Care and Handling of Coaxial Connectors the Quick, Foolproof Way
August 1970 Popular Electronics
You have probably seen some pretty atrocious coaxial cable connector installations. You
might have even been responsible for a few of them. It could be tempting, at least for
frequencies in the lower megahertz range, to allow yourself to be a little sloppy with
coaxial cable preparation and connector attachment, but doing so can result in marginal
functionality if power levels are high or if power levels are very low. When voltage levels
are high, excessive air gaps between the inner and outer conductors can result in arcs, and
poor connections can generate intermodulation products high enough to cause interference
(possibly subjecting you to a violation citation from the FCC). At low power levels, poor
distortions and lack of symmetry in the interface between the cable and the connector can
result in high loss and a high voltage standing wave ratio (VSWR), which might result in
lower received power and accompanying lower signal-to-noise ratio (SNR).
August 1970 Popular Electronics
of Contents]People old and young enjoy waxing nostalgic about and learning some of the history
of early electronics. Popular Electronics was published from October 1954 through April 1985. All copyrights (if any) are hereby acknowledged.
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Care and Handling of Coaxial Connectors
the Quick, Foolproof WayBy William I. Orr, W6SAI
Many of the so-called UHF connectors were developed during World War II for use with medium
size coaxial r.f. cables (such as RG-8/U and RG-11/U). Now generally supplanted by the newer
Series N connectors in commercial equipment, these inexpensive and readily available UHF connectors
are still widely used on amateur, CB, and SWL equipment. The most common members of this family
are the male plugs (PL-259, PL-259A, and UG-295/U) and the female receptacles (SO-239, UG-296/U).
For RG-8A/U and RG-58/U Cable
Adapters for RG-58/U: UG-175/U, UG-410/U
UG-297/U, UG-646/U, M-359
Adapter, straight (female-female): PL-258, UG-360/U, UG-299/U
Receptacle: S0-239, UG-296/U
Adapter, straight (male-male): Dow-Key F-2
UHF (female) to BNC (male): UG-255/U
UHF (male) to BNC (female): UG-273/U
UHF (female) to N (male): UG-146A/U
UHF (male) to N (female): UG-83B/U
to male phono connector: Dow-Key A-210
UHF (male) to male phono connector: Dow-Key A-211
UHF plug (solderless): Amphenol 83-851 (for RG-8A/U)
The male plug, a beguilingly simple affair, has a non-constant impedance, is a non-waterproof
device and (to many exasperated amateurs and CB'ers) is an invention of the devil. A look at
the PL-259 plug shows instantly how it should fit on the end of a piece of coax cable; the installation
is self-evident! But, alas, getting the plug properly astride the cable end and soldered firmly
in place is a frustrating and time-consuming task. In too many instances, the user simply gives
up the battle, jams the connector on the end of the cable, and solders what he can, leaving
whiskers of copper braid ready to short out the plug.
True, the plug manufacturers provide
nifty little drawings showing how the plug should be placed on the cable; but these pieces of
advertising art merely make the frustrating experience seem more bitter, since sooner or later
most amateurs come to the reluctant conclusion that the PL-259 plug was never intended to be
placed on a coaxial cable by the hand of man!
I have battled the PL-259 plug problem
for longer than I care to admit and I finally solved the dilemma by switching to the newer and
better type N coaxial fittings, which were seemingly designed by a sane mind. However, time
does not march on, and a large amount of gear in the W6SAI station is equipped with the PL-259's
matching partner, the ubiquitous SO-239.
Finally, with the assistance of W6CYL, who
had made his peace with the coaxial plug problem, it was decided to try a system approach that
would solve the PL-259 question once and for all. Here is the solution.
Assembly. The mating cable must be properly prepared if the connector is expected to operate
to its fullest capability. With a little care and some inexpensive tools, a well-engineered
assembly may be made in a few minutes. In addition to a soldering iron or gun, you will need:
a ruler, a sharp knife (the Stanley 99A Shop Knife is recommended), and a tubing cutter (the
General Hardware #123 Midget Tubing Cutter is recommended). Oh yes, you'll need a pair of wire
cutters to snip the cable to proper length, also.
Follow this procedure carefully:
By the time you have finished step 4, the end of your RG-8A/U cable should look like this.
Step 1. Slide the coupling ring of the PL-259 over
the coaxial line. Next, take the shop knife and circumscribe a cut in the outer, black jacket
of the cable about 1 1/2" back from the end. Make the cut at right angles to the cable so that
the end of the vinyl jacket will be square and ship-shape. Slit the free end of the jacket with
the knife and peel it off.
Step 2. You now have part of the outer braided shield exposed.
Using a hot soldering iron or gun, quickly and smoothly tin the braid, making the shield a solid
entity. Do this quickly so as not to unduly overheat the inner polyethylene insulation of the
cable. If you take too long, the inner insulation will melt and "squirt" out between the interstices
of the braid. Don't worry; you'll obtain expertise in soldering the braid once you set your
hand to it. Clean the left-over flux from the braid with paint thinner after the solder cools.
Step 3. Next, cut the soldered braid with the tubing cutter. You'll want to cut it so
that 7/16" is left exposed. Using a soft pencil, make a mark on the braid exactly 7/16" out
from the black jacket. Place the tubing cutter over the braid so that the cutter wheel falls
on the pencil mark. Tighten the cutter a bit and slowly revolve it about the cable. Tighten
the cutter wheel once or twice again and continue to revolve the cutter. Four or five revolutions,
and the tubing cutter will neatly slice the solid braid. The unwanted braid end may be easily
pulled off, using the wire cutters as snips.
Step 4. Trim the inner polyethylene insulation
of the cable. It should be cut cleanly (using the utility knife) so that a collar about 1/16"
wide is left at the end of the outer braid which was just trimmed. Go slowly, so that you do
not nick the inner conductor. Once the slug of insulation is free, it may be removed from the
cable by grasping it with your fingers and slowly but firmly pulling and rotating it at the
same time. When the slug is off, tin the inner conductor.
Step 5. You have now come to the moment of truth. The cable is ready for the PL-259 shell. It
should be pushed on the cable end and rotated with the fingers so that the internal threads
of the shell are screwed onto the outer vinyl jacket of the cable. As the plug is screwed onto
the cable, you should see the tinned outer jacket appear through the four solder holes of the
plug. Continue twisting the plug onto the cable until the braid is completely visible through
Photo shows, from top to bottom, the results of steps in preparing the cable.
Step 6. The last step is to solder the braid through the solder holes of
the plug and solder the center conductor to the center terminal of the plug. Use an iron or
gun with a small point and make neat connections to the braid, taking care that the solder does
not run over the outer threads of the plug. With a little care, you'll have a work of art. When
the joints cool, examine your masterpiece and then slide the coupling ring down over the plug.
Sealing for Outdoor Use. The PL-259 is not waterproof and must be protected against
moisture by an additional covering. If water does get into the plug, it can be very quickly
sucked down the coaxial cable by capillary action. Soon the entire outer braid becomes corroded
and line loss rises rapidly.
To seal the plug and line properly, the mating surface
between the plug and the matching SO-239 receptacle should be packed with silicone grease. The
connectors are then mated and the excess grease is forced out of the joint and wiped off. The
next step is to wrap the coaxial joint thoroughly with pressure sensitive vinyl electrical tape.
Several layers of tape should be used; and the wrappings should extend beyond each connector
a minimum of four inches, making the total wrap about ten inches long. The tape should be put
on under tension, with one layer overlapping the one beneath. As a final precaution, the cable
run should be dressed so that water cannot run to a joint and stand there.
Small Cables. The popular PL-259 UHF plug may be used with small-diameter coaxial cables (such
as RG-58/U and RG-59/U) by adding a reduction adapter. For example, RG-58/U (52-ohm cable) requires
a UG-175/U adapter and RG-59/U (72-ohm cable) requires a UG-176/U adapter. Follow much the same
procedure detailed above with the exceptions noted below.
Step 1. Insert the cable end
through the coupling ring and the adapter. Note that the knurled end of the ring and the narrow
end of the adapter face the open end of the cable. Cut the end off 3/4" of the cable jacket
with the utility knife.
Step 2. Fan the braid out slightly and fold it back over the
Step 3. Push the adapter forward under the braid and trim the braid with
small, sharp scissors to a length of 3/8". Next, using the utility knife, remove 5/8" of the
insulation from the center conductor. Be careful not to nick the conductor. Tin the exposed
conductor quickly with a small soldering iron.
Step 4. Carefully screw the plug assembly
onto the adapter. The center conductor will pass through the center pin and the braid should
appear through the side holes of the plug assembly. Using an iron with a small soldering tip,
solder the braid through the plug assembly holes. Use just enough heat to bond the braid to
the shell. After these have cooled, solder the center connector to the tip of the plug. Finally,
screw the coupling ring on the assembly.
Waterproofing and sealing are even more important
when using either the RG-58/U or RG-59/U cable.
Posted March 17, 2014