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36 copper contacts and 50 microns of gold plating. A rigid plastic dielectric acts as the insulator, and they include a silicone- based elastomer seal. 38999 MIL-DTL-38999 connectors are miniature, high-density circular designs for meeting the stringent mil-spec requirements set out by the US Department of Defense. They come in various coupling options, including bayonet and threaded, as well as in metal or composite construction. They are well suited to applications in harsh environments. Within the 33899 standard there are two types of connector – quadrax and twinax (as opposed to a coax, or coaxial, connection). The quadrax connector has four pins connected to a single cable, providing two-way Ethernet data comms. The twinax connector with two pins, provides one-way comms. Two twinax connectors and two wires are required for two-way comms, which adds up to about 50% more weight than a quadrax connection, but twinax connectors have proved to be highly reliable and easy to maintain. Quadrax connectors are more difficult to maintain in the field and are yet to be thoroughly proven for reliability. Depending on the application, the end-user will prefer one or the other – for example, a European aircraft manufacturer prefers quadrax while its US rival prefers twinax. High-speed quadrax contacts consist of an outer contact with four inner contacts spaced in two 100 or 150 Ω controlled impedance differential pairs. Both contacts, when used in MIL_DTL- 38999 and ARINC-type connectors, provide an alternative for harsh environment applications for high-speed protocols such as: • Ethernet 100 Base-T 100 Ω • Gigabit Ethernet 1000 Base-T 100 Ω , 1000 Base-CX, 150 Ω • Fibre Channel 150 Ω , 1G/2G • IEEE 1394B FireWire 110 Ω • Serial FPDP applications, 2.5 Gbit/s • SCSCI-2, 3.2 Gbit/s There are differential contacts for power, crimp or printed circuit board termination and the incorporation of quadrax contacts into ground plane connectors. They have conductive inserts that ground the outer conductor of the contact to the connector shell, and accommodate size 8 and 12 shielded contacts, of which size 8 can be the quadrax type. 83513 Micro-D Micro D-Subminiature connectors fit in half the space of a standard D-Sub for avionics and control systems. These can be all-plastic, metal, angled or straight shell, and can be tested to the MIL- DTL-83513 standard to ensure consistent and predictable performance. They are commonly used as small connectors. BACC 26500 Circular BACC connectors are qualified for aircraft designs with shielding, environmental sealing, fluid resistance and vibration so that they can be used in engines and rocket boosters, and are made to the MIL-DTL-26500 specification for a major US aircraft builder. Shells include composite, stainless steel, aluminium and quadrax- compatible. Composite shells are best for weight-sensitive applications such as fuel efficiency in aerospace; quadrax connectors terminate quadraxial Ethernet and Fibre Channel cables designed for high-speed avionics systems, comms, aircraft data networks and space applications. Aluminium, electroless nickel-cadmium over nickel finishes are also available. Additions to the standard connectors include elements to stop the connectors rotating, reduced elastomer barriers for use with wires of different generations, shell-to-shell metal bottoms and systems for alternate terminations styles or low- profile packaging. For example, BACC 5015 series connectors use rear-release crimp contacts with a retention clip. These provide higher environmental performance than older MIL-DTL-5015 connectors as they are sealed to withstand moisture, condensation, vibration and flash-over. Numerous layouts are available in arrangements that allow for just power or signal, or a mix of both contact types. BACC 63 connectors are bayonet- coupled and vibration-resistant, while BACC 45 can be bayonet or threaded and have rear insertion of the contact and front release. Rectangular Many connector types start out as proprietary and become a de facto standard. That is particularly true for rectangular connector blocks that can be defined in different ways with different pin pitches and combinations of different February/March 2017 | Unmanned Systems Technology Focus | Connectors A 1.27 mm, 10 A powered contact handles a temperature range of -55 to 125 C (de-rating with the increased current) and is a smaller version of a 2 mm, 20 A connector system that weighs less (Courtesy of Ulti-Mate Connector)