BUTTER07

Features

• Low Pass Butterworth Filter
  • 7th Order Butterworth Filter
  • Shunt first
  • 4 caps, 3 inductors
• Bourns Inductors, 0603, CS160808 family - inexpensive
• Can mount end launch SMT connectors or three pin headers
• 50 Ohms in/out

Calculator (7 MHz example)

• Filter Values Calculator

Parts

Cutoff Freq (MHz)	C1/C7 (pF)	C3/C5 (pF)	L2/L6 (uH)	L4 (uH)
4	360	1500	2.4	3.9
7	200	820	1.5	2.2
14	100	390	0.68	1.1
21	68	270	0.47	0.75
28	51	200	0.36	0.56

BUTTER07 Design

BUTTER07 Values

Cutoff Freq (MHz)	C1/C4 (pF)	C2/C3 (pF)	L1/L3 (uH)	L2 (uH)
1.8	820	3300	5.6	9.1
3.5	390	1600	2.7	4.7
7	200	820	1.5	2.2
14	100	390	0.68	1.1
21	68	270	0.47	0.75
28	51	200	0.36	0.56

CWAZ Filter

• 2nd-Harmonic-Optimized LPFs by By Ed Wetherhold, W3NQN
  • Notches out 2nd harmonic
  • Additional capacitor on center inductor
  • Other values are different from the calculator values

Cutoff Freq (MHz)	C1/C7 (pF)	C3/C5 (pF)	C4 (pF)	L2/L6 (uH)	L4 (uH)
1.8	1659	2631	378	5.21	4.73
3.5	853	1302	194	2.68	2.43
7	727	651	97	1.34	1.22
10.1	296	451	67	0.928	0.843
14	213	325	49	0.67	0.608
18.068	165	252	38	0.519	0.471
21	142	217	32	0.446	0.406
24.89	120	183	27	0.377	0.342
28	107	163	24	0.335	0.304

Built on BUTTER07 Board

• BUTTER07 with extra capacitor for 2nd order harmonic suppression
• L2 and C5 are piggybacked
• 9 MHz

3D