August 1970 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
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
Care and Handling of Coaxial Connectors the Quick, Foolproof
By 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).
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
For RG-8A/U and RG-58/U
Plugs: PL-259, PL-259A, UG-295/U
RG-58/U: UG-175/U, UG-410/U
Right-angle adapter: UG-297/U,
Adapter, straight (female-female): PL-258,
Receptacle: S0-239, UG-296/U
straight (male-male): Dow-Key F-2
(female) to BNC (male): UG-255/U
UHF (male) to BNC (female):
UHF (female) to N (male): UG-146A/U
to N (female): UG-83B/U
UHF (female) to male phono connector:
UHF (male) to male phono connector: Dow-Key
UHF plug (solderless): Amphenol 83-851 (for RG-8A/U)
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.
Coaxial Connector 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:
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.
By the time you have finished step 4, the
end of your RG-8A/U cable should look like this.
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 all holes.
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.
Photo shows, from top to bottom, the results
of steps in preparing the cable.
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
Use With 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 outer jacket.
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
Waterproofing and sealing are even more important when using
either the RG-58/U or RG-59/U cable.
Posted March 17, 2014