That paper explains why Elecraft has begun to call it "roofing" when it is not what most designers think of when they speak of a "roofing filter".
Call it what you want, the primary function of the first I.F. crystal filter in the K3 is selectivity. The term "roofing filter" came into use when receiver designers started up-converting to a first I.F. in the VHF range. There are no practical narrow filters at those frequencies but it was necessary to filter out mixing products far from the desired frequency, so very wide (several kHz wide) filters were used to define the general range to be further processed. That filter set the "roof" on the frequency range of interest as David noted earlier in his post. The VHF I.F. was then down-converted to a lower frequency were selectivity was taken with narrow filters. The K3 does not use this scheme but early on many people who did not understand the origin of "roofing filter" were confused, so Wayne has written that paper and added "roofing filter" in parenthesis in places in the Owner's manual to help those people understand. It appears the meaning of "roofing filter" is becoming lost through careless use. It won't be the first time - or the last time - that happens. Ron AC7AC -----Original Message----- Yes, they do. Elecraft presents it's position on the term "Roofing Filter" here: http://www.elecraft.com/K3/Roofing_Filters.htm where the "protective" function is emphasized. Bob NW8L On Thu, Oct 28, 2010 at 5:37 PM, Wes Stewart <n...@yahoo.com> wrote: > Unfortunately, they do. Personally I dislike the term. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
