US2453905A - Facsimile recorder control circuit - Google Patents

Description

Nov. 16, 1948. B. F. GRIB FACSIIILE RECORDER CONTROL CIRCUIT Filed March 15, 1946 1 MIR i to Lamp 8 or Valve 7 1 .2

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Bar/Is [Gr/b Z/lm I213 Aifarngy Patented Nov. 16, 1948 2,453,905 FACSIMILE RECORDER CONTROLgCIRCUIT Boris F. Grib, Brooklyn, N. Y., asllgnor to Times.

Facsimile Corporation poratlon of New York New York, N. Y a cor- Appllcation March 15, 194.8, Serial No. 854,559 6 Claims. (01. 178 6.7)

1 This invention relates to signal inverters for electrical communication equipment, particularly telefacsimile receivers and recorders. In telefacsimile systems, the signals transmitted are either directly or inversely proportional to the amount of light reflected from the copy in the usual form of transmitter, depending upon whether a negative or a positive transmissionis made. At the receiver, the signals may be employed to energize a recording lamp to reproduce the picture by exposing the photographic film or Paper at each elemental area in accordance with the amplitude of the transmitted signal. In this manner, a reproduction of the copy is obtained which is either a "positive" or a negative" depending upon the character of the signals transmitted from the transmitting station. However, by inverting the signals at the receiver so that the current through .the recorder lamp increases as the received signals decrease, a positive recording may be made from a negative transmission and vice versa.

In the transmission of news photographs, it is usually desirable'to record the picture on the light-sensitive film as a negative, since as many prints can be made from the negative as are required. However, this method requires development of the film and the printing of a positive before the plate is made. Occasionally when the time is short for meeting a publication deadline, it would be preferable to receive and record the news photodirectly as a positive on photographic paper. Accordingly it is an object of the invention to provide an improved signal-inverting recording apparatus adapted for this purpose, so that the operator at the receiving station can elect to record either positive or negative.

The tone values of the recorded picture are affected by several factors, some of which are not under the control of the receiving operator. They are dependent for example upon the'con'trast of the original copy and the characteristics of the photocell modulator and amplifier of the transmitter. as well as the characteristics of the recording lamp and of the recording sheet or film. Greatly improved results in the appearance of the received picture can often be obtained by expanding the tone range over the entire scale-of the re-- cording or a part thereof, and it is another object of the invention to provide a signal inverter which embodies improved means for expanding. the signals applied to the recording element or for changing the recording characteristics by expanding or contracting the tone range as desired.

Another object of the invention is to provide a simple and reliable signal inverter which will not change in adjustment or characteristics over a long period of time.

Other objects and advantages of the invention will appear from the following description of the preferred embodiments thereof shown in the accompanying drawings, wherein Fig. 1 is a schematic diagram of a preferred signal inverter; and

Fig. 2 is a similar view of a'modiflcation.

Referring to Fig. 1, there are shown in this figure the elements of a recording system which may be used to record pictures received from a remote facsimile transmitter of conventional type.

Transmitted signals in the form of an amplitudemodulated carrier are impressed upon the terminals ill of the recorder equipment. An amplifier I I is shown connected to the terminals i0 through a condenser l2, resistor l3 and gain control H for amplifying the received signals. The amplified signals are impressed upon a transformer it, in the embodiment of the invention shown by way of example, the secondary winding of the transformer I! being connected to a rectifier i6 and low-pass filter II. In this manner a direct-current signal is obtained in the output conductors I8 of the filter. which is proportional to the instantaneous amplitude of the facsimile signal carrier impressed upon the recorder. It will be understood that the amplifying and rectifying system shown forms no part of the present invention except as it is used in connection therewith.

The purpose of the low-pass filter I! is to smooth out the double-frequency ripple from the full-wave rectifier I6 and, in case of an unbalance in the rectifier l6 or in the windings of transformer ii, to filter out the component resulting fr m such unbalance which has .a frequency equal to the carrier frequency. The carrier signal impressed upon the terminals Ill varies during transmission between predetermined minimum and maximum values. It will be assumed for purposes of explanation that a negative transmission is bein received, 1. e. a train of signals in which the maximum signal corresponds to the whitest portion of the copy and the minimum signal to the black shading or tone.

In accordance with the invention, when the switch II is in the position shown, the potential across the output conductors i8 of the filter I7 is impressed upon a vacuum tube or space-discharge device 22 in such a manner as to vary the current through the recorder lamp 23, in series with said tube, directly in accordance with the amplitude of said potential. Thus the current through the lamp 2!. which is indicated on the associated level meter 24, varies directly with the amplitude of the transmitted carrier and the lamp may be employed to expose a photographic film (not shown) to produce a negative recording. The film may be supported upon a rotating drum which is kept in synchronism with the drum supporting the copy at the transmitting station in accordance with the usual practice. Obviously a light valve or other equivalent device may be substituted for the recorder lamp 23. However the use of a recorder lamp that emits a quantity of light which varies with the amount of current traversing the lamp, such as the Sylvania lamp #R-llSOB, is preferred.

As shown the vacuum tube 22, which may be an ordinary triode or tetrode. has the anode thereof connected directly to the source of space current and the cathode connected to ground through the recorder lamp, and also through a shunt path including a voltage regulator tube 28 and a resistor 21! as shown. The voltage regulator tube 26 is' a gas-filled diode having a constant voltage-drop over a wide current range and is preferably an RCA #991 tube, or equivalent. The voltage regulator tube, being in series with the cathode of the space-discharge tube 22, maintains the cathode bias of the tube substantially constant. It also provides a voltage reference point for use with controls 28 and 29.

With the switch 2i in the position shown, for negative recording, the positive conductor it is connected through the normally closed righthand contacts of the switch to the control else trode of the tube 22. The negative conductor i8 is connected through the normally closed lefthand contacts of switch 2i to the adjustable tap onthe potentiometer 28 connected in shunt relation to the voltage regulator tube 26. With this arrangement it will be seen that the grid-bias on the control-electrode of the tube 22 is equal to the rectified potential across the conductors it plus the drop of potential across the portion of the potentiometer 28 between the adjustable tap and the cathode of tube 22. The latter potential is constant because of the constant voltage= drop in the voltage regulator tube 25. Accordingly the potential of the control electrode of the tube 22 varies directly in accordance with the amplitude of the rectified output voltage of the filter ll or as a direct function thereof. Since current traversing the tube 22 and the regrid of the tube 22, thus reducing the recorder lamp current as the amplitude of the impressedcarrier from the transmitting station increases.

:1 the transmitted carrier. and the grid voltagecorder lamp 23 in series relation therewith increases as the transmitted carrier increases, negative recording is obtained. The adjustment of the potentiometer 2t enables the proper point on the characteristic curve of the tube 22 to be selected in order to obtain any desired expansion of the tone scale by causing the applied signals to saturate the tube 22 or to operate over a selected portion of the characteristic curve of said tube. After the potentiometer 28 has been properly adjusted, no readjustment is required for subsequent transmissions unless themaximum and minimum amplitudes of the transmitted carrier V y.

In order to invert the signals, for positive recording, the switch 2i is actuated to its alternate position in which the negative conductor iii is connected to the control electrode of the tube 22 and the positive conductor it is connected to the adjustable tap on a second potentiometer 29 in shunt relation to the voltage regulator tube 26. In this case, an increase in the potential across the output conductors iii of the filter ii increases the negative bias applied to the controlplate current characteristic of the tube employed. After proper adjustment of the potentiometer 28 or 29 has been made, no further adjustment during the transmission of successive pictures is ordinarily required.

The purpose of the voltage regulator tube 28 is to maintain the voltage drop across potentiometer 28 or 29 constant during variations of the applied signals. A shunt resistor 3| may be connected in parallel with the cathode-anode circuit of the tube 22 if desired, for the purpose of supplying current to the voltage regulator tube 26 when the current through the tube 22 drops to zero. The resistance of the resistor 3| may be of the order of A; or /2 megohm. In case the modulation frequencies are relatively high, bypass condensers 32 and 33 may be connected as shown to prevent slight fluctuations in the voltage across the regulator tube 26 resulting from the signal variations.

The signal inverter shown works equally well in the event of a positive transmission, but in that case a negative recording is effected when the switch 2| is actuated.

Fig. 2 shows a" modification of the invention which employs pulsating current for recording. In this modification, no filter is employed and the output of the rectifier l6, shunted by a resistor 35 to provide a direct-current return, is impressed through contacts of a switch 36 upon a control tube or space-discharge device 31. The switch 86 corresponds to the switch 2! of Fig. l, and when actuated, changes the recording from negative to positive (assuming that a negative transmission is impressed upon the recorder). The tube 31 may be a pentagrid converter. as shown. and is employed to key the carrier current of fixed amplitude supplied from an external source 38. The frequency of the carrier supplied from the source 38 is preferably twice or more than twice the frquency of the facsimile carrier received from the remote transmitter. In this modification, the recording lampor valve is connected through a condenser 39 to the anode of the converter tube 31. The cathode and control element circuits of the tube 31 are connected to the rectifier it in the same manner as in Fig. 1 except that no filter is shown. The cathode circuit includes a voltage regulator tube 4! corresponding to the tube 26 and shunt potentiometers 42 and 23 corresponding to the potentiometers 28 and 29 of Fig. 1. Similarly the series resistor M and bypass condensers 55 and 46 correspond to the elements 21 and 32 and 33 of Fig. 1.

In this modification, with the switch 36 in the position shown, the potential of the control element of the converter tube 31 varies directly in accordance with the amplitude of carrier signals received from the transmitter. Consequently the output current of the converter varies in a manner to effect negative recording. However if the switch 36 is actuated to its alternate position, the grid variations of the tube 3! are reversed and positive recording is effected. The potentiometers t2 and t3 permit the adjustment of the anode current of the tube 3'! to obtain proper recording level.

It will be evident that the invention provides a simple and effective arrangement whereby the receiving operator can record either positive or negative at will by simply throwing the switch operating the inverter circuit. In some cases the filter shown in Fig. 1 may be omitted or a filter employed in the arrangement shown in Fig. 2.

It is to be understood that the phrase recording lamp as used herein shall be construed as including a light valve or equivalent device capable of modulating a beamof light.

While I have shown two embodiments of the invention for the purpose of explaining the principles thereof, it is not limited to the apparatus or circuits shown by way of example. Variousmodifications in the apparatus and circuits described above will occur to those skilled in the art and may be made without departing from the scope of the invention as defined in the appended claims.

I claim:

1. A facsimile recorder comprising means for rectifying an amplitude-modulated carrier, a space-discharge device provided with an anode, a cathode and a control electrode, a voltage regulator tube connected in the cathode-anode circuit of said space-discharge device, said voltage regulator tube being of the type having substantially constant voltage drop across the terminals thereof, a connection from the negative terminal of the rectifying means to the control electrode of said space-discharge device, a connection from the positive terminal of said rectifying means to said voltage regulator tube whereby the rectified carrier signals are inverted in the space-discharge device and a recording device in circuit with said space-discharge device.

2. A facsimile recorder comprising means for rectifying an amplitude-modulated carrier, a space-discharge device provided with an anode, a cathode and a control electrode, a voltage regulator tube connected in series relation with the cathode-anode circuit of said space-discharge device, said voltage regulator tube being of the type having a substantially constant voltage drop across the terminals thereof, means for biasing the potential of the control electrode of said space-discharge device Jointly in accordance with the output potential of said rectifying means and with the voltage drop across said voltage regulator tube, said biasing means including a connection from said rectifying means to said voltage regulator tube for opposing the voltage drop in the voltage regulator tube by the rectified signal potential and thereby inverting the signals in the output circuit of saidspa'ce-discharge device with respect to the amplitude variations of said carrier, and recording means in the output circuit of said space-discharge device.

3. A facsimile recorder comprising means for rectifying an amplitude-modulated carrier, a space-discharge device provided with an anode, a cathode and a control electrodes. voltage regulator tube connected in the cathode-anode circuit of said space-discharge device, said voltage regulator tube being of the type having substantially constant voltage drop across the terminals thereof, a potentiometer in shunt relation to said voltage regulator tube, connections between said potentiometer and said space-discharge device for biasing the control electrode ofsaid space-discharge device jointly in accordance with the outacross said potentiometer'and a recording lamp connected to said space-discharge device whereby the current traversing said lamp is controlled by the amplitude of the rectified carrier and the adjustment of said potentiometer.

4. A facsimile recorder comprising means for rectifying an amplitude-modulated carrier, a space-discharge device provided with an anode, a cathode and a control electrode, input and output circuits for said space-discharge device, said input circuit including said control electrode, a recording lamp in the output circuit of said space-discharge device, a voltage regulator tube connected in series relation with the cathodeanode circuit of said space-discharge device, said voltage regulator tube being of the type having substantially constant voltage drop across the terminals thereof, a two-position switch and means including said switch for connecting the rectified carrier voltage to the control electrode of the space-discharge device either additively or in opposition to a portion of the potential across said voltage regulator tube to effect either positive or negative recording as desired.

5. A facsimile recorder comprising means for rectifying an amplitude-modulated carrier, a

space-discharge device provided with an anode, a cathode and a control electrode, a voltage regulator tube connected in series relation with the cathode-anode circuit of said space-discharge device, said voltage regulator tube being of the type having substantially constant voltage drop across the terminals thereof, two potentiometers in shunt relation with each other and with said voltage regulator tube, means including said rec tifying means for impressing rectifying signals of reversed polarity upon said control electrode and the adjustable tap of the respective potenput voltage of said rectifying means and the drop tiometers and a recordilng lamp connected to said space-discharge device.

6. A facsimile recorder comprising means for rectifying an amplitude-modulated carrier, a space-discharge device provided with an anode, a cathode, 'a control grid and an injector grid, a voltage, regulator tube connected to said spacedischarge device, said voltage regulator tube being of the type having substantially constant voltage drop across the terminals thereof, means for controlling the potential of said control grid jointly in accordance with the output of said rectifying means and the drop in said voltage regulator tube, the polarity of the connections of said rectifying means and voltage regulator tube to said control grid being such as to invert the signals, and a source of alternating current connected to said injector grid whereby the anode current of said space-discharge device comprises a modulated alternating current of the same frequency as said source and varying inversely to the variations of said rectified carrier.

BORIS F. GRIB.

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

UNITED STlk'IES PATENTS Number Name Date 2,185,139 Wurzburg Dec. 26, 1939 2,250,730 Stewart July 29, 1941 2,315,362 Wise Mar. 30, 1943 2,397,559 OBrien Apr. 2, 1946

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