Installing RF Connectors
on Coax

Wiring up RF connectors can be done in one of two ways - the wrong way and the right way. The wrong way will lead to undesired losses, intermittent comms, and an unreliable system as a whole.

Only two commonly used connectors are suitable for RF work being 'N-type' and the smaller derivative, 'BNC' (short for Bayonet N Connector). There is one connector often used known as a PL259 or UHF connector, in short, no serious designer would consider this a RF connector.

There is, unfortunately, no hard and fast way of putting RF connectors on the end of coaxes as there are many manufacturers of connectors, each with their own unique method of securing a reliable connection. There is, however, one rule that can be applied. The construction and assembly of the connector will always be such that impedance is maintained. The impedance is defined by the ratio of the outside diameter of the inner core to the inner diameter of the outer core or shield. Although connectors will use larger diameters the ratio will be maintained and observing the bits making up the connector with this rule in mind will help understand how it fits together. Once together the last important action is to ensure the connector is done up tightly if it is to remain reliable.

A word about crimp-on connectors; There is absolutely nothing wrong with using these connectors but experience has shown two weaknesses, apart from the fact they must only be crimped with the proper tool. One, these connectors are not suitable for re-use. Once on, that's it or cut off and start again. Two, never crimp the inner connection, always solder. There are two reasons for this. When used on a 'solid inner' coax the copper of the inner core and the material (usually an alloy used on the connector have different expansion coefficients therefore as the connector changes in temperature the bonding between the connector part and the cable changes and become a bad joint.

When used on a multicore inner coax the crimping places such a large amount of stress on the individual cores, at the point where the crimping begins, the cores break as the temperature changes and the different metals expand and contract at different rates.

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