US2436512A - Pulse frequency selective recorder - Google Patents

Description

Feh 4, 1948. J. M. HOLLYWOOD 2,

PULSE FREQUENCY SELECTIVE RECORDER Filed Jan. 17, 1946 AMPLIFIER TRIGGER RECORDER CIRCUIT r n INTERMITTENTLY I In] ENERGIZED Z5 FILTER I9 F I .2 INTERMITTENTLY G ENERGIZED a ig 13 27 TO RECORDER cmcun FROM TRIGGER CIRCUIT FIG.3 AG [souRcE' 5| s3-\ ess I. 5 6 RECORDING 29 59 DEVICE 3: FROM TRIGGER CIRCUIT & 40 FILTER nvvnvrok JOHN M. HOLLYWOOD BY.

A T TOR/V5 Y Patented Feb. 24, 1948 PULSE FREQUENCY SELECTIVE REcORDER John M. Hollywood, Washington, D. 0., assignor to the United States of America, as represented by the Secretary of War Application January 17, 1946, Serial No. 641,841

1 Claim. (Cl. 234-15) This invention relates, in general, to electrical circuits and more particularly to circuits for differentiating between pulsed signals of difiering pulse repetition frequencies.

It is often desirable to provide a circuit which will give an indication when receiving pulsed signals of a particular pulse repetition frequency, hereinafter referred to as P. R. F., and another indication when receiving pulsed signals of other P. R. F.s. It is an object, therefore, of this invention to provide a circuit which will produce an indication when pulsed signals of a particular P. R. F. are received.

It is a further object of this invention to provide a circuit which will give a differing indication when pulse signals of P. R. F.s other than the desired are being received. It is a still further object of this invention to provide a circuit which will be activated only by the fundamental frequency of the pulse signals and not by harmonics thereof.

In general, this invention utilizes a trigger circuit followed by a conventional band-pass filter. Incoming pulses cause the trigger circuit to operate, thereby producing a square wave output, each half cycle being initiated by each incoming pulse. The filter is tuned to the square wave voltage frequency,-which in turn is one half the pulse frequency of the desired incoming signals. Only pulses of twice the resonant frequency of the filter circuit will cause an indication.

Other objects features and advantages of this invention will suggest themselves to those skilled in the art and will become apparent from the following description of the invention taken in connection with the accompanying drawing in which:

Fig. l is a schematic block diagram showing broadly my invention;

Fig. 2 is a schematic circuit diagram of a filter circuit; and

Fig. 3 is a schematic circuit diagram of a recorder circuit.

Referring now more particularly to Fig. 1, pulses from an external source appear at point II and are applied to amplifier l3. The output of the amplifier is applied to a trigger circuit l5 whose output in turn is applied to a recorder ll. A filter circuit l9 may be switched in and out of the output of the trigger circuit l5 by means of the switch 2|.

The filter circuit might be, for example, similar to the one shown in Fig. 2 in which the output from the trigger circuit l5 appears at terminal 22 and is connected through switching means 2| to filter circuit l9 which is normally of the band-pass type. Output is taken at terminal 2?. Switching means 2| is used to switch the filter ill in and out of the circuit.

The recorder [7 might be, for example, similar to the one shown in Fig. 3 in which the output of the trigger circuit l5 appears at terminal at, being coupled through capacitor 3| to the grids 33 and 35 of thyratrons 3'! and 39, respectively. Resistor 40 returns the grids 33 and 35 to ground. Potentiometer ll is connected between a' source of positive potential and ground. The cathodes t3 and 45 of thyratrons 31 and 39 are connected together and connected through resistor 4'! to arm 49 of potentiometer 4|. An A. C. voltage source is applied to primary winding 5| of transformer 53. The secondary winding 51 is connected between plates 59 and BI of thyratrons 3'! and 39. The voltage at center tap 63 of secondary 51 is applied to recording device 55. Resistor E1 is connected between the center tap 83 and ground.

In operation, pulse signals from an external source are applied to the amplifier l3, amplified, and applied to the trigger circuit iii. The output of the trigger circuit is a square-wave voltage each half cycle of which is initiated by each of the incoming pulses. Therefore, the frequency of the square-wave voltage is one-half that of the frequency of the incoming pulses. If switch 2| is closed and the filter circuit I9 is tuned to the square-wave voltage, the filter l9 will transfer voltage of the fundamental frequency of the square-wave voltage to its output connections. Therefore the fundamental frequency voltage will appear at the input of the recorder I! with substantially no attenuation. At other frequencies, however, the filter 19 will not transfer voltage to its output connections and substantially no signal will appear at the input to the recorder II. In the event that the resonant frequency of the filter l9 coincides with a harmonic frequency of the square-wave voltage, the recorder ll will not be actuated since it is designed to respond only to signals above a particular level.

Referring now to Fig. 3, with the filter l9 switched out, the square-wave output of the trigger circuit appears at point 29 and at the grids 33 and 35. The plates 59 and GI are fed in pushpull, that is, the voltage at plate 59 will be out of phase with plate Bl. Each thyratron will conduct when its grid voltage is above cut-off and its plate voltage reaches the ignition voltage at the beginning of a positive cycle. Conduction will continue during the positive cycle at the plate until the extinction voltage is reached. Tube currents flow through resistor 61 causing a pulsed voltage at twice the frequency of the A. C. source by the pulsed voltage appearing at the input of the recording device 65. If desired, visual indication means may be used. Also, in practice, the filter i9 is switched in and out of the .circuitat a regular rate by means of switch2lcontrolled by intermittently energized relay coil 23. It will be seen then that when a pulsed signal, ata P. R. F. for which this circuit was designed,

is received, switching the filter l9 in and but ofthe circuit will have essentially no effect and the recording device 65 will recordsubstantially a solid line. However, if the pulsed signals received are at another P. R. the output of the recorder I! will be a series. of regularly. spaced dashes, since the filter iSattenuates the outputof trigger circuit i2- and effectively removes the. input to the recorder l1 when the switch 2iisin the position indicated in the drawings,

It shouldbe noted that the amplitudeof the output of 'thetrigger circuit l5 is-of a constant value regardless of the amplitude of its: input. The output I being essentially a a square-wave voltage will contain only odd-order harmonics and the third harmonic'will have an amplitude one-third the amplitude ofthe fundamental. Therefore, if the potentiometer 4i isset so that only signals above a value one-third of the fundamental frequency will cause the tubes 3'! and 39 to conduct, no harmonics will actuate the recorder H.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled-intheart that various changes and modifications may be made therein without departing from the scope of the invention as set forth in l the appended claim, and I claim all such changes and modificationsas fall fairly within the spirit and scope of the invention.

Wh is claim d i -A- combination for recording pulse signals including signals of predetermined pulse frequency, comprising, -a square wave generator controlled by successive pulses to generate successive half cycles of square wave output, means to apply the output of said square wave generator to a recorder alternately directly and through a filter, said filter having a ,pass band of one-half the predetermined pulse frequency, whereby signals of said predetermined pulse frequencyare continuously recorded and signals of other pulse. frequencies are. intermittently recorded.

. QH HQL YW QD- Cox May 19, 1942 .I-Iansell "July.v 6, 1943 Number

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