Re: 80 meter bpf toroid winding 30 turns givel 4.3 micro Henrys, not 3.8
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As mentioned earlier by someone else, compressing or spreading
the turns on a toroid core probably does not change the inductance
very much (the number of turns remains the same). What it does
do is to change the distributed capacitance between turns.
Also mentioned by others is that the apparent inductance of metallic
cores does change with frequency. This could be a factor if you are
operating the core at widely different frequencies.
DC loading also causes toroidal cores to change apparent
inductance. While probably not an issue with DC isolated
filters, it could be problematic for tank circuits that carry DC