SU754699A1 - Method of measuring recurring interference in tv signal - Google Patents

Description

The invention relates to television and can be used to measure the effective value of interference and the signal-to-interference ratio in the broadcast television (TV) path at the output of various parts of it, both during the transmission of a TV program, and in its absence, during the transmission of special measurement signals.

There is a method of measuring periodic noise in a television signal, based on the formation of a sequence of sampling pulses synchronous with television clock pulses, their amplitude modulation by a television signal with interference and measuring the effective value of the received signal [1].

However, the measurement of periodic interference in a known manner has insufficient accuracy.

The purpose of the invention is to improve the measurement accuracy.

To do this, in the method of measuring periodic noise in a television signal, based on the formation of a sequence of sampling pulses synchronous with television clock pulses, their amplitude modulation by television

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signal with interference and measurement of the effective value of the received signal, during the formation of sampling pulses produce their phase modulation for a given random law, for example, uniform, with an amplitude of more than half the period of the lowest frequency of the measured interference.

FIG. 1 shows the structural electrical circuit of the device that implements the proposed method; in fig. 2 - we are a diagram explaining the essence of the method of measurement.

A device for implementing the proposed method comprises a preprocessing unit 1, a video signal source 2, a sampler 3, a discrete ¹⁵ value processing block 4, an indicator 5, a selector block 6 and row selector, a sampling pulse generator 7, a random voltage generator 8.

The method is carried out as follows.

From the full video signal containing periodic noise, in the pre-processing unit 1, a temporary selection of the line (or lines) free

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from the image signal, pre-amplification of the portion of the video signal containing periodic noise. In the same block, an additional search can be carried out (automatically or non-automatically) for a frequency band in the region of the television spectrum in which periodic noise is concentrated. This is done to separate the periodic noise arising in the TV path from the fluctuation noise (AF). To this end, the signal from the output of the time selection circuit of the preprocessing block 1 is supplied, for example, to the inputs of successively switched bandpass filters of the same block, alternately allocating different parts of the spectrum in the video frequency band. The signal received at the output of the filter is detected and compared in span with a reference voltage equal to the minimum amplitude of the periodic disturbance. The presence of periodic interference in a certain part of the spectrum is indicated by the operation of the comparison circuit.

At this, the “search” for interference ends, and the voltage from the output of the corresponding filter of the pre-processing unit 1 is fed to the input of the sampler (modulator) 3, to another input of which the sampling pulses are received, the duration of which is about 5-10 ns and which are formed in the driver 7 sampling pulses.

In the process of their formation, the phase modulation of each of the pulses relative to its average position (Fig. 2 a) is carried out with a random voltage generated in the random voltage generator 8. The interval of time deviation of these pulses from their average position should be greater than the half-period of the measured periodic interference of the lowest frequency. It can be shown, for example, that the distribution of the instantaneous values of the modulating random voltage should be uniform.

Thus, at the output of discretization unit 3, a sequence of pulses is formed, modulated in amplitude according to a random law and having uncorrelated discrete values. By processing this set of discrete values by analog method or digital by one of the known algorithms, one can find the effective value of the envelope of the amplitudes of these pulses, approaching the effective value of the periodic noise with an infinite increase in the number of discrete values.

The indicator 5 is calibrated in units of the magnitude of interference, taking into account the accepted method of its rationing.

The described device can serve as part of a device for measuring the ratio of the signal swing to the swing of the periodic noise, and the signal swing can be measured by one of the known methods.

Not exclude a variant of the device in which the generator 8 is missing, and instead of it is turned on between the discretization unit 3 and the processing unit of discrete values 4, a delay line with a controlled random voltage delay. In this case, the phase of interference (Fig. 2 6) changes randomly with respect to its average temporal position.

In the case of quantization noise measurement, the preprocessing unit 1 may contain a scheme for temporal selection of a certain part of the video signal, as well as a frequency selection scheme for the test signal using an appropriate blocking filter whose amplitude-frequency characteristic (AFC) corresponds to the spectral density used for measuring the test signal.

If it is used as a package of sinusoidal oscillations, then the process of further measurements does not change. In this case, the interval of random movement of the sampling pulse relative to the measured noise should be no less than the period of the test sinusoidal signal.

Using the proposed method, it is possible to create a meter that has several modes of operation, according to which an automatic measurement is carried out in the process of transmitting an FP program, periodic noise, quantization noise, as well as periodically non-stationary noise in time with minimal changes in the meter circuit corresponding to each of these modes .

Claims (1)

Claim A method of measuring periodic noise in a television signal, based on the formation of a sequence of sampling pulses synchronous with television clock pulses, their amplitude modulation by a television signal with interference, and measuring the effective value of the received signal, characterized by the formation of sampling pulses in order to improve measurement accuracy phase modulation for a given random law, for example, a uniform one with an amplitude of more than half the period is the lowest the frequency of the measured interference.