SPLITTING HAIRS TO SPEED CALLS (Jun, 1954)
SPLITTING HAIRS TO SPEED CALLS
To triple the voice-carrying capacity of coaxial cable, Bell Laboratories engineers had to create new amplifying tubes with the grid placed only two-thirds of a hairs breadth from the cathode. Furthermore, the grid wires had to be held rigidly in position; one-quarter of a hairs shifting would cut amplification in half.
Working with their Bell System manufacturing partners at Western Electric, the engineers developed precise optical means for measuring critical spacing insulators. On a rigid molybdenum grid frame they wound tungsten wire three ten-thousandths of an inch thick. To prevent the slightest movement they stretched the wire under more tension for its size than suspension bridge cables, then bonded it to the frame by a new process.
The resulting tube increases coaxial’s capacity from 600 to 1800 simultaneous voices —another example of how Bell Telephone Laboratories research helps keep your telephone system growing at the lowest possible cost.
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