* Active Audio Filter for CW Reception, QST, June 2006, page 32 * LI 7 60 1.8 200 1400 plot node 7, 60 lines, 1.8V max scale, 200-1400 Hz VS 1 0 1. 0. voltage source on node 1 at 0 degrees (not shown) R 1 2 1.5e6 0. R1 is a 1.5 megohm resistor from node 1 to node 2 R 2 0 33000 0. R2 is a 33 k ohm resistor from node 2 to ground R 3 4 3.3e6 0. R3 is a 3.3 megohm resistor from 3 to 4 R 5 0 470. 0. R5 is a 470 ohm resistor from node 5 to ground R 4 8 1.5e6 0. R6 is a 1.5 megohm resistor from node 4 to node 8 R 8 0 33000 0. R7 is a 33 k ohm resistor from node 8 to ground R 6 7 3.3e6 0. R8 is a 3.3 megohm resistor from node 6 to node 7 RC 2 4 0. 680.e-12 C1 is a 680 picofarad capacitor from nodes 2 to 4 RC 2 3 0. 680.e-12 C2 is a 680 picofarad capacitor from nodes 2 to 3 RC 5 0 0. 47.0e-6 C3 is a 47 microfarad cap from node 5 to ground RC 8 7 0. 680.e-12 C4 is a 680 picofarad capacitor from nodes 8 to 7 RC 8 6 0. 680.e-12 C5 is a 680 picofarad capacitor from nodes 8 to 6 OA 5 3 4 10000. operational amplifier, + - output nodes, gain=1e4 OA 5 6 7 10000. operational amplifier, + - output nodes, gain=1e4