Registered Jack

Amateur radio manufacturers generally use one or more “registered jacks” to connect transceiver to microphones and remotely located controls. The term “registered jack” (RJ) is a consequence of the Bell System’s settlement with the Department of Justice in January, 1982, under which the Bell System agreed to divest its local exchange service operating companies in return for a chance to go into the computer business. Standardized connections to wireline services were required to permit competitors to access home and office telephone systems. Accordingly registered jacks became the means for interconnecting data or telecommunications devices to service providers. Although technically “RJ” refers to jacks, the term applies currently to both plugs and jacks.

RJ Examples

Initially, RJ modular connections were named RJ11, RJ12, RJ21, RJ41, etc. However, they differed only in the number of positions and conductors. For example. the RJ12 jack has six positions and six conductors and is often identified as “6P6C.” The RJ11, physically identical to the RJ12, has only four conductors and is identified as 6P4C. Jacks are downward compatible with plugs having fewer positions. Thus, a 6P6C jack physically accommodates 4P4C plugs. However, only the inner 4 conductors of a 6P6C jack are connected to the 4P4C conductors. Similarly, an 8P8C jack accommodates 6P and 4P plugs. Because plugs with fewer positions fit into 8P8C jacks, an RJ jack with eight positions and eight conductors is ideal for interconnecting amateur radio devices that use 4P4C, 6P6C, and 8P8C plugs and jacks. Figure 1 illustrates common ham radio connection cables.


The defacto standard 8P8C jack is usually referred to as an “RJ45.” There are many variations of 8P8C jacks but all have the form of a “generic” RJ45. The SMR’s RJ45s are 8P8C registered jacks that accommodate RJ plugs with fewer positions and/or conductors. Most amateur radio manufacturers use cables compatible with RJ45 jacks to connect microphones and control heads to transceivers. A representative RJ45 is shown in Figure 2.