US2401619A - Pulse signaling system - Google Patents

Description

.Bime 4,1946. a TREVOR v 2,401,619

, PULSE SIGNALING SYSTEM Original Filed Dec. 24, 1940 2 Sheets-Sheet 1 012a rrwmz er/(wedm INVENTOR ATTO-RNIEY June 4, 1946. B. TREVOR I PULSE SIGNALING SYSTEM 2 Sheets-Sheet 2 Original Fi led Dec. 24. 1940 Patented June 4, 1946 PULSE SIGNALING SYSTEM Bertram Trevor, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Original application December 24, 1940, Serial No.

371,551, now Patent No. 2,361,437, dated October 13, 1944. Divided and this application August 19, 1944, Serial No. 550,180

9 Claims. 1

This invention is a division of my copending application, Serial No. 371,551, filed December 24, 1940, now U. S. Patent 2,361,437, granted October 13, 1944.

The invention makes use of the fact that if a transmitter is keyed with regularly spaced short pulses having a duration of only a fraction of the total time, the peak power transmitted can be correspondingly increased Without exceeding the normal dissipation rating of the tubes. This increases the efliciency of operation at the transmitter, and when used with novel receiving means arranged as I will disclose hereinafter, raises the signal-to-noise ratio at the receiver, and improves the receiver threshold level, thereby improving the reception obtainable heretofore with a given power transmitter or permits equivalent reception with a transmitter of less power.

In describing my invention, reference will he made to the attached drawings wherein:

Figs. 1 and 2 show the form of the Wave energy transmitted by my system, and Fig. 3 diagrammatically illustrates means for generating and transmitting a signal of the form illustrated in Figs. 1 and 2.

I Asan example, suppose a transmitter were to be keyed on for a time duration of 5 microseconds and ofi for a time duration of 50 microseconds in regular intervals then the peak power of the pulses could be made ten times the normal steadystate peak power. In Fig. 1 is shown a typical example of the output of a transmitter of this nature. The transmitter is on a small fraction of the transmitting time. The rate of keying off and on of the transmitter is above audibility. Each of the impulses are modulated as for example by wide band frequency modulation. The

' nature of the impulses, so modulated, are shown in Fig. 2.

It is proposed that the transmitter be of the wide band frequency modulation type having, in addition, the pulse keyer described herein. The transmitter used herein may be in many respects as disclosed in Crosbys United States application Ser. No. 136,578, filed April 13, 1937, Patent No. 2,279,659, issued April 14, 1942, and in Crosbys United States application Ser. No. 358,385, filed September 26, 1940, with modifications in accordance with my invention.

In Fig. 3, I have shown a transmitter satisfactory for the production of frequency modulated waves'in accordance with my invention. In Fig. 3, I00 i a. wave generator of the electron discharge tube type having its anode coupled as shown to the desired amplifier and/or frequency multipliers comprising cascaded stages I02 and I04 which, in turn, may be coupled to additional stages and any other output arrangement desired. The oscillator I00 includes a tuned tank circuit I06 connected between its anode and controlg'rid and operating regenerativel for the production of oscillations to be frequency modulated and transmitted.

The frequency of the produced oscillations are modulated by modulating potentials supplied to the primary winding of a transformer'IUB, the secondary winding of which is connected between the grid H0 and cathode H2 of a reactance tube I I4. Reactance tubes are well known in the art and this tube may be, in general, as disclosed in the said Crosby applications and other applications. The anode H6 of this tube is connected to a point on the tank circuit I06 to derive therefrom a radio-frequency potential of a predetermined phase. A phase shifting circuit C, R, R, and the inherent grid-to-cathode capacitance of grid H8 and. cathode H2, supplies radio-frequency voltage to grid H8 in this tube substantially in phase quadrature with the anode voltage to produce in the tube .a reactive effect which supplements the reactance of the tank circuit I06. Thi reactive effect is inductive or capacitive, depending on whether the current in the tube to the plate leads or lags the plate voltage. In the modification illustrated, the current leads the plate voltage and the reactive effect is complex but may be considered capacitive. Modulation of the tube current modulates the said capacitive effect thereby modulating the reactance in the tank circuit and the frequency of the oscillations generated in accordance with the modulating potentials supplied to the grid 0. Radio-frequency voltage is also supplied from tank circuit I06 by inductance I20 to the tuned circuit I24 connected with the grid I26 to a mixer tube I28 also supplied at its grid I30 with oscillations of substantially constant but 'difierent frequency from a source I32. from tank circuit I06 and source I32 are mixed in tube I28 and a beat frequency is supplied to a frequency discriminator circuit I34. In this discriminator circuit the frequency variations or drifts of mean frequency of the oscillator. I00 are converted to amplitude variations, rectified in diodes I38 to cause corresponding currents to H flow in resistance I31 and I39 to produce therein potential variations, the difference of which is supplied by lead I40 to the controlgrid lle of The oscillations I reactance tube H4 to additionally control the reactance which tube '4 adds to tank I06 and this control is in the direction to counteract any tendency of the oscillator I to deviate in frequency of operation from its assigned mean frequency. The resistance R2 and condenser 01 are of a value to filter out all variations in potential of a frequency greater than the lower modulation potential frequency.

In order to monitor the wave generator, wave stabilizing and wavelength modulatin action of the reactance tube controlled oscillator, I connect the grid G of an amplifier and coupling tube T through a coupling condenser CC to the lead I40, and couple the cathode K of this tube to the anode end of resistance I 3 9. The output of this tube is supplied to a meter or other potential and/or current variation indicating means through a transformer T1.

The .frequency stabilized and frequency modulated oscillations produced in the means described above are as stated hereinbefore, amplified and/or frequency multiplied in stages I02 and I for transmission purposes. .In accordance with my invention, I interrupt this frequency modulated wave transmission as illustrated in Figs. 1 and 2; and in Fig. 3 I have illustrated one means for doing this. The square wave form generator I of any desired type such as, for example, the type used for testing television video equipment is used to provide waves of square wave form and supply the same by way of a network comprising a variable condenser C2 and resistance R to a diode I" having in its output-a resistance I28. The rectified potentials from resistance I28 (of the frequency of the square wave) are supplied to the control grid T30 of a wave amplitude limiting tube I32 and from the anode I34 of this tube to the control grid I 36 of "a wave amplitude limiting tube I38 having its anode I40" connected to an adjustable resistance I42. The resistance I42 is connected to the "control grid I46 of a frequency multiplier and/.oriamplifier stage comprising tube IM. This output may be supplied to additional stages, if desired.

Adjustable condenser C2 and diode bias re- :sistOrR' Ipermit adjustment :of the effectiveness of the square wave from 12.0 o diode 12:6 to thereby permit adjustment of the time duration of the pulses supplied by the rectifier to the grid I30' 0f the next stage amplifying these pulses. That is, bythe use of condenser C2 aandres-istance .R', the percent of mark time and space time .is .adjusted as desired. These impulses are impressed on the grid I39 for limiting :in tube I32 and then impressed on the grid 4.3.8 for limiting in tube I38 to give desirable fiat-top form. The output impulses by means of I42 are adjusted in amplitude ,to a value such that Itube I415 .is biased to be inactive the desired time duration .and active the remaining transmission time to produce an output as illustrated 'in'Figs. 1 and 2. With the transmitter in operation, and with a receiver wherein reception occurs only during the pulse .time,'it will be observed that no reception of signal or noise occurs during the interval between pulses. In this Way, the peak power of the transmitterucan be increased as the percent .mark of the pulses is decreasedwithout exceeding the normal dissipation of thetubes.

IA's an example, SHPDOse we have a frequencymodulation transmitter operating at some ultra- Ihighzfrequency having amaxim-um deviation frequency of +90 kc. and a maximum modulation frequency of 10 kc. Under these conditions, the normal receiver band width would be 200 kc. Suppose that the transmitter pulses occur every microseconds and each pulse is 10 microsecends in duration. A receiver band width of 200 kc. is then required to accept these pulses and a receiver band Width of 200+200=400 kc. is required to accept the pulse composed of the above frequency-modulated carrier. It will now be observed that the transmitter is on the air only of the total time so that its peak power may be raised to ten times normal which is an increase of 10 db. 'This gives a signal-to-noise ratio 10 db. greater than that obtained with the original wide "band frequency-modulated signal when working above the threshold of the, receiver. Since the intermediate-frequency band has been increased in the ratio 400/200=2=3 db., the threshold has been lowered (improved) by 103='7 db.

With the system just described we have 'had to widen the receiver band widthto 410.0 he. Suppose we had made use of this wider band width with normal frequency-modulation transmission by increasing the deviation to 1 90 kc. This would give a gain of /90=2.1=6.5 db. improvement in signal-to-noise ratio over the 200 kc. band width system. Here the threshold would have been raised (made poorer) by 3 db. So, with the 400 kc. band using pulse transmissiomwe'have gained l06.5=3.5 db. improvement in signal-to-noise ratio above the threshold and we have improved the threshold by 7+3=10 d'b.

The advantages for'this system are that a'small transmitter may be used to give an equivalent power output many times its normal rating, and, atthe same time-the threshold at the receiver has been lowered by a very substantial amount which means greater service "range. The 'use of frequency multipliers H32, 104 in the transmitter prevents interruptions or keying of the frequency modulated carrier wave from reacting in an undesirable manner upon the oscillator I09. The tubes Hi2 and +04 serve to isolate, so to speak, the oscillator I00 from the square Wave generator I20 and its associated circuit elements 126, 1 32 and 146.

What Iclaimis:

1. A radio transmitter for producing pulses :of high frequency energy which are short compared to the time intervals between them, comprising oscillation generator of high frequency waves, means for varyin the wavelength of said waves in accordance with modulation potentials, a vacuum tube-in the output-of said generator for passing the modulated waves, and keying means coupled to an electrode of said vacuum tube for periodically blocking the passage of waves through said tube for equal time durations which are "short compared to the timerintervals between intermintions, the peak power of sai transmitter bein higher than the average for steady state power.

.2. .A radio transmitter .tor producing pulses of high frequency energy which are short -.compar.ed to :the time intervals between them, comprising an oscillation generator of Zhigh frequency waves, a react-ance tub-e modulator coupled to said genera-tor for varying-the instantaneous wavelength of said waves in accordance with modulation potentials, a multiplier vacuum tube in the output of said generator, a wave radiating structure coupled to the output of said multiplier, and a keyer circuit coupled to an electrode of said multiplier for periodically biasing said multiplier to the output current cut-off condition for time durations which are equal and short compared to the time intervals between interruptions.

3. A radio transmitter for producing pulses of high frequency energy which are short compared to the time intervals between them, comprising an oscillation generator of high frequency waves, a reactance tube modulator coupled to said generator for varying the frequency of said waves in accordance with the signal intelligence to be conveyed, a frequency multiplier vacuum tube coupled to the output of said generator, sai multiplier having an anode and a, grid, a wave radiating structure coupled to the anode of said multiplier tube, and an interrupter circuit coupled to the grid of said multiplier tube for periodically biasin said tube to the anode current cut-off condition for time durations which are equal and short compared to the time intervals between interruptions.

4. A radio transmitter for producing pulses of high frequency energy which are short compared to the time intervals between them, comprising an oscillation generator of high frequency waves,

a reactance tube modulator coupled to said generator for varying the instantaneous wavelength of said waves in accordance with modulation potentials, a multiplier vacuum tube in the output of said generator, a wave radiating structure coupled to the output of said multiplier, and a keyer circuit coupled to an electrode of said multiplier for periodically biasing said multiplier to the output current cut-off condition for time durations which are equal and short compared to the time intervals between interruptions, said keyer circuit including a rectangular wave generator, and a wave limiting tube in the output of said rectangular wave generator.

5. A radio transmitter for producing pulses of high frequency energy which are short compared to the time intervals between them, comprising an oscillation generator of high frequency waves, a reactance tube modulator coupled to said generator for varying the instantaneous wavelength of said waves in accordance with modulation potentials, a multiplier vacuum tube in the output of said generator, a wave radiating structure coupled to the output of said multiplier, and a keyer circuit coupled to an electrode of said multiplier for periodically biasing said multiplier to the output current cut-off condition for time durations which are equal and short compared to the time intervals between interruptions, said keyer circuit including a rectangular wave generator, a wave limiting tube in the output of said rectangular wave generator, and an adjustable impedance element for varying the efiective length of the output wave from said rectangular wave generator which is applied to said limiting tube.

6. A radio transmitter for producing pulses of high frequency energy which are short compared to the time interval between them, comprising an oscillation generator of ,high frequency waves, a reactance tube modulator coupled to said generator for varying the instantaneous wavelength of said waves in accordance with modulation potentials, a multiplier vacuum tube in the output of said generator, a wave radiating structure coupled to the output of said multiplier, and a keyer circuit coupled to an electrode of said multiplier for periodically biasing said multiplier to the output current cut-off condition for time durations which are equal and short compared to the time intervals between interruptions, said keyer circuit including a square wave generator, an adjustable condenser shunted by a resistor in the output of said square wave generator, a rectifier coupled to said square wave generator through said condenser, a limiter tube following said rectifier, and a coupling circuit from the output of said limiter tube to said electrode of said multiplier.

7. A pulse type frequency modulation transmitter comprising an oscillator, a frequency modulator for changing the frequency of oscillations of said oscillator in accordance with signal modulation, means for multiplying the frequency of the frequency modulated oscillations, a pulse generator for interrupting the continuous wave output of said last means to produce pulses, an amplifier for said pulses, and an antenna coupled to said last amplifier.

8. A pulse type transmitter comprising a source of carrier waves, means for varying the instantaneous length of the carrier waves in accordance with signal modulation, means for multiplying the frequency of the modulated waves, an amplifier for amplifying said last waves, a pulse generator coupled to said last amplifier for causing an interrupted flow of waves therethrough, an amplifier for said interrupted waves, and an antenna coupled to the output of said last amplifier.

9. A radio transmitter for producing pulses of high frequency energy which are short compared to the time intervals between them, comprising an oscillation generator of high frequency waves, means for varying the wavelength of said waves in accordance with modulation potentials, a vacuum tube in the output of said generator for passing the modulated waves, and keying means coupled to an electrode of said vacuum tube for periodically blocking the passage of waves through said tube for time durations which are short compared to the time intervals between interruptions, the peak power of said transmitter being higher than the average or steady state power.

BERTRAM TREVOR.

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