Coaxial FAQ

A coaxial type product is one that has two conductors (inner & outer) forming a closed transmission medium.

Coaxial products are typically used for the transmission of radio frequency (RF) energy.

BNC stands for Bayonet Neill Concelman, who were the people who designed it. BNC is a type of coaxial connector used extensively in CCTV. It's a quick connect/disconnect radio frequency connector.

As an industry rule of thumb, we always say that a “Plug = male and a Jack = female”. SMB connectors unfortunately do not follow this rule. An SMB Plug actually has a female basket within a male coupling nut mechanism, while an SMB Jack contains a male center pin.

Some of the common connector types used on coaxial cable are BNC, SMA, SMB, SMC, MCX, TNC, N, SMC, MMCX, F, and UHF. These connector types come in male and female versions.

Coaxial devices work by transmitting energy along a path between the center conductor and the outer conductor.

Typically there are three broad categories:

Flexible: Similar in feel to a power cord, this type cable is flexible.

Semi-Rigid: This type of cable has a soft outer metal jacket and has limited forming properties.

Rigid: This type of cable has a metal pipe like structure with little or no bending capabilities.

A majority of coaxial cable types have their origins in the military world and are identified as RG (Radio frequency,Government ) Some common types of RG cable are RG6, RG59, RG62, RG58, RG142, RG174, RG188 and RG316.

Each cable type has performance or physical characteristics that differentiate it such as size, frequency, power, insertion loss, impedance or operating temperature.

Coaxial products are often used in broadcast, network, communications, audio/video and test applications.

The BA29, BA38, and BA23 Coax Adapters are rated for DC – 1Ghz.

RG316/U designates a special form of coaxial cable. This coax cable has a 50 Ohm impedance (figure 1), making it ideal for data transmission. RG316/U has a small diameter (0.098" nominal), is extremely flexible due to its stranded center conductor (helpful video tip), and has an FEP outer jacket that lends it an operating temperature of up to 200°C.

Common applications for RG316/U include linking test or data machines being used in a hot environment, LAN/WAN or GPS where high temperature performance is needed, labs where potentially flammable chemicals are used, and construction situations where fire codes require FEP rated cable. RG316/U is easy to work with given its flexibility. For that reason, L-com Global Connectivity sells RG316/U bulk cable in three lengths: 100 foot coax coil, 500 foot coax spool, and 1000 foot coax spool. L-com also manufacture plenty of coaxial connectors specifically shaped for thinner cables like RG316/U. Pre-terminated RG316/U cables are also available, made with SMA, SMB, SMC, and MCX connectors.

MCX Connectors conform to the European CECC 22220 spec and were introduced in the 1980s. While the MCX uses identical inner contact and insulator dimensions as the SMB, the outer diameter is approximately 30% smaller than the SMB Connector. MCX Connectors are a good option where weight and physical space are limited.

MCX connectors come in 50 Ohm or 75 Ohm, have very good electrical performance, and can accommodate a wide range of miniature RG/U flexible coaxial cables. They are commonly found in U.S. digital cellular PCN (Personal Communications Network) Infrastructure, Global Positioning Systems (GPS), Instrumentation, and Wireless LAN Systems.

50 and 75 Ohm values refer to the impedance of the coaxial cable. Impedance is a measure of resistance, in the cable, to the flow of electrical energy. There really is no “good” or “bad” impedance, just the right impedance for your application. For 75 Ohm cable, the primary application is the transmission of a video signal. In the case of 50 Ohm cable, it is a data signal that is for the most part being transmitted. Simply put, 75 Ohm is for pictures and 50 Ohm is for information.

The term low loss refers to the cables relative low attenuation (loss) over distance. The main difference between standard RG cable and low loss coaxial cable is the shielding. Low loss cable has far better shielding than typical RG style cable thus achieving better low loss characteristics. Additionally, low loss coaxial cables use solid center conductors which offer lower attenuation than stranded conductors that are sometimes found on RG style cables. Low loss coaxial cables are typically used in WLAN, Cellular, PCS, ISM and many other wireless applications.

You may have heard of low loss coaxial cable referred to by brand names (such as "LMR"), but all low loss coax cable has the similar characteristic of having a low attenuation rate even at very high frequencies (above 400 MHz). L-com carries a wide variety of high-quality low loss cable assemblies and bulk cable for applications that require a high frequency, such as wireless communication. As most other manufacturers do, we identify them by the series number, such as low loss 100 series.

Frequency is the number of times a periodic action occurs in one second. The unit of measure is hertz.

Attenuation, often called insertion loss, is a loss of signal power. This term is used in both coaxial and fiber optic products.

VSWR stands for Voltage Standing Wave Ratio. It is the amount of reflected power expressed as a ratio (1.25:1).

In simple terms, impedance, in a coaxial product, is the measurement of resistance to the flow of current. The unit of measurement is Ohms. The following is a more technically correct definition: Transmission line impedance, also known as characteristic impedance, is the ratio of the amplitudes of a single pair of voltage and current waves propagating along an infinitely long transmission line with absence of any reflections. Characteristic impedance measures like resistance when dealing coaxial cable types. Characteristic impedance is a relationship between the capacitance per unit length and the inductance per unit length. The inner and outer coaxial diameter ratios and the dielectric constant in the cable define the parameters involved in determining characteristic impedance.

A coaxial switch is used to switch energy from an input port to one of a number of output ports.

The function of a balun (acronym for BALanced/UNbalanced) is to change from one transmission medium with a defined impedance (i.e. 75 Ohms coaxial) to another transmission medium with a different impedance (ie. 120 Ohms twisted pair).

Double shielding in a coaxial cable indicates two layers of outer conductor shielding. Often one layer is a metallized foil while the other layer is a metallic braid. These two layers decrease the leakage of energy from the cable.

In a coaxial cable assembly as frequency increases so does attenuation and VSWR. Each type of coaxial cable and connector also has a cutoff frequency which is the maximum operating frequency that they can operate at.

Crimp and clamp are terms used to describe the method used to attach a connector to coaxial cable. With a crimp connector, a ring is crimped around the outer conductor (shield) to a slotted or knurled stem. A clamp connector uses a V-shaped wedge ring to secure the outer conductor (shield) to the connector body.

A twin axial cable is similar to a coaxial cable except that in a twin axial cable there are two center conductors within one outer conductor/dielectric structure.

The primary impedance standards for coaxial cable are as follows:

1. 75 Ohms, used by the telephone and broadcast industry for the transmission of voice, video and data.

2. 50 Ohms, developed by the military for ship to ship and air to ground communications.

3. 93 Ohms, developed as a low capacitance instrumentation cable.

Some of the major factors which influence shielding effectiveness of flexible coaxial cable assemblies are as follows:

1. Number of shields (flat braid, round braid and helical wrap)

2. Braid style and coverage (flat vs. round)

3. Thickness of shield material and plating.

4. Connector and style of attachment.

A solid center conductor coaxial cable will have lower attenuation per foot than a stranded center conductor coaxial cable. A stranded center conductor coaxial cable will however be more flexible than a solid center conductor coaxial cable.

The function of an auto terminating connector is to create an internal termination (resistive load) when there is no mating connector attached. When mating connectors are attached the resistor is disengaged and a transmission path is created. This eliminates the need to attach terminators (dummy loads) to unconnected ports.

An SMA connector is a semi-precision subminiature connector with a screw type coupling mechanism, 50 Ohm impedance and a typical operating frequency of DC to 18GHz.

An MCX connector utilizes a snap on coupling mechanism and has a typical operating frequency of DC to 6 GHz. This style connector is offered in both 50 and 75 Ohm versions.

An SMB connector is a reduced size version of an SMA connector with a snap on coupling mechanism. The typical operating frequency of an SMB connector is DC to 4 GHz. This style interface is offered in both 50 and 75 Ohm versions.

A BNC connector is a connector with a bayonet locking mechanism and comes in both 50 and 75 Ohm versions. BNC connectors are typically used in applications below 4GHz.

F connectors are threaded coupling connectors that have a maximum operating frequency of 1 GHz. The F type connector is a 75 Ohm impedance connector with wide use in the CATV industry.

A TNC connector is similar in size to a BNC except it features a threaded coupling nut and a typical operating frequency up to 11GHz. TNC connectors are widely used in telecommunications infrastructure applications.

An N connector features a threaded coupling nut and a typical operating frequency up to 11GHz. N connectors have a 50 Ohm impedance.

A UHF connector is the original radio frequency connector with an operating frequency range from DC to 300MHz. The UHF connector features a threaded coupling mechanism and is widely used in low frequency applications.

A reverse polarized connector is a non standard type interface that utilizes a male center conductor with a female style outer conductor coupling mechanism and a female center conductor with a male style outer conductor coupling mechanism. These types of non standard interfaces are required by FCC part 15.203 for use on specific types of wireless devices. Common types of reverse polarized connectors are TNC, SMA and N.