"Cecil Moore" wrote
Something else that I have wondered about:
Given a threaded rod with about double the surface
area of a piece of tubing, does the VF decrease?
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The velocity of propagation of Andrew HJ8-50B, 3" OD, air-dielectric
Heliax® is 0.933c.

Both the inner and outer conductors of that coaxial cable are heavily
corrugated, so using threaded rod instead of smooth tubing may not
matter much to v.p.

RF