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Re: Self resonance of a coil
>Hi Group,
>If I know the dimensions of a coil, i.e. r=diameter/2, wire gauge,
>l=length, n=number of turns,
>is there an approximate formula for the self-resonance? I thought I had it
>but can't find it now,
>or maybe it doesn't matter if the coil is top loaded with a large toroid. I
>know the
>inductance is found approximately by L=n*n(r*r/(9*r+10*l)) so I use the
>1/2PIsqr(LC).
>Just curious,
>Dave
>
Dave,
Just for the secondary itself, I have done a couple of things. I first
use the resonance formula (1/2*pi*sqrt(LC)), after knowing the coil's
inductance value of course, and plug in 1pf (.000000000001 Farad)
as C and write down that value. Then I made a 555 timer
circuit to come close to that frequency and applied the signal to one
end of the secondary and an oscilliscope to the other and adjust the
frequency around until I see the signal max out on the scope. Others
have done the same with a signal generator (which I dont have).
When the signal maxes, I used the scope to determine frequency.
Crude but very close. The frequency is of importance when you
add a torroid. It changes. Use the above resonance formula and
solve for frequency when C is 1pf - 25pf in increments of 1pf
and chart in down on paper (or use qbasic or something). I did
this once and was surprised of the frequency change with just
a small change in C.
Hope this helps,
Bob Schumann