Talk:Prototype filter

clarification for us hams
this fomula is not really clear to me, as to how it is implemented.

$$i \omega \to \left( \frac{\omega_c'}{\omega_c}\right) i \omega $$

Maybe you mean

$$i \omega _n  =\left( \frac{\omega_c'}{\omega_c}\right) i \omega _o$$

where the o is the old value and the n is the new value?

Is this how it is used? An example of the use of each formula would be nice, or at least an example of the first few formulas.... Baruchatta (talk) 15:57, 17 November 2009 (UTC)


 * Agreed. I assume that "i" is the imaginary number described in https://en.wikipedia.org/wiki/Imaginary_number, and thus just a book-keeping notation, and I similarly assume that "w" is either a generic placeholder (in which case I question why the common "x" wasn't used instead) or denotes a frequency in radians, but none of these things are actually mentioned. The article is fairly nice, but it's internal notation is insufficiently documented. 2602:301:7764:AC00:2107:543D:AD78:5200 (talk) 07:31, 30 March 2022 (UTC)


 * The symbol $$\omega$$ is a lowercase omega, not a w. This is the usual, widely used, symbol for angular frequency and is defined as such earlier in the page, but admittedly only with respect to a specific frequency with a subscript.  It is written in that form because the transfer functions of passive filters are always a rational function of $$i \omega$$.  Now the $$i$$ can be cancelled out in this case, but it can't in the more complex transformations discussed later in the article so I left it in for consistency.  The transfomation is applied by replacing $$i \omega$$ with the transform everywher it appears in the transfer function.  Likewise, the components of the filter can be determined by making the same transformation to the expression for the impedance of the component. SpinningSpark 08:40, 30 March 2022 (UTC)