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<TD borderColor=#6699ff><FONT size=2>您的位置：技术园地>技术讲座-扩频通信</FONT></TD></TR>
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color=#000080 size=5>第六讲 </FONT></SPAN><FONT size=5><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><SPAN
style="COLOR: #333399; FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">跳频</SPAN><FONT
color=#000080>系统(2)</FONT></SPAN></FONT></B></FONT></DIV></TD></TR>
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<P class=MsoNormal
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color=#800080 size=4><SPAN lang=EN-US>6.2<SPAN
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style="FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">跳频信号的发送与接收</SPAN></FONT><SPAN
lang=EN-US style="FONT-SIZE: 12pt"> </SPAN></B></P>
<P class=MsoNormal
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lang=EN-US style="FONT-SIZE: 12pt; COLOR: navy">6.2.1<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'">怎祥产生跳频信号</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'">在传统的定频通信系统中，发射机中的主振荡器的振荡频率是固定设置的，<BR>因而它的载波频率是固定的。为了得到载波频率是跳变的跳频信号，要求主振荡</SPAN><SPAN
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</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">器的频率应能遵照控制指令而改变。这种产生跳频信号的装置叫跳频器。通常，跳频器是由频率合成器和跳频指令发生器构成的，如见图</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">6</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</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'">。</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'">图中，如果将跳频器看作是主振荡器，则与传统的发信机没有区别。被传送的信息可以是模拟的或数字的信号形式</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">图中标示的为信码入</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'">，经过调制器的相应调制，便获得副载波频率固定的已调波信号，再与频率合成器输出的主载波频率信号进行混频，其输出的已调波信号的载波频率达到射频通带的要求，经过高通滤波器后馈至天线发射出去。这就是定频信号的发送过程。</SPAN><SPAN
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</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">跳频系统的频率合成器输出什么频率的载波信号是受跳频指令控制的。在时钟的作用下，跳频指令发生器不断地发出控制指令，频率合成器不断地改变其输</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">出载波的频率。因此，混频器输出的已调波的载波频率也将随着指令不断地跳变，从而经高通滤波器和天线发送出去的就是跳频信号。</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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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'">跳频器输出的跳变的频率序列，就是跳频图案。因此，有什么样的跳频指令就会产生什么样的跳频图案?</SPAN></P>
<P class=MsoNormal
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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'"> 通常，是利用伪随机发生器来产生跳频指令的，或者由软件编程来产生跳频指令。所以，跳频系统的关键部件是跳频器，更具体地，是能产生频谱纯度好的快速切换的频率合成器和伪随机性好的跳频指令发生器。</SPAN><SPAN
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