INSTALLING PL259s ON SMALL COAX

Probably the most common coaxial connector that we encounter is the “UHF fitting” or PL259.Introduced during World War II as a secure replacement for the banana plug, it has become the standard for HF and VHF radio frequency connectors. It will handle over a kilowatt at these frequencies, is simple, and durable. Although this connector is designed for the large .4 inch diameter cable (like RG-8 or RG-11) we usually use a smaller transmission line such as RG-58 or RG-8x since it is much more convenient as an interconnect and in vehicular installations.

Firstly, choose a good quality connector. Amphenol makes the model 83-1SP that has proven reliable and is common enough that the price is downright cheap. The connector body is brass, plated with silver and the shell is nickel. It has a nice feel compared to the foreign copies and often costs less. You can find these at most amateur radio suppliers for under $4 each or Mouser Electronics www.mouser.com for a bit more (less in quantity). For the small cables you will also need a reducer; UG-175 (Amphenol #83-185-RFX) for the .2” RG58 or the UG-176 (Amphenol #83-168-RFX) for the 1⁄4“ RG-8x. Expect to pay around a buck each for these.

Often the Amphenols show up at swap-meets for a buck apiece new and in the bag. Avoid old and tarnished ones. If you are using other brands be sure to check that the reducer reaches the bottom of the connector body! There are some that will not. These will not work. Also check that the shell is completely threaded. I have found a few that weren't threaded at all. Check them when and where you buy them. It saves time and frustration.

You could also choose to use a crimp-on connector and avoid soldering. The manufacturers would love you to do this. Those connectors are single-use only. Any mistake made installing it will mean that you will buy another connector. Any cable repair means the same thing. You would need an expensive crimper and a different set of dies for each type of cable and for different connectors. Mixing brands of crimpers and connectors is not suggested. Also you would be advised to use a special cable stripping tool for each type of cable and connector. Yes, they would appreciate your business.

The tools that you will need to install the connector will be wire cutters, a knife, a soldering gun, pliers and some good rosin-core solder. I would suggest a 150 watt soldering gun for outdoor use but I frequently use my 60 watt temperature controlled workbench iron for the small cables. Channel-lock (“water pump”) pliers provide a good grip on the connector body and smaller pliers will grip the reducer.

The first step is to remove the shell from the body of the connector and slide it onto the cable. Make certain that the threaded portion faces the connector end of the cable. Next slip on the reducer, skinny end toward the connector. Now hold up the cable end next to the connector body and align the end beside the end of the center conductor. Grasp the cable with your finger nails at a point where the four small soldering point holes appear on the body, faintly marking the jacket by pressing into the cable jacket. This is where you are going to strip the jacket off of the coax. About 3⁄4 of an inch from the end.With a sharp knife carefully score the jacket where you marked it (or are still grasping it) with your fingernails. Do not cut all the way through the jacket, just score it all around the periphery so that, when flexed, the jacket parts and reveals the shield. This is the most difficult part of the process, not nicking that shield. If you do then you will release numerous small little bits of wire that we refer to as “Murphy's Whiskers”. You remember Murphy's Law? Yep! These microscopic little wires are the enablers, lurking until the worst possible moment, just waiting to leap across the center conductor to shield and short out your connection. So don't let them loose.

Work the jacket off the end of the cable. If it just simply refuses to slip off then you must resort to scoring the jacket at a right angle to your first cut all the way to the end. Again, avoid cutting through to the shield. Split the jacket open and remove it. If any shield wires fall off then you should consider cutting off the cable at your original stripping point and discarding that inch of line and beginning again. If nothing else it is good practice. You don't lose much.

Slide the reducer to the point where the jacket now ends, fold the shield straight back over the reducer, and trim it off so that it just quite doesn't reach the threads. Small telephone lineman's snips work the best but any good quality wire cutters will suffice. Keep these little trimmings away from the work area or the connector. They will do anything to cause trouble so do not allow them the opportunity.Score and trim the dielectric from about 1⁄4 of an inch from where the shield now wraps around the reducer to the end of the cable. Use the same technique as the jacket except that now, if the insulation won't release, you cannot laterally split the plastic. Rather, you will need to carefully use a wire stripper, the snips, or wire cutters with the jaws agape and gently pull that little piece of insulation off. If the center conductor is stranded wire then gently twist it into a coherent filament and lightly tin it with solder. Just enough to hold it together, not so much that it doesn't slide into the center conductor pin of the connector body. Straighten the center conductor, if necessary, for its entry into the connector.

Inspect your work. Look for any stray strands. Knock the connector body on a hard surface to dislodge anything lurking within and then check visually for the same. It's best to find any problems at this point before final assembly. Figure it as a couple of seconds well spent.

While holding the cable and the reducer in one hand, slip the connector body over the end. Slightly rotating the connector will ensure that the center conductor finds the pin. When the connector contacts the reducer and stops then begin rotating the connector body and threading it onto the reducer. When it gets finger tight you should be able to see the coax center conductor appearing within the connector center pin. If not, back it out and see what went wrong.

Gripping the connector body firmly with pliers at the knurled area (not so forcefully that you distort it), use another set of pliers on the reducer flange to tighten it firmly. Very firmly. The center pin of the connector has a bevel on one side, hold the assembly horizontally with the bevel upward. Solder the center conductor wire to the pin being careful to use enough heat to make a good joint but not so much as to damage the insulator attaching it to the connector body. Be very careful not to get any solder on the outside of the center pin. If you do, it will distort any jack that it is inserted into and damage it: Lots of trouble to repair later on (we're talking about your expensive radios and test equipment here!). In a perfect world the wire is visible within the pin but not protruding past the end of it. If it is sticking out then snip it off so that the pin is longer than the wire within.

A gentle tug on the connector should demonstrate a snug, firm connection. A quick test with an ohm meter should result in an absolute open between shield and center conductor, assuming that the far end of the cable is also open. Slide the shell down onto the body and thread it on. Your PL259 is now installed.

With practice your installation will become progressively easier, taking less than a minute. You will appreciate the ease of removing the connector; Just cut the cable at the back of the reducer, remove that reducer, heat the center pin with the soldering iron and pull out the cable, and tap the connector on the edge of a hard surface (pin still hot and aimed downward) to knock the molten solder out of the pin and clear it.

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