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???????????????????????????????????????????????????泻??澹�????????????? ?????????????????????????????????????????????????????????????????????? ???????????????????????????妫�??????????????????????????? ??????????些 ????????????????????????????尉?????????????????????
?????????????????
????????????????薪?10???????????????????????????????????3?????????????? ??????????????????????????????????????????????0.5%??谐???????????????? ????????????????????????
0dBSPL=2??10-5Pa
???????????????????????y???????????????????????????????????? ?妾�?????????????????????????????????????????????
1.?????
????????????位????????????????????????????????位??mV/Pa??????路?械?? ???????锟�??????????????????????????????位dBm??dBV?????
0dBm=1mW/Pa??????1Pa??????????600???????????1mW????????????0dB??
0dBV=1V/??bar??????1??bar????????2?????1V???????????0dB??
????????????位dB??????
0dB??=0.775V/Pa??????1Pa???????????0.775V???????????0dB(????????????????? ????????????????????路?????????0dB??=0.775V????慰???位)??
????????????????伪??????????????????dB??????????????????Pa?????位??
???纾篘EUMANNU89????????????8mV/Pa?????????
20lg[(0.008V/Pa)??(0.775V/Pa)]
?贸??????????-40dB???
???纾篈KGC414???????????-60dBV????
0dBV=1V/??bar=10V/Pa
?????1Pa?????-60dBV????????X??
20lg[(XV/Pa)??(10V/Pa)]=-60
?贸?X=0.01(V)??????????????10mV/Pa???????
20lg[(0.01V/Pa)??(0.775V/Pa)]
????????????-37dB??
2.?????????
??????????????????渭????????????????????????????????????????????????? ????????????????????????????????????????????????????????????????????? ????????????????????????????????????????
????NEUMANNU89????????????????8mV/Pa???????????????134dBSPL(??10dB?????????)???? ???????????????????????????????????????????????0dBSPL=2??10-5Pa?????????????? X????
134dBSPL=20lgX/2??10-5Pa
?贸?X=100(Pa)?????????8mV/Pa???100Pa????????800mV????????????????
20lg[(0.8V/Pa)??(0.775V/Pa)]
??0dB??????U89?????????????????????????????????????????10dB?????(??? ??????????)??????????????????????U89??????????????????????????位?渭? 124dBSPL??????????????????????????0dB???
?????????????????????
?????????????????????????????????????????????????瓒�?????????????????婕�??( ????泄???????????????????????????)?????????????????谐??????????????? ??0dB????????蔚????围????????
???????????????????????????????????????????????????????????????????? ????????????????????????????????????????????????????(??????)?????????妫� ????????渭????????????????????????
??????????????????????U89?????AMEKRemBandt????????????????????????????? 70cm?????????????????112dBSPL(?????A???)???????????????????????????124dB?????? ????8mV/Pa??????
112dBSPL=20lgX/2??10-5
???112dB?????????8Pa???????????8Pa??8mV/Pa=64mV?????????????械???????
20lg[(0.064V/Pa)??(0.775V/Pa)]=-22dB??
???????????70dB???????妤�?????????????????谐???????0.017%??12dB?????????(?? ???????路????????????28dB??)????+12dB???????????34dB??????(+12dB-(-22dB)=34dB)?? ????????????械????????妾�???????????????????????
???????校???????????????????????谐????????0.017%????????????????????????? ????????????????????路???????????????????????????????????????????????????0dB?? ??位????????????????????????????????????????????????????浣�??????????