I CANT FINISH MY THESIS:RESONANT FREQ OF HELICAL COIL

Given a helical coil with parameters below:
a-radius of the coil
b-inner radius of a wire
s-spacing b/w turns
n-turn
h- height of the coil

How can I determine the effective inductance and effective capacitance
of the coil so that I can get ots resonance frequency?

Is there any formulas or references?
Pls. I need it ASAP.
TNX.

For inductance of single layer helical coil formula Nagaoka can be used or similar other formulas. It is empirical equations, so there are more than one. You may search Google for Nagaoka and get this formula. I may check my library but in about 10 hours. It is a bit harder fro self-capacitance for such a coil. I saw such formulas in old RF books (these coils used a lot long time ago, now mostly chip inductors in usage). Then, for calculating the resonant frequency you may use Thomson formula as approximation or check my topic: ,
and there in the last post I gave solution for more precise calculation with consideration of coil’s ESR.
This is all what I can tell you right now and will try to find more a bit later.

Added after 1 hours 35 minutes:

Here are a couple of links that may be helpful:

**broken link removed**

http://www.ajdesigner.com/phpinductor/inductor_equation.php

Hello,

If I chime in with these links, they may be of some further help for you?

**broken link removed**

This software designs bandpass filters with helical elements and also a free program, maybe also useful:

http://tonnesoftware.com/helical.html

rgds, unkarc

PS: I noticed you are interested in helical antenna for 100MHz? Here is a nomograph (with the formula) for such: http://www.qsl.net/aa1ll/ (see the middle part of that long page)

and see this link too: http://www.daycounter.com/Calculators/Helical-Antenna-Design-Calculator.phtml

Here are some papers on inductor design. There still no information about between turns capacitance, I will check it later.

Here is link to good coil parameters calculator where you can calculate between turns capacitance:

https://hamwaves.com/antennas/inductance.html

and a few more information on this calculations in attached file.

This is also coils calculator program that may be helpful. Please change the extension from .jpg back to .exe in order to use it.

Hello paupau101,

I hope you did not tired yet from my posts. I found one more formula for coil self-capacitance calculation. This is a kind of scientific, not empirical, formula. It will not consider fringe effects, but for many practical cases this equation may be good.

This is the formula:

Ct=4*r*p*Er/((4*a-pi*r)*(n-1))

where: r is radius of copper part of the wire,
Er is dielectric constant for the wire isolation,
2*a is the distance between wire centers,
p is perimeter of the turn,
n is the number of turns.

When you do not know which formula is the best there is one proven way to get good result. Calculate your sought parameters with all of available tools. Then write all results in the order. Check all the numbers. If some of them differ too much they probably are not right. Try to exclude them. Then count all that are in reasonable deviation and take two calculations: arithmetic means and geometric means. Then compare these two values and chose one that is closer to what you expect. This method averages possible errors and usually provides the best results.


Best regards,
RF-OM

Tnx for the replies. It helps.

Added after 15 minutes:

Can anyone knows how to compute the resonant frequency of a loop antenna?
Does the computation the same as helical coil except it has no spacing b/w turns?

Correct me If I'm wrong.
Tnx.