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Passive 9th-order Elliptical Filter

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Passive 9th-order Elliptical Filter
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).
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor 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. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

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
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