History of the Atlantic Cable & Submarine Telegraphy - STC Repeaters

	History of the Atlantic Cable & Undersea Communications from the first submarine cable of 1850 to the worldwide fiber optic network
STC Repeaters - 1954

Introduction: Derrick Savage, who worked in the engineering development lab at the Submarine Systems division of Standard Telephones and Cables Ltd from 1979 until 2001, sends these photographs of early submarine cable repeaters. The repeaters were made in 1954 according to the nameplates, and were recovered from a system which had been laid somewhere in the far east.

--Bill Burns

Derrick writes:

One part of the assembly which is at present a mystery is a component attached to the end casting of the internal frame.

The part consists of a pressure capsule which is attached to the 'I' of an 'E' & 'I' Mullard feroxcube ferrite coil assembly. Closer inspection shows a gap between the 'E' & 'I'. There is a single coil wound on the 'E' and the ends of the coil pass into the main assembly of the repeater.

I would be very interested to hear from anyone who might be familiar with the equipment and can throw any light on this mystery item. My speculation on the function of this part is as follows:

When a repeater is laid in the deep sea the pressure inside the sea case should remain constant at 1 atmosphere. Unfortunately, with the extreme external sea pressure and, dependent much on where it is laid, electrolytically generated hydrogen will ingress into the repeater case via the cable.

Hydrogen has been an enemy to undersea repeatered systems from the beginning, right up to the present day optical fibre systems. Hydrogen is known to ingress into and degrade electronic components and even into the glass fibre we use now. The absorption of hydrogen into glass fibre puts a loss at the very worst place—very close to the zero dispersion wavelength of 1300 Nm.

So, was the coil of the mystery component mentioned above incorporated as an inductive element of an oscillator? The gap left on the ferrite assembly will change as a function of sea case pressure variations if hydrogen is ingressing into the case.

The variation of gap in the ferrite magnetic path will change the inductance of the coil and if incorporated in an oscillator will change its frequency. Therefore by pre-calibrating in a pressure chamber by plotting frequency change against pressure change, the arrangement can be used as a pressure sensor in a repeater sea case.

These repeaters used thermionic valves as an amplifying element so profligate use of additional valves for sensing purposes would be resisted as far as possible. However repeater supervisory communication was designed into these repeaters to indicate the repeater status back to the terminal buildings on shore.

The overall views of the repeater are followed by detail photographs showing the pressure capsule and its adjacent assembly. If any site visitor has further information on the function of this component, please email Derrick via the website address: billb@ftldesign.com

The pressure capsule is the ribbed copper-coloured
unit mounted to the lower part of the repeater

Detail showing the pressure capsule

Side view showing the pressure capsule

Last revised: 12 June, 2008

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