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 A_{L} 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:

Z_{6,7} = 6, 7 impedance in parallel

Z_{5,6,7} = 5, Z_{6,7} impedance in series

Z_{4,5,6,7} = 4, Z_{5,6,7} impedance in parallel

Z_{3,4,5,6,7} = 3, Z_{4,5,6,7} impedance in series

Z_{2,3,4,5,6,7} = 2, Z_{3,4,5,6,7} impedance in parallel

I_{5} = Vector sum of I_{6} and I_{7}

I_{3} = Vector sum of I_{4} and (I_{5})

I_{1}^{2} = (I_{2}^{2} + I_{3}^{2})^0.5

## Spreadsheet

5-pole Low-Pass Chebyshev Filter for 40m Band Excel Spreadsheet

## LTspice IV (Version 4.20m) Source File

5-pole Low-Pass Chebyshev Filter for 40m Band LTspice source file

## References

The design originated from from p7.18 of the Radio Communications Handbook 10th Ed.