US2490045A - Blanking system for locked sweeps in panoramic systems - Google Patents

Description

Dec. 6, 1949 B. R, GARDNER l-:T AL 2,490,045

BLANKING SYSTEM FOR LOCKED SWEEPS IN PANORAMIC SYSTEMS 3 Sheets-Sheet 1 Filed June 11, 1948 Dec. 6, 1949 E. R. GARDNER ET AL 2,490,045

BLANKIIG SYSTEM FOR LOCKED SWEEPS IN FANORAIVIIC SYSTEMS Filed June 11, 1948 3 Sheets-Sheet 2 WL@ www Dec. 6, 1949 B. R. GARDNER ET AL 2,490,045

BLANKING SYSTEM FOR LCKED SWEEPS IN PANORAMIC SYSTEMS Filed June ll, 1948 3 Shee'as--Sheecl 3 VWM' Patented Dec. 6, 1949 BLANKING SYSTEM FOR LOCKED SWEEPS IN PANORAMIC SYSTEMS Benjamin R. Gardner, Dayton, Ohio, Everett T. Wilbur, Ypsilanti, Mich., and Lee W. Aukerman,

Peru, Ind.

Application June 11, 1948, Serial No. 32,518

(Cl. Z50-20) 4 Claims.

(Granted under the act of March amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to us of any royalty thereon.

This invention relates to cathode-ray tube circuits and particularly to a means for producing correlated sweep and unblanking voltages for a cathode-ray tube.

It is the object of the invention to provide an unblanking pulse for a cathode-ray tube that is coordinated with the sweep voltage and the leading and trailing edges of which may be precisely adjusted with respect to time. This is accomplished in accordance with the invention by applying to the beam deflecting means of the cathode-ray tube a sweep voltage of greater duration than required and also applying this sweep voltage to a branch circuit having adjustable means for limiting the maximum and minimum amplitudes thereof and means for differentiating the resulting limited sweep voltage to produce the unblanking pulse. The times of occurrence of the leading and trailing edges of this pulse may be precisely controlled by adjusting the maximum and minimum amplitudes of the limited sweep voltage.

The circuit is particularly useful in connection with panoramic receivers in which case the cathode-ray tube sweep voltage is locked to the means for sweeping the receiver tuning over a band of frequencies. By adjusting the leading and trailing edges of the unblanking pulse as provided for in the invention the beam of the cathode-ray tube may be unblanked precisely for that period of time during which the receiver tuning is sweeping over the frequency band.

A specic embodiment of the invention is shown in connection with the accompanying drawings in which Fig. 1 shows a panoramic receiver embodying the invention,

Figs. 2, 3, 4, and 6 show structural features of variable condensers used in Fig. 1,

Fig. '7 is a series of graphs explaining the operation of Fig. l, and

Figs. 8 and 9 are views of indications produced on the cathode-ray tube screen in Fig. 1.

Referring to Fig. 1, the invention is shown embodied in a panoramic receiver. The particular receiver shown has two radio frequency sections, one tunable over the normal band of receivable frequencies and the other tunable over a band of frequencies having an image relationship to the normal band, so as to double the usable frequency range of the receiver. The first or normal radio frequency section comprises antenna I, an untuned radio frequency isolating stage 2, a resonant circuit 3 and a first detector 4. The resonant circuit 3 is composed of inductance 5, adjustable trimmer condenser 6 and a rotatable variable condenser 'I that serves to tune the circuit over the normal frequency band which in this case is 'I0-155 megacycles. The second or image radio frequency section comprises antenna 3, untuned radio frequency isolating stage 9, resonant circuit I0 and first detector II. This section is similar to the flrst section except that the rotating condenser I2 of circuit IG is designed to tune the circuit over the image band which in this case is 15G-235 megacycles. The local oscillator I3 has its frequency controlled by resonant circuit I4 the resonant frequency Aof which is made to vary by rotating condenser I5 over a frequency band midway between the normal and image frequency bands, or in this case, -195 megacycles. The condensers 1, I2 and I5 are caused to rotate together by a common shaft I6 as in the usual superheterodyne receiver. The output of oscillator I3` is applied to the two first detectors 4 and II by means of connection I'I where it beats with the frequencies of the normal and image sections to produce the intermediate frequency of 50 megacycles. Provision is made for applying a positive voltage through resistors I8 and I9 to first detectors 4 and II respectively. This voltage is applied to the cathodes of the detector tubes and is sufficient in magnitude to bias these tubes beyond the cut-off point and to thereby render them inoperative. A switch 20 is provided for grounding the low potential ends of either or both of resistors I8 and I9 so as to remove the high potential from the cathodes of either or both of detectors 4 and II thereby rendering them operative. Thus when switch 20 is in its upper position detector 4 is operative and detector II is inoperative so that signals in the normal band of frequencies are received, whereas in the lower position conditions are reversed and frequencies in the image band are received, and in the central position both detectors are operative and signals in both bands may be received.

The output of first detectors 4 and II is amplified by intermediate frequency amplifier 2| and applied to the second detector which comprises as resonant circuit tuned to the intermediate frequency and made up of inductance 22 and condenser 23, the diode section of tube 24, load resistor 25 and high frequency by-pass condenser 26. The resulting audio and direct voltages developed across resistor 25 are applied to the grid of the triode section of tube 24 which has an additional high frequency filter 26 in its output circuit. The audio components at the output of filter 25 are applied through condenser 21 and potential divider 28 to the grid of power amplifier 29 and thence through transformer 30 and volume control 3| to phone jack 32. The direct and audio components in the output of filter 26 are applied by means of connection 3 3 to the vertical deflecting plate 34 of cathode-ray tube 35. The other vertical deflecting plate 36 of this tube is connected to a point of positive potential on the potential divider made up of resistors V31 and 38. Resistor 38 is variable so that the potential of plate 36 maybe .varied foradjusting the rest position of the beam along the vertical axis.

Referring again to .condensers 1, I2 and I5, Ythese condensers are of the type having an isolated rotor, as shown in Fig. 2, and are actually :two equally varying condensers connected in series. However the exact design of these three condensers is not a `part of Athe invention and `any suitable type performing the same function inay be used. Condenser I has its plates shaped lasshown in Fig. 3 which gives a linear relation- Iship between capacity and angle of rotation. The plates are so designed that 90 of rotation changes .the capacity from its minimum to its maximum value and varies the resonant frequency of cirrcuit 3 from its highest value, 155 megacycles, to Lits lowest value, '10 megacycles. Likewise, for Vthe same 90 of rotation, condenser I5 changes the resonant frequency of Vcircuit I4 from its l.highest to its lowest value, namely 195 to 110 n iegacycles, and condenser VI 2 changes the resonant frequency of circuit I from its highest toits lowest value, namely 235' to 150 megacycles. `The general configurations of the plates of *condensers I5 and I2 are shown in Figs.v 4 vand 5 respectively and are such that the resonant frequency of circuit I4 is always 50 megacycles above that of circuit 3, and the resonant frequency of circuit I0 is always 50 megacycles above that ,of circuit I4. The design of condensers to produce tracking between the local oscillator and radio frequency circuits of a superheterodyne receiver is well known in the art and therefore discussion in greater detail than that given above is unnecessary in this disclosure.

When circuits 3 and I0 are-tuned over the band of receivable frequencies by condensers 'I and I2 any signals present in these ba-nds will cause positive voltages to be applied to vertical deflecting plate 34 of cathode-ray tube 35 as vthe circuits .are tuned through these frequencies. This voltage is made up of the rectied carrier with the carrier modulation, if any, superimposed therein, and acts to cause a vertical deflection .of the electron beam. In order to spread the frequency band along the horizontal axis of the Vcathoderay tube screen a sweep voltage synchronized with condensers 'I and I2 is required. The ciruit for generatingthe required sweepvoltage has its origin in oscillator 40 which generates an alternating voltage of relatively high frequency, A200 kilocycles per second being'the value used in this case. The output of this oscillator -is applied to a potential divider made up of rotating condenser 4I connected in series with impedance Z. The condenser 4I is also of the type shown in Fig. 2 `and is rotated along with condensers 1, I2 and I5 by shaft I5. This shaft is driven by motor 42 at a constant speed of 1200 revolutions per minute, although the speed is not critical.

The configuration of the plates in condenser 4I is shown in Fig. 6. As will be seen the rotor plates extend for and the stator plates for as compared with 90 for both rotor and stator plates in condensers l, I5 and I2 shown in Figs. 3, 4 and 5 respectively. Each of the condensers in Figs. 3, 4, 5 and 6 has a reference line drawn `through the angular center of the rotor plates. The Afour condensers are mounted on shaft IS so that the reference lines in Figs. 3, 4 and 5 occupy the same angular position on the shaft and so that the reference line in Fig. 6 lags the other reference lines by 45 as shown in these gures by the angle b referred to a vertical axis through the center of the shaft. The zero positions of the reference lines are indicated in each of the figures. These positions are determined by the positions of the reference lines when the leading edges of the' rotor plates of condenser 4I, shown in Fig'. 6, coincide with the vertical axis through the center of the shaft I6. In Figs. 3, 4, 5 and 6 the condensers are shown as having been rotated clockwise from the zero positions through an angle a.

Graphs (1) and 2) of Fig. 7 show the variation of capacity in condensers 'lV and 4I for values of angle a from 0 to 360. It will be noted that the capacity of condenser 4I begins to increase from its minimum value 10 Ybefore condenser 'I and reaches its lmaximum value 10 later than condenser l, the reason for which will be apparent later. Graph (3) shows ythe 200 kilocycle voltage developed across impedance Z. This voltage may be made to vary linearly with angle A by properly selecting -the value of Z or by so shaping the plates of condenser 4I Yas to achieve this result. The yvoltage shown in graph (3) is applied to a full Wave rectier comprising diodes 43 and 44 and associated load resistors 45 and 46 `so that a direct .voltage varying as thenegative envelope of the 200 kilocycle voltage is developed across resistor 4.5 and a direct voltage varying as the positive envelope is developed across resistor 46. These two voltages are of equal amplitude and opposed phase and .areapplied to the grids of amplifier tubes 4'! and 48; The adjuste able contact 49 is provided to adjust the relative amplitude of the .voltages `on these grids. The anode of tube 4'! `is connected to horizontal deecting plate 50 of tube 35 and through load resistor 53 to a source `of positive potential. Likewise the anode .of tube .48 is Connected -to horizontal deflection plate 5I and through load resistor 52 to the same source of positiveV potential. The cathode of Vtube 48 fis .connected'to fa Isc'nirce of positive potential through resistor 54 and to ground through variable `resistor 55 `whereby an adjustable biasing voltage may be applied -to this tube. The Vmanner in -which the potentials Aof the anodes of tubes AIl and 48 and deflection plates 5! and 5I vary with the ang-le A is shown in Fig. 7 (4). At 0 the potential .of `the anode to tube 4S (plate 5I) is higher than that of the anode of tube 41 (plate-50) so that the electron beam has its maximum deflection :to the right toward plate 5I.V As the angle A becomes larger the potential of anode 43 .decreases while-that of anode `4l increases until Iat 110 the potential of the ano/de of tube 4'lrexceeds ,that of the anode of tube 43v by the .maximumamount rso that the beam .has its mimum deflection to the left I,or

toward plate 50. The beam therefor sweepsfrom right to left as the angle A changes from to 110. The behavior of these voltages from 110 to 360 is unimportant at this point since the beam is cut off during this period as will be seen later. The amplitude of the sweep and the horizontal position of its starting point may be adjusted by variable Contact 49 and variable resistor 55 respectively.

In order to provide a blanking pulse for the cathode-ray tube the anode voltage of tube 41, which is shown in Fig. 7 (4), is utilized. This voltage is applied to a clipper circuit comprising resistor 56 connected in series with each of the two oppositely poled diode sections of tube 51. The two sections are differently biased as determined bythe positions of contacts 58 and 59. The clipper imposes adjustable upper and lower limits on the voltage applied to the grid of tube 60 by preventing the voltage from rising above the voltage of adjustable contact 59 or falling below the voltage of the adjustable contact 58. The voltage appearing across the load resistor 6| of the conventional cathode follower stage comprising tube 66 is shown in graph (5) of Fig. 7, somewhat increased in amplitude to aid in illustration. It will be noted that the values of angle A at which part C of this voltage starts and stops may be very accurately adjusted to occur within limits of 10 on either side of A=10 and A=100 by varying the maximum and minimum values of the voltage through adjustment of contacts 58 and 59.

The voltage developed acrossresistor 6| and shown in graph is applied to a differentiating circuit consisting of condenser 62 and resistor 63. The resulting voltage across resistor 63 is as shown in graph (6) of Fig. 7. It will be seen that part C of the voltage graph (5) which increases at a constant rate produces a positive pulse d, whereas the unvarying portions produce zero voltage and that part which decreases at a uniform rate produces the negative pulse e. It is the d pulse that is of interest and since the leading and trailing edges of this pulse coincide with the starting and stopping points respectively of portion c of graph (5) it is seen that the angular position of these edges may be adjusted to occur at any point within 10 on either side of A=10 and A=100 by adjustments of contacts 58 and 59 (Fig. 1) to alter the maximum and minimum limits in the voltage across resistor 6| shown in graph (5) The voltage across resistor 63 shown in graph (6) is amplified by conventional amplier stages employing tubes 64 and 65 and applied to the beam intensity control electrode 66 of tube 35 through condenser 61. Grid 66 is connected through resistor 68 to an adjustable contact 69 on potentiometer 'Il whereby a negative bias is placed on the grid which is somewhat in excess of the cut-olf bias of the tube. The diode 10 has its anode connected to the upper end of resistor 68 and its cathode to the adjustable contact 12 on potentiometer 1|. The anode of diode 10 is therefore negative with respect to its cathode by the amount of the voltage drop between contacts 69 and 12. By adjustment of contact 12 this voltage drop should be made equal to the rise in Voltage of grid 66 required to turn the beam on to the proper intensity. The diode will then prevent an increase in grid potential above this point, thus maintaining uniform beam intensity ln the presence of variable or noisy unblanking pulses applied through condenser 61.

The operation of the system may be understood by again considering Fig. 7. Assuming switch 20 (Fig. 1) in its uppermost position, as motor 42 rotates shaft I6 the tuning of the receiver is varied from 155 megacycles at angle A=10 to 70 megacycles at angle A=100 as shown in graph (1). However the deflection voltages shown in graph (4) start 10 earlier at A=0 and end 10 later at A=. This is due to the fact that the angular size of the rotor plates of condenser 4| exceed those of condenser 7 by 20 and insures the presence of a horizontal sweep at all times during the 90 rotation of condenser 1 between A==10 and A=`100. Therefore as the receiver is tuned over the band starting at the high end, the deflection voltage is present to move the electron beam from right tor left across the face of the cathode ray tube. The function of that part of the circuit beginning with tube 51 is to generate an unblanking pulse that may be adjusted inlength and position to turn the beam of tube 35 on for precisely that period of time during which the tuning of the receiver is changing from to 70 megacycles. This is the pulse d in graph (6). `During the presence of this pulse, which is applied to grid 66 after amplification in tubes 64 and 65, the electron beam is on, while during all other periods of the voltage in graph (6) the beam is cut off or blanked, since at these times the voltage applied to grid 66 by the unblanking circuit is either zero or negative and does not overcome the constant negative bias applied to the grid from potentiometer 1l. The screen ofthe cathode-ray tube 35 may be provided with a horizontal scale calibrated in frequency as shown in Figs. 8 and `9. When properly adjusted the zero vertical position of the beam will appearas a horizontal line f and signals present in the band will be indicated by vertical deflections from the zero line, as at g, h and i, at points opposite their frequencies. If it is desired to listen to one of the stations the motor 42 may be de-energized and the station manually tuned to the desired frequency by dial 39. This ,dial is mounted on shaft i6 and is graduated to read frequencies in the superimposed bands 'l0-155 megacycles and 150-235 megacycles (as illustrated in Fig. 1.) A reading of 155 or 235 megacycles on the dial corresponds to A=10 in Fig. 7.

In order to initially adjust the system, standard frequenciesof 155 and 70 megacycles are applied to the antenna I input. If adjustment is not correct the frequencies may appear, for example, as shown in Fig. 9. With contacts 58 and 59 adjusted to lengthen the unblanking pulse so that the zero position trace f extends considerably beyond the 70 and 155 megacycle deections, resistor 55 (Fig. 1) is adjusted until the 155 megacycle deflection aligns with the 155 megacycle mark on the scale and contact 49 is adjusted until the 70 megacycle deflection aligns with the 70 megacycle mark on the scale. Since adjustment of contact 49 has a light effect on the adjustment of resistor 55 it will be necessary to coordinate these two adjustments. After the above alignment is accomplished that part of trace f to the left of the 70 megacycle deflection is removed by adjusting contact 58 and the excess to the right of the 155 megacycle deflection is removed by adjustment of contact 59. The system is then adjusted for proper operation.

We claim as our invention:

1. An interlccked sweep voltage and unblanklng pulse generating circuit for a cathode-ray mascia time .of the Yharms team assessing means .and vbeam intensity control fmeans, .said circuit .comprising .means lfor generating la periodically ,beam intensitycontrol electrode of ysuicient-mag- .nitude when. acting alone to .out lcti sa-id? electron beam, Iand `means or .applying said pulse to said beam intensi-ty .control electrode -in opposition -to said 'bias `to turn- .on .said beam in the presence of said pulse.

2. Apanoramic receverzcomprisingfa variable ,condenserof the trotatingftype for tun-ing saidre- `ceiver .over .a fixed band offfrequencies in n degrees of rotationpfsald condenser, a. cathode-ray tube fhaving vertical ,and 'horizontal beam deecting means and a :beamintensity .control electrode, means iorapplying the output of ysaidv receiverto .said vertical beam `deecting means, a source of relatively high alternating voltage olf constant frequency, a potential .divider connected across the .output of said source, said potential divider `comprising a second rotating condenser moun-ted on a Acommon shaft .with said nrst lmentioned rp- .tating condenser .and- Vhav-ing plates slightly exkceedi-ngn degrees in angular size and positioned on lsaid shaft so that 4the voltage output Vof said `potentiometer increases constantly overa period of time centered with respect to and slightly ex'- ceeding .the time required for the first condenser vto tuneV said `receiver over said band, means for rectifyi-ng the output of said potential divider Ato produce a sweep voltage and meansfor Iapplying said sweep voltage toI said horizontal beam de- -ilecting means, means for adjustablyiimiting'tne maximum andminimum values of Aa voltage ap- A plied thereto. means for .also applying the ,output of said rectifying means to said limitingjmeans -for producing a limited sweep' voltage having maximum land minimum values determinedv by the settings of said limiting means, means for diiferen-tiating the output of saidjlimiting means to produce a voltage pulse of Vthe same time duratio-n -as said limited rsweep voltage, means for biasing said abeam intensity control electrode be- Kyond the cut-oli'v point, vand means for applying saidv voltage lpulseto said beam intensity 'control electrode iii-opposition to said bias.

3. Apparatus as claimed in claim 2 in which means are provided for limiting the maximum value of the voltage pulse applied to said beam intensity control electrode.

4. In a panoramic receiver of the type having tuning means for periodically sweeping the rec eiver tuning .over a xed frequency band and having a cathode-ray -tube indicator of the type lin which Ithe 'receiver output deflects the beam vertically and a sweep voltageA coordinated with the receiver ltuning deflects the -beam horizontal'- ly, a sweep voltage and unblanking pulse generating circuit, said circuit comprising means inter- `locked with said receiver tuning means for generating a sweep voltage extending over a time interval centered with respect to and of slightly greater duration than the time interval required Ito `sweep the tuning of vsaid receiver over said band, means for applying said Asweep voltage to the horizontal deflecting means of said cathoderay tube, adjustable maximum and minimumamplitude limiting means, means for also applying said sweep vol-tage to said limiting means for producing a limited sweep voltage, means for differentiating said limited sweep voltage to produce a Voltage pulse having its Alength and time position relative toV said receiver tuning sweep determined bythe maximumand minimum settings of said 'limiting means, means for applying'beam blank- ,ing voltage to said cathode-ray tube, and means for applying said voltage pulse to said cathoderaytu'be in'oppostion to said Vblanking voltage for unblanking said beam during the presence of .Said pulse.

' BENJAMIN R; GARDNER.

EVERETT fr. WILBUR.

W. AUKERMAN.

REFERENCES CITED T ne following references are o f record in the iile .ci this patent:

Number Name Date 2,412,991 Labin D ec. 24, 1,946 2,418,139 Preisinan s- Apr. 1, 1947 2,450,018 Preisman Sept 28, `1948 OTHER REFERENCES Radio-.,Craft, September 1944, The Etherscope, pp. 7.27, 7152-753. (Copy in Div. 51.)

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