Version 4
SHEET 1 1188 680
WIRE 96 32 32 32
WIRE 240 32 176 32
WIRE 304 32 240 32
WIRE 352 32 304 32
WIRE 480 32 432 32
WIRE 560 32 480 32
WIRE 656 32 560 32
WIRE 32 80 32 32
WIRE 304 96 304 32
WIRE 480 96 480 32
WIRE 656 96 656 32
WIRE 32 224 32 160
WIRE 304 224 304 176
WIRE 304 224 32 224
WIRE 480 224 480 176
WIRE 480 224 304 224
WIRE 656 224 656 176
WIRE 656 224 480 224
WIRE 32 256 32 224
FLAG 32 256 0
FLAG 240 32 in
FLAG 560 32 out
SYMBOL voltage 32 64 R0
WINDOW 123 24 132 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value2 AC 2
SYMATTR InstName V1
SYMATTR Value 0
SYMBOL Misc\\EuropeanResistor 80 48 R270
WINDOW 0 27 56 VTop 0
WINDOW 3 5 56 VBottom 0
SYMATTR InstName Rin
SYMATTR Value 300
SYMBOL Misc\\EuropeanResistor 336 48 R270
WINDOW 0 27 56 VTop 0
WINDOW 3 5 56 VBottom 0
SYMATTR InstName R2
SYMATTR Value 606.249
SYMBOL Misc\\EuropeanResistor 288 80 R0
SYMATTR InstName R1
SYMATTR Value 571.042
SYMBOL Misc\\EuropeanResistor 464 80 R0
SYMATTR InstName R3
SYMATTR Value 53.3204
SYMBOL Misc\\EuropeanResistor 640 80 R0
SYMATTR InstName Rout
SYMATTR Value 50
TEXT 32 -56 Left 0 !.ac dec 100 1 1k
TEXT 16 352 Left 0 ;* 20dB power attenuation -> Vout=0.1/sqrt(300/50)  \nVout=0.0408248 \nZin=300\nZout=50\nR1=(Zout*Zin-(Zin*Vout)^2)/(Zout+Zin*Vout^2-2*Zin*Vout)\nR3=Vout/(1/Zin-Vout/Zout-1/R1)\nR2=(1-Vout)*Zin*R1/(R1-Zin)
TEXT -8 -288 Left 0 ;PI-ATTENUATOR\n20dB power attenuation (27.78dB voltage attenuation)\nVoltage attenuation = power attenuation +10dB*log10(Zin/Zout)\nMinimum power attenuation = sqrt(Zin/Zout)+sqrt(Zin/Zout-1)\nPmindB = 13.42dB    VmindB = 21.20dB\nhttp://www.random-science-tools.com/electronics/PI_attenuator.html\nhttp://chemandy.com/calculators/matching-pi-attenuator-calculator.htm