Andy,

I don't think the helical shape of the element will have any significant
impact on performance unless the frequency is approaching half wave
resonance of the helix itself (by half-wave resonance I mean hi-z at the
ends, virtually non-terminated, with a current maximum at the center).

I'd guess that the helix will equal a tube of the same physical length
but with slightly less capacitance, perhaps moving the LF corner a
little bit up (depending on amplifier input R of course).

73
Johan SM6LKM

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Andy Talbot wrote:
> but then started wondering if doing that would make any
> difference to performance.