Please visit VK2TIP's Book Shelf. My personal recommendations, thanks.
Friday, 29-Jun-2018 02:34:40 PDT
•NEW! ‣ - Amazon Electronic Component Packs. Check out the Amazon Electronic Component Packs page.
Coil forms are used to hold a specified number of turns on a specified diameter former. The coil form may or may not be used in conjunction with a coil form "tuning slug". A tuning slug in a coil form leads to greater inductance with fewer turns.
Very good examples of coil forms surrounded by metal shields are the I.F. cans in AM / FM Radio Receivers as in figure 1 below.
Figure 1 - coil forms surrounded by metal shields
The shielded coil forms are indicated by "OSC" for the oscillator inductor and the "IFT" cans are the IF transformers tuned to 455 Khz. These shielded coil forms used as the IF transformers (IFT) probably have something like 140 turns wound on the primary which is a relatively tiny coil form and would yield an inductance of around 680 uH at a reasonable "Q".
Some other examples of these coil forms with and without the metal shield are in figure 2 below.
Figure 2 - coil forms with and without the metal shield
"photo courtesy of Coilcraft" with appreciation of their generous support.
These coil forms are numbered from 1 through 5. Number 1 is a coil form with a tuning slug (often called a "screw core" or "threaded core") and surrounded by a "cup core" to give increased inductance. By screwing the tuning slug in and out we are able to get wide variations in inductance. One example of these type of coil forms, sometimes also called "variable inductors" might be a former and cup core combination which produces say a nominal inductance of 68 uH per 100 turns over the frequency range of 1 to 10 Mhz.
If we wanted 12 uH at 5 Mhz we might select this combination of screw core and cup core. To determine the number of turns required we take 90% of the AL / 100 turns factor (i.e. 90% of the 68 uH = 61.2) To calculate the turns required we take the square root of our desired inductance (12 uH) divided by the AL (61.2) or (SQRT [ 12 / 61.2]) = 0.4428 which is then multiplied by 100 to give us 44.28 turns. Therefore we would wind 44 turns on our former. The tuning slug or "screw core", "threaded core" could give us an inductance variation of as much as 1.5 : 1
Number 2 could simply be number 1 enclosed in a metal shield (copper) to prevent interaction with adjacent components. Number 3 simply has a plastic cup core to protect the windings, it would have a dramatically reduced value of inductance in the absence of a magnetic cup core. Numbers 4 and 5 have no cup cores at all. I'm not even certain number 5 has a screw core.
These are simply a few examples of the hundreds of sizes and possible variations available.
ADDED - 28/1/13: Our friend Harry Lythall - SM0VPO has a particularly interesting page for "DIY IF cans for valves". As always, it shows Harry's creative and imaginative talents. Worth reading as well to get ideas.
BOOK - Inductor Handbook by Cletus J. Kaiser
If you are involved in electronics then consider joining our "electronics Questions and Answers" news group to ask your question there as well as sharing your thorny questions and answers. Help out your colleagues!.
The absolute fastest way to get your question answered and yes, I DO read most posts.
This is a mutual help group with a very professional air about it. I've learn't things. It is an excellent learning resource for lurkers as well as active contributors.
1. audio transformers
4. inductive reactance
5. mobius winding techniques
6. wide band rf transformers
7. Coilcraft Home Page
8. TOKO variable moulded coils
NEW! - How to link directly to this page
Want to create a page link to me from your site? It couldn't be easier. No HTML knowledge required; even the technophobes can do it. All you need to do is copy and paste, the following code. All links are greatly appreciated; I sincerely thank you for your support.
Copy and paste the following code for a text link:
and it should appear like this:
" target="_top">visit Ian Purdie VK2TIP's "Coil Forms" Page</a>
visit Ian Purdie VK2TIP's "Coil Forms" Page
and it should appear like this:
Looking for more? Visit my site map page:
This site is hosted at Press Wizards for better value.
the author Ian C. Purdie, VK2TIP of www.electronics-tutorials.com asserts the moral right to
be identified as the author of this web site and all contents herein. Copyright © 2000, all rights reserved. See copying and links.
These electronic tutorials are provided for individual private use and the author assumes no liability whatsoever for the application, use, misuse, of any of these projects or electronics tutorials that may result in the direct or indirect damage or loss that comes from these projects or tutorials. All materials are provided for free private and public use.
Commercial use prohibited without prior written permission from www.electronics-tutorials.com.
Copyright © 2000 - 2001, all rights reserved. URL - https://www.electronics-tutorials.com/basics/coil-forms.htm
Updated 6th May, 2001