[John KC0G]

I am curious to know the origins of these terms. The earliest references which I have seen are in an article (1970) and paper (1971) by B.M. Sosin of Marconi Communications Systems Ltd. They were motivated by the introduction of the H2900 series of receivers.

The article was: B.M. Sosin, "A breakthrough in h.f. receiver design", Point-to-Point Communication, January 1970, pp 4-14. On p.11, it states "In the second conversion, the frequency is changed down to 30MHz and a narrow band 'roofing' crystal filter is used. (The term 'roofing filter' is applied to a filter of narrow bandwidth, at an early stage in the receiver, to give protection against adjacent frequency interference)."

Pat Hawker, G3VA, referenced this paper and the term "roofing filter" in his Technical Topics column the RSGB's Radio Communication, February 1970, p. 92. He used a similar description is his June 1970 article in Wireless World on communications receivers.

The paper was: B.M. Sosin, "H.F. Communication Receiver Performance Requirements and Realization", The Radio and Electronic Engineer, Vol. 41, No. 7, July 1971, pp 321-329. This paper was in two main parts the first covering "Performance Considerations", and the second the "H2900 Solid State Receiver" The latter part referenced the earlier article. On p. 323 Sosin stated: "Only recently has a phenomena called 'reciprocal mixing' been appreciated.

This paper was presented at a meeting of the I.E.R.E. Communications Group in London on 7th October 1970. Pat Hawker was present and commented upon it in the RSGB's Radio Communication, January 1971, p 27, stating that it was the first time that he had heard the term (reciprocal mixing).

If any of you know earlier use or references to these terms, I would like to hear of them

Thanks and 73

John