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Paul Schnitzler





Digital Commutator



Ocean Cable Equalizer

The SG Ocean Cable Equalizer used a motor-driven 32-position commutating switch to select and set a wide range of cable corrections. The motor developed reliability problem and a stable replacement was necessary. This two-board module matches the standard extreme reliability of ocean system components.


Need: Fix an emergency reliability issue


Problem: The SG Undersea Telephone System used remote controlled equalizers to correct for changes in cable transmission properties. Over time the losses in the coaxial cable will change and the amplifier must be corrected to exactly match this change. The original design used a special, high-reliability, DC motor that would be directed to rotate a switch in order to make the necessary equalizer adjustments.


During tests in the factory, some time after the first system installation, this motor failed!


Approach: The physical design group decided that it was essential that this mechanical motor/switch assembly be replaced by an electronic circuit. The new unit would have to have the same physical size and electrical properties as the original one, i.e. be directly exchangeable with the original unit.


Paul Schnitzler designed the electronic “commutator” to replace the motor-driven module. It was based on a set of existing production integrated circuits that had a solid reliability history.


He also developed a test platform to “exercise” the module to uncover possible flaws.


Together with the Physical Designers at Bell Labs they built and installed this new device in several undersea systems.


Results: The commutator was placed in production and is now in service in undersea systems around the world.


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