JP4593870B2

JP4593870B2 - Indoor retransmission system and indoor retransmission apparatus

Info

Publication number: JP4593870B2
Application number: JP2002287646A
Authority: JP
Inventors: 佳弘梶村; 淳木下; 伊市若生; 功治坂内; 隆彦西澤; 孝敏城杉; 勉野田; 修一田胡
Original assignee: Hitachi Ltd; Yagi Antenna Co Ltd
Current assignee: Hitachi Ltd; Yagi Antenna Co Ltd
Priority date: 2002-09-30
Filing date: 2002-09-30
Publication date: 2010-12-08
Anticipated expiration: 2022-09-30
Also published as: JP2004128719A

Description

【０００１】
【発明の属する技術分野】
本発明は、地上デジタルテレビジョン放送をＣＡＴＶにより再送信を行なっている地域でポータブルテレビ等による視聴を可能にする室内再送信システム及び室内再送信装置に関する。
【０００２】
【従来の技術】
現在行なわれている地上波によるテレビ放送、すなわち、アナログテレビ放送の放送波はマルチパスや回り込みに耐性がなく、このため弱電界地域には周波数変換した放送波を再送信するか、ＣＡＴＶシステムによる送信又は再送信を行なっている。上記ＣＡＴＶシステムによりテレビ放送を送信又は再送信している地域では、オンエア電波のレベルが低いか、またはオンエア電波が届かないので、ポータブルテレビ等でテレビ放送を視聴しようとしても満足な画質を得ることができないという問題があった。
【０００３】
このため従来では、テレビ放送をビル内や家庭等の屋内でポータブルテレビにより視聴する場合、壁面等に設けられているＴＶ端子、すなわちＣＡＴＶ回線に接続されているＴＶ端子（Ｆ型ケーブルコネクタ）にポータブルテレビのアンテナ端子を直接接続したり、上記ＴＶ端子から取り出した信号を周波数変換すると共にレベル調整してアンテナにより室内のポータブルテレビに再送信する等の手段が用いられている。
【０００４】
しかし、上記従来のようにＴＶ端子にポータブルテレビのアンテナ端子を直接接続した場合には可搬性が著しく損なわれ、また、ＣＡＴＶによる放送信号を周波数変換して再送信する場合には専用のシステムが必要となる、といった問題があった。
【０００５】
現在では、上記したようにアナログによるテレビ放送が行なわれているが、２００３年からＵＨＦ帯を利用した地上デジタルテレビジョン放送（ＩＳＤＢ−Ｔ：Integrated Services Digital Broadcasting for Terrestrial Television Broadcasting ）の開始が予定されている。上記ＩＳＤＢ−Ｔは、マルチパスや回り込み等の電波の干渉に強い特性を持つＯＦＤＭ（Orthogonal Frequency Division Multiplexing）信号を用いており、このため単一周波数ネットワーク（ＳＦＮ：Single Frequency Network）が可能になる。
【０００６】
しかし、上記単一周波数ネットワークを実現させる際、親局から中継局への配信に放送波をそのまま再送信すると、中継局の送信アンテナから受信アンテナへの回り込みにより信号の劣化、特に回り込みのループ利得が１以上になると、発振してしまうという問題がある。このような問題に対処するため、中継局に回り込みをキャンセルするためのフィルタを設置する方式が種々提案されている（例えば特許文献１、２参照）。
【０００７】
【特許文献１】
特開２００２−１０１０３２号公報
【０００８】
【特許文献２】
特開２００２−１５８６３４号公報
【０００９】
【発明が解決しようとする課題】
しかし、上記従来の方式では、ＩＳＤＢ−Ｔ信号の変復調、周波数変換、チャンネル毎に回り込みキャンセル等の処理を行なう必要があり、構成が非常に複雑になるという問題がある。
【００１０】
本発明は、山陰やビル影等が原因となって、オンエア電波のレベルが低いか、またはオンエア電波が届かないためにＣＡＴＶによる地上デジタルテレビジョン放送の再送信を行なっている地域において、ＩＳＤＢ−ＴによるＯＦＤＭ信号のマルチパス、回り込みに対する耐性を利用して、屋内でポータブルテレビ等によりテレビジョン放送を簡易に受信できる室内再送信システム及び室内再送信装置を提供することを目的とする。
【００１１】
【課題を解決するための手段】
第１の発明は、ＣＡＴＶシステムの引き込み線からケーブルコネクタを介して、電波のレベルの低い屋内に引き込まれる地上デジタルテレビジョン放送の再送信された放送信号を入力信号とする増幅装置と、前記増幅装置の出力に接続される再送信用アンテナとからなる室内再送信システムにおいて、
前記増幅装置は前記入力信号を増幅する増幅器と、ＡＧＣ回路とからなり、
前記ＡＧＣ回路は、
前記入力信号を包絡線検波する第１の包絡線検波器と、前記増幅器の出力信号を包絡線検波する第２の包絡線検波器と、前記第２の包絡線検波器の出力電圧レベルを調整する可変減衰器と、前記第１の包絡線検波器の出力電圧と可変減衰器により調整された第２の包絡線検波器の出力電圧の差に応じた電圧値を出力する差動増幅器とからなり、
前記可変減衰器の減衰量を可変設定することで前記差動増幅器の出力電圧値を変えて前記増幅器の出力レベルを調整し、前記再送信用アンテナから再送信される信号の電界強度を所定レベル以下に維持して、電波により屋内の地上デジタルテレビジョン放送受信機に放送信号を再送信することを特徴とする。
第２の発明は、ＣＡＴＶシステムの引き込み線からケーブルコネクタを介して、電波のレベルの低い屋内に引き込まれる地上デジタルテレビジョン放送の再送信された放送信号を入力信号とする増幅装置と、前記増幅装置の出力に接続される再送信用アンテナとからなる室内再送信システムにおいて、
前記増幅装置は、前記入力信号を増幅する増幅器と、ＡＧＣ回路とからなり、
前記ＡＧＣ回路は、
前記入力信号を包絡線検波する第１の包絡線検波器と、前記増幅器の出力信号を包絡線検波する第２の包絡線検波器と、前記第２の包絡線検波器の出力電圧レベルを調整する可変減衰器と、前記第１の包絡線検波器の出力電圧と可変減衰器により調整された第２の包絡線検波器の出力電圧の差に応じた電圧値を出力する差動増幅器とからなり、
前記可変減衰器の減衰量を可変設定することで前記差動増幅器の出力電圧値を変えて前記増幅器の出力レベルを調整し、前記再送信用アンテナから再送信される信号の電界強度を所定レベル以下に維持して、電波により屋内に前記放送信号を再送信する第１の再送信装置を備えると共に、
前記第１の再送信装置から再送信される電波を受信用アンテナにより受信し、前記受信信号を入力信号とする増幅装置と、前記増幅装置の出力に接続される再送信用アンテナとからなる室内再送信システムにおいて、
前記増幅装置は前記入力信号を増幅する増幅器と、ＡＧＣ回路とからなり、
前記ＡＧＣ回路は、
前記入力信号を包絡線検波する第１の包絡線検波器と、前記増幅器の出力信号を包絡線検波する第２の包絡線検波器と、前記第２の包絡線検波器の出力電圧レベルを調整する可変減衰器と、前記第１の包絡線検波器の出力電圧と可変減衰器により調整された第２の包絡線検波器の出力電圧の差に応じた電圧値を出力する差動増幅器とからなり、
前記可変減衰器の減衰量を可変設定することで前記差動増幅器の出力電圧値を変えて前記増幅器の出力レベルを調整し、前記再送信用アンテナから再送信される信号の電界強度を所定レベル以下に維持して、電波により屋内の地上デジタルテレビジョン放送受信機に放送信号を再送信する第２の再送信装置を具備することを特徴とする。
【００１２】
第３の発明に係る室内再送信装置は、ＣＡＴＶシステムの引き込み線からケーブルコネクタを介して、電波のレベルの低い屋内に引き込まれる地上デジタルテレビジョン放送の再送信された放送信号を入力信号として増幅する増幅器及び該増幅器の出力レベルを制御するＡＧＣ回路を備えた増幅装置と、前記増幅装置の出力に接続される再送信用アンテナとからなり、
前記ＡＧＣ回路は、
前記入力信号を包絡線検波する第１の包絡線検波器と、前記増幅器の出力信号を包絡線検波する第２の包絡線検波器と、前記第２の包絡線検波器の出力電圧レベルを調整する可変減衰器と、前記第１の包絡線検波器の出力電圧と可変減衰器により調整された第２の包絡線検波器の出力電圧の差に応じた電圧値を出力する差動増幅器とからなり、
前記可変減衰器の減衰量を可変設定することで前記差動増幅器の出力電圧値を変えて前記増幅器の出力レベルを調整し、前記再送信用アンテナから再送信される信号の電界強度を所定レベル以下に維持して、電波により屋内の地上デジタルテレビジョン放送受信機に放送信号を再送信することを特徴とする。
第４の発明に係る室内再送信装置は、ＣＡＴＶシステムの引き込み線からケーブルコネクタを介して、電波のレベルの低い屋内に引き込まれる地上デジタルテレビジョン放送の再送信された放送信号を入力信号として増幅する増幅器及び該増幅器の出力レベルを制御するＡＧＣ回路を備えた増幅装置と、前記増幅装置の出力に接続される再送信用アンテナとからなり、
前記ＡＧＣ回路は、
前記入力信号を包絡線検波する第１の包絡線検波器と、前記増幅器の出力信号を包絡線検波する第２の包絡線検波器と、前記第２の包絡線検波器の出力電圧レベルを調整する可変減衰器と、前記第１の包絡線検波器の出力電圧と可変減衰器により調整された第２の包絡線検波器の出力電圧の差に応じた電圧値を出力する差動増幅器とからなり、
前記可変減衰器の減衰量を可変設定することで前記差動増幅器の出力電圧値を変えて前記増幅器の出力レベルを調整し、前記再送信用アンテナから再送信される信号の電界強度を所定レベル以下に維持して、電波により屋内に放送信号を再送信する第１の再送信装置と、
前記第１の再送信装置から再送信される放送信号を受信用アンテナにより受信し、前記受信信号を増幅する増幅器及び該増幅器の出力レベルを制御するＡＧＣ回路とを備えた増幅装置と、前記増幅装置の出力に接続される再送信用アンテナとからなり、
前記ＡＧＣ回路は、
前記入力信号を包絡線検波する第１の包絡線検波器と、前記増幅器の出力信号を包絡線検波する第２の包絡線検波器と、第２の包絡線検波器の出力電圧レベルを調整する可変減衰器と、前記第１の包絡線検波器の出力電圧と可変減衰器により調整された第２の包絡線検波器の出力電圧の差に応じた電圧値を出力する差動増幅器とからなり、
前記可変減衰器の減衰量を可変設定することで前記差動増幅器の出力電圧値を変えて前記増幅器の出力レベルを調整し、前記再送信用アンテナから再送信される信号の電界強度を所定レベル以下に維持して、電波により屋内の地上デジタルテレビジョン放送受信機に放送信号を再送信する第２の再送信装置とを具備することを特徴とする。
【００１３】
上記の構成によれば、地上デジタルテレビジョン信号の変復調、周波数変換、チャンネル毎に回り込みキャンセル等の処理を行なう必要がなく、簡素なシステム構成でＣＡＴＶによる地上デジタルテレビジョン信号を屋内に再送信でき、ポータブルテレビ等の地上デジタルテレビジョン放送受信機により地上デジタルテレビジョン放送を容易に視聴することができる。また、再送信信号の回り込みによる発振を防止できると共に再送信電波のレベルを常に最適レベルに保持することができる。
【００１４】
【発明の実施の形態】
以下、図面を参照して本発明の実施形態を説明する。
（第１実施形態）
図１は、本発明の一実施形態に係るＣＡＴＶによる地上デジタルテレビジョン放送の室内再送信システムの全体の構成を示すブロック図、図２は同実施形態の詳細を示すブロック図である。
【００１５】
図１において、１はビルや家屋等の建物で、この建物１の室内等の壁面に例えばＦ型ケーブルコネクタを用いたＴＶ端子２が設けられる。このＴＶ端子２には、ＩＳＤＢ−Ｔ（地上デジタルテレビジョン放送）を送信又は再送信するＣＡＴＶシステムの回線、すなわちＣＡＴＶ用ケーブル３が接続される。
【００１６】
そして、上記室内等には、再送信装置５が設置され，その入力端がケーブル４を介して上記ＴＶ端子２に接続される。上記再送信装置５は、ＣＡＴＶによるＩＳＤＢ−Ｔ信号を増幅する増幅装置６及びこの増幅装置６により増幅された信号を再送信する例えばダイポールアンテナ等の再送信用アンテナ７からなっている。
【００１７】
上記再送信用アンテナ７は、増幅装置６で増幅されたＩＳＤＢ−Ｔの信号を室内にあるポータブルテレビ等のＩＳＤＢ−Ｔ受信機８に再送信する。このＩＳＤＢ−Ｔ受信機８は、アンテナ９を備え、上記再送信装置５の再送信用アンテナ７から再送信される電波を受信する。上記送信又は再送信信号（ＩＳＤＢ−Ｔ信号）は、マルチパスや回り込み等の電波の干渉に強い特性を持つＯＦＤＭ（Orthogonal Frequency Division Multiplexing）による変調信号を使用する。
【００１８】
上記増幅装置６は、図２に示すように戻り防止回路１１、増幅器１２及びＡＧＣ回路１３からなっている。上記戻り防止回路１１は、ＣＡＴＶの上り信号帯域（１０〜５５ＭＨｚ）の信号が再送信用アンテナ７からＣＡＴＶ用ケーブル３へ戻ることを防止する回路で、例えばアッテネータ（ＡＴＴ）、フィルタ、アイソレータ等が用いられる。増幅器１２は、ＴＶ端子２から戻り防止回路１１を介して入力される信号を増幅し、ＡＧＣ回路１３及び再送信用アンテナ７に出力する。
【００１９】
上記ＡＧＣ回路１３は、図３に示すように増幅器１２の入力信号を包絡線検波して直流信号に変換する第１の包絡線検波器１５、増幅器１２の出力信号を包絡線検波して直流信号に変換する第２の包絡線検波器１６、この第２の包絡線検波器１６の出力電圧レベルを調整する可変減衰器１７、上記第１の包絡線検波器１５の出力電圧と可変減衰器１７により調整された第２の包絡線検波器１６の出力電圧の差に応じた電圧値を増幅器１２に出力して該増幅器１２の出力レベルを調整する差動増幅器１８からなっている。
【００２０】
上記ＡＧＣ回路１３は、増幅器１２の入力信号を第１の包絡線検波器１５により包絡線検波し、直流信号に変換して差動増幅器１８に入力すると共に、増幅器１２の出力信号を第２の包絡線検波器１６により包絡線検波して直流信号に変換し、可変減衰器１７を介して差動増幅器１８に入力する。差動増幅器１８は、上記第１の包絡線検波器１５の出力電圧と可変減衰器１７により調整された第２の包絡線検波器１６の出力電圧の差に応じた電圧値を増幅器１２に出力し、該増幅器１２の出力レベルを調整する。従って、可変減衰器１７の減衰量を可変設定することで差動増幅器１８の出力電圧値を変えて増幅器１２の出力電圧値を任意に調整することができる。
【００２１】
上記ＡＧＣ回路１３は、可変減衰器１７により増幅器１２の出力電圧レベルを調整し、再送信用アンテナ７から再送信される信号を例えば電波法施行規則第六条にある「著しく微弱な無線局」の３５μＶ／ｍ（周波数３２２ＭＨｚ〜１０ＧＨｚ）の電界強度を満たすように調整する。
【００２２】
また、ＡＧＣ回路１３のもう１つの役割として、回り込みによる発振が起きた場合、これを検知して発振を抑えるように再送信用アンテナ７から出力される信号の電界強度を調整する。
【００２３】
上記の構成において、ＣＡＴＶ用ケーブル３により送られてくるＩＳＤＢ−Ｔ信号は、建物１に設けられているＴＶ端子２からケーブル４を介して再送信装置５へ送られ、増幅装置６に入力される。この増幅装置６は、入力されたＩＳＤＢ−Ｔ信号を増幅器１２で増幅すると共にＡＧＣ回路１３で所定のレベル例えば弱電界のレベルに調整し、再送信用アンテナ７から室内のＩＳＤＢ−Ｔ受信機８に再送信する。ＩＳＤＢ−Ｔ受信機８は、上記再送信装置５の再送信用アンテナ７から再送信される電波を受信することにより、ＩＳＤＢ−Ｔの放送を視聴する。
【００２４】
上記のようにＣＡＴＶ用ケーブル３により送られてくるＩＳＤＢ−Ｔ信号を建物１内に設けた再送信装置５により受信して建物１内あるいは室内に再送信することにより、ＩＳＤＢ−Ｔ受信機８は建物１内あるいは室内の何処に移動しても、再送信装置５の再送信用アンテナ７から再送信される電波を確実に受信でき、ＩＳＤＢ−Ｔの放送を安定した状態で視聴することができる。
【００２５】
また、ＣＡＴＶ用ケーブル３によりＴＶ端子２に送られてくるＩＳＤＢ−Ｔ信号をケーブル４を介して再送信装置５の増幅装置６に入力することで、再送信信号が増幅装置６の入力側に回り込みにくい構成となり、回り込みによる発振を確実に防止することができる。また、増幅装置６内に戻り防止回路１１を設けているので、増幅器１２側からＣＡＴＶ用ケーブル３への信号の戻りを確実に防止することができる。
【００２６】
更に、増幅装置６にＡＧＣ回路１３を設けて増幅器１２から再送信用アンテナ７への信号レベルを調整しているので、ＩＳＤＢ−Ｔ受信機８に対して常に最適レベルの電波を送信することができる。
【００２７】
また、上記のように再送信装置５から弱電界で再送信すること、及び電波の漏れにくい室内で再送信することにより、室外への電波の漏れを確実に防止することができる。更に、ＩＳＤＢ−Ｔ信号にはガードインターバルが設けられているので、仮に電波が室外に漏れたとしても他の機器への妨害になりにくいという利点がある。
【００２８】
（第２実施形態）
次に本発明の第２実施形態について図４及び図５を参照して説明する。図４は本発明の第２実施形態に係る室内再送信システムの全体の構成を示すブロック図、図５は図４における増幅装置２２の詳細な構成を示すブロック図である。
【００２９】
本発明の第２実施形態に係る室内再送信システムは、上記図１に示した第１実施形態において、建物１内に第１の再送信装置５と共に第２の再送信装置２０を設けたものである。すなわち、建物１が広くて第１の再送信装置５からの再送信電波だけでは、建物１内の全てカバーできない場合に、第１の再送信装置５から再送信された電波を第２の再送信装置２０で受信し、ＩＳＤＢ−Ｔ受信機８に再送信するようにしたものである。この場合、第２の再送信装置２０は、第１の再送信装置５から再送信される電波が届く範囲内に設置する。
【００３０】
上記第１の再送信装置５は、再送信用アンテナ７から垂直偏波（又は水平偏波）、あるいは右旋円偏波（又は左旋円偏波）の電波を建物１内に再送信する。
【００３１】
第２の再送信装置２０は、受信用アンテナ２１、増幅装置２２、再送信用アンテナ２３からなり、受信用アンテナ２１の偏波面を第１の再送信装置５における再送信用アンテナ７の偏波面に合わせ、再送信用アンテナ２３を受信用アンテナ２１とは異なる偏波面に合わせる。例えば受信用アンテナ２１の偏波面を垂直偏波（又は水平偏波）に合わせた場合は、再送信用アンテナ２３の偏波面を水平偏波（又は垂直偏波）とする。また、受信用アンテナ２１の偏波面を右旋円偏波（又は左旋円偏波）に合わせた場合は、再送信用アンテナ２３の偏波面を左旋円偏波（又は右旋円偏波）とする。すなわち、受信用アンテナ２１と再送信用アンテナ２３の偏波面を変えることで、再送信用アンテナ２３から再送信される電波が受信用アンテナ２１へ回り込みにくい構成とする。
【００３２】
上記第２の再送信装置２０は、具体的には図５に示すように構成される。すなわち、受信用アンテナ２１及び再送信用アンテナ２３として例えばダイポールアンテナを使用し、受信用アンテナ２１により受信した信号を増幅装置２２に入力する。増幅装置２２は、増幅器３２及びＡＧＣ回路３３からなっている。増幅器３２は、受信用アンテナ２１から入力される信号を増幅し、ＡＧＣ回路３３及び再送信用アンテナ２３に出力する。なお、ＡＧＣ回路３３は、図３に詳細を示した第１の再送信装置５の増幅装置６内に設けられたＡＧＣ回路１３と同様に構成され、再送信用アンテナ２３から出力される再送信信号を上記第１実施形態と同様に３５μＶ／ｍ（周波数３２２ＭＨｚ〜１０ＧＨｚ）の電界強度を満たすように調整する。また、ＡＧＣ回路３３は、電波の回り込みによる発振が生じないように再送信用アンテナ２３による再送信電波のレベルを調整する。
【００３３】
また、第２の再送信装置２０においても、第１実施形態で示した再送信装置５と同様に、再送信信号として、マルチパスや回り込み等の電波の干渉に強い特性を持つＯＦＤＭによる変調信号を使用する。
【００３４】
上記のように建物１内に第１の再送信装置５を設置すると共に、この第１の再送信装置５からの再送信電波が届く範囲内に第２の再送信装置２０を設けて中継することにより、建物１が広い場合でもＩＳＤＢ−Ｔ受信機８は建物１内の何処に移動しても、第１の再送信装置５の再送信用アンテナ７、あるいは第２の再送信装置２０の再送信用アンテナ２３から再送信される電波を確実に受信でき、ＩＳＤＢ−Ｔの放送を安定した状態で視聴することができる。
【００３５】
【発明の効果】
以上説明したように本発明によれば、ＣＡＴＶ用ケーブルにより送られてくるＩＳＤＢ−Ｔ信号を建物に設けたＴＶ端子を介して再送信装置に入力し、増幅装置で増幅して再送信用アンテナから再送信するようにしたので、ＩＳＤＢ−Ｔ信号の変復調、周波数変換、チャンネル毎に回り込みキャンセル等の処理を行なう必要がなく、簡素なシステム構成でＵＨＦ帯全帯域の再送信を実現でき、ポータブルテレビ等のＩＳＤＢ−Ｔ受信機によりＩＳＤＢ−Ｔ信号を容易に視聴することができる。また、再送信信号の回り込みによる発振を防止できると共に、増幅器側からＣＡＴＶ用ケーブルへの信号の戻りを確実に防止でき、且つ、再送信電波のレベルを常に最適レベルに保持することができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態に係る室内再送信システムの全体の構成を示すブロック図。
【図２】同実施形態における要部の詳細を示すブロック図。
【図３】同実施形態におけるＡＧＣ回路の詳細な構成例を示すブロック図。
【図４】本発明の第２実施形態に係る室内再送信システムの全体の構成を示すブロック図。
【図５】同実施形態における第２の再送信装置の詳細を示すブロック図。
【符号の説明】
１…建物
２…ＴＶ端子
３…ＣＡＴＶ用ケーブル
４…ケーブル
５…再送信装置
６…増幅装置
７…再送信用アンテナ
８…ＩＳＤＢ−Ｔ受信機
９…アンテナ
１１…戻り防止回路
１２…増幅器
１３…ＡＧＣ回路
１５…第１の包絡線検波器
１６…第２の包絡線検波器
１７…可変減衰器
１８…差動増幅器
２０…第２の再送信装置
２１…受信用アンテナ
２２…増幅装置
２３…再送信用アンテナ
３２…増幅器
３３…ＡＧＣ回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an indoor re-transmission system and an indoor re-transmission apparatus that enable viewing on a portable television or the like in an area where digital terrestrial television broadcasting is re-transmitted by CATV.
[0002]
[Prior art]
Current terrestrial television broadcasts, that is, analog television broadcast waves, are not resistant to multipath and wraparound. Therefore, in the weak electric field area, the frequency-converted broadcast wave is retransmitted or the CATV system is used. Sending or retransmitting. In areas where TV broadcasts are transmitted or retransmitted by the above CATV system, the level of on-air radio waves is low or the on-air radio waves do not reach. There was a problem that could not.
[0003]
For this reason, conventionally, when a television broadcast is viewed on a portable television indoors such as in a building or at home, a TV terminal provided on a wall surface or the like, that is, a TV terminal (F type cable connector) connected to a CATV line is used. Means are used such as directly connecting an antenna terminal of a portable television or frequency-converting a signal taken out from the TV terminal and adjusting the level and retransmitting the signal to an indoor portable television using an antenna.
[0004]
However, when the portable TV antenna terminal is directly connected to the TV terminal as in the conventional case, the portability is remarkably impaired, and when a CATV broadcast signal is frequency-converted and retransmitted, a dedicated system is used. There was a problem that it was necessary.
[0005]
At present, analog television broadcasting is being carried out as described above, but from 2003, terrestrial digital television broadcasting (ISDB-T: Integrated Services Digital Broadcasting for Terrestrial Television Broadcasting) using the UHF band is scheduled to start. ing. The ISDB-T uses an OFDM (Orthogonal Frequency Division Multiplexing) signal having a characteristic that is strong against radio wave interference such as multipath and sneak, and thus enables a single frequency network (SFN). .
[0006]
However, when the above single frequency network is realized, if the broadcast wave is retransmitted as it is for distribution from the master station to the relay station, signal degradation, particularly loop loop gain, due to wraparound from the relay station's transmission antenna to the reception antenna There is a problem that oscillation occurs when the value becomes 1 or more. In order to deal with such a problem, various methods for installing a filter for canceling the wraparound in the relay station have been proposed (see, for example, Patent Documents 1 and 2).
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-101032
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-158634
[Problems to be solved by the invention]
However, the above-described conventional method requires processing such as modulation / demodulation of the ISDB-T signal, frequency conversion, wraparound cancellation for each channel, and the configuration is very complicated.
[0010]
The present invention is applied to an ISDB- in an area where CATV retransmits terrestrial digital television broadcasting because the level of on-air radio waves is low or the on-air radio waves do not reach due to the shadows of the mountains, buildings, etc. An object of the present invention is to provide an indoor retransmission system and an indoor retransmission apparatus that can easily receive a television broadcast indoors by a portable television or the like by utilizing the multipath and wraparound resistance of an OFDM signal by T.
[0011]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an amplifying apparatus that uses a retransmitted broadcast signal of a digital terrestrial television broadcast that is drawn into a low radio wave indoors from a lead-in line of a CATV system via a cable connector, and the amplification In an indoor retransmission system consisting of a retransmission trusted antenna connected to the output of the device,
The amplifying device comprises an amplifier that amplifies the input signal and an AGC circuit,
The AGC circuit
A first envelope detector for envelope detection of the input signal, a second envelope detector for envelope detection of the output signal of the amplifier, and an output voltage level of the second envelope detector are adjusted And a differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator. Become
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less The broadcast signal is retransmitted to an indoor terrestrial digital television broadcast receiver by radio waves.
According to a second aspect of the present invention, there is provided an amplifying apparatus that uses a retransmitted broadcast signal of a digital terrestrial television broadcast that is drawn into a low-level radio wave indoors from a CATV system lead-in via a cable connector, and the amplification In an indoor retransmission system consisting of a retransmission trusted antenna connected to the output of the device,
The amplification device includes an amplifier that amplifies the input signal and an AGC circuit,
The AGC circuit
A first envelope detector for envelope detection of the input signal, a second envelope detector for envelope detection of the output signal of the amplifier, and an output voltage level of the second envelope detector are adjusted And a differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator. Become
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less And a first retransmission device for retransmitting the broadcast signal indoors by radio waves,
An indoor re-transmission comprising: an amplifying apparatus that receives a radio wave retransmitted from the first retransmitting apparatus by a receiving antenna and uses the received signal as an input signal; and a retransmission credit antenna connected to an output of the amplifying apparatus. In the transmission system,
The amplifying device comprises an amplifier that amplifies the input signal and an AGC circuit,
The AGC circuit
A first envelope detector for envelope detection of the input signal, a second envelope detector for envelope detection of the output signal of the amplifier, and an output voltage level of the second envelope detector are adjusted And a differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator. Become
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less And a second retransmitting device for retransmitting a broadcast signal to an indoor terrestrial digital television broadcast receiver using radio waves.
[0012]
According to a third aspect of the present invention, an indoor retransmission apparatus amplifies a retransmitted broadcast signal of a digital terrestrial television broadcast, which is drawn indoors with a low radio wave level, from a lead wire of a CATV system via a cable connector as an input signal. An amplifier having an AGC circuit for controlling an output level of the amplifier and an output level of the amplifier, and a retransmission credit antenna connected to the output of the amplifier,
The AGC circuit
A first envelope detector for envelope detection of the input signal, a second envelope detector for envelope detection of the output signal of the amplifier, and an output voltage level of the second envelope detector are adjusted And a differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator. Become
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less The broadcast signal is retransmitted to an indoor terrestrial digital television broadcast receiver by radio waves.
According to a fourth aspect of the present invention, there is provided an indoor retransmitting apparatus which amplifies a retransmitted broadcast signal of a digital terrestrial television broadcast which is drawn indoors with a low radio wave level from a CATV system lead-in via a cable connector as an input signal. An amplifier having an AGC circuit for controlling an output level of the amplifier and an output level of the amplifier, and a retransmission credit antenna connected to the output of the amplifier,
The AGC circuit
A first envelope detector for envelope detection of the input signal, a second envelope detector for envelope detection of the output signal of the amplifier, and an output voltage level of the second envelope detector are adjusted And a differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator. Become
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less A first retransmission device that retransmits the broadcast signal indoors by radio waves,
An amplifying apparatus comprising: an amplifier for receiving a broadcast signal retransmitted from the first retransmitting apparatus by a receiving antenna; an amplifier for amplifying the received signal; and an AGC circuit for controlling an output level of the amplifier; It consists of a retransmission credit antenna connected to the output of the device,
The AGC circuit
A first envelope detector for detecting the input signal with an envelope, a second envelope detector for detecting the output signal of the amplifier with an envelope, and an output voltage level of the second envelope detector are adjusted. A variable attenuator; and a differential amplifier that outputs a voltage value corresponding to a difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator. ,
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less And a second re-transmission device that re-transmits a broadcast signal to an indoor terrestrial digital television broadcast receiver using radio waves.
[0013]
According to the above configuration, it is not necessary to perform processing such as modulation / demodulation of the terrestrial digital television signal, frequency conversion, wraparound cancellation for each channel, and the terrestrial digital television signal by CATV can be retransmitted indoors with a simple system configuration. The terrestrial digital television broadcast can be easily viewed by a terrestrial digital television broadcast receiver such as a portable television. Further, it is possible to prevent oscillation due to the sneak in the retransmit signal and to keep the retransmitted radio wave level at the optimum level.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing the overall configuration of an indoor retransmission system for digital terrestrial television broadcasting by CATV according to an embodiment of the present invention, and FIG. 2 is a block diagram showing details of the embodiment.
[0015]
In FIG. 1, reference numeral 1 denotes a building such as a building or a house, and a TV terminal 2 using, for example, an F-type cable connector is provided on a wall surface of the building 1 or the like. The TV terminal 2 is connected to a CATV system line for transmitting or retransmitting ISDB-T (terrestrial digital television broadcast), that is, a CATV cable 3.
[0016]
A re-transmission device 5 is installed in the room or the like, and its input end is connected to the TV terminal 2 via the cable 4. The retransmitting device 5 includes an amplifying device 6 that amplifies the ISDB-T signal by CATV, and a retransmission credit antenna 7 such as a dipole antenna that retransmits the signal amplified by the amplifying device 6.
[0017]
The retransmission credit antenna 7 retransmits the ISDB-T signal amplified by the amplification device 6 to an ISDB-T receiver 8 such as a portable television in the room. The ISDB-T receiver 8 includes an antenna 9 and receives a radio wave retransmitted from the retransmission credit antenna 7 of the retransmission apparatus 5. The transmission or re-transmission signal (ISDB-T signal) uses a modulation signal by OFDM (Orthogonal Frequency Division Multiplexing) having a characteristic strong against radio wave interference such as multipath and sneak current.
[0018]
As shown in FIG. 2, the amplification device 6 includes a return prevention circuit 11, an amplifier 12, and an AGC circuit 13. The return prevention circuit 11 is a circuit that prevents the CATV upstream signal band (10 to 55 MHz) signal from returning from the retransmission trust antenna 7 to the CATV cable 3, and is used, for example, by an attenuator (ATT), a filter, an isolator, or the like. It is done. The amplifier 12 amplifies the signal input from the TV terminal 2 via the return prevention circuit 11 and outputs the amplified signal to the AGC circuit 13 and the retransmission credit antenna 7.
[0019]
As shown in FIG. 3, the AGC circuit 13 includes a first envelope detector 15 for detecting an input signal of the amplifier 12 and converting it to a DC signal, and envelope detecting the output signal of the amplifier 12 to detect a DC signal. The second envelope detector 16 to be converted into the first envelope detector 16, the variable attenuator 17 for adjusting the output voltage level of the second envelope detector 16, the output voltage of the first envelope detector 15 and the variable attenuator 17. It comprises a differential amplifier 18 for adjusting the output level of the amplifier 12 by outputting to the amplifier 12 a voltage value corresponding to the difference in the output voltage of the second envelope detector 16 adjusted by the above.
[0020]
The AGC circuit 13 envelope-detects the input signal of the amplifier 12 by the first envelope detector 15, converts it to a DC signal, inputs it to the differential amplifier 18, and outputs the output signal of the amplifier 12 to the second signal. The envelope detector 16 detects the envelope and converts it into a DC signal, which is input to the differential amplifier 18 via the variable attenuator 17. The differential amplifier 18 outputs to the amplifier 12 a voltage value corresponding to the difference between the output voltage of the first envelope detector 15 and the output voltage of the second envelope detector 16 adjusted by the variable attenuator 17. Then, the output level of the amplifier 12 is adjusted. Accordingly, the output voltage value of the amplifier 12 can be arbitrarily adjusted by changing the output voltage value of the differential amplifier 18 by variably setting the attenuation amount of the variable attenuator 17.
[0021]
The AGC circuit 13 adjusts the output voltage level of the amplifier 12 by the variable attenuator 17, and transmits the signal retransmitted from the retransmission credit antenna 7 to, for example, the “remarkably weak radio station” in Article 6 of the Radio Law Enforcement Regulations. It adjusts so that the electric field strength of 35 microvolt / m (frequency 322MHz-10GHz) may be satisfy | filled.
[0022]
Further, as another role of the AGC circuit 13, when oscillation due to wraparound occurs, the electric field strength of the signal output from the retransmission credit antenna 7 is adjusted so as to detect this and suppress the oscillation.
[0023]
In the above configuration, the ISDB-T signal sent by the CATV cable 3 is sent from the TV terminal 2 provided in the building 1 to the retransmitting device 5 via the cable 4 and input to the amplifying device 6. The The amplifying device 6 amplifies the input ISDB-T signal by the amplifier 12 and adjusts it to a predetermined level, for example, a weak electric field level by the AGC circuit 13, and sends it from the retransmission credit antenna 7 to the indoor ISDB-T receiver 8. Resend. The ISDB-T receiver 8 views the ISDB-T broadcast by receiving radio waves retransmitted from the retransmission credit antenna 7 of the retransmission apparatus 5.
[0024]
As described above, the ISDB-T signal sent by the CATV cable 3 is received by the retransmitting device 5 provided in the building 1 and retransmitted in the building 1 or in the room, whereby the ISDB-T receiver 8. Can reliably receive radio waves retransmitted from the re-transmission credit antenna 7 of the re-transmission device 5 wherever it moves in the building 1 or in the room, and can watch the ISDB-T broadcast in a stable state. .
[0025]
Further, the ISDB-T signal sent to the TV terminal 2 by the CATV cable 3 is input to the amplifying device 6 of the retransmitting device 5 through the cable 4 so that the retransmitted signal is input to the input side of the amplifying device 6. This makes it difficult to sneak around, and can reliably prevent oscillation caused by sneaking around. Further, since the return prevention circuit 11 is provided in the amplification device 6, it is possible to reliably prevent the signal from returning from the amplifier 12 side to the CATV cable 3.
[0026]
Furthermore, since the AGC circuit 13 is provided in the amplifying device 6 to adjust the signal level from the amplifier 12 to the retransmission credit antenna 7, it is possible to always transmit an optimal level of radio waves to the ISDB-T receiver 8. .
[0027]
Further, as described above, re-transmission with a weak electric field from the re-transmission device 5 and re-transmission in a room where radio waves are difficult to leak can reliably prevent leakage of radio waves to the outside. Furthermore, since the ISDB-T signal is provided with a guard interval, there is an advantage that even if radio waves leak outside the room, it is difficult to interfere with other devices.
[0028]
(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a block diagram showing the overall configuration of the indoor retransmission system according to the second embodiment of the present invention, and FIG. 5 is a block diagram showing the detailed configuration of the amplifying device 22 in FIG.
[0029]
The indoor retransmission system according to the second embodiment of the present invention is the one in which the second retransmission apparatus 20 is provided in the building 1 together with the first retransmission apparatus 5 in the first embodiment shown in FIG. It is. That is, when the building 1 is wide and the retransmitted radio waves from the first retransmitting device 5 alone cannot cover all the inside of the building 1, the radio waves retransmitted from the first retransmitting device 5 are converted to the second retransmitted radio waves. The data is received by the transmission device 20 and retransmitted to the ISDB-T receiver 8. In this case, the second retransmitting device 20 is installed within a range where radio waves retransmitted from the first retransmitting device 5 reach.
[0030]
The first retransmitting device 5 retransmits a vertically polarized wave (or horizontally polarized wave) or right-handed circularly polarized wave (or left-handed circularly polarized wave) from the retransmission credit antenna 7 into the building 1.
[0031]
The second retransmission apparatus 20 includes a reception antenna 21, an amplification apparatus 22, and a retransmission trust antenna 23, and the polarization plane of the reception antenna 21 is matched with the polarization plane of the retransmission trust antenna 7 in the first retransmission apparatus 5. The retransmission credit antenna 23 is set to a polarization plane different from that of the reception antenna 21. For example, when the polarization plane of the receiving antenna 21 is set to the vertical polarization (or horizontal polarization), the polarization plane of the retransmission credit antenna 23 is set to horizontal polarization (or vertical polarization). When the polarization plane of the receiving antenna 21 is matched with right-handed circular polarization (or left-handed circular polarization), the polarization plane of the retransmission credit antenna 23 is set to left-handed circular polarization (or right-handed circular polarization). . In other words, by changing the polarization planes of the receiving antenna 21 and the retransmission trust antenna 23, the radio wave retransmitted from the retransmission trust antenna 23 is less likely to enter the reception antenna 21.
[0032]
Specifically, the second retransmission apparatus 20 is configured as shown in FIG. That is, for example, a dipole antenna is used as the reception antenna 21 and the retransmission trust antenna 23, and a signal received by the reception antenna 21 is input to the amplification device 22. The amplifying device 22 includes an amplifier 32 and an AGC circuit 33. The amplifier 32 amplifies the signal input from the receiving antenna 21 and outputs the amplified signal to the AGC circuit 33 and the retransmission credit antenna 23. The AGC circuit 33 is configured in the same manner as the AGC circuit 13 provided in the amplification device 6 of the first retransmission device 5 shown in detail in FIG. Is adjusted to satisfy the electric field strength of 35 μV / m (frequency: 322 MHz to 10 GHz) as in the first embodiment. Further, the AGC circuit 33 adjusts the level of the retransmitted radio wave by the retransmission credit antenna 23 so that the oscillation due to the wraparound of the radio wave does not occur.
[0033]
Also in the second retransmitting apparatus 20, similar to the retransmitting apparatus 5 shown in the first embodiment, the retransmitted signal is a modulated signal by OFDM having a characteristic strong against radio wave interference such as multipath and sneak current. Is used.
[0034]
As described above, the first retransmitting device 5 is installed in the building 1, and the second retransmitting device 20 is provided and relayed within a range where the retransmitted radio wave from the first retransmitting device 5 reaches. As a result, even if the building 1 is large, the ISDB-T receiver 8 can be retransmitted by the retransmission antenna 7 of the first retransmission device 5 or the retransmission of the second retransmission device 20 regardless of where the ISDB-T receiver 8 moves. Radio waves retransmitted from the trusted antenna 23 can be reliably received, and the ISDB-T broadcast can be viewed in a stable state.
[0035]
【The invention's effect】
As described above, according to the present invention, the ISDB-T signal transmitted by the cable for CATV is input to the retransmitting device via the TV terminal provided in the building, amplified by the amplifying device, and transmitted from the retransmission credit antenna. Since retransmission is performed, there is no need to perform processing such as modulation / demodulation of ISDB-T signals, frequency conversion, and wraparound cancellation for each channel, and retransmission of the entire UHF band can be realized with a simple system configuration. The ISDB-T signal can be easily viewed using an ISDB-T receiver such as the above. In addition, it is possible to prevent oscillation due to the sneak in the retransmitted signal, to reliably prevent the signal from returning from the amplifier side to the CATV cable, and to keep the retransmitted radio wave level at the optimum level.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of an indoor retransmission system according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing details of a main part in the embodiment.
FIG. 3 is an exemplary block diagram showing a detailed configuration example of an AGC circuit according to the embodiment;
FIG. 4 is a block diagram showing the overall configuration of an indoor retransmission system according to a second embodiment of the present invention.
FIG. 5 is an exemplary block diagram showing details of a second retransmission apparatus in the embodiment;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Building 2 ... TV terminal 3 ... CATV cable 4 ... Cable 5 ... Retransmission device 6 ... Amplification device 7 ... Retransmission credit antenna 8 ... ISDB-T receiver 9 ... Antenna 11 ... Return prevention circuit 12 ... Amplifier 13 ... AGC Circuit 15 ... first envelope detector 16 ... second envelope detector 17 ... variable attenuator 18 ... differential amplifier 20 ... second retransmitting device 21 ... receiving antenna 22 ... amplifying device 23 ... retransmission credit Antenna 32 ... Amplifier 33 ... AGC circuit

Claims

An amplifying device using a retransmitted broadcast signal of a terrestrial digital television broadcast drawn into a low-level radio wave indoors via a cable connector from a lead wire of the CATV system, and an output of the amplifying device. In the indoor retransmission system consisting of
The amplifying device comprises an amplifier that amplifies the input signal and an AGC circuit,
The AGC circuit
A first envelope detector for envelope detection of the input signal;
A second envelope detector for envelope detection of the output signal of the amplifier;
A variable attenuator for adjusting the output voltage level of the second envelope detector;
A differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator;
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less An indoor re-transmission system characterized in that the broadcast signal is re-transmitted to an indoor terrestrial digital television broadcast receiver using radio waves.

2. The indoor retransmission system according to claim 1, wherein a return prevention circuit for preventing a signal from returning is provided on the input side of the amplifier in the amplification device.

An amplifying device using a retransmitted broadcast signal of a terrestrial digital television broadcast drawn into a low-level radio wave indoors via a cable connector from a lead wire of the CATV system, and an output of the amplifying device. In the indoor retransmission system consisting of
The amplification device includes an amplifier that amplifies the input signal and an AGC circuit,
The AGC circuit
A first envelope detector for envelope detection of the input signal;
A second envelope detector for envelope detection of the output signal of the amplifier;
A variable attenuator for adjusting the output voltage level of the second envelope detector;
A differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator;
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less And a first retransmission device for retransmitting the broadcast signal indoors by radio waves,
An indoor re-transmission comprising: an amplifying apparatus that receives a radio wave retransmitted from the first retransmitting apparatus by a receiving antenna and uses the received signal as an input signal; and a retransmission credit antenna connected to an output of the amplifying apparatus In the transmission system,
The amplifying device comprises an amplifier that amplifies the input signal and an AGC circuit,
The AGC circuit
A first envelope detector for envelope detection of the input signal;
A second envelope detector for envelope detection of the output signal of the amplifier;
A variable attenuator for adjusting the output voltage level of the second envelope detector;
A differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator;
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less And a second re-transmission device that retransmits a broadcast signal to an indoor terrestrial digital television broadcast receiver using radio waves.

An amplifier for amplifying a retransmitted broadcast signal of digital terrestrial television broadcasting that is drawn indoors with a low radio wave level from the lead-in line of the CATV system through a cable connector, and an AGC that controls the output level of the amplifier An amplification device with a circuit;
A retransmission credit antenna connected to the output of the amplification device,
The AGC circuit
A first envelope detector for envelope detection of the input signal;
A second envelope detector for envelope detection of the output signal of the amplifier;
A variable attenuator for adjusting the output voltage level of the second envelope detector,
Consists of a differential amplifier for outputting the first voltage value corresponding to the difference between the second output voltage of the envelope detector, which is adjusted by the output voltage of the envelope detector and the variable attenuator,
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less And retransmitting the broadcast signal to an indoor terrestrial digital television broadcast receiver using radio waves.

5. The indoor retransmission apparatus according to claim 4 , wherein in the amplification apparatus, a return prevention circuit for preventing a signal from returning is provided on an input side of the amplifier.

An amplifier for amplifying a retransmitted broadcast signal of digital terrestrial television broadcasting that is drawn indoors with a low radio wave level from the lead-in line of the CATV system through a cable connector, and an AGC that controls the output level of the amplifier An amplification device with a circuit;
A retransmission credit antenna connected to the output of the amplification device,
The AGC circuit
A first envelope detector for envelope detection of the input signal;
A second envelope detector for envelope detection of the output signal of the amplifier;
A variable attenuator for adjusting the output voltage level of the second envelope detector,
Consists of a differential amplifier for outputting the first voltage value corresponding to the difference between the second output voltage of the envelope detector, which is adjusted by the output voltage of the envelope detector and the variable attenuator,
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less A first retransmission device that retransmits the broadcast signal indoors by radio waves,
An amplifying apparatus comprising: an amplifier for receiving a broadcast signal retransmitted from the first retransmitting apparatus by a receiving antenna; an amplifier for amplifying the received signal; and an AGC circuit for controlling an output level of the amplifier; It consists of a retransmission credit antenna connected to the output of the device,
The AGC circuit
A first envelope detector for envelope detection of the input signal;
A second envelope detector for envelope detection of the output signal of the amplifier;
A variable attenuator for adjusting the output voltage level of the second envelope detector;
A differential amplifier that outputs a voltage value corresponding to the difference between the output voltage of the first envelope detector and the output voltage of the second envelope detector adjusted by the variable attenuator;
Adjusting the output level of the differential amplifier by changing the output voltage value of the differential amplifier by variably setting the attenuation amount of the variable attenuator, and reducing the electric field strength of the signal retransmitted from the retransmission credit antenna to a predetermined level or less And a second retransmitting device for retransmitting a broadcast signal to an indoor terrestrial digital television broadcast receiver by radio waves,
An indoor re-transmission device comprising:

7. The reception antenna and the retransmission trust antenna in the second retransmission apparatus are set to have different polarization planes, and radio waves that wrap around the reception antenna from the retransmission trust antenna are blocked. Indoor re-transmission device.