Re post #116 and the large number of Marconi receivers, this reminds of when I first read the article "Survey of Communications Receivers" by J. V. Beard in Point-to-Point Communication, August 1970, pp 110-120. This article has been mentioned before in this thread. See:
https://themarconifamily.pbworks.com...and%20Journals
I had a feeling that Marconi had deigned and manufactured a bunch of different receivers to meet a bunch of different specifications. As such they were tailored solutions produced by an engineering company. The Racal approach with the RA1772 seems to have been different, ie they made a common platform which met most needs and could take options for special needs. Others may disagree?
@Synchrodyne, re. post #117. I have seen the number of 20,000 before as the number of Racal RA17 receivers which were built. Do you have any sources for this data?
73 John KC0G/M0KCY