Re: Toroid winding numbers and measurements

Leland L. Bahr

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.

Lee, w0vt

On 11/1/2017 11:37 AM, w0eb@... wrote:
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

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