JP3944426B2 - Squelch control device and squelch control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a squelch control device and a squelch control method.
[0002]
[Prior art]
In an FM demodulator that demodulates an FM (Frequency Modulation) modulation signal, a squelch control device is used to suppress noise that increases while the FM demodulated signal is not received.
[0003]
The squelch control device includes a BPF (Band Pass Filter) that passes a high-frequency noise component of a demodulated signal, an amplifier that amplifies the band component that has passed through the BPF, and a rectifier circuit that rectifies the band component amplified by the amplifier. Become.
[0004]
Then, the detected signal is passed through a BPF having a center frequency in the range of 20 to 30 kHz, and only the high frequency noise component is extracted to rectify the high frequency noise component. The rectified voltage obtained by rectifying the noise decreases as the signal intensity of an RF (Radio Frequency) signal increases. When this rectified voltage exceeds a preset threshold value, the squelch device closes the squelch gate and prevents noise from being reproduced from the speaker as the reproducing device.
[0005]
[Problems to be solved by the invention]
Problems with this squelch control are blocking and large input interference.
Blocking means that the squelch is accidentally closed when an audio signal should be output to the speaker. Blocking occurs when the harmonics of the baseband signal pass through the noise extraction BPF, and the harmonics increase the level of the rectified voltage, resulting in the same state as when the signal strength of the RF signal decreases. appear.
[0006]
“Large input interference” refers to a situation in which reproduction of an audio signal from a speaker is to be stopped, and a squelch is accidentally opened by a nearby interference wave, thereby causing a reproduction operation. The large input disturbance is caused by causing a state similar to that when the signal strength of the RF signal is increased by reducing the noise component particularly on the high frequency side due to a nearby interference wave.
[0007]
In order to improve blocking, the center frequency of the noise extraction BPF may be increased to avoid the influence of the harmonics of the baseband signal. In order to improve the large input interference, the center frequency of the noise extraction BPF may be lowered to avoid the influence due to the reduction of the noise component.
[0008]
In this way, blocking and large input interference are in a trade-off relationship, and if the frequency of the BPF is increased in order to avoid the influence of blocking, it becomes weak against large input interference and strong against large input interference. Therefore, if the frequency of the BPF is lowered, it becomes weak against blocking.
[0009]
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a squelch control device and a squelch control method that can prevent malfunction.
[0010]
[Means for Solving the Problems]
In order to achieve this object, a squelch control device according to the first aspect of the present invention provides:
In the squelch control device that controls the squelch gate that opens and closes the output path of the detection signal according to the rectified voltage obtained by rectifying the noise component of the detection signal obtained by detecting the modulation signal
A plurality of noise component extraction means for filtering the detection signal and extracting noise components in different bands;
Rectifying each noise component extracted by the plurality of noise component extracting means, comparing the rectified voltage of each rectified noise component with a preset threshold value, and determining whether or not the rectified voltage of each noise component is greater than or equal to the threshold value Determination means to perform,
When the determination means determines that the rectified voltage of all noise components is equal to or greater than a threshold value, the open squelch gate is closed so as to prevent the output of the detection signal, and the determination means determines that the rectified voltage of all noise components is Control means for controlling to open the closed squelch gate so that the detection signal is output when it is determined to be less than the threshold value.
[0011]
At least one of the plurality of noise component extraction means extracts a noise component having a frequency between the mth (m ≧ 1) order harmonic and the (m ± 1) order harmonic of the baseband signal. It is preferable that
[0012]
It is preferable that the plurality of noise component extraction means have a band characteristic that prevents passage of interference waves.
[0013]
A squelch control method according to a second aspect of the present invention includes:
A squelch control method for controlling a squelch gate that opens and closes an output path of the detection signal according to a rectified voltage of a noise component of a detection signal obtained by detecting a modulation signal,
Filtering the detection signal obtained by detecting the modulation signal to extract noise components in different bands;
Rectifying each extracted noise component, comparing the rectified voltage of each rectified noise component with a preset threshold, and determining whether the rectified voltage of each noise component is greater than or equal to a threshold;
When it is determined that the rectified voltages of all noise components are equal to or higher than the threshold, the open squelch gate is closed, and when the rectified voltages of all noise components are determined to be less than the threshold, the closed squelch gate is opened. And.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a squelch control device according to an embodiment of the present invention will be described with reference to the drawings.
In this embodiment, a case where the squelch control device is applied to an FM demodulation device will be described.
The configuration of the FM demodulator according to the present embodiment is shown in FIG.
The FM demodulator according to the present embodiment demodulates an FM modulated signal, and includes a detector 11, an A / D converter 12, a BPF 13, a de-emphasis circuit 14, and a D / A converter 15. A squelch gate 16, an AF amplifier 17, a speaker 18, and a squelch control unit 19.
[0015]
The detector 11 demodulates the FM modulation signal. The detector 11 is configured by a quadrature detector, and includes a limiter amplifier 31, a π / 2 phase shifter 32, a multiplier 33, and an LPF 34 as shown in FIG.
[0016]
The limiter amplifier 31 is for shaping the FM wave into a square wave by setting an upper limit on the amplitude of the FM wave in order to remove amplitude fluctuation.
The π / 2 phase shifter 32 shifts the square wave shaped by the limiter amplifier 31 by π / 2.
[0017]
The multiplier 33 extracts a signal wave by multiplying the square wave shaped by the limiter amplifier 31 by the square wave phase shifted by π / 2 by the π / 2 phase shifter 32.
The LPF 34 extracts a low frequency component of the signal wave extracted by the multiplier 33.
[0018]
Returning to FIG. 1, the A / D converter 12 converts the analog demodulated signal demodulated by the detector 11 into a digital signal.
[0019]
The BPF 13 is a filter for limiting the band of the digital demodulated signal output from the A / D converter 12 to a band of an AF (Audio Frequency) frequency (for example, 300 Hz to 5 kHz).
The de-emphasis circuit 14 is for correcting the level of the emphasized frequency component among the signal components output from the BPF 13 so as to restore the original frequency characteristic.
[0020]
The D / A converter 15 is for converting a digital signal into an analog signal.
The squelch gate 16 is for opening and closing an output path between the D / A converter 15 and the AF amplifier 17. When the squelch gate 16 is opened, an output path between the D / A converter 15 and the AF amplifier 17 is formed, and when the squelch gate 16 is closed, the formed output path is blocked.
[0021]
The AF amplifier 17 amplifies the audio signal converted into an analog signal by the D / A converter 15.
The speaker 18 outputs the audio signal amplified by the AF amplifier 17 as sound.
[0022]
The squelch control unit 19 extracts a high-frequency noise component from the digital demodulated signal converted by the A / D converter 12, and controls opening and closing of the squelch gate 16 based on the rectified voltage. The BPF 21-1 to 21-n, amplifiers 22-1 to 22-n, rectifiers 23-1 to 23-n, and a controller 24 are included.
[0023]
The BPFs 21-1 to 21-n are filters having different passband characteristics.
The amplifiers 22-1 to 22-n are for amplifying the intensity of noise components output from the BPFs 21-1 to 21-n, respectively.
[0024]
The rectifiers 23-1 to 23-n are for rectifying noise components output from the amplifiers 22-1 to 22-n, respectively.
[0025]
The controller 24 includes an MPU (Micro Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and squelch based on the rectified voltage of the noise component output from the rectifiers 23-1 to 23-n. The opening / closing control of the gate 16 is performed. Note that a threshold value for determining the level of the rectified voltage of the noise component is preset, and the controller 24 stores this threshold value in a memory (not shown).
[0026]
Note that the BPF 13, the de-emphasis circuit 14, and the squelch control unit 19 can be configured by a DSP (Digital Signal Processor).
[0027]
Next, the operation of the FM demodulator according to the present embodiment will be described.
The detector 11 demodulates the FM modulation signal. That is, the limiter amplifier 31 sets the upper limit of the FM wave and shapes the FM modulated signal into a square wave. The π / 2 phase shifter 32 shifts the square wave shaped by the limiter amplifier 31 by π / 2. The multiplier 33 multiplies the square wave shaped by the limiter amplifier 31 by the square wave phase shifted by π / 2 by the π / 2 phase shifter 32, thereby extracting a signal wave. The LPF 34 extracts a low frequency component of the signal wave extracted by the multiplier 33.
[0028]
The A / D converter 12 converts the signal demodulated by the detector 11 into a digital signal. The BPF 13 passes only the frequency component of the band whose intensity is to be corrected among the components of the digital demodulated signal output from the A / D converter 12.
[0029]
The de-emphasis circuit 14 corrects the signal component output from the BPF 13 so as to restore the original frequency characteristic by suppressing the level of the emphasized frequency component.
[0030]
The D / A converter 15 converts the digital signal into an analog signal.
The AF amplifier 17 amplifies the signal that has passed through the squelch gate 16.
The speaker 18 outputs the audio signal amplified by the AF amplifier 17 as sound.
[0031]
The squelch control unit 19 controls the squelch gate 16 based on the rectified voltage of the noise component. First, the BPFs 21-1 to 21-n filter the digital demodulated signals converted by the A / D converter 12 and extract noise components having different bands from each other.
[0032]
The amplifiers 22-1 to 22-n amplify the noise components output from the BPFs 21-1 to 21-n, respectively. The rectifiers 23-1 to 23-n rectify the noise components output from the amplifiers 22-1 to 22-n, and output the noise components of the rectified voltages (values) V1 to Vn, respectively.
[0033]
When the RF signal is weak or there is no RF signal, the detection signal output from the detector 11 has a voltage-frequency characteristic as shown in FIG.
[0034]
BPF 21-1 to 21-n are three BPF 21-1 to 21-3, and each pass band has a frequency f (p-1) as shown in FIG. 3 (b) to FIG. 3 (d). , F (p), and f (p + 1) are set to bands. The amplifiers 22-1 to 22-3 amplify the noise components that have passed through the BPFs 21-1 to 21-3, respectively. When the rectifiers 23-1 to 23-3 rectify, all the rectified voltages rectified by the rectifiers 23-1 to 23-3 exceed a preset threshold value.
[0035]
On the other hand, as shown in FIG. 4A, the detection signal includes noise components of frequencies f (m−1), f (m), and f (m + 1) due to the characteristics of the detector 11. Furthermore, it is assumed that the BPFs 21-1 to 21-3 having pass band characteristics as shown in FIGS. 4B to 4D filter this detection signal.
[0036]
It is due to the limiter amplifier 31 and the LPF 34 of the detector 11 that noise components of the frequencies f (m−1), f (m), and f (m + 1) are included in the detection signal. That is, the limiter amplifier 31 generates a square wave, and the LPF 34 integrates the voltage level output from the multiplier 33. Therefore, the sawtooth signal generated by the LPF 34 may be superimposed on the detection signal. In this case, noise components of frequencies f (m−1), f (m), and f (m + 1) are output from the detector 11 as harmonics of the baseband signal. The noise components of the frequencies f (m−1), f (m), and f (m + 1) also cause blocking.
[0037]
In this case, the frequency f (m) is included in the pass band f (p) of the BPF 21-2, and the frequencies f (m-1) and f (m + 1) are included in the pass band of the BPF 21-1 to BPF 21-3. Not included. Then, only the BPF 21-2 outputs a noise component having a frequency f (m) as shown in FIG. The amplifiers 22-1 to 22-3 amplify the noise components output from the BPFs 21-1 to 21-3, respectively. When the rectifiers 23-1 to 23-3 rectify the amplified noise components, the frequency f Only the rectified voltage of the noise component of (m) exceeds the threshold.
[0038]
The controller 24 compares the rectified voltages V1 to Vn of the noise components output from the rectifiers 23-1 to 23-n with a preset threshold value.
[0039]
A hysteresis can be provided for opening and closing the squelch gate 16. In this case, an upper limit value Vmax and a lower limit value Vmin are provided as threshold values. For example, as shown in FIG. 5, the squelch level is set to 3, and the upper limit value Vmax and the lower limit value Vmin are set as threshold values. The upper limit value Vmax is a threshold value for closing the open squelch gate 16, and the lower limit value Vmin is a threshold value for opening the closed squelch gate 16. Hysteresis is formed by comparing the rectified voltages V1 to Vn of the noise component with the upper limit value Vmax and the lower limit value Vmin.
[0040]
Further, the squelch level is for adjusting the level at which the squelch gate 16 is opened and closed in accordance with the antenna input (rectified voltage). Here, the squelch level has 15 levels of squelch levels between −120 dBm and −110. Is set. The squelch level is appropriately selected according to the antenna input, and the upper limit value Vmax and the lower limit value Vmin can be set according to the squelch level.
[0041]
The controller 24 controls the opening and closing of the squelch gate 16 based on the result of comparing the rectified voltages V1 to Vn of the noise component with the upper limit value Vmax and the lower limit value Vmin.
[0042]
This operation will be described based on the flowchart shown in FIG.
The controller 24 determines whether or not the squelch gate 16 is open (step S11).
[0043]
When it is determined that the squelch gate 16 is open (Yes in Step S11), the controller 24 takes in the rectified voltage V1 of the noise component that has passed through the BPF 21-1 from the rectifier 23-1 (Step S12).
[0044]
The controller 24 compares the acquired rectified voltage V1 with the upper limit value Vmax, and determines whether or not the rectified voltage V1 exceeds the threshold value Vmax (step S13).
[0045]
When it is determined that the rectified voltage V1 exceeds the upper limit value Vmax (Vmax <V1) (Yes in step S13), the controller 24 similarly performs noise components that have passed through the BPFs 21-2 to 21-n, respectively. Are sequentially taken from the rectifiers 23-2 to 23-n (step S14).
[0046]
The controller 24 sequentially performs the comparison determination on the acquired rectified voltages V2 to Vn as in step S13 (step S15).
[0047]
When the controller 24 determines that all of the acquired rectified voltages V2 to Vn exceed the upper limit value Vmax (Vmax <V2 to Vn) (Yes in step S15), the controller 24 closes the squelch gate 16 (step S16). .
[0048]
On the other hand, when it is determined that at least one of the acquired rectified voltages V1 to Vn is equal to or lower than the upper limit value Vmax (Vmax ≧ V1,... Or Vmax ≧ Vn) (No in steps S13 and 15), the controller 24 Terminates this process with the squelch gate 16 open.
[0049]
Next, when it is determined that the squelch gate 16 is closed (No in Step S11), the controller 24 takes in the rectified voltage V1 of the noise component that has passed through the BPF 21-1 from the rectifier 23-1 (Step S17).
[0050]
The controller 24 compares the acquired rectified voltage V1 with the lower limit value Vmin, and determines whether or not the rectified voltage V1 is less than the lower limit value Vmin (step S18).
[0051]
When it is determined that the rectified voltage V1 is less than the lower limit value Vmin (Vmin> V1) (Yes in step S18), the controller 24 sequentially applies the rectified voltages V2 to Vn that have passed through the BPF 21-2 to the rectifiers 23-2 to 23-2. 23-n (step S19).
[0052]
The controller 24 sequentially performs the comparison determination similarly to step S18 for the acquired rectified voltages V2 to Vn (step S20).
[0053]
When it is determined that all of the rectified voltages V2 to Vn taken are less than the lower limit value Vmin (Vmin> V2 to Vn) (Yes in step S20), the controller 24 opens the squelch gate 16 (step S21).
[0054]
On the other hand, when it is determined that at least one of the acquired rectified voltages V1 to Vn is equal to or higher than the lower limit value Vmax (Vmin ≦ V1,... Or Vmin ≦ Vn) (No in steps S18 and S20), the controller 24 Terminates this process with the squelch gate 16 closed.
[0055]
Next, the operation of the squelch control unit 19 will be specifically described.
First, the passbands of BPF 21-1 to 21-n are set.
As shown in FIG. 7, the pass bands of the BPFs 21-1 to 21-n are up to the band of the ninth harmonic (f9) of the AF frequency. This is because harmonics are attenuated to such an extent that blocking does not occur in a band higher than the ninth harmonic of the AF frequency.
[0056]
Further, as an embodiment when performing digital signal processing, when the sampling frequency fs of the A / D converter 12 is 38.4 kHz, the upper limit of the pass band of the BPF 21-1 to 21-n is 19.2 (= fs × 0.5) It is desirable to set to kHz.
[0057]
Further, the frequency of the large input disturbance wave is about 1 kHz, and the lower limit of the pass band of the BPF 21-1 to 21-n is set to 2.0 kHz so as not to be affected by the large input disturbance wave. As a result, the BPFs 21-1 to 21-n block the passage of interference waves.
[0058]
In this range, even if the detection signal includes harmonics generated by the characteristics of the detector 11, at least one of the BPFs 21-1 to 21-n prevents passage of the harmonics. The pass bands of the BPFs 21-1 to 21-n are set.
[0059]
For example, it is assumed that the AF frequency of the detection signal is 3.8 kHz. As shown in FIG. 7, the harmonic of the AF frequency of 3.8 kHz is 7.6 kHz to 34.2 kHz.
[0060]
Here, among the BPF 21-1 to 21-n, the BPF 21-1 and the BPF 21-2 are used, and the pass band of the BPF 21-1 is set to 18.5 to 19.0 kHz. The reason why the width of the pass band is set to about 0.5 kHz is that if the width of the pass band is widened, the pass bands of the BPF 21-1 and the BPF 21-2 are overlapped, and the controller 24 makes an erroneous determination. .
[0061]
When the pass band of the BPF 21-1 is set in this way, the fifth harmonic f5 having an AF frequency of 3.8 kHz passes through the BPF 21-1, and the level of the rectified voltage exceeds the threshold value. For this reason, the pass band of the BPF 21-2 is set so as not to include harmonics 7.6 kHz to 34.2 kHz of the detection signal having the AF frequency of 3.8 kHz. This is to prevent malfunction due to the detection signal containing harmonics generated by the characteristics of the detector 11.
[0062]
Specifically, the pass band of BPF 21-2 is set between 7.6 kHz to 34.2 kHz, for example, between 11.4 kHz and 15.2 kHz. If the pass band of the BPF 21-2 is set in this way, the harmonics of the detection signal having the AF frequency of 3.8 kHz will not pass through the BPF 21-2.
[0063]
If the passbands are separated from each other, harmonics of the AF frequency during that time cannot be extracted. Also, as shown in FIG. 7, if the pass band of the BPF 21-2 is set to 15.0 to 15.5 kHz and an attempt is made to extract the fifth harmonic (f5 = 15.0 kHz) with an AF frequency of 3.0 kHz. In addition to this harmonic, the fourth harmonic (f4 = 15.2 kHz) with an AF frequency of 3.8 kHz also passes through the BPF 21-2. Therefore, the pass bands of the BPF 21-1 and the BPF 21-2 are made as close as possible. As a result, the pass band of the BPF 21-2 is set to 17.0 to 17.5 kHz.
[0064]
When the passbands of the BPF 21-1 and the BPF 21-2 are set as described above, the BPF 21-1 prevents passage of harmonics having the same AF frequency as shown in FIG.
[0065]
The controller 24 controls the opening and closing of the squelch gate 16 based on the harmonic rectified voltages that have passed through the BPF 21-1 and the BPF 21-2 in which the band characteristics are set as described above.
[0066]
When the intensity of the RF signal is weak, or when there is no RF signal, the noise components pass through the BPF 21-1 and the BPF 21-2, respectively, as shown in FIG. When this noise component is amplified and rectified, all of the rectified voltages exceed the upper limit value Vmax. If any of the rectified voltages exceeds the upper limit value Vmax, the controller 24 determines that the intensity of the RF signal is weak or that there is no RF signal, and closes the squelch gate 16.
[0067]
On the other hand, when this detection signal includes harmonics due to the characteristics of the detector 11, as shown in FIG. 9, the harmonic of 19.0 kHz which is the fifth harmonic f5 of the AF frequency of 3.8 kHz is BPF21−. Pass 1 The harmonic rectified voltage output from the BPF 21-1 exceeds the upper limit value Vmax. However, the harmonic voltage output from the BPF 21-1 is almost zero. For this reason, the controller 24 determines that the harmonic wave that has passed through the BPF 21-1 is a harmonic wave due to the characteristics of the detector 11, and keeps the squelch gate 16 open. Therefore, blocking is avoided and malfunction of squelch is prevented.
[0068]
As described above, according to the present embodiment, n BPF 21-1 to 21-n are provided. The controller 24 opens the closed squelch gate 16 only when all the rectified voltages of the noise components that have passed through the BPF 21-1 to BPF 21-n exceed the upper limit value Vmax, and all the rectified voltages have the lower limit value Vmin. The open squelch gate 16 is closed only when it becomes less than.
[0069]
Therefore, even if there is an RF signal and harmonics generated by the characteristics of the detector 11 are included in the detection signal, malfunction of the squelch can be prevented.
[0070]
Further, since the pass band of BPF 21-1 to BPF 21-n is set to be a band for blocking the passage of the disturbing wave, it is not affected by the disturbing wave. Therefore, the two problems of squelch blocking and large input interference can be improved at the same time.
[0071]
In carrying out the present invention, various forms are conceivable and the present invention is not limited to the above embodiment.
For example, in the above embodiment, the case where the squelch control device is applied to the FM demodulation device has been described. However, it is not limited to this. That is, the squelch control device can be applied to an AM (Amplitude Modulation) demodulator and a PM (Phase Modulation) demodulator, and can also be applied to digital communication in which a signal is an encoded pulse.
[0072]
The present embodiment is not limited to the case of digital signal processing, and an analog signal output from the detector 11 can be processed as it is. In this case, the A / D converter 12 and the D / A converter 15 are not necessary.
[0073]
【The invention's effect】
As described above, according to the present invention, malfunction can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a squelch device according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of the detector in FIG. 1;
FIG. 3 is an explanatory diagram showing an operation of the squelch control unit in FIG. 1;
4 is an explanatory diagram showing an operation of the squelch control unit of FIG. 1; FIG.
FIG. 5 is an explanatory diagram showing a squelch level of the squelch control unit in FIG. 1;
6 is a flowchart showing the operation of the squelch control unit in FIG. 1. FIG.
7 is an explanatory diagram showing setting of AF frequency and its harmonics and BPF characteristics of the squelch control unit of FIG. 1; FIG.
FIG. 8 is an explanatory diagram showing the operation of the squelch control unit when the RF signal is weak or when there is no RF signal.
FIG. 9 is an explanatory diagram showing the operation of the squelch control unit when the RF signal contains harmonics due to the characteristics of the detector.
[Explanation of symbols]
11 detector 16 squelch gate 19 squelch control unit 21-1 to 21-n BPF
22-1 to 22-n Amplifiers 23-1 to 23-n Rectifier

Claims (4)

In the squelch control device that controls the squelch gate that opens and closes the output path of the detection signal according to the rectified voltage obtained by rectifying the noise component of the detection signal obtained by detecting the modulation signal,
A plurality of noise component extraction means for filtering the detection signal and extracting noise components in different bands;
Rectifying each noise component extracted by the plurality of noise component extracting means, comparing the rectified voltage of each rectified noise component with a preset threshold value, and determining whether the rectified voltage of each noise component is equal to or greater than the threshold value Determination means to perform,
When the determination means determines that the rectified voltage of all noise components is equal to or greater than a threshold value, the open squelch gate is closed so as to prevent the output of the detection signal, and the determination means determines that the rectified voltage of all noise components is Control means for controlling to open the closed squelch gate so that the detection signal is output when determined to be less than a threshold value,
A squelch control device. At least one of the plurality of noise component extraction means extracts a noise component having a frequency between the mth (m ≧ 1) order harmonic and the (m ± 1) order harmonic of the baseband signal. To do,
The squelch control device according to claim 1. The plurality of noise component extraction means have a band characteristic that prevents passage of interference waves,
The squelch control device according to claim 1 or 2, characterized by the above. A squelch control method for controlling a squelch gate that opens and closes an output path of the detection signal according to a rectified voltage of a noise component of a detection signal obtained by detecting a modulation signal,
Filtering a detection signal obtained by detecting the modulation signal to extract noise components in different bands; and
Rectifying each extracted noise component, comparing the rectified voltage of each rectified noise component with a preset threshold, and determining whether the rectified voltage of each noise component is greater than or equal to a threshold;
When it is determined that the rectified voltages of all noise components are equal to or greater than the threshold, the open squelch gate is closed, and when the rectified voltages of all noise components are determined to be less than the threshold, the closed squelch gate is opened. And with,
A squelch control method characterized by the above.

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