One last caveat: The measured inductance will very with the
frequency used to measure the inductance. Hans has not told us if
he just calculated it or if he measured the best inductance with
an instrument. If he used an instrument we would have to know the
frequency used. In other words if you remove or add turns to
acquire the exact inductance needed but did this at a different
frequency because your meter is on a different frequency, your
results will not be what is required. In my estimation one is
playing with fire trying to match inductance without knowing the
standard's test parameters. A lot of hams don't realize
inductance of an inductor changes with frequency. An inductor
tested at one frequency will give a different inductance if tested
at a different frequency.
I'm still waiting
for my 40 meter version (#943) but shipping has resumed again as
of yesterday so hopefully by the end of this month.
I have all the proper cores for all the toroids called for in the
construction manual, and after reading this thread I decided to
wind a set and measure the inductance with my AADE L/C meter which
has proven to be quite accurate.
To achieve the proper inductance for L4, I had to use 1 turn less
than called for so I wound L2 next - same thing - 1 turn less to
get the right inductance for the band. I wound L1 and L3 with 1
turn less and they came out very close to the called for value.
Now, a caveat - NOT ALL TOROID CORES ARE CREATED EQUAL!
Especially if they are Chinese made - LOL. Depending on the actual
permeability of the core, the inductance will most likely vary a
bit with the same turns count. Also I saw something earlier about
spread of turns VS inductance. Close winding gives the MOST
inductance and if you spread the turns out you will reduce the
inductance somewhat. Not by much but it will be less with wider
spaced turns by the theory of inductors and I confirmed this by
measuring each of the above coils. I first used the called for
number of turns and they all measured up to a half microhenry
high. Spreading the turns got it down about .2 microhenry but
they still were too high so I removed a turn from each which with
close to even spacing over the core got them within .02 microhenry
which I think should be close enough. Just my experience with the
set of cores I had on hand. Your mileage will most certainly vary
so don't take this as gospel, just as a point of information and a
starting point for troubleshooting.
I'm looking forward to receiving my QCX so I can guit it built and
hopefully confirm my observations on the LPF coils.
Jim - W0EB