce a positive pulse in the anode circuit of one of the electrode structures of coupling tube |00. This positive pulse is applied in parallel to the two grids of coupling tube |02 via lead and also applied to the grid of the other electrode structure of coupling tube |00 through condenser |2. The pulse applied to the lower electrode structure of coupling tube |00 is inverted in its anode circuit and appears as a negative pulse which is then passed on to the pulse rate selective circuit |0 The anode of one electrode structure of coupling tube |02 supplies a negative pulse to the trigegr circuit I3 of the delay network |03, while the other anode of tube |02 supplies a negative pulse to the delay network |04. Delay circuit I|04 is shown only in box form lbecause it is identical with delay circuit |03 except for the fact that a negative pulse is taken from the coupling tube of |04 to operate the blocking device |09, lwhereas a positive pulse is taken from the coupling tube of the delay circuit |03.

Delay network |04 includes a trigger circuit like trigger circuit |3 of delay circuit |03. This trigger circuit comprises a pair of evacuated triode structures having their grids and anodes interconnected regeneratively. These trigger circuits have one degree of electrical stability, and require a tripping pulse to change the trigger from the stable to the active state. The trigger, when tripped, will remain in the active state for a time interval depending upon its time cnstants, after which it restores itself to normal. The trigger is so arranged that when one electrode structure thereof passes current, the other will be non-conductive, and vice-versa. Although the electrode structures of the trigger circuits have been shown contained Within a single envelope, it will be evident that the tube structures can have individual envelopes, if desired.

Considering the delay network |03 for the present, the application of a negative tripping pulse from coupling tube |02 to the grid of the normally conducting electrode'structure of trigger |3 will trip the trigger to its active state. A negative output pulse is taken from trigger I3 and supplied to lead is. This output pulse is differentiated by condenser |5 and resistor I6 and the positive peak impulse resulting from this differentiation is utilized to render vacuum tube I1 conducting. The diiferentiator circuit l5, I6 serves to convert the start and trailing edges of the rectangular pulse in the output of trigger |3 to sharp triangular pulses of opposite polarities. Vacuum tube I7 is normally biased to cut-off and requires a positive pulse to overcome its negative grid bias and thus render the tube conducting. The output from tube |'l is a sharp positrigger |3 depends upon the time constants of the circuit and upon the value or" the bias on the grid G. The bias on grid G is in turn dependent upon the adjustment of the resistor 20. Since it is only the trailing edge of this output pulse which produces the sharp positive triangular-shaped peak impulse in the differentiator, in turn controlling the transmitter, it will be appreciated that the circuit |03 delays the transmission of signal pulses by the length or duration of the trigger output pulse, and by varying this duration it is possible to vary the timing of the generation of currents by the transmitter. In order to enable the local attendant to superimpose a variable pulse rate on the retransmitted signals, whenever he desires to break in on the circuit, the resistor 20 is connected in series with the secondary winding of an audio transformer 2|, the latter in turn being connected to audio amplier |08. Circuit |08 is connected to a suitable local modulation device, such as a microphone, as shown. The result of this local modulation circuit is to produce phase modulated pulses.

Considering now the action of delay circuit I0@ and device |09, a negative output pulse from coupling tube |02 applied to the grid of the normally conducting electrode structure of the trigger of circuit |04 will trip this trigger to its active state. A negative output pulse is takenv from the plate of the coupling tube of delay circuit |04 and is supplied to the blocking oi device |09. Device |99 includes a trigger |20 having one degree of electrical stability and a Vacuum tubeV |2| in its output circuit, in turn coupled to the screen grids of the intermediate frequency ampliers 92. The negative pulse from delay circuit |04 is applied to the normally conducting electrode structure of trigger 20 in order to trip this trigger. Vacuum tube 2| is normally biased to cut-ofland requires a positive pulse on its grid to overcome theV cut-on" bias and thus render the tube conducting. The anode of tube |2| obtains its positive .polarizing potential through a voltage divider composed of resistors 22 and 23 connected to a source of 250 volts positive. A large condenser 25 in shunt to resistor 23 minimizes fluctuations in voltage across this resistor. The anode of tube |2| is also directly connected to the screen grid electrodes of the intermediate frequency ampliiiers 92. It will thus be seen that the screen grids of intermedin ate frequency ampliiiers 92 and the anode of tube |2| obtain their positive polarizing potentials from the same connection through a resistor 2li. The application of a positive pulse to the control grid of tube |2|, obtained from trigger |20, will cause tube |2| to pass current, as a result of which current flows in resistors 22 and 24 and produces an IR drop which reduces the screen grid voltage available for the amplifiers. This reduction in the screengrid voltage for the intermediate frequency ampliers 92 renders these ampliiiers insensitive and cuts off the receiving channel. The adjustment of cathode resistor |22 in trigger circuit |20 provides a variation in the amount of time that the receiver channel is blocked. The delay circuit IM is so designed that its inherent delay delays the operation of circuit |09 with respect to the negative tripping pulse applied to |04.

It will be evident from the foregoing that incoming signal pulses of variable pulse rate or phase which are collected on the receiving antenna will modulate or control the transmitter at the repeater station to cause it to send out pulses of similar variable pulse rate or phase. Also, that the incoming pulses are so spaced and the time constants of the repeater station so arranged that the receiving channel is blocked off' between incoming pulses, at which time the local transmitter is turned on.

What is claimed is:

1. A relay station for relaying pulses of high frequency energy which have a short duration relative to the time interval between them comprising a receiving antenna, a receiver coupled to said antenna and having means for changing said pulses of high frequency energy to pulses of direct current, a clipper coupled to the outut of said receiver for removing noise ripples in said direct current pulses, a coupling tube coupled to said clipper and providing two outputs. separate pulse delay circuits for said last two outputs, a blocking device coupled between one of said delay circuits and said receiver, said blocking device being so constructed and arranged and said one delay circuit having such time constants that said receiver is blocked during the interval between incoming pulses of high frequency energy, a pulse generator coupled to said other delay circuit and responsive to a pulse therefrom. for producing another pulse of desired polarity, said other delay circuit providing such, delay that the pulse produced by said pulse generator occurs during the interval between incoming pulses of high frequency energy at which time the receiver is blocked, a radio frequency generator coupled to said pulse generator and responsive to a pulse therefrom to produce a pulse of radio frequency energy, and a transmitting antenna coupled to the output of said radio frequency generator.

2. A relay station for relaying pulses of high frequency energy which have a short duration relative to the time interval between them comprising a receiving antenna, a receiver coupled to said antenna and having means for changing said pulses of high frequency energy to pulses of direct current, a clipper coupled to the output of said receiver for removing noise ripples in said direct current pulses, a coupling tube coupledr to said clipper and providing two outputs, sepa# rate and independently adjustable pulse delay circuits for said last two outputs, a blocking device coupled between one of said delay circuits and said receiver, said blocking device being so constructed and arranged and said one delay circuit having such time constants that said receiver is blocked during the interval between incoming pulses of high frequency energy, a pulse generator coupled to said other delay circuit and responsive to a pulse therefrom fo-r producing another pulse of desired polarity, said other delay circuit providing such delay that the pulse produced by said pulse generato-r occurs during the interval between incoming pulses of high frequency energy at which time the receiver is blocked, a radio frequency generator coupled to said pulse generator and responsive to a pulse therefrom to produce a pulse of radio frequency energy, and a transmitting antenna coupled to the output of said radio frequency generator, and a monitor circuit also coupled to the output of said receiver, said monitor including a pulse rate selective circuit, a limiter, a discriminator and an audio frequency utilization circuit.

3. A relay station for relaying pulses of high frequency energy which have a short duration relative to the time interval between them comprising a receiving antenna, a receiver coupled to said antenna and having means for changing said pulses of high frequency energy to pulses of direct current, a clipper coupled to the output of said receiver for removing noise ripples in said direct current pulses, a coupling tube coupled to said clipper and providing two outputs, separate pulse delay circuits for said last two outputs, a blocking device coupled between one of said delay circuits and said receiver, said blocking device being so constructed and arranged and said one delay circuit having such time constants that said receiver is blocked during the interval be'- tween incoming pulses of high frequency energy, a pulse generato-r coupled to said other delay circuit and responsive to a pulse therefrom for producing another pulse of desired polarity, said other delay circuit providing such delay that the pulse produced by said pulse generator occurs during the interval between incoming pulses of high frequency energy at which time the receiver is blocked, a local modulation circuit for controlling the amount of delay provided by said last delay circuit, a radio frequency generator coupled to said pulse generatorV and responsive to a pulse therefrom to produce a pulse of radio frequency energy, and a transmitting antenna coupled to the output of said radio frequency generator.

4. A relay station for relaying pulses of high frequency energy which have a short duration compared to the time intervals between them comprising a receiver coupled to said antenna and having means for changing said pulses of high frequency energy to pulses of direct current, a top and bottom clipper stage for removing noise from said direct current pulses, a pulse rate selective circuit coupled to the output of said clipper, a limiter coupled to the output of said selective circuit, a balanced discriminator and detector coupled. to the output of said limiter for changing frequency or phase variations in the output of` said limiter to variations in amplitude, a low pass filter for passing the rectified output of said discriminator, and an audio frequency utilization circuit coupled to said filter, an adjustable delay circuit also coupled to the output of said clipper, a pulse generator coupled to said delay circuit and responsive to a pulse therefrom for producing another pulse of desired polarity, a radio frequency transmitter coupled to said pulse generator and responsive to a pulse therefrom to produce a pulse of radio frequency energy, and a transmitting antenna for said transmitter, said delay circuit providing such delay that the pulse producedY thereby occurs during the interval between incoming pulses of high frequency energy applied to said receiver.

5. A relay station for relaying pulses of high frequency energy which have a short duration compared to the time intervals between them comprising a receiver coupled to said antenna and having means for changing said pulses of high frequency energy to pulses of direct current, a top and bottom clipper stage for removing noise from said direct current pulses, a pulse rate selective circuit coupled to the output of said clipper, a limiter coupled to the output of said selective circuit, a balanced discriminator and detector coupled to the output of said limiter for changing frequency or phase variations in the output of saidlimiter to variations in amplitude, a low pass 9 filter for passing the rectied output of said discriminator, and an audio frequency utilization circuit coupled to said lter, iirst and second adjustable delay circuits having their inputs coupled in parallel to the output of said clipper, a blocking device coupled between said iirst delay circuit and said receiver, said blocking device being so constructed and arranged and said first delay circuit having such time constants that said receiver is blocked during the interval between incoming pulses oi high frequency energy applied to said receiver, a pulse generator coupled to said second delay circuit and responsive to a pulse therefrom for producing another pulse of,

desired polarity, a radio frequency transmitter coupled to said pulse generator and responsive to a pulse therefrom to produce a pulse of radio frequency energy, and a transmitting antenna for said transmitter, said second delay circuit providing such delay that the pulse produced thereby to control said pulse generator occurs during the interval between pulses of high frequency energy applied to said receiver.

6. A relay station for relaying pulses of high frequency energy which have a short duration compared to the time intervals between them, a receiving antenna, a receiver coupled to said antenna and having means for rectifying vsaid pulses, a coupling tube responsive to said rectied pulses for producing two pulse outputs of diierent polarities, a monitor circuit for one of said outputs, another coupling tube for the other output, said last coupling tube also providing two pulse outputs of the same polarity, separate pulse delay circuits for said last two pulse outputs, a blocking device coupled between one of said delay circuits and said receiver, said blocking device being so constructed and arranged and said one delay circuit having such time constants that said receiver is blocked during the interval between incoming pulses of high frequency energy, a pulse generator coupled to said other delay circuit and responsive to a pulse therefrom for producing another pulse of desired polarity, said other delay circuit providing such delay that the pulse produced by said pulse generator occurs during the interval between incoming pulses f high frequency energy at which time the receiver is blocked, a radio frequency generator coupled to said pulse generator and responsive to a pulse therefrom to produce a pulse of radio frequency energy, and a transmitting antenna coupled to the output oi said radio frequency generator.

7. A pulse delay circuit comprising a trigger circuit having a pair of vacuum tube electrode structures, the grids and anodes of said vacuum tube electrode structures being cross-coupled, means for unsymmetrically biasing the grids to thereby produce a trigger circuit having one degree of electrical stability, a connection for supplying a unidirectional current tripping pulse of predetermined polarity and magnitude to said trigger circuit for changing it from its stable to its active state, a vacuum tube normally biased to cut-off, a diierentiator circuit coupled between the negative pulse output terminal of said trigger circuit and the input of said last vacuum tube, said diiierentiator circuit serving to produce a sharp positive pulse from the trailing edge of the negative output pulse produced by said trigger of such magnitude as to overcome the cut-off bias of said last tube and render it momentarily conductive, said last tube producing a pulse when it becomes momentarily conductive, and a pulse reaizait l0 sponsive circuit coupled to the cathode of said last tube.

8. In combination, a pulse delay circuit comprising a trigger circuit having a pair of vacuum tube electrode structures, the grids and anodes of said vacuum tube electrode structures being cross-coupled, means for unsymmetrically biasing the grids to thereby produce a trigger circuit having one degree of electrical stability, a connection for supplying a unidirectional current tripping pulse of predetermined polarity and magnitude tc said trigger circuit for changing it from its stable to its active state, a vacuum tube normally biased to cut-oir, a diiferentiator circuit coupled between the negative pulse out- I put terminal of said trigger circuit and the input of said last vacuum tube, said diiierentiator circuit serving to produce a sharp positive pulse from the trailing edge of the negative output pulse produced by said trigger of such magnitude as to overcome the cut-olf bias of said last tube and render it momentarily conductive, said last tube producing a pulse `when it becomes momentarily conductive, and a radio transmitter normally biased to cut-off coupled to an electrode of said last tube and responsive to the pulse produced thereby to generate a pulse of high frequency energy.

9. A p-ulse delay circuit comprising a trigger circuit having a pair of vacuum tube electrode structures, the grids and anodes of said vacuum tube electrode structures being cross-coupled, means for unsymmetrically biasing the grids to thereby product a trigger circuit having one degree of electrical stability, a connection for supplying a unidirectional current tripping pulse of predetermined polarity and magnitude to said trigger circuit for changing it from its stable to its active state, a vacuum tube normally biased to cut-off, a diierentiatcr circuit coupled between the negative pulse output terminal of said trigger circuit and the input of said last vacuum tube, said diferentiator circuit serving to produce a sharp positive pulse from the trailing edge of the negative output pulse produced by said trigger of such magnitude as to overcome the cut-off bias of said last tube and render it momentarily conductive, said last tube producing a pulse when it becomes momentarily conductive, and a pulse responsive circuit coupled to an electrode of said tube and responsive to the pulse produced thereby to generate another pulse of the same relative polarity.

10. In combination, an electron discharge device trigger circuit having one degree of electrical stability, a connection for supplying a unidirectional current tripping pulse of a predetermined polarity and magnitude to said trigger circuit for changing it from its stable to its active state, an electron discharge device normally biased to cut-off, a diierentiator circuit coupled :between the negative pulse output terminal of said trigger circuit and the input of said last electron discharge device, said dirferentiator circuit serving to produce a sharp positive pulse from the trailing edge of the negative output pulse produced by said trigger circuit of such magnitude as to overcome the cut-oir" bias of said device and render it momentarily conductive, said last device producing a pulse when it becomes momentarily conductive. Y

11. A phase modulation pulse system comprising a trigger circuit having one degree' of electrical stability, said trigger having a stable state and an active state, a source of recurring pulses for repeatedly tripping said trigger at the rate of said recurring pulses, and means for varying the active time of said trigger in accordance with signal modulation to thereby produce output pulses from said trigger circuit whose width varies in accordance with said modulation, a differentiator circuit for producing short pulses from the trailing edges of said variable width pulses, and a utilization circuit responsive solely to said short pulses produced from said trailing edges.

12. A phase modulation pulse system comprising a trigger circuit having one degree of electrical stability, said trigger having a stable state and an active state, a source of recurring pulses for repeatedly tripping said trigger at the rate of said recurring pulses, and means for varying the active time of said trigger in accordance with signal modulation to thereby produce output pulses from said trigger circuit whose width varies in accordance with said modulation, a differentiator circuit for producing short pulses from the starting and trailing edges of said variable width pulses, means for discarding the short pulses obtained from said starting edges, and means for utilizing solely those short pulses obtained from said trailing edges.

13. A system in accordance with claim 11, characterized in this that said source f recurring pulses comprises a radio receiver, and said utilization circuit comprises a radio transmitter.

14. The method of generating phase modulated pulses which comprises generating substantially square wave pulses under control of a series of recurring pulses, varying the width of said generated square wave pulses in accordance with signal modulation, and utilizing the trailing edges only of said variable Width pulses to generate additional pulses whose timing is a function of the signal modulation.

15. In combination, a trigger circuit having one degree of electrical stability and including two electrode structures each comprising an anode, a cathode and a grid, impedance elements interconnecting the grid of each structure with the anode of the other structure in regenerative manner, a cathode bias resistor for at least one of said structures, a source of tripping pulses for said trigger circuit, and a modulation circuit coupled to said cathode resistor for varying the bias of said one structure in accordance with modulation potentials.

16. In combination, a trigger circuit having one degree of electrical stability and including two electrode structures each comprising an anode, a cathode and a grid, impedance elements interconnecting the grid of each structure with the anode of the other structure in regenerative manner, a common cathode bias resistor for said structures, a source of tripping pulses for said trigger circuit to thereby change said trigger circuit from its stable to its active state, and a signal modulation circuit coupled to said common cathode bias resistor for varying the active time of said trigger circuit in accordance with the signal modulation.

17. A pulse system involving pulses of high frequency energy which have a short duration compared to the time intervals between them, comprising an antenna, a receiver coupled thereto including a rectifier for rectifying the received pulses, a transmitter under control of said rectined pulses, and means coupled to said rectier and back coupled to a preceding stage in 'said receiver for blocking said receiver during the intervals between received pulses, said means including an electron discharge device trigger circuit having an adjustable element for varying the active time of said trigger circuitto thereby vary the time of occurrence and the time during which said receiver is blocked.

18. A pulse modulation system comprising a trigger circuit having one degree of electrical stability, said trigger having a stable state and an active state, a source of recurring pulses for repeatedly tripping said trigger at the rate of said recurring pulses, and means for varying the active time of said trigger in accordance with signal modulation to thereby produce output pulses from said trigger circuit whose Width varies in accordance with said modulation, a differentiator circuit for producing short pulses from the starting and trailing edges of said variable width pulses, and a utilization circuit responsive solely to those short pulses which are produced from the trailing edges.

19. A receiver for receiving pulses which are modulated in phase or timing, comprising an electron discharge device stage through which the received signal pulses are adapted to pass, and an electron discharge device self-restoring trigger circuit responsive to the received signal pulses for blocking the passage of signals through said stage in accordance with the timing modu lations in the received pulses,

20. A radio receiver adapted to receive pulses which are transmitted from a remote radio transmitter and which are modulated in phase or timing, comprising a receiver having circuits for beating the carrier of the incoming signal pulses with locally produced oscillations to thereby produce pulses of intermediate frequency energy, a screen grid electron discharge device intermediate frequency amplifier therefor, a rectier coupled to the output of said amplifier, and vacuum tube circuits responsive to the rectied energy for varying the conductivity of said amplier substantially in accordance with the variations in timing of the received pulses, said vacuum tube circuits being coupled between the output of said rectifier and the screen grid electrode of said amplier.

2,1. A receiver for receiving pulses which are modulated in phase or timing, comprising an electron discharge device stage through which the received signal pulses are adapted to pass, andra trigger circuit responsive to the received signal pulses for blocking the passage of signals throughY said stage for xed time intervals in accordance with the timing modulations in the received pulses, said trigger circuit comprising a pair of vacuuml tube electrode structures Whose grids and anodes are regeneratively coupled together.

22. A receiver for receiving pulses of radio frequency energy which are modulated in phase or timing comprising an electron discharge device stage through which the received signal pulses are adapted to pass, a detector circuit following said stage for changing said pulses of radio frequency energy to unidirectional current pulses, and a trigger circuit coupled between the output of said detector and said stage for varying the conductivity of said stage in accordance with the variations in timing of the received pulses.

23. A pulse system involving pulses of high frequency energy which have a short durationcompared to the time intervals between them, comprising an antenna, a receiver coupled thereto including a Vrectiiier for rectifying the received pulses, a transmitter under control of said rectified pulses, and means coupled to said rectii'ler and back coupled to a preceding stage in said receiver for blocking said receiver during the intervals between received pulses, said means including an electron discharge device trigger circuit having an adjustable element for varying the active time of said trigger circuit to thereby vary the time of occurrence and the time during which said receiver is blocked.

24. A pulse repeater station comprising pulse receiving apparatus, pulse transmitting apparatus, a delay circuit between the output of said receiver and the input of said transmitter, and means for modulating the effective amount of delay produced by said delay circuit in accordance with signal modulation.

25. A radio pulse repeater station comprising radio pulse receiving apparatus, means for converting the received radio pulses to unidirectional current pulses, radio transmitting apparatus, a delay circuit responsive to said unidirectional current pulses for controlling the radio transmitting apparatus to send out pulses of energy a desired interval of time later than the received pulses, and means for modulating the time delay of said delay circuit in accordance with signals.

26. A pulse type communication system comprising a pair of stations separated by a wave transmitting medium, each station including apparatus for producing pulses which are short compared to the time intervals between them, and each station including a receiver for demodulating received pulses, means associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, an adjustable pulse delayer in circuit with the receiver of each station and receiving pulses therefrom, said delayer controlling the rate of production of pulses in the transmitter of the same station, and means coupled to said adjustable pulse delayer for modulating the timing of the pulses passed thereby to said transmitter.

27. A pulse type communication system comprising a pair of stations separated by a wave transmitting medium, each station including apparatus for producing pulses which are short compared to the time intervals between them, and each station including a. receiver for demodulating received pulses, means associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, an adjust- 14 able vacuum tube pulse delayer in circuit with the receiver of each station and receiving pulses therefrom, said delayer being so constructed and arranged as to be responsive to pulses solely of a predetermined polarity above a certain value which are impressed thereon for controlling the rate of production of pulses in the transmitter of the same station, and means coupled to said adjustable pulse delayer for modulating the timing of the pulses passed thereby to said transmitter.

28. A communications system comprising pulse repeater stations, means at each station to delay and to modulate the delay of pulses transmitted in response to received pulses, and demodulating means responsive to modulations of the frequency of the pulses.

29. A pulse modulation system comprising a trigger circuit having one degree of electrical stability, said trigger circuit having a stable state and an active state, said trigger including two electron discharge device electrode structures each having an anode, a grid and a cathode, impedance elements cross-connecting the anodes with the grids of the devices, regeneratively, a direct connection between the cathodes, a common cathode resistor for said electrode structures, and means in circuit with said common cathode resistor for supplying recurring tripping pulses of a variable pulse rate to thereby cause said trigger circuit to produce unidirectional output pulses containing the modulation components.

30. A communications system comprising pulse repeater stations, means at each station to delay and to modulate the delay of pulses transmitted in response to received pulses, and demodulating means responsive to modulations of the pulses.

JOHN B. ATWOOD. HAROLD O. PETERSON.

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

UNITED STATES PATENTS Number Name Date 2,262,838 Deloraine et al Nov. 18, 1941 2,266,401 Reeves Dec. 16, 1941 2,113,214 Luck Apr. 5, 1938 1,433,599 Bown Oct. 31, 1922 2,045,244 Gerhard June 23, 1936 2,199,179 Koch Apr. 30, 1940 1,798,066 Clement Mar. 24, 1931 2,034,738 Beverage Mar. 24, 1936

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