JP2003023364A - Pilot signal detector - Google Patents

Abstract

(57) [Problem] To provide an economical and high-performance pilot signal detection device that prevents erroneous detection due to noise and detects a normal demodulated signal output. SOLUTION: A signal input detecting means 2, an FM demodulating means 3,
A filter 4, a pilot signal detecting means 5, and an alarm generating means 6 are provided.
Is not detected, an alarm drive signal SA2 is generated from the input signal detecting means 2, and an alarm is forcibly generated to reliably prevent erroneous detection due to the noise SNO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pilot signal detecting device which detects the presence or absence of an FM modulated signal and determines the abnormality of a demodulated signal.

[0002]

2. Description of the Related Art FIG. 4 shows a block diagram of a conventional pilot signal detecting apparatus. In FIG. 4, the pilot signal detection device 50 includes an FM demodulation device 52, a bandpass filter 53, a pilot signal detection unit 54, and an alarm generation device 55.

The FM demodulation device 52 demodulates the FM modulation signal SFM supplied from the signal source 51, outputs the demodulation signal SDM and the pilot signal SPLO to an external device, etc., and also outputs the demodulation signal SDM and the pilot signal SPLO. It is supplied to the bandpass filter 53.

When the FM modulation signal SFM is not supplied from the signal source 51, the FM demodulator 52 demodulates (amplifies) the noise SN1 and outputs the noise SN2 to the external device, and the band pass filter 53. Is supplied to.

The bandpass filter 53 passes the frequency band of the pilot signal SPLO of the demodulated signal SDM and pilot signal SPLO supplied from the FM demodulator 52, and the pilot signal SPL is supplied to the pilot signal detector 54. . It should be noted that the noise component SNO also passes through the noise component SNO in the frequency band of the pilot signal SPLO.
NO is supplied to the pilot signal detector 54.

The pilot signal detector 54 is composed of a voltage level detector composed of a full-wave rectifier and a smoothing capacitor, a window comparator having a lower limit reference value VK1 and an upper limit reference value VK2, and is supplied from the bandpass filter 53. After detecting the voltage level of the signal SPLO, if the voltage level is in the range of the lower limit reference value VK1 to the upper limit reference value VK2, the demodulation signal SDM is determined to be normal.

On the other hand, when the voltage level of the pilot signal SPLO is out of the range of the lower limit reference value VK1 to the upper limit reference value VK2, the pilot signal detecting section 54 determines that the demodulation signal SDM is abnormal and outputs the alarm drive signal SA. Alarm generation means 5
5, and an alarm is generated from the alarm generating means 55.

Since the voltage level of the noise SNO is usually lower than the lower limit reference value VK1, the pilot signal detecting section 54
The alarm drive signal SA is supplied to the alarm generating means 55 from the alarm generating means 55, and an alarm is generated from the alarm generating means 55.

As described above, the conventional pilot signal detecting apparatus 50 has the FM modulation signal SFM supplied from the signal source 51.
Demodulates the demodulated signal SDM and outputs the demodulated signal SDM.
The pilot signal SPL included in DM is detected at the voltage level, and the voltage level of the pilot signal SPL is set to 2 in advance.
If it is within one reference level range, the demodulated signal SDM is determined to be normal. On the other hand, when the voltage level of pilot signal SPL exceeds two preset reference level ranges, demodulated signal SDM is determined to be abnormal and an alarm is generated.

Further, a conventional pilot signal detecting device 50
When the FM modulation signal SFM is not supplied from the signal source 51, the noise SN1 is demodulated to output the noise SN2, and the noise SNO filtered by the bandpass filter 53 is detected at the voltage level. Since the voltage level falls outside the preset two reference level ranges, it is determined that there is no pilot signal SPL (no demodulation signal SDM) and an alarm is generated.

FIG. 5 shows a level frequency spectrum diagram of the pilot signal and noise of the conventional pilot signal detecting device. (A) is the pilot signal SPLO of the demodulation output when the FM modulation signal is input, (b) is the pilot signal SPL after passing through the bandpass filter, and (c) is the noise SN2 of the demodulation output when the FM modulation signal is not input. , (D) shows the noise SNO after passing through the bandpass filter. Note that Vk1 and Vk2 in FIGS. 4B and 4D represent the lower limit reference value VK1 and the upper limit reference value VK2 of the pilot signal detector 54 shown in FIG.

In FIG. 1A, when the FM modulation signal SMF is being output, the pilot signal SPLO output from the FM demodulator 52 is at a normal level. On the other hand, the noise SN2 output from the FM demodulator 52 has a wide frequency band but a low level.

FIG. 2B shows a bandpass filter (BP) for the pilot signal SPLO and noise SN2 shown in FIG.
F), and the level of the pilot signal SPL is within the range between the lower limit reference value VK1 and the upper limit reference value VK2, indicating that the demodulated signal SDM is normal. On the other hand, in the noise SNO, components on the low frequency side and the wide frequency side are removed by a band pass filter (BPF), and the integrated value of the hatched portion corresponds to the voltage level, but the lower limit reference value VK1 and the upper limit reference value VK2 Is out of range.

[0014]

In the conventional pilot signal detecting apparatus 50, as shown in FIG. 7C, when the FM modulated signal SMF is not output, the FM demodulating apparatus 52 outputs only the noise SN2. However, when the noise SN1 input to the FM demodulator 52 is large, the noise SN2 is
Due to the integration process and the amplification action of the demodulation device 52, the level becomes high over a wide frequency band.

FIG. 3D shows the noise SN2 shown in FIG. 3C passed through a bandpass filter (BPF).
The noise SNO has a high level in the pass band of the pilot signal SPL, and the voltage level (= noise SNO) of the integrated value (noise level × BPF band) in the shaded area is the lower reference value VK1 and the upper reference value VK2. It may fall within the range, and there is a problem of making an erroneous determination that the demodulation signal SDM is normally output from the FM demodulation device 52, although the FM modulation signal SMF is not output.

Further, narrowing the pass band of the band pass filter (BPF) and increasing the amount of attenuation can prevent erroneous detection due to noise, but such a band pass filter is difficult to obtain and expensive. A new problem arises.

Further, when the FM modulation signal SMF is not output, the noise SN2 output from the FM demodulator 52 is output.
There is a possibility that the level of will increase and adversely affect external devices and the like.

The present invention has been made to solve such a problem, and its purpose is to prevent erroneous detection due to noise, detect a normal demodulated signal output, and output an excessive level noise to an external device or the like. An object is to provide an economical and high-performance pilot signal detection device that prevents

[0019]

In order to solve the above-mentioned problems, a pilot signal detecting apparatus according to the present invention is a signal input detecting means for detecting an FM modulated signal, and an FM modulated signal supplied from the signal input detecting means. FM demodulation means for outputting a demodulated signal by means of the above, a filter for extracting a pilot signal from the demodulated signal, a pilot signal detection means for detecting the voltage level of the pilot signal supplied from the filter and comparing it with a reference level, and a pilot signal When the voltage level of the pilot signal supplied from the detection means is outside the preset reference level range, an alarm generation means for generating an alarm is provided, and the signal input detection means is an FM modulated signal. If the alarm is not detected, the alarm drive signal is output and the alarm is generated forcibly. The features.

In the pilot signal detecting device according to the present invention, when the signal input detecting means does not detect the FM modulated signal, the alarm drive signal is outputted to forcibly generate the alarm, so that the erroneous detection due to the noise is surely performed. It is possible to prevent it, and to improve the performance. In addition, since an expensive filter is not used, it is possible to achieve economic efficiency.

Further, the pilot signal detecting apparatus according to the present invention comprises signal input detecting means for detecting an FM modulated signal,
FM demodulating means for demodulating the FM modulated signal supplied from the signal input detecting means and outputting a demodulated signal, a filter for extracting a pilot signal from the demodulated signal, and detecting the voltage level of the pilot signal supplied from the filter, Pilot signal detection means for comparing with a reference level, alarm generation means for generating an alarm when the voltage level of the pilot signal supplied from the pilot signal detection means is outside the preset reference level range, and demodulation signal The signal input detection means supplies a cutoff signal to the signal cutoff means to cut off the noise output from the FM demodulation means when the FM modulated signal is not detected. An alarm is generated from the alarm generating means.

In the pilot signal detecting apparatus according to the present invention, when the FM modulation signal is not detected, the cutoff signal is supplied to the signal cutoff means to cut off the noise output from the FM demodulation means, and the alarm generation means outputs an alarm. As a result, erroneous detection due to noise can be reliably prevented, and an excessive level of noise output to an external device or the like can be prevented, so that performance can be improved.

Further, the signal cutoff means according to the present invention is
It is a signal attenuator capable of varying the amount of noise level attenuation.

Since the signal cutoff means according to the present invention is a signal attenuator capable of varying the attenuation amount of the noise level, the performance of the filter can be lowered and the cost can be reduced.

Further, the pilot signal detecting apparatus according to the present invention comprises signal input detecting means for detecting an FM modulated signal,
FM demodulating means for demodulating the FM modulated signal supplied from the signal input detecting means and outputting a demodulated signal, a filter for extracting a pilot signal from the demodulated signal, and detecting the voltage level of the pilot signal supplied from the filter, Pilot signal detection means for comparing with the reference level, alarm generation means for generating an alarm when the voltage level of the pilot signal supplied from the pilot signal detection means is outside the preset reference level, and FM demodulation The signal input detection means supplies a bias stop signal to the bias control means to stop the operation of the FM demodulation means when the FM modulation signal is not detected. However, an alarm is generated from the alarm generating means.

In the pilot signal detecting device according to the present invention, when the FM modulation signal is not detected, the bias stop signal is supplied to the bias control means to stop the operation of the FM demodulation means and the alarm generation means generates an alarm. As a result, erroneous detection due to noise can be reliably prevented, and noise at an excessive level can be prevented from being output to an external device or the like, and performance can be improved.

Further, the bias control means according to the present invention is characterized in that the FM demodulation means is provided with a voltage bias or a current bias.

The bias control means according to the present invention is an FM
Since a voltage bias or a current bias is provided to the demodulation means, the voltage bias or the current bias can be stopped by the bias stop signal to stop the operation of the FM demodulation means, and the erroneous detection due to noise can be reliably prevented with a simple configuration. In addition, it is possible to prevent an excessive level of noise output to an external device or the like.

Further, the filter according to the present invention is characterized by being a bandpass filter or a lowpass filter.

Since the filter according to the present invention can be constituted by a simple band-pass filter or a low-pass filter, cost reduction can be realized.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the present invention is to prevent the erroneous detection of the presence of the FM modulation signal due to noise by forcibly generating an alarm sound when the FM modulation signal is not detected.

Further, according to the present invention, when the FM modulation signal is not detected, an alarm sound is generated to prevent erroneous detection that there is an FM modulation signal due to noise, and noise output is stopped to adversely affect an external device or the like. Is to prevent.

FIG. 1 is a basic block configuration diagram of an embodiment of a pilot signal detecting apparatus according to the present invention. In FIG. 1, the pilot signal detection device 1 includes a signal input detection means 2, an FM demodulation means 3, a filter 4, a pilot signal detection means 5, and an alarm sound generation means 6.

The signal input detecting means 2 is a rectifying / smoothing circuit,
A signal generation circuit and the like are provided, and the MF modulated signal S is output from the signal source 10.
When the MF is supplied, the MF modulated signal SMF is branched and detected by the direct current, and the MF modulated signal SMF is also demodulated by the FM demodulation means 3
Supply to.

Further, the signal input detection means 2 outputs the alarm sound drive signal S when the MF modulation signal SMF is not supplied.
A2 is generated and the alarm sound drive signal SA2 is supplied to the alarm sound generating means 6.

The FM demodulation means 3 is composed of an FM demodulation circuit, and the MF modulation signal S supplied from the signal input detection means 2 is supplied.
The MF is demodulated, the demodulated signal SDM is output to an external device, and the demodulated signal SD including the pilot signal SPLO is output.
Supply M to the filter 4.

Further, the FM demodulation means 3 uses the MF modulated signal S
When MF is not supplied, the noise SN1 is integrated and then voltage-amplified and the noise SN2 is output to an external device or the like, and the noise SN2 is supplied to the filter 4.

The filter 4 is a simple band-pass filter (BPF) or low-pass filter (L) that is generally used.
PF) or high pass filter (HPF)
The demodulation signal SDM including the pilot signal SPLO or the noise SN2 supplied from the M demodulation means 3 is filtered to attenuate the signal or noise in the frequency band determined by the filter to extract the pilot signal SPL, and the pilot signal SPL or The noise SNO is supplied to the pilot signal detecting means 5.

Thus, the filter 4 according to the present invention
Can be configured with a simple band-pass filter or a low-pass filter, so that cost reduction can be realized.

The pilot signal detecting means 5 is a signal detecting circuit of a rectifying / smoothing circuit, a lower limit reference value VK1 and an upper limit reference value VK2.
Filter 4 including a window comparator having
After rectifying and smoothing the pilot signal SPL or noise SNO supplied from the converter and converting it to a DC voltage level, the converted voltage level is compared with the lower limit reference value VK1 and the upper limit reference value VK2, and the voltage level is lower limit reference value VK1. ~ Upper limit reference value VK2
Within the range (VK1 ≦ voltage level ≦ VK2), it is determined that the demodulation signal SDM is normally output, and the alarm sound drive signal SA1 is not output to the alarm sound generating means 6. Therefore, no alarm sound is generated from the alarm sound generating means 6.

On the other hand, when the voltage level is out of the range of the lower limit reference value VK1 to the upper limit reference value VK2 (VK1> voltage level, voltage level> VK2), it is determined that the demodulated signal SDM is abnormally output. The alarm sound drive signal SA1 is supplied to the alarm sound generating means 6 to cause the alarm sound generating means 6 to generate an alarm sound.

The alarm sound generating means 6 is an OR logic circuit,
An alarm sound signal is formed by an alarm sound signal generating circuit, a speaker, etc., and an alarm sound signal is formed by an OR logic signal of the alarm sound drive signal SA2 supplied from the signal input detection means 2 or the alarm sound drive signal SA1 supplied from the pilot signal detection means 5. Sound is generated and an alarm sound is generated from the speaker.

Since the alarm sound drive signal SA2 is always output when the signal input detection means 2 cannot detect the MF modulation signal SMF, the alarm sound drive signal SA2 is output regardless of whether or not the alarm sound drive signal SA1 is output. The alarm sound can be forcibly output from the generating means 6.

Therefore, the pilot signal detecting means 5 detects the voltage level of the noise SNO within the range of the lower limit reference value VK1 to the upper limit reference value VK2 (VK1≤voltage level≤VK2),
Even if the MF modulation signal SFM is not present, even if the alarm sound drive signal SA1 is not supplied due to the erroneous detection as if the normal MF modulation signal SFM is present, the alarm sound drive signal SA2 can generate the alarm sound. it can.

As described above, in the pilot signal detecting apparatus 1 according to the present invention, the signal input detecting means 2 has the FM modulation signal S.
If the MF is not detected, the alarm sound drive signal SA2 is output and the alarm sound is forcibly generated.
False detection due to NO can be reliably prevented, and performance can be improved. In addition, since an expensive filter is not used, it is possible to achieve economic efficiency.

FIG. 2 is a block diagram of the main part of another embodiment of the pilot signal detecting device according to the present invention. In FIG. 2, the pilot signal detection device 11 includes a signal input detection means 2, an FM demodulation means 3, a filter 4, a pilot signal detection means 5, an alarm sound generation means 6, and a signal cutoff means 7. The pilot signal detection device 11 differs from the pilot signal detection device 1 shown in FIG. 1 in that the signal input detection means 2 and the alarm sound generation means 6 are partly different in configuration, and that a signal cutoff means 7 is added. FM because it is different
Descriptions of the demodulation means 3, the filter 4, and the pilot signal detection means 5 are omitted.

The signal input detecting means 2 is a rectifying / smoothing circuit,
A signal generation circuit and the like are provided, and the MF modulated signal S is output from the signal source 10.
When the MF is supplied, the MF modulated signal SMF is branched and detected by the direct current, and the MF modulated signal SMF is also demodulated by the FM demodulation means 3
Supply to.

When the MF modulation signal SMF is not supplied, the signal input detection means 2 generates the cutoff signal SOF and supplies the cutoff signal SOF to the signal cutoff means 7.

The signal cutoff means 7 is composed of a signal attenuator (attenuator or the like) whose attenuation amount can be varied, and attenuates based on the cutoff signal SOF supplied when the signal input detection means 2 does not detect the MF modulated signal SMF. The amount is set large, and the FM demodulating means 3 attenuates a large level of noise SN2 that has been integrated and voltage amplified.

Further, the signal cutoff means 7 is composed of an electronic switch, and turns off the switch based on the cutoff signal SOF supplied when the signal input detection means 2 does not detect the MF modulation signal SMF (for example, noise cutoff operation). Alternatively, it is turned on (for example, a noise short circuit operation), and the FM demodulation means 3 performs integration processing,
It blocks a large level of noise SN2 that has been voltage amplified.

By the operation of the signal blocking means 7, the modulation signal S
When no MF is detected, a large level of noise SN2 output from the FM demodulation means 3 can be blocked, and the noise level to the external device and the noise level to the filter 4 can be minimized.

Therefore, since the level of the noise SNO output from the filter 4 is small and the voltage level of the noise detected by the pilot signal detecting means 5 is also small, the lower limit reference value VK1 to the upper limit set in the window comparator of the pilot signal detecting means 5 is increased. Outside the range of reference value VK2 (lower limit reference value VK1
, And the pilot signal detecting means 5 generates the alarm drive signal SA1.

The alarm generating means 6 comprises an alarm signal generating circuit, a speaker, etc., and the pilot signal detecting means 5
An alarm signal is generated based on the alarm drive signal SA1 supplied from the speaker, and an alarm sound is generated from the speaker.

The pilot signal detecting device 11 is arranged so that when the signal input detecting means 2 does not detect the MF modulated signal SMF,
An alarm sound is generated from the alarm generating means 6.

As described with reference to FIG. 1, the pilot signal detection device 11 detects the pilot signal detection means 5 when the signal input detection means 2 detects the MF modulated signal SMF.
When it is determined that the pilot signal SPL is abnormal (lower limit reference value VK1> SPL or SPL> upper limit reference value VK2), the alarm generating means 6 generates an alarm sound.

By disposing the signal blocking means 7 between the filter 4 and the pilot signal detecting means 5,
Similar to the pilot signal detection device 1 shown in FIG. 3, it is possible to reliably prevent erroneous detection due to noise.

As described above, the pilot signal detecting device 11 according to the present invention supplies the cutoff signal SOF to the signal cutoff means 7 when the FM modulated signal SMF is not detected.
Since the noise SN2 output from the demodulation means 3 is cut off and the alarm is generated from the alarm generation means 6, it is possible to reliably prevent erroneous detection due to noise and prevent an excessive level of noise output to an external device or the like. The performance can be improved.

The signal cutoff means 7 according to the present invention is
Since the signal attenuator is capable of varying the attenuation amount of the noise level, the performance of the filter 4 can be lowered and the cost can be reduced.

FIG. 3 is a block diagram showing the main part of another embodiment of the pilot signal detecting device according to the present invention. In FIG. 3, the pilot signal detection device 21 includes a signal input detection means 2, an FM demodulation means 3, a filter 4, a pilot signal detection means 5, an alarm generation means 6, and a bias control means 8.
Equipped with. The pilot signal detecting device 21 is different from the pilot signal detecting device 11 shown in FIG. 2 in that part of the configurations of the signal input detecting means 2 and the FM demodulating means 3 is different, and that the bias control means 8 is added. Therefore, the description of the filter 4, the pilot signal detecting means 5, and the alarm generating means 6 will be omitted.

The signal input detecting means 2 is provided with a rectifying / smoothing circuit, and when the MF modulation signal SMF is supplied from the signal source 10, the MF modulation signal SMF is branched and detected by the direct current, and the MF modulation signal SMF is detected. It is supplied to the FM demodulation means 3.

The signal input detecting means 2 is provided with a signal generating circuit and the like, and when the MF modulated signal SMF is supplied,
The bias control signal SB is generated, and the bias control signal SB is supplied to the bias control means 8. On the other hand, the MF modulated signal S
When MF is not supplied, the bias stop signal SBT is generated and the bias stop signal SBT is supplied to the bias control means 8.

The FM demodulation means 3 is composed of an FM demodulation circuit provided with a bias circuit, operates the FM demodulation circuit based on the bias control signal SB supplied from the signal input detection means 2, and outputs from the signal input detection means 2. The supplied MF modulated signal SMF is demodulated, the demodulated signal SDM is output to an external device or the like, and the demodulated signal SDM including the pilot signal SPLO is supplied to the filter 4.

Further, the FM demodulation means 3 uses the MF modulated signal S
When MF is not supplied, the FM demodulation circuit is stopped based on the bias stop signal SBT supplied from the signal input detection means 2 so that the noise SN1 input to the FM demodulation means 3 is not output from the FM demodulation means 3. . Therefore, the noise output to the external device or the like and the noise input to the filter 4 are only the noise existing in the output of the FM demodulation means 3, and the noise level can be minimized.

The bias control means 8 is composed of a bias supply circuit, and based on the bias control signal SB supplied from the signal input detection means 2, the bias demodulation means 3 is driven by the bias circuit (voltage drive or current drive). The corresponding voltage bias VB or current bias IB is provided to the FM demodulation means 3 to execute the demodulation operation.

The bias control means 8 stops the voltage bias VB or the current bias IB based on the bias stop signal SBT supplied from the signal input detection means 2,
The demodulation operation of the FM demodulation means 3 is stopped.

By the operation of the bias control means 8, when the FM modulation signal SMF is not detected, the demodulation operation of the FM demodulation means 3 is stopped to minimize the noise level to the external device and the noise level to the filter 4. be able to.

Therefore, since the level of the noise SNO output from the filter 4 is small and the voltage level of the noise detected by the pilot signal detecting means 5 is also small, the lower limit reference value VK1 to the upper limit set in the window comparator of the pilot signal detecting means 5 is increased. Outside the range of reference value VK2 (lower limit reference value VK1
Therefore, the pilot signal detection means 5 can generate the alarm drive signal SA1 and the alarm generation means 6 can generate the alarm sound.

The pilot signal detecting device 21 detects that the MF modulated signal SMF is not detected by the signal input detecting means 2.
An alarm sound is generated from the alarm generating means 6.

As described with reference to FIG. 1, the pilot signal detecting device 21 detects the pilot signal detecting means 5 when the signal input detecting means 2 detects the MF modulated signal SMF.
When it is determined that the pilot signal SPL is abnormal (lower limit reference value VK1> SPL or SPL> upper limit reference value VK2), the alarm generating means 6 generates an alarm sound.

As described above, the pilot signal detecting device 21 according to the present invention supplies the bias stop signal SBT to the bias control means 8 to stop the operation of the FM demodulation means 3 when the FM modulation signal SFM is not detected. However, since the alarm is generated by the alarm generating means 6, it is possible to reliably prevent erroneous detection due to noise, and prevent excessive level noise output to an external device or the like, so that performance can be improved.

Further, the bias control means 8 according to the present invention.
Provides the voltage bias VB or the current bias IB to the FM demodulation means 3, so that the bias stop signal SBT stops the voltage bias VB or the current bias IB and the FM
The operation of the demodulation means 3 can be stopped, and erroneous detection due to noise can be reliably prevented with a simple configuration, and an excessive level of noise output to an external device or the like can be prevented.

[0072]

As described above, in the pilot signal detecting device according to the present invention, when the signal input detecting means does not detect the FM modulated signal, the alarm drive signal is output to forcibly generate the alarm. Therefore, erroneous detection due to noise can be reliably prevented, and performance can be improved. In addition, since an expensive filter is not used, it is possible to achieve economic efficiency.

Further, in the pilot signal detecting apparatus according to the present invention, when the FM modulation signal is not detected, the cutoff signal is supplied to the signal cutoff means to cut off the noise output from the FM demodulation means and the alarm generation means. Since the alarm is generated from the above, it is possible to reliably prevent erroneous detection due to noise, and prevent excessive level noise output to an external device or the like, so that performance improvement can be realized.

Further, the signal cutoff means according to the present invention is
Since the signal attenuator is capable of varying the noise level attenuation amount, the performance of the filter can be reduced and the cost can be reduced.

Further, in the pilot signal detecting apparatus according to the present invention, when the FM modulation signal is not detected, the bias stop signal is supplied to the bias control means to stop the operation of the FM demodulation means, and the alarm generation means outputs an alarm. As a result, erroneous detection due to noise can be reliably prevented, and an excessive level of noise output to an external device or the like can be prevented, so that performance can be improved.

Further, since the bias control means according to the present invention provides the voltage demodulation means or the current bias to the FM demodulation means, the operation of the FM demodulation means is stopped by stopping the voltage bias or the current bias by the bias stop signal. With a simple configuration, it is possible to reliably prevent erroneous detection due to noise, and prevent excessive level noise output to an external device or the like.

Further, since the filter according to the present invention can be constituted by a simple band-pass filter or low-pass filter, cost reduction can be realized.

[Brief description of drawings]

FIG. 1 is a basic block configuration diagram of an embodiment of a pilot signal detecting device according to the present invention.

FIG. 2 is a block diagram of the main part of another embodiment of the pilot signal detecting device according to the present invention.

FIG. 3 is a block diagram of the main part of another embodiment of the pilot signal detecting device according to the present invention.

FIG. 4 is a block diagram of a conventional pilot signal detecting device.

FIG. 5 is a level frequency spectrum diagram of a pilot signal and noise of a conventional pilot signal detection device.

[Explanation of symbols]

1,11,21 Pilot signal detection device 2 Signal input detection means 3 FM demodulation means 4 filters 5 Pilot signal detection means 6 Alarm generation means 7 Signal blocking means 8 Bias control means 10 signal source SMF MF modulation signal SDM demodulated signal SA1, SA2 alarm drive signal SPL, SPLO pilot signal SN1, SN2, SNO noise SOF cutoff signal SB bias control signal SBT bias stop signal VB voltage bias IB current bias

Claims (6)

[Claims] 1. A signal input detecting means for detecting an FM modulated signal, an FM demodulating means for demodulating the FM modulated signal supplied from the signal input detecting means to output a demodulated signal, and a pilot signal extracted from the demodulated signal. Filter, a pilot signal detecting means for detecting the voltage level of the pilot signal supplied from the filter and comparing the voltage level with a reference level, and a reference level for which the voltage level of the pilot signal supplied from the pilot signal detecting means is preset. Alarm generating means for generating an alarm when the frequency is out of the range, the signal input detecting means outputs an alarm drive signal when the FM modulated signal is not detected, and the alarm generating means A pilot signal detecting device characterized in that an alarm is forcibly generated from the device. 2. A signal input detecting means for detecting an FM modulated signal, an FM demodulating means for demodulating the FM modulated signal supplied from the signal input detecting means to output a demodulated signal, and a pilot signal extracted from the demodulated signal. Filter, a pilot signal detecting means for detecting the voltage level of the pilot signal supplied from the filter and comparing the voltage level with a reference level, and a reference level for which the voltage level of the pilot signal supplied from the pilot signal detecting means is preset. An alarm generation means for generating an alarm when the level is out of the range and a signal cutoff means for cutting off the demodulation signal are provided, and the signal input detection means is a cutoff signal when the FM modulation signal is not detected. To the signal cut-off means to cut off the noise output from the FM demodulation means, and the alarm generation means The pilot signal detecting apparatus characterized by generating a beam. 3. The pilot signal detecting device according to claim 2, wherein the signal cut-off means is a signal attenuator capable of varying a noise level attenuation amount. 4. A signal input detecting means for detecting an FM modulated signal, an FM demodulating means for demodulating the FM modulated signal supplied from the signal input detecting means and outputting a demodulated signal, and a pilot signal extracted from the demodulated signal. Filter, a pilot signal detecting means for detecting the voltage level of the pilot signal supplied from the filter and comparing the voltage level with a reference level, and a reference level for which the voltage level of the pilot signal supplied from the pilot signal detecting means is preset. An alarm generation unit that generates an alarm when the level is out of the range and a bias control unit that controls the bias of the FM demodulation unit are provided, and the signal input detection unit is provided when the FM modulation signal is not detected. Supplies a bias stop signal to the bias control means to stop the operation of the FM demodulation means, The pilot signal detecting apparatus characterized by generating an alarm from the beam generating means. 5. The pilot signal detection device according to claim 4, wherein the bias control means provides a voltage bias or a current bias to the FM demodulation means. 6. The pilot signal detection device according to claim 1, wherein the filter is a bandpass filter or a lowpass filter.