Our radio broadcast facilities
depend on many coaxial cables to get signals from one place to another. There
are good and bad ways to install connectors on those cables, which can lead to
reliable performance or to headaches. I’ve seen a number of connectors “kluge installed”
by people who didn’t know the correct methodology.
The work is
not difficult. You just have to know how and it involves a little patience.
Type N and BNC
connectors are similar, but differ in size. Both are “coaxial,” which means
that there is an inner conductor and an outer shield.
is to solder with a clamp rather than crimp connectors. This may seem like the
old-school method, but it is reliable. I remember receiving a factory-made
cable that was crimped. When I picked it up I heard a clinking sound on the
floor. A crimped center pin had fallen off. Right then, I knew that soldered
connectors are much better.
through the installation procedure for type N male connectors with the plan to
get good results.
common cables are 50 ohm with a .405 inch (10.29 mm) outer jacket, such as
RG-8, RG-213, RG-214, Belden 9913, Times Microwave LMR400 and other variants of
this popular size.
A good connector to
use on these is the Amphenol 82-202-1006, available from many places, as well
as Digi-Key, where the part number is ARF1020-ND.
cutting the end of the cable at 90 degrees. Cut it again if it is crooked. Open
the connector package and remove the contents. Save the bag to the end in case
you missed removing a part, such as the center pin. Slide the back nut, flat
washer and rubber or plastic gasket washer over the end of the cable. Then use
a box cutter tool to cut around the cable jacket about 5/16-inch back from the
end. Try not to cut into the cable outer braid. Instead, score and then pull
that end portion of the outer jacket away.
Then slide on the
clamp, sometimes called a tapered ring, followed by combing and pulling braid
back over the outside of this clamp. The backside of the clamp should fit
perfectly into a groove on the rubber washer. If not, the clamp is backwards. Trim
braid wires if they want to go back past the clamp lip.
Some engineers will
solder the cable braid to the clamp, but tolerances are tight and it can be a
tedious task involving filing down high parts so the connector fits together. I
do not normally do that.
Use the box cutter
again to cut dielectric away from the center conductor about flush with the
folded-over braid. Again, try not to damage the center conductor with the knife
blade. Slide the center pin over the center conductor. If it fits loose, then
remove the pin and use your soldering iron to “tin” the center conductor with
Slide the pin back on and feed solder into
the hole in the side of the pin. The plan is to have solder “suck” through the
hole to bond the center conductor of the cable to the pin. If there is excess
solder left over, use de-soldering braid to clean it up by pulling excess
solder off the outside of the center pin.
Use long-nose utility pliers
to pull on the center pin to assure yourself that it is firmly in place and
isn’t going to fall off the center conductor. Eyeball the center pin in
relation to the rest of the cable. Adjust its orientation as necessary to put
it straight. Then slide the main body/front side of the connector on, pushing
it until the tip of the center pin is flush with the end of the connector.
This is very
important. A pin that is too short may fail to make good contact and a pin that
is too long could damage the receiving pin on the connector to which it ultimately
In my case, I use 5/8-inch and 11/16-inch
mechanics wrenches on the connector body and nut. The important part here is to
turn the rear nut while holding the main body of the connector with the other
wrench. You don’t want to twist the main connector body on the cable as the
action can shear off outer cable shield strands.
When done right and
tightened, the connector will be firmly attached to the cable. Test it by
twisting the cable in one hand with the connector in the other hand. There
should be no give. If there is movement you have done it incorrectly. The
connector should be disassembled and installed again. A loose connector is
trouble waiting for a time to show itself.
Look at the end of the
connector. Is the center pin in the exact center? If not, use a jeweler’s
screwdriver to align it before you try to plug it with any other connector. An
off-center pin can damage the center-receiving pin on a mating connector.
Use an ohmmeter to
verify that the center pin on the connector gets to the other end of the cable
and that it is not shorted to the shield by mistake. Take your time and avoid
future problems now by doing it right.
Type N connectors are
available in 50 ohm and 75 ohm. The 75 ohm models have smaller inner pins. Do not interchange these; center pin damage
may result, or there might be an intermittent connection.
These are the most
practical tips that I can pass on after building literally hundreds of cables over
the years. Use them to get the job done right.
Persons WØMH is certified by the
Society of Broadcast Engineers as a Professional Broadcast Engineer with over
30 years experience. He has written numerous articles for industry publications
over the years. His website is www.mwpersons.com.