JPH0326958B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring television ghost waves.

In recent cities, the number of buildings such as skyscrapers has increased dramatically, and ghost interference due to building reflections has become a problem. The difficulty in viewing images with ghost disturbances is related to the intensity and phase of the ghost waves, and in order to solve the second problem, it is necessary to accurately measure these. In addition, in the synchronous broadcasting system that is being considered as a way to resolve the shortage of channels for television relay, the frequency difference between multiple relay stations must be kept within 0.05Hz, so equipment that measures this frequency difference is required. It is urgently needed.

Figure 1 shows an example of a conventional ghost wave measuring device.
is a synchronous detection demodulator for in-phase components, 2 is a synchronous detection demodulator for quadrature components, 3 is a 90-degree phase shifter, 4 is a carrier extraction circuit, 5 is a down converter, 6 is a high-speed A/D converter for in-phase components, 7 is a high-speed A/D converter for orthogonal components, 8 is a high-speed memory for in-phase components, 9 is a high-speed memory for orthogonal components, and 10 is a processing circuit. Conventional methods use the leading edge of the vertical synchronization pulse of the video signal, so if there is waveform distortion such as smear or overshoot, accurate measurements cannot be made. Furthermore, since measured values usually include errors due to noise, averaging must be performed several dozen times to obtain highly accurate values. However, 1
Since measurement can be performed only once in a field period, a long time is required for averaging processing, making it impossible to measure fast changes in ghost waves. Furthermore, as shown in FIG. 1, the configuration of the conventional method requires a high-speed A/D converter for video and a high-speed memory, making the circuit complex and expensive.

The present invention uses vertical synchronization pulses and equalization pulses that are repeatedly sent during the vertical retrace period of a video signal, samples the peak values of the desired wave and ghost wave pulses, performs A/D conversion, and performs arithmetic processing. By obtaining a plurality of measured values within one field and averaging them, highly accurate values can be obtained in a short time. Furthermore, it does not require a high-speed A/D converter for video or high-speed memory,
This method measures ghost waves with a simple circuit configuration.

FIG. 2 shows an embodiment of the present invention, in which circuits 1 to 5 are the same as those in FIG. The /D converter 14 is an arithmetic circuit that processes the digitized signal.

The television radio wave containing the ghost wave is turned into a baseband video signal by the in-phase component synchronous detection demodulator 1. At the same time, the orthogonal component synchronous detection demodulator 2 performs detection with a phase shift of 90 degrees to obtain the orthogonal component of the video signal. This situation will be explained using a vector diagram. FIG. 3 shows a vector diagram showing the relationship between desired waves and ghost waves. Let the intensity of the desired wave 15 be D, the intensity of the ghost wave 16 be U, and the phase difference between them be θ. The in-phase component video waveform, that is, the output of the synchronous detection demodulator 1, is the waveform of the desired wave 15 and the ghost wave 16 viewed from the detection axis A, and the orthogonal component video waveform, ie, the output of the synchronous detection demodulator 2, is the waveform of the desired wave 15 and the ghost wave 16 viewed from the detection axis B. It becomes a waveform. These waveforms are
As shown in the figure. Figure 4 shows one pulse waveform of the vertical blanking period in the video signal, 17 and 1.
9 is a desired wave, and 18 and 20 are ghost waves. These amplitude voltages are collected by the sampling circuit 11
A to 11D and the sampling pulse generation circuit 12 are held by A/D converters 13A to 13D.
This situation will be explained using the waveform diagram shown in FIG. First, the sampling pulse generation circuit 12 generates a sampling pulse when at least one of the video waveforms exceeds the threshold value 23. 21 is a sampling pulse of the desired wave, which is generated when the in-phase component of the desired wave exceeds the threshold value 23; 22 is a sampling pulse of the ghost wave, which is generated when the in-phase component 18 or the quadrature component 20 of the ghost wave exceeds the threshold value 23. The sampling pulse 21 created in this way causes the sampling circuit 11A to
and 11C holds the amplitude voltage of the desired wave. Furthermore, due to the sampling pulse amplitude 22, the sampling circuits 11B and 11D maintain the amplitude voltage of the ghost wave. This amplitude voltage is applied to the A/D converter 1
Digitized by 3A to 13D, arithmetic circuit 1
4, the characteristics of the ghost wave are calculated according to the following principle.

The amplitude UA of the in-phase component 18 of the ghost wave is the third
From the vector relationship in the figure, it is expressed as UA=Ucosθ. Also, the amplitude UB of the orthogonal component 20 of the ghost wave
is expressed as UB=Usinθ. From these relationships,
The phase θ of the ghost wave is θ=tan−1 (UB/UA)
It can be found from In addition, the intensity ratio D/U of the desired wave and ghost wave is D/U=DA/√2+
It can be obtained from UB2. Furthermore, if the frequencies of the desired wave and the ghost wave are different, it can be determined as a time change in phase θ, and Δf=dθ/αt. The delay time of the ghost wave is the time interval T between the sampling pulse 21 and the sampling pulse 22.

The arithmetic circuit 14 performs the above-mentioned processing on the vertical synchronizing pulses and equalization pulses repeatedly sent during the vertical retrace period, and performs averaging processing to obtain highly accurate measured values. Among the vertical synchronization pulses and equalization pulses, there are 17 pulses that can be used with this device, but if you use all of them, it will be faster than conventional devices.
Measurements can be made in 1/17th of an hour. Furthermore, since the measurement accuracy is proportional to the square root of the number of averages, it is possible to obtain four times the accuracy of the conventional device for the same measurement time.

As described above, in the present invention, since multiple pulses in the vertical retrace period of the video signal are used for measurement, highly accurate measurements can be made for each field period (approximately 1/60). It is possible to determine the degree of ghost interference, flutter interference caused by airplanes, and ghost interference in interference areas in synchronous broadcasting. Furthermore, in the present invention, since the pulse amplitude is sampled and then subjected to arithmetic processing, a measuring instrument can be realized with a simple circuit configuration without requiring a high-speed A/D converter for video or a high-speed memory. Furthermore, by combining the present invention with a ghost removal device, it is possible to reduce ghost disturbances with fast phase fluctuations.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional ghost measurement device, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is a block diagram showing the relationship between desired waves and ghost waves, and Fig. 4 shows the operation. It is a waveform diagram for explanation. 1... Synchronous detection demodulator for in-phase component, 2... Synchronous detection demodulator for quadrature component, 3... 90 degree phase shifter, 4...
...Carrier extraction circuit, 5... Down converter, 6
...High-speed A/D converter for in-phase components, 7... High-speed A/D converter for orthogonal components, 8... High-speed memory for in-phase components, 9... High-speed memory for orthogonal components, 10... Processing circuit, 11A ...Sampling circuit for the in-phase component of the desired wave, 11B...Sampling circuit for the in-phase component of the ghost wave, 11C...Sampling circuit for the orthogonal component of the desired wave, 11D...Sampling circuit for the orthogonal component of the ghost wave, 12... Sampling pulse generation circuit, 13A...A/D converter for the in-phase component of the desired wave, 13B...A/D converter for the in-phase component of the ghost wave, 13C...A/D converter for the orthogonal component of the desired wave, 13D...A/D converter for orthogonal component of ghost wave, 14... Arithmetic circuit, 15... Vector of desired wave, 16... Vector of ghost wave, 17... In-phase component of desired wave, 18... Ghost In-phase component of the wave, 19...Orthogonal component of the desired wave, 2
0...Orthogonal component of ghost wave, 21...Sampling pulse of desired wave, 22...Sampling pulse of ghost wave, 23...Threshold value.

Claims (1)

[Claims] 1 In an apparatus for analyzing ghost waves of television, circuits 1 to 5 synchronously detect television radio waves and demodulate in-phase component video signals and quadrature component video signals, and pulse amplitude voltages and pulse amplitudes of in-phase and quadrature components of desired waves. A sampling circuit 11 that holds the pulse amplitude voltages of the in-phase and quadrature components of the ghost wave.
A to 11D, a sampling pulse generation circuit 12 for driving the sampling circuit, A/D conversion circuits 13A to 13D for converting the output voltage of the sampling circuit into a digital value, and
It has an arithmetic circuit 14 that calculates ghost wave characteristics from the values obtained by the D conversion circuit, and calculates the pulse amplitude voltage of the equalization pulse and the vertical synchronization pulse, which are inserted in the vertical blanking period of the video signal. A ghost wave measuring device characterized by measuring characteristics of ghost waves with high accuracy in a short time by measuring and averaging processing.