Re: 8 pole vs 5 pole..I knew this would happen

Posted by Jack Smith-6 on May 03, 2007; 6:07pm
URL: http://elecraft.85.s1.nabble.com/8-pole-vs-5-pole-I-knew-this-would-happen-tp446796p446797.html

The term "roofing filter" has been around a long time, at least 20 years.

Usually used in the context of up-converting  receivers, where the first
IF is 40.455 MHz, or 45.000 MHz or even higher. The term means the first
selective filter in the receiver. If the first IF is > 30 MHz, the
roofing filter is generally wider than one normally needs for SSB or
even AM, and the receiver's ultimate selectivity is provided in a later
IF stage.

As to why it is called a "roofing" filter, I imagine it derives from the
fact that it puts a "roof" over the receiver's selectivity.


Jack K8ZOA


Fred (FL) wrote:

> I think, still, someone needs to define what a ROOFING
> FILTER is.   Say for sake of argument - I have a
> passive or active or crystal filter - and it is to
> be used as a ROOFING FILTER.   Why is it called this?
>
> Why is the filter itself, called a ROOFING FILTER?
> And where does the adjective, ROOFING, come into
> play?
>
> ...... I'm sure I'm dumb on this one - but would
> like to learn.  Not until the K3 came on the
> Elecraft scene - did anyone mention or get
> concerned about the need for ROOFING FILTERS.
> Now they're all the rage?
>
> Fred, N3CSY
>
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