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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