US2328056A - Keying arrangement for electric signaling systems - Google Patents

Description

Aug. 31, 1943.

JENER A. G. COOLEY KEYING ARRANGEMENT FOR ELECTRIC SIGNALING SYSTEMS Filed June 11, 1941 INVENTOR AUSTIN G. COOLEY Patented Aug. 31, 1943 KEYING ARRANGEMENT FOR ELECTRIC. SIGNALING SYSTEMS Austin G. Cooley, Hudson View Gardens, N. Y.,

assignor, by mesne assignments, to Times Telephoto Equipment Inc.. New York, N. Y., a corporation of New York Application June 11, 1941, Serial No. 397,513

11 Claims.

This invention relates to signaling systems and more especially to keying control arrangements for facsimile telegraph systems and the like.

A principal object is to provide a signal control arrangement for telegraph systems and the like whereby a keying device or a signal receiving device can be selectively switched from spacing to marking with a maximum of sharpness between spacing and marking signal conditions.

Another object is to provide a keying arrangement whereby a selectively operable keying member or signal receiving member is switched to marking and spacing positions by current impulses of respectively different amplitudes and wherein the switching is efiected substantially coincident with the change from one amplitude to the other.

Another object is to provide a keying arrangetubes are rendered alternately conductive undercontrol of respective received signals of difierent amplitudes. As a result of this arrangement, the push-pull tubes are rendered alternately conductlve and non-conductive for a very small difference in amplitude of the two classes of signals so that the possibility of half-way operation of the said member is avoided.

A further feature relates to an improved circuit control arrangement for a telegraph receiver whereby zero wander of the signal reproducing member is substantially eliminated.

A further feature relates to a push-pull telegraph signal control arrangement wherein the sections of the push-pull control are Jointly controlled by a single gaseous discharge tube, for example a two-electrodegas lamp of the neon type or the like.

A still further feature relates to the novel organization. arrangement and relative interconnection of parts which cooperate to produce a simple and efilcient keying control for telegraph systems, wherein the switching from marking to spacing can be effected with a. difierence in amplitude of as little as & decibel above or below the predetermined keying'point.

Other features and advantages not, specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention will be illustrated and described as embodied in one particular kind of signaling system e. g. facsimile telegraph system,

it will be understood that this is done merely for explaining the inventive concept and not by way of limitation. Furthermore, since the various elements such as electron tubes, gaseous discharge tubes, keying devices, frequency converters and signal receiving and recording devices such as facsimile scanners are well-known in the telegraph signaling art, they are illustrated herein is converted into two signal conditions e. g. spac-- ing and marking. For this purpose, device I may be a facsimile or telegraph transmitter which controls the production of signal currents of two different levels, the lower level representing for example marking, and the upper level representing for example spacing or vice versa. Device I may be a facsimile scanning mechanism of any known construction such for example as a scanning' drum upon which is wrapped. the printed matter to be transmitted, and as a result of which the white areas are translated into an audio frequency carrier, for example 1800 c. p. s and the black areas are translated into an 1800 c. p. s. carrier of a different amplitude. For a detailed description of such mechanism, reference may be had to my Patent No. 1,719,392 or Patent No. 2,015,742. It will be understood of course that any other well-known telegraph keying arrangement may be employed for generating the two signal conditions of different relative amplitudes. Thus the device I may take the form of an oscillator whose amplitude is controlled by a telegraph key or automatic telegraph transmitter in accordance with respective spacing and marking signals.

At the receiving end of the signaling channel a frequency doubler I of any well-known type, whereby the 1800 c. p. a. signal amplitudes are converted into a corresponding 3600 c. p. s. signal amplitudes. The 3600 c. p. s. signals are then impressed by means of transformer l on a fullwave rectifier tube 5. A small smoothing condenser 6 and a bleeding load resistor I are connected across the output of the rectifier, the polarity of the rectified current being as indicated in the drawing. Connected in series across resistor I are a gaseous discharge lamp s and a resistor 9. Device 8 may be of any well-known gaseous conduction type such as an evacuated bulb containing two electrodes and having a filling of one or more of the inert gases such as neon. helium or argon. Devices of this type as. is well-known have a minimum breakdown voltage and do not pass appreciable current until such minimum voltage is applied to the electrodes.

Associated with device and resistor l are two grid-controlled vacuum tubes "I, ll. While these tubes are shown as of the triode type, it will be understood that tubes having two or more grids may be employed e. g. shield-grid tubes, pentodes and the like. The resistance 0 is connected across the cathode l2 and control grid it through grid its cathode i2 when the device 8 is non-conduc tive. The plate electrodes of tubes l0 and ii are connected in balanced relation through two operating windings i1 and i8 and through a battery or plate supply ll.

Associated with windings ll, II, is an armature or bar 20 which is mounted for swinging movement and is adapted to be actuated in one direction or the other depending upon which of the windings I1, is, is energized. The member 20 cooperates with any well-known form of telegraph signal recorder schematically illustrated by the rotating drum 2|. Merely by way of example, drum 2! (Fig. 2) may have around its periphery in helical form a rib or knife edge 25 and the member 20 may carry a knife edged bar 22 which extends substantially parallel to the axis of drum II, a suitable recording web or tape II being positioned between bar 22 and the knife edge on drum 2!. when the member 20 is in spacing position, bar I! is clear of the recording paper. when a marking signal is received, bar I! is moved to engage the recording paper where.- upon a suitable mark is made thereon. Thus bar 21 may be connected to one side of a source of recording potential and the knife edge on drum 11 may be connected to the other side oi this source, so that when the bar 1! is moved to marking. the recording paper is acted upon either by an electric discharge, spark. or by current conducticn through the paper to produce the record. It will be understood that member 20 may be used to control the recording when of any wellknown type of telegraph syphon recorder, or if desired the member 20 may be used itself as a keying control for repeating spacing and marking signals to another point.

In the arrangement illustrated, member 20 and windings l1, I8, may form part of any wellknown construction such as used in radio loud L, the signals are passed through a filter or ad- Justable attenuator pad 2 and thence through speakers of the movable armature type, the armature being connected to member 20. As an alternative, members ll, it and 20 may constitute any. well-known form of telegraph relay construction. a

The tube i0 and winding H are the marking control for moving member 20 to marking position, while tube I I and winding it are the spacing control for moving member to spacing position. Tubes II and H are connected in pushpull relation for alternate on-and-of! control which is determined primarily by the breakdown of the gaseous device I. For, low level signals transmitted from device I, corresponding for example to marking, the device 8 does not receive suilicient voltage to break it down, so that the grid it is at substantially zero potential with respect to its cathode i2. and therefore considerable plate current passes through winding II. The plate current through winding i1 holds the member 20 to marking. Under this condition the plate current of tube ll flows through resistor is thus applying a relatively strong negative bias to grid 23 with respect to its cathode 24 blocking off plate current through tube H. Member 20 therefore\ remains in marking position so long as the marking signal condition continues.

When an increased signal level, corresponding to spacing, is transmitted from device I, a suillcient voltage is developed across device 8 to break it down and current therefore passes through resistor 0. The voltage drop developed in resister 8 applies a negative bias to grid it thereby blocking tube It. The blocking bias on grid 23 is simultaneously removed and tube ll becomes conductive whereby winding i8 is enersized to hold member 20 in spacing position. The plate current of tube ll flowing through resistor It produces a slight negative bias on grid 23 but not suillcient to block tube II. It will be understood of course that tubes I0 and H can be chosen of such characteristics that the current flowing through winding [1 for spacing is equal to the cu1rent flowing through winding 18 for marking.

However, preferably the tubes and associated circuit elements are proportioned so that a slightly greater current flows for marking than for spacing because during marking there is amechanical load on the member 20 while no load exists during spacing. For extremely fast action in switching from marking to spacing and vice versa. the capacity 8 should be very small. If it is desired to cause the device 8 to break down at a lower voltage than normally provided across resistor '1, a blessing voltage can be connected in series with device l at any convenient point in the circuit.

The manner of operation is along the following lines. Assuming that the device i is transmitting an 1800 c. p. s. marking signal, this signal is then amplified, and after suitable amplification it is passed through the attenuator pad 2 to adjust the signal level and thereupon the signal is passed through a frequency doubler 3, thus Droviding a 3600 c. p. a. signal of marking amplitude. This signal after passing the rectifier 5 is or insuiiicient voltage to cause breakdown of device 8, and therefore grid II is at substantially the same potential as cathode l2 and a marking current flows through winding I! to cause member 20 to operate barn to make a mark on the recording tape or web. In the case of a recorder oi the type where the drum I has a helically arranged knife edge 25 intersecting cooperation with bar 22, the drum 2| will beconstantly rotating in synchronlsm with the corresponding drum or scanning portion of device I while the recording paper is stationary except for line-feeding movementwhich may be controlled as explained in said Patent No. 1,719,392. The eiIect of rotation of the helical knife edge with respect to the bar 22 is, as is well-known in the facsimile art, to scan the'recording tape in successive transverse parallel lines. As each transverse line is thus scanned, the tape is fed in the direction of its length a distance corresponding to a line thickness so as to present the next line for scanning.

Upon the receipt of a spacing signal, the voltage developed across device 8 rises to the point where device 8 becomes conductive thus blocking tube and rendering tube' ll conductive and holding member 20 in spacing position.

.With the foregoing arrangement, I have found that the operation of member 20 is so sharp that a swing of as little as decibel above or below the critical keying potential is all that is required to switch from markihg to spacing and vice versa. If even sharper control is required, it may be had by removing condenser 6 if some vibration of the arm 20 can be tolerated when it is on the spacing side and if its mechanical inertia is made suiiicient to prevent it from swinging over to marking side with condenser 6 removed. Ihavefound it possible to obtain complete marking and spacing recordings on the web 26 with a signal voltage variation of less than one part in twenty live.

If condenser 6 is large, it is necessary that the voltage across the resistor 1 swing a little more than the difference between the striking and operating voltage characteristic of the gas tube 8. Such a large swing is not necessary if the filtering of the rectifier output is reduced or eliminated since the dip in the signal (lower side of the ripple) drops low enough to deionize the tube 8, 3600 times per second in the case illustrated. If the peak signal across 1 is just a trifle below the striking voltage of 8, the signal will be recorded as marking. If the peak signal across I is just a trifle above the striking voltage of 8,'the tube will start conducting at the peak and during that portion of the cycle which is above the operating portion of the tube characteristic. During this time the armature 20 is moved to spacing. By

properproportioning of mechanical inertia, travel of armature, and spring biasing, it is possible to prevent the arm 22 from reaching the marking position during the remaining portion of the cycle. It will be understood of course that various changes and modifications may be made in the particular embodiment disclosed without departingfrom the spirit and scope of the invention. Thus while a frequency doubler is shown, that may be dispensed with and the received frequency can be applied to the keying control circuit. In the case where channel L is a radio channel, a suitable detecting arrangement will be used at the receiving end to detect the original marking and spacing signals.

What I claim is:

1. In an electric signaling system, a signal device having a member to be selectively set in at least two signal-controlled positions corresponding to two diiierent signals, a pair of control windings associated with said -member each arranged to be energized in response to a corresponding one of said signals, a pair of grid-controlled vacuum tubes having their output circuits connected in divided relation to said windings, means responsive to one of said signals for biassing the control grid of one of said tubes substantially to plate current cutofi and to maintain it so biassed as long as said signal continues, and means responsive to the other of said signals to bias the control grid of said other tube to substantial plate current cutoil and to maintain it so biassed as longas said other signal continues, and means whereby the current inthe output circuit of one tube during the reception of one of said signals is greater than the current in the output circuit of the other tube during the reception of the other signal.

'2. A signal responsive arrangement for responding selectively to high and low amplitude signals comprising a signal device movable to two positions corresponding respectively to said high and low amplitudeslgnals, first and second gridcontrolled vacuum tubes adapted to be alternately biassed to plate current cutoif, means to impress both said signals directly only on the control grid of said first tube, the control grid of said second tube deriving its grid potential from the plate current of the first tube, a D. C. bias circuit for the grid of said first tube for normally biassing said first tube to pass substantial plate current so long as low amplitude signals are being received, and a device which responds only to the high amplitude signals, said device being connected to said D. C. bias circuit to change the control grid bias of said first tube to plate current cutoff, and thereby simultaneously to change the control grid bias of said second tube to allow plate current to pass.

3. In an electric signaling system, a signal device having a member to be set in at least two signal-controlled positions in response to two difierent signals, first and second grid-controlled tubes having their output circuits connected in divided relation to control the selective setting of said member, means responsive to one of said signals to bias the grid of the first tube to pass I substantial plate current and to maintain it so biased as long as said signal continues, means controlled by said plate current to bias the grid of the'second tube to substantial plate current cutoff and to maintain it so biased so long as said signal continues, and a gaseous conduction tube responsive to the other signal to bias the grid of the first tube to substantially plate current cutofi and to maintain it so biased so long as said other signal continues, whereby said other tube substantially immediately passes plate current in response to said other signal.

4. In an electric signaling system, a signal device having a member to be selectively set in at least two signal-controlled positions, first and second grid-controlled vacuum tubes having their output circuits connected in divided relation to control the selective setting of said member, and means to bias said tubes successively to substan-,

tial plate current cutofl' in response to successive signals of different characters, the biasing of each tube being'maintained so long as the corresponding signal is being received, the last-mentioned means including a gaseous discharge tube which applies a cutoff bias to the first tube only in response to one of said signal conditions, and also including a connection from the output circuit of the first tube to apply a cutoti bias to the second tube during the cessation of said one or the signal conditions.

5. In a telegraph signaling system, a telegraph signal device having a member to be selectively set to marking and spacing positions in accord,- ance with signal voltages of different relative amplitude but of the same polarity, first and 4 second grid-controlled vacuum tubes having their plate circuits connected to control respectively the selective setting of said member, means to apply both signals so that the conductivity of only the first tube is controlled directly by received marking and spacing signals, the conductivity of the second tube being controlled by the plate current of the first tube, and a two-element gaseous discharge tube responsive only to one of said signal voltages for controlling the application of a cutoi! grid bias to said first tube.

6. In a telegraph signaling system, first and second grid-controlled vacuum tubes, means normally connecting the grid of the first tube to its cathode whereby said first tube normally passes substantial plate current, means responsive to a telegraph signal to apply a plate current cutofi bias to the grid of said first tube including a twoelement gaseous discharge tube which becomes conductive only in response to said signal, and means responsive to the fiow of plate current in said first tube for biassing the second tube to plate current cutofl and for maintaining it so biased.

7. In a telegraph signaling system, means for producing marking and spacing signals of difierent amplitudes, first and second grid-controlled vacuum tubes, the second tube being normally biassed to substantial plate current cutoi! while the first tube is passing substantial plate current, a grid bias resistor tor the second tube, said resistor being connected in the plate-cathode circuit of the first tube, means for blocking the signal of lower amplitude from afiecting the bias on said second tube, and means responsive to the higher amplitude signal to render said first tube substantially non-conductive while simultane-- ously rendering the second tube conductive.

8. A telegraph system according to claim 7 in which there is abias resistor in the grid circuit of said first tube and said blocking means inveludes a gaseous discharge tube ior controlling 2,828,056 stantial plate current, a gaseous discharge tube in series with said resistance but normally noncondu'ctive for one signal condition, means responsive to another signal condition to render said gaseous tube conductive and thereby to apply a blocking bias through said resistance to said first tube, and means responsive to the application of said blocking bias to said first; tube to remove-a blocking bias from the second tube.

10. A telegraph keying system comprising means to receive signals or one ran ers amplitudes representing one signal condition and to receive signals of a difi'erent range oi amplitudes representing a difierent signal condition, a twoelement gaseous discharge tube to which said signals are applied, said gaseous discharge tube being non-conductive so long as one or said conditions continues and being conductive so long as the other of said signal conditions continues, a bias resistor responsive to current through said gaseous tube to develop a predetermined potential drop therein, a first grid-controlled vacuum tube which is normally biassed to pass substantial plate current and means connecting said resistor to the grid of said first grid-controlled vacuum tube to apply a plate current cutofi bias thereto when said gaseous tube becomes conductive, a second grid-controlled vacuum tube having a grid bias resistor through which the plate current or the first vacuum tube passes, said vacuum tubes and bias resistors being connected so that when said first tube passes substantial plate current the plate current of the other is substantially reduced.

11. A telegraph keying system comprising a first grid-controlled vacuum tube, a second gridcontrolled vacuum tube, a resistance in. the plate circuit r the first tube, said resistance also being connected in the grid circuit of the second tube to bias it'substantially to plate current cutoii! under control of the plate current or the first tube, means including a bias resistance connectpasses substantial plate current, and a source or signal voltage and a two-element gaseous discharge tube connected in series with thelastmentioned bias resistance, said gaseous discharge tube being conductive only in response to'telegraph signals oi a predetermined minimum amplitude.

AUSTIN G. COOLEY.

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