BNC connector cable assembly: How to connect a BNC connector to a coax cable?

A large number of radio frequency connectors are working with coaxial cables.

These connectors help maintain the shielding of coaxial cables and have a fastening mechanism of different types.

BNC connectors are common among different types.

How does the BNC connector cable assembly benefit us?

What are BNC connectors?

BNC connectors are small RF (radio frequency) connectors connecting with coaxial cables.

These connectors first came into existence in military radio equipment in the year 1940, and since then, they have been widely used in radio systems.

These connectors help maintain the characteristic impedance of the cables at either 50 or 75 ohms.

You can use them for radio and video frequency connections with frequencies ranging up to 2 Giga Hertz and up to around 500 volts. 

Disassembled BNC connector

BNC connector construction

The female connector in the BNC connector has two bayonet lugs, while the male part has a slot.

You can ensure complete mating by turning the connector a quarter from the coupling nut.

Both male and female connectors have an outer conductor with slots with plastic dielectric.

Due to this dielectric, the connector experiences signal losses at high frequencies.

For frequencies up to 4 GigaHertz, the outer slots radiate signals and thus make the connector usable.

However, for frequencies higher than this, like about 11 GigaHertz, these connectors are not stable.

You can find the interface-related specifications of the BNC connectors in MIL-STD-348.

BNC connector uses

These connectors were mainly planned for military applications.

Nowadays, along with the radio, you can use them with miniature or subminiature coaxial cables in television and various other RF equipment. 

Additionally, manufacturers used them in early computer works, such as the IBM Personal Computer network and ARCnet. 

So you can see BNC connectors on thin 10BASE2 Ethernet cables and network cards.

Further, you can use them on commercial video devices for mixed video. In such conditions, use consumer electronics with RCA jacks and commercial video equipment with BNC jacks only with the help of an adapter. 

You may also notice BNC connectors in studios where recording equipment uses BNC connections to synchronize various components. 

In BNC connections, the male part fits the cable while the female part attaches to a section of the equipment for signal connections like

• Radio antennas
• Nuclear instrumentation
• Test equipment
• Analog and serial digital interface video signals
• Aerospace electronics

The coaxial cable on panel telecommunications

BNC connector types, formats, and variants

Apart from these types, 50 ohms and 75 ohms, there is a variation of BNC connectors, i.e., RP-BNC or BNC Connectors with Reverse Polarity.

As the name indicates, in this connector, the polarity of the BNC connector reverses.

Here, the female part you usually see in the jack is in the plug, and the male is in the jack.

The reverse polarity connector does not connect with the common interface connector.

An example of this reverse polarity BNC variant is the SHV (Safe High Voltage) connector.

In addition, some miniature versions of these connectors are Mini BNC, and another is high-density BNC.

These connectors retain the original characteristics but have reduced footprints with high pack density on their circuit boards.

Such connectors have 75 ohms impedance, so you can use them with High-Density video applications.

Also, there are some straight and right-angled variants of BNC connectors.

Of these, the straight ones are more common.

You can use the right-angled connectors, where a cable separates with the plug at right angles.

Right-angled connectors are suitable for various applications like this so that the cable detaches from the connector in a tidy manner.

There is a drawback with right-angled connectors, i.e., these connectors lead to higher signal losses than straight ones.

For many applications, signal loss is insignificant for operational limit frequencies, and the difference becomes higher.

There are several BNC connector variants based on the different female sockets.

In a basic BNC connector, the socket has a panel mounting assembly having a solo connection for the coax cable.

For Earth, you can use the panel and do it with the help of a single nut. Some other connectors have bolts and four nuts to allow them to fix the panel.

However, this arrangement is suitable only for low-frequency applications and not for radio-frequency applications where you must match impedance.

For such applications, bulkhead mounting connectors are available for different cable dimensions.

You may also find adapters and attenuators beside the plugs and sockets.

Compatibility

The best part of BNC connectors is that all their different versions can manage without any doubt.

The 50-ohm and 75-ohm versions are compatible with the 2007 IEC 60169-8 and can mate with each other. 

When the frequencies are very low, i.e., below 10 MegHertz, there is some impedance mismatch between a 50-ohms cable/connector and a 75-ohms connector bit with insignificant effects.

There were 50 ohms versions of BNC connectors that you could use with cables of any impedance.

Thus, frequency mismatch becomes significant and may lead to reflections in signals.

BNC vs. SMA

Consumers may be more familiar with SMA connectors because television cable connections in homes mainly use them.

The difference is that SMA connectors are threaded, and BNC connectors are not.

What is the BNC connector cable assembly?

In the BNC connectors, the male part attaches to the ends of the coaxial cables.

It has a metal tube or ring-like structure that surrounds a pin.

This pin connects to the coaxial cable and acts as a transmission between the cable and the device connected to the cable.

BNC connector cable assembly method

The BNC connector cable assembly method has four.

Twist on 

As the name suggests, these connector types twist onto the cable.

So it is easy to use and does not need special tools.

You may need a wire stripper only to remove the cable’s insulation.

However, some people do not find twist-on connectors as reliable and secure.

Crimp-on

These crimp-on connectors have two styles: two pieces and three pieces.

Between these two, two-piece connectors are more common.

And this type of assembly requires a particular type of crimping tool for proper crimping.

Follow the below procedure for making a two-piece crimp-type assembly:

• First, slide the ferrule (a hollow tube-like portion of the connector) over the cable. Slide it a few feet so that it gets out of the way.
• Second, cut the cable end neatly and cleanly.
• Third, strip the cable with the help of a stripping tool. Make sure you strip the outer jacket about ½ inch back of the cable, strip the braided sheath about ¼ inch, and then strip the insulation about 3/16 inch from the cable end.
• Now, insert the solid central conductor of the cable into the connector’s center pin. Try to slide the center pin downwards to cover the inner insulation.
• Take a crimping tool and crimp the center pin.
• Now, slide the body of the connector on the center pin and the insulation under the braided shield. Once you start pushing, you will hear a clicking sound.
• Next, move the ferrule forward to touch the connector’s body. Finally, crimp it also with the crimping tool.

For the  three-piece crimp-type assembly:

• There is a center pin that you have to crimp to the central conductor of the cable. 
• After that, you can push this crimped pin into the correct location of an inner ferrule which separates the internal insulation and cable braid. 
• Once pushed, you can crimp the outer ferrule to the braid and external insulation to fix the cable firmly to the connector. 

Cable assembling with these connectors can take longer than the others, but finally, you will get a secure connection that will not become loose over time.

Generally speaking, these connectors are suitable for large production runs.

However, you cannot use them for rework once crimped.

F-compression

Attaching an F compression connector to the coaxial cable and then fixing it to the BNC connector.

In this method, the connector has a center pin known as a solder pin.

You can expand this compression gland to hold the sheath or braid of the cable.

You can use this type of connector with limited cable sizes.

Thus, this method and connector are suitable for small quantities of production. 

Most people prefer the second method as it does not require estimating the coax cable length as the core is visible. So there are lesser chances of error.  

F-crimp

 Like the F-compression connector, the F-connector crimps onto the cable first, and then you can screw it to the BNC connector.

Caption: Three main components of a BNC connector 

Conclusion

BNC connectors have become standard RF connectors as they are easy to use, durable, cost-effective, and easy to assemble.

However, the crucial point is knowing which connector type to pick among many variants that suit your Coaxial Cable Assembly.

If you need any help, contact Cloom.