JPH07336246A - Method and device for detecting interference in fm signal - Google Patents

Abstract

PURPOSE:To discriminate a degree of interference disturbance with high sensitivity based on the detection of a DU ratio regardless of simple equipment configuration by detecting the reciprocal of envelope modulation of an FM object wave subjected to interference disturbance as the DU ratio (D/U). CONSTITUTION:An envelope detector 2 detects the envelope waveform of an FM object wave subjected to interference disturbance and a D/U representing a degree of interference disturbance is directly obtained from a divider 8. When an FM modulation wave is taken over, since a reception electric field strength is increased by, e.g. 3dB or over, the output of a 1st comparator 16 and the output of a 2nd comparator 18 are given to an AND gate 22 to obtain take-over information. When the level of a disturbing wave is higher than that of the object wave, the DC component corresponding to a received electric field strength is applied to a 3rd comparator 20 to detect the increase in the reception electric field strength. When the take-over information is outputted, the take- over of a broadcast program is prevented by replacing a usual STL channel with other channel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an FM interference detection method and apparatus for automatically detecting the interference interference state in the presence of an FM interference wave that causes interference to the FM target wave. Especially.

More specifically, the present invention relates to an FM interference detection method and apparatus for automatically detecting the presence or absence of interference on the basis of a DU ratio (ratio between a target wave signal level and an interfering wave signal level). is there.

[0003]

2. Description of the Related Art Conventionally, a reception level detection method, a space diver method, a baseband squelch method, and the like are known as methods for detecting the degree of FM wave interference. The outlines of these FM interference detection methods are as listed below.

Reception level detection method: A method of detecting an increase in the received input electric field due to the addition of an interfering wave to the target wave.

Space diver method: A method in which two or more lines are installed and the program contents are compared.

Baseband squelch method: A method of detecting that high frequency noise is mixed in the FM detection output when there is an interfering wave.

[0007]

However, the above-mentioned conventional reception level detecting method has a drawback that the detection sensitivity for detecting FM interference is poor and the detection result is unstable.

In the space diver method described above,
The detection sensitivity is poor and the installation cost is high.

Similarly, the above-mentioned baseband squelch method also has a drawback that the detection sensitivity is poor.

In addition, in the above-mentioned conventional interference detection method, the DU ratio (hereinafter
(Abbreviated as D / U) could not be detected.

Therefore, in view of the above points, an object of the present invention is to provide an FM interference detection method and apparatus which can detect the degree of interference interference with high sensitivity based on the detection of the D / U despite the simple device configuration. To do.

[0012]

In order to achieve the above object, an FM interference detection method according to the present invention obtains an envelope modulation degree of an FM target wave which is subject to interference, and calculates the reciprocal of the envelope modulation degree. It is detected as a DU ratio. Here, as the step of obtaining the envelope modulation degree, the envelope waveform of the FM target wave that is subject to interference interference is detected, the AC component and the DC component of the envelope waveform are detected, and the ratio of the AC component and the DC component is detected. Is obtained to obtain the envelope modulation degree. Also,
It is preferable to output the interference occurrence information when the DU ratio is less than or equal to a predetermined value. Furthermore, when the magnitude of the DC component exceeds a predetermined range and the interference occurrence information is output, it is preferable to output the takeover information of the FM target wave.

An FM interference detection apparatus according to the present invention is a detection means for extracting an envelope waveform from an FM target wave which is subject to interference interference, a modulation degree detection means for detecting an envelope modulation degree from the envelope waveform, and the envelope. It is provided with a D / U output means for outputting the reciprocal of the modulation degree as a DU ratio. Here, the modulation degree detecting means includes an AC separating means and a DC separating means for detecting an AC component and a DC component of the envelope waveform, respectively, and a dividing unit for obtaining a ratio of the AC component and the DC component.
Further, it is preferable to further include first comparing means for outputting interference occurrence information when the DU ratio is equal to or less than a predetermined value. Further, when the magnitude of the DC component exceeds a predetermined value and the interference occurrence information is output, F
It is preferable that the second comparison means for outputting the takeover information of the M target wave is further provided.

[0014]

In the FM interference detection method and apparatus according to the present invention, when the FM target wave and the FM interference wave exist, the envelope modulation degree (= (A-B ) / (A + B): A
Is the maximum amplitude value and B is the minimum amplitude value), and the presence or absence of the interference state or the degree of interference is detected based on the envelope modulation degree being equal to the reciprocal of D / U.

In addition, focusing on the fact that the received input electric field value increases by 3 dB or more when the FM target wave is multiplied by the FM interference wave, based on the DC component of the envelope waveform and the interference detection result of the present invention, It is also possible to obtain takeover information.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings.

First, it will be described that the reciprocal of D / U can be obtained by obtaining the envelope modulation factor of the FM wave that has been subjected to interference interference. The “envelope modulation degree” described here is synonymous with the AM modulation degree. That is, paying attention to the envelope of the FM wave subjected to the interference interference, from the maximum amplitude value A and the minimum amplitude value B shown in FIG. 4, (A−B) /
The value of (A + B) is called the envelope modulation degree.

(1) When the frequencies of the target wave and the interfering wave are different
If now, _d D the maximum value of the electric field intensity of the object wave, the angular frequency of interest wave omega, the maximum value of the electric field intensity of the interference wave U, when the difference between the angular frequency of interest wave and the disturbance wave is [Delta] [omega, object The combined signal E of the wave and the interfering wave is expressed by the following equation.

[0019]

[Equation 1] E = D cos ω _d t + U cos (ω _d + Δω) t (1) When the above equation (1) is rearranged,

[0020]

[Number 2] ^{E = (D 2 + 2DU ·} cos Δωt + U 2) 1/2 · cos (ω d t + θ) ... (2) here

[0021]

[Equation 3] θ = tan ⁻¹ {(−U sin Δωt) / (D + U cos Δωt)} (3) Therefore, the maximum value E _max of the envelope of the FM wave subjected to the interference is

[0022]

[Equation 4] E _max = D + U (4) Further, the minimum value E _{min of the} envelope is

[0023]

[Equation 5] E _min = D−U (5) From this, the envelope modulation degree E _am is

[0024]

[Equation 6]

Therefore, the degree of envelope modulation E _am is equal to the reciprocal of D / U representing the degree of interference.

Moreover, when the frequencies of the target wave and the interfering wave are different, the beat of the frequency difference between the two waves appears on the envelope, so that D / U detection can be performed even without modulation.

(2) When the frequencies of the target wave and the interfering wave are equal
The combined signal E in this case is represented by the following equation.

[0028]

Equation 7] E = D cos (ωt + θ d) + U cos (ωt + θ u) ... (7) where _{θ d = F d cos pt F} d: object wave modulation index p: object wave modulation angular frequency .theta.u = F _u cos qt F _u : Interfering wave modulation index q: Interfering wave modulation angular frequency When the above equation (7) is rearranged,

[0029]

[Equation 8] E = (D ² + 2DU ・ cos (θ _d −θ _u ) ＋ U ² ) ^1/2・ cos (ωt + θ _r ) ... (8) where,

[0030]

[Equation 9] θ _r = tan ^-1 {(D sin θ _d + U sin θ _u ) / (D cos θ _d + U cos θ _u )} (9) Therefore, the maximum of the FM wave envelope subjected to interference The value E _max is

[0031]

[Equation 10] E _max = D + U (10) Further, the minimum value E _{min of the} envelope is

[0032]

[Equation 11] E _min = D−U (11) From this, the envelope modulation degree E _am is

[0033]

[Equation 12]

Therefore, the degree of envelope modulation E _am is equal to the reciprocal of D / U representing the degree of interference.

Next, the condition for deriving the equations (7) to (12), that is, the FM modulation degree (%) required to _satisfy E _am = U / D will be described.

If the interfering wave is unmodulated now, a modulation index of π [rad] or more is required for the amplitude term of the equation (8) to exhibit the maximum value and the minimum value. On the other hand,
In a general FM broadcast wave, the modulation index is 75 [rad] at 1 kHz 100% modulation, so π / 7
5 = 4.1% or more modulation is applied, equation (12)
It is possible to accurately detect D / U indicating the degree of interference interference from E _am = U / D of.

As described above, the method of detecting the degree of interference or the interference state from the envelope modulation degree is superior in stability to the “reception level detection method” described as the prior art,
It is clear that it is more cost effective than the "space diver method". Further, the detection sensitivity is significantly higher than that of the conventional "baseband squelch method" for the reason described below with reference to FIG.

FIG. 1 shows the state of FM wave interference. In this figure, when the vector of the target wave is A and the vector of the interfering wave is B, the tip of the vector B rotates about the point P at an angular velocity corresponding to the frequency difference between the target wave and the interfering wave. The distance between the tip of the vector B and the origin of coordinates is represented on the time axis as the envelope detection output shown on the right side of FIG. As described above, the degree of envelope modulation of this envelope detection output is the reciprocal of D / U which indicates the degree of interference.

Next, based on the degree of envelope modulation, D /
The detection sensitivity when performing U detection will be described. In the FM modulated wave, the AM content rate is deteriorated even by the multipath of the transmission system. If the AM content rate due to multipath is set to 30 dB in consideration of the actual condition of a general transmission system, the upper limit of detection sensitivity for interference detection is 30 dB.

Next, the detection sensitivity of the base band squelch method described as the prior art will be considered. The swing width θ of the straight line drawn from the tip of the vector B (interfering wave) shown in FIG. 1 to the coordinate origin is the amount of phase change that the interfering wave exerts on the target wave, and the result of FM detection of this is displayed in the baseband. It is the noise that is heard. For example, D / U indicating the degree of interference
Is 20 dB, vector A = 1, vector B = 0.
Since it is 1, the phase angle θ = tan ⁻¹ 1/10 = 0.1
It becomes [rad].

On the other hand, the phase change amount ψ of the vector A when the target wave is modulated at 1 kHz and 100% is ψ
= 75 [kHz] / 1 [kHz] = 75 [rad], which is very large. Here, the D / U indicating the degree of interference is 20
When the S / N at dB is calculated,

[0042]

[Equation 13] S / N = 20 log (75 [rad] /0.1 [rad]) = 57.5 [dB] (13) That is, it can be understood that even if there is some interference, the influence of the interference hardly appears on the FM detection output. Generally, it is said that the influence of the interference wave appears in the FM detection output when the D / U, which indicates the degree of interference, is within 3 dB.

From the above, the method of obtaining D / U from the degree of envelope modulation has a high detection sensitivity of about 27 (= 30−3) dB as compared with the conventional baseband squelch method.

FIG. 2 shows an embodiment of an FM interference detection device to which the present invention is applied. In the figure, reference numeral 2 denotes an envelope detector, which detects the envelope waveform of the FM target wave that is subject to interference. 4 is an AC component separation circuit,
A voltage corresponding to (E _max −E _min ) / 2 shown in FIG. 1 is detected from the envelope waveform. Reference numeral 6 denotes a DC component separation circuit, which detects a voltage corresponding to (E _max + E _min ) / 2 shown in FIG. 1 from the envelope waveform.

Numeral 8 is a divider for obtaining the ratio of the direct current component and the alternating current component. That is,

[0046]

(14) Since (E _max + E _min ) / (E _max −E _min ) = 1 / (envelope modulation degree) = D / U (14), the degree of interference interference is calculated from the divider 8. The D / U represented will be directly obtained.

A peak detector 10 outputs the absolute value of D / U. 12 is a meter for analog display of the D / U, 14 is a buffer amplifier for outputting an analog D / U signal to the outside, 16 is interference when the D / U exceeds a predetermined threshold value First to output information
Is a comparator of.

Reference numerals 18 and 20 output the take-over information when the DC components (corresponding to the received electric field values) output from the DC component separation circuit 6 exceed their respective predetermined threshold values. Is a comparator of. 22 is AN
D gate and 24 are OR gates. That is, when the FM modulated wave is taken over, the received electric field value increases by 3 dB or more. Therefore, by applying this phenomenon, the first comparator 1
By inputting the output of 6 (interference occurrence information) and the output of the second comparator 18 (increasing information of the received electric field) to the AND gate 22, the takeover occurrence information is obtained. Also,
When the interfering wave is very large compared to the target wave (for example, 2
If it is 0 dB or more), the AM content will decrease. Therefore, in order to detect the takeover even in such a case, the DC component is applied to the third comparator 20 to detect a large increase in the received electric field.

When this takeover information is output, for example, as shown in FIG. 3, an operation such as switching from a normal STL (studio / transmitter / link) line to another line is performed, and the broadcast program is executed. It is possible to prevent the hijacking of the vehicle.

[0050]

As described above, according to the present invention, the D / U representing the degree of interference is determined based on the envelope modulation degree of the FM modulated wave, and the received input electric field is increased due to addition of the interference. Can be detected to detect the presence or absence of hijacking of the broadcast, and therefore the effects listed below can be obtained.

The FM interference detection method and apparatus according to the present invention can be applied in a wide range of fields because the detection procedure and apparatus configuration are very simple. Especially in the broadcasting industry, it is possible to fulfill the social mission of protecting broadcasting from intentional or accidental interference. Specifically, the present invention can be applied to radio and television STL (studio / transmitter / link) devices, which are mostly FM modulation systems, and FM relay broadcasting devices.

Further, as compared with the prior art, in addition to being excellent in economical efficiency, stability, and detection sensitivity, it has a feature that D / U indicating the degree of interference interference can be detected. Widely applicable as a takeover prevention device.

Since the sensitivity is good, the occurrence of interference can be detected before the interference is visually or visually sensed, and time can be taken as countermeasures.

By having the function of measuring the reception input level, it is possible to detect whether or not the broadcast or communication is taken over. In this case, broadcasting or communication can be protected by switching to another line or disconnecting the input.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an FM wave interference situation.

FIG. 2 is a block diagram showing an embodiment of the present invention.

FIG. 3 is a diagram illustrating an application example of the present invention.

FIG. 4 is an explanatory diagram of an envelope modulation degree.

[Explanation of symbols]

 2 Envelope detector 4 AC separation circuit 6 DC separation circuit 8 Divider 10 Peak detector 12 Analog D / U display meter 14 Buffer amplifier 16, 18, 20 Comparator 22 AND gate 24 OR gate

Claims (8)

[Claims] 1. The method according to claim 1, wherein an envelope modulation degree of an FM target wave subjected to interference is determined, and an inverse number of the envelope modulation degree is detected as a DU ratio (ratio between a target wave signal level and an interference wave signal level). FM interference detection method. 2. The step of obtaining the envelope modulation degree according to claim 1, wherein an envelope waveform of an FM target wave that is subject to interference is detected, and an alternating current component and a direct current component of the envelope waveform are detected. The FM interference detection method is characterized in that the envelope modulation degree is obtained by obtaining a ratio of the minute component and the direct current component. 3. The FM interference detection method according to claim 1, wherein the interference occurrence information is output when the DU ratio is less than or equal to a predetermined value. 4. When the magnitude of the direct current component exceeds a predetermined range and the interference occurrence information is output, the FM objective wave takeover information is output according to claim 3. FM interference detection method. 5. A detection means for extracting an envelope waveform from an FM target wave that is subject to interference, a modulation degree detection means for detecting an envelope modulation degree from the envelope waveform, and a reciprocal of the envelope modulation degree as a DU ratio. An FM interference detection device comprising a D / U output means for outputting. 6. The modulation degree detecting means according to claim 5, wherein an AC separating means and a DC separating means for respectively detecting an AC component and a DC component of the envelope waveform, and a ratio of the AC component and the DC component are obtained. An FM interference detection device comprising: a dividing unit. 7. The FM interference detection device according to claim 5, further comprising first comparing means for outputting interference occurrence information when the DU ratio is equal to or less than a predetermined value. 8. The second comparison according to claim 7, wherein when the magnitude of the direct current component exceeds a predetermined value and the interference occurrence information is output, the FM target wave takeover information is output. An FM interference detection device further comprising means.