JPS6057277B2 - Interference measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring interference waves, and in particular uses a simple device to compare two waveforms to enable accurate measurement.

In general, the transmission system for the sub-modulation signal is as shown in FIG.
This modulates the carrier wave of angular frequency ωc supplied to the angular frequency ωc with a modulation degree m.

The output of this modulator 1 is (1+mg())cosωct
When the impulse response waveform passes through the transmission system 2, the modulated signal d obtained as the output of the transmission system 2 becomes as shown in the first equation. d(wo)■re(wo)ki [(1+mg
()) cos6) ct) ゛...(1) However, it represents the sum and convolution integral.

When this equation (1) is Fourier transformed, D(ω)=H(ω
)・DD(ω7...(2).

However, D(ω) is the Fourier transform (frequency characteristic) of d(O
Fourier transform (frequency characteristics) of H(ω)(O) DD(ω7 is the Fourier transform of (1+mg())cosωct.

By the way, television radio waves are transmitted in the form of residual sideband modulation, and the characteristics of this system are determined by H(ω).

That is, the spectrum IDD of a signal subjected to double-sided band amplitude modulation at the carrier angular frequency ωc. ω, l become as shown in Figure 2A, but when this is passed through a filter with the characteristic Hβ(ω) as shown in Figure 2B, the lower sideband component becomes as shown in Figure 2C. Some will remain. In order to express this signal concisely in the time domain, 1(ω×ωcmβ) H1(ω)(-ωcmβ≦ω<-ωc+β) Hβ(ω)■ ...(3) O(-ωc+β≦ω≦ ωcmβ) Hr(ω)(ωcmβ×ω×ωc+β) 1(ωc+β≦ω).

However, ω is the angular frequency, H1 (ω) is the roll-off characteristic of Hβ (ω) in the negative frequency band, Hr (ω) is the roll-off characteristic of Hβ (ω) in the positive frequency band, The consideration of positive and negative frequency bands is merely for the convenience of analysis. Furthermore, to simplify the expression, if we move the coordinate axes of Hl(ω) and Hr(ω) as shown in Figure 2D, we get (.

However, F.

(ν) is F. (β)=112, which is an arbitrary odd function.
Here, instead of H(ω) in equation (2), Hβ(
ω) as a proxy, the frequency characteristic Dβ of the residual sideband modulation signal is
(ω) becomes .

By performing an inverse Fourier transform on this equation (5), the inverse Fourier transform of the residual sideband modulation signal dβ,o, that is, DD,ω, in the time domain is (1+Mg(t))COsω.

t and using equation (4), it can be expressed as follows.

However, G(ω) is the frequency characteristic of the modulation signal (Fourier transform of g(t)).

Equation (6) is the component 112(1+Mg(t
)) COsωCt and the component orthogonal to the carrier wave 112gβ(
t) is expressed as a linear combination of SinωCt.

This orthogonal component is generated because it is residual sideband modulation, and if Wβ(ω) in equation (8) that defines the roll-off characteristic of the residual sideband filter Hβ(ω) is given, then (7)
It can be seen that it can be obtained from the formula. Next, when the response waveform of the actual television signal transmission path is expressed using the previously defined function, it becomes as shown in FIG.

However, the frequency characteristic G(ω) of the video signal is approximated by a straight line such as the formula 00i, and this is shown in FIG. 3A.

Moreover, the residual sideband roll-off characteristic Wβ(ω) is the (11th)
It is expressed by approximating a straight line as shown in the equation.

(RO6l\wノ ■Vvl'rThis is shown in Figure 3B.

When the frequency characteristics are expressed in this way, the waveform of the video signal in the time domain can be expressed as shown in equation (12) by inverse Fourier transform.

This is shown in Figure 3D.

Further, the residual sideband roll-off characteristic is expressed as shown in equation (13).

This is shown in Figure 3E.

Further, if the frequency characteristic of the residual sideband modulated signal is Gβ(ω), this is shown in FIG. 3C.

This is given by inverse Fourier transform. This is the third
Shown in Figure F. The above study shows that the vestigial sideband modulated signal is represented by a linear combination of an in-phase component and a quadrature component, and that the quadrature component is determined by the roll-off characteristic of the vestigial sideband filter.

Next, let's analyze a television signal containing ghost waves.

Ghosts in television signals are thought to be distortions that occur because television waves pass through many propagation paths. Therefore, the amplitude ratio of the ghost wave u(t) to the desired wave dβ(t) can be expressed as follows, where the R1 delay time is τ.

Also, using equation (6), for the ghost wave in equation (16), φ is the carrier phase angle of the propagation path i1, and φ=ω.

It is expressed as τ-2kπ (k is any integer). For this reason,
The intermediate frequency signal P(t) is defined as (10 below) An embodiment of the present invention will be described with reference to the drawings.

In FIG. 4, reference numeral 3 denotes an input terminal which supplies an intermediate frequency signal from this input terminal 3 to a carrier wave extraction circuit 4 and synchronous detection circuits 5 and 6.

Then, the phase of the carrier wave extracted from the carrier wave extraction circuit 4 is delayed by 0 by the variable phase shifter 7. And this variable phase shifter 7
The output is directly supplied to the synchronous detection circuit 5 and is supplied to the synchronous detection circuit 6 via a π/2 phase shifter 8 having a function of delaying the phase by π/2. The output of the synchronous detection circuit 5 is supplied to one input terminal of the oscilloscope 9, for example channel 1, and the output of the synchronous detection circuit 6 is supplied to the other input terminal of the oscilloscope 9, for example channel 2. A method of measuring interference waves measured by such a device will be explained below.

The carrier wave from the carrier wave sampling circuit 4 in FIG.
If OSωCt, the output from variable phase shifter 7 is K2cO
s(ωCt-0), and this output K2cOs(ω.

t-θ) and an intermediate frequency signal is supplied. On the other hand, the output K2cOs(ω.

t-0) is shifted in phase by π/2 by the π/2 phase shifter 8 to become an output K3COS (ωCt-θ-π/2), which is supplied to the synchronous detection circuit 6 together with the intermediate frequency signal. However, Kl, K2 and K3 are proportional constants. Here, if the output of the synchronous detection circuit 5 is Pθ(t) and the output of the synchronous detection circuit 6 is PO+π12(t), then the following equation is obtained.

When identifying ghosts, it is usually desirable to be able to compare delays and levels with some reference waveform.

However, this cannot be expected at present. Therefore, the equalization pulse or horizontal synchronization pulse during the vertical retrace period is used as a reference. Here, an example using horizontal synchronization pulses will be described. If the undistorted detection output of this horizontal synchronization signal (the desired signal is synchronously detected with a local signal in phase with the carrier wave) is GH(t), and the orthogonal component is GHβ(t), then the above will be obtained.

Here, R1 is the amplitude ratio of the interference wave to the desired wave, τ1 is the delay time, φ1 is the carrier phase angle, and φ1=ω. τ1-2k
j (k is any integer). For example, R1=0.5τ1
? The case where 15μSecφ1 = -π/4 is illustrated as shown in FIG. 5, and when R1=0.飄τ1mi2
．． The case where 5μSec1φ1=-I is illustrated in FIG. 6. Here, Pθ(t) and PO+H(
Observe the two signals of t) simultaneously with an oscilloscope, and
1゛=KlRlCOSφ1! After reading =KlRlSinφ1 and the peak value k1 of the reference signal GH(t), Rl,φ1- can be determined by performing the following calculation.

(''- Also, the delay time can be easily read on an oscilloscope.

Still another measurement method can be considered using the measurement circuit shown in FIG.

That is, by adjusting the variable phase shifter 7, the amplitude K of the fundamental wave at this time,
and the phase indication β=β1 of the variable phase shifter 7.
Next, adjust the variable phase shifter 7 so that X2=0, and the interference wave becomes G
Adjust the variable phase shifter 7 until it becomes similar to Hβ(t), and read the phase display β=β2 at this time. At this time, X1 is KlR
It is l. Therefore, R=X1/k1 (at β=β2).

Also, γ1 can be easily read on an oscilloscope. Further, the case of double ghost is shown in FIGS. 1 and 8.

Here, τ1, φ are the basic parameters of the first ghost, and τ2, φ2 are the basic parameters of the second ghost. In this case, measurement can be performed by determining the ghost of interest. Furthermore, measurements can be made in the same way not only in the case of double ghosts but also in the case of multiple ghosts and preceding ghosts. As described above, according to the present invention, accurate measurement can be performed using a simple device and only by adjusting the phase of the variable phase shifter 7 using an oscilloscope.

[Brief explanation of drawings]

Figures 1, 2, and 3 are explanatory diagrams for facilitating understanding of the present invention, Figure 4 is a configuration diagram used to explain one embodiment of the present invention, and Figures 5 to 8 are It is a line diagram provided for explanation of a figure. 4 is a carrier wave sampling circuit, 5 and 6 are synchronous detection circuits, 7 is a variable phase shifter, 8 is a π/2 phase shifter, and 9 is an oscilloscope.

Claims (1)

[Claims] 1 Supplying an intermediate frequency signal to the first and second synchronous detection circuits, and supplying a local signal having the same frequency as the carrier signal of the intermediate frequency signal to the first synchronous detection circuit via a variable phase shifter. At the same time, the output of the variable phase shifter is phase-shifted by 90 degrees and supplied to the second synchronous detection circuit, and the waveforms of at least the reference signals output from the first and second synchronous detection circuits are observed simultaneously. An interference wave measurement method that measures the amplitude ratio, time difference, and phase difference of carrier wave components of interference waves.