Re: Origin of terms "Roofing filter" and "Reciprocal mixing"
In ‘Technical Topics’ for 1966 July, Pat Hawker included the comment:
“Although it is not our intention to draw paper comparisons, it may be noted that the direct single conversion to a fixed first i.f. used in the PR155 and the RC410R allows a preliminary crystal filter to be inserted immediately following the first mixer which in the PR155 is of the balanced ring type.
This was part of an item looking at transistor HF receivers generally, and the GEC RC410R, Plessey PR155 and Racal RA217 in particular.
His use of the term “preliminary crystal filter” for what were in fact roofing filters suggests that at the time, the author was not aware of the term “roofing filter”, and given how widely he read the available technical literature, one may infer that if it were in use at all back then, it still had limited circulation.
Cheers,
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