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Jabber (watchdog timer) - Built into controller units and transceiver units.

Jabber, jabbering - In LAN technology, continuously sending random data (garbage); normally used to describe the action of a station (whose circuitry or logic has failed) that locks up the network with its incessant transmission.

Jack - A plug-in type terminal widely used in electronic apparatus for temporary connections.

Jacket - Pertaining to wire and cable, the outer sheath that protects against the environment and may also provide additional insulation.

Jam - A short encoded sequence emitted by a node to ensure that all other nodes have detected a collision.

Jan specification - Joint Army-Navy specification (replaced by current military specifications).

JBOD (just a bunch of disks) - Used to refer to hard disks that aren’t configured according to RAID; a subsystem of disk drives that improves performance and fault tolerance.

Jet starter cable - Single conductor 600 V cable used for external aircraft power.

Jitter - The slight movement of a transmission signal in time or phase that can introduce errors and loss of synchronization in high speed synchronous communications.

Joint - That portion of the conductor where the ends of two wires, rods or groups of wires are joined by brazing, soldering, welding or by mechanical means.

Joule - A unit of energy defined as the work done when the point of application of one Newton is displaced one meter in the direction of the force.

Joule’s law - When electricity flows through a material the rate of heating in watts will equal the resistance of the material in ohms times the square of the current in amperes. W = I2R.

Jumper - 1. A wire used to connect equipment and cable on a distributing frame. 2. When errors are found on printed circuit boards, a jumper cable is sometimes soldered in to correct the problem.

Jumper cable - Extra flexible cables with high-voltage insulation for use as temporary connections. Usually has a red jacket.

Jumper wire - A short length of wire to route a circuit by linking two cross-connect termination points.

Junction box - Metal box inside which cables are connected together.