LC FILTERS

Introduction

This tutorial on LC filter design should allow you to incorporate into your radio design low pass, high pass and bandpass filters. Your electronic project should then hopefully perform the way you want it to.

Low pass and high pass filters are easy to design and implement. A high pass filter is really just the complement of a low pass filter. On the other hand bandpass filters can get quite complex. Also whilst a LC bandpass filter is particularly helpful in reducing image interference it is not the panacea for all ills. A properly designed, carefully constructed and aligned lc bandpass filter will give you a fractional bandwidth of about 2%. It is likely the percentage bandwidth might be somewhat worse than that.

Bandwiths of LC bandpass filters are more a function of the loaded Q of the circuit which in turn is determined by the terminating resistances. The shape factor i.e. - 6dB to - 60 dB points for LC bandpass filters is more a function of the number of resonators.

1. How this electronic tutorial is organised:

I would suggest you create a separate directory called lc-filters, perhaps with a sub-directory called tutorials.

Then I would advise you to save each LC filter lesson as you go. In this way if you wish to refer back later then you can. At times I will recommend you print directly from your online browser. This is because I have graphics files embedded throughout the lc filter lessons and these will not be saved with File|Save As|. The graphic files are to give you some schematics and also because some mathematical formula can't be readily inserted into the text.

Alternatively save the file and then right click to save any graphic you encounter to your new directory also.

2. Basis of the Tutorial

Clearly I must assume my reader will range from those who know nothing at all about LC filters - why else would you be here - to those who know just this and only that and then on up to those people who possibly know more than I do.

3. Tutorial Layout

I have endeavoued to provide sufficient hyperlinks to filter basics, low pass, high pass and bandpass filters so you can jump out if necessary and then come back to me. I have done some layout revision because it was pretty scatty - thanks to all those who continue to email constructive comments and suggestions.

Just follow the links forward and/or backward. Hopefully it will work. If it doesn't let me know because it is quite common for links to become corrupted over time..

4. Tutorial Quiz

I must assume my reader will be enthusiastic enough to want to do a few self-tests. You can look up the answers when you're finished.

5. L.C. Filter Tutorials

1. Basics you must learn to proceed further.

2. How low pass filters are designed - the basis of many other filters.

3. Again you could need a  high pass  filter in your application.

4. Down to a simple band pass  filter for many purposes.

5. Next we have  multi-pole  narrow band pass filters.

6. How did they design I.F. Amplifier filters in the olden days anyway?. Still have their many uses - even today!.

7. Tutorial Answers - see if you got it right.

the author Ian C. Purdie asserts the moral right to be identified as the author of this web site and all contents herein. All rights reserved. See copying and links. These electronic projects are provided for individual private use and the author assumes no liability whatsoever for the application, use, misuse, of these projects that result in the direct or indirect damage or loss that comes from these projects. All materials are provided for free private and public use. Commercial use prohibited without prior written permission from Ian C. Purdie.