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Publication numberUS2751429 A
Publication typeGrant
Publication dateJun 19, 1956
Filing dateJun 3, 1954
Priority dateJun 3, 1954
Publication numberUS 2751429 A, US 2751429A, US-A-2751429, US2751429 A, US2751429A
InventorsKurt Schlesinger
Original AssigneeMotorola Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Vectorscope
US 2751429 A
Abstract  available in
Images(3)
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Claims  available in
Description  (OCR text may contain errors)

K. SCHLESINGER 2,751,429

vEcToRscoPE 3 Sheets-Sheetl June 19, 1956 Filed June 5, 1954 June 19, 1956 K. SCHH-:SINGER VECTORSCOPE 3 Sheets-Sheet 2 Filed June 3, 1954 INVENToR .Ku/ Sc/i/@s/hger w SM June 19, 1956 K. SCHLESINGER 2,751,429

VECTORSCOPE Filed June 3, 1954 3 Sheets-Sheet 3 N? v r Q X W MH m. m, T M y nl ig Lim .m $5 Eh ,l W@ Q m N5 m o w E S 1 H ma ms L u t ml K S Y si w B 11 L w m Gm MGS@ SSG.

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United States Patent-'O VECTORSCOPE Kurt Schlesinger, Maywood, lll., assigner to Motorola, Inc., Chicago, lll., a corporation of illinois Application June 3, 1954, Serial No. 434,144

13 Claims. (Cl. 178-5.4)

The present invention relates generally to apparatus for indicating the amplitude of a signal to be tested and the phase of such a signal with respect to a reference signal, and more particularly to such apparatus which includes a cathode ray tube for displaying a representation of the signal to be tested, preferably, as a vector indicating the amplitude of the signal and its phase displacement from the reference signal.

There are many instances in which it is desired to observe the relative phase of signals generated in various types of electronic equipment. For example, in color television systems of the type utilizing a color television signal of present day standardized composition, it is desirable to provide an indication of the phase relations of the various color subcarrier components of the color television signal with respect to the color reference signal burst components thereof.

It is accordingly an object of the present invention to provide improved apparatus for indicating visually the amplitude of a signal to be tested and the phase displacement of such a signal from a reference signal.

A further object of the invention is to provide such improved phase and amplitude measuring apparatus in which the phase of an unknown signal with respect to a reference signal and the amplitude of the unknown signal is shown as a vector or dot position with respect to a reference axis.

Yet another object of the invention is to provide such improved phase and amplitude indicating apparatus in which the phase of an unknown signal with respect to the reference signal and its amplitude is directly displayed on the screen of an oscilloscope by the use of signals derived from a combination of the unknown signal and the reference signal by relatively simple circuits contained within the apparatus.

Yet another object of the invention is to provide such improved amplitude and phase measuring apparatus which may be adapted for use in conjunction with a color television signal of present-day standardized `composition andl which is constructed to respond to the color television signal itself to provide an indication of the various components contained in the signal.

A still further object of the invention is to provide such improved amplitude and phase measuring apparatus that may be adapted to provide a visual indication of the frequency deviation of a frequency modulation receiver from the center frequency.

Yet another object of the invention is to provide such improved phase and amplitude measuring apparatus that may be adapted to provide a visual indication of the characteristics of a passive network throughout a selected frequency band.

A feature lof the invention is the provision of a phase and amplitude measuring apparatus in which an unknown signal is compared with an in-phase component and with a phase-quadrature component of a reference signal in a circuit containing a pair of discharge devices biased to a Class B condition for the reference signal to provide 2,751,429 Patented June 19, 1956 ice rst and second control signals, the first control signal having an amplitude corresponding to the amplitude of the unknown signal and its phase displacement from the in-phase component of the reference signal and the second control signal having an amplitude corresponding to the amplitude `of the unknown signal and its phase displa-cement from the phase-quadrature component of the reference signal.

Another feature of the invention is the provision of such improved amplitude and phase measuring apparatus which incorporates an improved phase-quadrature network for deriving the phase-quadrature component of the reference signal in such a manner that amplitude balance adjustments in the apparatus have no effect on the phase-quadrature characteristics of the network.

Another feature of the invention is the provision of such improved amplitude and phase measuring apparatus which may be directly connected to a source of a presentday standard color television signal and which includes circuit means for recovering the color reference bursts from the color television signal and for using such bursts to produce a reference signal of the frequency and phase of the bursts, and which selects the chrominance subcarrier components of the -color television signal for comparison with the derived reference signal to provide a visual indication of the respective amplitudes of the subcarrier components and the phase relation of each with respect to the reference bursts.

Yet another feature lof the invention is the provision of such improved amplitude and phase measuring apparatus which includes circuit means for converting frequency variations into phase variations so that the apparatus can be used to measure, for example, the modulation deviation of a frequency modulated transmitter from its center frequency.

The above and other features of the invention which are believed to be new are set forth with particularity in the appended claims. The invention itself, however, together with vfurther objects and advantages thereof may best be understood by reference to the following description when taken in conjunction with the accompanying drawing in which:

Fig. l is a schematic yrepresentation of the improved amplitude and phase measuring apparatus of the invention adapted for use in conjunction with a color television system utilizing a present-day standard color television signal;

Fig. 2 is a wiring diagram of a phase detector portion of the apparatus of Fig. l;

Fig. 3 is a wiring diagram of the remainder 'of the apparatus of Fig. l;

Fig. 4 is a mechanical representation of a manually variable delay line used in the circuit of Fig. 2;

Fig. 5 shows the display on the screen of the reproducing tube used in the apparatus of Fig. l indicating various -chrominance sub-carrier components of standard color television' signal;

Fig. 6 shows a modification of the improved apparatus for use in measuring the frequency deviation of a frequency modulated signal from the center frequency;

Fig. 7 shows the display of such frequency deviation on the screen of the reproducing tube; and

Fig. 8 is another modilication of the improved apparatus of the invention for use as a measuring means of the characteristics of a passive four-terminal network.

The invention provides apparatus for indicating the amplitude of a signal to be tested and the phase of such a signal with respect to a reference signal of greater amplitude and of like frequency. The apparatus comprises rst and second discharge devices with means for biasing the devices to a Class B condition for the reference signals. A lirst input circuit is coupled to the dis- Vacross the screen in a vertical direction.

charge devices for impressing thereon the signal to be tested; and a second input circuit is coupled to the first discharge device for impressing an in-phase component of the reference signal on the lirst device, and the second' input circuit includes a phase-quadrature network for impressing a phase-quadrature'component of the reference signal on the second device. A cathode-ray tube is provided which has a viewing screen, and which also hasl iirst-and second deflection means for deiiecting the cathode-ray beam therein across the screen in mutually perpendicular directions. A irst output circuit is coupled to the Yiirst discharge device for deriving a first control signal having an amplitude correspondingto the ampli- Ytude of the signal to be tested and also to the phase displacement of that signal from the in-phase component of the reference signal. A second output circuit is coupled to the seconddevic'e for deriving a second control signal having an amplitude corresponding to the amplitude of the signal to be tested and also to the phase displacement of the signal from the phase-quadrature component ofthe reference signal. Final-ly,- rn-eans is provided for irnpre'ssing the nrst and second control signals respectively on the iirst and second deflection means of the cathode-ray tube.

As previously stated, the apparatus of Fig. l isV constructed to be utilized in conjunction with a color television system of present-day standardized composition; The apparatus includes a first probe which will be referred to herein as the test signa probe, and probe 10 is coupled to a band pass ampliiier 11 through a variable resistor 12 having one side connected to a point of reference potential or ground. Unit 11 is coupled tov a modulator amplitier 13, and a local oscillator 14 is also coupled to this amplier. The output terminals of unit 13 are coupled to a variable delay line 15 which, in turn, is coupled to a phase and amplitude detector 16 and to a phase and amplitude detector 17.

The apparatus also includes a probe 18 which will be referred to herein as the reference signal probe, and probe 18 isconnected to an amplilier and color synchroni'zirng burst separator 19 through a variablepresistor 20, the resistor having one side connected to the point of reference potential. Unit 19 is connected through a burst regenerator 21 to an amplitude limiter stage 22. The output terminals of limiter 22 are connected to detector 16 and through a quadrature network 23 to detector 17.

'A cathode-ray reproducing tube 24 is provided and this tube has a pair of deflection'electrodes 25 for deflecting the cathode ray beam therein in a horizontal direction across the viewingV screen 10'7 and the tube also has a pair of deflection electrodes 2,6 for deilectingthe beam The'pout'put terminals of detector 16 are connected to thehorizontal d'efiection electrodes 2S, and the output terminals of detectorV 17 are connected to the vertical deflection electrodes 26. f

As is well-known, the present-day standardized color television signal includes monochrome video-frequency components, synchronizing components, color reference signal color bursts, and a chrominance sub-carrier amplitude modulated in Vphase quadrature by respective chrominance signals.` BlockV30 represents a source of such a television signal, and this source may be a color television receiver or monitor or any other apparatus in which'it is desired to determine the amplitude of the chrominancesub-carrier components and their phase displacement from reference as the television signal appears at various points in the apparatus.

Probes 10, 18 are of the low capacity type. The arrangement is such that probe 18 can be connectedl to a point where the color television signal appears, and itschannel automatically derives a reference signal from the color televisionsignal. When so desired, however, probe 18 can be connected to any reference signal source of appropriate frequency. Probe 10, onV the other hand, can be connected to any point in source 30 wherein it is desired to measure the amplitude of the chrominance sub-carrier components and their phase relations with the color signal bursts, and its channel is capable of selecting these components from the color television signal. Y Probe 18, however, can. be connected to any point where a signal appears Whose amplitude and phase relation with a reference signal is of interest.

The color television signal as picked up by probe 10 is ampliiied in ampliiier 11.` As previously noted, the amplifier is of the bandpass type, and it is selective only to the frequency range ofthe chrominance sub-carrier components (for example, from 2.5-4.7 megacycles), and it rejects interference such as motorboating, microphonics and hum. The amplified chrominance sub-carrier cornponents are supplied to detectors 16 and 17 through units 13 and 15.

The color television signal picked up by probe 1S, on the other hand, is amplified by the amplifier inunit 19 which responds to the full frequency range of the color television signal. (For example, from 0 5 megacycles). Unit 19 also includes circuitry for removing the synchronizing components from the color television signal and for using these components to recover the color reference bursts from the television signal. The recovered color reference bursts are impressed 'on the burst regenerator 21 and cause it`to generate a continuous wave reference signal havingV the phase and frequency of the reference color bursts. The reference signal from Vunit 21 is amplitude limited in limiter 22 to a constant value at Yleast Vtwice the maximum amplitude of the chrominance sub-carrier components, and the amplitudelimited reference signal impressed on detector 16 and through phase-quadrature network 23 on detector 16.

Detector 16 responds to the chrominance sub-carrier components and to the in-phas'e component of the reference signal from limiter 22 yto produce for each of the subcarrier components a unidirectional control signal having an amplitude corresponding to the amplitude of the corresponding sub-carrier componentand also corresponding to its phase displacement from the in-phase component of the reference signal. Detector 17, on the other hand, responds to the sub-carrier Components and to a phase-quadrature component of thereference signal to produce-for each of the sub-carrier components a unidirectional control potential having an amplitude corresponding to the amplitude'of the corresponding sub-carrier component and also corresponding to its phase dispiacement from` the phase-quadrature component of the referencel signali The unidirectional control signal from detector 16 is applied to defiection electrodes 25", and it deiiects the cathode-ray beam inrreproducin'g device 24 along the horizontal aXis inV a direction and by'an amount corresponding'to the amplitude of each ofthe sub-carrier cornponents and also corresponding to the respective phase displacement thereof from the'Vin-phase component of the reference signal. The control potential from detector 17 is` applied to the vertical electrodes 26 to denect the cathode-ray beam along a vertical axis in a direction and by an amount corresponding to the amplitude of the respective sub-carrier components and -also corresponding to their respective phase displacements from'V the phase-quadrature Vcomponent ofthe reference signal. The resulting indication on they screen of device 24 is a series of uorescent dots displacedV from the center of the screen by amounts corresponding respectively to the amplitudesof the sub-carrier components and having angular positions 'corresponding' respectively to the phase displacements of the sub-carrierV components from the reference signal.

It is convenient that the indicationY be. represented by vectors rather'than dots, andfor thatxreason; theV local oscillator 14 is provided which generates a signal, preferably a sawtooth wave (of, forlexample, -10 kilocycles), which periodically reduces the gain of amplier 13 to zero to produce an amplitude modulation on the subcarrier components. This simple expedient causes the dots referred to previously herein to be periodically swept to zero so that the respective indications are by vectors rather than dots.

Any one of the vectors or dots referred to above can be aligned with a reference axis on the screen of device 24 by manually adjusting variable delay line 15. Such manual adjustment imparts a uniform delay to each of the sub-carrier components which causes their indications to rotate on the screen of the reproducing device.

Fig. 5 shows a typical indication on the screen of the reproducing device 24 of the usual sub-carrier components in a standard color television signal. This particular indication corresponds to the transmission of vertical color bars. The colors transmitted were red, yellow, green and blue. The angles and radials of the display are compared for test purposes with the standard values tabulated below:

A circuit diagram for units 13-17 and 23 is shown in Fig. 2, and as shown in that figure, modulator amplier 13 includes an electron discharge device 40 connected in known manner to constitute an ampliiier stage. Local oscillator 14 includes an electron discharge device 41 connected in known manner as a blocking oscillator to constitute a sawtooth generator. The anode of device 41 is coupled to the screen electrode of device 40 to impress the sawtooth wave on the screen electrode of the latter device. This causes the gain of the amplifier periodically to be reduced to zero, and the subcarrier components translated thereby to be 100% amplitude modulated by the sawtooth signal.

The anode of device 40 is coupled to the input terminal of variable delay line through a triple tuned coupling network L11a-41e of known construction and exhibiting relatively wide band pass characteristics. Network lila-41e passes the band of a chrominance sub-carrier components extending, for example, from 2.5-4.7 megacycles, and supplies these components to the delay line 15. The band-pass network 11a- 41e is damped by the resistors 42, 43 in the anode circuit of device 40 which assist in providing a uniform response characteristic for the network over the band-pass range. Delay line 15 includes an inductance coil 46 having an input terminal connected to the junction of coils 41C and 41e, this terminal being coupled to ground through a capacitor 45. Coil 46 has an output terminal connected to ground through an inductance coil 47 and series resistor 48. Elements 47, 4S serve to terminate the delay line in its characteristic impedance to prevent standing waves in the line. This termination also provides a resistive input impedance for the delay line which further damps network 4in-41e and assists in providing uniform bandpass characteristics over its band-pass range.

The variable delay line 15 has a moveable coil 49 whose sides are connected respectively to the inner and outer lines of a coaxial conductor 50. The inner line of conductor 50 is connected to the control electrode of an electron discharge device 51. Device 51 is connected as an amplifier and is cascade coupled to a second amplier including discharge device 52. The anode of device 52 is coupled to ground through a capacitor 53 and a series-connected inductance coil 54, and the juncytion of elements 53, 54 is coupled through a capacitor 55 Vto thel control electrode of an electron discharge device 56.

The mechanical details ofthe variable delay line 15 are shown in Fig. 4, and this delay line comprises a single layer helix coil 46that is wound around a grounded metal tube 57 composed, for example, of brass and having a longitudinal slot 58 extending along its length. The tube, for example, may be 9 long with an inside diameter of 1/2 and an outside diameter of 1%6", and with a Ms wide slot. These dimensions are appropriate for a 3.6 megacycle chrominance sub-carrier as is presently used, and establish a full Wavelength of such sub-carrier along the line. The moving pickup coil 49 is closely wound in an annular slot around the periphery of a moveable member 59 composed, for example, of bakelite or other insulating material and having an outside diameter, for example, of l. The width of the peripheral slot may, for example, be 1A" and its depth l/le. The inner member 59 is manually slidable within tube 57 to provide a complete 360 time delay of the signals translated by the unit.

Device 56 is connected to form, in conjunction with a device 65, the detector 16 of Fig. l. These devices preferably are beam tetrodes and are connected in push pull to have an overall gain, for example, of :1. This detector is in the form of a pulsed envelope detector of a type similar to those disclosed and claimed in copending application Serial No. 372,697 iiled August 6, 1953, in the name of the present inventor. As fully discussed in that application, a pulsed envelope detector is predicated on the principle that half wave rectification of a composite signal formed by an amplitude modulated test signal and reference signal of the same frequency and at least double the amplitude produces an output signal corresponding to the amplitude modulation of the test signal and to the phase displacement of the test signal from the reference signal.

To perform the function described above, devices 56 and 65 are biased to function as Class B amplifiers for the reference signal impressed thereon, and this bias is obtained by returning the respective control electrodes of these devices through a grid leak resistor 66 to the negative terminal of a biasing source C-. source may be a battery or any other convenient source of negative unidirectional potential of the appropriate value to bias the devices to Class B operation for the reference signal.

The cathodes of devices 65 are connected together through a phase inverting inductance coil 67, preferably of bi-filar construction, whose midpoint is connected to the point of reference potential or ground. The anodes of the devices 56 and 65 are connected to the positive terminal B-I--lthrough respective band-rejection filters 68a-68d, 69a-69d; and through respective low-pass lters 68e-68k, 69e-69k. These lilters reject the subcarrier and its sidebands and pass only the detected components from 0-11 kilocycles. The connection to the positive terminal B-I--I- is made through a variable potentiometer 70 whose moveable tap can be adjusted to control the horizontal centering on reproducer 24.

The screen electrodes of devices 56, 65 are connected to the positive terminal B-lthrough a screen dropping resistor 44a and are coupled to ground through respective bypassing capacitors 44b, 44e. A neon tube 44d is also coupled between these screen electrodes and ground to assure constant potential on the screens in the presence of control signal variations of the control electrodes.

The cathode of device 56 is coupled to the cathode of an electron discharge device 71 through a variable capacitor 72, and the junction of the capacitor and the cathode of device 71 is connected to the point of reference potential through a variable resistor 73. The output circuit of the amplifier of discharge device 52 is coupled to the control electrode of device 71 through a capacitor 74, and this output circuit is connected to ground through a pair of series resistors 75, 76, resistors 75 being variable This biasing 7 for Vgrain balancepurposes to compensate for deflection irregularities in reproducing tube `24. Y Y

Device '71 anda further ydevice 92,`like devices 56 and 65, are connected as Class B amplifiers for the reference signal Ycomponent applied thereto. To achieve this, the control electrodes of Vthese devices are also connected to the negativeV biasing terminal C through a Vtive'low-pass 'filter and band rejection networks 79, 80 which perform the'same function as networks 685;-68/c,

69-.69k; and the kanodes are connected to the positive terminal through aV variable potentiometer Si which provides vertical centering for reproducer 24. The screen electrodesof devices 71, 92 are connected to the screen electrodes of Vdevices 56, 65.

The .circuits of devices 56, 65 are connected respectively to the horizontal deflection electrodes of device 24 andrprovidre a direct-current path thereto; and the circuits 79, `80 of devices 71, 92 are connected respectively toV the vertical deflection electrodes 26 of the reproducer and provide a direct-current path thereto. The arrangement of Fig. 2 has an input terminal Q that is coupled through a blocking capacitor 81 to the cathode of device 56.

in the circuit of Fig. 2, itis assumed that one or more signals to be tested are impressed across input terminal P and ground; that a like frequency double amplitude reference signal is impressed between the terminal Q and ground. The signal to be tested is impressed with like phase on the control electrodes of devices 56, 65, 71 and 92. The reference signal, on the other hand, is impressed on the cathode of device 56 with its original phase, but is impressed on the cathode of device 65 with inverted phase for push-pull operation of devices 56, 65, the phase inversion being achieved by inductance coil 67. As previously noted, thedevices are biased to function as Class B amplifiers for reference signal components impressed thereon and produce in their respective output circuits a signal corresponding to the amplitude of the test signal and to the phase displacement thereof from the reference signal. Due to the push-pull operation of the devices, the control signal produced in their output circuits are of opposite polarity which is desired so that these output control signals may be applied to the deflection electrodes 25 of device 24. Y

Capacitor 72 (c) in conjunction with the equal inductance portions (L) of inductance coils 67 and 78 connected between that capacitor and the point of reference potential, and variable resistor 75 (r2) form a low impedance quadrature network of a tuned lt type, and the quadrature phase between the output and input of this network is unaffected by variations in the load balance resistor 75, just as long as one `Lc branch is tuned to resonance. The basic relations of the tuned A are described by the equations: ez=e1jr2/Z (where e2 is output signal, er is input signal, and Z=\/L/c), and w2Lc=l. The input limpedance is a pure resistance r1=Z2/r2. Therefore, the amplitude balance between the reference signal and its phase quadrature component can be adjusted by varying resistor 75, but the input impedance stays resistive and the phase-quadrature relation is not changed.

The phase quadrature component of thereference signal from the quadrature network described above is supplied to the cathode of device 71, and this component is phase inverted by inductance coil 78 and applied to the cathode of device 92.V The circuits Vof devices 71, 92, therefore, compare the signal to be tested with the phase quadrature component of the reference signal; these de- 'i8 vices produce inntheirroutputk circuits a pair of push-pull control signals respectivelycorresponding to the amplitude of the test signal and the phase displacement `thereof from the reference signal.

Thecathode ray beamin device 24, therefore, is deflected along its X axis by an amount corresponding to the amplitude of the test signal and its phase displacement from the in-phase component of the reference signal. Moreover, the deflection of the cathode ray beam along its Y axis corresponds to the amplitude of the test signal and its phase displacement from the phase quadrature component of the reference signal. The beam, therefore, is established at a position representing the amplitude and phase ,displacement of the test signal from the reference signal. As previously noted, the periodic reduction if the amplitude of the test signal to zero produces a vector representation of the test signal rather than a dot representation.

Expressed mathematically: Y

The signal input to devices 56, 65 and 71, 92Y may be expressed as:

e=A cos (wt-Hp) (l) where:

A is the amplitude of the test signal o is the phase displacement of the test signal fromrtheV reference signal.

The reference signal input may be expressed as:

eT=2 cos wt The amplitude factor 2 is chosen to indicate the use The circuit of devices 71, 92 operates on the signal (l) and on the phase quadrature component of the signal (72)., that is:

The filtered low frequency output of the circuit of devices 71,'92 then becomes:

-The detected control potentials ex and ey result in a stationary dot on the screen of reproducer 24 with the desired polar co-ordinates A (t) (t). As previously noted, it is frequently desirable to enhance visibility of the display by providing radials from each dot to center. This eUzA sin qb may be'accomplished by periodically keying the signal i amplitude to zero ata specified rate. The keying process in the present instance is shown as accomplished in unit 13 (Fig. l) prior to detection which is inherently simpler than Vpost detection methods.

The circuit of Fig. 2 may be considered to represent the basic circuit of the vectorscope, whereas the circuit of Fig. 3 represents the 'additional circuitry necessary to adapt the vectorscope to a direct indication of the'various components of a color television constituted in accordance with present-day standards, and as described in conjunction with Fig. l.

As shown in Fig. 3, .the test signal probe 10 of Fig. l is coupled through variable potentiometer 12 and a capacitor 91 to the control electrode Vof an electron dischargedevice 93. Device .93 in conjunction with an electron discharge device 94 forms the amplifier 11 of Fig. l. This amplifier is of the feedback type and is connected in known manner as a band-pass amplifier. That is, vthe `amplifier formed by devices 493, '94 .selects .only the'2;45

4.7 megacycle band occupied by the chrominance spectrum so that only the color sub-carrier components are selected and supplied to terminal P of the vectorscope.

The reference signal probe 18 of Fig. 1 is coupled through potentiometer 20 to the input circuit of an electron discharge device 96, the input circuit including a series capacitor 97 and grid leak resistor 98, the latter connecting the control electrode to the point of reference potential or ground. Device 96 is connected in cascade with an additional electron discharge device 99 as a feedback amplifier. This amplifier is of known construction, and is designed to select the complete Video spectrum of the color television signal from zero to megacycles.

The anode of device 99 is coupled to the control electrode of an electron discharge device 100. Device 100 functions as a phase splitter stage, and its circuit includes a switch 101 which in one position couples its cathode to the control electrode of an electron discharge device 102 and which in its other position couples the anode of device 100 to the control electrode of device 102.

Device 102 is cathode coupled to a pair of electron discharge devices 103, 104, the latter two devices functioning as a synchronizing signal separator. The separator circuit of devices 103, 104 includes a cathode feedback connection so that the circuit saturates at two denite signal levels for ecient separation of the synchronizing components from the color television signal.

The separator circuit of devices 103, 104 is connected through a delay line 105 to the control electrode of an electron discharge device 106. The anode of device 102 is also coupled to the control electrode of device 106 through a coupling transformer 107 which is tuned to the color subcarrier frequency, the connection from the delay line to the control electrode being made through the secondary winding of the transformer.

Device 106 is connected as an amplifier circuit and its output circuit is connected through a switch 108 to a crystal burst regenerator circuit including an electron discharge device 109. This circuit is known, and it responds to the color reference bursts to produce a continuous wave signal having the frequency and phase of these bursts. Device 109 is connected to a discharge device 110 so that when switch 108 is moved from its L to its O position, an oscillator circuit is established whose frequency is stabilized by crystal 111. The anode of device 109 is coupled to the control electrode of an electron discharge device 112 which functions as an amplitude limiter. The anode of device 112 is connected to the positive terminal B-lthrough a variable inductance coil 113 and a resistor 114. The junction of these elements is coupled to the terminal Q of the circuit of Fig. 2 through a coupling capacitor 115. As shown in Fig. 2, input terminal 4 is connected to quadrature network 67, 72, 78, and as previously pointed out, the input impedance of this network is resistive when it is tuned to the frequency of the reference signal. For appropriate high power coupling between limiter 112 and the quadrature network, coil 113 is tuned to resonate with the plate capacitance 116 of device 112 at the reference signal frequency.

The operation of this channel of the receiver has been described previously herein, but this operation will be reiterated briey and is as follows. 'I'he demodulated color television signal is amplied by the amplifier circuit of devices 96, 99 and impressed on the phase splitter circuit of device 100. The phase splitter circuit is included so that the instrument may be used when the demodulated signal has a positive-going synchronizing polarity or a negative-going synchronizing polarity. For either polarity, it.. is merely necessary to set switch 101 in such a manner that the demodulated color television signal is impressed on device 102 with its synchronizing components extending in a positive-going direction. The demodulated color television signal appears in the cathode circuit of device 102 and the synchronizing components are selected therefrom in the circuit of devices 103, 104. The selected syn- `10 chronizing components are delayed in delay line sd that they appear in time coincidence with the color reference bursts, and the delayed synchronizing pulses are used as gating pulses for device 106. The cathode of device 106 is returned to ground through a relatively high biasing resistor 117 to enable the device properly to provide the gating function. The anode circuit of device 102 impresses the demodulated color television signal on the control electrode of device 106, and this control electrode is pulsed by the pulses generated by delay line 105 so that device 106 translates only the color reference bursts.

The circuit of crystal 111 and discharge device 109 is usually termed the burst regenerator, and when switch 108 is in its L position, the color reference bursts impressed on the crystal cause the circuit to produce a reference signal having a frequency of, for example, 3.58 megacycles corresponding to the frequency of the reference signal bursts and to the frequency of the subcarrier components, and having a phase corresponding to the phase of the reference signal bursts.

The television signal is sufficiently amplified in channel described above so that the reference signal developed' by the burst regenerator has an amplitude exceeding twice the amplitude of each of the subcarrier components. This: reference signal is amplitude limited by device 112 so'- that the reference signal impressed on terminal Y has a; constant amplitude that is at least double the amplitude:

of the sub-carrier components.

The circuit of Fig. 2 may also be adapted so that the instrument may be used to measure the frequency deviation of a frequency modulation signal from its center frequency. Such an adaptation is shown in Fig. 6. That figure shows a source of frequency modulated signals such as a frequency modulation monitor receiver including the usual radio frequency amplifier 120, first detector 121, intermediate frequency amplifier and limiter 122, second detector 123, audio amplier 124, and sound reproducer 125, all of these stages being cascade connected in known manner. A probe 126 is connected to the output of intermediate frequency amplier and limiter 122 to derive the frequency-modulated amplitude-limited signal. Probe 126 is coupled through a time delay network 128 to a modulator 129. The probe is also connected through a modulator 130 and band-pass ilter 131 to the modulator 129. A reference signal generator 132 is connected to the modulator 130; and modulator 129 and generator 132 are respectively connected to the terminals P and Q of Fig. 2. It is to be noted that the burst regenerator 21 of Fig. 3 can conveniently be used to function as the reference signal generator 132, it being merely necessary to change the position of switch 10S to the oscillator position O to derive a constant amplitude reference signal at the instrument frequency. This signal may conveniently be derived from terminals 127 (Fig. 3) connected to an inductance coil 133 which, in turn, is coupled to coil 113 in the anode circuit of limiter device 1,12.

The amplitude-limited frequency-modulated signal from probe 126 (foiAf) is heterodyned in modulator 130 with the reference signal (fr) from generator 132. Modulator 130 develops the sum and difference frequencies of the signals, and bandpass lter 131 selects the sum frequency (fo-Hr) iAf. The band-pass filter produces, therefore, a series of frequency-displaced heterodyned signal components resulting from the heterodyne action of the frequency-rnodulated signal (faihf) with the reference signal (fr) from generator 132.

The amplitude-limited frequency-modulated signal (foiAf) from probe 126 is time delayed in delay network 128 which imparts a phase shift to each of the sideband components thereof proportional to its deviation from center frequency (fo). A ferrite core delay line made by the Columbia Technical Corporation is especially suited for this purpose. The output signal (einem) 2,55 ifie The-circuit of Fig. 2 compares the reference signal withY the output signal of modulator 129 to produce a display on kthe-screen of reproduced device 24 such as shown in Fig. 7. It is preferable that the time delay network 123 be designed so thatthe maximum permissible frequencyl displacement produces 180 deviations on the screen .of tube 24. By present day frequency modulation standards, the allowed deviations are plus or minus 75 kc. so that the required delay of network 1'28 equals l 4 6),- 3.3 microseconds The instrument can Valso beused to monitor the frequencymodulated intercarrier sound component `of a televisionsignal. In the latter system, the allowed deviation of the frequency modulated signal is 25 kilooycles so that the required delay of line 128 is 10 microseconds.

Therefore, Awhenever the frequency-modulated signal exceeds the permissible deviation, the display on the screen of .reproducing device 24 immediately indicates this fact bythe segment of the traced signal exceeding 180. Moreover, the Vfan shaped path reaches ya spread of 180 only for peak deviations. In addition, the fanned out area will be a segment ofa circle as long as the receiver limiter is operating properly, andany spurious amplitude modulation is readily detected as a known circularity of the displayed boundary. As in the preceding instance, the display may be in the form of a vector representation by the modulation of amplifier 13 (Fig. 2); and the display-may be angularly positioned on the screen of tube 24 by manual Aadjustment of delay line 15 (Fig. 2).

The circuit .of Fig. 2 can also be adapted to measure tude Vin each cycle. Generator 135 is coupled to a phase splitter circuit including an electron discharge device 138. Device .138, in turn, is coupled to a pair of discharge devices 139, 140. Devices '139, 140 are connected -to frequency modulate the output signal of an oscillator including a ydischarge device 141, this frequency modulation being in accordance with the signal derived from generator 135. In this manner the oscillator of device 141 generates a signal having, for example, a center frequency of 10.7 megacycles which is frequency modulated so that a total deviation of i one megacycle is accomplished in steps, each 200 kc. apart', at a repetition rate of 60 cycles.

The circuit of devices 138, 139, 140, 141 is generally termed an electronic wobbulator circuit, and the illustrated circuit may be replaced by others of this type. For example, a klystron'wobbulator circuit can be used, and this type is capable of providing a relatively wide kfrequency deviation at a relatively large number of discrete steps. It is desirable that generator 135 produce Ystepped waves .that increase linearly to maximum amplitude, so as to avo'id spurious indications on the Screen of tube 24.

TheV frequency-modulated output signal from oscillator 141 is supplied to an amplitude limiter stage 142, and

the limiter is coupled through the network under vtest 143 Y to the modulator 129. e The limiter 142 yis also coupled through the modulator 130 and band-passiilter -131Ytoithe modulator r129. The reference signal generator 132 is coupled to modulator 130 and tofterminal Q of the cir- 12 cuit 'of Fig. 2, whereas modulator 129 is coupled to terminal l of the `circuit of Fig. 2.

The amplitude-limited frequency-modulated signal from limiter 142 is applied to the network under test, so that the latter network develops an output .signal having a plurality of discrete frequency components, each of the components having a phase displacement and amplitude corresponding to the phase-shift and attenuation character'istics of the network at Vthat particular frequency.

The signal from limiter 142 is also heterodyned in modulator with the reference signal from generator 132, and as in the system of Fig. 6, the sum frequency heterodyne components are passed to modulator 129 by band-pass filter 131.Y Modulator 129 heterodynes the various components of the output signal from the network under test in each instance to the reference frequency. Therefore, reference signal generator Y13 2 impresses the reference frequency signal on terminal Q, .and modulator.

129-impresses a series of discrete signals on terminal P each having the reference frequency, and each being displaced in phase by ,an amount corresponding to thephase displacement characteristics of the network under test at the different frequencies. Moreover, each component of Vthe output signal from network 143 has an amplitude corresponding to the `attentuation characteristics of the' network at the various frequencies. Therefore, the vectorscope indicates visually .the phase displacement characteristics of the vnetwork ,under test at various discrete frequencies, and also indicates the attenuation of the net-VY work at .each such frequency. In other words, if the network under testis a bandpass lter, the passband vis recognized as that section ofthe vector envelope which most nearly approaches -a circle through the originV at= maximum radius. Constant phase delay, on the other hand, is recognized by equal angles between consecutive radials. Crowding or spreading of these angles signifies phase distortion at the respective frequencies.V

The invention provides, therefore, an improved appa-V ratus for indicating the phase displacement -of a signal under test from a reference signal and also the amplitude of the test signal. As described herein, the indication is direct and easily ascertained, and the instrument can be adapted to have a wide variety of uses.

VWhile particular embodiments of the invention have' beeny shown and described, modifications may be made and it is intended in the appended claims to .cover :all such modifications Vas fall within the true spirit vand scope of the invention.

I claim:

l.V Apparatus for indicating vectorially the `amplitude of a signal to be'tested and the phase of such .a signal with respect Vto a reference signal of like frequencywand .of Vat least double ythe amplitude thereof, said-apparatus including in combination, rstand Vsecond detector means each responsive to Va pair .-of input signals of like frequency for producing an output signal of an amplitude corresponding to the amplitude of one of the input signals Aand to the phase relation between such input signals, a first input circuit for ,impressing the signal .to .be :tested on said first and second detector'means, yfirst circuit meansfor supplying thesignal to be tested to said iirst input circuit, a modulator 'included in .said first circuit means *for periodically varying .the amplitude Yof the test signal, a second input circuit for impressing .an in-.phase component of the reference .signal on said iirst detector means and ray tubehaving ,aviewing screen and ,furtherih'aving first and -second'deflection means for deilecting a cathode-ray" beam in the tube across said viewing screen in mutually pelpendicular directions, a rst output circuit coupled to said first detector means for deriving a rst control signal therefrom having an amplitude corresponding to the amplitude of the signal to be tested and to the phase displacement of such signal from the in-phase component of the reference signal, a second output circuit coupled to said second detector means for deriving a second control signal therefrom having an amplitude corresponding to the amplitude of the signal to be tested and to the phase displacement of such signal from the phase-quadrature component of the reference signal, means for impressing said rst control signal on said irst deflection means of said cathode-ray tube, and means for impressing said second control signal on said second deflection means of said cathode-ray tube.

2. Apparatus for indicating the individual amplitudes of a series of like-frequency phase-displaced signals to be tested and the phase of each of such signals with respect to a reference signal of like-frequency and of at least double the amplitude of each such signal, said apparatus including in combination, iirst and second detector means each responsive to a pair of input signals of like frequency for producing an output signal of an amplitude corresponding to the amplitude of one of the input signals and to the phase relation between such input signals, a first input circuit for impressing the signals to be tested on said first and second detector means, first circuit means for supplying the signals to be tested to said rst input circuit and including manually operated variable time-delay means, a second input circuit for impressing an in-phase component of the reference signal on said first` detector means, and including a phase-quadrature network for impressing a phase-quadrature component of the reference signal on said second detector means, second circuit means for supplying the reference signal to said second input circuit and including amplitude limiter means for establishing the reference signal at a constant amplitude of at least double the amplitude of the signals to be tested, a cathoderay tube having a viewing screen and further having first and second deflection means for deiiecting a cathode-ray beam in the tube across said viewing screen in mutually perpendicular directions, a rst output circuit coupled to said rst detector means for deriving a plurality of control signals therefrom each having an amplitude corresponding to the amplitude of corresponding ones of the signals to be tested and to the phase displacement of each such signal from the in-phase component of the reference signal, a second output circuit coupled to said second detector means for deriving a further plurality of control signals therefrom each having an amplitude corresponding to the amplitude of corresponding ones of the signals to be tested and to the phase displacement of each such signal from the phase-quadrature component of the reference signal, means for impressing said inst-mentioned plurality of control signals on said rst deection means of said cathode-ray tube and means for impressing said further plurality of control signals on said second deflection means of said cathode-ray tube.

3. Apparatus for indicating the amplitude of a signal to be tested and the phase of such a signal with respect to a reference signal of like frequency, said apparatus including in combination, irst and second electron discharge devices each including an anode, a cathode and a control electrode; a first input circuit for impressing the signal to be tested on the respective control electrodes of said first and second discharge devices; a second input circuit for impressing an in-phase component of the reference signal on said cathode of said rst device and including a phase-quadrature network for impressing a phase-quadrature component of the reference signal on said cathode of said second discharge device; means for applying a bias potential between the respective control electrodes and cathodes of said first and second devices to cause said devices to operate as half-wave rectiers to the reference signal components applied thereto; a cath= ode-ray tube having a viewing screen and further having first and second dellection means for deflecting a cathoderay beam in the tube across said screen in mutually per'- pendicular directions, a rst output circuit coupled to the anode of said first device for impressing on said iir'st deection means a first control signal having' an' amplitude corresponding to the amplitude of the signal to be tested and to the phase displacement of such signal from the inphase component of the reference signal; and a second output circuit coupled to the anode of said second device for impressing on said second deflection means a second control signal having an amplitude corresponding to the amplitude of the signal to be tested and to the phase displacement of such signal from the phase-quadrature component of the reference signal.

4. Apparatus for indicating the amplitude of a signal to be tested and the phase of such a signal with respect to a reference signal of at least double the amplitude thereof and of like frequency, said apparatus including in combination, rst and second pairs of electron discharge devices, with each of said devices including an anode, a cathode and a control electrode; a iirst input circuit for impressing the signal to be tested on the respective control electrodes of said rst and second pairs of devices in like phase; a second input circuit for impressing an in-phase component of the reference signal on the respective cathodes of said rst pair of devices in push-pull relation and including a phase-quadrature network for impressing a phasequadrature component of the reference signal on said cathodes of said second pair of devices in push-pull relation; means for applying a negative bias potential to the respective control electrodes of said devices of said iirst and second pairs to cause said devices to operate as half-wave rectiiiers to the reference signal components applied thereto; a cathode-ray tube having a viewing screen and further having rst and second pairs of deflection electrodes for deflecting a cathode-ray beam in the tube across said screen in mutually perpendicular directions; a rst pair of output circuit respectively coupled to the anodes of said iirst pair of devices for impressing on said rst pair of deection electrodes a first control signal having an amplitude corresponding to the amplitude of the signal to be tested and to the phase displacement of such signal from the in-phase component of the reference signal; and a second pair of output circuits respectively coupled to the anodes of said second pair of devices for impressing on said second pair of deiiection electrodes a second control signal having an amplitude corresponding to the amplitude of the signal to be tested and to the phase displacement of such signal from the phase-quadrature component of the reference signal.

5. Apparatus for indicating the amplitude of a signal to be tested and the phase of such a signal with respect to a reference signal of at least double the amplitude thereof and of like frequency, said apparatus including in combination, rst and second pairs of electron discharge devices, with each of said devices including an anode, a cathode and a control electrode; a first input circuit for impressing the signal to be tested on the respective control electrodes of said tirst and second pairs of devices in like phase; iirst and second phase-inverting inductive means respectively coupled between the cathodes of said irst and of said second pairs of devices and each having an intermediate point thereon connected to a point of reference potential; capacitive means coupling the cathode of one of the devices of said iirst pair to the cathode of one of said devices of said second pair and forming a resonant network with portions of said first and second inductive means; resistor means connecting said last-named cathode to said point of reference potential; a second input circuit for impressing the reference signal on said cathode of said one of the devices of said rst 'l Y Y A pair; means for applying a negative bias potential to the respective control electrodes of said devices of said first and secondpairs to cause said devices to operate `as half- Wave rectiiiers to the reference signal components applied thereto; a cathode-ray tube having a viewing screen and further having rst and second pairs of detlection electrodes for deecting a cathode-ray beam in 'the tube across said screen in mutually perpendicular directions; a first pair of output circuits respectively coupled to the anodes of said first pair of devices for impressing on said first pair of deflection electrodes a rst control signal having an amplitude corresponding to the amplitude of the signal to be tested and to the phase displacement of such signal from the reference signal; and a second pair of output circuits respectively coupled to Vthe anodes of said second pair of devices for impressing on said second pair of deection electrodes a second control signal having an amplitude corresponding to the amplitude of the signal to ybe tested and to the phase displacement of such signal from a phase-quadrature component of the reference signal.

6. Apparatus for deriving first and second control signals having respective amplitudes corresponding to the amplitude of an applied test signal and to the phase disi placements of such test signal from a like frequency and at least double amplitude reference signal and from a phase-quadrature component of such reference signal, said apparatus including in combination, irst and second pairs of electron discharge devices, with each of said devices including an anode, a cathode and a control electrode; a rst input circuit for impressing the test signal on the respective control electrodes of said iirst and second pairs of devices in like phase; first and second phase-inverting inductive means respectively coupled between the cathodes of said first and second pairs of devices and each having an intermediate point thereon connected to a point of reference potential; capacitive means coupling the cathode of one of the devices of said first pair to the cathode of one of said devices of said second pair; resistor means connecting said last-named cathode to said point of reference potential; a second input circuit for impressing the reference signal on said cathode of said one of the devices of said rst pair; means for applying a negative bias potential to the respective control electrodes of said devices of said first and second pairs to cause said devices to operate as halfwave rectiiiers; a rst pair of output circuits respectively coupled to the anodes of said iirst pair of devices for deriving the iirst control signal therefrom; anda second pair of output circuits respectively coupled to the anodes of said second pair of devices for deriving the second control signal therefrom.

7. Apparatus for deriving lirst and second control signals having respective amplitudes corresponding to the amplitude of an applied test signal and to the phase displacements of such test signal from a like frequency and at least double amplitude reference signal and from a phase-quadrature component of such reference signal, said apparatus including in combination, first and-second electron discharge devices each including an anode, a cathode and a control electrode; a iirst input circuit for impressing the test signal on the respective'control electrodes of said first and second discharge devices; first and second inductive means respectively coupled between the cathodes of said first and second devices and a point of reference potentials; capacitive means coupling the cathode of said first device to the cathode of said Ysecond device; variable resistor means connecting said cathode of said second device to said point of reference potential; a second input circuit for impressing the reference signal on said cathode of said first device; means for applying a negative bias potential to the respective control electrodes of saiddevices to cause said devices to operate as 'half-wave rectiers; a first output circuit Y 16 t coupled to said anode of said first device for deriving the first control signal therefrom; and a second output circuit coupled to the anode of said second device for deriving the second control signal therefrom. n

8. Apparatus for deriving first and second control signals having respective amplitudes corresponding to the amplitude of an applied test signal and to the phase displacements of such test signal from a like frequency reference signal and from a phase-quadrature component of such reference signal; said apparatus including in combination, lirst and second phase detectors for individually producing a signal having an amplitude licorresponding to the phase displacement of a pair of like frequency signals applied thereto and to the amplitude of at least one of the applied signals; a first input circuit connected to a point of reference potential for impressing the test signal on said rst and second phase detectors; a second input circuit connected to said point of reference potential Vfor impressing the reference signal on said first phase detector; capacitive means coupling said second Vinput circuit to said second phase detector; lirst and second inductive means respectivelyconnected from the junctions of said capacitive means with said second input circuit and with said second phase detector to said point of reference potential; variable resistor means connected from said junction of said capacitive meansrwith said second detector to said point of reference potential; and

iirst andV second output circuits respectively coupled toV said phase detectors for deriving'the first and second concomponents, and bursts of a color reference signal having a selected timing with respect to the synchronizing components and having the frequency of the Vsub-'carrier components and a selected phase relation therewith, said apparatus including in combination, .a first channel for selecting the sub-carrier components of the color television signal; a second channel for selecting the color television signal and for producing a reference signal having the phase and frequency of the reference signal bursts in response to the color television signal; said second channel inciuding a separator circuit for separating the synchronizing components from the color television signal, a delay line for delaying theseparated synchronizing components so that such components occur in time coincidence with the bursts of color reference signal,

a gated circuit responding to the delayed synchronizing frequency and phase of the color bursts, av tirst phase detector coupled to said first and second channels kfor producing a first series of control signals having individual amplitudes corresponding to the amplitudes of the chroma sub-carrier components and to the phase displacements of such components from the reference signal, a quadrature phase shifting network coupled to said second channel, a second phase detector coupled to said first channel and to said quadrature phase shifting network for producing a second series of control signals having individual amplitudes corresponding to the amplitudes of the chroma sub-carrier components and to the phase displacements of such components from a phase-quadrature component of the reference signal; .a cathode-ray reproducing tube including iirst and second deflection means for deecting a cathode-ray beam in the-tube in mutually perpendicular directions; and means for VYimpressing said first and second series of control signals modulating the sub-carrier components translated thereby by a periodic signal to vary the amplitude of such components repeatedly between zero and a predetermined maximum.

l1. The apparatus defined in claim 9 in which said second channel includes an amplitude limiter stage for limiting the amplitude of the reference signal to a constant amplitude at least double the amplitude of each of the sub-carrier components applied by said first channel to said first and second phase detectors.

12. Apparatus for indicating the frequency deviation from center frequency of an amplitude-limited frequencymodulated signal, said apparatus including in combination, a time-delay network, means for impressing the frequencymodulated signal on said network to cause said network to transform frequency variations of such signal from the center frequency into phase variations; a source of a reference frequency signal; a first modulator coupled to said source; means for impressing the frequency-modulated signal on said rst modulator to be heterodyned therein with the reference frequency signal; a second modulator coupled to said time-delay network and to said first modulator to heterodyne the phase-varying signal from said network with the signal from said first modulator to produce an output signal having the frequency of the reference signal and having phase variations with respect thereto corresponding to the frequency variations of the frequency-modulated signal; a first phase detector coupled to said reference signal source and to said second modulator for producing a first control signal having amplitude variation scorresponding to the phase variations of the output signal from said second modulator with respect to said reference signal; a quadrature phase shifting network coupled to said reference signal source; a second phase detector coupled to said quadrature phase shifting network and to said second modulator for producing a second control signal having amplitude variations corresponding to the phase variations of the output signal from said second modulator with respect to a phase-quadrature component of said reference signal; a cathode-ray reproducing tube including lirst and second deflection means for deecting a cathode-ray beam in the tube in mutually perpendicular directions; and means for impressing said rst and second series of control signals respectively on said first and second deection means.

13. Apparatus for indicating characteristics of a passive network under test, said apparatus including in combination, a signal generator for producing a standard signal of a selected frequency, means for frequency modulating the standard signal recurrently in equal discrete steps to produce a repeating series of successive signal components each of a different frequency, means for impressing such signal components on a network under test, a source of a reference frequency signal, a first modulator coupled to said source, means for impressing said repeating series of successive signals on said first modulator to cause such signals to be heterodyned by the reference frequency signal, a second modulator coupled to said first modulator, means for impressing the signals translated by the network under test on said second modulator to cause such signals to be heterodyned by signals from said rst modulator, whereby said second modulator produces a series of signal components each having the frequency of said reference signal and having respective phase displacements from said reference signal corresponding to the phaseshifting characteristics of the network under test at the respective frequencies of the signals impressed thereon, said series of signal components from said second modulator further having respective amplitudes corresponding to the attenuation of the network under test at the respective frequencies of the signal impressed thereon, a first phase detector coupled to said reference signal source and to said second modulator for producing a series of control signals having individual amplitudes corresponding to the amplitudes of said second modulator signal components and to the respective phase displacements thereof from said reference signal, a quadrature phase shifting network coupled to said reference signal source, a second phase detector coupled to said quadrature phase shifting network and to said second modulator for producing a second series of control signals having individual amplitudes corresponding to the amplitudes of said second modulator signal components and to the respective phase displacements thereof from a phase quadrature component of said reference signal, a cathode-ray reproducing tube including first and second deection means for deflecting a cathode-ray beam in the tube in mutually perpendicular directions, and means for impressing said rst and second series of control signals respectively on said rst and second deflection means.

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US2903508 *Jul 1, 1955Sep 8, 1959Rca CorpAudience survey system
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Classifications
U.S. Classification348/186, 324/88, 348/E17.4
International ClassificationH04N17/02, G01R13/20
Cooperative ClassificationH04N17/02, G01R13/208
European ClassificationG01R13/20E, H04N17/02