Hi Dave

One of the pitfalls is that although a VF of .66 (or .87 for foam) is
common it can vary considerably.

I dont think I have ever seen manufacturers VF specs with a tolerance
listed. In fact I dont think I have ever seen a manufacturers spec
include VF!

Of course it depends on how critical the application is. In my
experience for example 4:1 coaxial baluns on 2m always need to be tuned...

Cheers Bob VK2YQA

Dave wrote:
f


with velocity factor of .66 for generic rg-213 i get 12.988MHz being 2
wavelengths... but why do you care?

here is how to calculate the right length, no fancy measurement equipment
needed.
http://www.qsl.net/w4sat/howlong.htm