# Need help with resonance algebra

Discussion in 'Mathematics and Physics' started by cyb0rg777, Apr 15, 2007.

1. ### cyb0rg777New Member

Joined:
Jan 17, 2006
Messages:
121
Likes:
0
I was figuring up some resonant circuits.
I haven't had time to learn latex very well so I'll try to do the best I can.
So I started with this resonant formula.

I found the value for L with a 20pf capacitor at 440mhz by changing it to this formula.

Now I'm looking for how many turns of an air core inductor I need to make a 6.5419nH coil with a diameter of 3.175mm(.125") and 12.7mm(.5") length.

I'm starting with this formula.

L= inductance in henries
l=length in meters
N= number of turns

So I rearranged it to this to get the number of turns.

But when I check my answer it comes out wrong.
Could you help me out ?
My math is not very good.

Last edited: Apr 15, 2007
2. ### cyb0rg777New Member

Joined:
Jan 17, 2006
Messages:
121
Likes:
0
I think I got it .
I might have been forgetting to take the square root on the last formula.
It comes up to 1.6 turns .I think I'll try it with a smaller capacitor to get more turns.

3. ### Nigel GoodwinSuper ModeratorMost Helpful Member

Joined:
Nov 17, 2003
Messages:
39,324
Likes:
653
Location:
Derbyshire, UK
Assuming you're hoping to construct such a coil?, you need to be aware that stray capacitance and inductance will completely change your calculations!.

Joined:
Jan 12, 1997
Messages:
-
Likes:
0

5. ### cyb0rg777New Member

Joined:
Jan 17, 2006
Messages:
121
Likes:
0

I was hoping to adjust the coils by spreading them apart and squeezing them together but I've never built anything like that from scratch.From following a set of instructions yes but not from my own design.

6. ### Hero999Banned

Joined:
Apr 6, 2006
Messages:
14,902
Likes:
79
Location:
England
Spread apart is often best because it will keep the parasitic capacitance as low a as possible and a long and thin coil is supposed to be better than a long a short and fat coil.