[Elecraft] 8 pole vs 5 pole..I knew this would happen

[Geoffrey Mackenzie-Kennedy]

Just cannot resist saying this Jack, the term "roofing filter" has certainly 
been around for a long time - close to 50 years I believe, possibly longer. 
I think that I first ran across the term being used to identify the first IF 
filter in an Independent Sideband Receiver which the company for whom I 
worked manufactured for HF Point-to-Point applications in the very late 
1950's, along with companion high power ISB transmitters.

Perhaps some other term might be less confusing and prevent any misuse of 
the term , but don't let us change from "roofing filter" now!!

73,
Geoff
GM4ESD

Jack Smith wrote:


> 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.