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face=楷體_GB2312 color=#000066
size=3>射頻跳頻是將話音信號用固定的發(fā)射機(jī)，由跳頻序列控制，采用不同頻率發(fā)射，原理圖如圖<SPAN
lang=EN-US>3-37所示，實(shí)施框圖如圖3-38所示。需要說明的是，射<SPAN
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</SPAN>頻跳頻必須有兩個發(fā)射機(jī)，一個固定發(fā)射載頻Fo，因它帶有控制信道BCCH；另一發(fā)射機(jī)載波頻率可隨著跳頻序列的序列值的改變而改變。<O:P>
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<IMG height=83 src="g3-10.files/g3-10.3.gif" width=293
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face=楷體_GB2312 color=#000066 size=3>圖<SPAN lang=EN-US>3-37 射頻跳頻<O:P>
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style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'"><FONT
face=楷體_GB2312 color=#000066 size=3>圖<SPAN lang=EN-US>3-38
射頻跳頻實(shí)施框圖<O:P> </O:P></SPAN></FONT><FONT face=楷體_GB2312 size=3><SPAN
lang=EN-US><O:P></O:P></SPAN></FONT><FONT face=楷體_GB2312
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face=楷體_GB2312 color=#000066
size=3>射頻跳頻比基帶跳頻具有更高的性能改善和抗同頻干擾能力，但其缺點(diǎn)是：</FONT><FONT size=3><SPAN
lang=EN-US><O:P> </O:P></SPAN></FONT></SPAN></P>
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</SPAN><FONT face=楷體_GB2312 color=#000066>(1) <SPAN lang=EN-US
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'">射頻跳頻目前還不成熟。<O:P>
</O:P></SPAN></FONT></SPAN></FONT></P>
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</SPAN><FONT face=楷體_GB2312>(2)<SPAN lang=EN-US
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射頻跳頻只有當(dāng)每小區(qū)擁有4個頻率以上時效果比較明顯。<O:P> </O:P></SPAN></FONT><SPAN lang=EN-US
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<O:P></O:P></SPAN></SPAN></FONT></P>
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</SPAN>(3)<SPAN lang=EN-US
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射頻跳頻必須使用HIBRID合成器，每小區(qū)如使用4個載頻就需要配置3個HIBRID，損耗約6dB，比空腔合成器的損耗大3dB
左右。對基站覆蓋范圍有一定影響。<O:P> </O:P></SPAN></SPAN></FONT></P>
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style="mso-hansi-font-family: Times New Roman">(4)<SPAN lang=EN-US
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合成器要求網(wǎng)路中各基站必須同步，而目前很多供貨商難滿足。<O:P> </O:P></SPAN></SPAN></FONT></P>
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<O:P></O:P></SPAN></SPAN></FONT><FONT
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</SPAN><FONT face=楷體_GB2312
color=#000066>綜上原因，大多數(shù)廠家的BTS是采用基帶跳頻技術(shù)，而不采射頻跳頻技術(shù)。<O:P>
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