# how to find inductor value on fr formula?

Discussion in 'Homework Help' started by kee23, Sep 20, 2012.

1. ### kee23 Thread Starter New Member

Feb 1, 2012
10
0
Hello,

on the question it says i need to find a resistor and inductor values if i have
fr= 10.7Mhz Capacitance=0.1nF BW=200kHz
I was guessing that I can use the frequency resonance formulas and after that, i don't know to simply it to find Inductor value.

Can someone show me the steps to simplify on the formulas? or am i thinking it wrong?

Thanks.

2. ### mlog Member

Feb 11, 2012
276
36
Do you know the equation for resonant frequency? If you knew it, could you use algebra to manipulate the equation and solve it for a variable? Is your filter supposed to be passive; that is without any electronic amplification?

3. ### kee23 Thread Starter New Member

Feb 1, 2012
10
0
it's an active filter, but not much need to worry. and formula should be 1/2pi square root LC that's what i meant, i don't seem to know how to do it

Last edited: Sep 20, 2012
4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
$f_r=\frac{1}{2\pi \sqrt{LC}}$

${f_r}^2=\frac{1}{4\pi^2 LC}$

Now make L the subject of the equation.

Presumably this is a series LC circuit - otherwise you must apply the parallel case equation - which in your case would require the concurrent solution for the R value as part of the exercise.

5. ### Dodgydave AAC Fanatic!

Jun 22, 2012
7,653
1,272

2.2uH
Calculator for resonance
http://www.1728.org/resfreq.htm