US2406882A

US2406882A - Radio impulse system

Info

Publication number: US2406882A
Application number: US469044A
Authority: US
Inventors: Jr Norman H Young
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1942-12-15
Filing date: 1942-12-15
Publication date: 1946-09-03
Anticipated expiration: 1963-09-03
Also published as: GB586176A

Description

Sept. 3, 1946.

N. H. YOUNG, JR

RADIO IMPULSE SYSTEM y Filed Dec. 15, 1942 PULSE INPUT 7 [12' 1 ,1 1% H4753 CLIPPER '34 INVENTOR. IVO/PMFIN h. you/v6, JR.

BY my Patented Sept. 3, 1946 UNITED STATES ATENT OFFICE RADIO IMPULSE SYSTEM ware Application December 15, 1942, Serial No. 469,044 6 Claims. (Cl. 178-44) This invention relates to radio impulse systems and more particularly to systems for selectively filtering pulse modulated waves in accordance with the amplitude of the pulses.

In the copending application of D. Grieg entitled Receiver system, Serial No. 467,516, filed December 1, 1942, methods and means are disclosed for selectively filtering a wave modulated with pulses differing in amplitude so as to eliminate unwanted pulses whether or not they are of less or greater amplitude than wanted pulses.

It is an object of my invention to provide an additional method and means for accomplishing the same result.

Another object of my invention is to provide a method and means for amplifying a pulse modulated wave to reduce the amplitude of the pulses greater than a given amplitude.

The reduction in amplitude or the elimination of the pulses of amplitude greater than a given amplitude such as the amplitude of a Wanted pulse is accomplished in accordance with my invention by applying the pulse modulated wave to an amplifier having an input-output characteristic such that an increase of input potential causes the output thereof to increase to a maximum and then to decrease toward zero. The gain of the amplifier may be adjusted so that the peak of the wanted pulse lies near the maximum of the input-output characteristic so that the wanted pulse is amplified a desired value and the pulses of greater amplitude are distorted. The distortion produces sharp pulse portions defining the leading and trailing edges of the larger pulses according to the amounts they extend beyond the maximum of the amplifier input-output characteristic. These sharp pulse portions are limited in amplitude by the maximum of the input-output characteristic of the amplifier. The amplitude of the sharp portions may be reduced further by passing the output of the amplifier through a filter to eliminate the higher harmonics. This reduces the amplitude of the sharper pulse portions with respect to the amplitude of the wanted pulse which, of course, is of greater duration than the duraton of the sharp pulse portions. By proper adjustment of the gain of the amplifier and the proper filtering of the output thereof, an output will be obtained in which the wanted pulses have greater amplitude than the unwanted pulses. By clipping this pulse output at a level beyond the maximum amplitude of the unwanted pulses, a pulse wave will be obtained containing the pulse energy according to the occurrence of the 2 wanted pulses with substantially a complete elimination of unwanted pulses.

For a further understanding of the invention reference may be had to the following detailed description to be read in connection with the accompanying drawing, in which:

Fig. l is a schematic illustration of a circuit in accordance with my invention, and

Fig. 2 is a graphical illustration showing the pulse reduction and eliminating features of the invention.

Referring to Fig. 1, the pulse reducing and eliminating system of my invention comprises an amplifier circuit ID, a filter l2 and a clipper IS. The amplifier circuit may comprise any arrangement of elements whereby an input-output characteristic is established so that an increase of input potential causes the output to increase to maximum and then to decrease toward zero. Such a. characteristic is illustrated at IS in Fig. 2.

For purposes of illustration, I have shown in Fig. 1 an amplifier circuit comprising an input vacuum tube l6 having zero bias and two amplifier tubes 2| and 22 the

grids

23 and 24 of which are connected to the anode I1 and the cathode l8 of the tube IS in push-pull arrangement. The anode I l is provided with a positive bias through a resistor I 9, and is connected to the grid 23 through a coupling condenser 2'5. The grid 23 is provided with a negative bias C1 through a resister 21. The cathode l8 of the tube I6 is connected through a resistor 28 to ground. The cathode I8 is also connected to the grid 24 through a coupling condenser 29. The grid 24 is biased negatively by a potential C2 through a resistor 30. The cathodes of the tubes 2| and 22 are connected together and grounded at 32. The anodes or plates of the

tubes

21 and 22 are connected together to provide an outlet 33, the latter being connected to a positive potential through a resistor 34.

The input tube l6 operates to apply the input pulse or potential to tube 22 without inversion of polarity and simultaneously to apply the input potential to tube 2| with inverted polarity. In the absence of an input potential, the tube 2| is biased beyond plate cut-oil while the tube 22 is biased to a value permitting a normal plate current. As the grid Id of tube 16 is made increasingly negative by an increasing input potential, the grid 24 of tube 22 is made more and more negative thereby resulting in a reduction of its plate current. This causes a rising potential to occur at the plate output connection 33 as indicated between points and 4| on the ever,

are the unwanted pulses.

Fig. 2. At point 4|, tube 22 is at cut-off. During the interval between All and M the Voltage on the grid 23 of tube 2! increases in a positive direction, but since bias C1 is so chosen to cause the tube 2| to remain at cut-off, the tube contributes nothing to this part of the curve. However, the instant tube 22 reaches cut-off, the grid potential of tube 2! begins to rise above cut-off. As the amplitude of the input potential continues to rise, the grid 23 of tube 2| becomes more and more positive and the tube conducts more and more current causing the potential at the plate connection 33 to decrease as indicatedbetween 4| and 42 on the curve l5. put potential has reached a value sufficient to cause cut-oil of the tube l6 and any further increase in potential on the grid H! of the tube l6 results in no further change in potential at 33.

While I have shown the increasing and decreasing portions of thecharacteristic curve l5 to have substantially the same slope .in the inverse direction, it will be understood that the characteristics of the tubes may be such as'to provide curve I5 of plate current entirely different slopes anduifie'ent maximum and minimum ipoints M and M1, 42' respectively, for the curve. The main feature of the invention, however, is 'toprov'ide the input. and output characteristic curve with a maximum point whereby pulses applied to the amplifier extending in amplitude beyond the maximum point of the curve are distorted and limited in "amplitude.

Assume that the'input to the grid M of the tube H3 is a modulated wave having a series of pulses '5l, 52, '53 and 54,*with the pulse 5| re- 'peated as indicated. The wave, of course, may contain other pulses which occur at random or ata given frequency not shown with the group illustrated in Fig. -2. "The pulses illustrated, howare representative in that the pulse 5| is the wanted pulse while the pulses-52, 53 and 54 The 'pulses '52 and '53 are of greater amplitude than the 'wanted pulse while the pulse 54 is "of less amplitude.

To eliminate the unwanted pulses, the gain of the amplifier H) is adjusted so that'the amplitude of the wanted'pulse 5| is brought near and preferably slightly under the maximumpoint 4| of the input-output characteristic of the amplifier. The output pulse 51a is thereby produced in substantially'the same shape as the input pulse "5|. The pulse52, however, is greatly distorted since it extends beyond 'the maximum point 4| and-in fact beyondthe 'tzero point 42 of the curve. When this pulse is applied to the ampliher, the tube 2| passes the pulse potential up to the maximum level as indicated at'=a'"thereby producing a leading 'edge'55. Then the tube 22 takes over for the potential of the pulse above the level a thereby providing "a'return trailing edge 55 to zero. The decreasing potential on the trailing sides of the pulse-52 provides a second sharp pulse from zero aSJin'dicated by'the leading edge 51 which extends to'the level a'for the maximumpoint '4 The tube'Z I "then takes over for theremaining decrease in potential below the level a thereby providing a'trailing edge 58. Thus, the distorted pulse output for the large input pulse 52 provides a sharp pulse 52a which definesithe leadin'g edge of the'input pulse 52 and a second sharp pulse 521) which defines the trailing edge "thereof. The "amplitudes of the

pulses

52a and 52b are limited by'the maximum point 4| of the characteristic curve l5.

The third input pulse At point 42 the in- 53,'while of amplitude greater than the pulse 5|, does not extend through the decreasing portion between the maximum 4| and the zero point 42 of the characteristic curve I5. The output for the pulse 53 is shown at 53a. The leading edge of the pulse 53 provides a leading edge 60 for the pulse 530. which extends to the level a. Since the input pulse 53 extends above the maximum level a the tube 22 takes over and provides a decreasing or trailing edge 6| until the top level b of the pulse 53 is reached. This provides a sharp pulse portion overlying the leading edge the input pulse 53 decreases the potential input applied to theamplifier, a return through the characteristic curve is obtained whereby a second sharp pulse portion 54 is formed defining the trailing edgeof the output pulse 53a. The pulse 53 is thus distorted by the portion thereof extending beyond the maximum 4| of the characteristic curve l5.

Thepulse 54 of amplitude less than the wanted pulse 5| providesan output which in accordance with the adjustment of the amplifienmay be smaller as indicated at 55a than the input pulse 54.

As shown in Fig. '2, the

pulse portions

52a, 52b,

53 and 54 defining the leading and trailing edges of the larger input "pulses-52 and *53 respectively,

are sharper pulses than the pulse 'output'SIa of the wanted'pulse 5L By suitably filtering out the higher harmonics, the sharp pulse porfinal output wave 80 is obtained having pulse energy 8| which correspond to the pulses 5|. Thus, the interfering '

pulses

52, 53 and 54 are effectively eliminated. The outputpulse energy 8| may, of course, be sharpened or otherwise treated as may be desired depending on the use intended forthe pulse energy thus obtained.

While I have described the principles of my invention in connection with a specific system, it will be understood that the system herein shown anddescribed is not to be considered as a limitation on'the scope of my invention as set forth in the'objects thereof and in the appended claims.

I claim:

1. A method of eliminating from a wave modulated with substantially unidirectional pulses of diirerent amplitude and of appreciable duration thosepulses of greater and'lesser amplitude than a wanted pulse comprising distorting the pulses of greater amplitude by producing sharp pulse portions having high harmonic content from the leading and trailing edges of the pulses of greater amplitude while leaving the wanted pulse substantially unchanged in form, filtering said waves to eliminate the higher'harmonics of the pulses thereby reducing'theamplitudes of the distorted pulses with respect'to the amplitude of the wanted pulse, and clipping the output pulses at a level above'the maximum output amplitude of the unwanted pulses.

2. A method. of eliminating from the wave modulated with pulses of different amplitude and of appreciable duration those pulses of greater and lesser amplitude than a wanted pulse comprising applying the wave to an amplifier having an input-output characteristic in which an increase cf input potential causes the output to'increase to maximumand then to decrease toward zero, adjusting the gain of the amplifier so .that

60., When the trailing edge of.

the peak of the wanted pulse lies near the maximum of said characteristic so that the wanted pulse is amplified a desired amount without substantial distortion and the pulses of greater appreciablecduration from a wave modulated with pulses of difierent amplitude having pulses of greater and lesser amplitude than a wanted pulse comprising an amplifier to distort the pulses of greater amplitude than the wanted pulse, the distortion producing sharp pulse portions of high harmonic content defining the leading and trailing edges of the pulses of greater amplitude, means to filter the pulses to eliminate the higher harmonics and thereby reduce the amplitudes of the distorted pulse with respect to the amplitude of said Wanted pulse, and means to clip the ou put pulses at a level above the maximum output amplitude of the unwanted pulses.

4. The system defined in claim 3 wherein the amplifier comprises a pair of tubes connected in push-pull arrangement, one of the tubes providing an input-output characteristic extending from zero to a maximum and the other of said tubes providing an input-output characteristic extending from said maximum to zero.

5. The system defined in claim 3 wherein the amplifier comprises a circuit having a pair of tubes connected in push-pull arrangement and a third tube tocontrol the input potential on said tubes so as to produce an input-output characteristic extending from a minimum value to a maximum value and then from said maximum value toward said minimum value.

6. A method of eliminating from a wave modulated with substantially unidirectional pulses of difierent amplitude having a predetermined fundamental frequency content, those pulses having amplitude greater or lesser than a predetermined level, comprising distorting pulses above a given amplitude thereby producing sharp pulse portions and relatively increasing the harmonic content in varying degree, from the leading and trailing edges of the pulses above the given amplitude, filtering said waves to eliminate the higher harmonics of the pulses thereby reducing the amplitude of the distorted pulses substantially proportionally to their harmonic content, and clipping the output pulses at a level above that of the greater amplitude pulse after reduction.

NORMAN H. YOUNG, JR.