Question:How do I determine which connector to use for coaxial cable?

Answer:
Coaxial connectors should appear electrically as extensions to the cable; in other words, they should connect to the cable with as little disruption of the electrical signal as possible. Thus a connector is usually specified by its nominal impedance and its allowable Voltage Standing Wave Ratio, (VSWR).

Just as MIL-C-17 covers the main types of coaxial cables, MIL-C-39012 covers many popular types of coaxial connectors. It includes mating and overall dimensions, materials, performance, and testing procedures for each type of connector.

In selecting a connector, users generally consider cable size, frequency range, and coupling method.

Cable size determines the connector series as subminiature, miniature, medium or large.

Frequency range determines the upper frequency limit of the applications. The connectors can be used at lower frequencies but are not recommended at higher frequencies where performance (especially VSWR) becomes degraded. Both BNC and TNC series connectors, for instance, can be used with miniature cable. The TNC connector however is usable to 11 GHz, while the BNC is limited to 4 GHz. (This is due to the difference between bayonet and screw couplings.) If the highest frequency of the application is 2 Ghz, either connector can be used. If the highest frequency is 8 Ghz, the TNC is the obvious choice.

Coupling method determines the procedure for joining two mating connectors. The three common types are bayonet, screw and snap-on. Often the coupling method is the main difference between two series of connectors. For example, the BNC connector uses bayonet coupling; the TNC connector is the essentially the same, but with a threaded coupling.

Question: Does tubing have a shelf-life?

Answer:
Yes, but most polymers, when stored properly, will last many years. A cool, dry environment, away from sunlight, is best for storing heat shrink tubing. Since polymers have different shelf lives, contact us for more information.

Question: What is the difference between
Thermocouple wire and Thermocouple Extension cable?

Answer:
Extension grade cables have a smaller temperature range than Thermocouple wire. Please note that the temperature range that is being referred to here is with respect to a thermocouple junction meeting the ISA/ANSI requirements for limits of error. If the conductors do not form a thermocouple junction, then there is no performance difference between the two. Additionally the maximum temperature rating of the cable is less than the thermocouple junction rating is.

The cable temperature must never be exceeded.

Do you have questions? E-mail Patti Dykstra of Anixter Wire & Cable and she will provide you with the answers. Wiring Harness News prints this column each issue as a service to our readers. E-mail: patti.dykstra@anixter.com