Frequency Division Multiplex on Open Wire Lines

FDM, or Frequency Division Multiplexing, came about through investigations on how to devise a proper form of loading for open wire and cables.  An AT&T engineer, George Campbell was one of several investigating loading aerial wire and multi-pair cables’ effects and stumbled upon the various complexities of induction through his theoretical work.

Well aware of the load coil’s negating effect on frequencies whereby higher frequencies were sliced off, Campbell also surmised these effects might have positive repercussions on the design of proper filters for voice and carrier transmission systems.