JPS606911Y2 - Reversal phenomenon measuring device - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an inversion phenomenon setting device.

When recording a video signal with FM modulation, if overmodulation occurs and the carrier wave of the FM signal is swung to a higher frequency than necessary, in a general VTR, the carrier wave will be higher on the white side, reducing recording efficiency and causing problems during playback. Since the carrier wave level is lowered, it becomes lower than the lower sideband level, resulting in a so-called inversion phenomenon.

Therefore, the standard VTR equipped with the magnetic head under test
By applying a test signal to the recording/playback device under test and observing the occurrence of the reversal phenomenon, it is possible to determine whether the supply magnetic head is good or bad.

In the conventional method, a measurer observes a test pattern displayed on a monitor, and so-called human error is unavoidable.

The present invention aims to provide a device that can quantitatively measure the reversal phenomenon caused by a test recording/playback device, mainly in order to determine the quality of the magnetic head.

Next, the present invention will be explained based on FIG. 1, which shows an embodiment thereof in a block diagram together with a test recording/playback device.

The test recording/reproducing device (hereinafter referred to as "test VTR") 1 is composed of a test magnetic head 1a and a standard deck 1b when determining the quality of the magnetic head. It is constructed so that it can be attached and detached each time for inspection.

Reference numeral 2 denotes a measuring device according to the present invention, which includes a signal supply section 3 for applying a test signal to the VTR under test, and a signal processing section 4 for processing a reproduced signal from the VTR under test.

The signal supply unit 3 includes a synchronization signal generation circuit 5, a test signal generation circuit 6 that generates a test signal in synchronization with the synchronization signal from the circuit, and mixes the test signal and the synchronization signal to derive a video signal. and a video amplifier 8 for amplifying this video signal in order to record it on the VTR 1 under test.

The test signal has black and white information in the horizontal scanning line direction displayed on the monitor screen as shown in Figure 2, for example, and the video signal for one line is as shown in Figure 3 A. It is.

Stripe B with four hatchings in Figure 2
□ to B4 indicate black information, and white stripes W1 to W indicate white information.

The signal processing unit 4 is supplied with a video amplifier 9 that inputs the reproduced signal from the VTR 1 under test, a synchronization separation circuit 10, and the output from the video amplifier 9 as shown in FIG. An inverting circuit 11 that inverts the inversion, inputs the signal from this inverting circuit (see Fig. 3), and the video signal from the video amplifier 8 (see Fig. 3A), and generates a signal corresponding to the difference between them (see Fig. 3A).
It is provided with a comparison circuit 12 for deriving the phase difference component (2) in FIG. 3, and means 13 for quantitatively displaying this phase difference component.

Note that in order to maintain the synchronization relationship between the two signals to be compared, a reproduced synchronization signal from the synchronization separation circuit 10 is applied to the synchronization signal generation circuit 5.

The reversal phenomenon is reported in Magazine 1 Radio Science 1 April 1987 issue pp. 1
As described in 60-161, this occurs when the video signal suddenly rises from black to white.

FIG. 4 is a waveform diagram for explaining the reversal phenomenon.

A video signal that changes rapidly from black to white, as shown in (a), is
M modulation results in a signal like that shown in (b).

When this signal is reproduced, if the characteristics of the head are poor, the waveform will be distorted as shown in (C), and if this signal is directly applied to the transmitter, the zero point will be lost and the demodulated signal will be as shown in (d).
It becomes like this.

In other words, what should originally be white becomes black.

Compared to signals (a) and (b), the timing of white is delayed, and both signals (a)
), (d) there will be a phase difference.

Therefore, when the magnetic head under test is a good product and no so-called inversion phenomenon occurs, the output of the video amplifier 8 and the output of the inversion circuit 11 are in phase, and the output of the comparator circuit 12 does not appear, but the magnetic head under test When the frequency characteristics of the oscillator are inferior to those of the standard one, an inversion phenomenon occurs over the period τ shown in FIG. 3, for example, and the amount of inversion is displayed accordingly.

When the amount of reversal exceeds a permissible value, the magnetic head under test is treated as a defective product.

The device of the present invention is a test VTR equipped with a test magnetic head.
A test signal is applied to and recorded on the test signal, and the phase of the test signal is compared with the phase-inverted version of the reproduced raw signal from the test VTR, and the error output is quantitatively displayed. It is practical because it is possible to quantitatively determine the quality of the product through the reversal phenomenon that is quantitatively displayed in this way.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the device of the present invention, FIG. 2 shows an image of a test signal on a screen, and FIG. 3 shows a waveform diagram of the main part of FIG. 1. FIG. 4 is a waveform diagram for explaining the reversal phenomenon. 6... Test signal generation circuit, 1... Recording/playback device under test, 8... Test signal supply circuit (video amplifier), 9... Playback signal Input circuit (video amplifier), 11... Phase inversion circuit, 12...
...Comparison circuit, 13...Quantitative display means.

Claims (1)

[Scope of utility model registration request] A circuit that generates a test signal having black and white information in the horizontal scanning line direction, a circuit that supplies the test signal from the generation circuit to the recording/playback device under test, and a circuit that inputs the playback signal from the recording/playback device. An inversion phenomenon measuring device, comprising: a circuit that inputs the test signal and the reproduced signal and derives a phase difference component between the two signals; and means for quantitatively displaying the phase difference component.