Frequency-division multiplexing

Starting in 1911, blast networks acclimated frequency-division multiplexing to backpack several articulation channels on a individual concrete circuit, alpha with the aboriginal Type C carrier in that year, which heterodyned three articulation channels ample on top of one articulation circuit2. L-carrier systems were loaded by multiplexing and supermultiplexing individual sideband channels, application the long-standard 12 approach articulation "group" produced by Type A approach banks, application a abundance spectrum amid 60 and 108 KHz. This basal "group" was the absolute band spectrum on antecedent continued booty carrier systems, such as Types J and K. The aboriginal Type A-1 approach banks appeared for use on Type J accessible wire carrier in 1934.3 If was the plan of the above Espenschied and Herman Affel of Bell Labs who patented their piezoelectric clear "lattice" filters to accommodate aciculate bandpass blow that fabricated all single-sideband carrier plan developed at Bell Labs possible. Such "lattice" filters were the affection of all analog circuitous systems application single-sideband/carrier suppressed architectonics until alive IC-based clarification became accessible in the mid-1970s.

In single-sideband accentuation schemes, twelve articulation channels would be articulate into a approach group. In turn, 5 groups could themselves be multiplexed by a agnate adjustment into a supergroup, absolute 60 articulation channels. One 48 kHz group-band ambit was sometimes acclimated for a individual top acceleration abstracts hotlink rather than for articulation circuits. Also, absolute supergroups could be committed as a individual abstracts approach active a abstracts amount of 56 Kb/s as aboriginal as the backward 1960s.

In continued ambit systems, supergroups were multiplexed into mastergroups of 300 articulation channels (European CCITT hierarchy) or 600 (AT&T Continued Lines Type L-600 Multiplex) for manual by coaxial cable or microwave.