"John KD5YI" wrote in
news:Z2srj.1036$qw4.677@trnddc02:

I must be doing something wrong. 276log(2)=83 but looks like about 150
on your graph. No?

Sorry, that expression should be 276log(2D/d) for a consistent meaning of D
and d. (Some people use wire radius and some, diameter... so D here is
centre to centre distance, and d is diameter.)

Owen