What is a coaxial connector?

A coaxial connector is an electronic component. People often call it a coax connector or a coax plug. Its job is quite simple. It connects a special kind of wire, the coaxial cable, to a device. Or it connects two coaxial cables together. This connector is very important. It must be made well, because it has to protect the signal inside the wire. It also has to make sure the signal can travel fast and clean, so data is not lost.

Understanding the Coaxial Cable

We must first talk about the coaxial cable. The connector is built just for this kind of cable. A coaxial cable is a special type of electrical wire. It is not just several wires twisted together. It has four layers. These four layers and how they are placed are extremely important.

Layer One: The Center Conductor

This wire is in the very middle. It is usually a solid copper wire, or it is a copper-plated steel wire. This is the path for the signal. The electrical signal runs through this conductor.

Layer Two: The Dielectric (Insulator)

The dielectric is outside the center conductor. It is made of plastic or foam material. Its job is to wrap the center wire. It stops the center wire from touching the next outer layer. This insulating layer is very important, because it must keep the center wire and the outer layer at the exact same distance apart everywhere.

Layer Three: The Shield

The shield layer is outside the dielectric. It is usually a braid of metal wires or a foil made of aluminum. This shield acts like protective armor. Its job is to protect the signal inside. There is a lot of electrical interference outside the cable. This interference can ruin the signal. The shield blocks this outside interference. And it also stops the signal inside from escaping.

Layer Four: The Jacket

The jacket is the outermost layer. It is a thick layer of plastic or rubber. Its job is to protect all the inside layers. It stops the wire from being damaged by water, dirt, or physical force. The four layers work together. The signal travels in the space between the center conductor and the shield. This structure is very good, so the coaxial cable can carry very high-frequency signals. And the signal stays very clean.

The Job of the Coaxial Connector

The coaxial connector's main job is to perfectly bring the signal out of the cable.

The wire must connect to a TV, or to a radio transmitter, or to a test device. You cannot just tape the wire ends to the equipment. You need the connector.

The connector is a bridge. It perfectly connects the cable's four layers to the device's interface. It must do two main things.

First: Physical Connection

The connector must connect the cable's inner center conductor very precisely to the device's center contact point. Then it must connect the cable's outer shield very precisely to the device's outer metal body. This connection must be very tight, because it must not move or break.

Second: Signal Impedance Matching

This is the most important job. The connector must keep the signal's "impedance" the same.

Impedance is like the electrical resistance the signal feels as it travels down the cable. Coaxial cables usually have an impedance of 50 Ohms or 75 Ohms.

The connector must make sure its own impedance is also 50 Ohms or 75 Ohms. If the cable impedance is 50 Ohms, but the connector impedance suddenly changes to 100 Ohms, then the signal will have a major problem.

A signal traveling down the line hits the change in impedance. It is like a wave hitting a sudden wall. Part of the signal will "bounce back." This is called "reflection." The reflected signal travels backward. And it mixes with the forward signal. So the signal gets weak, and it causes many errors.

A good coaxial connector keeps the impedance of the cable perfectly steady into the device. So the signal does not bounce back, and it can travel a long distance very fast.

The Structure of the Connector

A connector looks like a small piece of metal. But it has many precise parts inside. It also must have a structure that mirrors the cable's four layers.

The Center Pin

This is the very middle part of the connector. It is often plated with gold, because gold conducts electricity very well. Its job is to connect to the cable's center conductor. This pin must be very straight and very smooth. The center pin can be the male part (plug) or the female part (jack).

The Insulator

The insulator is a small ring made of plastic or ceramic. Its job is to keep the center pin separate from the outer metal shell. It makes sure the pin and the shell never touch. The material and the size of this insulator are very important, because they directly control the connector's impedance.

The Outer Body

The outer body is the largest part of the connector. It is usually made of brass. It has threads or a coupling mechanism on it. Its job is to connect to the cable's shield. It also gives the connector its strength and physical protection. When the connector is attached, the outer body becomes part of the signal shield.

The Coupling Mechanis

This is the part on the outer body that locks the connector onto the device. It can be threads or a bayonet lock.

Some connectors use threads. You must twist them until they are tight. Threaded connections are very tight, so they are very stable and secure. Some connectors use a bayonet lock. You push them on, and then you turn a quarter of a turn. They lock into place. Bayonet connections are fast to connect, but they are not as stable as threaded ones.

The whole connector design is very precise. It must ensure that every layer of the cable connects perfectly to the corresponding part of the connector. And it must ensure that the impedance at this connection point does not change.

Why Impedance is the Key Problem

The concept of impedance is difficult, but it is the most crucial part of the connector's job. Impedance is measured in Ohms. Coaxial systems are designed to operate at two main impedance levels: 50 Ohms or 75 Ohms.

50-Ohm Systems

50-Ohm is the standard for almost all data communication. This includes radio, Wi-Fi, cell phone networks, and most test equipment. 50 Ohms is chosen because it is a good balance. It allows the cable to handle the most electrical power and to have a low loss of signal. This is very important for transmitting signals over antennas.

75-Ohm Systems

75-Ohm is the standard for video signals. This includes cable TV, satellite signals, and old analog video systems. 75 Ohms is chosen because it results in the lowest signal loss over a long cable. This is important for delivering clean video into homes.

The cable, the connector, and the device must all match. If you use a 50-Ohm cable with a 75-Ohm connector, the system will not work well.

The connector is where the impedance is most likely to fail. This happens because the cable's shield and center conductor change their relative positions inside the connector's small space. If the insulator inside the connector is too thin, the impedance will drop. If the insulator is too thick, the impedance will rise.

A bad connection causes "signal reflection." The signal hits the mismatch, and then a portion of the signal bounces back. This bouncing signal is bad, because it cancels out part of the forward signal. So the overall signal strength decreases. And it causes distortion and errors in digital data.

Engineers use a measurement called VSWR (Voltage Standing Wave Ratio) to test this. A low VSWR means the impedance is perfectly matched, and the signal loss is low. A high VSWR means the impedance is mismatched, and the signal is bouncing back badly. The connector must be designed to keep the VSWR as low as possible. This means the connector must maintain the impedance perfectly.

Common Types of Coaxial Connectors

There are many different types of coaxial connectors. People name them based on their size, their connection method, or their frequency use. They all share the same basic goal: protect the signal and match the impedance.

BNC Connector

The BNC connector is very common. It uses the bayonet locking system. You push it on, and then you turn it a quarter of a turn to lock it. So it connects and disconnects very quickly.

BNC connectors are often used in video surveillance systems. They are also used in test equipment, like in a laboratory where engineers connect them to oscilloscopes. BNC connectors are generally used for signals below 4 Gigahertz.

SMA Connector

The SMA connector is short for "Sub-Miniature A." It uses a threaded coupling mechanism. It is small, but it is very reliable. You must twist it to tighten it. The threaded connection is very strong, so it holds up well against vibration and movement.

SMA connectors are mostly used in wireless communication. For example, they are used for Wi-Fi antennas, cell phone signal boosters, or satellite communication. They are good at handling very high frequencies, up to 18 Gigahertz and sometimes more.

N-Type Connector

The N-Type connector is much larger. It is also a threaded connector. It is designed to be very rugged, so it can handle very high electrical power. And it is often designed to be waterproof, so it is used outdoors.

N-Type connectors are used in large antenna systems. This includes radio broadcast towers or major radar installations. Because it is large, it can handle high power. And it can work at high frequencies, sometimes up to 18 Gigahertz.

TNC Connector

The TNC connector looks like the BNC connector. But the TNC uses threads, and the BNC uses a bayonet lock. It is more stable than the BNC connector. The threaded connection makes the connection tighter. So the TNC performs better in environments with high vibration. It is also used for higher frequencies than the standard BNC.

F-Type Connector

The F-Type connector is the most common one found in homes. It is used for television, cable TV, or satellite receivers.

The F-Type connector structure is very simple. It is cheap to make, so it is used widely in civilian and consumer applications. Its impedance is always 75 Ohms, because 75 Ohms is the standard for television signals.

Other Types

There are many other types of connectors, like SMB, MMCX, and QMA. Some are for smaller size, and some are for faster connection. But they all share the same core design. They all must maintain the coaxial cable's impedance.

Correct Connector Installation

Buying a good coaxial connector is only part of the job. You must install it correctly onto the cable because only then can it work properly. A wrong installation can cause severe signal problems.

Step One: Cable Stripping

The first step is stripping the cable. You must use special tools. You have to remove the cable's four layers at exact, specific lengths. The center conductor must be bare for a short length, and the dielectric must be left for another length. And the shield must be exposed just right. If you strip the cable too short or too long, the connector will not work right.

Step Two: Pin Insertion

Then you attach the center pin to the center conductor. Some connectors need soldering. Some need crimping. But in all cases, the pin must make excellent electrical contact with the center conductor. This is the main path for the signal.

Step Three: Crimping and Securing

The final step is crimping. You use a special crimping tool to press the connector's outer body tightly onto the cable's jacket and shield. This crimping must be very tight. It fixes the shield in place, and it ensures the shield makes a very good electrical connection with the connector's outer body.

Consequences of Bad Installation

A bad installation leads to many problems.

• Shield Failure: If the shield does not connect completely to the connector, outside interference can enter the cable. So the signal quality gets very poor.
• Impedance Mismatch: If the stripping is not correct, the length of the exposed dielectric is wrong. Then the impedance suddenly changes where the cable meets the connector. So the signal reflects severely. Reflection slows down the data speed.
• Physical Movement: If the connector is not twisted tight or not crimped hard enough, it can move. Movement causes the signal to cut in and out.

A good coaxial connector and a perfect installation together ensure signal security. So professional installers are always very careful when they do this work.

A coaxial connector is a small component. But it is very important in modern communication. Its main job is to connect the cable. But it is much more than a simple physical connection. It is an impedance matcher. It must make sure the resistance of the signal path is continuous from the cable to the device. So the signal can travel far and fast.

About the Author

I'm an engineer at JINXINYANG Technology, specializing in the IC chip field. I'm dedicated to exploring how various chip technologies work together to drive progress in the digital world. With cutting-edge technology, JINXINYANG provides exceptional IC chip solutions, building a powerful and stable core for your devices.