JPH09154117A - Filter and broad band television modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the C/N from being deteriorated even when television channel signals from plural modulator units are mixed. SOLUTION: Filters BPF-1 to BPF-n are provided respectively to an output side of a modulator unit. The configuration of the filters BPF-1 to BPF-n is selected identically and each of the filters BPF-1 to BPF-n is made up of filters 1-5 which have a different pass band being divisions of a CATV band and any filter is selected automatically in response to a frequency of a television channel signal sent by the modulator unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter device capable of reducing spurious and obtaining a good C / N, and a wide band television modulator provided with such a filter device.

[0002]

2. Description of the Related Art In recent years, CATV (Cable Television) capable of performing tens of channels of television broadcasting has become widespread. The CATV can take in not only television broadcasting but also broadcasting media such as high-definition television, facsimile, and PCM music broadcasting to provide services to the homes of the respective subscribing companies. FIG. 8 shows an example of a conventional configuration of such a broadband modulator for CATV. In this figure, a video signal (V) and an audio signal (A) are input to the IF modulator 101, and the video intermediate frequency 3
It is modulated to 8.9 MHz and an audio intermediate frequency of 32.4 MHz. The converted video intermediate frequency signal and audio intermediate frequency signal are multiplexed by the multiplexer 102 and input to the first mixer 103.

The first mixer 103 is supplied with the first local frequency F1 of 573.85 MHz from the first station 104, and the video intermediate frequency signal and the audio intermediate frequency signal are frequency-converted to a video carrier 612.75 MHz. At the same time, the voice carrier is converted to 606.25 MHz. The video carrier signal converted by the mixer 103 and the audio carrier signal are band-pass filters (IF / BPF) 1
The unnecessary band component is removed by 05, and the second mixer 10
6 is input. Then, it is converted into a desired television channel in the second mixer 106.
Therefore, the second mixer 106 has 662.5 MHz to 1
The second local frequency F2 is supplied from the second local oscillator 107 capable of oscillating a frequency of 156 MHz.

Further, the television channel signal converted by the second mixer 106 is amplified by a wide band high frequency amplifier (RF Amp) including an amplifier 108, a level adjuster 109, and an amplifier 110, and a band pass filter (BPF) 111 is obtained. Is entered. The television channel signal from which spurious and unnecessary band noise have been removed by the bandpass filter 111 is input to the mixer 170.

In this way, the IF modulator 101 to BPF1
The modulator unit having the configurations up to 11 has the same configuration as the other modulator units having the configurations up to the IF modulation unit 121 to the BPF 131, and further includes the configurations up to the IF modulation unit 151 to the BPF 161. The modulator unit has the same configuration. In such a plurality of modulator units, the video signal and the audio signal are modulated, converted into different television channel signals, and supplied to the mixer 170.

As a result, the television channel signals of different channels output from the plurality of modulator units are combined in the mixer 170 to be CAT.
It will be output as a V signal. In addition, BPF11
An example of the pass characteristics (attenuation characteristics) of 1 to BPF 161 is shown in FIG. 9. The pass characteristics shown in A, B, C, ... G are frequency bandwidths corresponding to one TV channel, respectively. ing. C output from the mixer 170
The ATV signal is transmitted through the cable to be served to each subscriber's house.

[0007]

The reason why the BPF is provided at the end of each modulator unit is as follows. Each modulator unit is provided with a wide band RF Amp, but because this amplifier has a wide band, C
Noise will be output at the same level over the entire ATV band. Here, if the BPF is not provided, the noise over the entire band is output from each modulator unit and mixed in the mixer 170, so that the noise is added.

For example, when n modulator units are provided, noise increases by 10 log (n-1) dB from the mixer 170 that mixes the outputs of the n modulator units. become. If 10 modulator units are provided, noise increases by 10 log (10-1) = 9.5 dB. In this case, assuming that the C / N of the modulator unit alone is 60 dB, the C / N of the CATV signal becomes 60−9.5 = 50.5 dB, which may not satisfy the C / N regulation. In addition,
Generally, it is sufficient that the C / N is 52 dB or more.

As described above, the broadband noise is generated by the mixer 17
When mixed with 0, C / N deteriorates. Therefore, in order to prevent this, it is necessary to insert a BPF having a pass band width for one channel as shown in FIG. 9 into each modulator unit. -ing However, CA
The arrangement of television channels of TV stations is often different for each CATV station, so that it is necessary to fabricate a wide band television modulator having a BPF in which BPFs having different pass bands are combined for each CATV station. Then CAT
Since the configuration (circuit) of the BPF is different for each V,
There is a problem that the cost becomes high because it becomes a custom-made wide band television modulator.

Therefore, an object of the present invention is to provide a general-purpose wide band television modulator which does not change the configuration even if the television channel required for each CATV is different. Another object of the present invention is to provide a filter device that can be provided in a general-purpose broadband television modulator or the like.

[0011]

In order to achieve the above-mentioned object, a filter device of the present invention has a plurality of filters each having a different pass band arranged in parallel. Selection means for selecting a filter is provided, and the pass bands of the plurality of filters are limited to block a frequency that is twice the lowest frequency of the pass band, and the highest frequency of the pass band is limited. , Which is almost the same as the lowest frequency in the adjacent pass band.

In order to achieve the above-mentioned object, the wide band television modulator of the present invention includes a television modulator unit for modulating a carrier wave of a desired television channel with a video signal and an audio signal and outputting the modulated carrier. A mixer that mixes and outputs respective outputs of a plurality of television modulator units, and a filter device is respectively connected between the plurality of television modulator units and the mixer, and the filter device is , A plurality of filters each having a different pass band are arranged in parallel, selection means for selecting one of the plurality of filters is provided,
The pass bands of the plurality of filters are limited so as to block a frequency that is twice the lowest frequency of the pass bands, and the highest frequency of the pass bands is substantially the same as the lowest frequency of the adjacent pass bands. That is what is done.

Further, in the above-mentioned wideband television modulator, each of the plurality of television modulator units is provided with frequency varying means for generating a carrier wave of the desired television channel, and the frequency varying means is provided. When the control is performed, the filter having the optimum pass band is automatically selected by the selecting means.

According to such a filter device of the present invention, no matter which television channel is selected in the modulator unit, the frequency band of noise is limited by selecting one of the filters arranged in parallel. Will be able to. Further, according to the wide band television modulator of the present invention, even if a large number of modulator units are provided, it is possible to prevent the C / N of the CATV signal from being deteriorated as much as possible, and obtain a good CATV signal. You can

[0015]

1 is a block diagram showing the configuration of an embodiment of a wide band modulator unit of the present invention including a filter device of the present invention.
Shown in In FIG. 1, a video signal (V) and an audio signal (A) are input to the IF modulator 1, and the video intermediate frequency is 38.9 MHz and the audio intermediate frequency is 32.4 M, respectively.
Is modulated to Hz. The converted video intermediate frequency signal and audio intermediate frequency signal are multiplexed by the multiplexer 2 and input to the first mixer 3.

In the first mixer 3, the first stations 4 to 573.
The first local frequency F1 of 85 MHz is supplied, and the video intermediate frequency signal and the audio intermediate frequency signal are frequency-converted and converted into the video carrier 612.75 MHz and the audio carrier 606.25 MHz. The video carrier signal and the audio carrier signal converted by the mixer 3 have unnecessary band components removed by a bandpass filter (IF / BPF) 5 and input to the second mixer 6. Then, it is converted into a desired television channel in the second mixer 6. Therefore, the second mixer 6 is supplied with the second local frequency F2 from the second local oscillator 7 capable of oscillating a frequency of 662.5 MHz to 1156 MHz.

Further, the television channel signal converted by the second mixer 6 is a wide band high frequency amplifier (RF) including an amplifier 8, a level adjuster 9 and an amplifier 10.
Amp) is amplified and input to the filter device BPF-1. The filter device BPF-1 selects a filter capable of removing spurious and unwanted band noises, and the resulting signal is input to the mixer 50 as a television channel signal from which spurious and unwanted band noises have been eliminated.

In this way, the modulator unit having the structure from the IF modulator 1 to the filter device BPF-1 and the IF
The modulator unit 11 and the filter device BPF-2 have the same configuration as the other modulator units, and the IF modulator unit 21 and the filter device BPF-n further constitute another modulator unit. It has the same configuration as. In such a plurality of modulator units, the video signal and the audio signal are modulated, converted into different television channel signals, and supplied to the mixer 50.

As a result, the television channel signals of different channels output from the plurality of modulator units are combined in the mixer 50 and the CATV is generated.
It will be output as a signal. The CATV signal output from the mixer 50 is transmitted to the subscriber's house by being transmitted through the cable.

Next, the filter device will be described.
Filter device BPF-1, BPF-2, ... BPF-
n has the same configuration, and as shown in FIG. 1, five filters are arranged in parallel, and one of the five CATV frequency bands divided into five is assigned to each of these five filters. ing. One of these filters is selected in each modulator unit. In this case, the television channel output from the second mixer is changed in response to the change of the second local frequency F2 generated by the second station, but the changed television channel is within the pass band. The filter that is said to be selected automatically.

Here, the detailed structure of the filter device is shown in FIG.
, The filters F1, F2, F3 arranged in parallel are shown in FIG.
F4 and F5 and the first switches SW1-1, SW1-2, SW1-3 and SW respectively connected to the input sides thereof.
1-4, SW1-5 and second switches SW2-1, SW2-2, SW2-3, SW connected to the output side thereof
2-4 and SW2-5. The first switches SW1-1 to SW1-5 and the second switches SW2-1 to SW2-1
As described above, the SW2-5 has the second local frequency F2.
When is changed, it is switched at the same time. This switching is performed in conjunction with, for example, a switch for changing the second local frequency F2. Further, this switching may be automatically performed by a control circuit such as a microcomputer.

Next, the filters F1, F2, F3, F4,
Explaining the pass band of F5, the filter F1 has 4
It has a pass band for four channels from 9.75 MHz to 84.0 MHz, and the filter F2 is 85.25 M.
The filter F3 has a pass band for 5 channels of 14 Hz to 143.0 MHz, the filter F3 has a pass band for 13 channels of 145.25 MHz to 247.0 MHz, and the filter F4 has a pass band of 248.25 MHz to 303. The filter F5 has a pass band for 7 channels of 0 MHz, and the pass band for 30 channels of 304.25 MHz or more.

FIGS. 3 to 7 show the gain characteristics and the reflection loss characteristics that are integrated with the RF Amp when these filters are connected in series to the RF Amp. FIG. 3 shows the gain characteristic and the reflection loss characteristic of the filter F1. The filter F1 has at least the pass band width of the above-mentioned four channels, and the filter F1 has a pass band width of 1
Channel carrier video carrier frequency 49.75MHz 2
Large attenuation (about 2
The gain characteristic is 2.7 dB). This is because a spurious having a frequency twice that of the carrier spur is a spurious with a high level, and if the spurious is allowed to pass, the signal quality will be significantly deteriorated. Therefore, 99.5MHz
Although the large spurious noises located at are removed, it is possible to simultaneously remove the high level spurious noises in other carriers. As a result, CA
It is possible to prevent beat troubles from other channels in the TV and obtain good image quality.

Further, FIG. 4 shows the gain characteristic and the reflection loss characteristic of the filter F2. This filter F2 has at least the pass band width of the above-mentioned five channels, and one channel within the pass band. 170.5 MHz, which is twice the frequency of the eye carrier frequency of 85.25 MHz
The gain characteristic is such that a large attenuation (about 28.7 dB) can be obtained at z. The reason for this is the above-mentioned filter F.
The reason is the same as in 1. Further, the lowest frequency of the pass band of the filter F2 is set to be substantially the same as the highest frequency of the pass band of the filter F1.

Further, FIG. 5 shows the gain characteristic and the reflection loss characteristic of the filter F3. This filter F3 has at least the pass band width of 13 channels, and one channel in the pass band is shown. The frequency 288. which is twice the image carrier frequency 144.25 MHz of the eye.
The gain characteristic is such that large attenuation (about 31.5 dB) is obtained at 5 MHz. The reason for this is the same as that for the filter F1 described above. Filter F
The lowest frequency of the pass band of No. 3 is almost the same as the highest frequency of the pass band of the filter F2.

Further, FIG. 6 shows the gain characteristic and the reflection loss characteristic of the filter F4.
4 has at least the pass band width for 7 channels, and has a frequency 49 which is twice the video carrier frequency 248.25 MHz of the first channel in the pass band.
The gain characteristic is such that large attenuation (about 48.3 dB) is obtained at 6.5 MHz. The reason for this is the same as that for the filter F1 described above. Further, the lowest frequency of the pass band of the filter F4 is set to be substantially the same as the highest frequency of the pass band of the filter F3.

Furthermore, FIG. 7 shows the gain characteristic and the reflection loss characteristic of the filter F5.
5 has at least the pass band width of 30 channels. However, since the frequency 608.5 MHz, which is twice the frequency 304.25 MHz of the image carrier of the first channel in the pass band, is an out-of-band frequency of the CATV signal, characteristics at that frequency are not shown. The minimum frequency of the pass band of the filter F5 is
The frequency is almost the same as the highest frequency of the pass band of the filter F4. The filter F1 shown in FIGS.
The gain characteristic of the filter F5 has been described above.
The reflection loss characteristics of these filters are all sufficiently good in the pass band.

By the way, the pass band width of the filter F1 is 4
Since it has a bandwidth for channels, it is conceivable that all four adjacent channels are used. Therefore, the C / N obtained in this case will be calculated. At this time, the C / N of the modulator unit alone is 60 dB
I do. Then, C / N = 60-10 log (4-1) ≈55.2 dB, and a sufficient C / N value can be obtained. Since the adjacent 4 channel video and audio signals are band-limited by the IF / BPF having the pass bandwidth of 1 channel in the modulator unit, respectively, the band of the superimposed noise is Will be shifted for each channel, and will actually exceed this C / N value.

Further, although the filter F3 has a pass band width of 13 channels, the number of channels actually broadcast within this band is 7. Therefore, the C / N is calculated and viewed assuming that all the adjacent 7 channels are used. However, as described above, the band of noise to be superimposed can be shifted for each channel, and empirically, noise of two channels can be superimposed on three channels. Therefore, C / N = 60-10 log {7 × (2/3) -1} ≈5
It becomes 4.3 dB, and a sufficient C / N value can be obtained. The C / N value is almost the same as the actually measured value.

As described above, by providing the above-mentioned filter device on the output side of the modulator unit, it is possible to reduce the deterioration amount of C / N deteriorated when mixed in the mixer 50 as much as possible. Further, by allocating the channels so that the number of channels used in each filter of the filter device is reduced, it is possible to further prevent the deterioration of C / N.

[0031]

Since the filter device of the present invention is configured as described above, no matter which television channel is selected in the modulator unit, spurious can be obtained by selecting any one of the filters arranged in parallel. Can be removed and the frequency band of noise can be limited, so that the influence of noise on the television channel outside the filter band can be suppressed. Further, since the wide band television modulator of the present invention is configured as described above, even if a large number of modulator units are provided, it is possible to prevent the C / N of the CATV signal from being deteriorated as much as possible. A good CATV signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a wide band television modulator of the present invention.

FIG. 2 is a diagram showing the configuration of the filter device of the present invention provided in the wide band television modulator of the present invention.

FIG. 3 is a diagram showing a gain characteristic and a reflection loss characteristic of a filter F1 in the filter device of the present invention.

FIG. 4 is a diagram showing a gain characteristic and a reflection loss characteristic of a filter F2 in the filter device of the present invention.

FIG. 5 is a diagram showing a gain characteristic and a reflection loss characteristic of a filter F3 in the filter device of the present invention.

FIG. 6 is a diagram showing a gain characteristic and a reflection loss characteristic of a filter F4 in the filter device of the present invention.

FIG. 7 is a diagram showing gain characteristics and reflection loss characteristics of a filter F5 in the filter device of the present invention.

FIG. 8 is a diagram showing a configuration of a conventional broadband television modulator.

FIG. 9 is a diagram showing an attenuation characteristic of a filter provided in a conventional wide band television modulator.

[Explanation of symbols]

1,11,21 IF modulator 2,12,22 Multiplexer 3,13,23 First mixer 4,14,24 First station departure 5,15,25 IF / BPF 6,16,26 Second mixer 7 , 17,27 Second station departure 8,18,28 Amplifier 9,19,29 Level adjuster 10,20,30 Amplifier 50 Mixer BPF-1, BPF-2, BPF-3, BPF-4, B
PF-5 filter device F1, F2, F3, F4, F5 filter

Claims (3)

[Claims] 1. A plurality of filters each having a different pass band are arranged in parallel, selection means for selecting one of the plurality of filters is provided, and pass bands of the plurality of filters are provided. Is restricted so as to block a frequency twice as high as the lowest frequency of the pass band, and the highest frequency of the pass band is almost the same as the lowest frequency of the adjacent pass band. Filter device. 2. A plurality of television modulator units that modulate and output a carrier wave of a desired television channel with a video signal and an audio signal, and a mixer that mixes and outputs each output of the plurality of television modulator units. A filter device is connected between the plurality of television modulator units and the mixer, and the filter device has a plurality of filters each having a different pass band arranged in parallel. Selection means for selecting any one of the plurality of filters is provided, and the pass bands of the plurality of filters are restricted so as to block a frequency that is twice the lowest frequency of the pass band. In addition, the maximum frequency of the pass band is set to be almost the same as the minimum frequency of the adjacent pass band. Band TV modulator. 3. Each of the plurality of television modulator units is provided with frequency varying means for generating a carrier wave of the desired television channel, and when the frequency varying means is controlled, it is automatically operated. 3. The wide band television modulator according to claim 2, wherein the filter having the optimum pass band is selected by the selecting means.