JP7502926B2 - Level Adjustment Device - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Masato Kawagoe published in the Abstracts of the 73rd Hokkaido Broadcasting Technology Report Meeting on April 17, 2020.

The present invention relates to a level adjustment device.

To eliminate the difficulty of viewing television broadcasts, facilities (communal viewing facilities) have been set up, as shown in Figure 10, where broadcast waves of multiple channels transmitted from a transmitting station 1 are received by a receiving antenna 2 installed at a specified receiving point, and the received signal of the receiving antenna 2 is transmitted by a transmitter 3 to an optical receiver 4 installed in each home or the like. Traditionally, the transmitter 3 and the receiver 4 were connected via a coaxial cable, but in recent years, progress has been made in upgrading from the coaxial cable to an optical cable.

In the shared viewing facilities mentioned above, the signal level of the received signal can sometimes drop due to the effects of fading caused by marine propagation of broadcast waves, long-distance propagation, topography, or natural phenomena. When using coaxial cable, a unit that adjusts the signal level is provided for each channel, and the signal level is adjusted by this unit before being transmitted to the receiver. However, when the coaxial cable was replaced by optical cable, the above-mentioned unit was removed, and poor reception due to a drop in the signal level of the received signal has become an issue.

Patent Document 1 describes a retransmission device equipped with a retransmission unit that retransmits received terrestrial digital broadcast signals. The retransmission unit uses a local oscillation signal to down-convert signals of up to three consecutive channels into intermediate frequency band signals, and inputs the intermediate frequency band signals into three SAW filters with pass bands that differ by 6 MHz each, extracting the signals of each channel. The retransmission unit adjusts the levels of the extracted signals of each channel, and mixes and outputs the level-adjusted signals.

JP 2009-30312 A

It is known that amplifiers with an AGC (Auto Gain Control) function (AGC amplifiers) are effective in dealing with poor reception caused by fading. The AGC function adjusts the gain in response to fluctuations in the input signal level, and controls the output signal level to a constant level. By using an AGC amplifier, the output signal level can be kept constant even if the signal level of the received signal fluctuates.

Due to the frequency characteristics of each channel receiving a signal at a shared viewing facility, the signal level of the received signal of only some channels may behave differently from the signal level of the received signal of other channels. The AGC amplifier adjusts the gain based on the sum of the signal levels of all input channels (total power detection method), so it functions effectively when the signal levels of all channels fluctuate in the same manner. However, if the signal levels of only some channels receive signals that behave differently from the signal levels of other channels, even if an AGC amplifier is used, it may not be able to follow the fluctuations in the signal level of some channels, resulting in poor reception.

In the retransmission device described in Patent Document 1, multiple retransmission units with different numbers of channels they can process and different arrangements must be prepared, and multiple retransmission units (three or four depending on the region) must be combined according to the channel arrangement in each region, which leads to increased costs and a more complicated configuration. Therefore, there is a demand for technology that can adjust the signal levels of received signals of multiple channels with a simpler configuration.

The object of the present invention is to solve the above-mentioned problems and provide a level adjustment device that can adjust the signal levels of received signals of multiple channels with a simpler configuration.

In order to solve the above problem, the level adjustment device of the present invention is a level adjustment device that adjusts and outputs the signal levels of received signals of multiple channels in a first frequency band, and includes a local oscillator that outputs a local oscillation signal, a first frequency conversion unit that uses the local oscillation signal to perform frequency conversion of the received signals of the multiple channels to a second frequency band lower than the first frequency band, a separation unit that separates the signal after frequency conversion by the first frequency conversion unit into a signal of the first band and a signal of a second band higher than the first band within the second frequency band, a second frequency conversion unit that uses the local oscillation signal to perform frequency conversion of the signal of the first band from the second frequency band to the first frequency band, and a frequency conversion unit that uses the local oscillation signal to perform frequency conversion of the signal of the first band from the second frequency band to the first frequency band. a third frequency conversion unit that performs frequency conversion of the signal of the second band from the frequency band of the first frequency band to the first frequency band; a first level adjustment unit that performs level adjustment of the signal after frequency conversion by the second frequency conversion unit; a second level adjustment unit that performs level adjustment of the signal after frequency conversion by the third frequency conversion unit; a mixer that mixes and outputs the signal after level adjustment by the first level adjustment unit and the signal after level adjustment by the second level adjustment unit; and a control unit that controls the frequency of the local oscillation signal so that the received signals of the multiple channels are separated into the first band and the second band according to a second channel among the multiple channels that has a correlation with a reference first channel lower than a predetermined threshold value.

In addition, the level adjustment device according to the present invention further includes a switching unit capable of switching the input destination of the received signals of the multiple channels of the first frequency band between the first frequency conversion unit and the first level adjustment unit, and it is preferable that the control unit controls the switching unit so that the received signals of the multiple channels are input to the first level adjustment unit when the correlation between the first channel and all channels other than the first channel among the multiple channels is equal to or greater than the predetermined threshold.

The level adjustment device of the present invention can adjust the signal levels of received signals on multiple channels with a simpler configuration.

1 is a diagram illustrating an example of the configuration of a level adjustment device according to an embodiment of the present invention. 2 is a diagram showing processing on the Low side in the level adjustment device shown in FIG. 1; 2 is a diagram showing processing on the High side in the level adjustment device shown in FIG. 1; 2 is a diagram showing a specific example of processing on the Low side in the level adjustment device shown in FIG. 1 . 2 is a diagram showing a specific example of processing on the High side in the level adjustment device shown in FIG. 1 . 4 is a flowchart showing an example of an operation of a control unit shown in FIG. 1 . 2 is a diagram showing an example of signal level fluctuations of received signals of a plurality of channels before signal level adjustment by the level adjustment device shown in FIG. 1 . 2 is a diagram showing an example of signal level fluctuations of received signals of multiple channels after signal level adjustment by the level adjustment device shown in FIG. 1 . 2 is a diagram showing an example of the presence or absence of signal separation by the level adjustment device shown in FIG. 1; FIG. 1 is a diagram for explaining a shared broadcast reception facility.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 is a diagram showing an example of the configuration of a level adjustment device 100 according to one embodiment of the present invention. The level adjustment device 100 according to this embodiment adjusts the signal levels of received signals of multiple channels received by a receiving antenna 2 shown in Figure 10, for example, and outputs the signals to a transmitter 3.

As shown in FIG. 1, the level adjustment device 100 according to this embodiment includes a local oscillator 101, distributors 102, 103, and 106, a switching unit 104, mixers 105, 109, and 110, bandpass filters (BPFs) 107, 108, 111, and 112, AGC amplifiers 113 and 114, a mixer 115, an accumulation unit 116, and a control unit 117.

The local oscillator 101 outputs a local oscillation signal of a predetermined frequency, which is lower than the frequency of the signal received by the receiving antenna 2, to the distributor 102. The signal received by the receiving antenna 2 is, for example, a signal in the UHF (Ultra High Frequency) band (first frequency band) of 470 to 710 MHz. The local oscillator 101 can control the frequency Lo of the local oscillation signal, for example, between 368 MHz and 440 MHz.

The distributor 102 outputs the local oscillation signal output from the local oscillator 101 to the mixer 105, the mixer 109, and the mixer 110.

The distributor 103 receives the received signals of multiple channels received by the receiving antenna 2. The distributor 103 outputs the received signals of multiple channels to the mixer 105 or the AGC amplifier 113 via the switching unit 104. The distributor 103 also outputs the received signals of multiple channels to the storage unit 116.

The switching unit 104, under the control of the control unit 117, switches the output destination of the signal from the distributor 103 between the mixer 105 and the AGC amplifier 113. The switching unit 104 makes it possible to switch the input destination of the received signals of multiple channels between the mixer 105 and the AGC amplifier 113.

The mixer 105, acting as a first frequency conversion unit, uses the local oscillation signal output from the distributor 102 to convert the frequency of the output signal of the distributor 103 (received signals of multiple channels) to a frequency band (second frequency band) lower than the frequency band of the output signal of the distributor 103. For example, the mixer 105 converts the frequency of the received signals of multiple channels from the UHF band to the VHF (Very High Frequency) band of 30 to 300 MHz. The mixer 105 outputs the signal after frequency conversion to the distributor 106.

The distributor 106 outputs the output signal of the mixer 105 (the signal after frequency conversion by the mixer 105) to the BPF 107 and the BPF 108.

The BPF 107 outputs (passes) to the mixer 109 a signal of a predetermined band (first band) among the signals output from the distributor 106 and frequency-converted by the mixer 105. The BPF 107 passes, for example, signals from 30 MHz to 108 MHz.

The BPF 108 outputs (passes) to the mixer 110 signals of a predetermined band (second band) higher than the band (first band) through which the BPF 107 passes signals, among the signals output from the distributor 106 and frequency-converted by the mixer 105. The BPF 108 passes signals from 114 MHz to 342 MHz, for example.

In general, it is easier to create a separation filter that is inexpensive and has good characteristics in the VHF band than in the UHF band. Therefore, as in this embodiment, by frequency converting the received signals of multiple channels in the UHF band to the VHF band and then inputting them to BPFs 107 and 108, it is possible to reduce costs and improve characteristics.

The distributor 106, the BPF 107, and the BPF 108 constitute the separation unit 118. The separation unit 118 separates the signal after frequency conversion by the mixer 105 into a signal in a first band (e.g., 30 MHz to 108 MHz) and a signal in a second band (114 MHz to 342 MHz) that is higher than the first band.

The mixer 109, which serves as a second frequency conversion unit, uses a local oscillation signal to convert the frequency of the output signal of the BPF 107 back to the original frequency band (first frequency band). The mixer 109 outputs the frequency-converted signal to the BPF 111.

The mixer 110, which serves as a third frequency conversion unit, uses a local oscillation signal to convert the frequency of the output signal of the BPF 108 back to the original frequency band (first frequency band). The mixer 110 outputs the frequency-converted signal to the BPF 112.

The BPF 111 outputs (passes) signals of a predetermined band among the signals frequency-converted by the mixer 109 to the AGC amplifier 113. For example, the BPF 111 passes signals from 470 MHz to 548 MHz.

The BPF 112 outputs (passes) signals of a predetermined band from the signals frequency-converted by the mixer 110 to the AGC amplifier 114. The BPF 112 passes signals from 482 MHz to 710 MHz, for example.

The AGC amplifier 113, which serves as the first level adjustment unit, adjusts the level of the output signal of the distributor 103 or the BPF 111, and outputs the level-adjusted signal to the mixer 115.

The AGC amplifier 114, which serves as a second level adjustment unit, adjusts the level of the output signal of the BPF 112 and outputs the level-adjusted signal to the mixer 115.

The mixer 115 mixes the signal level-adjusted by the AGC amplifier 113 with the signal level-adjusted by the AGC amplifier 114, and outputs the result to the transmitter 3.

The storage unit 116 stores signal level data of the output signal (received signals of multiple channels) of the distributor 103 for a predetermined period of time (e.g., 24 hours).

The control unit 117 controls the frequency of the local oscillation signal output by the local oscillator 101. Specifically, the control unit 117 controls the frequency Lo of the local oscillation signal so that the received signals of the multiple channels are separated into a first band through which the BPF 107 passes signals and a second band through which the BPF 108 passes signals, according to a channel (second channel) of the multiple channels of the received signal that has a correlation with a reference channel (first channel) lower than a predetermined threshold. In addition, when the control unit 117 separates the received signals as described above, it controls the switching unit 104 so that the output destination of the signal from the distributor 103 is the mixer 105. In addition, when the separation of the received signals as described above is not necessary, the control unit 117 controls the switching unit 104 so that the output destination of the signal from the distributor 103 is the AGC amplifier 113.

Next, the operation of the level adjustment device 100 according to this embodiment will be described. First, the separation of the received signals of multiple channels by the level adjustment device 100 according to this embodiment will be described. As described above, in the level adjustment device 100 according to this embodiment, the received signals of multiple channels are separated into a system consisting of BPF 107, mixer 109, and BPF 111, and a system consisting of BPF 108, mixer 110, and BPF 112, which has a higher frequency of the signal to be processed than the system. Hereinafter, the system processed by BPF 107, mixer 109, and BPF 111 will be referred to as the Low side, and the system processed by BPF 108, mixer 110, and BPF 112 will be referred to as the High side. In addition, the frequency band of the received signals of multiple channels is 470 MHz to 710 MHz. In addition, the frequency of the local oscillation signal is controllable in the range of 368 MHz to 440 MHz. Furthermore, BPF 107 passes signals from 30 MHz to 108 MHz, and BPF 108 passes signals from 114 MHz to 342 MHz. Furthermore, BPF 111 passes signals from 470 MHz to 548 MHz, and BPF 112 passes signals from 482 MHz to 710 MHz.

First, the low-side processing will be explained with reference to Figure 2.

The mixer 105 uses a local oscillation signal to perform frequency conversion of the received signals of multiple channels. The frequency of the signal after frequency conversion by the mixer 105 varies depending on the frequency Lo of the local oscillation signal. For example, if the frequency Lo of the local oscillation signal is 368 MHz, the frequency of the signal after frequency conversion by the mixer 105 will be 102 MHz to 342 MHz. If the frequency Lo of the local oscillation signal is 440 MHz, the frequency of the signal after frequency conversion by the mixer 105 will be 30 MHz to 270 MHz.

BPF 107 passes signals from 30 MHz to 108 MHz. Therefore, when the frequency Lo of the local oscillation signal is 368 MHz, BPF 107 outputs signals from 102 MHz to 108 MHz to mixer 109. Also, when the frequency Lo of the local oscillation signal is 440 MHz, BPF 107 outputs signals from 30 MHz to 108 MHz to mixer 109.

The mixer 109 uses the local oscillation signal to perform frequency conversion of the output signal of the BPF 107. When the frequency Lo of the local oscillation signal is 368 MHz, the mixer 109 frequency converts the output signal of the BPF 107 (signal of 102 MHz to 108 MHz) to a signal of 470 MHz to 476 MHz and outputs it to the BPF 111. When the frequency Lo of the local oscillation signal is 440 MHz, the mixer 109 frequency converts the output signal of the BPF 107 (signal of 30 MHz to 108 MHz) to a signal of 470 MHz to 548 MHz and outputs it to the BPF 111.

BPF111 passes signals from 470 MHz to 548 MHz. When the frequency Lo of the local oscillation signal is 368 MHz, BPF111 outputs signals from 470 MHz to 476 MHz to AGC amplifier 113. When the frequency Lo of the local oscillation signal is 440 MHz, BPF111 outputs signals from 470 MHz to 548 MHz to AGC amplifier 113.

Next, the High side processing will be explained with reference to Figure 3.

BPF 108 passes signals from 114 MHz to 342 MHz. Therefore, when the frequency Lo of the local oscillation signal is 368 MHz, BPF 108 outputs signals from 114 MHz to 342 MHz to mixer 110. Also, when the frequency Lo of the local oscillation signal is 440 MHz, BPF 108 outputs signals from 114 MHz to 270 MHz to mixer 110.

The mixer 110 uses the local oscillation signal to perform frequency conversion of the output signal of the BPF 108. When the frequency Lo of the local oscillation signal is 368 MHz, the mixer 110 frequency converts the output signal of the BPF 108 (signal of 114 MHz to 342 MHz) to a signal of 482 MHz to 710 MHz and outputs it to the BPF 112. When the frequency Lo of the local oscillation signal is 440 MHz, the mixer 110 frequency converts the output signal of the BPF 108 (signal of 114 MHz to 270 MHz) to a signal of 554 MHz to 710 MHz and outputs it to the BPF 112.

BPF 112 passes signals from 482 MHz to 710 MHz. When the frequency Lo of the local oscillation signal is 368 MHz, BPF 112 outputs signals from 482 MHz to 710 MHz to AGC amplifier 114. When the frequency Lo of the local oscillation signal is 440 MHz, BPF 112 outputs signals from 554 MHz to 710 MHz to AGC amplifier 114.

As described with reference to Figures 2 and 3, when the frequency Lo of the local oscillation signal is 368 MHz, the received signal is separated into two systems with a boundary of 476 MHz and input to AGC amplifiers 113 and 114. When the frequency Lo of the local oscillation signal is 440 MHz, the received signal is separated into two systems with a boundary of 548 MHz and input to AGC amplifiers 113 and 114. In this way, in the level adjustment device 100 according to this embodiment, the boundary between the signal separated to the Low side and the signal separated to the High side can be adjusted by adjusting the frequency Lo of the local oscillation signal.

The separation of received signals of multiple channels by the level adjustment device 100 according to this embodiment will be described in more detail with reference to Figs. 4 and 5. In Figs. 4 and 5, the received signals of 16ch and 20ch to 33ch will be described as examples. The received signal of 16ch is a signal of 488MHz to 494MHz. The received signals of 20ch to 30ch are each signals with a bandwidth of 6MHz between 500MHz and 600MHz. Below, an example of separation into a 16ch signal and the other channels (20ch to 33ch) will be described.

First, the low-side processing will be explained with reference to Figure 4.

The control unit 117 controls the frequency Lo of the local oscillation signal to, for example, 386 MHz. When the frequency Lo of the local oscillation signal is 386 MHz, the 16ch received signal is frequency converted to a signal of 102 MHz to 108 MHz. Therefore, the BPF 107 passes the 16ch received signal and cuts the signals of 20ch to 33ch. The mixer 109 frequency converts the output signal of the BPF 107 to a signal in the original frequency band (488 MHz to 494 MHz). Therefore, the 16ch received signal is input to the AGC amplifier 113.

Next, the High side processing will be explained with reference to Figure 5.

When the frequency Lo of the local oscillator signal is 386 MHz, the received signal of 16ch is frequency converted to a signal of 102 MHz to 108 MHz. The received signals of 20ch to 33ch are frequency converted in the range of 126 MHz to 210 MHz. Therefore, the BPF 108 passes the received signals of 20ch to 33ch and cuts the received signal of 16ch. The mixer 110 frequency converts the output signal of the BPF 108 to a signal in the original frequency band (between 512 MHz and 596 MHz). Therefore, the received signals of 20ch to 33ch are input to the AGC amplifier 114.

Next, the operation of the control unit 117 will be described with reference to FIG. 6. FIG. 6 is a flowchart showing an example of the operation of the control unit 117.

The control unit 117 sets an initial value (step S101). Specifically, the control unit 117 sets the smallest channel number of all channels received at the receiving point of the shared facility as A. The control unit 117 also sets the channel numbers of the other channels as B[m] (m = 0, 1, ...) in ascending order. As described later, the channel (chB[m]) with channel number B[m] is a channel whose signal is compared with the channel (chA) with channel number A. Hereinafter, chB[m] may be referred to as a comparison channel. The control unit 117 also sets the largest channel number of all channels in the area as MAXch. The control unit 117 also sets the largest channel number that can be separated to the Low side as MAXfreq. MAXfreq is determined according to the adjustable range of the frequency Lo of the local oscillation signal output by the local oscillator 101. The control unit 117 also sets a predetermined threshold value of the correlation coefficient as CORval. Additionally, the control unit 117 sets the largest channel number among the channels to be separated to the Low side as SEPch. Hereinafter, a channel with the channel number SEPch will be referred to as a separated channel.

The control unit 117 sets m = 0 and SEPch = MAXfeq + 1 (step S102) and initializes the comparison channel and separation channel.

The control unit 117 determines whether A≦MAXfreq (step S103). In other words, the control unit 117 determines whether chA is a channel within the range that can be separated to the Low side.

If it is determined that A≦MAXfreq (step S103: Yes), the control unit 117 acquires the signal level data of the received signals of chA and chB[m] stored in the storage unit 116 for a predetermined time period (for example, the past 24 hours, 12 hours, 6 hours, 1 hour, etc.). The control unit 117 calculates the correlation coefficient C between the received signal of chA and the received signal of chB[m] (step S104). In this way, the control unit 117 calculates the correlation between the received signal of chA and the received signal of chB[m] (second channel) which is a comparison channel, with chA as the reference channel (first channel). When the received signal of chA and the received signal of chB[m] fluctuate with the same tendency, the correlation coefficient C becomes large. On the other hand, when the received signal of chA and the received signal of chB[m] fluctuate with different tendencies, i.e., when the signal behavior is different, the correlation coefficient C becomes small.

The control unit 117 determines whether the calculated correlation coefficient C is greater than or equal to the threshold CORval (C≧CORval) (step S105).

If it is determined that C≧CORval (step S105: Yes), the control unit 117 determines whether B[m]=MAXch (step S106).

If it is determined that B[m]=MAXch is not true (step S106: No), the control unit 117 adds 1 to m (step S107) and returns to the processing of step S104.

If it is determined that C≧CORval is not satisfied (C<CORval) (step S105: No), the control unit 117 determines whether B[m]-1≦MAXfreq is satisfied (step S108). In other words, the control unit 117 determines whether it is possible to separate received signals of channels with channel numbers equal to or greater than B[m] into the High side and received signals of channels with channel numbers equal to or less than B[m]-1 into the Low side, with chB[m] as the separator.

If it is determined that B[m]-1≦MAXfreq (step S108: Yes), the control unit 117 sets SEPch=B[m]-1 (step S109).

If it is determined that B[m]-1≦MAXfreq is not true (B[m]-1>MAXfreq) (step S108: No), the control unit 117 sets SEPch=MAXfreq (step S110).

After processing step S109 or step S110, or if it is determined that B[m]=MAXch (step S106: Yes), the control unit 117 determines whether SEPch≦MAXfreq (step S111).

If it is determined that SEPch≦MAXfreq (step S111: Yes), the control unit 117 controls the switching unit 104 so that the received signals of multiple channels are input from the distributor 103 to the mixer 105. The control unit 117 also controls the frequency Lo of the local oscillation signal so that the received signals of channels whose channel numbers are equal to or less than SEPch pass through the low-side BPF 107, and the received signals of channels whose channel numbers are greater than SEPch pass through the high-side BPF 108 (step S112).

If it is determined that SEPch≦MAXfreq is not satisfied (SEPch>MAXfreq is satisfied) (step S111: No), the control unit 117 controls the switching unit 104 so that the received signals of multiple channels are input from the distributor 103 to the AGC amplifier 113 because the separated channel is not within the range that can be separated to the Low side.

As described with reference to FIG. 6, when the correlation coefficient C between the received signal of chA and the received signal of chB[m] is smaller than the threshold CORval and B[m]-1≦MAXfreq, the control unit 117 separates the received signals of multiple channels into two systems, with chB[m] as the separator. Specifically, the control unit 117 controls the frequency Lo of the local oscillation signal so that channels with channel numbers B[m]-1 or less are separated into the Low side, and channels with channel numbers B[m] or more are separated into the High side.

In addition, when the correlation coefficient C between the received signal of chA and the received signal of chB[m] is smaller than the threshold CORval and B[m]-1>MAXfreq, the control unit 117 separates the received signals of multiple channels into two systems, with the channel number MAXfreq as the separator. Specifically, the control unit 117 controls the frequency Lo of the local oscillation signal so that channels with channel numbers equal to or less than MAXfreq are separated into the Low side, and channels with channel numbers greater than MAXfreq are separated into the High side.

In this way, the control unit 117 controls the frequency Lo of the local oscillator signal so that the received signals of multiple channels are separated into a band (first band) through which the BPF 107 passes signals and a band (second band) through which the BPF 108 passes signals, depending on chB[m] whose correlation with the reference chA (first channel) is smaller than a predetermined threshold CORval.

Figure 7 shows an example of signal level fluctuations of received signals of multiple channels (16ch, 20ch, 22ch, 26ch, 29ch, 31ch, and 33ch) before signal level adjustment by the level adjustment device 100 according to this embodiment.

As shown in FIG. 7, the signal levels of the received signals of channels other than 16ch fluctuate between approximately 70 dBμV and approximately 85 dBμV, and the manner in which they increase or decrease is also roughly uniform. On the other hand, the signal level of the received signal of 16ch differs from the behavior of the signal levels of the received signals of the other channels, and there are periods of time when it drops to approximately 50 dBμV. In this way, the behavior of the signal level of the received signal of 16ch and the other channels is significantly different. Therefore, the level adjustment device 100 of this embodiment separates the received signal of 16ch to the low side and the received signals of the other channels to the high side, and adjusts the signal levels.

Figure 8 shows the signal level fluctuations of the received signals of the multiple channels after the level adjustment device 100 adjusts the signal levels of the received signals of the multiple channels shown in Figure 7.

As shown in FIG. 8, by adjusting the signal levels using the level adjustment device 100 according to this embodiment, the signal levels of the received signals of all channels can be kept roughly constant.

In this way, the level adjustment device 100 according to this embodiment can automatically determine whether or not control of the frequency Lo of the local oscillation signal is necessary and control of the frequency Lo of the local oscillation signal from the correlation of signals between channels without human intervention. Usually, the behavior of the level fluctuation of each channel changes over time. For example, there are cases where only 16ch behaves differently, and cases where only 16ch and 20ch behave differently from the other channels. In such cases, if automatic determination and control are not performed, the settings will be fixed in one of the cases, and there will be times when the AGC function does not work properly. On the other hand, by performing automatic determination and control like the level adjustment device 100 according to this embodiment, it is possible to separate the appropriate channels in accordance with the time changes and allow the AGC to function.

As explained with reference to FIG. 6, the control unit 117 sets SEPch=MAXfreq+1 when the correlation coefficient C between chA and each of the comparison channels is equal to or less than CORval. In this case, since SEPch>MAXfreq, the control unit 117 does not control the frequency Lo of the local oscillation signal, but controls the switching unit 104 so that the output signal of the distributor 103 is input to the AGC amplifier 113. Therefore, as shown in FIG. 9, the control unit 117 switches between the presence and absence of signal separation depending on the degree of correlation between each channel. This makes it possible to prevent unnecessary frequency conversion, etc. from being performed.

In this manner, in this embodiment, the level adjustment device 100 selects, among the multiple channels,
The frequency Lo of the local oscillation signal is controlled so that the received signals of multiple channels are separated into a band (first band) through which the BPF 107 passes signals and a band (second band) through which the BPF 108 transmits signals, depending on the channel (second channel) whose correlation with a reference channel (first channel) is lower than a predetermined threshold value.

Therefore, the reference channel and channels whose correlation with the reference channel is lower than a predetermined threshold value are input to different AGC amplifiers 113, 114, respectively, and the AGC function can improve the signal level of the channel with low correlation. In addition, by controlling the frequency Lo of the local oscillation signal, the boundary for separating the received signals of multiple channels can be adjusted, so that the signal level can be adjusted without using a dedicated configuration according to the channel arrangement for each region. Therefore, the signal levels of the received signals of multiple channels can be adjusted with a simpler configuration.

The above-mentioned embodiment has been described as a representative example, but it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the above-mentioned embodiment, and various modifications and changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple configuration blocks shown in the configuration diagram of the embodiment into one, or to divide one configuration block.

REFERENCE SIGNS LIST 1 transmitting station 2 receiving antenna 3 transmitter 4 receiver 100 level adjustment device 101 local oscillator 102, 103, 106 distributor 104 switching unit 105 mixer (first frequency conversion unit)
107, 108, 111, 112 Bandpass filters 109 Mixer (second frequency conversion section)
110 Mixer (third frequency conversion unit)
113 AGC amplifier (first level adjustment unit)
114 AGC amplifier (second level adjustment section)
115 Mixer 116 Storage section 117 Control section 118 Separation section

Claims (2)

A level adjustment device that adjusts and outputs signal levels of received signals of a plurality of channels in a first frequency band,
a local oscillator that outputs a local oscillation signal;
a first frequency conversion unit that converts the frequency of the received signals of the plurality of channels into a second frequency band that is lower than the first frequency band by using the local oscillation signal;
a separation unit that separates the signal after frequency conversion by the first frequency conversion unit into a signal in a first band and a signal in a second band within the second frequency band, the second band being higher than the first band;
a second frequency conversion unit that performs frequency conversion of a signal in the first band from the second frequency band to the first frequency band by using the local oscillation signal;
a third frequency conversion unit that performs frequency conversion of a signal in the second frequency band from the second frequency band to the first frequency band by using the local oscillation signal;
a first level adjustment unit that adjusts the level of a signal after frequency conversion by the second frequency conversion unit;
a second level adjustment unit that adjusts the level of the signal after frequency conversion by the third frequency conversion unit;
a mixer that mixes and outputs a signal level-adjusted by the first level adjustment unit and a signal level-adjusted by the second level adjustment unit;
a control unit that controls a frequency of the local oscillation signal in accordance with a second channel among the multiple channels, the second channel having a correlation with a reference first channel that is lower than a predetermined threshold value, so that received signals of the multiple channels are separated into the first band and the second band. 2. The level adjustment device according to claim 1,
a switching unit that can switch an input destination of the reception signals of the plurality of channels in the first frequency band between the first frequency conversion unit and the first level adjustment unit,
A level adjustment device in which the control unit controls the switching unit so that received signals of the multiple channels are input to the first level adjustment unit when the correlation between the first channel and all channels other than the first channel among the multiple channels is greater than or equal to the predetermined threshold.

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