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For example, RJ11 and RJ14 use female six-position modular connectors, and RJ21 uses a 25-pair (50-pin) miniature ribbon connector. RJ11 uses two conductors in a six-position female modular connector, so can be made with any female six-position modular connector, while RJ14 uses four, so can be made with either a 6P4C or a 6P6C connector.
The cubic design was changed to a round version (No. 505A) in the mid 1960s. The four-prong jack and plug combination was the standard line connection for all portable telephone sets until the conversion to modular jacks in the 1970s, typified by the Registered Jack standards promulgated in U.S. federal law.
The first types of small modular telephone connectors were created by AT&T in the mid-1960s for the plug-in handset and line cords of the Trimline telephone. [1] Driven by demand for multiple sets in residences with various lengths of cords, the Bell System introduced customer-connectable part kits and telephones, sold through PhoneCenter stores in the early 1970s. [2]
The third pin (top, horizontal) used to be connected to ground and was occasionally used with switchboards, but is now generally unused and left unconnected [citation needed]. Each pin is 12.5 millimetres (0.5 in) long, 10 millimetres (0.4 in) wide and about 2 millimetres (0.08 in) thick, compatible with one of the historic types of blade plugs .
The A leg goes to pin 5 and the B leg to pin 2 in the master socket. (Although all equipment will work with a reversed line, so a reverse wired socket is not strictly a fault.) When current is flowing on the line, the B leg voltage collapses to nearer ground and the A leg voltage moves nearer to the B leg voltage. The exact voltage drop is a ...
The demarcation point has a user accessible RJ-11 jack (a "test jack" or "demarcation jack"), which is connected directly to the telephone network, and a small loop of telephone cord connecting to the jack by a modular connector.
The number gives their outer screw thread diameter in millimeters as with the identically named screws. However, the connectors are further classified by a so-called coding, denoted by one or more letters, which defines things like pin layout, shape of connecting surfaces and electrical properties. [2] [3]
In the Trimline version designed for connection to an RJ11 telephone jack, pins 2 and 5 (black and yellow) may carry low-voltage AC or DC power. While the telephone line supplies enough power for most telephones, older telephone instruments with incandescent dial lights (such as the classic Western Electric Princess and Trimline models) needed ...