Multi-Band HF Band-pass Filter for Field Day and Contesting

  After operating last year's field day without band-pass filters, several of our operators complained about desensing in their receivers when another operator transmitted on a different band.  After researching several commercial band-pass filters, and the overall pricing, I decided to design and build some of my own.

  I wanted low insertion loss, with fifty ohms of impedance, and the ability to select between the 6 most popular ham bands, 160m, 80m, 40m, 20m, 15m and 10m.  After a lot of research, I opted for a 3 stage Butterworth band-pass design.

  The following project is the result of my requirements and calculations:

AI4JI Multi-Band HF Band-pass Filter Values

 

Band (MHz)        C/C (pf)             C (pf)                L/L (uH) L (uH)               L/L turns            L turns              Fr (MHz)

1.8                    4000                 400                   2.2                    22                     23                     70                     1.75

3.5                    2000                 200                   1.1                    11                     16                     50                     3.38

7                      1000                 100                   .55                    5.5                    11                     35                     6.78

14                     500                   50                     .28                    2.8                    8                      25                     13.56

21                     330                   33                     .18                    1.8                    7                      20                     20.65

28                     250                   25                     .14                    1.4                    6                      18                     27.39

 

C1, C3: 4000pf             C2:  400pf         L1, L3:  2.2mH               L2:  22uH

C4, C6:  2000pf              C5:  200pf         L4, L6:  1.1uH                L5:  11uH

C7, C9:  1000pf              C8:  100pf         L7, L9:  .55uH                L8:  5.5uH

C10, C12:  500pf            C11:  50pf         L10, L12:  .28uH L11:  2.8uH

C13, C15:  330pf            C14:  33pf         L13, L15:  .18uH L14:  1.8uH

C16, C18:  250pf            C17:  25pf         L16, L18:  .14uH L17:  1.4uH