US2605402A

US2605402A - Vacuum tube keying of resistance coupling amplifier

Info

Publication number: US2605402A
Application number: US163294A
Authority: US
Inventors: Clarence B Coleman
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-05-20
Filing date: 1950-05-20
Publication date: 1952-07-29
Anticipated expiration: 1969-07-29

Description

y 9, 1952 QB. COLEMAN 2,605,402

VACUUM TUBE KEYING OF RESISTANCE COUPLING AMPLIFIER Filed May 20, 1950 Multiplier Source of Oscillation 33 9.

. 8+ Amplifier i- -L- B'.;O 4.

39 4 3 4| 2; 3 1| v 9 r: 7 :2 2 5 I 255 45 37 Kyer wmusssss: INVENTOR Clorence B. co lerncm.

.provide a keyer. which; shallproduce sharply Patented July 29, 1952 v Y L 2,605,402. 7 v v VAC UM TUBE KEYING; F RESISTANCE i COUPLING U Clarence B. Coleman, Baltimore, MIL, assignor to westinghouse Electric, Corporation, ;East Pittsburgh,.Pa., a corporation of Pennsylvania Application MayZO, 1950, Serial No.1sa294 My invention relates to electric discharge appa- 9 Claims. (01.25%5271 V ratus and it has particular relation to electronic keyers. v -The Usselman Patent 2,153,656 is illustrative 'ofkeyers of the prior art ofwhic'h I am aware.

Such'keyers include one or more pentodes.' ,Oscillationsiderived from. an exciter are impressed between: the control grids and the cathodes, and

keying potential is impressed between the sup- 'pressor grids and the cathodes of the pentodes.

The anodes of the pentodes'are coupled to'the control grids of following amplifiers. keying potential is:varied, the pentodes pass from As the substantially conductive to a substantially-non- .conductive condition. During theintervalswhen the. pentodes are conductive, trains of oscillations derivedxfro'm the exciter are impressed on the -following amplifiers.

The variations in the pentode conductivity. are thus impressed as modulations-on :oscill'ations derived from the excite'r source. The signals transmitted when the pentodes are non-conductive may be designated as marksignals .and the signals transmitted when the-pentodes are conductive may be designated as gap signals. .iToachieve precision in signalling,v -it;is essential that the mark and: gap intervals be sharply defined; it is desirable then, that the trains of oscillations be initiated and terminated abruptly.

I have, found'that prior art keyersihave the serious disadvantage. :that the marksgap modulations are not sharplydefined. The transmitted signal appears to pass gradually-between:the='gap magnitude to the. mark magnitude; 5

i "It is, accordingly,-, an pbjejct of my invention to fined mark-gap signals.

A more specific object of my invention is to provide a keyercapacitively. coupled to follow .ing amplifying stages which shall produce sharpx1y defined;mark-gap signals.- v

'An auxiliary object of my invention is .toprovide a novel pentode circuit;

' My invention arises from therealization that the bluntness in the mark-gap signals is caused by the lag inthe reference to the keying variations of the coupling network between the keyed pentode and .the amplifiers. "This network may include'a coupling capacitor which is'cliarged and discharged as the conductivity of 'the'key'e'd pentode is varied by the keying oscillations. When the keyed pentode is substantially nonconductive, its anode and therefore'one plate or the coupling capacitor are substantially at the positivepotential of the supply. The coupling capacitor is, thereforegg; charged to the potential of the supply. When the keyed pentode becomes conductive, the potential of the above-specified plate T of :the, coupling capacitor I is substantially reduced andrthev capacitor tends to discharge.

.As the keying potentialis varied, the D. C. po-

tentialifrom the platesupply impressed on the capacitor lthus. varies in rhythm with the keying variation.=, Inefiect, then the oscillations from the .exciter are modulated, not'by a potential having the precise wave form of the keying potential, but by one having the wave form produced by thecharge and discharge of the capacitor. The

sharpness of this modulation is materiallylimited by thetimerequired, for the capacitor to discharge. 'Ihistime interval is, in turn, dependent on the resistance in the discharging circuit of the capacitor and sincethis resistance is substantial,

the rise and drop of the grid potential of the follcwving amplifier is relatively-gradual and the mark and gap signals are not sharply defined as is desirable. v =;In accordance with specific objects of my invention, I provide a'pairof pentodes on the suppressor grids of which the keying signal is impressed-and the screen grid of each of which is connected; to the anode of the other. The anode of one of the keyer tubes is capacitatively coupled to the grid of the following-amplifier. it is a property of-a pentodethat as the suppressor gridpotential isvaried, the total current drawn fromthecathode-by the screen gridand the anode remains. constant The variation in one senseotthe current flowing to the anode is compensated by corresponding variations in the opposite sense of.- current-fiowing to the screen grid.

.As-the current flow to the anode coupled to the amplifier varies; by reason of the keying variations, the -current flow to the screen grid of the other time yariesin such manner as to compensate .-for the former variations. The charge on thecoupling capacitor, therefore, remains substantially constant and the conductivity of the amplifier to which the keye'r is coupled is varied sharply. Themark gap modulations are, therefore, sharply distinguishable.

The novelfeatures that I consider characteristicofmy invention are set forth with particularityw n the appended claims. The invention .itself,-'"however, both as to its organization and its methodof operation, together with additional objects and advantages thereof will be understood from the following description of a specific 'embodimen'twhenread in connection with the accompanying drawing in which the single figure 3 is a circuit diagram of a preferred embodiment of my invention.

The apparatus shown in the drawing includes a first pentode I having an anode 3, a cathode 5, a control grid 1, a screen grid 9 and a suppressor grid II; and a second pentode I3 having similar electrodes I5, I'I, I9, 2I and 23 respectively' The anodes are suppliedfrom a suitable B supply (not shown) through

load resistors

24 and 25. The cathodes and I! are grounded through cathode resistors 26 and 21 respectively and by-passed by by-pass capacitors 29 and 3I respectively of suit able magnitude. The output of an oscillator 33 preferably of the CW type isv impressed between the control grid 1, and the cathode 5 of the'first pentode I through a grid resistor 35'. The sup- Grid resistor 45 of amplifier 43 B potential Keyer output potential pressor grids II and 23 respectively, are con- 1 nected together to the output of a keyer 31. The screen grid 9 and 21 of each pentode I and I3 respectively is connected directly or through a connection having substantially no impedance to the anode I5 and 3-of theother. I

The keyer 31 maybe of any well knowntype.

In the preferred practice of my invention, it supplies alternatively negative potentials of such magnitude that when they are impressed on the suppressor grids II and 23 the pentodesI and I3 are non-conductive and positive potentials. of

such magnitude that when they are impressed on the suppressor gridsfthe pentodes I and I3 are substantiallyconductive. Y

The anode'3 of the first pentode I is coupled through a-capacitor' 39' to the control grid M of a following amplifier 43. The latter grid'dl may be grounded through a grid resistor 45. Theoutput of theamplifier 43 may be coupled through frequency multipliers and output amplifiers 41 which may be, in turn; coupled to an antenna 49 1 of acommunication line. r Y

I have found that as a potential is supplied by the ,keyer, a signal having sharp mark and gap modulations is transmitted. When the keyer potential is negative, the anode current of both pentodes I and I3 is'substantially zero. However,

the screen gridZI of the second pentode I3 draws current substantially equal to the current drawn by the anode I5 of this pentode (and therefore, by the anode'f3 of the pentode I) when it is fully conductive and, therefore, the direct current drawn from the B -supply rem'ains unchanged. While thefirst pentod I is non-conductive,-the

carrier oscillations impressed on its control grid are not transmitted through the coupling capa'citor, therefore, these oscillations are not transmitted through the amplifier to the antenna.

When the potential derived from the keyer 31 is positive 'or'at such other magnitude as to render the first pentode l conductive, the D. C. current drawnfrom' the'supply remains unchanged.

'Ho'wever; the oscillations impressed from th'e'osvI clllator (i3 are now impressed through the coupling capacitor 39 on the amplifier 43 and transmitted'by the antenna 49.

'In the practice of my invention, the coupling capacitor 39 may also be connected to the anode pacitor 39 connected with the anode of the first path 1 i In a system in accordance with my invention which I have found to operate satisfactorily, the following components are included:

Load resistor 25 of second pentode 13 51.000 ohm Cathode resistor 26 of first pentodenu- 1.200 ohm Cathode resistor 27 of second pentode; 1.200 ohm By-pass capacitor 28 of first pent0de 0:1 mf. By-pass capacitor 31 of second pentode 0.1 mt. Grid resistor 35 of first pentode 51.000 ohm Coupling capacitor 39 0 1 mf. 100.000 ohm 250 Oscillator (33) potential 1 volt R. M. S.

While in accordance with the specific aspects of my invention a pair of pentodes I and I3 are included in the keying system, occasions may arise in which tubes of other types are applicable. For example, the pentodes may be included in a single envelope or a pair of pentagrid converters properly connected may have the properties necessary in the practice of my invention andmay be utilized. Under certain circumstances the capacitive coupling 39 may be replaced by an inductive coupling; a coupling transformer, for example. To th extent that the basic concepts of my invention are applied to such an inductively coupled system, such system lies within the scope of my invention. Under certain circumstances the keyer and control potentials may be distributed difierently among the grids of the pentodes.

than in the specific system illustrated. Such different distribution lies Wtihin the scope of the broad aspects of my invention.

My, invention is herein shown as applied to the keying of radio frequency oscillations. Itis also, applicable. to the keying of audio frequency oscillations. For example, the keyerin accordance with my invention may be connected to key the modulator'of a transmitter operating by transmitting .AM or FM modulated continuous waves. v i .While Ihave shown and described a specific embodiment of my invention, many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention: l. A keying circuit including a pair of pentodes and a network for impressing keying potentials simultaneously on the suppressor grids of said pentodes characterized. by the fact that the screen grid of each of said pentodes is connected to' the anode of the other" of said pentodes through a connection having substantially no impedance.

2. In combination, a first electric discharge path defined by. an anode and a cathode and ineluding-"a control grid; a screen grid and a suppressor grid; connections for impressing a signal on s'aidcontrol grid; a "second electric discharge path defined by an anode and a cathode and also including a control grid, a screen grid and a suppressor grid; a connection between said last-named'control grid .and cathode; a keying network; connections for impressing the output of said keying network on both said suppressor grids; a connection betweenthe screen gridof each of said paths and the anode of the other of said paths; and an output connection including a coupling capacitor connected to the anode of one of said paths. 1

3. 1m combination, a first electric discharge path defined by an anode and a cathode and including a control grid, a screen grid and a suppressor grid; a second electric discharge path defined by an anode and a cathode and also including a control grid, a screen grid and a suppressor grid; a keying network; connections for impressing the output of said keying network on said suppressor grids; a connection between the screen grid of each of said paths and the anode of the other of said paths; and an output connection including a coupling capacitor connected to the anode of one of said paths. v

4. In combination, a first electric discharge path defined by an anode and a cathode and including a control grid, a screen grid and a suppressor grid; a second electric discharge path defined by an anode and a cathode and also including a control grid; a screen grid and a suppressor grid; a network for impressing control potentials on said suppressor grids; a connection between the screen grid of each of said paths and the anode of the other of said paths; and an output connection including a coupling capacitor connected to the anode of one of said paths.

5. In combination, a first electric discharge path defined by an anode and a cathode and including a control grid, a screen grid and a suppressor grid; a second electric discharge path defined by an anode and a cathode and also including a control grid, a screen grid and a suppressor grid; a connection of substantially no impedance between the screen grid of each of said paths and the anode of the other of said paths; and an output connection connected to the anode of one of said paths.

6. In combination, a first electric discharge path defined by an anode and a cathode and including a control grid, a screen grid and a suppressor grid; connections for impressing a signal on said control grid; a second electric discharge path defined by an anode and a cathode and also including a control grid, a screen grid and a suppressor grid; a connection between said lastnamed control grid and cathode; a keying network adapted to supply as an output alternatively a first potential which when impressed on the suppressor grid of either of said paths is suflicient to reduce the conductivity of said path to a low magnitude or a second potential which when impressed on the suppressor grid of either of said paths is sufiicient to render said path substantially conductive; connections for impressing the output of said keying network on both said suppressor grids; a connection between the screen grid of each of said paths and the 6 anode of the other of said paths; and an output connection including a coupling capacitor connected to the anode of one of said paths. 7

'7. In combination, a first electric discharge path defined by ananode and a cathode and including a control grid, a screen grid and a suppressor grid; a second electric discharge path defined by an anode and a cathode and also including a control grid, a screen grid and a suppressor grid; connections between said control grids and their associated cathodes, respectively; a keying network; connections for impressing the output of said keying network on said suppressor grids, a connection between the screen grid of each of said paths and the anode of the other of said paths; and an output connection including a coupling capacitor connected to the anode of one of said paths.

8. In combination, a first electric discharge path defined by an anode and a cathode and including a control grid, a screen grid and a suppressor grid; 9. second electric discharge path defined by an anode and a cathode and also including a control grid, a screen grid and a suppressor grid; connections between said control grids and their associated cathodes respectively; a connection between the screen grid of each of said paths and the anode of the other of said paths; and an output connection connected to the anode of one of said paths.

9. In combination, a first electric discharge path defined by an anode and a cathode and having a plurality of grids; a second discharge path defined by an anode and a cathode and also having a plurality of grids; a keyer; connections for impressing the output of said keyer on corresponding first grids of each of said paths; connections for impressing a signal on a second grid of said first path; connections between a second grid of. said second path corresponding to said second grid of said first path and said cathode CLARENCE B. COLEMAN.

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

UNITED-STATES PATENTS Name Date De Rosa May 25, 1948 Number