BNC Connectors - Terminology and termination

Used for applications including video, radio frequency signals, digital audio and test equipment the BNC connector has a long history.

Impedance

They are available in two impedances, 75 ohms and 50 ohms; all BNCs supplied by Canford and virtually all current designs conform to IEC 169-8. The IEC specification defines that the mating interface of 50 ohm and 75 ohm BNC connectors are mechanically compatible and will mate in a non-destructive manner. They are not however electrically compatible for high frequency or high bit-rate applications.

BNC Cable Connectors - Male - 75 ohm types

These are offered as standard and HD types, see below, and either crimp or solder fitting. They inter-mate fully with 50 ohm BNC sockets found on some older equipment.

BNC Cable Connectors - Male - 50 ohm types

The 50 ohm connectors offered by Canford should be used only with 50 ohm cables, for instance in RF systems.

Termination Types

There is a choice of two methods of termination:

Crimp Types

Crimp types have a crimp centre pin that ‘clicks’ home into the insulator and a crimp outer sleeve (‘ferrule’). Crimp termination offers the most reliable and highest specification solution when connectors are accurately matched to the cable size. Canford works closely with suppliers to ensure total compatibility with the cables and tooling listed and the optimisation of electrical and mechanical performance. See Crimping BNC Connectors, below.

Solder Types

Solder types have a solder centre pin and compression gland to anchor the cable and connect the braid to an inner ferrule, with hex nut fixing. In general these are considerably more difficult to fit than crimp types, but can be useful where only a few are to be fitted, and a crimp tool is not available.

Precision

They are offered in two grades of precision:

BNC Connectors - Standard

These are termed simply ‘BNC’ connectors. Standard versions offered by Canford are suitable for analogue and SD video, and other less-critical applications. They may not be suitable for use with HDTV.

BNC HD Connectors - HDTV

These are suitable for use in HDTV applications. Canford uses the term HD to indicate this.

Crimping BNC Connectors

The ferrule is placed loose over the cable which is then is stripped to precise dimensions. The centre pin is placed over the centre conductor and crimped with a crimp tool fitted with an appropriate die. The cable and pin are inserted into the body of the connector with the braid outside the body. The ferrule is then pushed over the braid and crimped, again with an appropriate die in a crimp tool. Clearly the choice of tool and die must suit the cable and connector combination; the dimensions of both are critical.

Canford offers several crimp tools and ranges of dies which may be used with BNC crimp connectors:

Crimp Tools - Type-Specific

Some manufacturers produce tools and dies which are suitable for use with specific connectors from their range. It should not be assumed that they will produce an optimum crimp with any combination of connector and cable other than those stated.

Crimp Tools - Multi-purpose

Canford also offers crimp tools which can be used with a wider range of connectors, including MUSA and other co-axial types by the use of interchangeable dies. These are generally the choice of those who may have to crimp a wide range of cables and connectors in the future, rather than specific types known in advance.

Die Sets

A die set is a pair of jaws which will fit to specific crimp tools. The jaws are machined, usually with two apertures on each closing face, so that when the jaws are squeezed together by the tool, the exact amount of force will be applied to crimp the pin and ferrule respectively to the cable in use. Since the dimensions of the cable and the connector as well as the degree of softness or hardness of the materials used for the cable centre, braid and jacket as well as the centre contact body and ferrule can affect the success of the joint, it is clear that the correct die for the combination must be used.

Choice of Cable, Connector, Die-set combination: Groups

Co-axial cables offered by Canford, which are suitable for crimping, are categorised into ‘groups’ by Canford’s technical staff. The BNC connectors are similarly categorised where they will fit these cables. The die-sets offered are also categorised by group. Each combination of cable, connector, tool and die-set of the same group type is tested by Canford staff, and is effective in producing a good termination.