JP2009239628A - Digitalization method for existing common television facility and common cable television facility and amplifier for common television facility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To digitize an existing small-scaled common analog television facility at low costs without using any high level adjustment technology. <P>SOLUTION: An HE (head end) amplifier 36 of a temperature compensation system for receiving a ground digital broadcast signal, and for amplifying the broadcast signal is added to the television analog broadcast reception point of an existing common television facility. Furthermore, a trunk line amplifier installed for amplifying the existing analog broadcast signal is exchanged with trunk line amplifiers 18 to 22 of a temperature compensation system without changing the mounting position on a transmission path configured of a coaxial cable 16 from a multiplexer 38 to a subscriber's house. Trunk line amplifiers 18 to 20 change passage frequency characteristics according to an external temperature so that the levels of the analog broadcast signal and the ground digital broadcast signal can be obtained within a reference range at the output side of the following coaxial cable 16. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for digitizing an existing television broadcasting facility that upgrades an existing analog broadcasting television facility to a facility capable of receiving terrestrial digital broadcasting at low cost without using advanced adjustment technology. The present invention relates to a cable television facility and an amplifier for a television facility.

Small-scale CATV hearing systems using coaxial cables with a signal transmission band of about 222 MHz are widely adopted in mountainous areas for television viewing facilities for improving difficult viewing and in urban areas. Yes. In such television hearing facilities, repeater amplifiers are used to compensate for signal attenuation due to coaxial cables that transmit broadcast signals. In addition, it is known that the signal attenuation of the coaxial cable varies by about 0.2% every time the outside air temperature moves up and down by 1 degree Celsius. In order to suppress this variation, a pilot AGC method using a pilot signal is employed (Patent Document 1) (Patent Document 2). In addition, there is a facility that employs a thermal AGC system that directly controls the gain of the relay amplifier according to changes in the outside air temperature (Patent Document 3) (Patent Document 4).
JP-A-2005-33726 JP-A-62-38093 JP-A-6-6776 Japanese Patent No. 3238947

The known prior art has the following problems to be solved.
In a conventional television hearing facility, it is considered to introduce a digital terrestrial broadcasting by renovating an existing television hearing facility in accordance with a plan for a transition from analog broadcasting to terrestrial digital broadcasting. In order to transmit terrestrial digital broadcasting, a signal transmission band of about 770 MHz is required. It is sufficient to update all devices and adopt an optical fiber having a wide transmission band and little temperature fluctuation, but this requires a lot of capital investment.

  For the terrestrial digital broadcasting band, if the pilot AGC method is adopted, a television hearing facility using a coaxial cable can be realized. In that case, it is necessary to provide a pilot signal generator serving as a reference source signal on the signal transmission path, and to provide a pilot signal extraction filter and an AGC control unit in the amplifier. The new pilot signal is set to 451.25 MHz. The coaxial cable is required to have a signal transmission characteristic with a frequency of 90 to 770 MHz. However, many existing coaxial cables have products whose transmission characteristics are not guaranteed up to the UHF band. In addition, in order to control the gain and frequency characteristics of HE (head-end) amplifiers and relay amplifiers based on pilot signals, advanced adjustment technology for setting the AGC operating point to the optimum point is required when updating equipment. Required. In any case, there is a shortage of skilled technicians who can deal with a large number of television hearing facilities that require refurbishment.

  In the pilot AGC system, the gain of the relay amplifier is controlled so that the signal level on the output side is kept constant. However, the terrestrial digital broadcast signal is operated with a level ratio so that the signal level is lower by 10 to 15 dB than the analog broadcast signal. In the conventional pilot AGC system, when the signal level on the input side decreases, the C / N (signal-to-noise ratio) due to the decrease in the input signal is obtained by automatically increasing the output signal level based on the pilot signal and keeping it constant. May be worsened. This will cause some facilities that do not satisfy the standards of the Cable Television Broadcasting Act. The thermal AGC system that directly controls the gain of the relay amplifier has the same problem.

  In order to solve the above-mentioned problems, the present invention digitizes an existing small-scale analog television hearing facility and digitizes it at low cost without using advanced adjustment technology. The object is to provide a method and cable television hearing facility and an amplifier for a television hearing facility.

The following configurations are means for solving the above-described problems.
<Configuration 1>
A UHF broadcast receiver is added to the analog broadcast reception point of the existing television hearing facility, and this UHF broadcast receiver is provided with a HE (head end) amplifier that amplifies the received digital terrestrial broadcast signal. The amplified terrestrial digital broadcast signal is combined with the broadcast signal using a multiplexer, and the existing analog broadcast signal is amplified in the coaxial cable transmission path from the multiplexer to the subscriber's house. To replace the existing trunk amplifier with a bandwidth that amplifies both the existing analog broadcast signal and the terrestrial digital broadcast signal without changing the mounting position. The HE amplifier and the new main line amplifier are provided with a broadband amplifier, a broadband pseudo-line equivalent attenuator, and a temperature compensation circuit. The broadcast signal has an amplification characteristic that compensates for transmission loss of the coaxial cable over the entire frequency range, and the temperature compensation circuit supplies a control signal corresponding to a change in outside air temperature to the broadband pseudo-line equivalent attenuator, The broadband pseudo-line equivalent attenuator is designed so that the attenuation characteristic is equivalent to that of a coaxial cable in the entire frequency range of the input broadcast signal, and the analog broadcast signal and the ground signal are output on the output side of the subsequent coaxial cable. A method for digitizing an existing television hearing facility, characterized in that the pass frequency characteristic is changed according to the outside air temperature by the control signal output from the temperature compensation circuit so that the level of the digital broadcast signal falls within a reference range. .

  A facility that was unable to transmit terrestrial digital broadcasting at an existing television hearing facility in a region where analog broadcasting is difficult to view can be changed to one that can handle terrestrial digital broadcasting with minimal equipment disposal. . In the HE amplifier and the new main line amplifier, the broadcast signal level on the output side of the subsequent coaxial cable is temperature-compensated over the entire frequency band using a broadband pseudo-line equivalent attenuator.

<Configuration 2>
In the digitizing method of the existing television hearing facility described in the configuration 1, the frequency band correction for correcting the frequency characteristic of the existing coaxial cable and expanding the apparent bandwidth after the broadband pseudo-line equivalent attenuator. A method for digitizing an existing television hearing facility characterized by inserting a device.

  Even if there is a problem with the transmission characteristics of the existing coaxial cable, this can be forcibly widened. Therefore, it is possible to relieve small-scale facilities to an operable level.

<Configuration 3>
In the method for digitizing an existing television hearing facility according to Configuration 2, a control signal for maintaining the output level of the frequency band corrector at a constant level is set according to the characteristics of the frequency band corrector. A method for digitizing an existing television hearing facility, characterized in that a control circuit is provided for adjusting a signal attenuation amount in a broadband pseudo-line equivalent attenuator that is sent to the pseudo-line equivalent attenuator.

  The frequency band compensator is replaced according to the characteristics of the subsequent coaxial cable. At that time, by providing a circuit for outputting a predetermined control signal and adjusting the signal attenuation amount of the broadband pseudo-line equivalent attenuator, the output level of the frequency band corrector can be maintained at a constant level.

<Configuration 4>
In the method for digitizing an existing television hearing facility according to Configuration 2 or 3, the temperature compensation circuit provides a certain temperature range between a lower limit value and an upper limit value centered on a standard temperature, and the temperature range is within this temperature range. Then, the digitizing method of the existing television hearing facility characterized by fixing the said control signal to a standard value.

  The broadband pseudo-line equivalent attenuator can be made to respond gently to the outside air temperature, and an excessive response can be suppressed.

<Configuration 5>
In the digitizing method for an existing television hearing facility according to any one of Configurations 2 to 4, the temperature compensation circuit limits a control signal when an air temperature exceeding the limit range or an air temperature below the limit range is detected. A method for digitizing an existing television hearing facility, characterized in that the temperature of the range is maintained when it is detected.

  It is possible to realize a fail-safe structure against a temperature sensor failure or the like.

<Configuration 6>
6. A method for digitizing an existing television hearing facility according to any one of Structures 2 to 5, wherein the trunk television amplifier is used in a television hearing facility in which only three stages or less are cascade-connected. How to digitize John Hearing Facility.

  Digital terrestrial broadcast signals can be received relatively easily in a television listening facility for improving the difficulty of viewing and listening, where analog broadcast reception points are on the top of the mountain and broadcast signals are transmitted to the subscribers' homes using coaxial cables. You can switch to a possible system. If the number of stages is relatively small, signal quality can be guaranteed without performing feedback control by pilot AGC.

<Configuration 7>
At an analog broadcast reception point of an existing television hearing facility, a UHF broadcast receiver, a HE (head end) amplifier that amplifies a terrestrial digital broadcast signal received by the UHF broadcast receiver, and the existing analog broadcast signal A band for amplifying both the existing analog broadcast signal and the terrestrial digital broadcast signal in a coaxial cable transmission path from the multiplexer to the subscriber's house. The HE amplifier and the main line amplifier are provided with a wide band amplifier, a wide band pseudo-line equivalent attenuator, and a temperature compensation circuit. The wide band amplifier coaxially inputs an input broadcast signal over the entire frequency range. It has amplification characteristics to compensate for cable transmission loss, and the temperature compensation circuit sends the control signal according to the change of the outside temperature to the broadband pseudo line etc. The broadband pseudo-line equivalent attenuator supplied to the attenuator is designed so that the attenuation characteristic is equivalent to that of the coaxial cable in the entire frequency range of the input broadcast signal. A cable that changes a pass frequency characteristic according to an outside air temperature by a control signal output from the temperature compensation circuit so that the level of an analog broadcast signal and the digital terrestrial broadcast signal falls within a reference range. Television hearing facility.

<Configuration 8>
In the cable television hearing facility according to Configuration 7, a frequency band compensator for correcting the frequency characteristics of the existing coaxial cable and expanding the apparent bandwidth is inserted after the broadband pseudo-line equivalent attenuator. The cable television hearing facility characterized by being.

<Configuration 9>
In the cable television hearing facility according to Configuration 8, in accordance with the characteristics of the frequency band corrector, a control signal for maintaining the output level of the frequency band corrector at a constant level is converted into a broadband pseudo-line equivalent attenuation. A cable television hearing facility, characterized in that a control circuit for adjusting the signal attenuation in the broadband pseudo-line equivalent attenuator is provided.

<Configuration 10>
In the cable television hearing facility according to any one of Configurations 7 to 9, the temperature compensation circuit provides a constant temperature range between a lower limit value and an upper limit value centered on a standard temperature, and within this temperature range, A cable television hearing facility characterized by fixing control signals to standard values.

<Configuration 11>
In the cable television hearing facility according to any one of Configurations 7 to 9, when the temperature compensation circuit detects an air temperature exceeding the limit range or an air temperature below the limit range, the temperature signal in the limit range is detected by the control signal. A cable television hearing facility characterized by maintaining the state when it is detected.

<Configuration 12>
A broadband amplifier, a broadband pseudo-line equivalent attenuator, and a temperature compensation circuit are provided, and the temperature compensation circuit supplies a control signal corresponding to a change in outside air temperature to the broadband pseudo-line equivalent attenuator, and the broadband pseudo-line equivalent attenuation The device adjusts the output signal of the broadband amplifier with an attenuation characteristic according to temperature, and on the output side of the subsequent coaxial cable, the level of the analog broadcast signal and the digital terrestrial broadcast signal is within a reference range. An amplifier for a television hearing facility, which is a circuit that changes a passing frequency characteristic in accordance with an outside air temperature by a control signal output from the temperature compensation circuit.

<Configuration 13>
In the amplifier for a television hearing facility according to Configuration 12, a frequency band corrector that corrects the frequency characteristics of the existing coaxial cable and expands the apparent bandwidth is provided after the broadband pseudo-line equivalent attenuator. An amplifier for a television hearing facility characterized by being inserted.

<Configuration 14>
In the amplifier for a television hearing facility according to Configuration 13, a control signal for maintaining the output level of the frequency band corrector at a constant level according to the characteristics of the frequency band corrector An amplifier for a television hearing facility, comprising a control circuit for adjusting a signal attenuation in a broadband pseudo-line equivalent attenuator that is sent to an attenuator.

<Configuration 15>
15. The amplifier for a television hearing facility according to any one of Configurations 12 to 14, wherein the temperature compensation circuit sets a control signal to a maximum value in a certain temperature range between a lower limit value and an upper limit value centered on a standard temperature. And a control signal is fixed to a standard value when an air temperature lower than the limit range is detected.

<Configuration 16>
In the television hearing aid amplifier according to any one of Structures 12 to 14, when the temperature compensation circuit detects an air temperature exceeding the limit range or an air temperature below the limit range, the temperature compensation circuit sends a control signal to the temperature within the limit range. An amplifier for a television hearing facility, wherein the amplifier is held in a state where the signal is detected.

  Hereinafter, embodiments of the present invention will be described in detail for each example.

FIG. 1 is a block diagram of the cable television hearing facility of the first embodiment.
FIG. 1 shows a television common hearing facility installed in an analog broadcast difficult viewing area. This facility was obsolete before the change and was unable to receive terrestrial digital broadcasts. This existing television hearing facility was adapted to terrestrial digital broadcasting by the method of the present invention. In FIG. 1, the first antenna 12 and the first HE (head end) amplifier 14 have been provided at the analog broadcast reception point in the upper left part. The output signal was supplied to the subscriber house 26 through the coaxial cable 16.

  A UHF broadcast receiver 28 is added to the analog broadcast reception point. The UHF broadcast receiving unit 28 is provided with a second antenna 30, a preamplifier 32, a band pass filter 34 that attenuates an analog broadcast wave and selects a digital broadcast wave, and a second HE amplifier 36. The terrestrial digital broadcast signal received by the second antenna 30 is amplified by the preamplifier 32, and then the digital broadcast wave is selected by the band pass filter 34 and input to the second HE amplifier 36. The second HE amplifier 36 is a temperature-compensated amplifier that amplifies the terrestrial digital broadcast signal. The function will be described later with reference to FIG. The existing analog broadcast signal output from the first HE amplifier 14 and the terrestrial digital broadcast signal output from the second HE amplifier 36 are combined by a multiplexer 38.

  Trunk amplifiers are inserted at various locations of the coaxial cable 16 laid from the multiplexer 38 to the subscriber's house. Older trunk amplifiers do not have the function of transmitting terrestrial digital broadcast signals. Therefore, the old trunk amplifier is replaced with a new first trunk amplifier 18, second trunk amplifier 20, and third trunk amplifier 22. The main line amplifier provided for amplifying the existing analog broadcast signal is replaced without changing its mounting position. As a result, the installed coaxial cable can be used as it is, and only the main line amplifier can be replaced to improve the function at a minimum cost. The first trunk amplifier 18, the second trunk amplifier 20, and the third trunk amplifier 22 have bandwidths that amplify both existing analog broadcast signals and terrestrial digital broadcast signals.

  In the embodiment, a temperature-compensated amplifier having a bandwidth of 770 MHz is used for each of the second HE amplifier 36, the first trunk amplifier 18, the second trunk amplifier 20, and the third trunk amplifier 22. Conventionally, a pilot signal having a predetermined frequency and level is added to a broadcast wave on the output side of the receiving point HE amplifier and supplied to the coaxial cable, and the pilot signal is received by the next-stage trunk amplifier, and the attenuation of the pilot signal Accordingly, the gain of the amplifier is adjusted in accordance with the control so that the output level becomes constant. Further, in the conventional thermal AGC system, the gain is controlled so that the output level of the relay amplifier becomes constant according to the change in the outside air temperature. On the other hand, the amplifier used in the present invention has the following configuration. The outside air temperature is, for example, a value measured by a temperature sensor fixed on the case inner surface of the amplifier. Assuming that this temperature measurement value is equivalent to the temperature of the coaxial cable 16, the following control is performed.

FIG. 2 is a block diagram showing an embodiment of the internal circuit of the amplifier.
The second HE amplifier 36, the first trunk amplifier 18, the second trunk amplifier 20, and the third trunk amplifier 22 are all broadband amplifiers (first amplifier 42 and second amplifier 46) as shown in this block diagram. And a broadband pseudo-line equivalent attenuator 44 and a temperature compensation circuit 52. In the example shown in FIG. 2, a first amplifier 42, a broadband pseudo-line equivalent attenuator 44, a second amplifier 46, a frequency band corrector 48, and an output terminal 50 are connected to the input terminal 40 in order. The first amplifier 42 is a broadband amplifier that raises the level of the signal input to the broadband pseudo-line equivalent attenuator 44 to a predetermined level, and has an amplification characteristic that compensates the transmission loss of the coaxial cable for the input broadcast signal over the entire frequency range. . The second amplifier 46 is a similar broadband amplifier that raises the level of the signal input to the frequency band corrector 48 to a predetermined level, and this also amplifies the input broadcast signal to compensate for transmission loss of the coaxial cable over the entire frequency range. Has characteristics.

  The temperature compensation circuit 52 supplies a control signal corresponding to a change in the outside air temperature to the broadband pseudo-line equivalent attenuator 44. The broadband pseudo-line equivalent attenuator 44 attenuates the output signal of the first amplifier 42 in a substantially flat manner. At this time, an attenuation amount that anticipates the attenuation amount of the frequency band corrector is determined in advance. The broadband pseudo-line equivalent attenuator 44 corrects the cable equivalent fluctuation amount according to the outside air temperature according to the control signal output from the temperature compensation circuit 52, and changes the passing frequency characteristic (output level). Thereby, on the output side of the subsequent coaxial cable 16 (input of the next stage amplifier), the analog broadcast signal and the digital terrestrial broadcast signal operate so as to fall within the reference range.

FIG. 3 is a circuit diagram showing an example of the broadband pseudo-line equivalent attenuator 44.
As shown in the figure, this circuit includes an equivalent attenuation unit 64 capable of controlling attenuation equivalent to that of a coaxial cable and a flat attenuation unit 66 capable of controlling flat attenuation in a frequency band between 90 MHz and 770 MHz corresponding to the entire frequency range of the broadcast signal. It consists of two circuit blocks. The control signal output from the temperature compensation circuit 52 controls the current of the PIN diode 65 to change the characteristic of the equivalent attenuation unit 64. The control signal output from the frequency band corrector 48 controls the current of the PIN diode 67 and changes the characteristics of the flat attenuating unit 66. That is, the broadband pseudo-line equivalent attenuator 44 changes the resistance value by controlling the currents of the PIN diodes 65 and 67, determines the circuit constant of each attenuation unit, and obtains a predetermined pass frequency characteristic. The flat attenuator 66 is an attenuator having no frequency characteristics. As shown in FIG. 2, there is a second amplifier 46 immediately after, followed by a frequency band corrector 48. As will be described in the second embodiment, the flat attenuating unit 66 adjusts the amount of attenuation to set the output level of the frequency band corrector 48 to a predetermined level. Since the characteristic of the equivalent attenuation section 64 is a feature of the present invention, it will be described with reference to FIG.

  The graph of FIG. 4 shows the frequency characteristics of the transmission signal after passing through the coaxial cable according to the outside air temperature (input signal of the next-stage amplifier). In the figure, the horizontal axis represents the frequency of the transmission signal, and the vertical axis represents the signal level after passing through the coaxial cable (input of the next stage amplifier). A in the figure is the input signal level of the next-stage amplifier when the outside air temperature is low, for example, around −20 degrees Celsius. B is a standard input signal level of the next-stage amplifier when the outside air temperature is standard, for example, 15 degrees Celsius. C is the input signal level of the next-stage amplifier when the outside air temperature is 40 degrees Celsius. The higher the temperature, the more severe the attenuation of the high frequency part of the transmission signal. In actual operation, in the characteristics of B, the level ratio is set so that the terrestrial digital broadcast signal has a 10 to 15 dB signal level lower than the analog broadcast signal. It is sufficient that the system performance from the input end to the output end of the coaxial cable can be maintained, and a practical range is a level ratio of 10 to 15 dB.

  When a broadcast signal is input from the first trunk amplifier 18 shown in FIG. 1 to the second trunk amplifier 20 via the coaxial cable 16, the characteristics shown in the graph B of FIG. 4 are obtained regardless of the outside air temperature. When the temperature is high, the input signal of the second trunk amplifier 20 has a significantly lower high frequency level than the low frequency level as shown in FIG. 4C. Therefore, the level ratio between the terrestrial digital broadcast signal and the analog broadcast signal exceeds the practical range. Even if the C low frequency level is raised to the B level with the C characteristic signal, the level of the terrestrial digital broadcast signal is insufficient. This causes the C / N ratio to deteriorate. Therefore, in the first main line amplifier 18, the broadband pseudo-line equivalent attenuator 44 is controlled so that the level ratio does not widen (so that the input signal level of the next stage does not fluctuate), thereby This is achieved by suppressing the attenuation, comparing the output level of the amplifier with the standard time, and increasing the high frequency more than the low frequency.

FIG. 5 shows signal attenuation at each temperature by the broadband pseudo-line equivalent attenuator of the embodiment.
The usable ambient temperature range of the amplifier is set to minus 20 degrees Celsius to plus 40 degrees Celsius. The temperature range from the lowest temperature to the highest temperature during use is 60 degrees. When the outside temperature rises from minus 20 degrees Celsius to plus 40 degrees Celsius, the attenuation of the coaxial cable fluctuates by 1.7 / 2.8 / 5.6 dB (90/222/770 MHz) with a standard span length. . Therefore, the circuit constants of the respective attenuation units shown in FIG. 3 are selected so that the attenuation characteristics due to the coaxial cable are offset.

  According to known pilot signal control and temperature control, as shown in FIG. 5, when the temperature rises, the gain is increased for the reference frequency, and when the temperature falls, the gain is lowered for the reference frequency, and the input level fluctuates. However, it works to maintain a constant output so that the output level does not fluctuate. However, in such temperature control using a pilot signal, the C / N ratio deteriorates when the input signal decreases, but in the present invention, the output level is increased or decreased to keep the input level of the next stage constant. Since the control as shown in FIG. 4B is performed using the broadband pseudo-line equivalent attenuator 44, the deterioration of the C / N ratio is sufficiently prevented even with simple temperature control without high-precision feedback control. Can do.

  In the hearing equipment shown in FIG. 1, the fluctuation of the input level of the transmission signal can be suppressed with a sufficient margin within plus or minus 2 dB on the input side of the first trunk amplifier 18. On the input side of the second trunk amplifier 20, the fluctuation of the input level of the transmission signal is within ± 4 dB at the maximum. Therefore, it was found that sufficiently practical control can be performed up to a hearing facility in which another stage trunk line amplifier is provided next to the second trunk line amplifier 20.

  In a standard hearing instrument, the distance (span length) between the trunk amplifiers is selected to be almost constant. For example, each amplifier may be designed on the assumption of a system with a 0.8 span length in consideration of deterioration of a coaxial cable and a broadcast signal margin due to long-term use. Further, the distance between the first trunk amplifier (branch output) to which the distributor 24 of FIG. 1 is connected and the third trunk amplifier is short because the coaxial cable length is short. .

  With the above-described control, if the distance between the trunk amplifiers is unified with a span length of about 0.6 to 1.2 spans, even if there are various fluctuation factors, the input terminals of each trunk amplifier The level of the analog broadcast signal and the terrestrial digital broadcast signal can be kept within the reference range. In other words, without changing the position of the conventional main line amplifier, it is replaced with a new main line amplifier as it is, and the signal input fluctuation of the next stage main line amplifier can be suppressed to an appropriate level, so that it can be practically used. Is preserved. For example, in the case of a hearing facility for improving difficult viewing, an analog broadcast receiving point is on a mountain. Broadcast signals are transmitted through the coaxial cable 16 to the subscriber's home in the village. Such a system employs three or fewer cascaded trunk amplifiers, which is suitable for the implementation of the present invention.

FIG. 6 is a functional explanatory diagram of the frequency band corrector.
The frequency band compensator 48 provided at the subsequent stage of the broadband pseudo-line equivalent attenuator 44 has a function of correcting the frequency characteristic of the existing coaxial cable 16 and expanding the apparent bandwidth. The horizontal axis of FIG. 6 indicates the frequency of the broadcast signal, and the vertical axis indicates the output signal level of the frequency band corrector 48. For example, the coaxial cable 16 designed for 222 MHz has a higher attenuation in the high band than in the low band as shown by the characteristics P and Q in the figure. The frequency band corrector 48 has a function of further attenuating the low frequency range, and corrects the signal of the characteristic P as the characteristic R, for example. The signal band is shown at the bottom of the figure. The bandwidth of characteristic P is X. The bandwidth of characteristic Q is Y. The bandwidth of characteristic R is Z.

  That is, when the input signal having the characteristic P passes through the frequency band corrector 48, the characteristic R is obtained, and the apparent bandwidth is expanded from X to Z. At this time, since the entire signal level is lowered, adjustment is made by the flat attenuator 66 of the broadband pseudo-line equivalent attenuator 44. Thereby, even if the frequency characteristic of the existing coaxial cable 16 does not satisfy the 770 MHz band and deviates from the current standard value, it can be remedied. The frequency band corrector 48 preferably has a plug-in structure dedicated to the coaxial cable 16 to be corrected. As shown in FIG. 3, for example, the frequency band corrector 48 includes a control circuit 68 and a filter 69. The filter 69 has a fixed band filter characteristic in which the attenuation amount is larger as the frequency is lower. However, several types are prepared and selected according to the characteristics of the subsequent coaxial cable. At this time, regardless of which frequency band corrector 48 is selected, the output level of the frequency band corrector 48 must be maintained at a constant level according to the characteristics of the frequency band corrector 48. The control circuit 68 sends a control signal for this purpose, for example, a voltage signal obtained from a tap of a resistor connected in series, to the broadband pseudo-line equivalent attenuator 44. This control signal adjusts the signal attenuation amount of the flat attenuating unit 66 provided at the subsequent stage of the broadband pseudo-line equivalent attenuator 44. The second amplifier 46 always amplifies the input signal with a constant amplification factor. Therefore, even if the frequency band corrector 48 is replaced with any characteristic, the output of the amplifier for the television hearing facility can be stabilized by the control signal corresponding to the characteristic.

FIGS. 7A and 7B are explanatory diagrams of a control example by the temperature compensation circuit.
For example, in FIG. 2, the temperature compensation circuit 52 generates a control voltage that is proportional (or inversely proportional) to the output of the temperature sensor 62 and supplies the control voltage to the broadband pseudo-line equivalent attenuator 44. In particular, it is preferable to have a structure that changes the frequency characteristics of the passing signal. However, the change in characteristics of the coaxial cable with respect to the temperature change is not so severe, and the image quality of the television receiver is not greatly affected. Therefore, for example, as shown in FIG. 7, the average temperature, for example, 15 degrees Celsius is set as the standard temperature, and the control signal (control voltage or current) is set within a certain temperature range between the lower limit value and the upper limit value. Good) is fixed at the standard value. In this temperature range, for example, the lower limit is 5 degrees Celsius and the upper limit is 25 degrees Celsius. This range is called an AGC free range.

  By providing an AGC free range, it is possible to transmit terrestrial digital broadcast signals at a stable level throughout the year with simple adjustment. Also, in the unlikely event that the temperature compensation circuit breaks down, there is a risk of operating as if an air temperature exceeding the limit range has been detected. Therefore, it is preferable to adopt a fail-safe specification so that the temperature is controlled within the AGC free range when the temperature exceeding the limit range is detected. As a result, the system can be stabilized without excessively reacting to the outside air temperature. In the example of FIG. 5A, the broadband pseudo-line equivalent attenuator 44 is supplied with a control voltage proportional to the output of the temperature sensor 62 at a temperature lower than the AGC free range and at a temperature higher than the AGC free range. In the example of FIG. 5B, a control voltage that is one step lower than the AGC free range is output at a temperature lower than the AGC free range. At a temperature higher than the AGC free range, a control voltage that is one step higher than the AGC free range is output.

  In the circuit shown in FIG. 2, the output voltage of the temperature sensor 62 is input to the temperature compensation circuit 52 through the gate 54. The dead upper limit 58 and the dead lower limit 60 set the upper limit temperature and the lower limit temperature of the AGC free range. This range can be set by a variable resistor, for example. The comparator 56 is a circuit that compares the output voltage of the temperature sensor 62 with the upper limit temperature and the lower limit temperature of the AGC free range. When the outside air temperature is between the upper limit temperature and the lower limit temperature of the AGC free range, the gate 54 is closed. When the gate 54 is closed, the temperature compensation circuit 52 supplies a standard control signal (voltage value or current value) to the broadband pseudo-line equivalent attenuator 44. When the temperature range exceeds the upper limit temperature or below the lower limit temperature of the AGC free range, the gate 54 opens and the output voltage of the temperature sensor 62 is input to the temperature compensation circuit 52. The temperature compensation circuit 52 outputs a control signal (voltage value or current value) corresponding to the outside air temperature to the broadband pseudo-line equivalent attenuator 44. Further, when the output signal of the temperature sensor 62 shows an abnormal value, it may be a failure of the temperature sensor 62 or its detection circuit. Therefore, when the temperature exceeding the limit range or the temperature below the limit range is detected, the control signal is kept in the broadband pseudo-line equivalent attenuator so as to keep the control signal in the state when the limit range temperature is detected. 44 may be supplied. You may hold | maintain to the state of both ends, and may hold | maintain to a standard value. Thus, the above control can be realized.

  In the control as described above, the transmission signal input to the next trunk amplifier through the coaxial cable for one span can be kept at a practical appropriate level. According to the method described above, the amplifier of an existing small-scale analog television hearing facility can be adapted to terrestrial digital broadcasting without changing the position and number of the amplifiers without making a large-scale change. Moreover, since the AGC free range can be provided by temperature compensation control, the input signal is not excessively lowered, and deterioration of C / N can be prevented. Furthermore, the HE amplifier and the relay amplifier do not require cooperation, and are based on a temperature compensation system that independently controls the amplification factor, so that the amplifier configuration is simple, low cost, and does not require advanced adjustment techniques. . Since digital terrestrial broadcasting is transmitted at the same frequency without frequency conversion, it is not necessary to change the setting of the receiver, and a system that allows viewers to easily view can be realized.

It is a block diagram which shows the cable television hearing facility of Example 1. FIG. It is a block diagram which shows the Example of the internal circuit of an amplifier. It is a circuit diagram which shows an example of a broadband pseudo-line equivalent attenuator. It is explanatory drawing which shows the frequency characteristic of the transmission signal level (input of a next stage amplifier) after the coaxial cable passage according to external temperature. It is explanatory drawing which shows the signal attenuation amount in each temperature by a broadband pseudo-line equivalent attenuator. It is function explanatory drawing of a frequency band correction device. It is explanatory drawing of the example of control by a temperature compensation circuit.

Explanation of symbols

12 1st antenna 14 1st HE amplifier 16 coaxial cable 18 1st trunk amplifier 20 2nd trunk amplifier 22 3rd trunk amplifier 24 distributor 26 subscriber's house 28 UHF broadcast receiving part 30 2nd antenna 32 preamplifier 34 band pass filter 36 Second HE amplifier 38 Mux 40 Input terminal 42 First amplifier 44 Broadband pseudo-line equivalent attenuator 46 Second amplifier 48 Frequency band corrector 50 Output terminal 52 Thermal AGC circuit (temperature compensation circuit)
54 Gate 56 Comparator 58 Dead Dead Upper Limit 60 Dead Dead Lower Limit 62 Temperature Sensor 64 Equivalent Attenuator 65 PIN Diode 66 Flat Attenuator 67 PIN Diode 68 Control Circuit 69 Filter

Claims (16)

A UHF broadcast receiver is added to the analog broadcast reception point of the existing television hearing facility, and this UHF broadcast receiver is provided with a HE (head end) amplifier that amplifies the received digital terrestrial broadcast signal.
Combine the terrestrial digital broadcast signal after amplification into the existing analog broadcast signal using a multiplexer,
Furthermore, in the coaxial cable transmission path from this multiplexer to the subscriber's home, a new trunk amplifier is installed without changing the installation position of the trunk amplifier provided for amplifying the existing analog broadcast signal. And replacing it with a bandwidth that amplifies both the existing analog broadcast signal and the terrestrial digital broadcast signal,
The HE amplifier and the new main line amplifier are provided with a broadband amplifier, a broadband pseudo-line equivalent attenuator, and a temperature compensation circuit,
The broadband amplifier has an amplification characteristic that compensates for transmission loss of the coaxial cable over the entire frequency range of the input broadcast signal,
The temperature compensation circuit supplies a control signal corresponding to a change in outside air temperature to the broadband pseudo-line equivalent attenuator,
The broadband pseudo-line equivalent attenuator is designed so that the attenuation characteristic is equivalent to that of a coaxial cable in the entire frequency range of the input broadcast signal, and the analog broadcast signal and the ground are output on the output side of the subsequent coaxial cable. A method for digitizing an existing television hearing facility, wherein a pass frequency characteristic is changed according to an outside air temperature by a control signal output from the temperature compensation circuit so that a level of a digital broadcast signal falls within a reference range. . The method for digitizing an existing television hearing facility according to claim 1,
A digital of an existing television hearing facility, wherein a frequency band compensator for correcting the frequency characteristics of an existing coaxial cable and expanding an apparent bandwidth is inserted after the broadband pseudo-line equivalent attenuator. Method. The method for digitizing an existing television hearing facility according to claim 2,
According to the characteristics of the frequency band corrector, a control signal for maintaining the output level of the frequency band corrector at a constant level is sent to the broadband pseudo-line equivalent attenuator, and the signal attenuation in the broadband pseudo-line equivalent attenuator A method for digitizing an existing television hearing facility, characterized in that a control circuit for adjusting the amount is provided. The method for digitizing an existing television hearing facility according to claim 2 or 3,
The temperature compensation circuit provides a constant temperature range between a lower limit value and an upper limit value centered on a standard temperature, and the control signal is fixed to a standard value within the temperature range. How to digitize a hearing facility. In the digitization method of the existing television hearing facility in any one of Claims 2 thru | or 4,
The temperature compensation circuit holds the control signal in the state when the temperature in the limit range is detected when the temperature exceeding the limit range or the temperature below the limit range is detected. How to digitize a hearing facility. The method for digitizing an existing television hearing facility according to any one of claims 2 to 5,
A method for digitizing an existing television hearing facility, characterized in that the trunk line amplifier is employed in a hearing facility in which only three or fewer stages are cascade-connected. At an analog broadcast reception point of an existing television hearing facility, a UHF broadcast receiver, a HE (head end) amplifier that amplifies the terrestrial digital broadcast signal received by the UHF broadcast receiver, and the existing analog broadcast signal With a multiplexer that multiplexes digital terrestrial broadcast signals,
In the coaxial cable transmission path from the multiplexer to the subscriber's house, a bandwidth trunk amplifier that amplifies both the existing analog broadcast signal and the terrestrial digital broadcast signal is provided.
The HE amplifier and the main line amplifier are provided with a broadband amplifier, a broadband pseudo-line equivalent attenuator, and a temperature compensation circuit,
The wideband amplifier has an amplification characteristic that compensates for transmission loss of a coaxial cable over the entire frequency range of the input broadcast signal,
The temperature compensation circuit supplies a control signal corresponding to a change in outside air temperature to the broadband pseudo-line equivalent attenuator,
The broadband pseudo-line equivalent attenuator is designed so that the attenuation characteristic is equivalent to that of a coaxial cable in the entire frequency range of the input broadcast signal, and the analog broadcast signal and the ground are output on the output side of the subsequent coaxial cable. A cable television hearing facility characterized by being a circuit that changes a passing frequency characteristic according to an outside air temperature by a control signal output from the temperature compensation circuit so that a level of a digital broadcasting signal falls within a reference range. In the cable television hearing facility according to claim 7,
A cable television co-listening system, wherein a frequency band compensator for correcting the frequency characteristics of an existing coaxial cable and expanding an apparent bandwidth is inserted after the broadband pseudo-line equivalent attenuator. Facilities. In the cable television hearing facility according to claim 8,
According to the characteristics of the frequency band corrector, a control signal for maintaining the output level of the frequency band corrector at a constant level is sent to the broadband pseudo-line equivalent attenuator, and the signal attenuation in the broadband pseudo-line equivalent attenuator A cable television hearing facility characterized by a control circuit for adjusting the amount. In the cable television hearing facility according to any one of claims 7 to 9,
The temperature compensation circuit has a constant temperature range between a lower limit value and an upper limit value centered on a standard temperature, and the control signal is fixed to the standard value within this temperature range. Listening facility. In the cable television hearing facility according to any one of claims 7 to 9,
The temperature compensation circuit holds the control signal in a state where the temperature in the limit range is detected when the temperature exceeding the limit range or the temperature below the limit range is detected. Hearing facility.   A broadband amplifier, a broadband pseudo-line equivalent attenuator, and a temperature compensation circuit are provided, and the temperature compensation circuit supplies a control signal corresponding to a change in outside air temperature to the broadband pseudo-line equivalent attenuator, and the broadband pseudo-line equivalent attenuation The device adjusts the output signal of the broadband amplifier with an attenuation characteristic according to temperature, and on the output side of the subsequent coaxial cable, so that the level of the analog broadcast signal and the terrestrial digital broadcast signal falls within a reference range, An amplifier for a television hearing facility, which is a circuit that changes a passing frequency characteristic according to an outside air temperature by a control signal output from the temperature compensation circuit. The amplifier for a television hearing facility according to claim 12,
A television hearing facility characterized in that a frequency band compensator for correcting the frequency characteristics of an existing coaxial cable and expanding an apparent bandwidth is inserted after the broadband pseudo-line equivalent attenuator. Amplifier. The television hearing aid amplifier according to claim 13,
According to the characteristics of the frequency band corrector, a control signal for maintaining the output level of the frequency band corrector at a constant level is sent to the broadband pseudo-line equivalent attenuator, and the signal attenuation in the broadband pseudo-line equivalent attenuator An amplifier for a television hearing facility, comprising a control circuit for adjusting the amount. The amplifier for a television hearing facility according to any one of claims 12 to 14,
The temperature compensation circuit provides a constant temperature range between a lower limit value and an upper limit value centered on a standard temperature, and the control signal is fixed to the standard value within the temperature range. Facility amplifier. The amplifier for a television hearing facility according to any one of claims 12 to 14,
The temperature compensation circuit holds the control signal in a state where the temperature in the limit range is detected when the temperature exceeding the limit range or the temperature below the limit range is detected. Hearing facility amplifier.

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