제3장 변조이론 3.1 진폭 변조(AM, Amplitude …

1 3 (AM, Amplitude Modulation) o . o : o : (modulation) (demodulation) : o : ( (baseband) , (source) , (modulating) ) (carrier) o AM ( Amplitude Modulation) : ( ) o (Angle Modulation) : ( ) - (FM, Frequency Modulation).

2 - (PM, Phase Modulation) : AM AM : vm(t) : vc(t) : vAM(t) : AM fc +Wfc -Wfc-fc-fc -W -fc +WW-Wffftttvm(t)vc(t)=Vccos(2 fct)vAM(t)VAM(f)Vm(f)(USB)(LSB)fc-fcVc/2 Vc/2 AM : vm(t)=Vmcos(2 fmt) : vc(t)=Vccos(2 fct) vAM(t)=(Vc+vm(t))cos(2 fct) =(Vc+Vmcos(2 fmt))cos(2 fct) =Vc(1+VmVccos(2 fmt))cos(2 fct)=Vc(1+mcos(2 fmt))cos(2 fct) m=VmVc o AM : o AM : - : 1) (fc) 2) (fc+fm) : (Upper Side Band) 3) (fc-fm) : (Lower Side Band) W AM --> 2W fcfc+fmfc-fmVccmV21cmV21 AM AM.

3 O (R=1) fc : 12V2c=Pc fc-fm : 18m2V2c=Pm1 fc+fm : 18m2V2c=Pm2 fcfc+fmfc-fmPcPm1Pm2 o : ( 23 ) ( AM ) AM : m=VmVc=Vmax-VminVmax+Vmin , Vmax = Vc + Vm , Vmin = Vc - Vm VmaxVminVc AM (DSB-SC) DSB-SC(Double Side Band - Suppressed Carrier) : AM AM DSB-SC : fc-fm : 12(VcVm2)2=Pm1=12PT fc+fm : 12(VcVm2)2=Pm2=12PT fcfc+fmfc-fmPm1Pm2 DSB-SC W DSB-SC (SSB) (SSB, Single Side Band).

4 DSB-SC W SSB (VSB) (VSB, Vestigial Side Band) : SSB DSB-SC SSB fc VSB 4 (Angle Modulation)o ( ) (FM) (FM, Frequency Modulation) : o V(t)=Vcos i(t) fi(t)=12 d i(t)dt o vc(t)=Vccos(2 fct + ) fi(t)=12 d i(t)dt=fc FM fi(t)=fc+fdvm(t) fd = ( FM ) FM i(t)=2 t0fi( )d vFM(t)=Vccos(2 fct +2 fd t0vm( )d ) o vm(t)=Vmcos2 fmt vFM(t)

5 =Vccos(2 fct +2 fd t0vm( )d ) =Vccos(2 fct +2 Vmfd2 fmsin2 fmt)=Vccos(2 fct + ffmsin2 fmt) =Vccos(2 fct +mfsin2 fmt) f : , f=fd Vm mf : , mf= = ffm FM J0(mf)J1(mf)J2(mf)J3(mf)-J1(mf)J2(mf)-J3 (mf)fcfc+fmfc+2fmfc+3fmfc-fmfc-2fmfc-3fm FM FM o FM : 1) 2) 98% 3) - : nmax=mf+1 - : Carson BW=2(mf+1)fm=2(fm+ f) FM (Narrowband FM) : mf radian AM ( 180 ) FM 1) FM : o (VCO, Voltage Controlled Oscillator).

6 2) FM : o (IF, Intermediate Frequency) VCO (multiplier) (mixer) VCO180 KHz1800 MHz 180 KHz180 MHz 60 KHz60 MHz f0=1620 MHz 3X FM FM o (Frequency Discriminator) o 1) (PLL, Phase Locked Loop) VCO FM PLL FM 2) FM dtd ( 4-4) FM - : ddtvFM(t)=-Vc[2 fc+2 fdvm(t)]sin[2 fct+2 fd t0vm( ) d ] , vFM(t)=Vccos[2 fct+2 fd t0vm( ) d ] - Vc[2 fc+2 fdvm(t)] (PM) (PM, Phase Modulation) : PM (t)=Kpvm(t) ,Kp.

7 , vm(t) PM vPM(t)=Vccos(2 fct+Kpvm(t)) FM fi(t)=12 ddt (t)=fc+Kp2 ddtvm(t) vm(t)=Vmcos2 fmt vPM(t)=Vccos(2 fct+VmKpcos2 fmt) mp : , mp=VmKpPMFMAM AM FM PM PMFMAM AM FM PM AMFMPM AM FM PM