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Coaxial connector, full name is Triaxial Connector. Triaxial, literally, is the co-axis of three cylinders. Triaxial Cables are coaxial cables with two outer conductors, consisting of an inner core (main, corresponding connector as the center contact) and an endothelial signal layer (the corresponding connector is an intermediate cylindrical contact). The outer sheath is composed of layers (see Figure 1). The inner core mainly transmits signals (such as video signals) or powers the head, and the inner and inner cores form a loop. The outer layer is the shielding layer and the ground layer. The outer diameter of the connecting cable is Ф8mm, Ф6.1mm (such as RG58A/U) and Ф4.5mm (such as Microdot's 293-3930). The cable with a larger diameter is transmitted. The loss is small and the transmission distance is long. Compared with multi-core cables, triax cables are simple in structure and high in reliability; they have higher shielding performance and small signal transmission capability than two-core coaxial cables (see Figure 2). The shielding performance of the triax connector is 40~50dB higher than that of the unshielded connector, and the shielding efficiency of the triax cable is 9 times higher than that of the single-layer copper braided cable.

The triax connector is different from the ordinary two-core connector, and can connect the signal, the grounding and the shielding layer at the same time, and the shielding effect is good. The three-coaxial connector is contoured with a center contact and an intermediate cylindrical contact. The connection of the triax connector is generally a bayonet connection (TRB series) and a screw connection (TRT series), in addition to ultra-small TRS connectors, STRB connectors and STRT connectors. The bayonet type connection is usually a triax BNC connector. On the basis of two bayonet ports (2 ears), the socket adopts a three-pin (3 ears) connection structure, and the matched plug adopts a triple spiral groove (three bayonet) connection structure. This structure is convenient, reliable, and stable in electrical performance. It can be quickly inserted and removed. Its connection is more secure than the traditional BNC2 ear connector, and can withstand severe shock and vibration. The triax BNC connector is mainly used in sensitive electronic measuring systems and cannot be directly matched with ordinary BNC connectors, but can be connected to ordinary BNC connectors through adapters (or adapters).

In China, the triax RF connector was released in 1994 with the SJ 51212/4-1994 specification, which specifies the detailed requirements for the TRB series (connected cable) jack contact class 2 RF triax plug connector, suitable for use in radio TRB series 2 level RF triax connectors used in RF circuits of equipment and electronic instruments, connected to RF triax cables, with bayonet connection structure, and higher shielding performance for RF applications.

The connection between the triax connector and the cable is of the soldering type and the crimping type, and the cable connected thereto is generally a terminated shielded twisted pair cable and a triaxial cable. The purchase network will be described separately as “Terminal shielded twisted pair cable and twinaxial cable plug”.

Triax cables are usually RG58A/U, RG59/U, RG11/U, also used as Belden's 9272 and 9222 cables, and also as Microdot's 293-3930 cable. The outer diameter is increased, so size and flexibility can be a problem. RG-11 has lower losses for long distance transmission, while RG-59 has smaller shape and better flexibility. Triax cables are typically used for internal connections to cameras and related equipment. In terms of use, the quality requirements for triax cables are mainly flexibility and flex life. The typical products are Belden's 9267 and 9232 products with Hypalona sheath, which are turned from traditional solid center conductors to multi-strand conductors. The twisted center conductor to increase the flexibility of the cable. Typical product specifications for triax cables are as follows:

1, 8232 (Belden), RG-59/U, video triax cable, smaller than RG-11/U, flexible: 20AWG solid bare copper conductor, foamed polyethylene insulation, 2 layers of bare copper woven mesh shielding 95% shielding coverage, polyethylene insulation between shields, polyethylene sheath, 100% sweep test bandwidth 5-300MHz.

2、8233(Belden)、RG-11/U，视频三同轴电缆：14AWG实心裸铜导体，发泡聚乙烯绝缘，2层裸铜编织网屏蔽、95% 屏蔽覆盖率，屏蔽层之间为聚乙烯绝缘，聚乙烯护套、100%扫频测试频宽5-300MHz。

At present, RF triax cables and connectors for data buses have been widely used in surface ships, aviation, and many commercial fields, such as telemetry, radar, satellite signal transmission, data networks, airports, armored forces, and peripheral warnings of agencies. Occasionally, it is also widely used in digital data trunks, video pairs, baseband circuits and other noise-free advanced protection circuits. Because they improve the transmission and anti-jamming capabilities of data transmission systems, triax cables and connectors are widely used for transmission and measurement of weak signals such as low thermal potential EMF and high shielding requirements.