Frank,

Thank you. Your assumptions were correct. The only difference is 54 uH vs
75.

The model below runs on nec2. I tried a quick load it into 4nec2 without
success, it seems to be confused by the GH and GS cards. I will have to
pick this up tomorrow.

Thanks again - Dan

No problem Dan, I find all this very interesting. You could change all the
dimensions to metric, and drop the GS card. I don't know why it is having
trouble with GH. If you run some of the inductance programs, such as:
http://www.captain.at/electronics/coils/, where I have used the number of
turns as 14.7, and length and diameter 12"; the inductance calculates to
44.71 uH.

Minimizing the proximity effect, with #18 AWG, NEC computes z = 3.3 + j1274.
Therefore Q = 433, and L = 60.8 uH; an even greater difference that the
inductance programs, but closer to your requirement of 75 uH. I have tried
to run the program on NEC 4.1 to see if it agrees with NEC 2, but am having
trouble with connecting the helix since the end points don't appear to be in
the correct position.

Frank