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Helical_Bandpass_Filter_Designer.php   7114 Bytes    14-12-2014 21:19:16

Helical Bandpass Filter Designer

Suiteable for the VHF range ( 50 ... 1000 MHz )

Helix Bandpass Filter

Center Frequency [MHz]

Bandwidth [MHz]


System Impedance [Ω]

Maximum Passband loss [dB]


Resonator is in a

  enclosure / cavity




Unloaded Q of the Resonator

Impedance of the Resonator [Ω]

Diameter Helix [mm]

Height Helix [mm]

Number of turns

Wire Diameter [mm]

    ± 10 %.

Tap at [turns] [mm] [deg]

    from gnd.

Width Cavity [mm]

    if round then diameter.

Height Cavity [mm]

Height Separator [mm]

Space above/below Helix [mm]

✈ Hints

More information can be found in the ARRL handbook, chapter 12, "Helical Resonators".

A second source to be mentioned is the "Handbook of Filter Synthesis" by Anatol I. Zverev, ISBN: 9780471749424

Instead of the tuning slug, a trimmer capacitor mayst be used. This has the advantage, that the helix is mechanically stabilised.

✈ Share your thoughts

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t1 = 6585 d

t2 = 200 ms

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