Re: ISB Receivers
I have also found a bit more on the Marconi Hydrus point-to-point ISB receiver, attached. I have the impression that Marconi saw it as a much more compact, solid-state successor to its previous HR21/23/24 models. Possibly, in single-unit form, it also succeeded the “small” HR22. It was about 3 years or so ahead of the Apollo and Nebula SSB marine main receivers. The Nebula was a rebadged Eddystone EC958/5. Whereas the Apollo was essentially a marine receiver, the EC958 was multipurpose, and was issued in an ISB version, namely the EC958/12, in 1974. One may visualize that it provided a lower cost option than the simplest Hydrus installation.
Cheers,
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