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.
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