JPH06276026A - Contiguous disturbance detecting device for amplitude-modulated signal - Google Patents

Abstract

PURPOSE:To obtain the contiguous disturbance detecting device for the amplitude-modulated signal which can automatically be switched from disturbance of a contiguous channel and provides convenience to a user by providing with an intermediate frequency filter, a contiguous carrier detecting means, a low-pass filter, and a switch. CONSTITUTION:An independent sideband demodulator 20 which demodulates the intermediate frequency signal of the intermediate frequency filter 1 independently expands the band of the intermediate frequency filter 1 to a range including the carrier frequency of the contiguous channels. Contiguous carrier detecting means 21 and 22 input the upper side wave signal and lower side wave signal outputted by the independent sideband demodulator 20 respectively and detects a carrier of contiguous disturbance. Further, low-pass filters 23 and 24 input the modulated upper side wave signal and lower side wave signal respectively and remove the signal of the modulated carrier of the disturbance of the contiguous channels. Switches 25 and 26 switch the outputs of the low-pass filters 23 and 24 so as to output the opposite side wave signal from the side wave signal including the detected contiguous channel carrier signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an independent sideband receiving apparatus, and more particularly to the present invention relates to automatically selecting a sideband signal that has not received adjacent interfering waves.

[0002]

2. Description of the Related Art Conventionally, there are techniques described below as techniques in such a field. FIG. 7 is a diagram showing a conventional adjacent interference detection device for amplitude-modulated signals. Note that, throughout the drawings, the same reference numerals or symbols are used to represent the same components. The adjacent interference detection device for an amplitude-modulated signal shown in this figure is a part of an independent sideband (IndependentSideband) receiver, and the frequency of a high-frequency signal is an intermediate frequency (450K).
Hz) and remove the signal of the unnecessary frequency of the intermediate frequency, the independent sideband demodulator 20 connected to the intermediate frequency filter 1, and the independent sideband demodulator 10. And a switch 8 for switching the output of. The independent sideband demodulator 20 includes a 90 ° phase shifter 2 that forms a quadrature component with respect to the in-phase component that is the output of the intermediate frequency filter 1, an in-phase component that is the output of the intermediate frequency filter 1 and a 90 ° phaser. The multipliers 3 and 4 for synchronously detecting the quadrature component that is the output of 2 and the intermediate frequency filter 1
Is connected to each of the multipliers 3 and 4 and a phase-locked loop (PLL) 5 for extracting a carrier wave for inputting a signal from the input terminal to perform independent detection and outputting the carrier wave to the multipliers 3 and 4. = 9 KHz, the low pass filters 7 and 8 for band limiting, and φ2 = 12 if connected to the low pass filters 7 and 8 and φ1 = 30 ° in FIG.
Phase shifters 9 and 10 for making a 0 ° shift and a difference of 90 °, an adder 11 for forming a sum signal of output signals of the phase shifters 9 and 10 and extracting an upper side wave signal, Phaser 9
For switching the outputs of the adder 12 that forms the difference signal between the output signals of 10 and 10 and extracting the lower side signal and the outputs of the adders 11 and 12 and then performing signal processing such as amplification and outputting to a speaker (not shown). The switch 13 is provided.

Next, the operation of the adjacent interference detecting device for the amplitude modulated signal will be described. Generally, the amplitude-amplified signal (AM) at the point A in FIG. 1 is expressed as follows. (1 + asin (wm)) * cos (wc) where a is the amplitude, wm is the angular frequency of the modulated signal, and wc is the angular frequency of the carrier signal. When this is developed and rearranged so as to match the image, it becomes [cos (wc) + a / 2 {sin (wc + wm) -sin (wc-wm)}.

The signal at point B with a 90 ° phase shift is expressed as follows. [Sin (wc) + a / 2 {cos (wc + wm) -cos (wc-wm)}. The signal at point C at the output of the phase locked loop 5 is represented as: cos (wc) Accordingly, the signal at the point I, which is the output of the multiplier 3, can be expressed as follows.

[Cos (wc) + a / 2 {sin (wc + wm) -sin (wc-wm)} × cos (wc) = 1/2 {cos (2wc) +1} + a / 4 {sin (2wc + wm) ) + Sin (wm)}-(upper side wave) a / 4 {sin (2wc-wm) + sin (-wm)} (lower side wave) Moreover, the signal of the point J which is the output of the multiplier 3 is as follows. Can be represented.

[Sin (wc) + a / 2 {cos (wc + wm) -cos (wc-wm)} * cos (wc) = 1/2 {sin (2wc)} + a / 4 {cos (2wc + wm) + Cos (wm)}-(upper side wave) a / 4 {cos (2wc-wm) + cos (-wm)} (lower side wave) The high pass component is removed by the low pass filters 7 and 8, and the phase shifter 9 and When φ1 = 0 ° and φ2 = 90 ° by 10, the signal at point E can be expressed as follows.

[0007] Further, at the point F, it can be expressed as follows. Thus, the upper side wave signal and the lower side wave signal can be separated by the adders 11 and 12, and the upper side wave signal, H
At that point the lower side signal can be obtained. That is, in this way, demodulation is independently performed for each of the upper side wave signal and the lower side wave signal.

By the way, the bandwidth of the intermediate frequency filter 1 is usually 450 ± 7K in order to avoid mixing from an adjacent broadcasting station.
It is set to Hz. However, due to the influence of the ionosphere or the like, a signal from a distant broadcasting station may be mixed in as interference of an adjacent channel, resulting in deterioration of sound quality. For this reason, when the listener detects the adjacent disturbance based on the sound reproduced by the speaker, the listener can select the other side wave signal by the switch 13 to secure better sound quality.

[0009]

However, in the conventional apparatus for detecting the adjacent interference of the amplitude-modulated signal, the user has to switch the operation by his / her own judgment, which is inconvenient when the receiving apparatus is mounted on the vehicle. There is a problem that is. Therefore, in view of the above problems, it is an object of the present invention to provide a device for detecting adjacent interference of an amplitude-modulated signal which can automatically switch from interference of adjacent channels and which is convenient for the user.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention receives a side-wave signal of an amplitude-modulated signal and a side-side signal of the amplitude-modulated signal, and has a side-channel signal having an adjacent channel that interferes with reception. In the adjacent interference detection device for the amplitude-modulated signal for detecting an adjacent channel and switching to a side wave signal in which no adjacent channel exists, an intermediate frequency filter, an adjacent carrier wave detection means,
Provide a low pass filter and switch.

The intermediate frequency filter is designed to widen the band for converting the high frequency signal into the intermediate frequency signal to the extent that the carrier frequency of the adjacent channel is included. The adjacent carrier wave detecting means detects the carrier wave signals of adjacent channels included in the upper side wave signal and the lower side wave signal formed by demodulating the intermediate frequency signal.

The low pass filter is band-limited to remove adjacent channel carriers contained in the demodulated upper side signal and lower side wave signal. The switch is configured to switch the output of the low pass filter so as to output a side wave signal opposite to the detected side wave signal including the adjacent channel carrier signal.

It is also possible to switch to the output of the side wave signal having the smaller level of the detected adjacent channel carrier signal.

[0014]

According to the adjacent interference detecting apparatus for the amplitude-modulated signal of the present invention, the intermediate frequency filter widens the band for converting the high frequency signal into the intermediate frequency signal to the extent that the carrier frequency of the adjacent channel is included. The carrier signals of the adjacent channels included in the upper side signal and the lower side signal formed by demodulating the frequency signal are respectively detected, and at the same time, included in the demodulated upper side signal and the lower side signal by band limitation. The adjacent channel carrier is removed, and the side signal opposite to the detected side channel signal including the adjacent channel carrier signal is output, so that the automatic switching can be performed, and the listener needs to manually switch as in the past. Is gone. Also, by switching to the output of the side signal whose detected level of the adjacent channel carrier signal is lower, even if there are adjacent channels in both of the side bands at the same time, it is automatically switched to a more advantageous side band. it can.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a first example of an adjacent interference detection device for an amplitude modulated signal according to an embodiment of the present invention. In the adjacent interference detection device for an amplitude-modulated signal shown in the figure, the independent sideband demodulator 20 that independently demodulates the intermediate frequency signal of the intermediate frequency filter 1 as described above, sets the band of the intermediate frequency filter 1 to the adjacent channel. Adjacent carrier detection means 21 and 22 for expanding to a range including a carrier frequency and inputting an upper side wave signal and a lower side wave signal which are outputs thereof to detect a carrier wave of adjacent interference, and an independent side band demodulator. The low-pass filters 23 and 24 for inputting the upper-side signal and the lower-side signal, respectively, which are the outputs of 20 and removing the demodulated signals of the interfering carrier waves of the adjacent channels, and the low-pass filters 23 and 24, respectively. Switches 25 and 26 which are connected and are switched by the outputs of the adjacent carrier wave detecting means 21 and 22 and the result is output to a speaker or the like not shown.
And.

FIG. 2 is a diagram for explaining the configuration of the adjacent carrier wave detecting means 21 and 22 of FIG. The adjacent carrier wave detecting means 21 and 22 shown in this figure are connected to the independent sideband demodulator 20 and are connected to the bandpass filter 31 for extracting a signal having a center frequency of 9 kHz, and are connected to the bandpass filter 31 to rectify an AC signal. Level forming means 32 for converting into a DC component to form a signal level, and comparing means 33 for comparing the signal level obtained by the level forming means 32 with a reference value to determine the presence or absence of an adjacent carrier.

FIG. 3 is a diagram for explaining the pass band of the intermediate frequency filter 1 of the independent sideband demodulator 20 of FIG. This figure (a) is a figure explaining the pass band of the conventional intermediate frequency filter 1. As shown in FIG. For example, in Japan, AM broadcasting has an inter-channel frequency of 9 KHz, so the pass band of the intermediate frequency filter 1 of the receiver is usually set to 450 ± 7 KHz as described above. When an adjacent channel is received while receiving a signal in a sideband for a desired carrier, sideband accompanying the carrier causes interference as shown by the hatched portion in FIG. On the other hand, this figure (b) is a figure explaining the pass band of the intermediate frequency filter 1 of this invention.
The intermediate frequency filter 1 shown in the figure is composed of a band pass filter, and its pass band is widened so that carrier signals of upper and lower adjacent channels can be taken in with an intermediate frequency of 450 KHz as a center frequency. That is, considering that the frequency between adjacent channels is 9 KHz, the intermediate frequency is set to 450 KHz ± 10 KHz.

FIG. 4 is a diagram for explaining the characteristics of the adjacent carrier wave detecting means 21 and 22 and the low pass filters 23 and 24 of FIG. This figure (a) shows the pass band after being demodulated by the independent side band demodulator 20 with respect to the pass band of the intermediate frequency filter 1, and shows the side wave signal of the desired carrier, the signal of the adjacent channel and its side wave signal. Some pass. This figure (b) is a diagram showing the pass band of the adjacent carrier wave detecting means 21 and 22, and only the carrier wave signal of the adjacent channel passes through the adjacent carrier wave detecting means 21 and 22, whereby the adjacent channel can be detected. . This figure (c) is a figure which shows the pass band of the low-pass filters 23 and 24, and these low-pass filters 23 and 24 perform a band limitation narrowed by the band widened by the intermediate frequency filter 1, and play a part. The carrier of the included adjacent channel is removed.

Therefore, the adjacent carrier wave detecting means 21 and 22 of this embodiment detect whether an adjacent channel exists in the upper side wave or the lower side wave signal, and the low pass filter is detected in the direction in which the adjacent channel does not exist. Since 23 and 24 are switched and output, it is possible to automatically switch and it is not necessary for the listener to manually switch as in the conventional case.

Although the above description has been made in the case where the adjacent channel exists in either one of the side signal, the case where the adjacent channel exists in both of the side signals at the same time has a lower probability as compared with the above. Therefore, automatic switching in this case will be described. FIG. 5 is a diagram showing a second example of the adjacent interference detection of the adjacent interference detection device for the amplitude modulated signal according to the embodiment of the present invention, and FIG. 6 is an adjacent carrier wave detecting means 31 of FIG.
It is a figure which shows the structure of 32.

The configuration shown in this figure differs from that of FIG. 1 in the adjacent carrier wave detecting means 31 and 32 and the comparing means 33. As shown in FIG. 6, the adjacent carrier wave detecting means 31 and 32 have substantially the same configuration as that of FIG. 2, but a comparing means 43 is provided instead of the comparing section 33 of the adjacent carrier wave detecting means 21 and 22. . Adjacent carrier wave detection means 41 and 4
When the adjacent channels are simultaneously detected in 2, the comparison means 4
It is configured such that which of the detection levels is smaller is determined by 3 and the output of the low pass filters 23 and 24 is switched to the one having the smaller detection level.

[0022]

As described above, according to the present invention, the upper band formed by demodulating the intermediate frequency signal by widening the band for converting the high frequency signal into the intermediate frequency signal to the extent that the carrier frequencies of the adjacent channels are included. The carrier signals of the adjacent channels included in the wave signal and the lower side signal are detected, respectively, and at the same time, the carrier signals of the adjacent channels included in the demodulated upper wave signal and the lower side wave signal are removed by band limitation and detected. Since the side signal that is the opposite of the side signal including the adjacent channel carrier signal is output, it is possible to automatically switch, and the listener does not have to manually switch as in the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing a first example of an adjacent interference detection device for an amplitude-modulated signal according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of adjacent carrier wave detecting means 21 and 22 of FIG.

3 is a diagram illustrating a pass band of an intermediate frequency filter 1 of the independent sideband demodulator 20 of FIG.

FIG. 4 is a diagram for explaining the characteristics of adjacent carrier wave detecting means 21 and 22 and low pass filters 23 and 24 of FIG.

FIG. 5 is a diagram showing a second example of the adjacent interference detection device for amplitude-modulated signals according to the embodiment of the present invention.

6 is a diagram showing a configuration of adjacent carrier wave detection means 31 and 32 of FIG.

FIG. 7 is a diagram showing a conventional adjacent-channel interference detection device for amplitude-modulated signals.

[Explanation of symbols]

 1 ... Intermediate frequency filter 2 ... 90 degree phase shifter 3, 4 ... Multiplier 5 ... Phase lock loop 7, 8, 23, 24 ... Low pass filter 9, 10 ... Phase shifter 11, 12 ... Adder 13, 25, 26 ... Switch 20 ... Independent sideband demodulator 21, 22 ... Adjacent carrier detecting means

Claims (2)

[Claims] 1. An amplitude-modulated signal which receives an upper-side signal and a lower-side signal of an amplitude-modulated signal, detects a side-wave signal having an adjacent channel that interferes with reception, and switches to a side-wave signal having no adjacent channel. In an apparatus for detecting adjacent signal interference, an intermediate frequency filter (1) that widens a band for converting a high frequency signal into an intermediate frequency signal to the extent that a carrier frequency of an adjacent channel is included; and an upper side wave formed by demodulating the intermediate frequency signal. Adjacent carrier detecting means (11, 12) for detecting the carrier signals of the adjacent channels included in the signal and the lower side signal, and removing the carrier of the adjacent channels included in the demodulated upper side signal and the lower side signal. A low pass filter (13, 14) for band limiting in order to: a side wave opposite to the side wave signal containing the detected adjacent channel carrier signal Said switch switches the output of the low-pass filter (13, 14) to output a No. (1
5, 16), and an adjacent interference detection device for an amplitude-modulated signal. 2. The adjacent carrier wave detection means (11, 12)
Instead of the above, the amplitude modulated modulation according to claim 1, further comprising adjacent carrier detecting means (31, 32) for switching to the output of the side wave signal having a smaller level of the detected adjacent channel carrier signal. Signal adjacent interference detection device.