# 5-Pole Low-Pass Chebyshev Filter for 40m Band

The circuit below is for a 5-pole Low-Pass Chebyshev Filter for the Amateur Radio 40m band. The component values are summarised in the table below.

Designator Value
R1 50 Ohm
C2 360 pF
L3 1.3 uH
C4 680 pF
L5 1.3 uH
C6 360 pF
R7 50 Ohm

The inductors are formed from 18 turns of 20 swg enameled copper wire on a T50-6 toroidal core. This has an AL value of 40 µH per 100 turns, so a quick check of the inductance is as follows:

LµH = AL x ( N / 100 ) ^ 2

= 40 x 0.18^2

= 1.296 µH

In the spreadsheet below I have started to do some mathematical analysis of this circuit, based on the following ideas:

Z6,7 = 6, 7 impedance in parallel

Z5,6,7 = 5, Z6,7 impedance in series

Z4,5,6,7 = 4, Z5,6,7 impedance in parallel

Z3,4,5,6,7 = 3, Z4,5,6,7 impedance in series

Z2,3,4,5,6,7 = 2, Z3,4,5,6,7 impedance in parallel

I5 = Vector sum of I6 and I7

I3 = Vector sum of I4 and (I5)

I12 = (I22 + I32)^0.5 5-pole Low-Pass Chebyshev Filter for 40m Band Excel Spreadsheet 5-pole Low-Pass Chebyshev Filter for 40m Band LTspice source file