[time-nuts] sub cables

Alan Melia alan.melia at btinternet.com
Thu May 1 06:13:48 EDT 2008

Hi Didier yes trawlermen's axes are a worse problem than anchors !! I have
seen a pic of the remenants of an axe head with a large chunk taken out of
it. The fisherman survived but was a bit shaken ! Of course the cut was made
near the end on the continental shelf so the volts were quite high!!

All systems are now digital optical repeaters but powerfeed is the same. You
need to be able to power the damaged system to interrogate individual
repeaters to determine where the fault is....then you cant just haul an
oceanic cable in from one end!! In fact you cant just pull it up !! you have
to cut it and lift the two ends separately which finish up several miles
apart at the surface so you then need to splice in a new length of cable and
carefully drop it again in a nice loop. The length hanging on the cableship
in mid ocean weighs many tons even in seawater. So the loop is dropped with
small parachutes or drogues to let it down gently.

At least with the optical cables it is only the powerfeed circuit that gets
the surge not the amplifier front end as it was in the FDM systems.

I always thought the terminal equipment was a slighly lower reliability
requirement than the submerged parts but these days the loss of revenue even
with an easily accessed terminal is very high.

Alan G3NYK

----- Original Message -----
From: "Didier Juges" <didier at cox.net>
To: "'Discussion of precise time and frequency measurement'"
<time-nuts at febo.com>
Sent: Thursday, May 01, 2008 2:05 AM
Subject: Re: [time-nuts] sub cables

> 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
> The power comes from two current limited 1A 10,000V supplies, a positive
> 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
> 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
> 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.
> Didier KO4BB

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