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Using the experience of vector oscillograph

Author: Anonymous From: www.yourpaper.net Posted: 2009-03-31 11:07:34 Read:
Abstract: I am while using MD 1721 type vector oscillograph, there is not characters that prove to find the figure in the operation instructions of instrument, It is extremely inconvenient to use, I am summarized by practice, Rescan to the figure in the manual, editor's additional remarks. Sketch its operation principle and from the method of examining besides, The differential gains the distortion and Phase place of differential distortion; measurement method. And the instrument use the points for attention and maintains.

Keyword: Vector oscillograph; The differential gains the distortion; Phase place of differential distortion; Safeguard

MD1721 type vector oscilloscope is a special instrument used for measuring the PAL color TV signal, it has dual input circuit structure, the inner scale, high brightness and special oscilloscope tube.The panel control using microprocessor control.Has the characteristics of high precision, convenient operation, it is particularly suitable for the truck, color television center and other occasions check color coding, but also suitable for video transmission system differential gain distortion, differential phase distortion parameters test.Widely used in education, scientific research, television equipment, video equipment field.

1. the working principle and the tube inner scale

The TV signal from the A channel or the B channel output to the input of the amplifier, the circuit switching and amplification is divided into two paths, one path for the chrominance signal gain control and demodulation circuit is sent to the demodulator.Another way for the TV signal, the signal is divided into two road, a road through the chroma amplifier, by an electronic switch circuit, and good synchronization signal, sent to the subcarrier lock unit; the other path through a sync separator separates the synchronization signal, and then sent to the H circuit, the -H pulse synchronization and synchronization signal.The -H pulse by monostable delay, electronic switch to phase locked circuit, used to control the synchronous signal from the chrominance signal well.While -H pulse by the RP, to the phase-locked circuit, used to synchronize the top clamp.

Subcarrier lock unit containing loop phase, quadrature demodulation, loop filter, error amplifier, voltage controlled oscillation.The output of the continuous subcarrier signal after the phase shift circuit and amplifying circuit, all the way to B-Y (U) demodulator; through a 90 degree phase shift, and by the 180 กใ phase converter control, to the R-Y (V) demodulator.The demodulator demodulates the U, V color difference signal, the low pass filter, filter the subcarrier signal, then amplified by the amplifier, and sent to the B-Y (U) deflection amplifier and R-Y (V) deflection amplifier, driving display horizontal deflection plate wave tube and the vertical deflection plates, and then display.

I in the original oscillographic tube calibration software 1~15 digital and notes (Figure 1)

1, the vertical deflection scale; phase calibration, calibration round 2; 3, 135 กใ color synchronous vector position; 4, 225 กใ burst position vector; phase scale 5, calibration round; 6, U chroma scale; 7, V chroma scales; phase calibration, calibration round 8 each pellet, 10 กใ; 9, differential phase distortion measuring scale, each big 2 กใ; 10, vector display test frame.11, applied to the calibration of measurement system for video linear distortion; 12, for the measurement of test pulse falling edge ringing distortion Peugeot; 13, color, luminance delay difference and gain the scale line; 14, subcarrier cycle scale; 15, the horizontal scale.


Fig. 1 original oscillographic tube calibration software 1~15 digital

2 self-test method

The power supply is switched on, the instrument preheating, brightness is moderate, not too bright.Adjustable horizontal and vertical displacement.The spot node in the V and U axis.Television signal generator output standard color bar signal, via a socket cable connected to the CH-A, another socket must be connected to the last 75? the terminal load (or through a cable connected to a video instrument loop input).The phase shifter, which burst into vector point of 135 กใ, 225 กใ and oscilloscope calibration the coordinate of the color of synchronous vector scale coincide, the instrument display vector measured signal as shown in figure 2B, PAL line and NTSC line of colored vector.By not PAL/ V button, V lights, to NTSC display mode is displayed, i.e. PAL and NTSC phase after the superposition display, as shown in figure 2A.By adjusting the "shifter", make the best graphics coincidence.

I in the original vector graph on the spot and the letters and notes (Figure 2)


Figure 2 shows the original vector diagram on the spot and the letters and notes that

(YL: white, yellow, 167 กใ), and (CY: cyan, 283.5 กใ), and (G: green, 240.5 กใ), and (MG: purple, 60.5 กใ), and (R: red, 103.5 กใ), and (B: blue, 347 กใ),, black.

3 differential gain distortion of DG and differential phase distortion measurement of DP

Will the ladder wave superimposed on 280mv subcarrier as the measured signal, the panel of the CH-A socket cable to the machine.Synchronous reference: reference INI lights; channel selection: A channel CHA lights; color: 75%; PAL/ V: PAL; gain selection: a variable gain, the red ON lights.

Adjust the phase shifter, the subcarrier vector point to U axis regulation left, gain the spot into the figure eight big box, you can also read the differential gain and differential phase distortion.

4 conclusion

I have two experience in using vector oscillograph: one is because it is used to test the high frequency signal instruments, attention should be paid to it in the test, input port vector oscillograph don't have to be connected to the 75? the terminal load, otherwise no display; two is because it with ordinary oscilloscope, waveform display but not light display therefore, the spot, not transfer too bright, so as not to burn the fluorescent screen.In addition, the instrument is in use, should avoid excessive vibration, should not be placed around the high fever, electric, magnetic device.


References:
[1] Hefei Anshi science and Technology Development Co., Ltd., MD1721 vector oscillograph user manual
.
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