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Retrotechtacular: Submarine Cable Splicing is Serious Business

Really. As this wonderfully narrated talkie picture from 1939 will attest, keeping even one drop of water from penetrating undersea cables is of the utmost importance.

How do they do it? Many, many layers of protection, including several of jute wrapping. The video centers on splicing a new cable to an existing one in the San Francisco Bay to bring the wonder of telephony to a man-made island created for the Golden Gate International Expo.

The narrator makes these men out to be heroes, and when you see how much lead they came into contact with, you’ll understand what he means. Each of the 1,056 individually insulated wires must be spliced by hand. After that comes a boiling out process in which petrolatum is poured over the splice to remove all moisture. Then, a lead sleeve is pulled over the connections. Molten lead is poured over the sleeve and smoothed out by hand.

At this point, the splice is tested. The sleeve is punctured and nitrogen gas is pumped in at 20psi.  Then comes the most important step: the entire sleeve is painted with soap suds.  Any gas that escapes will make telltale bubbles.

Once they are satisfied with the integrity of the sheath, they wrap the whole thing in what appears to be lead cables and pound them into submission. Surely that would be enough, don’t you think?  Nope.  They weld the cables all around and then apply two coats of tar-treated jute wrapping, which retards saltwater corrosion considerably.

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An excellent introduction to transmission lines

[Bertho] sent in a great tutorial on terminating transmission lines. If you’ve ever tried to send a high frequency signal a long way down a wire, you know the problems that can crop up due to electronic strangeness. Luckily [Bertho]‘s tutorial explains just about everything, from where and when to terminate a cable and why signals get screwed up in long wires.

[Bertho] begins his lesson by taking two oscilloscopes and 20 m of CAT5 cable with the twisted pairs wired in series to make an 80 meter long transmission line. A ~100kHz square wave was sent down the cable after being displayed on the first oscilloscope, and picked up on the other end by the second oscilloscope. It’s a great way to show the changes in a signal over a long cable run, and how small changes in the circuit (just adding a simple resistor) can affect the signal coming out of a cable.

It’s a great post that demystifies the strange electrical gremlins that pop up when you’re running a length of wire. Great job, [Bertho].

The integrated desk


Since it happens to be the day after a nice holiday break, many of us are finding ourselves back in front of our desk once again. Perhaps some of you never left it the entire weekend. In any case, it seems fitting to take a look at a few interesting integrated desks we’ve come across lately. Follow through after the break to see our favorites.

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