Re: ISB Receivers
This is my first post, and having followed this topic for most of the last 7 years I have to say that the quality of the discussion is superb.
I possess none of the receivers under discussion (although a Marconi ICS3 is winging its way as I write!) but I do have a H1541 drive, which has the same architecture as the H2540 receiver, ie a narrowband IF of 68.6Mhz and a second IF of 1.4Mhz.
For the later H2550 receiver again a similar structure is used, but with figures of 62.5MHz and 2.5MHz respectively.
From the earlier period, the ICS3 and H2900 have identical architectures, and probably at least similar circuitry. In fact, I suspect that the H2900 did indeed turn out to be a "concept" design, produced in very limited numbers, but probably sporned the slightly later ICS3, which was produced in relatively large (for Marconi) numbers.
But talk of architectures ignores the important related topics of mechanical construction and intended market. Take for example the H2540 and H2550. Assuming the former construction is similar to the related drive, it is quite clear that the H2540 is intended for a fixed location only, whilst the H2550 has a much more rugged construction, suitable for the shock and vibration environment of shipborne operation. I have only seem rather poor photographs of the H2900. but again I would say it is designed for a fixed location, whilst the ICS3 was widely used by the Royal Navy and US Navy
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