Editing T-carrier (section)

==Higher bandwidth carriers==
In the 1970s, Bell Labs developed higher rate systems. T1C with a more sophisticated modulation scheme carried 3&nbsp;Mbit/s, on those balanced pair cables that could support it. T-2 carried 6.312&nbsp;Mbit/s, requiring a special low-capacitance cable with foam insulation. This was standard for [[videophone|Picturephone]]. T-4 and T-5 used coaxial cables, similar to the old [[L-carrier]]s used by AT&T Long Lines. TD [[microwave radio relay]] systems were also fitted with high rate modems to allow them to carry a [[Digital Signal 1|DS1]] signal in a portion of their FM spectrum that had too poor quality for voice service.<ref>{{citation |url=http://long-lines.net/tech-equip/radio/BLR1273/DUV1-1273.html |title=The 1A Radio System Makes "Data Under Voice" A Reality |author1=Ronald C. Prime |author2=Laurence L. Sheets |work=Bell Laboratories Record |date=December 1973}}</ref> Later they carried [[Digital Signal 3|DS3]] and DS4 signals. During the 1980s companies such as RLH Industries, Inc. developed T1 over optical fiber. The industry soon developed and evolved with multiplexed T1 transmission schemes.