in a tracked vehicle, a Remote Terminal might acquire data from an inertial navigational subsystem, and send that data over a 1553 data bus to another Remote Terminal, for display on a crew instrument. Simpler examples of Remote Terminals might be interfaces that switch on the headlights, the landing lights, or the annunciators in an aircraft. Test Plans for Remote Terminals: The RT Validation Test Plan is intended for design verification of Remote Terminals designed to meet the requirements of AS 15531 and MIL-STD-1553B with Notice 2. This test plan was initially defined in MIL-HDBK-1553, Appendix A. It was updated in MIL-HDBK-1553A, Section 100. The test plan is now maintained by the SAE AS-1A Avionic Networks Subcommittee as AS4111. The RT Production Test Plan is a simplified subset of the validation test plan and is intended for production testing of Remote Terminals. This test plan is maintained by the SAE AS-1A Avionic Networks Subcommittee as AS4112. Bus hardware characteristics The bus hardware encompasses (1) cabling, (2) bus couplers, (3) terminators and (4) connectors. Cabling The industry has standardized the cable type as a twinax cable with a characteristic impedance of 78 ohms, which is almost the midpoint of the specification range of 70 to 85 ohms. MIL-STD-1553B does not specify the length of the cable. However, the maximum length of cable is directly related to the gauge of the cable conductor and time delay of the transmitted signal. A smaller conductor attenuates the signal more than a larger conductor. Typical propagation delay for a 1553B cable is 1.6 nanoseconds per foot. Thus, the end-to-end would have a 160 nanosecond propagation delay, which is equal to the average rise time of a 1553B signal. According to MIL-HDBK-1553A, when a signal's propagation delay time is more than 50% of the rise or fall time, it is necessary to consider transmission line effects. This delay time is proportional to the distance propagated. Also, consideration must be given to the actual distance between the transmitter and receiver, and the individual waveform characteristics of the transmitters and receivers. MIL-STD-1553B specifies that the longest stub length is for transformer coupled stubs, but can be exceeded. With no stubs attached, the main bus looks like an infinite length transmission line with no disturbing reflections. When a stub is added, the bus is loaded and a mismatch occurs with resulting reflections. The degree of mismatch and signal distortion