JPH0654266A - Microwave transmission system - Google Patents

Abstract

PURPOSE:To reduce the beat component due to transmission characteristic, especially, intermodulation to increase the output up to the saturation output of a used device without degrading the picture quality by directly performing amplitude modulation in the SHF band to prevent expansion of the occupied band while simplifying the circuit constitution and eliminating the SHF amplitude part of a modulated wave to eliminate the nonlinear distortion. CONSTITUTION:A carrier signal of the SHF band is generated by an SHF local oscillation circuit 6 and is amplified by an SHF amplifying circuit 7, and an audio signal as the object is subjected to FM modulation by an FM modulating circuit 3 and is synthesized with a video signal as the transmission object by a video synthesizing circuit 5, and the carrier signal of the SHF band is subjected to AM modulation in an AM modulation circuit 8 by the composite signal obtained by synthesizing operation, and the vestigial sideband is cut by a VSBF circuit 9 to generate a transmission signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave transmission system for transmitting a video signal and an audio signal by using a radio wave in the microwave band (a radio wave having a frequency of about 3 GHz to 30 GHz).

SUMMARY OF THE INVENTION The present invention relates to a baseband video signal and a frequency-modulated audio signal when transmitting a video signal and an audio signal using a microwave band (hereinafter referred to as SHF band) radio wave. And are used as subcarriers, and the amplitude modulation (hereinafter,
By performing the AM modulation) and transmitting, the occupied bandwidth is halved as compared with the transmission method using the conventional frequency modulation (hereinafter referred to as FM modulation), and the conventional SHF is used.
The output is significantly increased compared to the AM modulation method using an amplifier circuit.

[0003]

2. Description of the Related Art As a transmission method for transmitting a video signal and an audio signal using SHF radio waves, a baseband video signal and an audio signal obtained by FM-modulating a 5.8 MHz or 6.2 MHz subcarrier signal have been conventionally used. And an FM transmission method for FM-modulating a signal obtained by multiplexing and transmitting the signal, and an FM signal for an audio signal and an FM signal for an audio signal, which are then combined to form an intermediate frequency (hereinafter referred to as an IF frequency). ) Is further combined, and the AM transmission system is known in which the frequency is converted to the SHF band after the combination.

FIG. 10 is a block diagram showing an example of a transmitter using the FM transmission method described above.

The transmitter shown in this figure takes in a voice signal to be transmitted and amplifies it, and a voice signal outputted from the voice amplifier circuit 5.8.
An FM modulation circuit 152 for FM-modulating a subcarrier signal of MHz or 6.2 MHz, a video amplification circuit 153 for amplifying a baseband video signal to be transmitted, a video signal output from the video amplification circuit 153, and the FM. A video sound synthesizing circuit 154 that multiplexes and synthesizes a sound signal output from the modulation circuit 152, an SHF local oscillator circuit 155 that generates a carrier signal in a preset SHF wave band, and this SHF local oscillator circuit 155. SHF amplifier circuit 156 for amplifying a carrier signal output from the video signal synthesis circuit 15
The composite signal output from the SHF amplifier circuit 156
An FM modulation circuit 157 that FM-modulates a carrier signal output from the SH modulator, and an SH output from the FM modulation circuit 157.
An SHF amplifier circuit 158 that amplifies a signal in the F band (modulated wave signal) and outputs the amplified signal as a transmission signal.

Then, the baseband video signal to be transmitted is amplified, and a subcarrier signal of 5.8 MHz or 6.2 MHz is FM-transmitted as an audio signal to be transmitted.
After modulating and multiplexing the audio signal and the video signal obtained by each of these processes, the SHF wave band signal is FM-modulated by this composite signal, and this is amplified and transmitted.

FIG. 11 is a block diagram showing an example of a transmitter using the AM transmission method described above.

The transmitting apparatus shown in this figure takes in an audio amplifier circuit 161 for taking in and amplifying an audio signal to be transmitted, and a subcarrier signal of a frequency preset by the audio signal output from this audio amplifier circuit 161. FM modulating FM
A modulation circuit 162, a video amplification circuit 163 that amplifies a baseband video signal to be transmitted, and an AM modulation that AM-modulates a subcarrier signal having a frequency preset by an audio signal output from the video amplification circuit 163. Circuit 164
A video signal synthesizing circuit 165 for multiplexing and synthesizing the video signal output from the AM modulation circuit 164 and the audio signal output from the FM modulation circuit 162, and a signal having a preset frequency (IF signal). ) Is generated by the IF local oscillator circuit 166, and I output from the IF local oscillator circuit 166.
A frequency conversion circuit 167 that frequency-converts the composite signal output from the audio-voice synthesis circuit 165 with an F signal, and a frequency-converted IF output from the frequency conversion circuit 167.
An IF amplifier circuit 168 for amplifying a signal, an SHF local oscillator circuit 169 for generating a carrier signal of a preset SHF wave band, and an IF output from the IF amplifier circuit 168.
SHF output from the SHF local oscillator circuit 169 as a signal
Frequency conversion circuit 17 for frequency-converting carrier wave signal in waveband
0 and the SHF output from this frequency conversion circuit 170
S that amplifies the waveband signal and outputs it as a transmission signal
And an HF amplifier circuit 171.

Then, after amplifying the baseband video signal to be transmitted, it is AM-modulated, and the subcarrier signal having a frequency preset by the audio signal to be transmitted is FM-modulated. The obtained audio signal and video signal are multiplexed, and the IF signal having a frequency preset by the composite signal is frequency-converted, and then the SHF wave band signal is frequency-converted by the IF signal. The converted SHF band signal is amplified and transmitted.

[0010]

However, the above-mentioned conventional microwave transmission system has the following problems.

First, the FM modulation type transmission system shown in FIG. 10 has an advantage that the circuit configuration can be simplified, but has a problem that the occupied bandwidth of the transmission signal becomes wide.

Further, in the AM modulation type transmission system shown in FIG. 11, the non-linear distortion of the SHF amplifier circuit 171 causes a cross modulation component due to a video frequency, an audio frequency, and a color carrier, and a third order cross modulation of this cross modulation component. Due to the component, there is a problem that a spurious component is generated at a video frequency of ± 920 KHz and the image quality is deteriorated.

In order to solve such a problem, therefore, in such an AM modulation type transmission system, a device having a high intercept point level is selected and the saturation output is about one-tenth of the saturated output of the device used. By making the output, the spurious component in the portion of the video frequency ± 920 KHz is reduced and the required image quality is ensured.

However, such a method has a problem in that it is possible to obtain only about 1/10 of the saturated output of the device used.

In view of the above-mentioned circumstances, the present invention makes it possible to prevent the occupied band from expanding while performing the amplitude modulation directly in the SHF wave band, while keeping the circuit structure simple and preventing the occupied band from expanding. To eliminate the nonlinear distortion and thereby reduce the transmission characteristics, especially the beat component due to intermodulation, thereby increasing the output up to near the saturated output of the device used without degrading the image quality. It is intended to provide a scheme.

[0016]

In order to achieve the above object, the microwave transmission system according to the present invention takes in a signal to be transmitted, converts it into a transmission signal in the SHF band, and transmits it. In a microwave transmission method that receives a transmission signal in the SHF band, demodulates it, and reproduces the transmitted signal, in the transmission side, while generating a carrier signal in the SHF band, the audio signal to be transmitted is FM-modulated. At the same time, the audio signal and the video signal to be transmitted are combined, and the composite signal obtained by this combining operation is used for the S
The carrier signal in the HF band is AM-modulated at the final stage to generate a transmission signal, the reception signal receives the transmission signal, frequency-converts this, and then AM demodulates and performs separation processing to reproduce a video signal. In addition, the audio signal obtained by the separation processing is FM-demodulated to reproduce the audio signal.

[0017]

In the above structure, while the carrier signal of the SHF band is generated on the transmitting side, the voice signal to be transmitted is F
While M-modulating, the audio signal and the video signal to be transmitted are combined, and the composite signal obtained by the combining operation is AM-modulated on the carrier signal in the SHF band to generate a transmission signal. After receiving the transmission signal and frequency-converting the transmission signal, AM demodulation and separation processing are performed to reproduce a video signal, and the audio signal obtained by the separation processing is FM demodulated to reproduce an audio signal. As a result, by directly performing amplitude modulation in the SHF wave band, while simplifying the circuit configuration, the occupied band is prevented from widening, and the SHF amplification part of the modulated wave is eliminated to eliminate the nonlinear distortion, which results in the transmission characteristics. In particular, the output is increased to near the saturated output of the device used without deteriorating the image quality by reducing the beat component due to intermodulation.

[0018]

1 is a block diagram showing an example of a transmitting apparatus to which a first embodiment of a microwave transmission system according to the present invention is applied, and FIG. 2 is a block showing an example of a receiving apparatus to which the first embodiment is applied. It is a figure.

The microwave transmitter shown in FIG. 1 has a voice amplifier circuit 2 for taking in and amplifying a voice signal to be transmitted.
And an FM modulation circuit 3 that FM-modulates a sub-carrier signal having a frequency (4.5 MHz) preset by an audio signal output from the audio amplification circuit 2, and a baseband video signal to be transmitted is amplified. A video amplification circuit 4, a video sound synthesis circuit 5 for multiplexing and synthesizing a video signal output from the video amplification circuit 4 and an audio signal output from the FM modulation circuit 3, and a preset SHF wave. The SHF local oscillator circuit 6 that generates a band carrier signal, the SHF amplifier circuit 7 that amplifies the carrier signal output from the SHF local oscillator circuit 6, and the composite signal output from the video sound synthesis circuit 5 The carrier signal output from the amplifier circuit 7 is A
An AM modulation circuit 8 that performs M modulation, and a residual sideband filter circuit (VSBF) that takes in the SHF waveband modulated signal output from the AM modulation circuit 8 and cuts the residual sideband portion
Circuit) 9.

Next, the operation of this transmitter will be described with reference to the frequency spectrum diagrams shown in FIGS.

First, the SHF local oscillator circuit 6 generates a carrier signal in the SHF band, the SHF amplifier circuit 7 amplifies the carrier signal, and the video amplifier circuit 4 takes in a baseband video signal to be transmitted and captures it. Along with the amplification, the audio amplification circuit 2 takes in and amplifies the audio signal to be transmitted.

Then, the audio signal output from the audio amplifier circuit 2 is taken in by the FM modulator circuit 3, and the subcarrier signal of the frequency preset by the audio signal is F
After M-modulation, the audio signal and the video signal obtained by the above-mentioned respective processes are multiplexed by the image sound synthesis circuit 5 to generate the composite signal shown in FIG.

After that, the SHF amplifier circuit 7 outputs the composite signal output from the video sound synthesis circuit 5 by the AM modulation circuit 8.
The signal in the SHF band output from the AM is AM-modulated to form the modulated signal in the SHF band shown in FIG. 4, and the residual side band is cut by the vestigial side band filter circuit 9 to transmit the signal shown in FIG. Generate a signal and output it.

The microwave receiving apparatus shown in FIG. 2 includes a low noise type SHF receiving circuit 10 for receiving a transmission signal in the SHF band and an SHF local oscillator for generating a preset local oscillation signal in the SHF band. A circuit 11, a local oscillator signal output from the SHF local oscillator circuit 11, and the SHF receiving circuit 10
A frequency conversion circuit 12 that mixes a received signal output from the frequency conversion circuit 12 to perform frequency conversion to generate an IF signal; an IF amplification circuit 13 that amplifies the IF signal output from the frequency conversion circuit 12; IF local oscillator circuit 14 for generating a local oscillator signal in the IF band, the local oscillator signal output from the IF local oscillator circuit 14, and the IF amplifier circuit 1
And a frequency conversion circuit 15 that mixes the IF signal output from 3 to perform frequency conversion to generate an IF signal.

Further, this receiving device takes in the signal output from the frequency conversion circuit 15 and performs AM demodulation on it.
An M demodulation circuit 16, a video sound separation circuit 17 that separates the demodulated signal output from the AM demodulation circuit 16 into a video signal and an audio signal, and a video that amplifies the video signal output from the video sound separation circuit 17. An amplifier circuit 18, an FM demodulation circuit 19 for FM demodulating the audio signal output from the video sound separation circuit 17, and an audio amplifier circuit 20 for amplifying the audio signal output from the FM demodulation circuit 19 are provided. .

Then, the SHF receiving circuit 10 causes the SH
The F-band transmission signal is received, frequency-converted into an IF-band signal by the SHF local oscillator circuit 11 and the frequency conversion circuit 12, and then amplified by the IF amplification circuit 13.

Then, the I output from the IF amplification circuit 13 by the IF local oscillator circuit 14 and the frequency conversion circuit 15 is performed.
The F signal is frequency-converted, the AM demodulation circuit 16 performs AM demodulation, and the after-image separation circuit 17 separates the video signal and the audio signal.

The video amplification circuit 18 amplifies and outputs the video signal output from the video sound separation circuit 17, and the FM demodulation circuit 19 FM demodulates the audio signal output from the video sound separation circuit 17. Then, the audio amplification circuit 20 amplifies and outputs.

As described above, in the first embodiment,
A carrier signal in the SHF band is generated, and while being amplified by the SHF amplifier circuit 7, the audio signal to be transmitted is FM-modulated and synthesized with the video signal to be transmitted, and a composite signal obtained by this synthesizing operation. Since the carrier signal in the SHF band is AM-modulated and the residual sideband is cut to generate the transmission signal, the occupied band is reduced while simplifying the circuit configuration to the same extent as the conventional AM modulation method. It is possible to prevent the spread and to eliminate the nonlinear distortion by eliminating the SHF amplification part of the modulated wave which has been a problem in the conventional AM modulation method, so that the transmission characteristic, especially the beat component due to the intermodulation is reduced. Thus, the output can be increased to near the saturated output of the device used without degrading the image quality.

FIG. 6 is a block diagram showing an example of a transmitting device to which the second embodiment of the microwave transmission system according to the present invention is applied, and FIG. 7 is a block diagram showing an example of a receiving device to which the second embodiment is applied. Is.

The transmitting apparatus shown in FIG. 6 comprises a first transmission signal generating section 25, a second transmission signal generating section 26, and a combining section 27, and the first transmission signal generating section 25 transmits the first channel. In addition to generating the signal, the second transmission signal generation unit 26 generates the transmission signal of the first channel, and the respective transmission signals are combined and output by the combining unit 27.

The first transmission signal generation unit 25 takes in an audio signal to be transmitted and amplifies it, and an audio signal output from the audio amplification circuit 28, which is a subcarrier signal having a frequency preset. FM modulation circuit 29 for FM-modulating, a video amplification circuit 30 for amplifying a baseband video signal to be transmitted, a video signal output from the video amplification circuit 30, and an audio signal output from the FM modulation circuit 29. Video sound synthesis circuit 3 for multiplexing and synthesizing
1, an SHF local oscillator circuit 32 for generating a carrier signal of a preset SHF wave band, and this SHF local oscillator circuit 32.
SHF amplifier circuit 3 for amplifying the carrier signal output from
3 and the composite signal output from the video sound synthesizing circuit 31 is the carrier signal output from the SHF amplifier circuit 33.
AM modulation circuit 34 for M modulation, and this AM modulation circuit 34
The vestigial sideband filter circuit (VS which takes in the SHF waveband modulated signal output from
BF circuit) 35.

Then, a carrier signal in the SHF band is generated, and while being amplified by the SHF amplifier circuit 33, the audio signal to be transmitted is FM-modulated and synthesized with the modulated audio signal and the video signal to be transmitted. Then, the carrier signal in the SHF band is A
M modulation is performed to cut off the residual sideband to generate a transmission signal of the first channel, which is supplied to the combining unit 27.

Further, the second transmission signal generation section 26 takes in an audio signal to be transmitted and amplifies the audio signal 36.
An FM modulation circuit 37 that FM-modulates a subcarrier signal having a preset frequency with an audio signal output from the audio amplification circuit 36; and an image amplification circuit 38 that amplifies a baseband video signal to be transmitted. A video sound synthesizing circuit 39 for multiplexing and synthesizing a video signal output from the video amplifying circuit 38 and an audio signal output from the FM modulating circuit 37, and a local oscillation signal in a preset IF band. The IF local oscillator circuit 40 to be generated, the local oscillator signal output from the IF local oscillator circuit 40 and the carrier signal in the SHF band output from the SHF local oscillator circuit 32 of the first transmission signal generator 25 are mixed. And a frequency conversion circuit 41 for generating a carrier signal having a frequency deviated from the frequency of the carrier signal by the frequency of the local oscillation signal. S for amplifying a carrier signal output
An HF amplifier circuit 42, an AM modulation circuit 43 that AM-modulates the carrier signal output from the SHF amplifier circuit 42 with the composite signal output from the video sound synthesis circuit 39, and
There is provided a vestigial sideband filter circuit (VSBF circuit) 44 which takes in the SHF waveband modulated signal output from the M modulation circuit 43 and cuts the vestigial sideband portion.

Then, the carrier signal in the SHF band output from the first transmission signal generating section 25 is fetched, and this is taken as an IF signal.
After frequency conversion is performed by the local oscillator circuit 40 and the frequency conversion circuit 41, the audio signal to be transmitted is FM-modulated while being amplified by the SHF amplifier circuit 42 to be combined with the modulated audio signal and the video signal to be transmitted. The carrier signal in the SHF band is AM-modulated with the composite signal obtained by this combining operation to cut the residual sideband to generate a second-channel transmission signal, which is supplied to the combining unit 27.

The synthesizer 27 is the first transmission signal generator 25.
The shared circuit 45 for synthesizing the transmission signal of the first channel output from the second transmission signal generation unit 26 and the transmission signal of the second channel output from the second transmission signal generation unit 26 is provided. The output signal of the first channel and the output signal of the second channel output from the second transmission signal generation unit 26 are combined to generate a transmission signal having two channels, and this is output.

The microwave receiver shown in FIG. 7 has a receiving / frequency converting section 46 and a first channel demodulating section 47.
And a second channel demodulation unit 48. The reception / frequency conversion unit 46 receives a transmission signal in the SHF band, frequency-converts this to an IF signal, and then the first channel demodulation unit 47 The first channel component in the IF signal is demodulated to generate the video signal and the audio signal on the first channel side and output, and the second channel demodulation unit 48 removes the second channel component in the IF signal. It demodulates to generate a video signal and an audio signal on the second channel side, and outputs this.

The reception / frequency conversion unit 46 is a low noise type SHF reception circuit 49 for receiving a transmission signal in the SHF band, and an SH for generating a local oscillation signal in the preset SHF band.
The F station originating circuit 50, a frequency converting circuit 51 which mixes the station originating signal output from the SHF station originating circuit 50 with the received signal output from the SHF receiving circuit 49 to perform frequency conversion to generate an IF signal. An IF amplifier circuit 52 that amplifies the IF signal output from the frequency conversion circuit 51, an IF local oscillator circuit 53 that generates a local oscillator signal in a preset IF band, and an IF local oscillator circuit 53. The IF signal output from the IF amplifier circuit 52 is mixed with the IF signal output from the IF amplifier circuit 52 to perform frequency conversion.
A frequency conversion circuit 54 that generates a signal and an IF demultiplexing circuit 55 that demultiplexes the IF signal output from the frequency conversion circuit 54 into a first channel component and a second channel component are provided, and the SHF band After receiving the transmission signal and frequency-converting the transmission signal into an IF signal, the IF signal is demultiplexed into a first channel component and a second channel component, and the first channel component is sent to the first channel demodulation unit 47. With supply
The second channel component is supplied to the second channel demodulation unit 48.

The first channel demodulation unit 47 takes in the first channel component output from the IF demultiplexing circuit 55 of the reception / frequency conversion unit 46 and performs AM demodulation on the AM demodulation circuit 56.
A video sound separation circuit 57 that separates the demodulated signal output from the AM demodulation circuit 56 into a video signal and an audio signal; and a video amplification circuit 58 that amplifies the video signal output from the video sound separation circuit 57. An FM demodulation circuit 59 that FM-demodulates the audio signal output from the video sound separation circuit 58 and an audio amplification circuit 60 that amplifies the audio signal output from the FM demodulation circuit 59 are provided. The first channel component output from the IF demultiplexing circuit 55 of the frequency conversion unit 46 is fetched, AM demodulated to reproduce the composite signal, and the composite signal is separated into a video signal and an audio signal. The audio signal is FM-demodulated to reproduce the audio signal, and the audio signal on the first channel side obtained by the FM demodulating operation and the first signal obtained by the separating operation.
Each of the video signals on the channel side is amplified and output.

The second channel demodulation unit 48 takes in the second channel component output from the IF demultiplexing circuit 55 of the reception / frequency conversion unit 46 and performs AM demodulation, and the AM demodulation circuit 61. A sound separation circuit 62 for separating the demodulated signal output from the video signal and the audio signal.
A video amplifier circuit 63 for amplifying the video signal output from the video sound separation circuit 62, and an FM demodulation circuit 64 for FM demodulating the audio signal output from the video sound separation circuit 63.
And an audio amplification circuit 65 for amplifying the audio signal output from the FM demodulation circuit 64, and a second output from the IF demultiplexing circuit 55 of the reception / frequency conversion unit 46.
After the channel component is taken in and AM demodulated to reproduce a composite signal, the composite signal is separated into a video signal and an audio signal, and the audio signal is FM demodulated to reproduce the audio signal, and the FM demodulation is performed. The audio signal on the second channel side obtained by the operation and the video signal on the second channel side obtained by the separating operation are amplified and output.

As described above, in this embodiment, the carrier signal in the SHF band is generated for each channel, and the voice signal to be transmitted is FM-modulated while being amplified by the SHF amplifier circuits 33 and 42. The carrier signal in the SHF band is AM-modulated with the composite signal obtained by this combining operation to cut the residual sideband to generate a transmission signal. , First
Similar to the embodiment, it is possible to keep the occupied band from widening while simplifying the circuit configuration to the same extent as the conventional AM modulation method, and to suppress the SHF of the modulated wave which has been a problem in the conventional AM modulation method. It is possible to increase the output up to near the saturated output of the device to be used without deteriorating the non-linear distortion by eliminating the amplifying portion and thereby reducing the transmission characteristic, particularly the beat component due to the intermodulation and degrading the image quality.

Further, in this second embodiment, SH
It is possible to transmit video signals and audio signals of several channels within one frequency allocation band of the F band, which can promote effective use of radio wave resources.

FIG. 8 is a block diagram showing an example of a transmitter / receiver to which a third embodiment of the microwave transmission system according to the present invention is applied.

The transmission / reception apparatus shown in this figure comprises a transmission signal generation section 70, a demultiplexing section 71, and a transmission signal reception section 72. When a video signal and an audio signal to be transmitted are input, The transmission signal generation unit 70 processes the video signal and the audio signal to generate a transmission signal in the SHF band, outputs the transmission signal via the demultiplexing unit 71, and when the transmission signal in the SHF band is received, The wave unit 71 takes in this signal, and the transmission signal receiving unit 72 demodulates it to reproduce a video signal and an audio signal.

The transmission signal generation unit 70 receives an audio signal to be transmitted and amplifies it, and an audio signal output from the audio amplifier circuit 73, which is a subcarrier signal having a frequency preset by FM. An FM modulation circuit 74 for modulating, a video amplification circuit 75 for amplifying a baseband video signal to be transmitted, a video signal output from the video amplification circuit 75, and an audio signal output from the FM modulation circuit 74. Video sound synthesizing circuit 76 for multiplexing and synthesizing
And an SHF local oscillator circuit 77 that generates a carrier signal in the preset SHF wave band, and an SHF amplifier circuit 78 that amplifies the carrier signal output from the SHF local oscillator circuit 77.
And a carrier signal output from the SHF amplifier circuit 78 is AM by a composite signal output from the video sound synthesis circuit 76.
An AM modulation circuit 79 for modulating, and a residual sideband filter circuit (VSB) for taking in the SHF waveband modulated signal output from the AM modulation circuit 79 and cutting the residual sideband portion.
F circuit) 80.

Then, a carrier signal in the SHF band is generated and, while being amplified by the SHF amplifier circuit 78, the audio signal to be transmitted is FM-modulated and synthesized with the modulated audio signal and the video signal to be transmitted. Then, the carrier signal in the SHF band is A
M modulation is performed to cut off the residual sideband to generate a transmission signal, which is supplied to the demultiplexing unit 71.

The demultiplexing unit 71 connects the transmission signal generating unit 70 and an antenna (not shown), or connects the transmission signal receiving unit 72 and the antenna to the demultiplexing circuit 8.
1 is provided, and when the transmission signal output from the transmission signal generation unit 70 is taken and output to the antenna side, or when the transmission signal in the SHF band is received by this antenna, the demultiplexing unit 71 is used. This is taken in and supplied to the transmission signal receiving section 72.

The transmission signal receiving section 72 is a low noise type SHF receiving circuit 82 for receiving a transmission signal in the SHF band, an SHF local oscillation circuit 83 for generating a preset local oscillation signal in the SHF band, and this SHF. A frequency conversion circuit 84 that mixes the local oscillation signal output from the local oscillation circuit 83 and the reception signal output from the SHF reception circuit 82 to perform frequency conversion to generate an IF signal, and the frequency conversion circuit 8
IF amplification circuit 85 for amplifying the IF signal output from
An IF local oscillator circuit 86 for generating a local oscillator signal in a preset IF band, a local oscillator signal output from the IF local oscillator circuit 86, and an I output from the IF amplifier circuit 85.
A frequency conversion circuit 87 that mixes with the F signal to perform frequency conversion to generate an IF signal, and an AM that takes in the signal output from this frequency conversion circuit 87 and performs AM demodulation
Demodulation circuit 88, video sound separation circuit 89 that separates the demodulated signal output from AM demodulation circuit 88 into a video signal and an audio signal, and video amplification that amplifies the video signal output from this video sound separation circuit 89. The circuit 90 and the video sound separation circuit 8
An FM demodulation circuit 91 that FM-demodulates the audio signal output from 9 and an audio amplification circuit 92 that amplifies the audio signal output from the FM demodulation circuit 91 are provided.

When a transmission signal in the SHF band is output from the demultiplexing unit 71, it is fetched and frequency-converted, and then the IF signal obtained by the frequency conversion operation is AM demodulated to reproduce a composite signal. The composite signal is further separated into a video signal and an audio signal, the audio signal is FM demodulated to reproduce the audio signal, and the audio signal obtained by this FM demodulation operation and the separation operation are obtained. Each of the above video signals is amplified and output.

As described above, in this embodiment, the transmission signal generator 70 FM-modulates the audio signal to be transmitted and synthesizes it with the video signal to be transmitted, and the composite signal obtained by this synthesizing operation is used to perform SHF. After the carrier signal of the band is AM-modulated, the residual sideband is cut to generate a transmission signal, which is transmitted from the antenna via the demultiplexing unit 71, and the transmission signal of the SHF band is received by this antenna. At this time, the demultiplexing unit 71 takes in the signal, frequency-converts it, and obtains I obtained by this frequency-converting operation.
The F signal is AM demodulated to reproduce a composite signal, the composite signal is further separated into a video signal and an audio signal, and the audio signal is FM demodulated to reproduce the audio signal.
Since the audio signal obtained by the demodulating operation and the video signal obtained by the separating operation are amplified and output, respectively, like the first and second embodiments,
While simplifying the circuit structure to the same extent as the conventional AM modulation method, it is possible to prevent the occupied band from expanding, and to eliminate the SHF amplification part of the modulated wave, which is a problem in the conventional AM modulation method, to make it non-linear. Eliminate distortion,
This makes it possible to increase the output up to near the saturated output of the device used without reducing the transmission characteristics, particularly the beat component due to intermodulation, and degrading the image quality.

Furthermore, in the third embodiment, bidirectional video and audio signals can be transmitted within one frequency allocation band of the SHF band by the combination with the same transmitting / receiving device, thereby effectively using radio resources. Can be promoted.

FIG. 9 is a block diagram showing an example of a VHF / UHF / SHF converter device to which the fourth embodiment of the microwave transmission system according to the present invention is applied.

The VHF / UHF / SHF converter device shown in this figure comprises a VHF / UHF receiving section 95 and an SHF transmitting section 96. The VHF / UHF receiving section 95 receives a transmission signal in the VHF / UHF band. The VHF is demodulated by the SHF transmitter 96 and
The video signal demodulated by the UHF receiving unit 95 and the audio signal are processed to generate a transmission signal in the SHF band, which is output.

The VHF / UHF receiving section 95 uses the VHF / UH
V / UHF receiving circuit 97 for receiving F band transmission signal
And a V / UHF local oscillator circuit 98 for generating a local oscillator signal in a preset VHF / UHF band, and this V / UHF
The local oscillator signal output from the local oscillator circuit 98 and the V / UHF
A frequency conversion circuit 99 that mixes a reception signal output from the reception circuit 97 to generate an IF signal by performing frequency conversion, an IF local oscillation circuit 100 that generates a local oscillation signal in a preset IF band, This IF station originating circuit 100
A frequency conversion circuit 10 that mixes the local oscillation signal output from the frequency conversion circuit 99 and the first IF signal output from the frequency conversion circuit 99 to perform frequency conversion to generate the next IF signal.
1 and a picture / sound separation circuit 10 for separating the IF signal output from the frequency conversion circuit 101 into a video signal and an audio signal.
2, an AM demodulation circuit 103 for AM demodulating the video signal output from the video sound separation circuit 102, a video amplification circuit 104 for amplifying the video signal output from the AM demodulation circuit 103, and the video sound separation circuit An FM demodulation circuit 105 for FM demodulating an audio signal output from
An audio amplification circuit 106 for amplifying the audio signal output from the demodulation circuit 105 is provided.

Then, the transmission signal in the VHF / UHF band is received, the frequency of the transmission signal is converted twice to generate the IF signal, the decoded signal is reproduced, and then separated into the video signal and the audio signal, One of them is AM demodulated to reproduce a video signal, the other of the signals obtained by the separation operation is FM demodulated to reproduce an audio signal, and the audio signal obtained by this FM demodulation operation and the AM demodulation are reproduced. Each of the video signals obtained by the operation is amplified and supplied to the SHF transmitter 96.

The SHF transmitting unit 96 FM-modulates the sub-carrier signal having a preset frequency with the audio signal output from the VHF / UHF receiving unit 95.
5, a video sound synthesizing circuit 108 for multiplexing and synthesizing a video signal output from the VHF / UHF receiving unit 95 and an audio signal output from the FM modulating circuit 105, and a preset SHF wave band. SH that generates the carrier signal of
An F station originating circuit 109 and an SHF amplifier circuit 110 for amplifying a carrier signal output from the SHF originating circuit 109.
An AM modulation circuit 111 that AM-modulates the carrier signal output from the SHF amplifier circuit 110 with the composite signal output from the audio-voice synthesis circuit 108, and the SHF wave band output from the AM modulation circuit 111. A vestigial sideband filter circuit (VSBF circuit) 112 that takes in a signal and cuts the vestigial sideband portion is provided.

Then, a carrier signal in the SHF band is generated, and the voice signal output from the VHF / UHF receiving unit 95 is F while the SHF amplifier circuit 110 amplifies the carrier signal.
This audio signal is M-modulated and synthesized with the video signal output from the VHF / UHF receiving unit 95, and the carrier signal in the SHF band is AM-modulated at the final stage by the composite signal obtained by this synthesizing operation. The residual sideband is cut to generate a transmission signal, which is output.

Thus, in this embodiment, VHF
The UHF receiving unit 95 receives a transmission signal in the VHF / UHF band, frequency-converts it twice to generate an IF signal, reproduces a decoded signal, and then separates this into a video signal and an audio signal. One of them is AM demodulated to reproduce a video signal, and the other of the signals obtained by the separation operation is FM demodulated to reproduce an audio signal.
6, the audio signal output from the VHF / UHF receiving unit 95 is FM-modulated, and the audio signal and the video signal output from the VHF / UHF receiving unit 95 are combined to obtain a composite obtained by this combining operation. SH at signal
After the carrier signal in the F band is AM-modulated at the final stage, the residual sideband is cut and a transmission signal is generated and output. Therefore, the transmission signal in the VHF / UHF band is received and this is SHF. It is possible to convert to a transmission signal of a band, and at this time, it is possible to prevent the occupied band of the transmission signal of the SHF band from expanding as in the above-described first to third embodiments, and at the same time, to improve the transmission characteristics, especially the mutual characteristics. Without degrading the image quality by reducing the beat component due to modulation,
The output can be increased to near the saturated output of the device used.

[0059]

As described above, according to the present invention, S
Direct amplitude modulation at the final stage of the HF wave band and VS
With the BF circuit, it is possible to keep the occupied band from expanding while simplifying the circuit configuration, and to eliminate the SHF amplification part of the modulated wave to eliminate the nonlinear distortion.
This makes it possible to increase the output up to near the saturated output of the device used without reducing the transmission characteristics, particularly the beat component due to intermodulation, and degrading the image quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a transmitter to which a first embodiment of a microwave transmission system according to the present invention is applied.

FIG. 2 is a block diagram showing an example of a receiver to which the first embodiment of the microwave transmission system according to the present invention is applied.

FIG. 3 is a frequency spectrum diagram showing an example of a frequency spectrum of a composite signal output from the video sound synthesis circuit shown in FIG.

4 is a frequency spectrum diagram showing an example of a frequency spectrum of a transmission signal output from the AM modulation circuit shown in FIG.

5 is a frequency spectrum diagram showing a frequency spectrum example of a transmission signal output from the vestigial sideband filter circuit shown in FIG.

FIG. 6 is a block diagram showing an example of a transmission device to which a second embodiment of a microwave transmission system according to the present invention is applied.

FIG. 7 is a block diagram showing an example of a receiver to which a second embodiment of the microwave transmission system according to the present invention is applied.

FIG. 8 is a block diagram showing an example of a transmitter / receiver to which a third embodiment of a microwave transmission system according to the present invention is applied.

FIG. 9 is a block diagram showing an example of a VHF / UHF / SHF converter device to which a fourth embodiment of a microwave transmission system according to the present invention is applied.

FIG. 10 is a block diagram showing an example of a transmission device using a conventionally known SHF band FM transmission system.

FIG. 11 is a block diagram showing an example of a transmission device that uses a conventionally known AM transmission system in the SHF band.

[Explanation of symbols]

 2 Audio amplification circuit 3 FM modulation circuit 4 Video amplification circuit 5 Video sound synthesis circuit 6 SHF local oscillation circuit 7 SHF amplification circuit 8 AM modulation circuit 9 Residual sideband filter circuit (VSBF circuit) 10 SHF reception circuit 11 SHF local oscillation circuit 12 frequency conversion circuit 13 IF amplification circuit 14 IF local oscillation circuit 15 frequency conversion circuit 16 AM demodulation circuit 17 video sound separation circuit 18 video amplification circuit 19 FM demodulation circuit 20 audio amplification circuit

Claims (1)

[Claims] 1. A SHF is used while a signal to be transmitted is taken in, converted into a SHF band transmission signal and transmitted.
In a microwave transmission system that receives a transmission signal in a band, demodulates it and reproduces it, while generating a carrier signal in the SHF band on the transmission side, the sound signal to be transmitted is FM-modulated and And a video signal to be transmitted are combined to generate a composite signal, the carrier signal in the SHF band is AM-modulated at the final stage by the composite signal to generate a transmission signal, and the reception signal is received by the receiving side. Then, after frequency-converting this, AM demodulation is performed and separation processing is performed to reproduce a video signal, and the audio signal obtained by the separation processing is FM.
A microwave transmission method characterized by demodulating and reproducing an audio signal.