Reg Edwards wrote:
Whilst on the romantic subject of coaxial attenuation -

A follow on from Reg's story, is that (in submarine the cables with
which I was familiar), there was another grade of cable also used, a
repair cable that had about two thirds the loss of the regular cable.

It was used when repair was necessary (eg repeater failure, cable damage
from anchors , earthquakes etc). It is not possible to effect a repair
without cutting the original cable in order to get the cable to the surface.

The technique used on CS Monarch and the like, was to use a special
grapnell that caught the cable (often after many days of steaming back
and forth across the suspected cable position) and hauled it up until a
pre-determine tension was reached which activated a cutter in the
grapnell, which separated each end off on a separate hauling line. One
was buoyed off, and the CS steamed toward the other cable end until
sound cable was retrieved. It was sealed and buoyed off. They then
steamed back to the other buoy and retreived the other end, again
steaming until sound cable was found. Calculations were then done of
depth, position, losses to find how much more cable was to be removed so
that when the repair cable was inserted, the S/N into each of the
affected repeaters was sufficient to allow normal operation (these were
linear FDM or carrier telephone cables). (In some cases, so much cable
was affected that a mix of original cable and repair cable was used.)

This operation could take several days in good weather, worse in bad seas.

Owen

PS: 4000 dB sounds a lot, but when it is stated as 40dB between
repeaters it sounds more manageable.