JP2666869B2 - Ghost measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the measurement of television ghosts.

[0002]

2. Description of the Related Art Conventional ghost measurements using GCR signals do not include phase.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for measuring a ghost phase using a GCR signal.

[0004]

The in-phase and quadrature component signals of the GCR signal are obtained by the quadrature two-axis synchronous detection means, and the differences are obtained to obtain the in-phase difference signal and the quadrature difference signal. A complex signal having the in-phase difference signal as a real component and the quadrature difference signal as an imaginary component is obtained. In the delay profile of the absolute value of the complex signal, isolated GORE
A time window that is sufficient and as short as possible to extract the
Is set, and the maximum value of the absolute value is set within the time window.
Find the delay time to be given. The maximum value is set to a preset value.
Ghost exists at the delay time when the sound level is higher than the sound level
Then, the phase of the complex signal at the delay time is
The strike phase. GCR signal ghosts through the time window
Move to a valid time range to detect ghosts and
In the same way.

A delay profile is obtained by smoothing the absolute value delay profile by a moving average or the like. The delay time that gives the maximum absolute value in the delay time section corresponding to the ghost is obtained from the smoothed delay profile, and the phase of the complex signal there is defined as the phase of the ghost.

[0006] Usually, the GCR signal consists of four color subcarriers.
It is handled by the sample value sampled at the double sampling frequency (14.3 MHz). In this case, the delay time at which the absolute value of the complex signal becomes maximum does not represent an accurate ghost delay time except when the ghost delay time is an integral multiple of the sampling period. Therefore, 14.
The complex signal in the vicinity of the delay time (between the sample time giving the maximum absolute value and the sample time giving the next largest value) obtained at the sampling frequency of 3 MHz is interpolated to further reduce the delay time of the maximum absolute value. Ask.

[0007]

The in-phase component signal p (t) and the quadrature component signal q (t) for one isolated ghost in the differential signal of the GCR signal subjected to quadrature two-axis synchronous detection are as follows. (T)
May be omitted to avoid complicating the equation.

[0008]

(Equation 1)

[0009]

(Equation 2) A complex signal x (t) having p (t) as a real component and q (t) as an imaginary component is defined.

[0010]

(Equation 3) The absolute value a (t) and the phase b (t) of the complex signal x (t) are as follows.

[0011]

(Equation 4)

[0012]

(Equation 5)

FIG. 1 shows a signal waveform of each part of a single ghost. The horizontal axis is time t, the vertical axis is the signal magnitude, and (1)
Is the in-phase component signal p (t), and (2) is the quadrature component signal q
(T) and (3) are absolute values a (t), and (4) is the phase b.
(T) and (5) are smoothed absolute values a (t). The vertical line in the center indicates the ghost delay time τ. Taking the arrival time of the desired wave as a time reference, the absolute value a (t) takes the maximum value within the time spread range of the signal at t = τ, regardless of the phase, and h (t = τ) = 0. Therefore, if normalized by g (0), the equations (4) and (5) become the following equations.

[0014]

(Equation 6)

[0015]

(Equation 7)

That is, the absolute value maximum delay time gives the ghost delay time τ, and the absolute value and phase at that delay time give the ghost specific intensity r and phase φ, respectively.

The delay profile around the ghost of the absolute value a (t) shown in FIG. 1 (3) has a maximum value of 3 in the signal spread L in which the energy of the GCR difference signal itself is concentrated.
Exist. The true delay time of the ghost is a delay time giving the maximum value of the absolute value in the signal spread L. A waveform am in which the absolute value is smoothed by the moving average is shown in FIG. 1 (5), and two valleys sandwiching the maximum value have disappeared. From this, the maximum value becomes the maximum value in the smoothed signal spread L of the absolute value, and the maximum position is obtained by the method of searching for the maximum position.

In the actual measurement, p and q are sample values, and the ghost delay time is an integral multiple of the sampling period.
Alternatively, except when the delay time is close to that, h (t =
τ) ≠ 0, resulting in a phase measurement error. For example, at a sampling frequency of 14.3 MHz, the worst value of the phase error generated within one sample period is ± 90 degrees (the measurement error of the specific intensity is 1.3 dB), so interpolation of sample points obtained by dividing one sample period by 9 or more is performed. The measurement error by 1
It can fit within 0 degrees.

[0019]

FIG. 2 is a block diagram of an embodiment of a ghost measurement to which the method of the present invention is applied, wherein 1 is an antenna, 2 is a television receiver having a quadrature two-axis synchronous detection function, and P is an in-phase component. Signal, Q is a quadrature component signal, 3 is a GCR signal extractor / differentiator for P, 4 is a GCR signal extractor / differentiator for Q, p is an in-phase component signal of a GCR differential signal, q is a quadrature component signal of a GCR differential signal, Reference numeral 5 denotes a signal processing unit for obtaining a ghost parameter, which obtains a complex signal, its absolute value, a delay time for giving a maximum absolute value, a specific intensity, and a phase from the GCR difference signals p and q.

A television wave is received by an antenna 1, and an in-phase component signal P and a quadrature component signal Q are obtained by a television receiver 2 having a quadrature two-axis synchronous detection function. Where P and Q are 1
It is assumed that sampling is performed at 4.3 MHz. In addition, synchronous addition may be performed to improve the signal-to-noise ratio. GCR signals are extracted from the GCR signal lines of the 8-field sequence by the GCR signal extraction / differentiators 3 and 4 from the signals P and Q, and the GCR signals are subtracted.
An R difference signal p and an orthogonal GCR difference signal q are obtained respectively.

The signal processing unit 5 obtains a delay profile of an absolute value by using a complex signal x having the real signals and the imaginary components of the differential signals p and q, respectively. A delay time section whose absolute value exceeds a preset level N, for example, a noise level of the measurement system, indicates the presence of the ghost U. Interpolation is made between the sample time giving the maximum absolute value and the sample time with the next largest absolute value in the delay time section using, for example, the sampling theorem. If the phase measurement error is suppressed to about 10 degrees, the absolute value a is obtained by interpolating the complex signal x at a point where the sampling period is divided into nine or more. The phase of the complex signal at the delay time at which the interpolated absolute value becomes the maximum is defined as the ghost phase. When calculating the absolute maximum delay time,
Or using the symmetry of a as shown in FIG. 1 (3), when obtaining the phase φ is, the use of linear change in the phase delay time can reduce the measurement error due to noise.

FIG. 3 is an actual measurement example of the absolute value delay profile. The vicinity of the delay time 0 is covered by the signal spread of the desired signal D itself. Approximately -2 to 17 μs delay time
There is a ghost U of 0 dB. According to the method of the present invention, the phase was -140 degrees. When there are a plurality of isolated ghosts, each ghost may be separated from the delay profile of the absolute value, and the phase of each ghost may be obtained by the above method. For example, in FIG. 3, there are several delay time sections that exceed level N in the vicinity of the right side of D, and ghost areas are separated by changing level N, the absolute value maximum delay time is obtained for each, and the phase is changed. Just ask.

[0023]

As described above, according to the present invention, G
Using a complex signal having a real component and an imaginary component of the in-phase component signal and the quadrature component signal of the CR difference signal, a delay time that gives the maximum value of the absolute value is accurately obtained by interpolation, and the complex time at the delay time is calculated. By determining the phase of the signal, the ghost phase can be measured. As a result, the ghost delay time can be accurately measured.

[Brief description of the drawings]

FIG. 1 shows various waveforms of a single ghost for explaining the method of the present invention.

FIG. 2 is a block diagram of a ghost measuring device for explaining the method of the present invention.

FIG. 3 is a ghost delay profile diagram for explaining the method of the present invention.

[Explanation of symbols]

p In-phase detection signal q Quadrature detection signal g In-phase component of GCR difference signal gc Cosine by ghost phase of in-phase component signal of GCR difference signal gs Sine by ghost phase of in-phase component signal of GCR difference signal h Quadrature component of GCR difference signal hc GCR Cosine of ghost phase of orthogonal component signal of differential signal hs Sine of ghost phase of orthogonal component signal of GCR differential signal L Time range in which energy of GCR differential signal is concentrated am Smoothed absolute value 1 Antenna 2 Quadrature two-axis synchronous detection function Television receiver having in-phase P In-phase component signal Q Quadrature component signal 3 GCR signal extraction / differentiator for in-phase component signal 4 GCR signal extraction / differentiator for quadrature component signal 5 Signal processing unit D Desired wave U Ghost to be measured N Ghost Preset level to look for

Claims (3)

(57) [Claims] 1. A GC obtained by orthogonal two-axis synchronous detection means.
The absolute value of a complex signal having a real component and an imaginary component of the in-phase difference signal and the quadrature difference signal, which are the difference signals of the in-phase component signal and the quadrature component signal of the R signal, is represented by the relationship between the delay time.
In the delay profile shown, the absolute value exceeds a set level higher than the noise level.
The maximum value in the delay time section of the ghost existence part
The given delay time is a ghost delay time, and the phase of the complex signal at the delay time is the ghost phase.
A ghost measurement method, characterized in that: 2. The ghost measurement method according to claim 1, wherein a smoothed delay profile is used in the absolute value delay profile. 3. The method according to claim 1, wherein the complex signal is interpolated on the delay time axis in order to accurately determine the delay time that gives the maximum value of the absolute value of the complex signal. The ghost measurement method described in 1 or 2.