US2464274A

US2464274A - Automatic positioning circuit for cathode-ray tubes

Info

Publication number: US2464274A
Application number: US662165A
Authority: US
Inventors: Todd William
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-04-15
Filing date: 1946-04-15
Publication date: 1949-03-15
Anticipated expiration: 1966-03-15

Description

arch l, 1949. w. TQDD I.

AUTOMATIC POSITIONING CIRCUIT FOR CATHODE-RAY TUBES Filed April 15, 1946 2 Sheets-Sheet l swEEP AND J36 SPREAD CONTROLLERS #35 24 so I $YNCHRONOUS VERTICAL AUTOMATIC DEFLECTION VERTICAL Q AMPLIFIER POSITIONING 38 i 47 .b- HORIZONTAL 4 4 f 46 48 DEFLECTION cIRcuIT (swE E P) 29 7 i0 RHEOSTAT gwue/IWM/ WILLIAM TOD D 2.22 FIG.2.

March 15, 1949. w. TQDD AUTOMATIC POSITIONING CIRCUIT OR CATHODE-RAY TUBES 2 Sheets-Sheet 2 Filed April 15, 1946 mmm 2::E:2:: ==L

d) O N gin um W5LLIAM. TODD -&Q J1

mmm N uE Patented Mar. 15, 1949 AUTOMATIC POSITIONING CIRCUIT FOR CATHODE-RAY TUBES (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 4 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

"This invention relates to circuits for automatic positioning of images on the screens of cathode ray tubes.

More particularly, the circuit comprises a network, the output of which is used for so biasing the vertical deflection plates of a cathode ray tube as to reproduce continuously on the oscilloscope screen the peaks of signals even if their amplitude varies so as to exceed the maximum deflection voltage necessary for producing maximum height images on the oscilloscope screen. Stated differently, sometimes the amplitudes of signals impressed on the vertical defiection plates in class A presentation of the signals, are too high for reproducing the entire signal on the oscilloscope screen. When this is the case,' the signal peaks will be completely ofi the oscilloscope screen and thus lost because the cathode ray beam will be deflected beyond the extreme boundaries of the screen. It is very Well known to provide a gain control for an oscilloscope to decrease the amplitudes for reproducing the entire signal within the boundaries of the screen. In the system disclosed by this invention such amplitude limiting would either impair or completely destroy the accuracy of the results, since the latter depends on the comparison of the height of adjacent images reproduced on the screen. Therefore, the conventional solution of this problem cannot be used. The invention discloses an automatic vertical positioning circuit which automatically depresses the position of the horizontal sweep line so that the unattenuated peaks of the signals would be brought onto the screen and their bottoms chopped off. The circuit of this type is of special value where the sought information is obtained by comparing the amplitudes or the height of visual images. When this is the case, even a moderately slow acting automatic volume control circuit in the receiver would not perform the desired function since such automatic volume control circuit would automatically reduce the amplitude of some of the signals and therefore diminish, or wipe off altogether, the difference in height of adjacent images with the concomitant reduction in accuracy of the desired information.

The automatic vertical positioning circuit has an additional application which relates to the automatic positioning of the sweep line on the transmitter.

oscilloscope screen so that it continuously coincides with the zero reading on the vertical scale of the screen. Because of the electrical memory of the intelligence channel using reactance coupling, this line has a. tendency to deviate from its intended zero position when there is a change in amplitude or wave shape of impressed signals. When keeping of this line on the zero position is important for measuring the amplitudes of the reproduced images, it becomes desirable to have some automatic means which would counteract the shifting of this line to any other position.

The invention will be described in connection with a meteorological radio direction finder designed to operate as part of a system to secure the direction. and speed of wind. The obtained information is of value for meteorological purposes. While the invention is described in connection with this specific radio system, it'is to be understood that it has wider application as will become more apparent from the description of the invention.

The meteorological radio direction finders may be considered as a special application of the radar systems to meteorological use. The only component that is lacking is the transmitting channel since the meteorological radio direction finders receive their signals from a radiosonde or portable radio transmitter carried by a balloon. Therefore, in this case, the signal comes from the object itself, and there is no necessity for transmitting an exploratory pulse for obtaining an echo. As a consequence there is no transmitting channel and no electrical echoes in the systems of this type. However, the receiver and the antenna array otherwise are essentially identical to those used in the radar systems. The antenna is a double tracking or split pattern tracking antenna, or, more specifically, the quadruple tracking antenna, two double tracking horizontally shifted lobes being used for determining azimuth, and two identical but vertically shifted lobes for determining elevations. This makes it possible to point the axis, perpendicular to the center of the plane of the antenna array directly at the source of signals for determining the azimuth and elevation of the The range is computed from pressure data taken during the flight of the balloon and the function. of the elevation angle to'the balloon.

Before the use of radio tracking methods, almost all winds-aloft observations were made by two methods. The first method, which is the optical method, used a right angle telescope to observe, at one minute intervals, the azimuth and elevation angles of a balloon during free flight. These angles, together with an assumed rate of ascent, were used to calculate the position of the balloon from minute to minute. In this way the direction and speed of the wind at various altitudes is computed; however, no other meteorological information is possible. The second method augments the optical method by tracking a balloon borne radiosonde transmitter with the theodolite, the radio equipment being used only to obtain information on humidity, pressure and temperature.

The principal disadvantage of the optical methods is the limitation caused by visibility.

Another disadvantage of. the first method is.

ascent rate is determined from pressure data taken during the flight of the balloon. The latter data is usually obtained through detection of a superimposed carrier modulation.

As mentioned previously, the azimuth and elevation angles are determined by means of split pattern tracking, the main lobe axis of the four lobes pointing directly at the balloon transmitter when the heights of four images reproduced on the oscilloscope screen are all equal. With the advent of the radio tracking method, it was soon discovered that tracking of the balloon is quite difficult at the higher angles of elevation because of very pronounced variations in the intensity of the signal reaching the receiver. This erratic fluctuation in the intensity of the signal is due to continuous swinging and erratic oscillations of the transmitting wire-antenna carried by the balloon radiosonde when the balloon is tossed about by varying air currents and sudden gusts of wind with the concomitant rotation of the transmitter about a vertical axis when the transmitter has a slightskew pattern the two phenomena combining to produce marked amplitude variations. Since proper'orientation of the receiving antenna array is possible only when the position of the received signals remains fairly stationary on the oscilloscope screen or, in an extreme case, there is no total disappearance of the peaks from the screen, it becomes necessary to provide some means, i. e.. the automatic vertical positioning circuit, for keeping the peaks of the signals continuously on screen even when the transmitter and its antenna are caused to rotate and oscillate by varying air currents.

It is therefore an object of this invention to provide an automatic vertical positioning circuit for the oscilloscope of meteorological radio direction finders, this circuit automatically keeping the peaks of the images on the oscilloscope screen even when the signals reaching the radio direction finder experience violent intensity variations.

An additional object of this invention is to provide an automatic vertical positioning circuit for a cathode ray oscilloscope which makes it possible to reproduce the peaks of images of signals on the oscilloscope screen even when the amplitudes of these signals are such as to produce, without the above-mentioned circuit, beam deflections beyond the boundaries of the screen.

Still another object of this invention is to provide an automatic vertical positioning circuit for electrically counteracting the vertical deflection of a cathode-ray beam in a cathode-ray oscilloscope in such a manner as to depress the bases of large amplitude signals when they reach such large values as to produce, without such counteracting, the beam deflections beyond the boundaries of the oscilloscope screen.

An additional object of this invention is to provide an automatic vertical positioning circuit whch is capable of keeping the position of the sweep line in class A presentation of images on the oscilloscope screen at a predetermined position on the screen in spite of large variations in the amplitude and duration of .intelligence signals, which, because of the inherent electrical memory of the intelligence channel, tend to shift the position of the sweep line of! its normal zero position.

These and other features of the invention will be more clearly understood from the following detailed description and the accompanying drawings in which:

Figure 1 is a block diagram of the radio direction finder;

Figure 2 is a schematic diagram of an automatic vertical positioning circuit;

Figure 3 illustrates images appearing on an oscilloscope screen in the systems of this type;

Figure 4 illustrates an approximate shape of the antenna lobes of the radio direction finder;

Figure 5 is a graphic illustration of the action of the automatic vertical positioning circuit;

Figure 6 illustrates modified connections of the automatic vertical positioning circuit to the intelligence channel. 7

Referring to Fig. 1, it discloses a block diagram of a portable meteorological radio direction flndei' with a balloon transmitter i0 illustrated to the left of the finder. The radiosonde consists of a hydrogen-filled balloon [2 which carries transmitter Ill. The latter is provided with an antenna ll, which is a half-wave-length wire suspended from the transmitter. Transmitter l0 transmits a U. H. F.-C. W. signal illustrated by an arrow it, which is intercepted by an antenna It provided with four phased lobe positions W, X, Y, and Z. A cigar-shaped lobe pattern is obtained for each lobe position. This system is known as doubletracking or split-pattern tracking; the principle of such tracking is illustrated in Fig. 4 for one component of direction; the same principle is used for both azimuth and elevation tracking. The lobing is controlled by motor 42 through shaft 35. The array is arranged so it can be rotated about both vertical and horizontal axes, which enables an operator to perform the actual tracking of the transmitter.

The directivity pattern has a directional lobe which points in the general direction of the transmitter. However, the lobe departs a few degrees (up-down or right-left) from a line drawn perpendicular to the center of the antenna plane, as illustrated in Fig. 4. The effect produced on the antenna system of this kind by the incoming C. W. signal is as follows: If a wave front arrives along line AO it will induce maximum signal voltage when the right-hand antenna lobe is effective; however, signals arriving at angles other than A-O will produce weaker signals. For example, a wave front arriving along line 3-0 would produce a signal proportional to the lengthcassava of line C-O. The same situation would exist it the transmitter position and antenna lobes were reversed. With a wave front arriving along line B- and the left antenna lobe efiective, a maximum signal voltage would be induced. This is represented by line B-O. With the left antenna lobe efiective and the wave front arriving along line A-O, the signal would be much weaker. If a wave front arrives along line E-O and the two antenna lobes are switched, the signal amplitudes will be equal.. This is represented by the lobes intersecting at point'E and equal length of line E-O for both lobes. The main lobes have been exaggerated for purposes of explanation and are not represented as the actual patterns. The output due to each lobe from theantenna will be the same when the antenna array is perpendicular to the plane of the wave front in both azimuth and elevation.

Shaft 35 is connected also to sweep and spread controllers 36 which control a sweep circuit 38. The output of sweep circuit 38 is connected to the horizontal deflection plates 40 and 4| of tube 21. Asynchronous motor 42 is used for controls ling the lobing of antenna l8 and sweep controllers 36. avoid possible undulations in the traces on the oscilloscope due to slight differences between the power line frequency and the frequencies generated by rotation of the switch. The sweep controllers initiate a saw-tooth wave sweep corresponding to each two successive lobe positions of the antenna, alternate sweeps being displaced by any known means for purpose of spread control. The result is that every second horizontal sweep of the oscilloscope spot on the screen begins from a point slightly to the right of the preceding sweep excursion which produces the lateral displacement of images illustrated in Fig. 3. Each sweep traverses the oscilloscope screen while the antenna passes through two lobe positions producing two modulation pulses. pip 300 and one azimuth pip 302 are thus presented for each sweep of the electron beam. The following sweep excursion traces the next elevation pip 304 and azimuth pip 306 produced by amplified, demodulated, and finally impressed as a video pulse on a vertical deflection amplifier 24. This permits the receiver output to be examined on each lobe position of the antenna.

The output of the receiver, as presented on oscilloscope, thus consists of a continuous series of pulses such as those illustrated in Fig. 3. These are impressed on the vertical deflection amplifier which uses a twin triode tube connected in a phase inverting circuit. Output signals from the amplifier 24 are applied through blocking

capacitors

44 and 46 and conductors 22| and 29 to the

vertical deflection plates

25 and 26 respec. tively of the oscilloscope. Since the signals impressed on

condensers

44 and 46 are in phase opposition, the A. C. voltage difference between

deflection plates

25 and 26 is doubled, providing greater deflection sensitivity.

One of the output circuits of the vertical deflection amplifier 24 is also connected through a coupling condenser 41 and a conductor 32 to the automatic vertical positioning circuit. This cir- Motor 42 is a synchronous motor to One elevation cuit automatically controls the position or the traces on the oscilloscope screen through a conductor 48, which connects its output to conductor 29. The automatic vertical positionin rcuit automatically biases the deflection plates so that the position of the tops of the four

pulses

300, 302, 304 and 306, will tend to remain on the screen even when large amplitude changes take place in the video signals impressed on the

deflection plates

25 and 26. If receiver saturation is reached. the amplitudes of all signals may temporarily become equal should the orientation of the antenna array be such as to produce receiver saturation on all four lobes. This keeping of the tops of the four pulses on the oscilloscope screen by the automatic vertical positioning circuit is accomplished by shifting the signal base line of the oscilloscope in synchronism with variations in average signal strength as illustrated by an approximate oscillogram in Fig. 5. Since, as mentioned previously, the operator judges whether the antenna points directly at the transmitter l0 by comparing the amplitudes of the images illustrated in Fig. 3, it is obvious that shifting of the signal base line 400 on the oscilloscope in synchronism with the variations in average signal strength will have no effect on the difference in the amplitude of the respective elevation and. azimuth signals. Consequently, the sensitivity of the antenna array setting is not impaired in any way by the automatic vertical positioning circuit but is enhanced by presenting the difference in heights upon a magnified scale. The schematic diagram of this circuit is illustrated in Fig. 2.

Referring now to Fig. 2, the schematic diagram begins with a twin triode 24, which corresponds to the vertical deflection amplifier 24 of Fig. 1;

it is connected to the output of receiver 22. In-

positive input signals 20! from the voltage amplifying stages of receiver 22 are appliedthrough blocking capacitor 200 to a vertical gain control resistor 202 and then to the grid of the first triode. Negative signals 203 of greater amplitude appear across plate load resistor 204, and are then applied through blocking capacitor 206 to a voltage dividing network consisting of

resistors

208 and 2 l0. Thus a portion of the output signal from the first triode section is applied to the second triode grid, and appears amplified as a positive signal 2 across a plate resistor 212. The voltages appearing across resistors 2l2 and 204 are applied through the blocking

capacitors

44 and 46 to the

vertical plates

25 and 26 respectively of the cathode ray tube 21 where they produce the vertical deflections illustrated in Fig. 3. Thenegative signal from the first stage of am plifier 24 is also applied through condenser 41 to the cathode 2; of the first section of triode 30, which is connected as a half-wave rectifier, the cathode being grounded through a resistance 2 l4, and the tied together grid and plate grounded through a resistance 2l8. When cathode 2H} is driven negative by the signals impressed upon it by condenser 41, the first half section of triode 30 draws current through grid resistor 2l8.- The latter is shunted with an integrating condenser 226, the time constant of resistance-condenser combination being adjusted so as to .provide proper average grid voltage for the second stage of triode 30. The voltage across this network is amplified by the second triode. As the signal amplitude increases, the plate current through plate load resistor 220 decreases, causing an increase in voltage across

resistors

222 and 224,

which are connected to the vertical plate 28 of the cathode ray tube over conductor 28. The voltage thus developed across

resistances

222 and 224 opposes the shifting in the tops of the traces caused by the increase in the average amplitude of the signal, and it is this voltage that acts as an electrical means for automatically keeping the tops of the four pulses on the screen even when the amplitude of the signals would otherwise deflect the oscilloscope beam beyond the boundaries of the screen.

The time constant of the automatic vertical positioning circuit is the sum of the'normal time constant of the output circuit of the vertical amplifier and the R.-C. circuit consisting of

resistancees

220, 222, 224 and condenser 228. The amplitude of the bias voltage applied to the deflection circuit is adjustable by rheostat 222, while its time constant is adjustable primarily by varying the capacitance of condenser 228. In general, the time constants of the entire oscilloscope deflection circuit are adjusted to conform to the repetition rate of the video intelligence and the period of the amplitude variations experienced in the course of average radio sondings.

This action of the automatic vertical positioning circuit is illustrated in Fig. where the negative signals 203 appearing in the output of the first stage of 24 are combined with the potential variations 500 appearing across resistor 224 due to the action of the automatic vertical positioning circuit. It is to be noted that in Fig. 5 the amplitude of voltage wave 500 increases with the increase in the amplitude of the signals 203, and vice-versa. The net result isthat the peaks of the signals 203 remain visible. The amplitude of the signals actually impressed on the deflection plates is illustrated by the difference in the amplitudes of the signal 203 and wave 500, this difierence being illustrated at 502. In practice the parameters of the automatic vertical positioning circuit should be adjusted also so as to hold the images on the screen in spite of the push-pull action of the signals 203 as well as 2| I.

Since the signals 2! I are impressed directly on the deflection plate 25 without any control by the automatic vertical positioning circuit, the entire amplitude control must be accomplished by controlling the push-pull action only through one side or end of this double-ended circuit.

Thus the function performed by the automatic vertical positioning circuit is to enable the operator to see a greater amplitude difierence in terms of actual greater linear distances between the peaks of the images appearing on the oscilloscope screen. This is accomplished by impressing the deflection voltages or. the deflection plates of the oscilloscope of such magnitude that if it were not for the automatic vertical positioning circuit, the peaks of the signals would be completely oil the oscilloscope screen. The automatic vertical positioning circuit however depresses the base line in such a manner that, in spite of the fact that the voltages impressed by the receiver on the oscilloscope are too high for their reproduction on the screen, the automatic vertical positioning circuit varies the position of the base line so that the intelligence contained in the diflerence in the amplitudes is reproduced on the screen without any attenuation. In a sense therefore the automatic vertical positioning circuit acts as a diiferential amplifier which amplifies very greatly the differences in the amplitudes of the different phase-position signals. Hence the reason for. making the statement that the automatic vertical positioning circuit enhances the accuracy of the Rawin" system by presenting the diiierence in heights of the intercepted signals upon a magnifled scale.

The disclosed automatic vertical positioning circuit has an additional application in the oscillographic art which is illustrated in Fig. 6. In Fig. 6 the automatic vertical positioning circuit is connected to upper conductor 22l rather than conductor 28, as it is the case in Fig. 2. the remaining connections of Fig. 6 being the same as those illustrated in Fig. 2. The function performed by the automatic vertical positioning circuit with this type of connection is as follows: it is quite customary, with type A presentation of images on the oscilloscope screen, to use a screen which has a transparent calibrated scale mounted on the face of the tube. This screen is then used for measuring the height or amplitude of the images appearing on the screen. The scale usually has a zero line corresponding to the zero reading of the vertical deflection, and the biasing of the vertical deflection plates is adjusted by means of a potentiometer, such as a potentiometer 225 in Fig. 2, so that the position of sweep coincides with the zero reading on the Y scale. The parameters of the intelligence channel in the oscilloscope circuit, which corresponds to the channel including a double triode 24, condensers- 44, 46,

vertical deflection plates

25, 26, etc., can not have zero time constant since it is obvious that any physical condenser-resistance combinations will have some finite time constants. Stated difierently, any electrical circuit of this type has a certain electrical memory, and as the amplitudeand duration of the signals impressed on the intelligence channel is varied, the eflect of this memory upon the position of the sweep line on the oscilloscope screen is that it wanders from its zero position in response to these variations. The deflection of the sweep line {rom zero position is always in the opposite direction to the direotion of increase in amplitude of the signals, 1. e., in the negative direction on the Y-scale when the amplitude or the duration of the signals are on the increase circuit. Therefore the polarity of the correction must be additive with respect to the intelligence signal. Potentiometer 225, as a rule, is an adjustable potentiometer and it is used for restoring the position of the sweep line to its zero position by manually adjusting the position of the potentiometer arm. Such method of adjusting the position of the zero line on the oscilloscope screen is quite tedious, and in some instances it is rather difllcult to follow the wanderings of the position of the sweep line with respect to the Y-axis with sufllcient degree of accuracy. When this is the case, all readings become inaccurate. It is possible to apply the disclosed automatic vertical positioning circuit for automatic positioning of the sweep line so that it remains continuously at zero on the Y-axis in spite of the memory eflect in the intelligence channel. For accomplishing this purpose, the output of the automatic vertical positioning circuit is connected to conductor 22l which impresses an automatically adjusted, variable positive biasing on the "deflection plate 25, which counteracts the varying negative memory effect. The parameters of the automatic vertical positioning circuit are in this case adjusted in the same manner as before by adjusting the setting of rheostat 222 and condenser 228. The selected values would obviously be such asto counterbalance the memory eflect oi the intelligence channel. It is to be noted that 9 the automatic vertical positioning circuit of the disclosed type is applicable to intelligence signals whose amplitude variation has a period at least as long as several cycles of intelligence signal; otherwise, distortion of the intelligence signal presentation will result.

In describing the automatic vertical positioning circuit in connection with its appl cation to the meteorological system and in illustrating its action in Fig. 5, it has been stated that the parameters of this circuit may be so adjusted that there may be a slight variation in the amplitude of the signals and in the amplitude of the images reproduced on the oscilloscope screen. The mode of operation of the automatic vertical positioning circuit however may be so adjusted it matches any given variation in the modulation of the signal, the only limitation being that the time constant be chosen to permit the desired correcting voltage to operate on the cathode ray tube.

- The amplification of the automatic vertical positioning circuit may then be adjusted to produce constant amplitude image on the screen of the oscilloscope. In the latter case the one extremity of all signals, i. e., the peaks, remain fixed on the oscilloscope screen.

While the invention has been described with reference to several particular embodiments, it will be understood that various modifications of the apparatus shown may be made within the scope of the following claims.

I claim:

1. A cathode ray oscilloscope circuit comprising, a cathode ray tube having a screen and means for deflecting the electron beam within said tube, a source of signals connected to said means, said source impressing signals of varying-= amplitude on said means, a vertical positioning to confine the peaks of said signals to said screen without affecting the difierences in the amplitudes of said signals.

3. A cathode ray oscilloscope comprising a cathode ray tube having a screen and means for deflecting the electron beam within said tube for presentation of images on said screen, an intelligence channel connected to said means, said channel impressing signal pulses of varying energy content on said means, said varying energy content capable of producing a shift in the position of a sweep base-line on said screen because of the electrical memory of said intelligence channel, and a positioning circuit connected with its input to said channel and with its output to said means, said circuit producing a voltage proportional to the mean value of said varying energy content and applying said voltage to said means to counteract said shift thereby maintaining the position of said base-line fixed on said screen during the variations in the energy content of said signal pulses.

4. A cathode ray oscilloscope comprising, a cathode ray tube having a screen, a Cartesian coordinates scale on said screen, opposing means in quadrature for deflecting the electron beam within said tube along said coordinates, a sawtooth oscillator connected to one pair of opposing means for deflecting said beam along X-axis for producing a base line, an intelligence channel connected to the other pair of opposing means for deflecting said beam along Y-axis, said channel impressing signals of varying energy on said circuit responsive to the strength of said signals having beam-deflecting means, said means being.

connected to said receiver for presentation of said pulses on the screen of said oscilloscope, and a vertical positioning circuit connected to said receiver and to said deflecting means, said circuit responsive to the mean amplitude of said video pulses to vary the mean voltage of said deflecting means to counteract the deflections of the cathode ray tube when the amplitudes of said signals exceed full-screen deflection voltage of said tube means, said varying energy capable of producing a shift along the Y-axis in the position of said base-line with respect to said scale because of the electrical memory of said intelligence channel and a corresponding shift of images on said screen, a rectifier connected to said channel and having an integrating network in its output, an amplifier connected to said network and having an integrating network of its own in its output circuit, and a connection between the latter network and said means, said latter network producing a voltage that is applied to said means to maintain said base-line in a constant position with respect to said scale.

I WILLIAM TODD.

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

UNITED STATES PATENTS Number Name Date 1,951,036 Parker Mar. 13, 1934 2,237,651 Bruche Apr. 8, 1941 2,312,761 Hershberger Mar. 2, 1943 2,358,545 Wendt Sept. 19, 1944 2,405,930 Goldberg et al Aug. 13, 1946 2,414,537 Lakatos Jan. 21, 1947