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Synchrodyne · 24th Apr 2016, 7:12 am

John, that’s certainly an impressive reading list!

I have a small number of the items listed, including the WW items and the Mellor & Sutton and Sutton Eddystone papers. I don’t have the Ford Eddystone paper, but the original EC958 development is also covered in “The Cooke Report”. I don’t have the infamous Sosin article, but I do have the review of it by Michael O’Beirne in Radio Bygones #87. Pat Hawker’s “Technical Topics” is still available and I have ordered a set. I suspect that “Point-to-Point Communications” would be hard to find in these parts.

The Marconi H2900 is certainly difficult to categorize, and does look more like a “concept” or “technology demonstration” unit. Hawker, in his WW 1970 communications receiver survey, said that the H2900 had synchronous demodulation (WW 1970 June p.260). The block schematic shown in Short Wave Magazine 1970 April shows filter separation of the sidebands and carrier, but not the origin of the demodulating 2 MHz carrier. That suggests that its origins were complex than simply limiting the output of the carrier filter and amplifier, which would have been easy to show on a basic diagram.

The above-mentioned O’Beirne article includes the relative price comparisons. One might say that Marconi seemed to have miscued on the Apollo SSB marine receiver, with a relative price of 2.5 as compared with the 1.9 of the Redifon R551. Thus it can be seen why it also offered the Nebula (Eddystone EC958/5), which I’d expect to be no more costly than the H2311, with a relative price of 1.8, and which was essentially the Eddystone EC958/7, the improved version of the EC958.

Where the R550 with the ISB option of the EC958/12 (ISB version of the EC958/7) would fit is hard to say, but perhaps in the 2.5-to-3.0 range. Then the Hydrus, at 3.8, looks logical as an economical purpose-designed point-to-point ISB receiver, more costly than optioned or “added-on to” communications receivers but well below the traditional “full works” models. I suspect that Redifon, Eddystone and others were probably not expecting more than a small proportion of their HF receivers to be specified with the ISB option, hence the “add-on” approach, albeit with designed-in capability rather than as an afterthought, but it was nevertheless worth doing.

In fact the “add-on” approach to SSB and ISB seems to go back quite a way, to the late 1940s GE YRS-1 at least. Racal had several SSB and ISB adaptors, including at least one, the RA98, with motor-driven AFC.

Peter, thanks for the detail on the Redifon R408 variable bandwidth system. I imagine that tuning two sets of LC IF filters over a small range whilst preserving their shape and symmetry could have been easier than varying the bandwidth of similar filters over quite a wide range.

Cheers,

24th Apr 2016, 7:12 am	#44
Synchrodyne Nonode Join Date: Jan 2009 Location: Papamoa Beach, Bay of Plenty, New Zealand Posts: 2,944	Re: ISB Receivers John, that’s certainly an impressive reading list! I have a small number of the items listed, including the WW items and the Mellor & Sutton and Sutton Eddystone papers. I don’t have the Ford Eddystone paper, but the original EC958 development is also covered in “The Cooke Report”. I don’t have the infamous Sosin article, but I do have the review of it by Michael O’Beirne in Radio Bygones #87. Pat Hawker’s “Technical Topics” is still available and I have ordered a set. I suspect that “Point-to-Point Communications” would be hard to find in these parts. The Marconi H2900 is certainly difficult to categorize, and does look more like a “concept” or “technology demonstration” unit. Hawker, in his WW 1970 communications receiver survey, said that the H2900 had synchronous demodulation (WW 1970 June p.260). The block schematic shown in Short Wave Magazine 1970 April shows filter separation of the sidebands and carrier, but not the origin of the demodulating 2 MHz carrier. That suggests that its origins were complex than simply limiting the output of the carrier filter and amplifier, which would have been easy to show on a basic diagram. The above-mentioned O’Beirne article includes the relative price comparisons. One might say that Marconi seemed to have miscued on the Apollo SSB marine receiver, with a relative price of 2.5 as compared with the 1.9 of the Redifon R551. Thus it can be seen why it also offered the Nebula (Eddystone EC958/5), which I’d expect to be no more costly than the H2311, with a relative price of 1.8, and which was essentially the Eddystone EC958/7, the improved version of the EC958. Where the R550 with the ISB option of the EC958/12 (ISB version of the EC958/7) would fit is hard to say, but perhaps in the 2.5-to-3.0 range. Then the Hydrus, at 3.8, looks logical as an economical purpose-designed point-to-point ISB receiver, more costly than optioned or “added-on to” communications receivers but well below the traditional “full works” models. I suspect that Redifon, Eddystone and others were probably not expecting more than a small proportion of their HF receivers to be specified with the ISB option, hence the “add-on” approach, albeit with designed-in capability rather than as an afterthought, but it was nevertheless worth doing. In fact the “add-on” approach to SSB and ISB seems to go back quite a way, to the late 1940s GE YRS-1 at least. Racal had several SSB and ISB adaptors, including at least one, the RA98, with motor-driven AFC. Peter, thanks for the detail on the Redifon R408 variable bandwidth system. I imagine that tuning two sets of LC IF filters over a small range whilst preserving their shape and symmetry could have been easier than varying the bandwidth of similar filters over quite a wide range. Cheers,