[time-nuts] sub cables
didier at cox.net
Wed Apr 30 21:05:54 EDT 2008
Interestingly, my company just received an RFQ for DC/DC converters for
trans-oceanic cables. Interesting specification. Among other things,
2,000,000 hours MTBF (the converters are multi-redundant) and, I like that
part, 100% altitude tested :-)
Something else you might find interesting: all repeaters are daisy chained.
The power comes from two current limited 1A 10,000V supplies, a positive one
at one end, and a negative one at the other end, so that if the cable is
grounded accidentally in the middle (say, by a boat anchor, just a guess...)
all the repeaters still get power. One supply can power the entire cable.
Two grounds, and you can lay another cable. The power return is through the
earth. Don’t swim near a head-end cable...
The capacitance of the cable is measured in Farads, and it takes several
hours to charge the cable at power up.
Some time ago, we bid on the head-end power supplies (we did not get that
job). It is interesting to observe that high reliability has a different
meaning in the under-sea cable business and in the military airborne
business. We do the latter.
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Alan Melia
> Sent: Wednesday, April 30, 2008 2:45 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] LED reliability and sub cables
> Mmmmmm LED operation is basically a bulk effect whereas the
> reliability of transistors depends more on surface effects.
> In 1960 AT&T chose to go with Germanium, but the British Post
> Office chose the new silicon planar technology for future
> submerged cables. Previously Dr Gilbert Metson had written a
> landmark series of papers on valve (tube) cathodes. Extensive
> work was done at the Research Department at Dollis Hill in
> North London. The "good" tubes were found totally by accident
> in a batch of wartime manufacture (I believe they were an
> SP41 (I dont know the US
> equivalent) but its a 4v heater pentode.) As a result of this
> probably the first repeatered telephone cable was laid
> between UK and Norther Ireland in around 1944/45. The
> original repeaters had redundant sets of tubes, but it was
> found that this made the system LESS reliable, than just a
> single string of reliable tubes. I joined the PO sub cable
> transistor Group in 1961 and from scratch we laid the first
> oceanic cable in 1968 (I think) between Cornwall and Lisbon.
> The second was laid the following year between Canada and
> Bermuda. The last of the tubed cables was laid about the same
> time. The transistors were nothing special technically 400Mhz
> ft ( bit like the
> 2N916) but made with care and cleanliness and 75% of the
> build of each batch was destructively life-tested ( by my
> Group). By 1967 we knew we could meet the the tube system
> crtiteria of not more than one system failure due to a
> component failure in 20 years. In fact I think most of these
> system continued carrying traffic for near 30 years.
> I am not sure about LEDs, though some work was done in the
> 1970s on the efficiency degradation-rate in opto-couplers for
> the telecomms business.....
> that is a difficult one to accelerate easily....sting in the
> tail MTBFs are meaninless !!
> Slightly OT but "life" is measured as elasped time....so I
> claim immunity from flames!!
> Best Wishes
> Alan G3NYK
> ----- Original Message -----
> From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Wednesday, April 30, 2008 6:12 PM
> Subject: Re: [time-nuts] LED reliability
> > In message
> <20080430165656.3C300BE3B at ip-64-139-1-69.sjc.megapath.net>,
> > Hal
> > ay writes:
> > >> LEDs been viable since at least the early 70's? Talk
> about planned
> > >> obsolescence...
> > >
> > >How reliable were the early LEDs? When did they start to
> get used in
> > >reliability applications?
> > Many of them are still happily emitting their faint red or
> green light.
> > >The best reliability story I heard (many years ago) was about
> > >installing another trans-Atlantic telephone cable. They
> used tubes
> > >long after transistors were out. They knew how long the
> tubes would
> > >last. They
> > >have much data on transistors yet.
> > Actually, that's not entirely correct: They had
> reliability info on
> > transistors and they sucked.
> > --
> > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> > phk at FreeBSD.ORG | TCP/IP since RFC 956
> > FreeBSD committer | BSD since 4.3-tahoe
> > Never attribute to malice what can adequately be explained by
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