The BNC connector is a miniature quick connect/disconnect radio frequency connector used for coaxial
cable. It features two bayonet lugs on the female connector; mating is fully achieved
with a quarter turn of the coupling nut. BNC connectors are used with miniature-to-subminiature
coaxial cable in radio, television, and other radio-frequency electronic equipment, test
instruments, and video signals. The BNC was commonly used with 10BASE2 computer networks.
BNC connectors are made to match the characteristic impedance of cable at either 50 ohms or 75
ohms. They are usually applied for frequencies below 4 GHz and voltages below 500 volts.
Similar connectors using the bayonet connection principle exist, and a threaded connector
is also available. United States military standard MIL-PRF-39012 entitled Connectors,
Coaxial, Radio Frequency, General Specification for covers the general requirements and tests
for radio frequency connectors used with flexible cables and certain other types of coaxial
transmission lines in military, aerospace, and spaceflight applications.
Use
The BNC was originally designed for military use and has gained wide acceptance in video
and RF applications to 2 GHz. The BNC uses a slotted outer conductor and some plastic
dielectric on each gender connector. This dielectric causes increasing losses at higher
frequencies. Above 4 GHz, the slots may radiate signals, so the connector is usable, but not
necessarily stable up to about 11 GHz. Both 50 ohm and 75 ohm versions are available.
The BNC connector is used for signal connections such as:
analog and serial digital interface video signals
amateur radio antennas aerospace electronics
test equipment.
The BNC connector is used for composite video on commercial video devices. Consumer electronics
devices with RCA connector jacks can be used with BNC-only commercial video equipment by
inserting an adapter. BNC connectors were commonly used on 10base2 thin Ethernet network
cables and network cards. BNC connections can also be found in recording studios. Digital
recording equipment uses the connection for synchronization of various components via
the transmission of word clock timing signals. Typically the male connector is fitted to
a cable, and the female to a panel on equipment. Cable connectors are often designed to be
fitted by crimping using a special power or manual tool. Wire strippers which strip outer
jacket, shield braid, and inner dielectric to the correct lengths in one operation are
used. Origin
The connector was named the BNC after its bayonet mount locking mechanism and its inventors,
Paul Neill and Carl Concelman. Neill worked at Bell Labs and also invented the N connector;
Concelman worked at Amphenol and also invented the C connector. A backronym has been mistakenly
applied to it: British Naval Connector. The basis for the development of the BNC connector
was largely the work of Octavio M. Salati, a graduate of the Moore School of Electrical
Engineering of the University of Pennsylvania. In 1945, while working at Hazeltine Electronics
Corporation, he filed a patent for a connector for coaxial cables that would minimize wave
reflection/loss. The patent was granted in 1951.
Types and compatibility
Types BNC connectors are most commonly made in 50
and 75 ohm versions, matched for use with cables of the same characteristic impedance.
The 75 ohm types can sometimes be recognized by the reduced or absent dielectric in the
mating ends but this is by no means reliable. There was a proposal in the early 1970s for
the dielectric material to be coloured red in 75 ohm connectors, and while this is occasionally
implemented, it did not become standard. The 75 ohm connector is dimensionally slightly
different from the 50 ohm variant, but the two nevertheless can be made to mate. The
50 ohm connectors are typically specified for use at frequencies up to 4 GHz and the
75 ohm version up to 2 GHz. A 95 ohm variant is used within the aerospace sector, but rarely
elsewhere. It is used with the 95 ohm video connections for glass cockpit displays on
some aircraft. Video and DS3 Telco central office applications
primarily use 75 ohm BNC connectors, whereas 50 ohm connectors are used for data and RF.
Many VHF receivers used 75 ohm antenna inputs, so they often used 75 ohm BNC connectors.
Reverse-polarity BNC is a variation of the BNC specification which reverses the polarity
of the interface. In a connector of this type, the female contact normally found in a jack
is usually in the plug, while the male contact normally found in a plug is in the jack. This
ensures that reverse polarity interface connectors do not mate with standard interface connectors.
The SHV connector is a high-voltage BNC variant that uses this reverse polarity configuration.
Smaller versions of the BNC connector, called Mini BNC and High Density BNC, are manufactured
by Amphenol. While retaining the electrical characteristics of the original specification,
they have smaller footprints giving a higher packing density on circuit boards and equipment
backplanes. These connectors have true 75 ohm impedance making them suitable for HD
video applications. Compatibility
The different versions are designed to mate with each other, and a 75 ohm and a 50 ohm
BNC connector which both comply with the 1978 standard, IEC 169-8, will mate non-destructively.
At least one manufacturer claims very high reliability for the connectors' compatibility.
At frequencies below 10 MHz the impedance mismatch between a 50 ohm connector or cable
and a 75 ohm one has negligible effects. BNC connectors were thus originally made only
in 50 ohm versions, for use with any impedance of cable. Above this frequency, however, the
mismatch becomes progressively more significant and can lead to signal reflections.
BNC inserter/remover tool A BNC inserter/remover tool also called a
BNC tool, BNC extraction tool, BNC wrench, or BNC apple corer, is used to insert or remove
BNC connectors in high density or hard-to-reach locations, such as densely wired patch panels
in broadcast facilities like central apparatus rooms.
BNC tools are usually light weight, made with stainless steel, and have screw driver type
plastic handle grips for applying rotating torque. Their shafts are usually double the
length of a standard screw driver. They help to safely, efficiently and quickly
connect and disconnect BNC connectors in jack fields. BNC tools facilitate access and minimize
the risk of accidentally disconnecting nearby connectors.
Similar connectors
SR-50 and SR-75
In the USSR, BNC connectors were copied as SR-50 and SR-75 connectors. As a result of
recalculating from imperial to metric measurements their dimensions differ slightly from those
of BNC. They are however generally interchangeable with them, sometimes with force applied.
TNC
A threaded version of the BNC connector, known as the TNC connector is also available. It
has superior performance to the BNC connector at microwave frequencies.
Twin BNC or twinax Twin BNC connectors use the same bayonet latching
shell as an ordinary BNC connector but contain two independent contact points, allowing the
connection of a 78 ohm or 95 ohm shielded differential pair such as RG-108A. They can
operate up to 100 MHz and 100 volts. They cannot mate with ordinary BNC connectors.
An abbreviation for twinax connectors has been BNO.
Triaxial Triaxial connectors are a variant on BNC that
carry a signal and guard as well as ground conductor. These are used in sensitive electronic
measurement systems, such as those made by Keithley Instruments. Early triaxial connectors
were designed with just an extra inner conductor, but later triaxial connectors also include
a three-lug arrangement to rule out an accidental forced mating with a BNC connector. Adaptors
exist to allow some interconnection possibilities between triaxial and BNC connectors. The triaxial
may also be known as a Trompeter connection. High voltage connectors
For higher voltages, MHV and SHV connectors are typically used. MHV connectors are easily
mistaken for BNC type, and can be made to mate with them by brute force. The SHV connector
was developed as a safer alternative, it will not mate with ordinary BNC connectors and
the inner conductor is much harder to accidentally contact.
Miniature connectors BNC connectors are commonly used in electronics,
but in some applications they are being replaced by LEMO 00 miniature connectors which allow
for significantly higher densities. In video broadcast industry, the DIN 1.0/2.3 and the
HD-BNC connector are used for higher density products
See also Coaxial cable
RF connector UHF connector
SMA connector, SMB connector, SMC connector TNC connector, N connector, C connector
References
External links Media related to Connectors at Wikimedia Commons
Media related to BNC connectors at Wikimedia Commons