Hi Carl,
That is a pretty broad definition. Every filter in my receiver from the
frontend bandpass filters to the first IF and second IF filters limit
bandwidth before the final audio filtering. So there is virtually no
filter, by that definition, that is not a roofing filter. I'm not
intending to be argumentative. I am just trying to find out what people
really mean by the term "roofing filter". I suspect that without a clear
definition, the term is being used slightly differently by every one who
uses it.
It seems that most of the time people are referring to a filter after
the first mixer (regardless of whether it is a up conversion to a higher
frequency IF or to a mid HF IF). Yet the term may also apply to narrow
tuning range (typically QRP rig) receivers that have a crystal filter
before any mixer stage. I have not heard anyone call an LC BPF a roofing
filter. So does it have to be a crystal filter to be "roofing"?
N6KB
Carl Moreschi wrote:
The term roofing filter means a filter that limits bandwidth before the
final stage of filtering. Because of this, roofing filters do not have to
have sharp shape factors.
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