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Synchrodyne · 4th Feb 2014, 4:13 am

What happened, in a general sense, with point-to-point ISB receivers following the general industry transition from valves to solid state devices?

In the valve era, ISB receivers appeared to have formed a well-defined subgroup amongst HF receivers generally, largely based upon precepts developed back in the 1930s. The attached block schematic of what I assume to be a Marconi receiver is I think representative. These receivers had three final IF channels, often at 100 kHz, one each for the upper sideband, lower sideband and the carrier, the transmissions at interest being of the reduced carrier type, not the fully suppressed carrier type. The carrier channel had a very narrow filter, typically 60 Hz, and fed the agc and afc circuitry, and via a limiter provided the “local” carrier for individual sideband product demodulation. The sideband filters were 100 to 3500 Hz or 100 to 6000 kHz, the first catering for voice traffic and the latter for broadcast relay traffic, or a pair of multiplexed voice channels. I should assume that the 100 Hz lower limit was derived from broadcast relay requirements, as 300 Hz would have been adequate for voice.

Such ISB receivers were also used for HF AM reception for broadcast relay purposes, given their ability to minimize selective fading distortion, this benefit derived from their use of product (quasi-synchronous or homodyne) demodulators. In fact some receivers of this type, such as the Marconi HR22 (discussed recently in this thread: https://www.vintage-radio.net/forum/...d.php?t=101833) seem to be been designed primarily for this purpose. ISB receivers could also be used for the reception of suppressed carrier SSB transmissions, although this was not their primary mission.

Comparable solid state dedicated ISB receivers seem to have been very scarce though, or at least not well-publicized in the usual places. One example from the late 1960s was the Marconi Hydrus, which does seem to have been a solid state successor to its previous valve models. Information on this is very scarce. Apart from the attached Wireless World advertisement, I have been able to ascertain that it was triple conversion, with IFs of 40 MHz, 5 MHz and 100 kHz, and that it might have been of the Wadley loop form.

Was it the case that dedicated ISB receivers were overtaken to some extent by a new generation of highly stable solid state general coverage receivers that had add-on or optional ISB facilities? The Eddystone EC958/12 was such an example, developed from the original EC958. The separate ISB section had the customary three 100 kHz IF channels, but in this case the recovered carrier was used to synchronize a PLL, thus sideband demodulation was fully synchronous. I am not sure what sideband filters were available, but voice bandwidth (300 to 3400 Hz) might have been the norm. The epoch-marking Racal RA1772 also had an ISB option, basically adding a second IF strip and product demodulator, and also an AFC option, which added a carrier IF and effectively locked the demodulator BFO to the incoming carrier on reduced carrier SSB and ISB transmissions.

That there was an ongoing need for the ISB-type receiver in the 1970s was apparent for example from BBC Engineering #84, 1970 October (http://downloads.bbc.co.uk/rd/pubs/a...neering_84.pdf) which notes that the BBC was expanding the use of HF SSB program links, having started in 1964, with use of ISB receivers for HF AM reception predating that. The BBC used a bandwidth of 90 to 6000 Hz.

So I am curious as to whether the Marconi Hydrus was a rare species, or whether there were other solid-state point-to-point ISB receivers that were distinct from the HF general coverage type.

The attached Marconi valve ISB receiver block schematic was taken from Radio & Television Engineers’ Reference Book, 3rd Edition. The model is not identified, but it might be or be close to the HR24.

Marconi evidently also supplied marine-oriented ISB receivers, as shown by the block schematic taken from Danielson & Mayoh, “Marine Radio Manual”.

Mullard also made a point-to-point ISB receiver in the 1950s, the GFR.552, per the attached Wireless World items.

The Marconi Hydrus advertisement notes that this receiver used field effect transistors. Given that it is from about the same period as the Eddystone EC958, that is not surprising, and being from Marconi, and in any event predating the era of bullet-proof high-level 1st mixers, I am guessing that it had reasonably good pre-mixer selectivity. Notwithstanding its significance in the ISB world, whatever that may be, it is also relevant to the current more general, although FET-oriented transition era thread: https://www.vintage-radio.net/forum/...ad.php?t=98398.

Cheers,

4th Feb 2014, 4:13 am	#1
Synchrodyne Nonode Join Date: Jan 2009 Location: Papamoa Beach, Bay of Plenty, New Zealand Posts: 2,944	ISB Receivers What happened, in a general sense, with point-to-point ISB receivers following the general industry transition from valves to solid state devices? In the valve era, ISB receivers appeared to have formed a well-defined subgroup amongst HF receivers generally, largely based upon precepts developed back in the 1930s. The attached block schematic of what I assume to be a Marconi receiver is I think representative. These receivers had three final IF channels, often at 100 kHz, one each for the upper sideband, lower sideband and the carrier, the transmissions at interest being of the reduced carrier type, not the fully suppressed carrier type. The carrier channel had a very narrow filter, typically 60 Hz, and fed the agc and afc circuitry, and via a limiter provided the “local” carrier for individual sideband product demodulation. The sideband filters were 100 to 3500 Hz or 100 to 6000 kHz, the first catering for voice traffic and the latter for broadcast relay traffic, or a pair of multiplexed voice channels. I should assume that the 100 Hz lower limit was derived from broadcast relay requirements, as 300 Hz would have been adequate for voice. Such ISB receivers were also used for HF AM reception for broadcast relay purposes, given their ability to minimize selective fading distortion, this benefit derived from their use of product (quasi-synchronous or homodyne) demodulators. In fact some receivers of this type, such as the Marconi HR22 (discussed recently in this thread: https://www.vintage-radio.net/forum/...d.php?t=101833) seem to be been designed primarily for this purpose. ISB receivers could also be used for the reception of suppressed carrier SSB transmissions, although this was not their primary mission. Comparable solid state dedicated ISB receivers seem to have been very scarce though, or at least not well-publicized in the usual places. One example from the late 1960s was the Marconi Hydrus, which does seem to have been a solid state successor to its previous valve models. Information on this is very scarce. Apart from the attached Wireless World advertisement, I have been able to ascertain that it was triple conversion, with IFs of 40 MHz, 5 MHz and 100 kHz, and that it might have been of the Wadley loop form. Was it the case that dedicated ISB receivers were overtaken to some extent by a new generation of highly stable solid state general coverage receivers that had add-on or optional ISB facilities? The Eddystone EC958/12 was such an example, developed from the original EC958. The separate ISB section had the customary three 100 kHz IF channels, but in this case the recovered carrier was used to synchronize a PLL, thus sideband demodulation was fully synchronous. I am not sure what sideband filters were available, but voice bandwidth (300 to 3400 Hz) might have been the norm. The epoch-marking Racal RA1772 also had an ISB option, basically adding a second IF strip and product demodulator, and also an AFC option, which added a carrier IF and effectively locked the demodulator BFO to the incoming carrier on reduced carrier SSB and ISB transmissions. That there was an ongoing need for the ISB-type receiver in the 1970s was apparent for example from BBC Engineering #84, 1970 October (http://downloads.bbc.co.uk/rd/pubs/a...neering_84.pdf) which notes that the BBC was expanding the use of HF SSB program links, having started in 1964, with use of ISB receivers for HF AM reception predating that. The BBC used a bandwidth of 90 to 6000 Hz. So I am curious as to whether the Marconi Hydrus was a rare species, or whether there were other solid-state point-to-point ISB receivers that were distinct from the HF general coverage type. The attached Marconi valve ISB receiver block schematic was taken from Radio & Television Engineers’ Reference Book, 3rd Edition. The model is not identified, but it might be or be close to the HR24. Marconi evidently also supplied marine-oriented ISB receivers, as shown by the block schematic taken from Danielson & Mayoh, “Marine Radio Manual”. Mullard also made a point-to-point ISB receiver in the 1950s, the GFR.552, per the attached Wireless World items. The Marconi Hydrus advertisement notes that this receiver used field effect transistors. Given that it is from about the same period as the Eddystone EC958, that is not surprising, and being from Marconi, and in any event predating the era of bullet-proof high-level 1st mixers, I am guessing that it had reasonably good pre-mixer selectivity. Notwithstanding its significance in the ISB world, whatever that may be, it is also relevant to the current more general, although FET-oriented transition era thread: https://www.vintage-radio.net/forum/...ad.php?t=98398. Cheers, Attached Thumbnails