s06-02.htm

关于扩频的一些好资料

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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">由跳频信号产生的过程可以看出，不论是数字的或模拟的定频发送系统，在原理上，只要加装上一个跳频器就可变成一个跳频的发送系统。但是在实际系统</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中尚需考虑信道机的通带宽度。</SPAN></P>
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            lang=EN-US style="FONT-SIZE: 12pt; COLOR: navy">6.2.2<SPAN 
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            style="FONT-SIZE: 12pt; COLOR: navy; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">怎样接收跳频信号</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">定频信号的接收设备中，一般都采用超外差式的接收方法，即接收机本地振荡器的频率比所接收的外来信号的载波频率相差一个中频，经过混频后产生一</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">个固定的中频信号和混频产生的组合波频率成分。经过中频带通滤波器的滤波作用，滤除组合波频率成分，而使中频信号进入解调器。解调器的输出就是所要传送给收端的信息。</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">跳频信号的接收，其过程与定频的相似。为了保证混频后获得中频信号，要求频率合成器的输出频率要比外来信号高出一个中频。因为外来的信号载波频率是跳变的，则要求本地频率合成器输出的频率也随着外来信号的跳变规律而跳变，这样才能通过混频获得一个固定的中颇信号。图</SPAN><SPAN 
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            lang=EN-US style="FONT-SIZE: 12pt">8(b)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">给出跳频信号接收</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">机的框图。图中的跳频器产生的跳频图案应当与所要要高出一个中频，并且要求收、发跳频完全同步。所以，接收机中的跳频器还需受同步指令的控制，以确定其跳频的起、止时刻。</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">可以看出，跳频器是跳频系统的关键部件，而跳频同步则是跳频系统的该心技术。</SPAN></P>
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            lang=EN-US style="FONT-SIZE: 12pt; COLOR: navy">6.2.3<SPAN 
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            style="FONT-SIZE: 12pt; COLOR: navy; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">正确接收跳频信号的条件</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">跳频系统要实现跳频通信，正确接收跳频信号的条件是跳频系统的同步。</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">系统的同步包括以下几项内容：</SPAN><SPAN 
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            收端和发端产生的跳频图案相同，即有相同的跳频规律。</SPAN><SPAN lang=EN-US 
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            收、发端的跳变频率应保证在接收端产生固定的中频信号，即跳变的载波频率与收端产生的本地跳变频率相差一个中频。</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">频率跳变的起止时刻在时间上同步，即同步跳变，或相位一致。</SPAN><SPAN 
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            在传送数字信息时，还应做到帧同步和位同步。</SPAN><SPAN lang=EN-US 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">示出跳频同步的几种情况。</SPAN><SPAN 
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            align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt">&nbsp;<IMG 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">其中，图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(a)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">只是跳频图案相同；图</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是跳频图案及跳频频率一致的情况；图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(c)</SPAN><SPAN