Re: ISB Receivers
The Redifon R550 and R551 were mentioned upthread as perhaps marking a convergence point in HF receivers, in that they covered general-purpose HF, marine HF and ISB applications. In the marine case the R551 was qualified against the then recently updated marine specifications for general-purpose and SSB receivers. Some additional information is provided in the attached WW items.
Before the R550/R551 though, there was the R408 of 1965, which appeared to cover all the bases, including ISB, and was qualified as a marine main receiver. I understand that it was also requalified as a marine SSB receiver when the marine SSB specifications arrived. And I have read somewhere that Marconi/MIMCO used it as a stopgap SSB main receiver when its own Apollo design was running late. The R408 was all solid-state, presumably mostly using germanium transistors.
Anyway, the marine world was using ISB/SSB for ancillary purposes for about two decades before SSB became the norm for “official” R/T communications. And as a result, nominally land-based receivers such as the Racal RA17 and Marconi HR22 were found in shipboard installations, alongside qualified marine receivers.
Cheers,
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