This coil calculator is a good place to start, as it is probably the most accurate
one available on the internet:http://hamwaves.com/antennas/inductance.html
Try changing the wire size and see what impact it has. In many coils it doesn't
make a lot of difference, but when a coil is close-wound the self-capacitance
between the turns can become significant. That is affected by the turns spacing
and the presence of insulation - increasing the spacing between the wire surfaces
by using a smaller wire will add an air gap between the insulation layers, which will
decrease the capacitance between adjacent turns.
Typically the difference is quite small - not more than the other expected variations
due to core material, measurement tolerances, etc., and is easily taken into account
during normal antenna tuning. But when the self-resonant frequency of a coil is
close to the operating frequency (as can be the case with heavily-loaded antennas)
then it starts to make more of a difference.
Will it work? Probably so - there is nothing particularly unconventional about that
arrangement as I see it, though the term "off centered" may be confusing. It looks
like just a shortened dipole with loading coils in each leg. Such an antenna can
have the loading coils positioned just about anywhere along the wire, though the
required loading inductance changes as you do so. You can tune it by adjusting
the number of turns on the loading coil or the length of either wire. Feedpoint
impedance is likely to be well below 50 ohms unless the coils are lossy.
But I'd guess that the inductance is 58.7 micro
henries (uH) rather thanmilli
If you wind 80 turns of closewound 18 gauge wire instead of 16 gauge the coil will
be slightly shorter, and therefore have higher inductance. That's probably close
enough, however: wind the coils, string it up, and check where the minimum SWR
is. Adjust the length of the wire ends as needed to move it to your favorite frequency.