JPS61193577A - Disturbing wave detecting device - Google Patents

Abstract

PURPOSE:To classify and detect plural disturbing waves, in which frequencies exist adjancently together in television signals, without mutual interference by using a narrow-band band-pass filter in the signals obtained from the television signals. CONSTITUTION:A frequency converting circuit 14 has a function of adjusting center frequency of the crystal filter 16 to coincide with that of the disturbing wave, and selects the oscillating frequency of the oscillator 15 to enable this operation. The crystal filter constitutes the narrow-band band-pass filter art 7 and the band of this filter is set in order to extract a certain wave of present disturbing waves. After converting the level by the log amplifier 17, a peak value sample hold circuit 18 sample-holds and outputs the level maximum value of disturbing wave with the horizontal driving signal 4 during this duration to detect the level of the disturbing wave by line cycle at a high speed. Thus the disturbing wave of the television signal can be detected at high sensitivity and high selectivity, which can be applied for fields such as the detection of the sporadic E-layer disturbing wave by making use of its operation.

Description

[Detailed Description of the Invention] (Technical Field) This invention deals with the problem in which frequency-modulated or phase-modulated radio waves propagate abnormally through the Svoradivuk E layer and mix into the video signal band of television broadcast waves, resulting in interference waves. case,
The aim is to detect these interference waves with high sensitivity.

(Prior Art) Conventionally, in order to remove this type of interference wave mixed into received television broadcast waves, a notch filter having a very narrow stopband corresponding to the frequency of the interference wave has been used, for example. The applicant filed an application for the configuration of one example in 1973.
9-5136 "Television Signal Receiving Apparatus", the block diagram is shown in FIG. 6.

In the configuration shown in FIG. 6, the constituent blocks for removing interference waves are a bandpass filter 21, a notch filter 22, a synchronous detection circuit 23, and a carrier regeneration circuit 24. Other constituent blocks further remove the frequency band of the television signal. This is to accomplish the purpose of converting the frequency and automatically following the frequency fluctuation of the interference wave to be removed while keeping the rejection frequency of the notch filter 22 fixed. However, the automatic tracking ability of the lever plays an important role in this type of interference wave removal device.

In the case of the device of this invention, for automatic tracking control, the beat detection circuit 29 detects residual interference wave components from the output television signal from which interference waves have been removed by the notch filter 22, and the local oscillator 26 is oscillated based on the detected value. It controls the frequency. Therefore, it is desired that the beat detection circuit 29 has a high detection sensitivity. Specifically, for example, the beat detection circuit 29 is designed to detect beats caused by interference waves during vertical retrace or horizontal retrace periods that do not include an image signal in a television signal. There is.

Furthermore, the present applicant has previously filed a patent application filed in 1983 for another conventional configuration for removing interference waves when frequency modulated (land) interference waves are mixed into television amplitude modulation (AM) broadcast waves.
This is shown in a block diagram in FIG. 7 with reference to the specification of No. 279768 "Interference wave removal device".

Also in Fig. 7, the configuration block for interference wave removal is F.
M demodulation circuit 32, FM modulation circuit 33, carrier regeneration circuit 3
4. The level adjustment circuit 35, the delay circuit 36, and the subtraction circuit 37 focus on the fact that by once demodulating the FM interference wave and then re-modulating it, it is possible to utilize the degree of FM improvement and extract pure collective interference wave components. This is a great invention.

However, in this patent application, the output signal of the interference wave detection circuit 42 is used to control the local oscillator 44 to convert the frequency of the interference wave.
While keeping the center frequency of the modulation circuit 33 fixed, it is possible to automatically remove interference waves at any frequency position in the television signal or whose frequency fluctuates, and residual interference waves used at this time are detected. Interference wave detection circuit 4 for
2 is also desired to have high sensitivity.

Therefore, in the interference wave detection circuit 42 of FIG. 7, in order to detect the residual interference wave component with high sensitivity, the output television signal of the subtraction circuit 37 is branched, and an IH delay circuit (H is one horizontal scanning period) is connected. The configuration is such that the comb filter used removes the luminance signal component in the television signal.

(Problem) In the first and second conventional examples described above, the objective of detecting the interference wave component with a certain degree of sensitivity has been achieved, but in the first conventional example (Fig. 6), ,
The method of extracting beats caused by interfering waves during the vertical or horizontal retrace interval itself has imperfections, and in the second conventional example (Fig. The disadvantages are that the removal of color signal components is incomplete, and the detection sensitivity deteriorates when there is no correlation between horizontal scanning lines (correlation between lines) in the video content.

(Summary of the Invention) An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to eliminate interference waves contained in high-frequency, intermediate-frequency, or baseband television signals with high sensitivity and even in close proximity with a simple configuration. An object of the present invention is to provide an interference wave detection device that can detect a plurality of interference waves existing in the same area separately without affecting each other.

In other words, the interference wave detection device of the present invention includes a soft gate circuit that allows the television signal to pass during the horizontal or vertical retrace period of the television signal, and a soft gate circuit that is arranged before or after the soft gate circuit and that detects the interference wave at each horizontal scanning frequency. To remove a brightness signal component of a television signal having a frequency spectrum distribution (including at least a rhombic filter circuit, and to remove a high frequency or intermediate frequency or A narrowband bandpass filter circuit is used to separate a plurality of interference waves whose frequencies are close to each other in a signal obtained through a baseband television signal without affecting each other. This feature is characterized in that it can be detected.

(for production) FIG. 1 shows the basic configuration of the interference wave detection device of the present invention.

In the figure, a television signal (intermediate frequency signal) containing interference waves is input to the input end. Comb filter section 1
A signal 2 in which the video carrier and luminance signal components have been suppressed is taken out on the output side. Here, it is assumed that the color signal has been removed in advance by a band rejection filter, and that no color signal is output to the output side of the comb filter section 1. next,
In the Gaussian waveform gate section 3, horizontal drive signal (HD) 4
Signal 2 is a time-domain Gaussian waveform gate signal created from
gate. In addition, from the vertical drive signal (VD) 5,
A signal is generated that removes signal components during the horizontal scanning period that cannot be suppressed by the comb filter section 1 during the vertical retrace period. Finally, the narrowband bandpass filter section 7 extracts one wave of interest from among the plurality of interference waves.

Next, the relationship between the time domain gate waveform and the frequency spectrum of the gated signal will be explained using FIG. First, if the interference wave is a single sine wave as shown on the left side of FIG. 2(a), its frequency spectrum will be as shown on the right side of FIG. 2(a). If the gate pulse is a rectangular wave (conventional extraction pulse waveform) like the time axis waveform on the left side of Figure 2(b), the frequency spectrum of the gate pulse will be as shown on the right side of Figure 2(b). Then, the frequency spectrum after gating the single sine wave becomes a convolution of both Figure 2 (a) and (b), as shown on the right side of Figure 2 (c), and the frequency band becomes wider. . In this case, if two interference waves exist very close to each other in terms of frequency, their frequency spectra overlap with each other, making it impossible to clearly distinguish them.

To improve this, consider the following two points. One of these is to suppress harmonics in the frequency spectrum, and the other is to suppress the spread of the frequency spectrum.

The shape of the frequency spectrum after gating a single sine wave is equal to the shape of the frequency spectrum of the gate pulse, so if you gate with a gate pulse that has a frequency spectrum with less spread of harmonics, the harmonics of the spectrum after gate will be reduced. The spread can be suppressed. In the apparatus of the present invention, a gate pulse having a characteristic that can be expressed as a Gaussian waveform in the time axis direction, for example, as shown on the left side of FIG. 2(d), is employed as the gate pulse. Regarding the Gaussian waveform gate pulse, the spread of its frequency spectrum is small as shown on the right side of FIG. 2(d). Therefore, the harmonics of the frequency spectrum are much smaller than those of a rectangular gate pulse, and the selectivity to adjacent interference waves can be increased.

Next, consider the spread of the frequency spectrum. When the gate pulse is a rectangular wave, paying attention to the first null point f+ of the frequency spectrum (see the right side of Figure 2 (b)), the value f,
is proportional to the reciprocal of the gate pulse duration τ (see left side of FIG. 2(b)). That is, if the duration of the gate pulse is increased, the spread of the frequency spectrum will be narrowed. This also applies to the case of a Gaussian waveform gate pulse.

Therefore, in order to narrow the spread of the spectrum,
People try to make the gate pulse width as wide as possible, but since the horizontal and vertical blanking periods of a television signal each have a fixed length, if the gate pulse width is widened beyond that period, , video periods other than the horizontal or vertical retrace periods are also gated, significantly impairing detection sensitivity.

Therefore, in the device of the present invention, a comb filter section is provided before or after the gate section, and this filter section suppresses all video signals (luminance signal components) including the synchronization period. The comb filter used for this purpose can be easily constructed using an IH delay circuit as is well known (see FIG. 3). In this example, since the comb filter is used in the intermediate frequency band, the frequency fC of the video carrier is
When a subtraction circuit is used as the addition or subtraction circuit 11 shown in the figure, fc = nfh (n: positive integer, fh: horizontal scanning frequency), and when an addition circuit is used, fe-(2n +1)
Just choose fh/2.

By employing the above comb filter, there is complete line-to-line correlation during the horizontal or vertical blanking period, so only uncorrelated interference waves can be left behind.
Most other video signals can also be suppressed, so even if the width of the gate pulse is slightly widened, the problem of video signal leakage does not occur. Thus, by using a Gaussian waveform gate circuit whose gate time is set to the horizontal or vertical retrace period in combination with a comb filter, it is possible to realize interference wave detection with high sensitivity and high selectivity.

Note that the gate circuit used in the present invention is not limited to the Gaussian waveform gate circuit described above, but also a sine square wave (sin"X) gate circuit.
So-called soft gate circuits with characteristics such as (sin be able to.

(Example) FIG. 3 shows an example of the apparatus of the present invention. In the figure, the input is a television signal (intermediate frequency signal) mixed with interference waves, and is guided to a distributor 8. The signal delayed by IH by the IH delay circuit 10 and the signal passed through the attenuator 9 are combined by an addition or subtraction circuit 11 to suppress particularly the video signal component of the television signal. The above are the parts constituting the comb filter section 1. As a result, the video carrier is suppressed by 45 dB or more. When FM broadcast waves are interfering waves, their maximum frequency deviation is as wide as ±75kHz, so even if some of the interfering waves are removed by a comb filter, the spectrum is insufficient to detect the level of the interfering waves. remain. At this time, if a frequency around 30 MH2 is selected as the intermediate frequency, a conventional glass delay line can be used as the IH delay circuit 10.

Next, a gate 12 gates the horizontal retrace period of the television signal. At this time, as mentioned earlier, widening the gate width will reduce the spread of the spectrum, but if it gets into the video signal, it will be affected by the video content. However, in this device, since the video signal component is suppressed by the comb filter section 1, the gate width can be made wider. Based on the horizontal drive signal (HD) 4, the waveform shaping circuit 13 generates a half width of 1.
It is possible to create a Gaussian waveform gate signal that suppresses the spectrum of 200 kHz or more from the center to 70 dB or less in 2 μsec. From the channel plan of the PM broadcast waves, it is thought that the frequency interval of the interference waves caused by the FM broadcast waves and passed through the Sporadic 8 layer is 200 kHz or more, so the above-mentioned Gaussian waveform gate signal is practically sufficient.

Although the base of the gate signal temporally enters the region of the video signal, the effect of the comb filter section 1 hardly affects the detection sensitivity.

In addition, since there is generally no correlation between lines in text multiplex signals, program control signals, etc. multiplexed with television signals, a control signal is created from the vertical drive signal (VD) 5 to prevent gating from occurring during this period. .

Furthermore, although it is statistically unlikely that the video signal is line uncorrelated, there remains a possibility that the effect of the comb filter section 1 will be lost when the video content is switched. In order to eliminate this, it is necessary to provide a circuit (not shown) in the comb filter section 1 to detect the level difference between the lines, and a circuit to temporarily stop detecting the interference wave if it is determined that there is no correlation. good.

The frequency conversion circuit 14 is for adjusting the center frequency of the crystal filter 16 to match the center frequency of the interfering wave, and selects the oscillation frequency of the oscillator 15 to make this possible. The crystal filter 16 constitutes the narrowband bandpass filter section 7, and the band of this filter is selected so as to extract one wave among the interference waves. A logarithmic (Log) amplifier 17 converts the level, and a peak value sample and hold circuit 18 uses a horizontal drive signal (HD) 4 to sample and hold the maximum level of the interference wave during this period and output it at high speed with a line period. to detect the level of interference waves.

FIG. 4 shows another example of the configuration of the comb filter section l shown in FIG. 3, and FIG. Another embodiment of the device of the present invention has been shown in which a plurality of filter sections are provided and the center frequencies of the respective filter sections are made different to simultaneously detect a plurality of interference waves.

4. Effects of the Invention The measurement results for the embodiment shown in FIG. 3 detailed above are shown in FIG. 8. This figure shows that the desired wave is a television broadcast wave,
In this, the FM modulated wave (1kHz 30% modulation) of the interference wave 1
It shows the detection level relative to the OU ratio (desired wave level/interfering wave level) when waves are mixed. In the figure, Δf indicates the interference wave frequency based on the video carrier of the desired wave. From the figure, the frequency of the interference wave is 50kHz from the video carrier.
It has been found that even when the frequency is very close to z, it is possible to detect a DU ratio of up to 40 dB, and when the frequency is 150 kHz or more away, a DI ratio of up to 60 dB can be detected.

Further, FIG. 9 shows the detection level when the frequency of the interference wave is changed, that is, the selectivity characteristic of the detection circuit. According to this figure, a characteristic of -40 dB or less is obtained at frequencies above 200 kHz. Therefore, when another interference wave exists at a distance of 200 kHz, if its DU ratio is 20 dB or more, the detection sensitivity of the target interference wave can be ensured up to 60 dB in terms of DU ratio.

As described above, in the device of the present invention, when gating the horizontal or vertical retrace period, the temporal waveform of the gate signal is set to a Gaussian waveform to suppress the spread of the frequency spectrum, and at the same time, a comb filter is also used. ,
Not only can the gate time width of the gate signal be widened, but also the selectivity to multiple adjacent interference waves can be increased, and the sensitivity is also high.

This invention has the ability to detect interference waves in television signals with high sensitivity and high selectivity, and therefore, the present invention utilizes this to be used in fields such as detection of sporadic 8 layer interference waves. suitable for. It can also be applied to high-sensitivity detection of unnecessary broadcast waves in offset beat disturbances, which pose problems in station placement plans.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic configuration of the interference wave detection device of the present invention, and Fig. 2 is a diagram showing the relationship between the time axis waveform and its frequency spectrum to explain the action of the gate pulse used in the present invention. where (a) is a single sine wave disturbance wave, (b) is a conventional square wave gate pulse, (c) is the state after the single sine wave is gated by a square wave, and (d) is according to the present invention. Gaussian waveform gate pulse, (e
) are diagrams showing the states after gating by Gaussian waveform gate pulses, FIG. 3 is a block diagram showing the configuration of one embodiment of the device of the present invention, and FIG. 4 is a diagram of another comb filter used in the present invention. A block diagram showing an embodiment; FIG. 5 is a block diagram showing another embodiment of the present invention that simultaneously detects a plurality of interference waves; FIGS. 6 and 7 show the first and second conventional examples, respectively. 8 and 9 are diagrams showing measurement results for explaining the present invention in detail,
FIG. 8 is a diagram showing the OU ratio versus detection level, and FIG. 9 is a diagram showing the detection circuit selectivity characteristic. 1...-Comb filter section 2--Output from the comb-shaped filter section 3--Gaussian waveform gate section 4--Horizontal drive signal (HD) 5--Vertical drive signal (VD) 6--Gaussian waveform Output from gate section Narrowband band pass filter section 8-Distributor 9-Attenuator 10-[Delay circuit 11...-Addition or subtraction circuit 12-Gate 13-Waveform shaping circuit 14-
- Frequency conversion circuit 15 - Oscillator 16 - Crystal filter 17 - Log amplifier 18 - Peak value sample hold circuit 21.27.
41-Band pass filter 22...Latch filter 23-Synchronous detection circuit 2
4.34--Carrier regeneration circuit 25.38.40--Frequency converter 26.44-Local oscillator 28-Video amplifier 29-Beat detection circuit 30--Synchronization separation circuit 31.43-Control circuit 32-・FM demodulation circuit 33-1M modulation circuit
35- Level adjustment circuit 36- Delay circuit 37-
- Subtraction circuit 39 - Bandpass filter and limiter 42 - Interference wave detection circuit Fig. 1 Fig. 2 Fig. 8 Fig. 9

Claims (1)

[Claims] 1. A soft gate circuit that passes the television signal during the horizontal or vertical blanking period of the television signal, and a soft gate circuit that is arranged before or after the soft gate circuit and that controls the frequency for each horizontal scanning frequency. a comb filter circuit for removing a luminance signal component of a television signal having a spectrum distribution; A narrowband bandpass filter circuit is used to separate and detect multiple interference waves whose frequencies exist close to each other in the television signal without affecting each other, from the signal obtained through the television signal. An interference wave detection device characterized in that it is capable of detecting interference waves. 2. The interference wave detection device according to claim 1, wherein the soft gate circuit has a characteristic that can be represented by a Gaussian waveform in the time axis direction.