# Marconi Marine 1974 GPS receiver



## GilesdeB (Aug 24, 2015)

Does anyone from MIMCO have details of the name or specs of such a receiver, please ?

Whilst training at AWA Marconi School of Wireless in Leichardt, Sydney, NSW we walked into the Morse room in 1974 to find a production receiver being tested for thermal stability. There was a large scale map on the wall and every (6?) hour a reading of lat long was taken and plotted with a pin into the map. Most were bang on, very few out to a quarter-mile. For us trainees - who included an RO who had served as a telegraphist in RAAF planes, then switched to commercial planes, then had to switch to Marine " in the hope it will see me to my pension" - this resulted in a stomach-churning, low-point as we saw that we were obsolete before even obtaining a ticket, let alone serving at sea.

Can anybody recall what this receiver was ? Thank you.


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## Varley (Oct 1, 2006)

Could not have been GPS in 1974. Must have been Transit if satellite but several hyperbolic terrestrial systems were about with makers introducing direct position readings instead of 'scope or 'Decometer' and overprinted charts.

(Loran, Decca, Omega). I first came to Transit on the Texaco Spain in 1975/6. I can't remember who made or what the received=r looked like but the computing was done in the Norcontrol DB4 (as on Texaco London it was carried out by the IBM System 7. On Conoco Europe the receiver was Magnavox and the computing by Honeywell) - if I remember correctly this also took Loran and spat out a lat/long from it. I don't recall MIMCO having a Transit product but I am sure Ron will know.


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## PeterY (Jun 24, 2008)

I worked at Leichhardt AWA deport at the time and the GPS was a Tracor transit GPS receiver.


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## Ron Stringer (Mar 15, 2005)

Marconi Marine did not manufacture any satnav systems. Apart from mf DF receivers the only radio navaid receiver that they designed and manufactured was for the Omega system, marketed as AlphaOmega. 

Clearly since 1974 was several years ahead of the introduction of GPS, if it was a satnav receiver it had to be a Transit satellite system receiver but Marconi Marine marketed several different types over the years (some of them under the maker's name, others were badged as Marconi Marine) but, sorry to say, my memory is not up to recalling them all. Tracor and Magnavox come to mind but little else. I do remember having to wait for long periods between satellite 'passes' to get an update, but not a lot else.


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## trotterdotpom (Apr 29, 2005)

I remember those early Satnav receivers - Tracor rings a bell. They were crap and lulled the mates into a false belief that their sextants, stop watches and logarithms were there to stay. Sadly, it wasn't many years before they were making their calculations agree with the infernal machine. 

John T


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## Searcher2004 (May 3, 2012)

trotterdotpom said:


> I remember those early Satnav receivers - Tracor rings a bell. They were crap and lulled the mates into a false belief that their sextants, stop watches and logarithms were there to stay. Sadly, it wasn't many years before they were making their calculations agree with the infernal machine.
> 
> John T


I worked with the Magnavox 702 Transit system in the mid-70s for positioning oil rigs prior to spudding-in. The receiver, antenna and supporting computer/printer/tape-reader would fill a Sea-King size chopper. The system only gave a fix when the satellite was overhead, the computer system had a facility to generate pass-times ("Alerts") so it often took 24-48hrs of passes to get a final fix. Have some photos somewhere.

Roger


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## Varley (Oct 1, 2006)

I think it actually had to have passed level (not necessarily overhead) so that both the rate of change of doppler shift and the null point could be used to make the fix. Can't remember what technique was used to determine which side of the satellite the correct fix was - perhaps we did need more than one at a time?


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## Searcher2004 (May 3, 2012)

Varley said:


> I think it actually had to have passed level (not necessarily overhead) so that both the rate of change of doppler shift and the null point could be used to make the fix. Can't remember what technique was used to determine which side of the satellite the correct fix was - perhaps we did need more than one at a time?


I'm sure you're right but I've forgotten what little training I had on the 702 and the navigation aspect was looked after by a surveyor, I just hooked it up and lugged the damned heavy antenna up to the chosen spot. 

There was a successor to the Magnavox 702, the 1502, which was luggable and was technically better, but still needed to sit in one place for a while to get a fix.

R


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## Vital Sparks (Sep 19, 2007)

Satellite orbits passing directly overhead were unusable because one of the error components in the system was directly proportional to the tan of the elevation angle and the tan of 90 degees is infinity. Transit receivers did measure the "zero point" in the doppler curve and later receivers were fast enough to predict the curve in advance and refine their solution as the satellite passed by. It was a fundementally a hyperbolic system similar to Decca\Loran and did produce two possible positions on opposite sides of the satellite orbit. The navigators manually entered "starting" position was used to disambiguate them.


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## Searcher2004 (May 3, 2012)

Vital Sparks said:


> Satellite orbits passing directly overhead were unusable because one of the error components in the system was directly proportional to the tan of the elevation angle and the tan of 90 degees is infinity. Transit receivers did measure the "zero point" in the doppler curve and later receivers were fast enough to predict the curve in advance and refine their solution as the satellite passed by. It was a fundementally a hyperbolic system similar to Decca\Loran and did produce two possible positions on opposite sides of the satellite orbit. The navigators manually entered "starting" position was used to disambiguate them.


Thanks for that, VS. As regards the ambiguity, we used several other navigation systems, as available, as a Transit check. I've attached a pic of a ship-borne temporary set-up and the two items on the deck are Racal Pulse/8 sets, which were similar to Loran.

Roger


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## GilesdeB (Aug 24, 2015)

Thanks for all the illuminating replies and to PeterY for his precision.
73 Giles


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## Naytikos (Oct 20, 2008)

When I was doing my ticket in the mid-60s some US warships visited Plymouth and one of the officers gave a lecture on the, then just-made-public, magic satellite navigation system. I slept through most of it.

However I had a lot of fun with the early Transit system. Niarchos bought a Magnavox/HP system for one VLCC and an ITT system for another to compare performance. This would have been 1973, I think.

I got the Magnavox/HP version. This was a Magnavox dual frequency receiver with a Hewlett-Packard 'mini-computer' together with a teleprinter. The computer and receiver can be seen in Searcher's photograph.

One had to update the geodetic height regularly, and the computer crashed every other day. It had a massive 4K magnetic-bubble memory. 
One could switch frequencies (nominally 400 & 150Mc/s) to achieve more iterations when propagation was less than favourable, or leave the receiver to choose by itself.

Note the 'Do not disturb' notice in the photograph: This was a removable key which could lock the computer so that keyboard entries by the teleprinter were ineffective. The first master to experience it with me decreed that I should keep the key and no-one but he or I should touch the whole thing. All of the buttons shown on the front panel of the computer are actual switches/lamps whereby the contents of the several registers could be seen at any time. Naturally these all flashed rapidly when everything worked properly. When it crashed one could change a register setting and sometimes get it running again. The alternative was to reload the software from paper tape which took around 45 minutes. This, of course, was before PCs, when 'mini-computers' like this used small-scale versions of main-frame architecture.

ITT gave up on satellite navigation systems and took back the system Niarchos had bought so the VLCC fleet all ended up with Magnavox, albeit a year or so later the teleprinters were replaced by small VDU terminals with numeric keypads and the software came on 1/4 inch tape cassettes.

Why was the Transit system like a bank?

Because a bank will only lend you what you already have (in the form of collateral); the Transit system could only produce a position if you entered a pretty accurate DR position for it to start from.


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## J. Davies (Dec 29, 2010)

Transit was in use until the late 80's I seem to remember. GPS started around 1986 but only became worldwide 24/7 in 1991.

When Transit was in use the 2nd mate would wait eagerly for the 4-hourly overhead satellite pass and rush out to the monkey island with his sextant, declaring that the satellite fix was several miles out. That was real professionalism.

Then you had the lost Korean bulk carriers in the middle of the Pacific calling us on VHF 16 asking if we had a satellite fix. One old man told the Mates to either ignore them or give a wrong position!

30 years later and all our jobs have gone to them anyway.


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