Thread: ISB Receivers
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Old 20th May 2014, 5:05 am   #12
Synchrodyne
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Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: ISB Receivers

The Redifon R550 series might have been a better and earlier nodal point in the commercial HF receiver “convergence” than the Marconi H2900.

I think that it dated from 1969. The R550 was the base model for point-to-point use, etc. The R551 was the marine version, qualified as a marine SSB main receiver. There was an optional ISB unit available for. So Redifon was covering most of the bases with one design; commercial point-to-point, all modes, and merchant marine SSB (and ISB if required). Quite possibly it also offered an R550 variant for aviation use, base stations at least.

It would seem that Redifon had taken a bigger step at the beginning of the marine SSB era than had Marconi Marine with its Apollo. Whereas the later more-or-less followed traditional HF receiver layout, the R550 series was of the synthesized upconversion form. The R550 series also seems to have been an early example of a commercial HF receiver that used a 1.4 MHz final IF, a number later made well-known by the Racal RA1772 of 1974, and subsequently used by others.

Meanwhile I have not succeeded in finding any material information on the Marconi Hydrus, which with looks to have been an interesting transitional design, both looking back to the large dedicated three-channel valve-era ISB receivers and looking forward to the more compact solid state multipurpose designs. With a 40 MHz 1st IF it was at least upconversion, and one uncorroborated reference suggests that it was of Wadley Loop form. I have a suspicion that the H2900, which was a couple of years later than the Hydrus, might have been the first synthesized receiver from any Marconi division.

Does anyone know what kinds of ISB receivers were used by the BBC World Service for broadcast relay purposes, both from HF broadcasts per se and in the 1970s, from its own ISB relay transmitters? I should guess that in the valve era that it might have used receivers such as the Marconi HR21 and the Mullard GFR.552, and possibly even the “small” Marconi HR22. But it seems likely that in the 1970s it would have acquired solid state ISB receiving equipment as well.

Cheers,
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