JP3892707B2

JP3892707B2 - Television signal transmitter

Info

Publication number: JP3892707B2
Application number: JP2001343803A
Authority: JP
Inventors: 明秀安達
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 2001-11-08
Filing date: 2001-11-08
Publication date: 2007-03-14
Anticipated expiration: 2021-11-08
Also published as: JP2003153096A

Description

【０００１】
【発明の属する技術分野】
本発明は、ＣＡＴＶシステム等に使用されるテレビジョン信号送信機に関し、詳しくは映像及び音声信号によって変調された映像及び音声中間周波信号を送信すべきテレビビジョン信号に周波数変換するテレビジョン信号送信機に関する。
【０００２】
【従来の技術】
従来のテレビジョン信号送信機の構成を図３によって説明する。第一の混合器２１には映像信号及びび音声信号で変調された映像／音声中間周波信号（米国仕様では映像中間周波信号ＰＩＦが４５．７５ＭＨｚ、音声中間周波信号ＳＩＦが４１．２５ＭＨｚ）と第一の局部発振器２２から出力された第一の局部発振信号とが入力される。第一の局部発振器２２は発振周波数が１２５４．２５ＭＨｚとなるように第一のＰＬＬ回路２３によって制御される。よって、第一の混合器２１からは映像搬送波が１３００ＭＨｚ、音声搬送波が１２９５．５ＭＨｚの中間周波信号が出力される。
【０００３】
第一の混合器２１には中間周波増幅器２４、バンドパスフィルタ２５、中間周波増幅器２６、第二の混合器２７が順次縦続接続される。
【０００４】
第二の混合器２７には中間周波信号と第二の局部発振器２８から出力された第二の局部発振信号とが入力される。第二の局部発振器２８は第二のＰＬＬ回路２９によって制御され、およそ１３５０ＭＨｚから２３００ＭＨｚまでの間のいずれかの周波数で発振する。そして、中間周波信号の周波数と第二の局部発振信号の周波数との差であるおよそ５０ＭＨｚから１０００ＭＨｚの間のいずれかのテレビジョン信号が出力される。例えば第二の局部発信周波数が１３５５．２５ＭＨｚであれば、中間周波信号の周波数との差が５５．２５ＭＨｚ（映像搬送波）となり、チャンネル２のテレビジョン信号が出力される。
【０００５】
【発明が解決しようとする課題】
上記の構成では、図４に示すように中間周波信号Ｆｉの周波数が１３００ＭＨｚ、第二局部発振信号Ｌｏ２の周波数が１３５０ＭＨｚ〜２３００ＭＨｚであるから、出力されるテレビジョン信号Ｆｏの周波数は５０ＭＨｚ〜１０００ＭＨｚとなる。しかし、レベルは低いものの第二の混合器２７には中間周波信号の２倍高調波２Ｆｉ（２６００ＭＨｚ）が入力されていると、第二の局部発振信号Ｌｏ２との周波数差によって３００ＭＨｚ〜１２５０ＭＨｚの偽の信号Ｆｏ’が出力され、出力すべきテレビジョン信号Ｆｏの周波数と偽の信号Ｆｏ’の周波数とが一致する場合がある。
すなわち、Ｆｏ＝Ｌｏ−Ｆｉ、Ｆｏ’＝２Ｆｉ−ＬｏであるからＦｏ＝Ｆｏ’とすればＦｏ＝Ｆｉ／２＝６５０ＭＨｚとなる。またこの時はＬｏ＝３×Ｆｉ／２＝１９５０ＭＨｚとなる。
つまり、中間周波信号Ｆｉの１／２の周波数となるテレビジョン信号Ｆｏを出力するときには必然的に偽の信号Ｆｏ’との周波数が一致し、これによって妨害をうける。
【０００６】
具体的には、例えばＣＡＴＶのチャンネルＮｏ・１００のテレビジョン信号を出力しようとした場合、その映像搬送波は中間周波信号のほぼ１／２となる６４９．２５ＭＨｚであるので、第二の局部発振信号Ｌｏ２の周波数は１９４９．２５ＭＨｚとなる。そして６５０．７５ＭＨｚの偽の信号Ｆｏ’が発生する。これは同じチャンネル（Ｎｏ・１００）の映像搬送波とは２ＭＨｚ以内の位置で帯域内に入るため除去することが出来ず、妨害信号となる。
【０００７】
なお、上記の関係を成り立たせないようにするには、中間周波信号の周波数を高くして、テレビジョン信号の最高周波数の２倍（２０００ＭＨｚ）以上とすれば良いが、第一の局部発振周波数と第二の局部発振信号が極めて高くなるので、第一及び第二の局部発振器の構成が困難となる。
【０００８】
そこで、本発明は、局部発振器の発振周波数を高くすることなく、出力されるテレビジョン信号の周波数が中間周波信号の周波数の１／２となった場合でも中間周波信号の２倍高調波に基づく妨害信号を発生させないようにすることを目的とする。
【０００９】
【課題を解決するための手段】
上記課題の解決のために、本発明では、入力された映像及び音声中間周波信号を第一の局部発振信号の周波数の切替に応じてそれよりも周波数が高い第一の中間周波信号又は前記第一の中間周波信号よりも周波数が低い第二の中間周波信号にアップコンバートする第一の混合器と、前記第一及び第二の中間周波信号を所定の周波数範囲内のいずれかのテレビジョン信号にダウンコンバートする第二の混合器とを備え、前記第二の混合器は前記第一の中間周波信号をそれよりも周波数が高い第二の局部発振信号によって前記所定の周波数範囲における所定の周波数までの前記テレビジョン信号にダウンコンバートすると共に、前記第二の中間周波信号をそれよりも周波数が高い第二の局部発振信号によって前記所定の周波数範囲における前記所定の周波数以上の前記テレビジョン信号にダウンコンバートし、前記第一の中間周波信号の周波数を前記所定の周波数の２倍以上に設定し、前記第二の中間周波信号の周波数を前記所定の周波数の２倍以下に設定した。
【００１０】
また、前記第一の中間周波信号の周波数と前記第二の中間周波信号の周波数とを前記所定の周波数範囲のテレビジョン信号の最高周波数よりも高くした。
【００１１】
また、前記第一の周波数を１３００ＭＨｚ、前記第二の周波数を１０８０ＭＨｚとした。
【００１２】
また、前記所定の周波数範囲の最低周波数はほぼ５０ＭＨｚであり、前記所定の周波数をほぼ６００ＭＨｚとした。
【００１３】
また、前記第一の中間周波信号を通過する第一のバンドパスフィルタと、前記第二の中間周波信号を通過する第二のバンドパスフィルタとを設け、前記第一の局部発振信号の周波数の切替に対応して前記第一又は第二のバンドパスフィルタの一方を前記第一の混合器と前記第二の混合器との間に介挿した。
【００１４】
【発明の実施の形態】
本発明のテレビジョン信号送信機の構成を図１及び図２によって説明する。第一の混合器１には映像信号及びび音声信号で変調された映像／音声中間周波信号（米国仕様では映像中間周波信号ＰＩＦが４５．７５ＭＨｚ、音声中間周波信号ＳＩＦが４１．２５ＭＨｚであるが、以下では代表して映像中間周波信号という）と、第一の局部発振器２から出力された第一の局部発振信号とが入力される。第一の局部発振器２はその発振周波数（第一局部発振周波数数という）が１２５４．２５ＭＨｚ又は１０３４．２５ＭＨｚに切り替えられるように第一のＰＬＬ回路３によって制御される。よって、第一の混合器１からは映像搬送波が１３００ＭＨｚで音声搬送波が１２９５．５ＭＨｚとなる第一の中間周波信号Ｆｉ１、又は映像搬送波が１０８０ＭＨｚで音声搬送波が１０７５．５ＭＨｚとなる第二の中間周波信号Ｆｉ２が出力される。映像搬送波と音声搬送波とは４．５ＭＨｚの間隔であるので、以下においては映像搬送波の周波数で代表して説明する。また、中間周波信号の周波数を中間周波数という。
【００１５】
第一の混合器１の次段には第一の中間周波増幅器４が設けられ、その次段には第一の切替手段５が設けられる。第一の切替手段５の次段には第一のバンドパスフィルタ６と第二のバンドパスフィルタ７とが併設され、いずれか一方が切替手段５によって第一の中間周波増幅器４に接続される。また、二つのバンドパスフィルタ６、７の次段には第二の切替手段８が設けられ、いずれか一方が次段の第二の中間周波増幅器９に接続される。第一のバンドパスフィルタ６はほぼ１３００ＭＨｚを通過し、第二のバンドパスフィルタ７はほぼ１０８０ＭＨｚを通過する。第一の切替手段５と第二の切替手段８との切り替え動作は連動する。第二の中間周波増幅器９の次段には第二の混合器１０が設けられる。
【００１６】
第二の混合器１０には中間周波信号と第二の局部発振器１１から出力された第二の局部発振信号とが入力される。第二の局部発振器１１は第二のＰＬＬ回路１２によって制御され、およそ１３５０ＭＨｚから１９００ＭＨｚまでの低域側局部発振信号Ｌｏ２１又は１６８０ＭＨｚから２０８０ＭＨｚまでの高域側局部発振信号Ｌｏ２２を出力する。以下、第二の局部発振信号の周波数を第二局部発振周波数、低域側局部発振信号の周波数を低域側局部発振周波数、高域側局部発振信号の周波数を高域側局部発振周波数という。
【００１７】
以上の構成において、映像中間周波信号は１２５４．２５ＭＨｚ又は１０３４．２５ＭＨｚの第一の局部発振信号によって１３００ＭＨｚ又は１０８０ＭＨｚの中間周波信号Ｆｉ１、Ｆｉ２に変換されて第一の混合器１から出力される。中間周波数が１３００ＭＨｚのときは第一及び第二の切替手段５、８によって第一のバンドパスフィルタ６が選択されて第一の中間周波増幅器４と第二の中間周波増幅器８との間に介挿され、中間周波数が１０８０ＭＨｚのときは第二のバンドパスフィルタ７が選択されて第一の中間周波増幅器４と第二の中間周波増幅器８との間に介挿される。
【００１８】
また、中間周波信号は第二の局部発振信号によって所定の周波数範囲、例えば５０ＭＨｚ〜１０００ＭＨｚの間のいずれかの周波数のテレビジョン信号Ｆｏに変換されて第二の混合器１０から出力される。
【００１９】
ここで、出力すべきテレビジョン信号Ｆｏの最高周波数が中間周波数Ｆｉの１／２以下であれば、中間周波信号Ｆｉの２倍高調波２Ｆｉと第二の局部発振信号Ｌｏ２とによって発生する偽の信号Ｆｏ’がテレビジョン信号Ｆｏと同じ周波数に一致しないことが分かっているので、５０ＭＨｚから所定の周波数Ｆｃ、例えば６００ＭＨｚ（米国仕様のチャンネルＮｏ・８６）までのテレビジョン信号Ｆｏ１を出力する時には第一の局部発振周波数を１２５４．２５ＭＨｚとし、図２Ａに示すように、１３００ＭＨｚの第一の中間周波信号Ｆｉ１にしている。この時は第二の局部発振器は必然的に１３５０ＭＨｚから１９００ＭＨｚまでの低域側局部発振信号Ｌｏ２１を出力する。
【００２０】
この条件では、第一の中間周波信号Ｆｉ１の２倍高調波２Ｆｉと低域側局部発振信号Ｌｏ２１とによる偽の信号の最低周波数は７００ＭＨｚ（＝２６００ＭＨｚ−１９００ＭＨｚ）となり、出力すべきテレビジョン信号の周波数（最高周波数が６００ＭＨｚ）とは１００ＭＨｚ離れて重ならない。
【００２１】
また、６００ＭＨｚ（米国仕様のチャンネルＮｏ・８７）以上のテレビジョン信号Ｆｏ２を出力する時には第一の局部発振周波数を１０３４．２５ＭＨｚとし、図２Ｂに示すように、第二の中間周波信号Ｆｉ２の周波数を６００ＭＨｚの２倍以下である１０８０ＭＨｚにしている。この時は第二の局部発振器は必然的に１６８０ＭＨｚから２０８０ＭＨｚまでの高域側局部発振信号Ｌｏ２２を出力する。
【００２２】
この条件では第二の中間周波信号Ｆｉ２の周波数は６００ＭＨｚの１／２以上であるので第二の中間周波信号Ｆｉ２の２倍高調波２Ｆｉ２と高域側局部発振信号Ｌｏ２２とによる偽の信号Ｆｏ２’の最高周波数は４８０ＭＨｚ（＝２１６０ＭＨｚ−１６８０ＭＨｚ）となり、出力すべきテレビジョン信号Ｆｏ２の周波数（最低周波数が６００ＭＨｚ）とは１２０ＭＨｚ離れて重ならない。
【００２３】
また、第一及び第二の中間周信号Ｆｉ１、Ｆｉ２のいずれの周波数も出力されるテレビジョン信号Ｆｏの最高周波数よりも５０ＭＨｚ以上高いので出力するテレビジョン信号Ｆｏに重畳される心配はない。
【００２４】
【発明の効果】
以上説明したように、本発明では、第二の混合器は第一の中間周波信号をそれよりも周波数が高い第二の局部発振信号によって所定の周波数範囲における所定の周波数までのテレビジョン信号にダウンコンバートすると共に、第二の中間周波信号をそれよりも周波数が高い第二の局部発振信号によって所定の周波数範囲における所定の周波数以上のテレビジョン信号にダウンコンバートし、第一の中間周波信号の周波数を所定の周波数の２倍以上に設定し、第二の中間周波信号の周波数を前記所定の周波数の２倍以下に設定したので、いずれの中間周波信号の２倍高調波と第二局部発振信号との差による偽の信号が、出力されるテレビジョン信号のいずれとも周波数が合致することはなく、妨害を受けない。
【００２５】
また、第一の中間周波信号の周波数と第二の中間周波信号の周波数とを所定の周波数範囲のテレビジョン信号の最高周波数よりも高くしたので、出力されるテレビジョン信号が中間周波信号によって妨害を受けない。
【００２６】
また、第一の周波数を１３００ＭＨｚ、第二の周波数を１０８０ＭＨｚとしたので、第二の局部発振信号を低くすることが出来る。
【００２７】
また、所定の周波数範囲の最低周波数はほぼ５０ＭＨｚであり、所定の周波数をほぼ６００ＭＨｚとしたので、米国仕様のＣＡＴＶシステムに使用することが出来る。
【００２８】
また、第一の中間周波信号を通過する第一のバンドパスフィルタと、第二の中間周波信号を通過する第二のバンドパスフィルタとを設け、第一の局部発振信号の周波数の切替に対応して第一又は第二のバンドパスフィルタの一方を第一の混合器と第二の混合器との間に介挿したので、一方の中間周波信号のみを第二の混合器に入力出来る。
【図面の簡単な説明】
【図１】本発明のテレビジョン信号送信機の構成を示すブロック図である。
【図２】本発明のテレビジョン信号送信機における周波数変換の様子を示す図である。
【図３】従来のテレビジョン信号送信機の構成を示すブロック図である。
【図４】従来のテレビジョン信号送信機における周波数変換の様子を示す図である。
【符号の説明】
１第一の混合器
２第一の局部発振器
３第一のＰＬＬ回路
４第一の中間周波増幅器
５第一の切替手段
６第一のバンドパスフィルタ
７第二のバンドパスフィルタ
８第二の切替手段
９第二の中間周波増幅器
１０第二の混合器
１１第二の局部発振器
１２第二のＰＬＬ回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a television signal transmitter used in a CATV system or the like, and more particularly, a television signal transmitter that converts a video and audio intermediate frequency signal modulated by a video and audio signal into a television vision signal to be transmitted. About.
[0002]
[Prior art]
The configuration of a conventional television signal transmitter will be described with reference to FIG. The first mixer 21 includes a video / audio intermediate frequency signal modulated by the video signal and the audio signal (in the US specification, the video intermediate frequency signal PIF is 45.75 MHz and the audio intermediate frequency signal SIF is 41.25 MHz). The first local oscillation signal output from one local oscillator 22 is input. The first local oscillator 22 is controlled by the first PLL circuit 23 so that the oscillation frequency becomes 1254.25 MHz. Therefore, the first mixer 21 outputs an intermediate frequency signal having a video carrier wave of 1300 MHz and an audio carrier wave of 1295.5 MHz.
[0003]
An intermediate frequency amplifier 24, a band pass filter 25, an intermediate frequency amplifier 26, and a second mixer 27 are connected in cascade to the first mixer 21.
[0004]
The intermediate frequency signal and the second local oscillation signal output from the second local oscillator 28 are input to the second mixer 27. The second local oscillator 28 is controlled by the second PLL circuit 29 and oscillates at any frequency between approximately 1350 MHz and 2300 MHz. Then, any television signal between about 50 MHz and 1000 MHz, which is the difference between the frequency of the intermediate frequency signal and the frequency of the second local oscillation signal, is output. For example, if the second local transmission frequency is 1355.25 MHz, the difference from the frequency of the intermediate frequency signal is 55.25 MHz (video carrier wave), and the television signal of channel 2 is output.
[0005]
[Problems to be solved by the invention]
In the above configuration, since the frequency of the intermediate frequency signal Fi is 1300 MHz and the frequency of the second local oscillation signal Lo2 is 1350 MHz to 2300 MHz as shown in FIG. 4, the frequency of the output television signal Fo is 50 MHz to 1000 MHz. Become. However, although the level is low, if the second harmonic wave 2Fi (2600 MHz) of the intermediate frequency signal is input to the second mixer 27, a false frequency of 300 MHz to 1250 MHz is caused by the frequency difference with the second local oscillation signal Lo2. Signal Fo ′ is output, and the frequency of the television signal Fo to be output may coincide with the frequency of the false signal Fo ′.
That is, since Fo = Lo−Fi and Fo ′ = 2Fi−Lo, if Fo = Fo ′, Fo = Fi / 2 = 650 MHz. At this time, Lo = 3 × Fi / 2 = 1950 MHz.
That is, when a television signal Fo having a frequency half that of the intermediate frequency signal Fi is output, the frequency of the fake signal Fo ′ is necessarily matched, thereby being disturbed.
[0006]
More specifically, for example, when a television signal of CATV channel No. 100 is to be output, the video carrier is 649.25 MHz, which is almost a half of the intermediate frequency signal. The frequency of Lo2 is 1949.25 MHz. Then, a false signal Fo ′ of 650.75 MHz is generated. Since this is within the band at a position within 2 MHz from the video carrier of the same channel (No. 100), it cannot be removed and becomes an interference signal.
[0007]
In order to prevent the above relationship from being established, the frequency of the intermediate frequency signal may be increased so that it is at least twice the maximum frequency of the television signal (2000 MHz). Since the second local oscillation signal becomes extremely high, the configuration of the first and second local oscillators becomes difficult.
[0008]
Therefore, the present invention is based on the second harmonic of the intermediate frequency signal even when the frequency of the output television signal is ½ of the frequency of the intermediate frequency signal without increasing the oscillation frequency of the local oscillator. The purpose is to prevent generation of interference signals.
[0009]
[Means for Solving the Problems]
In order to solve the above problem, in the present invention, the input video and audio intermediate frequency signal is converted into the first intermediate frequency signal having a frequency higher than that of the first local oscillation signal according to the switching of the frequency of the first local oscillation signal or the first intermediate frequency signal. A first mixer for up-converting to a second intermediate frequency signal having a frequency lower than that of the one intermediate frequency signal, and the first and second intermediate frequency signals within a predetermined frequency range; A second mixer that down-converts the first intermediate frequency signal to a predetermined frequency in the predetermined frequency range by a second local oscillation signal having a higher frequency than that of the first intermediate frequency signal. Down to the television signal up to and including the second intermediate frequency signal in the predetermined frequency range by a second local oscillation signal having a higher frequency. Down-converting the television signal to a frequency equal to or higher than a predetermined frequency, setting the frequency of the first intermediate frequency signal to at least twice the predetermined frequency, and changing the frequency of the second intermediate frequency signal to the predetermined frequency. It was set to 2 times or less.
[0010]
Further, the frequency of the first intermediate frequency signal and the frequency of the second intermediate frequency signal are set higher than the highest frequency of the television signal in the predetermined frequency range.
[0011]
The first frequency was 1300 MHz and the second frequency was 1080 MHz.
[0012]
The minimum frequency in the predetermined frequency range is approximately 50 MHz, and the predetermined frequency is approximately 600 MHz.
[0013]
In addition, a first bandpass filter that passes the first intermediate frequency signal and a second bandpass filter that passes the second intermediate frequency signal are provided, and the frequency of the first local oscillation signal is increased. Corresponding to the switching, one of the first or second bandpass filter is inserted between the first mixer and the second mixer.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the television signal transmitter of the present invention will be described with reference to FIGS. The first mixer 1 has a video / audio intermediate frequency signal modulated by a video signal and an audio signal (in the US specification, the video intermediate frequency signal PIF is 45.75 MHz and the audio intermediate frequency signal SIF is 41.25 MHz. Hereinafter, the image intermediate frequency signal is representatively input) and the first local oscillation signal output from the first local oscillator 2 is input. The first local oscillator 2 is controlled by the first PLL circuit 3 so that the oscillation frequency (referred to as the first local oscillation frequency number) is switched to 1254.25 MHz or 1034.25 MHz. Therefore, from the first mixer 1, the first intermediate frequency signal Fi1 in which the video carrier is 1300 MHz and the audio carrier is 1295.5 MHz, or the second intermediate frequency in which the video carrier is 1080 MHz and the audio carrier is 1075.5 MHz. A signal Fi2 is output. Since the video carrier and the audio carrier are spaced at a frequency of 4.5 MHz, the following description will be made representatively using the frequency of the video carrier. The frequency of the intermediate frequency signal is referred to as an intermediate frequency.
[0015]
The first intermediate frequency amplifier 4 is provided in the next stage of the first mixer 1, and the first switching means 5 is provided in the next stage. A first band-pass filter 6 and a second band-pass filter 7 are provided next to the first switching means 5, and one of them is connected to the first intermediate frequency amplifier 4 by the switching means 5. . The second switching means 8 is provided in the next stage of the two band pass filters 6 and 7, and one of them is connected to the second intermediate frequency amplifier 9 in the next stage. The first bandpass filter 6 passes approximately 1300 MHz, and the second bandpass filter 7 passes approximately 1080 MHz. The switching operation of the first switching unit 5 and the second switching unit 8 is interlocked. A second mixer 10 is provided at the next stage of the second intermediate frequency amplifier 9.
[0016]
The second mixer 10 receives the intermediate frequency signal and the second local oscillation signal output from the second local oscillator 11. The second local oscillator 11 is controlled by the second PLL circuit 12 and outputs a low-frequency local oscillation signal Lo21 from approximately 1350 MHz to 1900 MHz or a high-frequency local oscillation signal Lo22 from 1680 MHz to 2080 MHz. Hereinafter, the frequency of the second local oscillation signal is referred to as a second local oscillation frequency, the frequency of the low frequency local oscillation signal is referred to as a low frequency local oscillation frequency, and the frequency of the high frequency local oscillation signal is referred to as a high frequency local oscillation frequency.
[0017]
In the above configuration, the video intermediate frequency signal is converted into 1300 MHz or 1080 MHz intermediate frequency signals Fi1 and Fi2 by the first local oscillation signal of 1254.25 MHz or 1034.25 MHz and output from the first mixer 1. When the intermediate frequency is 1300 MHz, the first band-pass filter 6 is selected by the first and second switching means 5, 8 and is interposed between the first intermediate frequency amplifier 4 and the second intermediate frequency amplifier 8. When the intermediate frequency is 1080 MHz, the second band-pass filter 7 is selected and inserted between the first intermediate frequency amplifier 4 and the second intermediate frequency amplifier 8.
[0018]
The intermediate frequency signal is converted into a television signal Fo having a predetermined frequency range, for example, a frequency between 50 MHz and 1000 MHz by the second local oscillation signal, and is output from the second mixer 10.
[0019]
Here, if the highest frequency of the television signal Fo to be output is equal to or less than ½ of the intermediate frequency Fi, a false harmonic generated by the second harmonic 2Fi of the intermediate frequency signal Fi and the second local oscillation signal Lo2. Since it is known that the signal Fo ′ does not coincide with the same frequency as the television signal Fo, when the television signal Fo1 from 50 MHz to a predetermined frequency Fc, for example, 600 MHz (US specification channel No. 86) is output, One local oscillation frequency is 1254.25 MHz, and as shown in FIG. 2A, a first intermediate frequency signal Fi1 of 1300 MHz is used. At this time, the second local oscillator inevitably outputs a low-frequency local oscillation signal Lo21 from 1350 MHz to 1900 MHz.
[0020]
Under this condition, the lowest frequency of the false signal generated by the second harmonic 2Fi of the first intermediate frequency signal Fi1 and the low-frequency local oscillation signal Lo21 is 700 MHz (= 2600 MHz-1900 MHz). It does not overlap with the frequency (the maximum frequency is 600 MHz) at a frequency of 100 MHz.
[0021]
Further, when outputting a television signal Fo2 of 600 MHz (channel No. 87 of the US specification) or higher, the first local oscillation frequency is set to 103.25 MHz, and the frequency of the second intermediate frequency signal Fi2 as shown in FIG. 2B. Is set to 1080 MHz, which is twice or less of 600 MHz. At this time, the second local oscillator inevitably outputs the high frequency side local oscillation signal Lo22 from 1680 MHz to 2080 MHz.
[0022]
Under this condition, since the frequency of the second intermediate frequency signal Fi2 is ½ or more of 600 MHz, the false signal Fo2 ′ due to the second harmonic 2Fi2 of the second intermediate frequency signal Fi2 and the high-frequency local oscillation signal Lo22. The maximum frequency of 480 is 480 MHz (= 2160 MHz-1680 MHz), and does not overlap with the frequency of the television signal Fo2 to be output (minimum frequency is 600 MHz) at 120 MHz.
[0023]
Further, since both the first and second intermediate frequency signals Fi1 and Fi2 are 50 MHz or more higher than the highest frequency of the output television signal Fo, there is no fear of being superimposed on the output television signal Fo.
[0024]
【The invention's effect】
As described above, in the present invention, the second mixer converts the first intermediate frequency signal into a television signal up to a predetermined frequency in a predetermined frequency range by the second local oscillation signal having a higher frequency. Down-converting and down-converting the second intermediate frequency signal to a television signal of a predetermined frequency or higher in a predetermined frequency range by a second local oscillation signal having a higher frequency than that of the first intermediate frequency signal Since the frequency is set to be twice or more of the predetermined frequency and the frequency of the second intermediate frequency signal is set to be not more than twice the predetermined frequency, the second harmonic of any intermediate frequency signal and the second local oscillation The false signal due to the difference from the signal does not match the frequency of any of the output television signals and is not disturbed.
[0025]
In addition, since the frequency of the first intermediate frequency signal and the frequency of the second intermediate frequency signal are set higher than the maximum frequency of the television signal in the predetermined frequency range, the output television signal is disturbed by the intermediate frequency signal. Not receive.
[0026]
Further, since the first frequency is 1300 MHz and the second frequency is 1080 MHz, the second local oscillation signal can be lowered.
[0027]
Further, since the minimum frequency in the predetermined frequency range is approximately 50 MHz and the predetermined frequency is approximately 600 MHz, it can be used for a CATV system of the US specification.
[0028]
A first band-pass filter that passes the first intermediate frequency signal and a second band-pass filter that passes the second intermediate frequency signal are provided to support frequency switching of the first local oscillation signal. Since one of the first and second bandpass filters is interposed between the first mixer and the second mixer, only one intermediate frequency signal can be input to the second mixer.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a television signal transmitter of the present invention.
FIG. 2 is a diagram showing a state of frequency conversion in the television signal transmitter of the present invention.
FIG. 3 is a block diagram showing a configuration of a conventional television signal transmitter.
FIG. 4 is a diagram showing a state of frequency conversion in a conventional television signal transmitter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st mixer 2 1st local oscillator 3 1st PLL circuit 4 1st intermediate frequency amplifier 5 1st switching means 6 1st band pass filter 7 2nd band pass filter 8 2nd switching Means 9 Second intermediate frequency amplifier 10 Second mixer 11 Second local oscillator 12 Second PLL circuit

Claims

The first intermediate frequency signal having a higher frequency than the first intermediate frequency signal in response to the switching of the frequency of the first local oscillation signal or the second lower frequency than the first intermediate frequency signal. And a second mixer for down-converting the first and second intermediate frequency signals into a television signal within a predetermined frequency range. And the second mixer downconverts the first intermediate frequency signal to the television signal up to a predetermined frequency in the predetermined frequency range by a second local oscillation signal having a higher frequency than the first intermediate frequency signal. The television signal having the second intermediate frequency signal equal to or higher than the predetermined frequency in the predetermined frequency range by a second local oscillation signal having a higher frequency than the second intermediate frequency signal. Down-converting, the frequency of the first intermediate frequency signal is set to be twice or more of the predetermined frequency, and the frequency of the second intermediate frequency signal is set to be twice or less of the predetermined frequency. A television signal transmitter.

2. The television according to claim 1, wherein the frequency of the first intermediate frequency signal and the frequency of the second intermediate frequency signal are set higher than the highest frequency of the television signal in the predetermined frequency range. Signal transmitter.

The television signal transmitter according to claim 1 or 2, wherein the first frequency is 1300 MHz and the second frequency is 1080 MHz.

4. The television signal transmitter according to claim 3, wherein the lowest frequency of the predetermined frequency range is approximately 50 MHz, and the predetermined frequency is approximately 600 MHz.

A first band-pass filter that passes the first intermediate frequency signal and a second band-pass filter that passes the second intermediate frequency signal are provided to switch the frequency of the first local oscillation signal. Correspondingly, one of the first or second band-pass filter is interposed between the first mixer and the second mixer. A television signal transmitter as described.