Hi Keith,
I first ran across the term "roofing filter" in the 1960's, whilst working
for Racal. Roofing filters have always been used in analogue up-converting
superhet receivers.
Here is an example of a mid-1990's Rockwell-Collins hybrid DSP receiver
design. Note the single 16kHz roofing filter, sufficiently wide to pass
multi-channel ISB and high-speed crypto.
http://www.ab4oj.com/icom/dsprcvr.html
Cheers for now, 73,
Adam VA7OJ/AB4OJ
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