3 ms·

I've read (or perhaps watched on YouTube) the same thing. Finding both ends of the cable to grab abd raise it took longer than the raise/splice operation. I s

I've read (or perhaps watched on YouTube) the same thing. Finding both ends of the cable to grab abd raise it took longer than the raise/splice operation. I suspect a sufficiently malicious attacker could intentionally cut the cable twice, so when the repair crew drag up one end of the cut they know about, the section between the cuts drags its other end away from it's cut-point making the second repair significantly more difficult...

pixl97 1y ago
Cutting twice wouldn't be an issue, they can send a signal from both ends to get a reflection of how much of the cable is dead.
staplung 1y ago
In most cases they can easily figure out approximately where the break is on the line by simply measuring the resistance in the cable's conductors (they have more than one but the big one caries a 10,000V feed to power the repeaters). A double cut would probably show up as resistances that didn't sum to the proper total.
- matt-p 1y ago
  You can only practically do that optically e.g through OTDR. You can't TDR steel conductors exposed to the ocean 500KM away with a ohm meter and a Murray loop, to even have a chance you need to put low voltage on it and it's not even close to as accurate.
  - robocat 1y ago
    Rubbish. TDR is not a Murray loop. https://en.m.wikipedia.org/wiki/Murray_loop_bridge https://en.m.wikipedia.org/wiki/Murray_loop_bridge Spread-spectrum time-domain reflectometry (SS-TDR) is often used to locate and characterize a fault on active cables. Traditional time-domain reflectometry, which sends signals down a conductor to determine where any impedance discontinuities are by timing any reflections that come back from any impedance discontinuities along the way, can’t be used on in-use undersea cables thanks to the high voltages involved. SS-TDR, which was originally developed to detect faults in the wiring of airplanes using 400-Hz AC power, uses modulated pseudo-noise (PN) signals rather than a plain square wave pulse. The signals still bounce off any impedance changes introduced by damage, but an algorithm is used to correlate the returned PN codes with what was sent and when, making it easier to make measurements in a noisy environment. Optical TDR can also be used to locate fiber breaks https://hackaday.com/2024/07/30/undersea-cable-repair/ https://hackaday.com/2024/07/30/undersea-cable-repair/ A little knowledge goes a long way

pixl97 1y ago

Cutting twice wouldn't be an issue, they can send a signal from both ends to get a reflection of how much of the cable is dead.

staplung 1y ago

In most cases they can easily figure out approximately where the break is on the line by simply measuring the resistance in the cable's conductors (they have more than one but the big one caries a 10,000V feed to power the repeaters). A double cut would probably show up as resistances that didn't sum to the proper total.

matt-p 1y ago
You can only practically do that optically e.g through OTDR. You can't TDR steel conductors exposed to the ocean 500KM away with a ohm meter and a Murray loop, to even have a chance you need to put low voltage on it and it's not even close to as accurate.
- robocat 1y ago
  Rubbish. TDR is not a Murray loop. https://en.m.wikipedia.org/wiki/Murray_loop_bridge https://en.m.wikipedia.org/wiki/Murray_loop_bridge Spread-spectrum time-domain reflectometry (SS-TDR) is often used to locate and characterize a fault on active cables. Traditional time-domain reflectometry, which sends signals down a conductor to determine where any impedance discontinuities are by timing any reflections that come back from any impedance discontinuities along the way, can’t be used on in-use undersea cables thanks to the high voltages involved. SS-TDR, which was originally developed to detect faults in the wiring of airplanes using 400-Hz AC power, uses modulated pseudo-noise (PN) signals rather than a plain square wave pulse. The signals still bounce off any impedance changes introduced by damage, but an algorithm is used to correlate the returned PN codes with what was sent and when, making it easier to make measurements in a noisy environment. Optical TDR can also be used to locate fiber breaks https://hackaday.com/2024/07/30/undersea-cable-repair/ https://hackaday.com/2024/07/30/undersea-cable-repair/ A little knowledge goes a long way