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Re: Self resonance of a coil
>>From tesla-at-america-dot-comSun Oct 13 22:16:08 1996
>Date: Sun, 13 Oct 96 08:48 EDT
>From: Bob Schumann <tesla-at-america-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: 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
>>
[self snippage]
Dave,
When I went back and re-read my post, I could see something
that could be misleading. In my 555 timer circuit, I have to account
for circuit capacitance (555 circuit). This can change the appearance
of the true resonant frequency. Doh!!! Sorry :(
Since I do not have a signal generator or freq. counter. I made the
chart as explained. (1pf - 25pf). Someone told me to figure 25pf for
torroid. I did and was off a bit. I think 25pf would be for a monster
size torroid. I figured between 10 and 15pf. My primary could cover
that range so all worked out okay.
Happy sparkin
Bob