dansawyeror wrote:
. . .
The question is: What is the basis of the difference between predicted
and measured values?

1. Have you decoupled your feedline? If you're not using a feedline,
have you decoupled your measurement device?

2. Have you substituted a lumped impedance of about 16 + j133 ohms for
the antenna and observed what your measurement equipment indicates?

Roy Lewallen, W7EL