Hi Ken,
Maybe it would be helpful if the "origin" of the term could be
identified.
Bob W7WO
On May 31, 2006, at 1:23 PM, Ken Brown wrote:
> I have received quite a few responses to my request for a clear
> definition of the term "roofing filter". Most of the respondents
> seem to
> think that they know exactly what a roofing filter is, yet they don't
> all agree exactly with each other. The best (in my opinion) and most
> thorough response was from Bill W4ZV, who also included some reference
> links.
>
> I got a chuckle from the opening sentence of one link, from Inrad: "
> "roofing filter" is the current buzzword in high-end radios. "
>
> I agree with that, though there is no doubt that a better first IF
> filter can make a big improvement in receiver performance.
>
> The way the term is being used in some advertisements sort of
> reminds me
> of "Solid State", "Transistorized", and "Digital". And remember
> "Color"
> TV antennas?
>
> Most everyone agrees that (lately) a roofing filter is the first
> bandpass filter after the first mixer in a superheterodyne receiver.
> (Once upon a time a roofing filter was a lowpass filter, not
> necessarily
> in the IF of a receiver.) There is some consensus that a roofing
> filter
> is not the narrowest or final filter (or filtering process in the case
> of a DSP receiver) in the IF. Perhaps the later, narrower filters are
> "ceiling filters." It seems that we have always had roofing
> filters, we
> just didn't call them that until a few years ago.
>
> There is also an implication that a roofing filter must be a crystal
> filter with a fairly narrow bandwidth, on the order of a few times
> the
> bandwidth needed for the mode of operation. I have not yet heard
> anyone
> refer to an LC BPF or IF transformer as a "roofing filter". Or perhaps
> the first filter after the mixer is always a roofing filter,
> regardless
> of type, or bandwidth?
>
> Is the first IF transformer in my Hammarlund Super-Pro a roofing
> filter?
>
> DE N6KB
>
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