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Calculating the frequency based on LC circuit

by guns
Tags: based, circuit, frequency
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guns
#1
Mar23-13, 11:23 AM
P: 4
Hi all,

I am currently building up a lightning detector based on this website: http://www.techlib.com/electronics/lightningnew.htm
as the diagrams shows, the resonance tank included a 10mH inductor and a 10pF capacitor.
As I want to calculate the resonant frequency (using the formula f = 1/2pi*sqrt(LC)), the answer was 5Hz, which is far from the desired range (should be around 200kHz)
is there any mistake in my calculation or concept? Thanks for your help.

Guns
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mfb
#2
Mar23-13, 12:00 PM
Mentor
P: 11,911
How did you get your answer? Did you consider the SI prefixes (milli, pico)?
I think there are brackets missing in your equation.
guns
#3
Mar23-13, 12:34 PM
P: 4
mfb,
I did it this way:
1/2pi*sqrt(10^(-3)*10^(-12))
which approxmately equals to 5 Hz.

milesyoung
#4
Mar23-13, 01:02 PM
P: 520
Calculating the frequency based on LC circuit

Following up on mfb's post, you're missing brackets and are using the wrong values for the SI units:

10 mH = 10*10^(-3) H
10 pF = 10*10^(-12) F

1/(2*pi*sqrt(10*10^(-3)*10*10^(-12))) Hz = 503.3*10^3 Hz = 503.3 kHz
guns
#5
Mar24-13, 09:30 AM
P: 4
oh my, silly me.
Thanks mfb and milesyoung!


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