US1958212A - Modulated oscillator - Google Patents

Description

May 8, 1934. H, SHORE 1,958,212

MODULATOR OSCILLATOR Filed Jan. 30, 1932 OUTPUT INVENTOR HENRY SHORE ATTORNEY Patented May 8, 1934 UNITED STATES MODULATED OSCILLATOR Henry Shore, Elizabeth, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 30, 1932, Serial No. 589,857

2 Claims.

The present invention relates to a system for directly modulating constant frequency generated oscillations so as to produce changes in the amplitude of these oscillations in accordance with 5 a predetermined type of message transmission.

Fundamentally the invention is designated for use with radio communication systems, although it is to be understood that it is likewise applicable to wire or network transmission by making,

where necessary or desirable, a suitable adjustment of the frequency of the generated oscillations.

In connection with facsimile transmission systems and also with television transmission sys- 115 tems it is quite desirable to have the exploring 1 record subject are transferred to a photoelectric element, usually includes also an amplifier from the output of which signals are fed to a modulating device to which energy of a frequency corresponding to a source of oscillations is also connected. With most facsimile apparatus this entire assembly is mounted within a container and is positioned adjacent the record carrying drum and as the record is explored either the record is moved relative to the scanning head,

or the scanning head is moved relative to the record.

To provide a system which is considerably simplified it has been an object of this invention to utilize the dynatron type of oscillator and to modulate this oscillator directly from the output energy of a photo tube which has been subjected to light of varying intensities, which variations take place in accordance with the change between light and dark on successive elemental areas of a record subject of which the image is to be transmitted.

It has been found from experiments that a dynatron is extremely sensitive to small changes in grid potential and that these changes in grid potential tend to produce a considerable change in the output current from the tube when the dynatron is operating at a point substantially near the cut-off point. It is these characteristics of the dynatron which have been used herein to provide a system wherein the oscillator frequency may be maintained constant while varied directly as to its amplitude and thus make it possible to shift the amplitude of the generated oscillations in proportion to the intensity of the record subject for transmission. Inher- 6 0 ently, the dynatron is an extremely stable device and when the frequency of oscillation is once established there is substantially no tendency toward variation, due to changing load circuits or similar disturbing influences.

Therefore, as an object of the present invention, I have sought to provide ways and means by which the dynatron, as an oscillator, may be used at the same time as a modulating element for facsimile or picture record signals for transmission.

A further object of the invention is to simplify to a considerable extent the existing means for transmitting picture record signals.

Another object of the invention is to provide a modulated oscillator wherein the input signal may be of relatively small strength and still produce a relatively great change in output amplitude.

Still a further object of the invention is to so provide a modulating system which is simple in its construction and arrangement; a system which is inherently stable; a system which will follow faithfully all changes in intensity of input energy to produce a correspondingly modulated 35 output; and a system of modulation which can be arranged through the use of a correct combination of elements and circuit characteristics at present obtainable.

Other objects and advantages of the invention will, of course, become apparent and at once suggest themselves to those skilled in the art to which the invention is directed, by reading the following specification and claims in connection with the accompanying drawing, wherein 5 Figure 1 illustrates conventionally one form of circuit arrangement which the invention may assume, and Figure 2 indicates a series of curves plotting plate current against plate voltage for different grid voltages to illustrate the extent of response of the system to varying potentials supplied to the control grid.

Referring now to the drawing, the picture record for transmission, assuming the invention is to be applied to facsimile message transmission, is carried upon a record holder 1 which rotates in a direction shown by the arrow. The picture carried upon the record holder 1 is illuminated from a light source 3 whose light is directed by means of an optical system, conveni cathode of a photo tube 13.

tionally shown as a lens 5, to a point 7 from which the diffusely reflected light is focussed by means of a second optical system, conventionally shown as the lens 9, upon the light sensitive In order to limit the amount of light reaching the photo tube, a diaphragm or the equivalent 15, which may be adjustable in two directions, that is, vertically and horizontally, although illustrated only in the horizontal plane, has been provided between the record holder and the optical system 9.

As light falls upon the light sensitive cathode 11 of the photo tube 13 electrons are emitted from the light sensitive element and flow toward the anode or positive electrode 17 of the photo tube. The photo tube anode 17 is supplied with operating voltages from a source 19 and consequently with changes in the electron stream flowing within the tube, due to varying light intensities falling thereon, variable drops in voltage will be produced across a resistor 21 connected across the photo tube electrodes. The resistor 21 is also connected with the grid and filament electrodes 23 and 25 respectively of the multi-electrode tube 27 through a grid biasing source 29. The tube filament or cathode 25 is preferably grounded at 31. The remaining cold electrodes commonly known as the screen 33 and anode or plate 35 are connected with a source of potential conventionally shown as 37.

In order to provide dynatron action within the tube 27, that is, to provide a tube wherein secondary electron emission takes place, the screen electrode is connected to the most positive point or the potential source 37 and the plate or anode electrode is connected through a tuned circuit 39 comprising the usual inductance 41 and capacity 43, each of which may be variable where desired, to a point on the potential source 37 which is less positive than the point of connection of the screen electrode.

By tuning the oscillatory or resonant circuit 39 by adjusting the value of the capacity and inductance or both 43 and 41, the period of oscillation of the system may be changed. Due to the secondary electron emission occurring within the tube, in order to form 'an oscillating arrangement there need be no direct circuit coupling between the plate and screen electrodes 33 and 35 since these are strictly dependent upon the secondary emission. 7

If, now, a load is to be applied to the system it will be noted that the frequency characteristic will not vary but will remain substantially constant. This load which, in the suggested form of the invention, may include a thermionic tube 43, is coupled by way of a capacity coupling through the capacity 45 and the grid voltage supplied to'the tube 43 is taken across the potentiometer 47 by means of a variable tap conventionally shown as 49. Biasing potentials for the grid of the coupling 43 are shown as being supplied from the battery 51'.

In the plate circuit of the tube 43, which connects to the potential source 37, is a'primary winding 53 of .a transformer whose secondary 55 connects with output terminals 57 from which energy may be supplied to a radio transmitter or to a wire line for transmission purposes. It is, of course, to be understood that the coupling tube 43 is not an essential part of the invention and that any other form of load circuit may be connected with the capacity 45 or that the direct connection may be made from the capacity to a transmitting circuit. 7

In order to illustrate the characteristics of the dynatron, Figiu'e 2 shows various operating curves wherein the ordinate represents the plate current and the abscissa represents the supplied plate voltage, and assuming that modulation takes place within the tube by virtue of varying potentials supplied to the grid 23 various curves to show the change in current occurring between black and white on the picture record carried on the record carrier 1 have been illustrated.

In this connection the curve ESG=K1 may rep resent one extreme intensity on the picture record and the curve ESG=K3 may represent the opposite extreme, with the curve Ese=K2 representing the intermediate value such as medium gray. The dotted portion of the curve immediately below the zero value of plate current is intended to illustrate the operating region of the tube and the fluctuation in current appearing in the output is a function of the amplitude changes on the grid electrode for varying changes in light intensity on the picture record or subject as affecting the photo tube 13 so that the current may vary within the limits of the dotted line portion or the characteristic curves.

It is, of course, to be understood that the curves illustrated are not intended to be exact curves of the operation but are merely drawn from a family of curves obtainable in the region where dynatron action may take place with varying operating voltages supplied to the grid electrode 23, and, therefore, these curves and the curve illustrating the variation in current flow within the tube must be regarded as merely illustrative and not limiting.

While the invention has been shown in only a single one of its preferred forms, it is, of course, to be recognized that the disclosure is capable of many changes and modification without departing materially from its spirit and scope and I therefore believe myself to be entitled to make and use any and all of these modifications such as those which would suggest themselves to those skilled in the art to which this invention relates, provided, of course, that such changes and modifications fall fairly within the spirit and scope of the hereinafter appended claims.

Having now described my invention, what I claim and desire to secure by Letters Patent, is the following:

1. An analyzing system for converting picture records into modulated electrical energy signals which comprises means to produce fluctuating currents of values proportionate to the intensities of light and shadow on successive elemental areas of a record subject of which an image is to be produced, a multi-electrode vacuum tube having its input circuit connected with said light converting means, an oscillatory circuit connected with the plate electrode of said tube, means for applying operating potentials to the other electrodes of said tube so as to cause secondary electron emission within the tube and to produce an oscillatory output of a frequency determinable by the resonant period of said oscillatory circuit, and means provided by the connection of said light translating means with the input circuit of said tube for modulating the resulting output energy.

2. An analyzing system for converting picture records into modulated electrical energy signals which comprises means to produce fluctuating currents of values proportionate to the intensities of light and shadow on successive elemental areas of a recordsubject of which an image is to be the resonant period of said oscillatory circuit means provided by the connection of said light translating means with the input circuit of said tube for modulating the resulting output energy, and a load circuit capacitively coupled with said oscillator.

HENRY SHORE.

Images