JP3867087B2 - Relay broadcast device - Google Patents

Description

  The present invention relates to a relay broadcast device suitable for application to a gap filler device or the like for relaying to a reception incapable area where a radio wave of a terrestrial digital television broadcast wave from a master station transmitting station cannot be directly received.

  Terrestrial digital broadcasting has been started since December 2003. In this terrestrial digital broadcasting, the UHF band is allocated. In the UHF band, since the straightness of radio waves is stronger than in the VHF band, there are many areas incapable of receiving direct waves from the master station near obstacles such as high-rise buildings or underground.

  As a device for eliminating this unreceivable area, there is a gap filler device as a low-cost and simple low-power broadcasting device that performs broadcasting locally. A gap filler device is a device that receives a broadcast wave from a previous-stage transmitter and re-broadcasts at the same or different frequency, like a relay broadcaster, and has a previous-stage broadcast wave receiving circuit and a local station transmission frequency transmission circuit. It is a simple device. And when a receiving circuit and a transmission circuit are installed in the position which left | separated, the space between them is connected by the coaxial cable (refer patent document 1). In addition, when the receiving circuit and the transmitting circuit are installed at positions separated from each other, the optical circuit cable may be connected between them.

  By the way, in a relay broadcasting device such as a gap filler device, for example, four channels (four waves) of television broadcasting waves are individually received and amplified, the amplified waves are combined, and a power amplifying circuit having an AGC circuit is used. It is possible to amplify and retransmit the data with power.

Japanese Patent Laying-Open No. 2003-78492 (FIG. 2)

  However, television broadcasts sometimes stop radio waves early in the morning or late at night, and the number of channels being transmitted changes during such time periods. Consider a case where the number of channels is, for example, 8 channels during normal daytime and 6 channels at midnight.

  In the ordinary technology, the output power is amplified by the amount of the reduced number of channels, and the control works to obtain the same power as the normal power with the total power of 6 waves. As a result, 1 channel of 6 channels of radio waves being transmitted The winning power is 8/6 times that at the time of a wave stop. In this case, since it is 1.33 times, the radio law mini-sate regulations (transmission power deviation is within 50% and within 50%).

  However, for example, in the Tokyo area that normally broadcasts 8 channels, if the worst case of 1 channel is considered in the middle of the night, the power per channel will be 8 times, and the radio wave law may be observed. Can not. In addition, when the power becomes 8 times, a service area more than twice that of normal time is formed, and it is considered that the relay broadcasting devices installed in other places will increase in the same way. In the midnight band, there is a problem that radio wave interference occurs with another relay broadcasting device or gap filler device.

  The present invention has been made in consideration of such problems, and even if the number of channels of terrestrial digital broadcast waves changes, the transmission power per channel (one wave) is set to a constant power or a value close to a constant power. It is an object of the present invention to provide a gap filler device that can be used.

  In this section, for ease of understanding, reference numerals in the attached drawings are used for explanation. Therefore, the contents described in this section should not be construed as being limited to those having the reference numerals.

As shown in FIGS . 1 and 4 , for example, the relay broadcast apparatus according to the present invention includes a receiving station (60), a transmission path (20) (21) connected to the output side of the receiving station, and this transmission. in the relay broadcasting apparatus comprising a transmitting station which is connected to the output side of the road and (70), the receiving stations is the terrestrial digital TV broadcast wave for a plurality of channels received, the reception of the plurality of channels to output as the received signal A circuit (51 to 53), a broadcast wave synthesizer (16) for synthesizing the reception signals of the plurality of channels, and a number of channels that are connected to the reception circuits of the reception circuits for the plurality of channels and continue broadcasting. the inversely proportional to having the levels, and the pilot signal generation circuit for generating a pilot signal inserted into out-of-band received signal of the plurality of channels (58), said pilot signal and a plurality A pilot insertion synthesizer (62) that synthesizes the synthesized signal of the channel reception signal and outputs a pilot insertion synthesis signal, and the transmission path transmits the pilot insertion synthesis signal, The transmitting station extracts a pilot signal from the pilot insertion combined signal output from the transmission line , and amplifies the pilot insertion combined signal so that the level of the extracted pilot signal becomes a constant level. A circuit (72); and a power amplification circuit (74) for amplifying the combined signal obtained by removing the pilot signal from the amplified pilot insertion combined signal and outputting the amplified signal as a transmission signal.

For example, as shown in FIG. 6, the relay broadcasting apparatus according to the present invention is connected to a receiving station (60C), a transmission line (20) connected to the output side of the receiving station, and an output side of the transmission line. In the relay broadcasting apparatus comprising the transmitting station (70), the receiving station outputs the received terrestrial digital television broadcast waves of a plurality of channels as received signals, respectively. And a broadcast wave synthesizer (16) that synthesizes the reception signals of the plurality of channels, and an integer of a number that is connected to each reception circuit of the reception circuits for the plurality of channels and that is inversely proportional to the number of channels that continue broadcasting, Alternatively, if the inversely proportional number does not become an integer, the number of the same power is close to the inversely proportional number and the pilot signals have different frequencies, and the received signals of the plurality of channels A pilot signal generating circuit (58C) that generates the pilot signal inserted out of the band, and a pilot insertion signal that combines the pilot signal and a composite signal of the reception signals of the plurality of channels and outputs a pilot insertion composite signal A combiner (62), wherein the transmission path transmits the pilot insertion combined signal, and the transmitting station extracts a pilot signal from the pilot insertion combined signal output from the transmission path. An automatic gain control circuit (72) for amplifying the pilot insertion combined signal so that the total power of the extracted pilot signal becomes a constant level, and the pilot signal is removed from the amplified pilot insertion combined signal A power amplifier circuit (74) for amplifying the combined signal and outputting it as a transmission signal.

  The broadcast wave synthesizer and the pilot insertion synthesizer can be configured integrally.

  As the transmission line, it is preferable to employ a coaxial cable when the distance between the receiving station and the transmitting station is short, and an optical fiber cable when the distance is long.

  According to the present invention, at a receiving station that receives terrestrial digital broadcast waves of a plurality of channels, a pilot signal is inserted into a received signal and synthesized, and the synthesized signal is transmitted through a transmission line. By controlling the automatic gain of the composite signal, the level of the transmission signal of each channel constituting the terrestrial digital broadcast wave (composite signal) of a plurality of channels retransmitted from the transmitting station can be suppressed to a predetermined level range. .

  In this case, the pilot signal generation circuit generates a pilot signal having a level that is inversely proportional to the number of channels that continue broadcasting, and the automatic gain control circuit increases the gain so that the level of the extracted pilot signal becomes a predetermined level. By making it variable, the level of each transmission signal of a plurality of channels can be made to be a constant level even if the number of channels on which broadcasting continues varies.

  The pilot signal generation circuit generates an integer number of pilot signals that is inversely proportional to or close to the number of channels that continue broadcasting, and the automatic gain control circuit determines the number of extracted pilot signals. By varying the gain in inverse proportion, the level of each transmission signal of a plurality of channels can be set to a constant level or a level close to the constant level even if the number of channels that continue broadcasting varies. .

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a technique that is a premise of the embodiments will be described.

A. Prerequisite technology In terrestrial digital broadcasting, radio waves from the master station are received at a receiving station where reception is good, for example, at the prefectural office, and the received signal is transmitted to a difficult-to-view area such as a municipality. However, in this case, a coaxial cable is used when the transmission path length from the receiving station to the transmitting station is short, but if it is long, the coaxial cable has a large transmission loss. . Thus, for example, transmission from a receiving station to a transmitting station can be considered by a self-managed optical fiber transmission line owned by a prefecture.

  FIG. 12 shows a configuration of the gap filler device 2 as an example of the relay broadcast device according to the base technology. The gap filler device 2 receives a plurality of channels (in this example, 3 channels as an example) of television broadcast waves received by the receiving antenna 6 at the receiving station 4 at the prefectural office location through a distributor (not shown), The signals are respectively received by the chB receiving circuit 12 and the chC receiving circuit 13, synthesized by the combiner 16, further converted into an optical signal by the electrical / optical conversion circuit (E / O conversion circuit) 18, and output.

  The optical signal as the combined signal is transmitted through the optical fiber cable 20 to the transmitting station 22 installed in the difficult viewing area.

  In the transmission station 22, an optical signal is converted into a transmission signal of a composite signal of three channels, which is an electrical signal, by an optical / electrical conversion circuit (O / E conversion circuit) 24. This transmission signal is collectively amplified by the power amplification circuit 28, and is amplified to a predetermined transmission output power by adjusting the gain of the power amplification circuit 28 by the AGC circuit 30 and retransmitted from the transmission antenna 32. The The power amplifier circuit 28 and the AGC circuit 30 constitute an automatic gain control circuit 26. Here, the reason that the power amplifying circuit 28 amplifies all at once is to avoid an increase in cost due to individual amplification for each channel.

  By the way, in this gap filler apparatus 2, when 2 waves stop, there exists a problem that the transmission power of the remaining 1 wave continuously broadcast will triple.

B. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings to be referred to below, the same reference numerals are assigned to the components corresponding to those shown in FIG. 12, and the detailed description thereof is omitted.

  FIG. 1 is a block diagram showing a configuration of a gap filler device 50 according to an embodiment of the relay broadcast device of the present invention.

  In this gap filler device 50, in order to facilitate understanding in this embodiment, it is assumed that terrestrial digital television broadcast waves of three channels chA, chB, and chC are handled. In the daytime, 3 channels (3 waves) are broadcasted. In the late night, only the chC broadcasting station stops, and the other 2 channels of chA and chB continue to be broadcast 24 hours a day. It shall be.

  The gap filler device 50 basically connects the receiving station 60 installed in the prefectural office location, the transmitting station 70 installed in the difficult viewing area, and the receiving station 60 and the transmitting station 70 via optical signals. And an optical fiber cable 20 as an optical transmission line.

  Here, the receiving station 60 receives a reception signal received via a receiving antenna 6 from a terrestrial digital television broadcast wave of 3 channels broadcast from a master station (not shown), via a duplexer (not shown). Corresponding receiving circuit (chA receiving circuit) 51, receiving circuit (chB receiving circuit) 52, receiving circuit (chC receiving circuit) 53, and broadcast that synthesizes the received signals that are output signals of these receiving circuits 51-53 A synthesizer 16 as a wave synthesizer and an automatic gain control circuit 56 that amplifies the output of the synthesizer 16 to a certain level are provided.

  Further, the receiving station 60 receives the broadcast wave presence / absence signals Sa, Sb, Sc from the receiving circuits 51 to 53, and receives the number of broadcast wave presence / absence signals Sa, Sb, Sc indicating the presence of the broadcast wave, in other words, actually. A pilot signal generation circuit (PL signal generation circuit) 58 that outputs a pilot signal Sp corresponding to the number of broadcast waves being generated, and the pilot signal Sp and the output signal of the automatic gain control circuit 56 are combined to generate a pilot insertion combined signal. A synthesizer 62 as a pilot insertion synthesizer to be output, and an electric / optical conversion circuit (E / O conversion) that converts the pilot insertion combined signal that is an output signal of the synthesizer 62 into an optical signal and outputs the optical signal to the optical fiber cable 20 Circuit) 18.

  Here, the broadcast wave presence / absence signals Sa, Sb, and Sc are compared with the detectors (not shown) in the receiving circuits 51 to 53, respectively, and the detected output is compared with a threshold value. When the value is less than the threshold value, a comparator (not shown) that outputs a signal indicating “None = 0” is provided, and can be obtained by each output of the comparators. The output of each comparator is a squelch output, and when the broadcast wave is stopped, the amplification degree of the corresponding receiving circuits 51 to 53 is reduced.

  The automatic gain control circuit 56 includes an AGC circuit 64 that creates an AGC (Automatic Gain Control) output proportional to the magnitude of the input signal to the synthesizer 62, and a variable gain amplifier 66 whose gain is variable by the AGC output. Even when the magnitude of the input signal of the variable gain amplifier 66 varies, the output signal of the variable gain amplifier 66, in other words, the input signal to the combiner 62 operates so as to have a constant output.

  The pilot signal generation circuit 58 generates a pilot signal Sp having a level that is inversely proportional to the number of “presence = 1” of the broadcast wave presence / absence signals Sa, Sb, Sc. The frequency of the pilot signal Sp is set to a frequency outside the frequency band of terrestrial digital broadcast waves (broadband of 470 to 770 [MHz] in Japan), for example, 400 [MHz].

  On the other hand, the transmitting station 70 receives an optical signal from the optical fiber cable 20 and restores it to a pilot insertion combined signal that is an electric signal corresponding to the output signal of the combiner 62 (O / E conversion circuit). ) 24, an automatic gain control circuit 72 that amplifies the restored pilot insertion combined signal to a predetermined level signal, and a combined signal obtained by removing the pilot signal from the constant level signal is amplified with a predetermined amplification factor, The power amplifier circuit 74 retransmits a terrestrial digital broadcast wave as a transmission signal. Since a band pass filter having a broadcast band of 470 to 770 [MHz] as a pass band is inserted on the input side of the power amplifier circuit 74, the pilot signal Sp is blocked by passing through the power amplifier circuit 74. (Removed).

  Here, the automatic gain control circuit 72 extracts the pilot signal Sp from the input signal to the power amplifier circuit 74 and outputs it, and the magnitude of the extracted pilot signal Sp. The AGC circuit 78 outputs a proportional AGC output, and a variable gain amplifier 80 whose gain is controlled by the AGC output. The automatic gain control circuit 72 performs control so that the level of the pilot signal Sp at the output becomes constant, so that the pilot insertion combined signal that is the output signal is constant even if the pilot insertion combined signal that is the input signal fluctuates. The gain of the variable gain amplifier 80 is controlled so as to be electric power. The automatic gain control circuit 72 is controlled so that the level of the pilot signal Sp is constant, so that transmission loss caused by a desired (arbitrary) transmission distance of the optical fiber cable 20 is also compensated simultaneously. Can do.

  In this embodiment, the loss from the input side of the electrical / optical conversion circuit 18 of the receiving station 60 to the output side of the optical / electrical conversion circuit 24 of the transmitting station 70 through the optical fiber cable 20 (loss in the optical fiber transmission circuit) is 3 [dB].

  The gap filler device 50 according to this embodiment is basically configured as described above. Next, regarding the operation of the gap filler device 50, the frequency spectrum diagrams shown in FIGS. 2A to 2C ( The horizontal axis represents frequency, and the vertical axis represents level.

  First, the operation during the daytime will be described. In the daytime, all three channels are broadcasting, and the three receiving circuits 51 to 53 in the receiving station 60 located at the prefectural office are all having the broadcast wave presence / absence signals Sa, Sb, and Sc “Yes = 1”: Active Is in a state of being broadcast.

  The pilot signal generation circuit 58 that detects the continuation of the three-wave broadcasting is a synthesizer for the pilot signal Sp in which the power of the signal outside the broadcast band, in this embodiment, the signal of 400 [MHz] is set to 1 [mW]. To 62.

  At this time, the output signals from the receiving circuits 51 to 53 are output by the automatic gain control circuit 56 at the output of the automatic gain control circuit 56, in other words, 30 [mW] (10 [mW per channel] at the input of the combiner 62. ]) To be AGC controlled.

  In this case, for example, if the AGC control is individually performed by the receiving circuits 51 to 53 so that the power per channel at the input of the combiner 16 can be accurately controlled to 10 [mW], the pilot signal Sp is combined with the combiner. 16, the automatic gain control circuit 56 and the combiner 62 can be omitted. If omitted, the output terminal of the synthesizer 16 may be connected to the input terminal of the electrical / optical conversion circuit 18.

  However, the input level of the electrical / optical conversion circuit 18 changes depending on the wave number, that is, the number of channels, the level of the optical signal changes depending on the wave number, and the dynamic range of the level of the optical signal decreases. In a system that performs long-distance transmission, it is preferable to provide an automatic gain control circuit 56 on the receiving station 60 side.

  FIG. 2A shows the frequency spectrum of the pilot insertion combined signal at the input of the electrical / optical conversion circuit 18 after AGC control by the automatic gain control circuit 56. The level of the pilot signal Sp having a frequency of 400 [MHz] is set to an appropriate level, for example, 1 [mW] that is sufficiently smaller than the level of the broadcast wave signal of chA to chC. In this case, the level of the broadcast wave of chA to chC The signal level is 10 [mW] in a predetermined broadcast frequency range.

  FIG. 2B shows the frequency of the pilot insertion combined signal at the output of the optical / electrical conversion circuit 24 after the signal shown in FIG. 2A passes through the electrical / optical conversion circuit 18, the optical fiber cable 20, and the optical / electrical conversion circuit 24. The spectrum is shown. That is, since the transmission loss between the electrical / optical conversion circuit 18, the optical fiber cable 20, and the optical / electrical conversion circuit 24 is 3 [dB], the level of the pilot signal Sp is attenuated to 0.5 [mW]. , ChA to chC broadcast wave signals are attenuated to 5 [mW] in a predetermined frequency range.

  At this time, first, a pilot signal Sp of 0.5 [mW] is extracted by the pilot signal extraction circuit 76 constituting the automatic gain control circuit 72 of the transmitting station 70 and input to the AGC circuit 78. The AGC circuit 78 controls the gain of the variable gain amplifier 80 to be four times so that the level of the pilot signal Sp extracted by the pilot signal extraction circuit 76 becomes a constant level of 2 [mW].

  By controlling the gain in this way, as shown in FIG. 2C, the broadcast wave signals of chA to chC are also controlled to be 5 × 4 = 20 [mW] per channel.

  When a pilot signal Sp of 2 [mW] and a broadcast wave signal of chA to chC of 20 [mW] are input to the power amplifier circuit 74, a band pass filter (not shown) on the input side of the power amplifier circuit 74 ( In the pass band, the pilot signal Sp is removed in a band in which the chA to chC broadcast waves are passed), and the chA to chC broadcast waves are amplified with a gain of 5 times and transmitted with a power of 100 [mW], respectively. .

  The above description is an explanation of the operation in the daytime zone that is broadcast on the three channels of chA to chC.

  Next, the operation at midnight will be described using the frequency spectrum diagrams of FIGS. 3A to 3C. In the midnight band, only two channels of chA and chB are broadcast, and only the broadcast wave presence / absence signal Sc from the chC receiving circuit 53 of the receiving station 60 is “nothing = 0”: an inactive stopped state. Yes.

  The pilot signal generation circuit 58 that detects that the two-wave broadcasting is in progress uses the power of the pilot signal Sp of 400 [MHz], which is a frequency outside the broadcasting band, 3/2 times that of the three-channel broadcasting, that is, 1 [mW] × 3/2 = 1.5 [mW] is set and output to the combiner 62. When the two channels stop, they are set to 3/1 times, that is, 1 [mW] × 3/1 = 3 [mW], and output to the combiner 62. Thus, the level of the pilot signal Sp is controlled by the pilot signal generation circuit 58 so as to have a level that is inversely proportional to the number of channels in which broadcasting is continued.

  At this time, the output signals from the receiving circuits 51 to 53 are output by the automatic gain control circuit 56 of the receiving station 60 at the output of the automatic gain control circuit 56, in other words, 30 [mW] (1 channel) at the input of the combiner 62. AGC control is performed so as to be 15 [mW].

  FIG. 3A shows the frequency spectrum of the pilot insertion combined signal at the input of the electrical / optical conversion circuit 18 after AGC control by the automatic gain control circuit 56. The level of the pilot signal Sp having a frequency of 400 [MHz] is 1.5 [mW], and the broadcast wave signals of chA and chB are each 15 [mW] in a predetermined frequency range.

  FIG. 3B shows the frequency of the combined pilot insertion signal at the output of the optical / electrical conversion circuit 24 after the signal shown in FIG. 3A passes through the electrical / optical conversion circuit 18, the optical fiber cable 20, and the optical / electrical conversion circuit 24. The spectrum is shown. Since the transmission loss during this period is 3 [dB], the level of the pilot signal Sp is attenuated to 0.75 [mW], and the broadcast wave signals of chA and chB are respectively 7.5 [mW in a predetermined frequency range. ] Is attenuated.

  Next, a pilot signal Sp of 0.75 [mW] is extracted by the pilot signal extraction circuit 76 constituting the automatic gain control circuit 72 and input to the AGC circuit 78. The AGC circuit 78 controls the gain of the variable gain amplifier 80 to 2 / 0.75 times so that the level of the pilot signal Sp extracted by the pilot signal extraction circuit 76 becomes 2 [mW].

  By controlling the gain in this way, the broadcast wave signals of chA and chB are controlled to be 7.5 × 2 / 0.75 = 20 [mW] per channel as shown in FIG. 3C. The

  When a pilot signal Sp of 2 [mW] and a broadcast wave signal of chA and chB of 20 [mW] are input to the power amplifier circuit 74, a band pass filter (pass) (not shown) on the input side of the power amplifier circuit 74 is provided. The pilot signal Sp is removed in a band (a band through which the chA and chB broadcast waves pass), and further amplified with a gain of 5 times, and the chA and chB broadcast waves are transmitted at 100 [mW].

  As described above, according to the gap filler device 50 of FIG. 1 described above, even if the number of channels during continuous broadcasting of the terrestrial digital broadcasting wave fluctuates, the broadcasting is continued by the pilot signal generation circuit 58 of the receiving station 60. A pilot signal Sp having a level inversely proportional to the number of channels is generated, and the automatic gain control circuit 72 of the transmitting station 70 controls the gain so that the level of the pilot signal Sp becomes 2 [mW] of constant power. Transmission power per channel can be transmitted as constant power.

  When the distance between the receiving station 60 and the transmitting station 70 is relatively short, the transmission line of the optical fiber cable 20 can be changed to the coaxial cable 21 as shown in FIG. When the coaxial cable 21 is changed, the gap filler device 50A has the same circuit configuration except that the receiving station 60A and the transmitting station 70A are omitted from the electrical / optical conversion circuit 18 and the optical / electrical conversion circuit 24. be able to.

  As described above, in the gap filler device 50 in the example of FIG. 1 (the same applies to the gap filler device 50A in the example of FIG. 4), the pilot signal generation circuit 58 of the receiving station 60 is inversely proportional to the number of channels that are currently being broadcast. A pilot signal Sp of power level is generated, and the level of the extracted pilot signal Sp is adjusted to 2 [mW] with a constant power by the automatic gain control circuit 72 of the transmitting station 70, so that the number of channels of the terrestrial digital broadcast wave can be reduced. Even if it changes, the transmission power per channel (one wave) is adjusted to be constant power, but it can be modified as shown in FIG.

  In the gap filler device 50B of FIG. 5, the pilot signal generation circuit 58B of the receiving station 60B is configured by a modulator such as a PSK modulator, an ASK modulator, or an FSK modulator, and the presence / absence of broadcast presence / absence signals Sa, Sb, Sc The 2-bit information indicating the state is output to the combiner 62 as a pilot signal Spb as a modulated wave modulated by the carrier wave 400 [MHz].

On the other hand, the pilot signal extraction circuit 76B constituting the automatic gain control circuit 72B of the transmitting station 70B is the corresponding PSK demodulator as demodulation device such as ASK demodulator or FSK demodulator, broadcast existence signal Sa, Sb, and Sc Bit information is restored and output to the AGC circuit 78B.

  The automatic gain control circuit 72B causes the AGC circuit 78B to set the transmission power of the pilot insertion combined signal to 60 [mW] when there are three channels according to the bit information of the broadcast presence / absence signals Sa, Sb, Sc. When the AGC output is 2 channels, the AGC circuit 78B causes the AGC circuit 78B to generate an AGC output such that the transmission power of the pilot insertion combined signal is 40 [mW]. AGC output is set to be 20 [mW], and output to the variable gain amplifier 80.

  The gap filler device 50B in the example of FIG. 5 can also make the transmission power per channel (one wave) constant even if the number of channels of the terrestrial digital broadcast wave changes.

  FIG. 6 shows the configuration of still another gap filler device 50C. In this gap filler device 50C, the pilot signal generation circuit 58C connected to the receiving circuits 51 to 53 has a number that is inversely proportional to the number of channels that continue broadcasting from the state of the broadcast presence / absence signals Sa, Sb, Sc, or inversely proportional. If the number is not equal to the number, an integer number of the same level pilot signals Sp (Sp = Sp1, Sp2, Sp3) close to an inversely proportional number are generated and output to the combiner 62. Here, the frequencies of the pilot signals Sp1, Sp2, and Sp3 are different frequencies, and are set to frequencies outside the broadcast band of 470 to 770 [MHz], for example, three frequency values in the vicinity of 400 [MHz].

  In the example of FIG. 6, when the number of channels that continue broadcasting is 3, for example, only one pilot signal Sp1 of 1 [mW] is output, and in the case of 1 channel, 1 [mW] The three pilot signals Sp1, Sp2, and Sp3 are output, and in the case of two channels, basically two pilot signals Sp1 and Sp2 are output, or in the case of two channels, one pilot signal is output. Only the signal Sp2 is output.

  The operation when the pilot signal Sp is generated in this way will be described with reference to the frequency spectrum diagrams of FIGS.

  As shown in FIG. 7A, FIG. 7B, and FIG. 7C, when the number of channels that continue broadcasting is three (three waves), only one pilot signal Spa of 1 [mW] indicated by the solid line Since it is output, the same operation as described with reference to FIGS. 2A, 2B, and 2C is performed.

  Also, as shown in FIGS. 8A, 8B, and 8C, when the number of channels for which broadcasting is continued is one channel (one wave), only chB is depicted as being continued. ) Three pilot signals Sp1, Sp2, and Sp3 of 1 [mW] are output. In this case, the frequency spectrum of the pilot insertion combined signal on the output side of the optical / electrical conversion circuit 24 is as shown in FIG. 8B.

  In the automatic gain control circuit 72, the total power of the three pilot signals Sp1, Sp2, and Sp3 is controlled to be 2 [mW]. Therefore, as shown in FIG. 8C, the level of one pilot signal is 2/3 [mW], and the chB transmission wave level is 15 × ((2/3) /0.5) = 20 [mW]. That is, even when three waves are reduced to one wave, transmission can be performed with the same transmission power.

  When the number of channels that continue broadcasting is two channels (two waves), as shown in FIGS. 9A, 9B, and 9C, the number of pilot signals Sp is two (pilot signals Sp1, Sp2), Alternatively, as shown in FIGS. 10A, 10B, and 10C, the number of pilot signals Sp is set to one (pilot signal Sp1).

  When the number of pilot signals Sp is one, as shown in FIG. 9C, the transmission power per channel (one wave) is 15 [mW], and when it is two, the transmission power is shown in FIG. 10C. As described above, the transmission power per channel (one wave) is 30 [mW], but in both cases of FIG. 9C and FIG. 10C, the fluctuation range is ± 50 [in the normal three-channel (three waves) broadcasting state. %].

  In the case where the number is not inversely proportional to the number of channels that are continuing to broadcast, or the number is not inversely proportional, an integer of the same level pilot signal Sp that is close to the inversely proportional number is generated and output to the combiner 62 in FIG. The illustrated gap filler device 50C can suppress the fluctuation range of transmission power within ± 50 [%] by applying it to a broadcast system that transmits broadcast waves of three or more channels during normal broadcasting.

  FIG. 11 shows a configuration of a gap filler device 50D of still another embodiment. Compared with the gap filler device 50 in the example of FIG. 1, the gap filler device 50D does not require the broadcast wave presence / absence signals Sa, Sb, Sc, and the pilot signal generation circuit 58D of the receiving station 60D always has 1 [mW The pilot signal Sp is combined with the outputs of the receiving circuits 51 to 53 by the combiner 16D, and the combiner 62 shown in FIG. 1 is omitted.

  The operation during the daytime will be described. In the daytime zone, all three channels are broadcast, and the pilot signal generation circuit 58D outputs a signal of 1 [mW] having a constant power of 400 [MHz], a frequency outside the broadcast band regardless of the number of channels being broadcast. It is output to the synthesizer 16D.

  Further, the chA, chB, and chC receiving circuits 51 to 53 perform AGC control so as to be 10 [mW], respectively, and output to the synthesizer 16D. The receiving circuits 51 to 53 perform AGC control corresponding to each channel, so that even if the frequency characteristics of the spatial propagation path deteriorate due to fading or the like and a difference occurs in the received power of each channel, the frequency characteristics As a result, the power of each channel transmitted to the optical fiber cable 20 can be made constant.

  In the automatic gain control circuit 56, AGC control is performed so as to be 30 [mW] at the input of the electrical / optical conversion circuit 18. Therefore, in this example, the gain of the automatic gain control circuit 56 is 0 [dB].

  Therefore, the frequency spectrum on the input side of the electrical / optical conversion circuit 18 at this time is as shown in FIG. 2A.

  These signals are subjected to electrical / optical conversion by the electrical / optical conversion circuit 18, and the optical signal is transmitted through the optical fiber cable 20 from the receiving station 60 </ b> D at the prefectural office location to the transmitting station 70 in the difficult viewing area.

  The loss in the optical signal transmission system including the optical fiber cable 20 (from the input of the electrical / optical conversion circuit 18 to the output side of the optical / electrical conversion circuit 24) is 3 [dB]. At this time, the frequency spectrum at the output of the photoelectric conversion circuit 24 of the transmitting station 70 in the difficult viewing area is as shown in FIG. 2B.

  Then, the pilot signal extraction circuit 76 constituting the automatic gain control circuit 72 of the transmitting station 70 extracts the pilot signal Sp of 0.5 [mW], and the pilot signal Sp becomes 2 [mW] by the AGC circuit 78. Control is performed as follows. As a result, as shown in FIG. 2C, the power of the broadcast wave is simultaneously controlled to 20 [mW] per channel. Thereafter, the pilot signal Sp is removed by the band-pass filter of the power amplifier circuit 74, and in the example of FIG. 11, each broadcast wave is transmitted at 100 [mW] with 5 times amplification.

  Next, the operation at midnight will be described. In the midnight band, broadcasting is performed on two channels, and it is assumed that there is no input to the chC receiving circuit 53 of the receiving station 60D in the prefectural office location. At this time, the receiving circuit 53 is in the maximum gain state, and noise is output. However, when the input becomes power corresponding to the threshold value of the squelch circuit or less, the output is cut off by the squelch circuit. State (minimizing the variable gain of the receiving circuit 53). However, without providing a squelch circuit, the maximum gain of a variable gain amplifier (not shown) of the receiving circuit 53 is optimized, and the squelch circuit is designed so that the noise level at the time of broadcasting stop is negligible. It can be omitted.

  In the late-night band in which 2-channel broadcasting is continued, on the output side of the synthesizer 16D, the broadcast wave is 10 [mW] × 2 channels = 20 [mW], and the pilot signal Sp is Sp = 1 [mW].

  Since the automatic gain control circuit 56 controls the total power to be 30 [mW], the gain is controlled to be 1.5 times. As shown in FIG. ] Of 30 [mW] and 1.5 [mW] of the pilot signal Sp are input to the electrical / optical conversion circuit 18.

  Also in this case, assuming that the loss in the optical signal transmission system including the optical fiber cable 20 (from the input of the electrical / optical conversion circuit 18 to the output side of the optical / electrical conversion circuit 24) is 3 [dB], The frequency spectrum at the output of the optical / electrical conversion circuit 24 of the transmitting station 70 is as shown in FIG. 3B.

  Then, the pilot signal extraction circuit 76 constituting the automatic gain control circuit 72 of the transmitting station 70 extracts the pilot signal Sp of 0.75 [mW], and the AGC circuit 78 converts the pilot signal Sp to 2 [mW]. Control is performed as follows. As a result, as shown in FIG. 3C, the power of the broadcast wave is simultaneously controlled to 20 [mW] per channel. Thereafter, the pilot signal Sp is removed by the band-pass filter of the power amplifier circuit 74, and in the example of FIG. 11, each broadcast wave is transmitted at 100 [mW] with 5 times amplification.

  In the gap filler device 50D of FIG. 11 example, the operation in the automatic gain control circuit 56 generates the level of the pilot signal Sp that is inversely proportional to the number of channels (wave number) that is continuing to be broadcast. The circuit 56 cannot be omitted.

  As described above, according to the gap filler device 50D of FIG. 11 example, the pilot signal generation circuit 58D of the receiving station 60D generates the pilot signal Sp of 1 [mW] at a constant level, and the pilot signal Sp and a plurality of channels. The received signal is synthesized by the synthesizer 16D, and the automatic gain control circuit 56 controls the synthesized signal so that the level of the synthesized signal becomes a constant level of 30 [mW]. The level is inversely proportional to the number of channels being continued.

  At the transmitting station 70, the pilot signal Sp is extracted by the pilot signal extraction circuit 76 from the pilot insertion combined signal output from the optical fiber cable 20 serving as the transmission path, and the level of the pilot signal Sp is 2 [ mW], by amplifying the pilot insertion composite signal with the variable gain amplifier 80, the level of each transmission signal of a plurality of channels becomes a constant level even if the number of channels for which broadcasting is continued fluctuates. Can be.

  Here, a brief description will be given of the control operation when broadcasting of all channels is stopped.

  In this case, in the gap filler device 50 and the like shown in FIGS. 1 and 4 to 6, the broadcast wave presence / absence signals Sa, Sb, and Sc become “none = 0” signals. The pilot signal Sp is not output at all. As a result, the pilot signal is not transmitted from the receiving station 60 or the like to the transmitting station 70 or the like.

  When the pilot signal extraction circuit 76 in the transmitting station 70 detects that the pilot signal Sp is not present, the gain of the variable gain amplifier 80 is minimized, or the input or output side of the power amplification circuit 74 is disconnected. A switch or a circuit is added to prevent noise from being transmitted from the transmitting station 70 or the like.

  Further, in the gap filler device 50D shown in FIG. 11, when broadcasting of all channels is stopped, for example, the output of the receiving circuits 51 to 53 is turned off by the squelch circuit, or the reception is performed without providing the squelch circuit. The maximum gain of a variable gain amplifier (not shown) of the circuits 51 to 53 is optimized, and the noise level at the time of broadcasting stop is designed to be a negligible level. At this time, the automatic gain control circuit 56 amplifies to the full gain, but when this full gain is detected, by adding a switch or a circuit that cuts off the input or output side of the electrical / optical conversion circuit 18, An operation equivalent to that of the gap filler device 50 shown in FIGS. 1 and 4 to 6 can be realized.

  Control operations such as minimizing the gain of the variable gain amplifier 80 when broadcasting of all channels is stopped are automatically applied even when the optical fiber cable 20 is disconnected, and the transmission station 70 and the like. Since unnecessary noise is prevented from being transmitted, there is no interference with neighboring relay devices and gap filler devices.

  Note that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted based on the contents described in this specification.

It is a lineblock diagram of the gap filler device concerning one embodiment of this invention. It is a frequency spectrum figure used for operation | movement description at the time of 3 channel (3 waves) broadcast. It is a frequency spectrum figure with which it uses for operation | movement explanation at the time of 2 channel (2 wave) broadcasting in which 1 wave stopped in 3 waves. It is a block diagram of the gap filler apparatus of the example which used the transmission line as the coaxial cable. It is a block diagram of the gap filler apparatus which made the pilot signal the modulation signal according to the number of broadcast waves. It is a block diagram of a gap filler device in which the number of pilot signals is inversely proportional to or approximately inversely proportional to the number of broadcast waves. FIG. 7 is a frequency spectrum diagram for explaining the operation of the example of FIG. 6 during three-channel broadcasting. FIG. 7 is a frequency spectrum diagram for explaining the operation of the example of FIG. 6 during 1-channel broadcasting. FIG. 7 is a frequency spectrum diagram for explaining the operation of the example of FIG. 6 during two-channel broadcasting. FIG. 7 is a frequency spectrum diagram for explaining another operation of the example of FIG. 6 during two-channel broadcasting. It is a block diagram of the gap filler apparatus which concerns on other embodiment. It is a block diagram of the gap filler apparatus used as the premise technique of this invention.

Explanation of symbols

2, 50, 50A-50D: Gap filler device 4, 60, 60A, 60B, 60D ... Reception station 6 ... Reception antennas 11-13, 51-53 ... Reception circuits 16, 16D, 62 ... Synthesizer 18 ... Electricity / light Conversion circuit (E / O conversion circuit)
20 ... Optical fiber cable 21 ... Coaxial cable 22, 70, 70A, 70B ... Transmitting station 24 ... Optical / electrical conversion circuit (O / E conversion circuit)
26, 56, 72, 72B ... automatic gain control circuits 28, 74 ... power amplification circuits 30, 64, 78, 78B ... AGC circuit 32 ... transmission antennas 58, 58B-58D ... pilot signal generation circuit (PL signal generation circuit)
66, 80 ... variable gain amplifiers 76, 76B ... pilot signal extraction circuit (PL signal extraction circuit)

Claims (3)

In a relay broadcasting device comprising a receiving station, a transmission path connected to the output side of the receiving station, and a transmitting station connected to the output side of the transmission path,
The receiving station is
A reception circuit for a plurality of channels that outputs the received terrestrial digital television broadcast waves of the plurality of channels as reception signals;
A broadcast wave synthesizer for synthesizing the reception signals of the plurality of channels;
A pilot signal that is connected to each receiving circuit of the receiving circuits for the plurality of channels, has a level inversely proportional to the number of channels that continue broadcasting, and is inserted outside the band of the received signals of the plurality of channels is generated. A pilot signal generation circuit;
A pilot insertion combiner that combines the pilot signal and a combined signal of the reception signals of the plurality of channels and outputs a pilot insertion combined signal;
The transmission path transmits the pilot insertion combined signal,
The transmitting station is
An automatic gain control circuit for extracting a pilot signal from the pilot insertion combined signal output from the transmission line, and amplifying the pilot insertion combined signal so that the level of the extracted pilot signal becomes a constant level ;
A relay broadcast apparatus comprising: a power amplifying circuit that amplifies the combined signal obtained by removing the pilot signal from the amplified pilot insertion combined signal and outputs the amplified signal as a transmission signal. In a relay broadcasting device comprising a receiving station, a transmission path connected to the output side of the receiving station, and a transmitting station connected to the output side of the transmission path,
The receiving station is
A reception circuit for a plurality of channels that outputs the received terrestrial digital television broadcast waves of the plurality of channels as reception signals;
A broadcast wave synthesizer for synthesizing the reception signals of the plurality of channels;
An integer that is connected to each receiving circuit of the receiving circuits for the plurality of channels and is inversely proportional to the number of channels that continue broadcasting, or an integer that is close to an inversely proportional number if the inversely proportional number is not an integer. A pilot signal generating circuit that generates pilot signals that have the same power and have different frequencies and are inserted outside the band of the reception signals of the plurality of channels;
A pilot insertion combiner that combines the pilot signal and a combined signal of the reception signals of the plurality of channels and outputs a pilot insertion combined signal;
The transmission path transmits the pilot insertion combined signal,
The transmitting station is
An automatic gain control circuit for extracting a pilot signal from the pilot insertion combined signal output from the transmission path, and amplifying the pilot insertion combined signal so that the total power of the extracted pilot signal becomes a constant level ;
A relay broadcast apparatus comprising: a power amplifying circuit that amplifies the combined signal obtained by removing the pilot signal from the amplified pilot insertion combined signal and outputs the amplified signal as a transmission signal. In the relay broadcast device according to claim 1 or 2 ,
The broadcast broadcasting device comprising the broadcast wave synthesizer and the pilot insertion synthesizer integrally.

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