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Old 10th Apr 2016, 7:19 am   #21
Radio Wrangler
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Default Re: ISB Receivers

STC also had links to ITT Mackay, of course.

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Old 12th Apr 2016, 4:48 am   #22
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Default Re: ISB Receivers

I’m not sure though how much interplay there was between STC and ITT Mackay when it came to the design of HF equipment. IMR was STC's subsidiary involved in the marine radio business. Its post-WWII marine main receiver, the IMR54, was designed by Eddystone, who also built the first run. Yet one imagines that there would have been suitable ITT Mackay models available, as marine receivers were core business for Mackay.

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Old 12th Apr 2016, 5:47 am   #23
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Default Re: ISB Receivers

The Redifon R550 and R551 were mentioned upthread as perhaps marking a convergence point in HF receivers, in that they covered general-purpose HF, marine HF and ISB applications. In the marine case the R551 was qualified against the then recently updated marine specifications for general-purpose and SSB receivers. Some additional information is provided in the attached WW items.

Before the R550/R551 though, there was the R408 of 1965, which appeared to cover all the bases, including ISB, and was qualified as a marine main receiver. I understand that it was also requalified as a marine SSB receiver when the marine SSB specifications arrived. And I have read somewhere that Marconi/MIMCO used it as a stopgap SSB main receiver when its own Apollo design was running late. The R408 was all solid-state, presumably mostly using germanium transistors.

Anyway, the marine world was using ISB/SSB for ancillary purposes for about two decades before SSB became the norm for “official” R/T communications. And as a result, nominally land-based receivers such as the Racal RA17 and Marconi HR22 were found in shipboard installations, alongside qualified marine receivers.

Cheers,
Attached Files
File Type: pdf WW 196903 p.136,137 Redifon R550.pdf (1.26 MB, 299 views)
File Type: pdf WW 197001 p.41 Redifon R551.pdf (1.34 MB, 207 views)
File Type: pdf WW 196510 p.526 Redifon R408.pdf (418.9 KB, 151 views)
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Old 12th Apr 2016, 6:50 am   #24
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Default Re: ISB Receivers

There's about as much work in getting a piece of radio equipment qualified as there is in developing the thing in the first place (I've spent the last ten years designing radio/radar gear that has to go through full qualification for certified aircraft) What used to make it worse was that until very recently different parts of the world had different formal requirements or sometimes the tests just had to be done different ways, so the qualifications tests and all the attendant paperwork had to be done multiple times. Of course, planes and ships bearing radio gear certified by one country often went into the territory of another, so everything had to interoperate, so the standards were really close equivalents. It's just taken a while for them to team up and start writing coordinated standards requirements. Some of the old standards haven't yet been harmonised completely. Yesterday I was checking a transmitter into 3:1 VSWR mismatches of swept phase angle, but the American standard meant I had to do it all over again into 2:1 VSWR, but with a different power reduction limit...

The marine main receiver qualification was a serious hurdle, but it was proof of some qualitues. Some other receivers would have passed without modification, but the manufacturers were concentrating on other markets and did not see al the hoop-jumping as profitable. Some receivers simply were not good enough in one or more performance areas. The RA17 would have not met the filter template requirements and would have had trouble with the intermod tests.

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Old 12th Apr 2016, 4:30 pm   #25
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Default Re: ISB Receivers

Just a note regarding the Redifon R408 Receiver.
I don't believe this receiver had an ISB capability as it was really a dedicated Ship's Main Receiver - though many did find their way into non-marine applications I think. Though SSB capability had been introduced as a mandatory requirement for larger vessels, the bulk of marine radio traffic was still handled using CW at this stage.
In addition to Marconi Marine, the receiver was also sold by Hagenuk of Germany - badged Hagenuk - and found its way into many other marine radio installations by a variety of companies.
The receiver uses primarily silicon transistors - the first Redifon solid state receiver to do so - and was streets ahead of rivals such as the Racal RA217 which used Germanium devices. It also featured variable IF bandwidth - based on the "sliding doors" arrangement - which was very popular with operators and is very pleasant to use.
The receiver was very successful, particularly in the marine market where it became the de facto standard in Europe. It is surprising that so few seem to have survived into private hands.
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Old 12th Apr 2016, 5:55 pm   #26
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Default Re: ISB Receivers

I've never seen a redifon 408 in the flesh.

It featured heavily on the cover of the first ever Wireless World I bought. "The Fabulous 408" cried the headline. I'd never come actoss WW before and it was a revelation. I spotted it on the magazine rack at Ryans newsagents, Byram st, Huddersfield, caught the bus home and attacked my piggy bank, and got an advance on the next weeks pocket money. I read the print off that magazine!

But in all the years since and many many amateur radio rallies, I've never seen one. Tons of RA17 family members, R390A, no bother, but never that Redifon I'd memorised.

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Old 12th Apr 2016, 6:23 pm   #27
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Default Re: ISB Receivers

I think I'd heard that commercial marine equipment was often effectively leased and had to be either destroyed when the vessel was scrapped or returned to the lessor- where the same fate was likely to ensue, as the supplying manufacturer was keen on keeping the flow of new kit going. Shame, as some rather good stuff must have been trashed.

Maybe I've mis-understood, or been told a tall tale, but the low survival rate would give credibilty. Military stuff was presumably effectively an outright purchase, so seemingly there was less incentive for a tightly accounting mechanism and a little of it came back to those who had coughed up the money in the first place....
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Old 12th Apr 2016, 11:57 pm   #28
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Default Re: ISB Receivers

The Redifon R408 must have been an early example of a receiver using mostly silicon transistors. As far as I know, the Ge-to-Si move started in earnest around 1966-67.

The Wireless World write-up on the R408 said: “The modes of operation include a.m., c.w., s.s.b. (pilot or suppressed carrier) and i.s.b. (switch selection of upper or lower sidebands).”

Whilst I initially interpreted that as having full ISB capability, upon reflection a better “translation” would be that its SSB capability allowed it to receiver either sideband of an ISB transmission, but not both simultaneously. One cannot be sure, but the way its SSB capability was described, it was able to make use of the pilot carrier when it was transmitted, rather than simply treating a pilot carrier transmission the same way as a suppressed carrier transmission.

Regarding the maritime mobile HF and MF R/T transition from AM to SSB, this was mentioned in an item in WW 1968 January, attached. But this would have referred to a mandatory change; presumably before then vessels were free to use SSB to the extent that shore stations could accommodate it.

Here is an ISB question though: when vessels used ISB for ancillary purposes, such as passenger telephone calls, did they use frequencies within the marine HF bands, or within the bands assigned for point-to-point communications? I suppose that may have depended upon the nature of the land-based station with which they connected. On the other hand, presumably transmission within the marine bands would have been limited to approved transmitter types, which could well have excluded the typical shipboard ISB equipment in the 1950s and 1960s.

Quote:
Originally Posted by Radio Wrangler View Post
The marine main receiver qualification was a serious hurdle, but it was proof of some qualities. Some other receivers would have passed without modification, but the manufacturers were concentrating on other markets and did not see al the hoop-jumping as profitable. Some receivers simply were not good enough in one or more performance areas. The RA17 would have not met the filter template requirements and would have had trouble with the intermod tests.
I have the impression that front-end selectivity may have been an issue for marine receiver qualification, and perhaps that was why in part at least Marconi with its Apollo and Eddystone with its EC958 chose traditional topologies with narrow-band tracking RF filters and lowish 1st IFs even when practice at the time was moving towards upconversion. Even then, the marine version of the EC958, the EC958/5 (Marconi Nebula) required a bandpass tuned input down to 54 kHz in order to pass the qualification tests, whereas the standard version was bandpass above 1.6 MHz, but single-tuned below. The Redifon R550/551 was upconversion with sub-octave filters, but with a wideband RF agc system operating a diode attenuator ahead of the push-pull amplifier with CATV transistors.

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File Type: pdf WW 196801 p.638 Marine SSB.pdf (710.9 KB, 212 views)
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Old 15th Apr 2016, 9:00 am   #29
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Default Re: ISB Receivers

Hi All,
I think it is correct that the bulk of marine radio equipment was scrapped with the ship or otherwise disposed of by the owner. Very little seems to survive, not just of Redifon but also Marconi, IMR etc. And ex-marine transmitters are a complete blank - too big to carry off the ship I suppose - great shame.
Military equipment - purchased with taxpayer's money - is already the property of the people and I think more generally auctioned off (except where safety/security concerns prevail) to avoid accusations of waste.
I have a Redifon R408 but I had to go to Holland for it. I believe there are a few others in the UK.
I am not sure about the use of ISB in the marine context. If it was used it must have been highly specialised, perhaps limited to a few of the great passenger liners of the day. Redifon sold many ISB capable transmitters but none of the "Marine" range of transmitters was ISB capable, from memory. If certain ships were equipped with ISB for passenger telephone calls it begs the further question of duplex working - not easy on a ship, even a very big one.
I don't recollect ever hearing of any coast station being equipped for ISB telephony - maybe others know more. The norm for passenger phone calls was VHF with the fitting of the "private deck" addition to the standard VHF ship-to-shore transceiver, which provided the additional frequencies and duplex capability to support phone calls. Most coast stations had the capability to link the VHF into the telephone network, I think. This facility obviously depended on being in VHF range of a coast station - once you were out of range then it was "Ship's Telegrams" which were the passenger's means of communication.
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Old 18th Apr 2016, 1:53 am   #30
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Default Re: ISB Receivers

Regarding the marine ISB and SSB before the 1970s, it seems not easy to estimate to what extent it was used.

I suspect that the Caronia installation may have started a trend for ocean-going passenger vessels that were often out of the range of VHF shore stations.

The Canberra was another example. Information here: http://www.seadogs-reunited.com/Canberra%20RR.htm mentions a Marconi NT201 transmitter and HR22 receivers, although the pictures show Racal RA17 receivers, not HR22s. Apparently in its original form, the Canberra had both a W/T room for the regular marine equipment and an R/T room for the ancillary equipment.

And per the attached item, the GPO cable-laying vessel HMTS Monarch was fitted with a Marconi NT201 ISB transmitter and a pair of NT203 wideband amplifiers. But then I guess that it [the Monarch] would have had business communications via the GPO point-to-point stations.

As far as I know the Marconi NT-series was primarily intended for naval applications; I imagine that some navies may have gone over to SSB/ISB before the merchant marine made its change to SSB.

Danielson & Mayoh, in the book “Marine Radio Manual” published in 1966, devoted a short chapter to SSB. They did not say in what situations it was being used, but simply made the general statement that the use of SSB equipment for marine communications was increasing. The worked example on the transmitting side wad said to be based upon a Marconi marine ISB unit. Possibly it was the NT201. The receiver worked example was not ascribed to any specific model, but it was of the ISB type with 2.9 MHz 1st IF, motor-driven AFC, and audio outputs for both sidebands, so it was not the Marconi HR22 for example. Both the transmitter and receiver were shown as having voice bandwidth (0.3 to 3 kHz) filters.

The QE2 was fitted with GPO Lincompex equipment, for which it had GEC RC410R receivers. Presumably Lincompex was used on telephone connections via GPO point-to-point stations, and not when communicating with marine shore stations. Working back from this, one might deduce that previous SSB/ISB installations on passenger vessels were linking with point-to-point stations, and not to marine shore stations.

Cheers,
Attached Thumbnails
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Name:	WW 196102 p.74 RMTS Monarch Marconi NT201.jpg
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Name:	WW 196807 p.204 QE2 Communications.jpg
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Old 18th Apr 2016, 1:56 am   #31
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Default Re: ISB Receivers

I have found a little more information on the Redifon R408, attached. That confirms that it was conceived as a marine HF receiver, but ended up as being suitable for use as a general purpose communications receiver.

The IF bandwidth was continuously variable from ±8 kHz to ±800 Hz, with half that said to be available for SSB operation, either LSB or USB. I’d assume that the basic variation was symmetrical about the final IF of 80 kHz. So in the SSB case, given that it was said that retuning was not needed when switching between sidebands, it looks as if the bandwidth range was either between 800 Hz and 8 kHz below 80 kHz, or 800 Hz to 8 kHz above 80 kHz. That then leads to the question as to was SSB sideband separation done with filters – one each for USB and LSB – that followed the main IF filters, in which case the emphasis would have been on carrier (IF) side cutoff, given that the outer cutoff was done by the main IF filters, or was it done in the AF domain by phase-shifting and matrixing (as I think was developed by Norgaard of GE and first used on the GE YRS-1 SSB adaptor). Whichever way it was done, the write-up included the comment: “In practice, during reception of i.s.b. transmissions containing teleprinter information in one sideband and audio information in the other, use of the sideband switching facility to listen to audio has completely eliminated any break through from the teleprinter intelligence, and vice versa.”
Cheers,
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Name:	WW 196604 p.157 Redifon R408.jpg
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Old 18th Apr 2016, 1:59 am   #32
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Default 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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Name:	WW 196805 p.138 Marconi Hydrus.jpg
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Name:	WW 195406 p.79 Marconi HR21.jpg
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Name:	WW 197112 p.609 Marconi Apollo, Nebula.jpg
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Old 18th Apr 2016, 10:09 am   #33
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Default Re: ISB Receivers

Synchrodyne, I installed and serviced R408s and recall them as only having one audio output from it's single IF. It couldn't do ISB. The bandwidth would go narrower than 1 KHz for CW. The receiver was very sensitive, quiet and repairable.

The R551 could not match it's performance on 500 kHz, but of course was good enough for type approval. I never saw an R551 with ISB capability but don't doubt the sales department brochure would cover all possibilities in the hope of more sales.

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Old 19th Apr 2016, 12:09 pm   #34
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Default Re: ISB Receivers

The Redifon R408 variable IF bandwidth is realised by the use of two 8kHz wide bandpass filters, one with a nominal centre frequency of 76kHz (the lower filter) and one with a nominal centre frequency of 84kHz (the upper filter) Both of these filters have tunable centre frequencies, the lower filter from 76kHz to 80kHz and the upper filter from 84kHz to 80kHz. Tuning is effected by the IF Bandwidth control and which filter moves and by how much is determined by the type of modulation selected.
The overall passband of the 80kHz IF stage is determined by the extent of the overlap of the passbands of the two filters.
So for AM, the lower filter centre frequency is moved up and the upper filter centre frequency is moved down to provide a symmetrical overlap passband.
For SSB, one filter is set to the nominal centre frequency - which puts one edge of the passband at 80kHz and the other filter is tuned to provide overlap. So for USB, the upper filter is set to the nominal centre frequency, such that the lower edge of the passband is at 80kHz, and the lower filter centre frequency is tuned to, say, 79kHz giving a passband overlap from 80kHz to 83khz.
If the sideband selected is now switched to LSB, then the filters are automatically moved so that the lower filter is at the nominal centre frequency, such that the upper edge of the passband is at 80kHz, and the upper filter is moved to a centre frequency of 81kHz giving a passband overlap from 80kHz to 77kHz.
There are no block filters of the type usually associated with true ISB receivers, and as there is only one 80kHz IF filter and one audio chain reception of both sidebands simultaneously is not possible. The wording used in the literature is confusing in this respect.
I think it must be correct that ships equipped for true ISB working for passenger telephone calls must have worked direct to PTT operated land stations rather than conventional coast stations. As far as I am aware, those ships which did have ISB telephony capability also carried a separate, conventional marine radio installation for normal ship's traffic. As to which land stations were used, I await somebody to let us know!
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Old 19th Apr 2016, 4:15 pm   #35
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Default Re: ISB Receivers

Much of the Marconi equipment being discussed in this thread was described in their in-house journal "Point-to-Point Telecommunications", which became "Point-to-Point Communication". Here is a list of references from the period in question, ie ca. 1968 to 1974.

1. P.L. Painter, Hydrus - a new H.F. Receiving Equipment, Point-to-Point Telecommunications, Vol. 12, no. 2, April 1968, pp 82-96

2, R.L.J. Awcock, A. Bell, and J.A. Gould, Naval Communications, Point-to-Point Telecommunications, Vol. 12 no. 4, October 1968, pp 198-212

3. K.A. Barratt, The Design of an M.F. and H.F. S.S.B. Spot-Frequency Receiver for Mercantile Marine Use, Point-to-Point Telecommunications, Vol. 12, no. 4, October 1968, pp 265-264
(Eddystone)

4. D.W. Ford, Solid-state General Purpose Receiver 10kHz to 30MHz, Point-to-Point Telecommunications, Vol. 13 no. 1, January 1969, pp 4-12
(Eddystone EC958 receiver)

5. B.M. Sosin, A Breakthrough in H.F. Receiver Design, Point-to-Point Communication, Vol. 14, no. 1, January 1970, pp 4-14
(H2901 receiver)

6. J.A. Gould, A new 100W Solid-state Transmitter and Receiver, Point-to-Point Communication, Vol. 14, no. 2, April 1970, pp 65-73
(HF1030 "Aries" transmitter, and HF2310 "Argo" receiver)

7. J.V. Beard, A Survey of Communication Receivers, Point-to-Point Communication, Vol. 14, no. 3, August 1970, pp 110-120
(covers H2102 MST, H2002 MST, H2001 Hydrus, H2900 series, EC958 series, H2310 Argo, N2020, N2023)

8. B.M. Sosin, H.F. Receiver Reception Failure Factor, Point-to-Point Communication, Vol. 18, no. 1, January 1974, pp 4-17
(corrected and re-issued as a separate publication, with the same title).

9. C.J. Mellor and R.T. Sutton, Improved General Purpose Communication Receiver, Point-to-Point Communication, Vol. 18, no. 1, January 1974,
(Eddystone EC958/7 receiver)

Pat Hawker, G3VA, often mentioned new professional equipment in his Technical Topics column in the RSGB's magazine, then called "Radio Communication". For example, some relevant items to the present discussions were::
Jan 1968 RA 217 and GEC RC410
Apr 1968 Redifon R499
May 1968 Marconi Hydrus, and references the article by Painter

Jan 1969 RX design, and references the article by Barratt
Feb 1969 Eddystone EC958, and references the article by Ford

Feb 1970 Marconi H2900, and references the article by Sosin

Jan 1971 Sosin and the term "Reciprocal Mixing"

Apr 1974 Sosin's (infamous) article on H.F Receiver Reception Failure Factor
Jun 1974 update on Sosin's article.
Dec 1974 Eddystone EC958/7, and references the article by Mellor and Sutton.

Other useful references are:

Pat Hawker, G3VA, Communications Receivers, Wireless World, June 1970, pp 256-260

Communications Receivers - abridged specifications, Wireless World, June 1970, pp 305-308, 310-311

R.T. Sutton, Eddystone Radio - A Short History of Radio Receiver Developments from 1965-1995, Conference on 100 Years of Radio, 5-7 September 1995, IEE Conference Publication No. 411, pp 134-140

73 John KC0G
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Old 19th Apr 2016, 4:44 pm   #36
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Default Re: ISB Receivers

Superb list!

I remember reading quite a number of them.

And when Marconi withdrew the issue with Sosin's 'regrettable' article, there was a bit of a queue at the library photocopiers before our issue was returned. If they wanted all the copies back there had to be something good in it!

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Old 19th Apr 2016, 5:19 pm   #37
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David, thank you.

Last week I was in Kansas City, Missouri, and spent some time at the Linda Hall Library. It is a privately endowed science and engineering library which is open to the public, with an emphasis on preserving periodicals. Their collections are quite superb. I know of nowhere else like it. It is also a beautiful building with nice lighting too. Their web site is www.lindahall.org

Any way I have copies of the text of both versions of the infamous Sosin article on H.F. receiver reception failure. I intend to compare them word for word.... I think that I know of at least 3 libraries which have the original publication. The Marconi Company was clearly doing some very wishful thinking if they began to think that all the copies would come back.

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Old 19th Apr 2016, 8:11 pm   #38
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Default Re: ISB Receivers

I shall try to fill in a bit of the background to Synchrodyne's queries about the Marconi H2001 Hydrus receiver.. I do not have the main reference, ie
.... P.L. Painter, Hydrus - a new H.F. Receiving Equipment, Point-to-Point Telecommunications, Vol. 12, no. 2, April 1968, pp 82-96
but I do have
....J.V. Beard, A Survey of Communication Receivers, Point-to-Point Communication, Vol. 14, no. 3, August 1970, pp 110-120
(covers H2102 MST, H2002 MST, H2001 Hydrus, H2900 series, EC958 series, H2310 Argo, N2020, N2023)
which helps to place it in context.

The H2102 (MST) receiver was primarily designed for point-to-point communications, including ISB as an option. It used the H1500 frequency synthesizer with 100Hz steps, and could be used with extended or remote control. It took about half of a full height rack. The H2002 (MST) receiver was a double diversity version of the H2102 for FSK operation. It took up about 3/4 of a full height rack.

The H2001 Hydrus receiver was designed to offer similar performance to the MST receivers, but without the remote or extended operation. Also to keep the cost down, the frequency synthesis system operated with 100kHz steps, and used a high-stability L-C oscillator for interpolation. It consisted of four 3U modules, and sat in a rack about 24" high. It could receive ISB, FSK, and voice-frequency tone (VFT) traffic. The article does not list it as being suitable for Piccolo service, or for use on ship-to-shore (naval) circuits. The Royal Navy had specific requirements for equipment to be operable by unskilled personnel, which effectively meant that equipment had to be fully synthesized.

The H2900 series which came later, was shown as being usable for most services including ISB and Piccolo (FSK required adaptors). Pat Hawker, G3VA, (Radio Communication, RSGB, Feb 1970, pp92-93) noted that the frequency synthesizer tuned in 1Hz steps, Interesting the radio was not shown as being appropriate for ship-to-shore (mercantile circuits). Presumably it was too expensive.

The Eddystone EC958 is described. It could not receive any of ISB, FSK, VFT traffic, or Piccolo. It was not suitable for ship-to-shore (naval) circuits. Again I think that it required a skilled operator. The H2310 Argo receiver was an enhanced version of the EC958, with a frequency counter which could then be used to lock the VFO. It is shown as being able to receive VFT traffic. It is also shown as being suitable for ship-to-shore (naval) circuits. Presumably it could be operated more easily.

The NC2020 was designed to meet "stringent naval specifications". It could be directly tuned by setting decade switches, Alll local-oscillator frequencies were generated by a frequency synthesizer. The N2023 was a version which was designed for dual-path diversity reception.

Pat Hawker, G3VA, (Radio Communication, RSGB, May 1968, pp 300-301) briefly mentioned some of the Hydrus circuit features, and noted the extensive use of FET's.

A block diagram of the Hydrus frequency synthesis system is shown in
....V.F. Kroupa, Frequency Synthesis - Theory Design and Applications, Charles Griffin (also published by John Wiley), 1973, pp 253-254, 262 and 158, ie Fig 8-14 and associated text.
Kroupa references [5.12]:
....The Marconi Company, Hydrus HF Receiver, Telecommunications, Vol. 2, July 1968, pp 40-41
There are two-drift-cancelling loops. The auxiliary one mixes the output of the interpolation VFO with one of 10 harmonics from a 100KHz crystal to give an interpolation range of 3 to 2 Mhz. This is then mixed into another drift-cancelling loop where the local oscillator was "tuned" in 1MHz steps. The first two IF frequencies were 39.5 to 40.5Mhz and 5MHz.

I cannot answer the question about how the carrier was extracted for ISB reception on the Hydrus. Somebody needs to turn up a copy of the article by Painter.

73 John KC0G
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Old 19th Apr 2016, 11:17 pm   #39
Radio Wrangler
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Default Re: ISB Receivers

Hi John,

I know Kansas city. We use a lab just to the south of it, to do the FCC testing for our products. It is more economical to use a US lab including air tickets, hotel and hire car than it is to use a European FCC approved lab! Boy it's flat out there - it's flatter than Lincolnshire on the day they ironed it.

I know the Marconi H2900 very well because I was given one of the prototypes about 20 years ago. The SMPS power transistors had been raided, but I used more modern equivalents, and I slowly brought the thing up to functionality. The motorised preselector was going, but getting the synthesiser going reliably was a challenge. I also had all the manuals. Ye gods was that thing heavy!

Anyway, once I'd explored it and tried it, I'd got all the value I could out of it. I have no use for a slow-settling thumbwheel tuned radio, so I passed t on for someone else to have fun with it (Graham Firth of the G-QRP club)

After that, I delved into a GEC RC410.

I spent a lot of years designing very high performance receiver structures, so it's interesting to see how other people did it.

David
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Old 20th Apr 2016, 4:49 am   #40
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Default Re: ISB Receivers

Andrew, Peter and John – thanks very much for the wealth of information, which I’ll take the time to digest before I reply.

Cheers,
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