Installing coaxial connectors

One of the mysteries faced by newcomers to the radio hobbies is the small matter of installing coaxial connectors. These connectors are used to electrically and mechanically fasten the coaxial cable transmission tine from the antenna to the receiver There are two basic forms of coaxial connector, both of which are shown in Fig. 1 -13 (along with an alligator clip and a banana-tip plug for size comparison)- The larger connector is the PL-259 UHF coimector, which is probably the most-common form used on radio receivers and transmitters (do not take the 4IUHF" too seriously, it is used at all frequencies). The PL-259 is a male connector, and it mates with the SO-239 female coaxial connector.

The smaller connector in Fig, 1-12 is a BNC connector, it is used mostly on electronic instrumentation, although it is used in some receivers (especially in handheld radios).

The BNC connector is a bit difficult, and very tedious, to correctly Install so 1 recommend that most readers do as 1 do: Buy them already mounted on the wire. But the PL-259 connector is another matter. Besides not being readily available already mounted very often, it is relatively easy to install.

Figure 1-14A shows the PL-259 coaxial connector disassembled. Also shown in Fig. 1-14A is the diameter-reducing adapter that makes the connector suitable for \

use with smaller cables. Without the adapter, the PL-259 connector is used for RG-8/U and RG-l 1AJ coaxial cable, but with the correct adapter, it will be used with smaller RG-58AJ or RG-59/U cables (different adapters are needed for each type).


Various types of coaxiaJ connectors, cable ends, and adapters.


Various types of coaxiaJ connectors, cable ends, and adapters.

Coaxial cable imnsmission line ("coax") 17

(A) Disassembled PL-29 connector

CB) Adapter and shield placed over the coax

(C) Coax stripped arid shield laid back onto adapter

(D) Adapter threaded into main barrel and soldered through holes in barrel

The first step is to slip the adapter and thread the outer shell of the PL-25<> over the end of the cable (Fig. l-l4B). You will be surprised at how many times, after the connector is installed, you find that one of these components is still sitting on the workbench . . . reqtiiring the whole job to he redone (sigh). If the cable is short enough that these components are likely to fall off the other end, or if the cable is dangling a particularly long distance, then it might be wise to trap the adapter and outer shell in a knotted loop of wire (note: the knot should not be so tight as to kink the cable).

The second step is to prepare the coaxial cable. There are a number of tools for stripping coaxial cable, but they are expensive and not terribly cost-effective for anyone who does not do this stuff for a living. You can do just as effective a job with a scalpel or X-acto knife, either of which cart be bought at hobby stores and some electronics parts stores. Follow these steps in preparing the cable:

1. Make a circumscribed cut around the body of the cable from the end, and then make a longitudinal cut. from the first cut to the end.

2. Now strip the outer insulation from the coax, exposing the shielded outer conductor.

3. Using a small, pointed tool, carefully unbraid the shield, being sure to separate the strands making up the shield. Lay it back over the outer insulation, out of the way,

4. Finally, using a wire stripper, side cutters or the scalpel, strip of the inner insulation away, exposing the inner conductor. You should now have of inner conductor and %" of inner insulation exposed, and the outer shield destranded and laid back over the outer insulation.

Next, slide the adapter up to the edge of the outer insulator and lay the un-braided outer conductor over the adapter (Fig. 1-14C). Be sure that the shield strands are neatly arranged and then, using side cutters, neatly trim it to avoid interfering with the threads. Once the shield is laid onto the adapter, slip the connector over the adapter and tighten the threads (Fig. 1-14D), Some of the threads should be visible in the solder holes that are found in the groove ahead of the threads. It might be a good idea to use an ohmmeter or continuity connector to be sure that there is no electrical connection between the shield and inner conductor (indicating a short, circuit).

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