Article
Passive 9th-order Elliptical Filter
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Steep filters can be realised in many different ways, for example by connecting active 2nd to 5th-order sections in series and calculating the component values for the higher order. They can also be made passive, but in practice this has a few difficulties associated with it. You cannot avoid the need for inductors with values that deviate from the standard series. You will have to wind them yourself on a specially selected core. The filter presented here was originally designed to enable measurements to be made on the Class-T Amplifier (yes indeed, the one in Elektor Electronics, June 2004).
Materials
Gerber file
CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.
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PCB
Component list
Resistors:
R1,R4 = 1k07
R2,R5 = 113k
R3 = not fitted *
Capacitors:
C1,C14 = not fitted *
C2,C5,C11,C13 = 1nF 500V 1% silvered mica (Farnell 868-012)
C3,C8,C12 = 120pF 500V 1% silvered mica (Farnell 867-901)
C4 = 6pF8 500V 1% silvered mica (Farnell 867-779)
C6,C15 = 270pF 500V 1% silvered mica (Farnell 867-949)
C7,C9 = 680pF 500V 1% silvered mica (Farnell 867-998)
C10,C18 = 180pF 500V 1% silvered mica (Farnell 867-925)
C16 = 220pF 500V 1% silvered mica (Farnell 867-937)
C17 = 470pF 500V 1% silvered mica (Farnell 867-974)
C19 = 100pF trimmer
Inductors:
L1 = 1mH15, 115 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell # 180-009)
L2 = 689µH, 89 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell # 180-009)
L3 = 557µH, 80 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell 1# 80-009)
L4 = 802µH, 96 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell # 180-009)
Miscellaneous:
K1,K2 = cinch socket, PCB mount, e.g., T-709G (Monacor/Monarch)
PCB, 044042-1
* see text
R1,R4 = 1k07
R2,R5 = 113k
R3 = not fitted *
Capacitors:
C1,C14 = not fitted *
C2,C5,C11,C13 = 1nF 500V 1% silvered mica (Farnell 868-012)
C3,C8,C12 = 120pF 500V 1% silvered mica (Farnell 867-901)
C4 = 6pF8 500V 1% silvered mica (Farnell 867-779)
C6,C15 = 270pF 500V 1% silvered mica (Farnell 867-949)
C7,C9 = 680pF 500V 1% silvered mica (Farnell 867-998)
C10,C18 = 180pF 500V 1% silvered mica (Farnell 867-925)
C16 = 220pF 500V 1% silvered mica (Farnell 867-937)
C17 = 470pF 500V 1% silvered mica (Farnell 867-974)
C19 = 100pF trimmer
Inductors:
L1 = 1mH15, 115 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell # 180-009)
L2 = 689µH, 89 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell # 180-009)
L3 = 557µH, 80 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell 1# 80-009)
L4 = 802µH, 96 turns of 0.5mm dia. ECW on core TN23/14/7-4C65 from BCcomponents (Farnell # 180-009)
Miscellaneous:
K1,K2 = cinch socket, PCB mount, e.g., T-709G (Monacor/Monarch)
PCB, 044042-1
* see text
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