JPH0721000Y2 - Mixer for television adjacent channel transmission - Google Patents

Description

[Detailed Description of the Invention] (Industrial field of application) The present invention relates to multi-channel transmission of a television common reception facility, and particularly a mixer for television adjacent channel transmission used in a VHF adjacent channel transmission system using a coaxial cable. It is about.

(Prior Art) Radio waves for television broadcasting include VHF, UHF, and SHF broadcasting bands, and the SHF band is used for special purposes. When this is transmitted by a coaxial cable, since the transmission loss of the signal is large in the UHF band, it is generally frequency-converted into the television high frequency signal VHF band of the UHF band for transmission.

Fig. 3 shows an example of a multi-channel transmission frequency array for cable television (CATV). The number on the top of the slender trapezoid with diagonal lines in the figure indicates the number of each television broadcast wave (6M
(Hz band) is the channel number. 7 in the arrangement example of FIG.
Waves (1,3,4,6,8,10,12 channels) can be transmitted without being VHF adjacent channels, but when 8 waves or more, they become adjacent channels and a maximum of 11 waves (2,5,9 , 11 channels can be added), which is called the adjacent channel transmission method.

Adjacent channel transmission has a problem of interference between adjacent channels. The main ones will be described with reference to FIG. 4. The video carrier 21 of the desired channel 19 and the lower adjacent channel audio carrier 20 are detected by video detection. 1.5M detected at the same time
There is interference that causes a beat streak of Hz, and interference of wind wiper interference that causes the video carrier 21 of the desired channel 19 to undergo cross modulation by the video carrier 24 of the upper adjacent channel. Comparing the former and latter by the D / U ratio, the detection limits are 18 dB and 10 dB, respectively, and the allowable limits are 8 dB and 0 dB, the former being more severe.

Therefore, in order to suppress this interference as much as possible, it is generally said that the audio carrier level of the lower channel is suppressed by about 14 dB less than the video carrier level of the desired channel before transmission, and notch is used to suppress the audio carrier level. Filters are typically used.

On the other hand, in the cable transmission of the television broadcast wave for the television common reception facility, the television high frequency signal received by the receiving antenna is amplified by the receiving amplifier for each receiving channel and sent to the main line. Main line amplifiers are inserted at regular intervals in the main line to guarantee its transmission loss.
As a result, the television high frequency signal is always transmitted by a cable at a certain signal level or higher. Certain conditions are imposed on the mixer for inserting a channel, which inserts an additional channel into such a transmission system and changes the main transmission which was a non-adjacent channel transmission to an adjacent channel transmission. The first is that the signal level of the main line does not change due to the mixer being inserted in the main line, and specifically, the main line signal level is not attenuated. Secondly, the above-mentioned measure for preventing interference due to the change to adjacent channel transmission is taken.

These conditions are satisfied, and for the convenience of handling as the insertion point of the mixer, it is selected whether immediately after the main amplifier (high level) or immediately after the main amplifier (low level) or just after (high level) the main amplifier. As a conventional example, the mixer having the configuration shown in the second drawing has been used. The figure (a) is a mixer for low level trunk line insertion, and the figure (b) is a mixer for high level trunk line insertion. In the figure, the filter unit 12 is a notch filter for suppressing the level of the voice carrier of the lower channel, and there is a loss of about 1 dB in this part. Since the loss in the mixing unit 13 is about 4 dB, the amplification unit 11 that amplifies about 5 dB for low levels (main line level 60 to 80 dBμ)
Is placed in front, and the amplification unit 11 is placed in the rear for high level (80 to 100 dμ).

(Problems to be solved by the invention) Conventional mixers for adjacent channel transmission have been developed for low-level input, high-level input, and individual-purpose type mixers. Therefore, in terms of reducing the overall cost, The types of voice carrier suppression that can be selected by the notch filter are either low level input or high level input.
It was about waves. Moreover, in both cases, the insertion wave to the insertion channel input section must be such that the level ratio (VA ratio) of the video and audio carrier waves is adjusted to prevent the interference of the adjacent channel transmission described above. That is, the audio level must be 14 dB or less compared to the video level. For example, the third
Explaining with the example of the channel arrangement shown in the figure, if channels 2, 5, 9 are transmitted by the existing trunk line and channels 3, 6, 10 are vacant, adjust the VA ratio of channels 2, 5, 9 Can be inserted into channels 3, 6 and 10.

Moreover, various inconveniences arise because the notch filter can select only three waves in terms of cost. For example, in the arrangement example shown in the third illustration, the main channel is 1,3,4,6,8,10,12, and the three levels are inserted into the existing main line where the level ratio (VA ratio) of the video carrier and the audio carrier is not adjusted. If you do (the VA ratio is adjusted for the inserted wave), the combination of channels to be inserted is 2, 5,
The problem arises that the mixer must be adjusted according to 9, or according to channels 5, 9, 11, etc.

Therefore, the purpose of the present invention is to add a mixer whose function is not intended for individual use, even if the manufacturing cost of the mixer itself is somewhat high, and which is equipped with a switching unit so as to be compatible with a wide variety of insertion waves or combinations thereof. It is an object of the present invention to provide a mixer for transmitting adjacent television channels, which is suitable for reducing the total cost involved in construction.

(Means for Solving the Problems) In order to achieve this object, a television adjacent channel transmission mixer of the present invention transmits a plurality of television signal waves simultaneously via a coaxial cable to prevent interference between adjacent channels. To prevent this, the VHF adjacent channel transmission method is used, in which the level of the audio carrier of the adjacent lower channel is suppressed by the filter with respect to the level of the image carrier of the desired channel and then transmitted, and multiple television signals are transmitted on multiple channels. In a mixer for television adjacent channel transmission, a television signal wave different from the plurality of television signal waves is inserted into one or more empty channels of the main cable channel to form an adjacent channel transmission mode. , The mixer is configured such that the plurality of television signal waves and the different television And a low-level amplifier circuit for amplifying the television signal wave, and
A first amplifying unit including a first signal switching unit for short-circuiting the input and output, and a television signal wave amplified by the first amplifying unit to receive audio of a plurality of predetermined channels. A second signal switch having a filter section for adjusting the carrier wave level to a predetermined level and outputting it, and a high-level amplifying circuit for amplifying a television signal wave, and for short-circuiting the input and output thereof. The second with the division
And an amplifier unit, wherein the mixing unit is placed in front of the input of the first amplifier unit or the second amplifier unit,
The first amplifying unit, the filter unit, and the second amplifying unit are connected in cascade so as to be configured.

Embodiments The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a block diagram of the structure of the mixer according to the present invention. In the structure shown in FIG. 1 (a) (first embodiment), the mixer according to the present invention comprises a mixing section 1 and a low input level. Amplification section 2 and a signal switching section 3 for short-circuiting its input and output, a filter section 4 having a notch filter (corresponding to, for example, 9 waves), a high input level amplification section 5 and a signal for short-circuiting the same. It is composed of a switching unit 6 and a branching unit 7.

Next, the operation and operation of each circuit unit shown in FIG. 1 (a) will be briefly described. The mixing circuit of the mixing unit 1 has additional channels such as a new channel added to an existing reception channel that has already transmitted the main cable. It is a circuit to mix. Amplifier 2,
Each VHF amplifier 5 is, for example, an amplifier for a low input level and an amplifier for a high input level, and it is preliminarily selected whether to use the amplification unit 2 or the amplification unit 5 by the switching units 3 and 6 depending on the magnitude of the input level. It is something to keep. That is, the insertion position of this mixer is selected depending on whether it is immediately after the above-mentioned main-line receiving amplifier, immediately before or after the main-line amplifier. Since the amplification levels of these amplifiers do not change at the level where the main line level mixer is inserted, they must cover signal attenuation due to the mixer and the filter. Attenuation of mixing section and filter section is -4 dB, for example
And -1dB, it is adjusted to + 5dB. Further, the filter unit 4 suppresses the level of the voice carrier of the necessary channel described above. For example, 1,2,3,4,5,6,8 (or 7), 9,10,1
To effectively use all 11 channels of 1,12, a notch filter for 9 waves, that is, 1,2,4,5,6,8,9,10,11 channels of voice carriers is required. By providing a notch filter for 9 waves in the filter section, it becomes possible to deal with both the main line and the inserted wave without any restriction even if the VA ratios are all unadjusted. The branch circuit of the branch unit 7 is a circuit for branching the mixed output signal level to the monitor terminal.

Further, the case of the configuration shown in FIG. 1 (b) (second embodiment) will be described. The mixer of the present invention is provided with a second mixing section 8 in addition to the configuration shown in FIG. 1 (a). As for its function and effect, when the VA ratio of the inserted wave has already been adjusted (in the case of the sixth (b) shown later), the changeover switch 9 switches the inserted wave and guides it to the second mixing section 8. It was done like this.

Next, the basic configuration of the television common reception facility will be outlined with reference to FIG. 5 in order to help understand the purpose, configuration, and effect of the present invention.

The television high frequency signal received by the receiving antenna is
It is amplified by the receiving amplifier HA (head amplifier) for each receiving channel and sent to the trunk line TL (trunk line). A trunk amplifier TA (trunk amplif
ier) or trunk branch amplifier TBA (trunk bridger amplif)
ier) is inserted at regular intervals, whereby the high frequency television signal is transmitted at a certain signal level or higher.

The television high frequency signal branched and amplified by the main branch amplifier passes through the branch line BL (branch line) and the branch amplifier BA (b
It is amplified by the ridger amplifier and the distribution line FL (feeder lin)
e), tap off TO (tap off) or distributor D (di
It is transmitted to the subscriber's house via a stributer) and a drop line (DL). When the distribution line is long, an extension amplifier EA (extender amplifier) is inserted in the middle thereof.

The present invention relates to a mixer for adding an additional transmission channel to an existing cable transmission trunk as shown in FIG. 5, and FIG. 6 shows two examples thereof.

FIG. 10A shows the insertion position of the mixer according to the present invention when mixing a trunk cable using a booster 32 (VA ratio cannot be adjusted) when a new reception channel is added. The reception channels are 1,3,4,6,8,10,12 channels, and the additional reception channels are 2,5,9,11 channels, which are four waves. When the mixer 31 according to the present invention is used by connecting it to the output side of the head end HE as shown by the solid line in the figure, the switching section 3 of the first amplifying section 2 in FIG. Is turned off (the low input level amplifier is not used), the switching unit 6 of the second amplification unit 5 is turned on (the high input level amplifier is used), and then the filter unit 4, 1, 2, 4, 5,8,9,
Turn on the notch filter for channels 10 and 11 and adjust the VA ratio (If you want to use channels 6 and 7 at the same time, use the notch filter for channel 6).
When the mixer 31 is used by connecting it to the input side of the head end HE as shown by the broken line in the figure, the switching unit 3 of the first amplification unit 2 is turned on and the switching unit 6 of the second amplification unit 5 is switched on. Turn off and use.

Also, as shown in FIG. 6 (b), for example, when the television broadcast by satellite is received and the program is used as an additional reception channel of the joint reception facility, the VA ratio is adjusted on the additional channel side, which is often seen. When a possible reception amplifier 33 is used, the first amplification section 2 is operated by the solid line in the figure and the second amplification section 5 is operated by the broken line in the figure depending on the insertion position of the mixer. , The switching units 3 and 6 may be turned on and off respectively, and the existing reception channels and additional reception channels are the same as those in FIG. 6 (a), and the additional reception channels are 2, 5, 9, If it is 4 waves of 11 channels, the notch filter of the filter unit should be turned on for channels 1, 4, 8 and 10 to adjust the VA ratio. Further, in such a case, using the mixer of the present invention having the configuration shown in FIG. 1 (b), the inserted wave already adjusted in the VA ratio is guided to the second mixing section by the changeover switch 9 without passing through the filter section. In addition, it can be stably mixed.

(Effects of the Invention) As described above in detail with respect to the mixer for transmitting adjacent channels of the television of the present invention, the mixer of this kind is conventionally used for low cost, low level input, high level input. And the notch filter for adjusting the VA ratio can select only 3 waves, and the type of the applicable mixer is selected according to the insertion position and the type of the transmission channel.
Moreover, it is possible to provide a mixer that can cover a wide range of application with a simple operation by improving the need to adjust and use a notch filter, and is particularly suitable for additional work to be performed by inserting into an existing trunk line. Moreover, it is now possible to provide a mixer suitable for change and adjustment work to cope with channel changes after additional work.

[Brief description of drawings]

FIG. 1 shows a block diagram of a mixer according to the present invention, FIG. 2 shows a block diagram of a conventional mixer structure example, and FIG. 3 shows an example of CATV multi-channel transmission frequency arrangement. , Fig. 4 shows the frequency relationship of each carrier wave, Fig. 5 shows the basic structure of a television common reception facility, and Fig. 6 shows an example of application of the mixer of the present invention to a CATV trunk line. 1,8,13 …… Mixing section, 2,5,11 …… Amplifying section 3,6 …… Switching section, 4,12 …… Filter section 7,14 …… Branching section, 9 …… Selection switch 15 …… Channel block 16,17,18 …… Low, mid, high band 19 …… desired channel, 20 …… lower audio carrier 21 …… video carrier, 22 …… color subcarrier 23 …… audio carrier, 24 …… Upper side image carrier 31 …… Inventor mixer, 32 …… Booster 33 …… Reception amplifier, HE …… Headend HA …… Reception amplifier, MIX …… Mixed TL …… Main line, TA …… Main line amplifier TBA …… Main line branch amplifier, BL ... Branch line BA ... Branch amplifier, FL ... Distribution line TO ... Tap-off, D ... Distributor DL ... Drop-in line, EA ... Extension amplifier SB ... Protector

Claims (3)

[Scope of utility model registration request] 1. A plurality of television signal waves are simultaneously transmitted through a coaxial cable, and in order to prevent interference between adjacent channels, a level of an audio carrier of an adjacent lower channel is filtered with respect to a level of an image carrier of a desired channel. A TV different from the plurality of television signal waves is provided in one or a plurality of vacant channels of a trunk cable channel that transmits a plurality of television signals in a plurality of channels by using a VHF adjacent channel transmission method In a television adjoining channel transmission mixer in which a television signal wave is inserted to form an adjacent channel transmission mode, the mixer mixes the plurality of television signal waves with the different television signal waves. A mixing section with a mixing circuit and a low-level boost for amplifying television signal waves. A first amplification section having a width circuit and having a first signal switching section for short-circuiting its input and output, and a television signal wave amplified by the first amplification section. Has a filter unit that adjusts and outputs the audio carrier levels of a plurality of predetermined channels to predetermined levels, respectively, and a high-level amplifier circuit that amplifies the television signal wave, and shorts the input and output. And a second amplification section with a second signal switching section for controlling the mixing section, wherein the mixing section is placed in front of the input of the first amplification section or the second amplification section, A television adjoining channel transmission mixer comprising a first amplification section, a filter section, and a second amplification section that are connected in cascade. 2. The mixer for television adjacent channel transmission according to claim 1, wherein the filter section is a notch filter capable of selectively suppressing a sound carrier of a nine-wave television signal. vessel. 3. The mixer according to claim 1, wherein
A first said mixing part is placed in front of the input of said first amplifying part,
And a second pre-positioned at the input of the second amplification section
And a mixing switch for guiding the inserted television signal wave to any one of the first mixing section and the second mixing section. Mixer for channel transmission.