US2416304A - Trigger circuit - Google Patents

Description

, u P ITU A TRAMSLAT NG Fan D. D. GRIEG TRIGGER CIRCUIT Filed Sept. 5,-1'942 ()RCUIT AMPLIFIER Feb. 25, 1947.

INVENTOR Y DONALD 0. GR/EG Arr RNEYI- Patented Feb. 25, 1947 TRIGGER CIRCUIT. I I, DonaldD. Grieg-, Forest Hills, Yaeassi'glnor:

Federal Telephone and Badiosflorporation az corporationof Delaware y Application September 5, 942; Serial-No: 457,396 (o1 zeal-e247 6 Claims.

This: invention relates to radio'frequency circuits: and more particularly to trigger circuits to be-controll'edby received radio frequency pulses.

For the purpose of economy in power and for preservation of, a modicum of 'secrecy, transmission of energy by time modulated impulses is often resorted to. This type of' system is quite fully: set forth in United States patents. to A. Reeves, Nosi 2266,40]. and 2256336 and in United States-patent-to Edmond M. Deloraine and A. ReevesNo. 2,262,383.

A particularly valuabletype of such systems from the standpoint of avoiding interception is that described in: the copendi'ng applications of Edmond M. Deloraineand Emile Labin, entitled "Pulse transmission system," Serial No. 425,108,

derived: from the input pulses; to a. circuit tuned to: indifferent: radio; frequency harmonically re.- lated. to the; pulse; envelope, a: series of output pulsesof a difierentcarrier radio frequency and thev same: relative time; spacings which; may be readily detected by known. means or used. for

' other: purposes: may be obtained:

filed December 31, 1941 and Emile'Labin, en-

titled Radio receiverfiSerial No. 449,595, filed July 3, 1942;

' In the last named application is described a system wherein received pulsesare amplified, detected and limited, after'whi'ch they are applied to a trigger circuit; The shaping circuit serves to give to the detected pulses a fixed duration independent of the duration of the receivedpulse.

cation; are applied over a resonant" circuit to the input 'oi'a translating circuit. This tri'gger circuit'is preferably i'nthe form-of a multi'-vibratorwith a fixed time constant of operation. The leading edge of an-i'ncomingradio irequency 'pul'se serves to operate the trigger circuit: and it remains/ int operation for a definite per-iod indeependentof the'l'ength oi the applied pulse. The

time period f'orwhi'ch thetrigger circuit remains operated is greater than the duration of the -applied' radio frequency pulse and therefore: producesa pulse in the output which hasa spacing; in time; dependent upon the applied radio: free quency 'pulsebut a duration independent thereof; The trigger circuitmay also servet'o produce pulses of an amplitude independent of'thel applied'radio frequency pulses. e l

By applying the envelope direjct -currentpulses A; better understanding" of my invention and the objectsandvfeaturesthereof' maybe had: from the particular description: of: an embodiment. of my invention made=withvreferenceto the acconrpanyin'g drawings in: whichz'.

Fig; 1 is' a? block di-agramaofj a receiver-incur porating: my invention;

Fig. 2 is: asset:- of curves: used in explaining theicperati'on of my invention;

Fig; 3 islthe' circuit diagram of' a: trigger circult in accordance with myrinvention and Fig.4 shows an additional output element which may be used with-.the trigger" circuit of Fig; 3., In Fig. 1= is shown diagrammatically a time modulated impulse receiving system incorporat ing my invention. This receiver includes the usual-antenna H3 and thelradio frequency ame plifier H which. may also serve to reduce the received radio frequencysignals to a common intermediate frequency. This" intermediate frequenc'y preferablyalso is in: the radio frequency range; If the system is to be used for reception of impulses from stations: transmitting at-dif ferent' frequencies, it is desirable that the received 'irequencies be; reduced to the sameinter cor-din gl'y; the-impulses in the output; of the-trig gercircuit will be in the formof' direct current impulses with allof the radio frequency carrier removed therefrom. Noseparate envelopede-' t'ector circuit andtriggercircuit is necessary as irrprevious circuits cit-his type. 5

Theoutput' signals from-trigger circuit i2 are then" applied to a detector I3 overa band pa'ss filter l 4 preferably: after being limited in' lime itei 55f If" the pulses are.- amplitudea medulated as; well: times: mcdulated, the signals; ire, the outputiof-i amplifier: l lament be applied to; another;

stead of a single tube structure.

detector l6 for deriving the amplitude modulated signal.

It will be recognized that the receiver circuit of Fig. 1 performs substantially the same function as the prior art system outlined above. The circuit according to my invention, however, does not require the detecting circuit for the 'pulses prior to application thereof to the trigger circuit. Likewise, the input limiter is unnecessary in this circuit in accordance with my invention as will be more clearly brought out in the specific description of the shaping circuit.

The trigger circuit which constitutes thejprincipal feature of my invention will now be described with reference to Figs. 2 and 3. The radio frequency impulses in the output of amplifier II will be in the form shown in curve A of Fig. 2.

The two pulses 20 and 2| which define one pair of time-modulated: impulses are each composed of a high frequency carrier wave as shown. Although only a relatively small number of oscillations are shown in the figure, the actual number of oscillations in each pulse may be fairly high. For example, if the entire pulse duration Y r is two microseconds and an intermediate frequency of 50 megacycles is used, there will be 100 oscillations during one pulse. With higher frequencies there will be a correspondingly larger number of oscillations per pulse. The pairs of pulses in the received series, 20, 2| and 22, 23 are separated by a relatively fixed period T.

The pulses of this received series are applied preferably to the tuned primary 30 (Fig. 3) of thetuned input circuit 3| of trigger circuit l2. This triggercircuit comprises a vacuum tube device 7 32 operating as a multivibrator or trigger circuit.

A common envelope with two sets of electrodes is shown but it should be understood that separate vacuum tubes may be used if desired in- This multivibrator circuit has two setsof electrodes, cathode 40, grid 4| and anode 42, and cathode 50, grid 5| and anode 52. The cathodes 40 and 50 are interconnected and coupled to ground through an adjustable resistor device 35. This adjustable resistor serves as a common'resistance in the anode-cathode circuit'of both sets-of electrodes and provides the feedback necessary for operation of the arrangement as a multi-vibrator. In the absence of a signal, grid 5| is maintained negative by means of a bias source-53 so that the corresponding set of electrodes is normally noneconductive. The energy flowing through the first section of this tube and through resistance 35 maintains 'grid 4| slightly negative in the normal condition. Grid 5| also tends to become more negative adding to the negative bias. Upon application of a predetermined negative voltage to grid 4| the electrode system 40, 4| and 42 provides an amplification of this voltage. This operation then swingsgrid 5| in a positive direction by reason of the drop through resistance 58 and the charge on condenser 55 overcoming the effect of the negative bias on this grid. Simultaneously, the electrode system 40, 4|, 42 is driven further negatively to cut-off by virtue of the feedback voltage across resistance 35. A0-

trodes 50 and 52 and the current between electrodes 40 and 42 commences. The duration of this operative condition of the multi-vibrator trigger means is determined by the adjustment of resistance 35 and the time constant of resistances 56 and 59, condenser 55 and anode load 55, the tube would remain inoperation.

' initiating cordingly, an. output signal is initiated in the V multi-vib-rator trigger circuit across resistance 51.. If the negative voltage applied to the grid does not continue the chargeon condenser 55 associated with grid 5| willleak ofi through resistance 56. As soon as this charge .has been reduced so that this section of thetube is again 7 cutoff by the bias, currentceases between elecsufficient potential to initiate operation of tube electrodes 40, 4| and 42. This developed potential is applied to the input over resistance 59 and coupling condensers 68, 6|. A decoupling resistance 52 of high value is arranged connected between tuned circuit 3| and ground. Normally, it will take a number of applied oscillations to cause this operation but this number will be relatively small compared to the .total numberin the pulse. Each negative swing of a received wave train pulse adds to the effect tending to make grid 4| negative. After operation of the trigger circuit, however, the initiated output pulse will last for a period of time determined by the circuit time constants and independent of the length of the applied impulses, 20, 2|, 22, etc. Accordingly, the output current from trig ger circuit !2 may be indicated by curve B of Fig. 2. It Will'be noted that the pulses 20A, ZIA, 22A and 23A are all initiated at substantially the same time with respect to the corresponding pulses 20, 2|, 22 and 23 and that they are all of equal dura tion, slightly greater than the duration of the pulses. Likewise, the amplitude of these output pulses is independent of the input amplitude since it is controlled entirely by the constants of the trigger circuit and the voltages 7 to a constant level before application to the trigger circuit. Furthermore, it is not necessary to firstdetectthe radio frequency pulses to envelope frequency before application to the multi-vibrator circuit since the multi-vibrator itself performs thefunction of detecting the signals and is triggered by them for the final signal reproduction.

The trigger circuit of Fig.3 has been described as an element of the receiver system of Fig. 1. It may,'however, be used in other connections. By adding a tuned circuit, Fig. 4, tothe output line as indicated at line 4-4 the circuit mayoperate as a frequency changer to convert the received radio frequency pulses to damped wavetrain pulses of a different radio frequency with-,- out disturbing their time spacing. By selecting the values of inductance 10 and-condenser 'H- to any frequency which is a harmonic of the pulses produced in the output of the multi-vibratorim-v pulses of thisharmonic frequency having an amplitude and duration determinedby thejoutput impulsesof the trig er circuit may be produced. These waves may; then be passed to any translating apparatus ,12 for further operation as desired.,

Generally, the direct current impulses in the output of the trigger circuit will not contain frequency components higher than the initiating ra-' when the constants of and H are properly chosen the trigger circuit may be used to produce reshaped output at the same radio frequency as the initiating pulses if desired.

It is clear that many other known forms of trigger circuits may be used in place of the particular circuit shown in Fig. 3. For example, any type of multi-vibrator circuit may be used so long as it is properly biased and is provided with a suitable tuned input circuit to develop the necessary operating voltage directly from the radio frequency impulses. It is further clear that an amplifier such as shown at I I is only necessary in order that the amplitude of the received impulses be increased. Even if no amplifier is provided, the trigger circuit will operate providing the received pulses are of sufiiciently great amplitude themselves.

While the trigger circuit of my invention is particularly useful in receivers for time modulated impulse systems or for converting the received radio frequency, it is clear that the rinciples of my invention are not limited to this particular combination. The trigger circuit may be useful in obstacle detection systems for reshaping the refiected impulses prior to applying them to the control electrodes of an indicator. Furthermore, in accordance with my invention, the trigger circuit disclosed may be used in any case where it is desired to produce direct current pulses corresponding in space to alternating current impulses but independent of these pulses in amplitude and duration.

Many modifications of my invention will occur to those skilled in the art and the particular examples described are not to be considered as limitations on the scope of my invention but merely as an illustration thereof.

What is claimed is:

1. A circuit for producing output direct current pulses of predetermined character in response to applied radio frequency pulses of a given duration comprising a trigger circuit for producing a pulse of predetermined duration at least as great as said given duration in response to applications to said circuit of a predetermined voltage, an input circuit for said trigger circuit comprising a tuned circuit resonant to the radio frequency of said radio frequency pulses for developing said predetermined voltage to cause operation of said trigger circuit, and an output circuit for said trigger circuit for deriving therefrom the produced direct current pulses.

2. A circuit according to claim 1, further comprising a circuit tuned to a predetermined radio frequency component of said direct current pulses coupled to said output circuit whereby radio frequency pulses whose duration is independent of said applied radio frequency pulses are obtained.

3. A radio receiver for time modulated pulse reception, comprising a receiving amplifying means for amplifying a succession of received pulses of a given radio frequency, a circuit for detecting said amplified radio frequency pulses and shaping the resultant detected pulses, said circuit comprising an input circuit tuned to said radio frequency for developing a predetermined voltage, a trigger circuit normally in unoperated condition and operative into operated condition in response to said predetermined voltage, means for coupling said tuned circuit to said trigger circuit, and time constant means for maintaining said trigger circuit operated for a substantially constant period of time at least as great as the duration time of said amplified pulses, means cou- I pled to the output of said circuit for deriving a 4. A radio receiver according to claim 3 where"- in said circuit further comprises means for determining operation of said trigger circuit to a predetermined amplitude, to control the amplitude level of said direct current pulses to substantially a constant value independent of said applied pulses. I

5. A radio receiver for time modulated pulse translation, comprising a receiving amplifying means for amplifying a succession of received pulses of a given radio frequency, a circuit for detecting and shaping the detected envelope of said amplified radio frequency pulses, said circuit comprising an input circuit tuned to said radio frequency for developing a predetermined voltage, a trigger circuit normally in unoperated condition and operative into operated condition in response to said predetermined voltage, means for coupling said tuned circuit to said trigger circuit and means for maintaining said trigger circuit operated for a substantially constant period of time at least as great as the duration time of said amplified pulses, means coupled to the outputof said circuit for deriving a direct current pulse in response to each operation of said circuit, and means tuned to a fixed radio frequency which is a component of said direct current pulses for deriving reshaped time modulated pulses from said direct current pulses.

6. A circuit for detecting radio frequency input pulses and producing therefrom output pulses having substantially the same timed relation to one another as the input pulsesand amplitudes and duration periods independent of those of the input pulses, comprising an impulse trigger circuit having an input circuit and an output circuit, means normally maintaining said trigger circuit in unoperated condition, means responsive to a predetermined input voltage for rendering said trigger circuit operative, duration I control means for maintaining said trigger on cuit operative for a predetermined interval after application of said predetermined voltage, means in said input circuit resonant to said radio frequency for receiving said radio frequency pulses and developing said predetermined voltage in response to each said received pulses to cause operation of said trigger circuit, and means in the output circuit of said trigger circuit for deriving pulses of predetermined amplitude and duration in response to operation of said trigger circuit.

DONALD D. GRIEG.

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

UNITED STATES PATENTS Garceau Dec. 1 1942

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