RF Connector Buying Guide

When it comes to transmitting radio frequencies over cable, you can't just hook up to any old wire. Coaxial cables are specially shielded to efficiently carry radio signals and are used for everything from Wi-Fi to Cable TV. Because of the way they're constructed, coaxial cables require special connectors that maintain the shielding from cable to board, and these connectors come in a variety of flavors. This guide will help you figure out which is best for your application!

For more information, please visit our website.

First, A Little Background...

Surely there are other ways to carry alternating current of radio frequency: Ladder-Line, Cage-Line, Stripline, Twisted Pairs; but the most common in the multi-megahertz range is the humble coaxial. Coaxial cable, so named because the conductor and shield share a geometric axis, was patented in by English engineer Oliver Heaviside. The advantage to using coaxial cable, and the reason it's frequently used in consumer electronics, is because they can be run near metal objects, twisted and bent without drastically affecting the signal. The reason behind that is the way that coaxial cable is constructed. By separating the central conductor from the shielding using a dielectric insulator, coaxial cables maintain a carefully controlled distance between elements regardless of the orientation of the cable. Being geometrically coaxial has its advantages as well, including the confinement of magnetic fields to the dielectric which allows for very little leakage outside the cable.

The one downside to using a coaxial cable is that you can't simply strip a couple of "coax" cables and solder them together. Okay, you can, but you create a sort of radio-frequency "kink" in the line that can interfere with your signal. To maintain the shielding effect of coaxial cable, you need to use coaxial connectors. Coaxial connectors range from millimeter-sized Hirose U.FL to (now outdated) EIA high-power connectors the size of plumbing pipe. Connectors are often patented by companies in the RF business and used to enforce standards. When those "standards" break down, connectors will sometimes be changed or deprecated. Over the years, this process along with the miniaturization of electronic devices has produced a diverse ecosystem of RF (radio frequency) connectors and cables. There are 3 or 4 different types that we deal with a lot here at SparkFun, so this guide is an attempt to give you enough info so that you can navigate to the connectors that you need.

SMA

The SMA (or Sub-Miniature A) connector has a 50Ω impedance and can handle frequencies up to 17 GHz. They're small enough for most consumer RF applications and they use a threaded housing to create strong mechanical connections. Male SMA connectors have a center pin and inner threads whereas female SMA connectors have a center sleeve and outer threads. SMA connectors are usually used for GPS and Cellular signal connections although they are used in other RF applications as well. The most common problem when working with SMA connectors is the possibility of confusion with Reverse Polarity SMA connectors.

Reverse Polarity SMA (RPSMA)

RPSMA connectors were initially introduced to prevent high-gain, professional grade antennas from being connected to commercial grade wireless equipment. Despite this, adapters and RPSMA antennas are both readily available now. Honestly, it wasn't a brilliant idea and it left consumers with a mess. But hey, hindsight's 20/20 right? RPSMA connectors are used mainly on WiFi and other consumer grade wireless equipment. Reverse Polarity SMA connectors have the same outer housing as SMA connectors, but the polarity of the connector is reversed. Male RPSMA connectors have a center sleeve and inside threads whereas female RPSMA connectors sport a center pin and outside threads. The term "Reverse Polarity" refers to this difference in connector polarity, not in any way to the signal polarity.

U.FL

The Hirose U.FL (Known by a variety of names including AMC, UMCC, IPX) is the smallest RF connector that we carry... and it's tiny! A mated connection only stands 2.5mm high! U.FL is good up to 6GHz and is usually used in applications where nothing else would fit. Often times they're used in laptop WiFi cards and embedded systems. Male U.FL connectors are surface-mount parts soldered directly into the host. Female connectors are usually manufactured as a cable assembly with a high-quality 1.32mm doubly shielded cable. Female U.FL connectors rely on pressure from the shape of the connector to keep it secure. This does form a very tight 'snap in' connection. As a result, female U.FL connectors will wear out after a several connections and will need to be replaced as they aren't generally intended to be connected and disconnected multiple times.

BNC

The BNC connector, named after its bayonet-style connector and its two inventors (Neill and Concelman) is a little bigger than the other connectors we've mentioned here. Also, because the BNC connector uses a slotted conductor, it can become an accidental radiator at at frequencies above 4GHz so its usually used for radio applications below 3GHz. You may have seen BNC connectors used for composite video on things like older studio equipment or CCTV cameras. They were also used on 10base2 this Ethernet networks. Today, they're used largely on amateur radio equipment and test equipment. You'll see these on things like oscilloscopes and different kinds of sensor connections.

Quick Reference Table

Here's a table that shows each connector, its attributes and a few products you'll find it on.

Armor-Clad (AC) Cable: AC cable includes THHN-insulated conductors with 16-gauge aluminum bond wire placed inside the armor to act as a grounding conductor.

Automotive Cable: This is a general-purpose thermoplastic (GPT) wire, also referred to as primary wire. Normal applications are within motor vehicles with limited exposure to fluids, physical wear and abuse.

Bayonet Neill-Concelman (BNC) Cable: BNC cables are small, quick-connect/disconnect radio frequency connectors used for coaxial cables.

Category Cable: This is used for systems and data networking systems. Cat 5e is the most common variety of category cable that&#;s used for computer networking on internet service installations. The conductor pairs are twisted together to prevent cross-talk and interference from other paired conductors in the cable, as well as external interference. The higher the megahertz (MHz) capability, the more twists per foot.

Coaxial Cable: This is a metallic cable that carries television and video signals. It connects to video equipment and features a central conductor with a dielectric insulator, metallic shield and plastic jacket.

Doorbell Wire: Doorbell wire is used to connect a wired doorbell or video doorbell to a home&#;s electrical system. 18-gauge wire is the variety most often used.

Dual Armored Cable: This is a durable cable that offers protection without employing electrical conduit, elbows, offsets (which can be expensive) or conduit couplings. For areas where the cable may be exposed to moisture, metal-clad armor prevents corrosion. 

RHT contains other products and information you need, so please check it out.

Flexible Cord: Typically used for industrial machinery, washing machines and large appliances, portable tools, equipment, and extension or power cords, flexible/power cord has its own naming convention based on a letter code, with a common option being SJEOOW.

• S: service cord (when not followed by a J, V or P; also indicates a rating of 600 volts)
• J: junior service cord, 300 volts
• T: thermoplastic
• E: elastomer, thermoplastic that looks and feels like rubber
• O: oil-resistant outer jacket
• OO: oil-resistant outer jacket and oil-resistant insulation
• P: parallel cord (light duty, flat)
• V: vacuum cleaner cord (light duty, round)
• W: sunlight- and moisture-resistant

Lamp Cord: Used with lamps, small appliances, radios and other similar products that don&#;t exceed 300 volts, lamp cord is available between 18- and 12-gauge sizes in a variety of colors. 

Landscape Lighting Low-Voltage (LV) Cable: This underground cable is suitable for outdoor accent lighting, landscape lighting and security lighting. Applications shouldn&#;t exceed 150 volts. It&#;s used for direct burial, is suitable for sunlight and is available between 16- and 8-gauge sizes.

Metal-Clad (MC) Cable: MC cable is used heavily in commercial electrical work, for running through concrete or in other commercial environments. Individual THHN wire conductors are run through an aluminum interlocked armor. It includes a grounding wire.

Mobile Home Feeder: This connects a mobile home to a supply of electricity where permanent wiring is required, and it&#;s suitable for direct burial and underground service entrance cable. It includes four RHH or RHW-2 conductors, with a white stripe for neutral and a green ground conductor. It&#;s sunlight-resistant.

Network and Data Cable: This comes in three types &#; fiber-optic, twisted-pair and coaxial cable &#; and is used to connect multiple networking devices or computers in a network.

NM-B: This is a non-metallic sheathed cable that&#;s used as a residential building wire for branch circuits for outlets, lighting and other residential applications. NM-B is available between 14 AWG and 6 AWG with two or three conductors.

Preassembled Whips: These are pre-cut lengths of armored cable designed to increase jobsite productivity. Assembly comes with pre-stripped THHN conductors and pre-installed zinc die-cast, snap-in fittings.

Residential Grounding Wire: This is bare copper wire that&#;s available in 4-, 6- and 8-gauge solid and stranded construction. It&#;s used to ground the residential electrical system, usually at the meter before it enters the dwelling. It&#;s also used for grounding the perimeter surface around pools.

Service Entrance Cable: This includes individual conductors rated XHHW-2 or THHN/THWN and feeds power from a main breaker to a subpanel. It can be exposed to direct sunlight and used in wet or dry locations.

• SE-R: Twisted together with a bare ground, SE-R is used to bring service from the panel to other panels in multiple-unit dwellings and in SE-U purposes.
• SE-U: Bare conductor strands are helically wound about the two paralleled insulated conductors. It&#;s used for single-family residential buildings to convey power from the service drop to the meter base and from the meter base to the distribution panel board.

Speaker Wire: Made of copper and designed to transport a low-voltage electrical current, speaker wire has a variety of wiring uses, including doorbells, thermostats, home security sensors, landscape lighting and other low-current systems. 

Sprinkler Wire: Multi-conductor sprinkler wire is suitable for direct burial on applications up to 30 volts. It&#;s used in central controls for underground sprinkler systems and is available in 18-gauge construction with up to 25 conductors.

Submersible Pump Cable: This includes THWN copper conductors that are heat-, moisture-, oil- and gasoline-resistant. It&#;s suitable for temperatures below 75 degrees Celsius with two or three conductors. It&#;s used for power and circuits for submersible pump systems.

Thermostat Wire: Used in heating and air conditioning systems, along with bell and alarm systems, thermostat wire is available in 20- or 18-gauge sizes with up to 10 conductors.

Underground (UF-B) Wire: A copper wire used for underground purposes, including direct burial, it comes in a gray jacket and can be used for deck lighting, outdoor water features, landscape lighting and air conditioner compressors.

Underground Residential Distribution (URD) Cable: Used for secondary distribution and underground service applications at 600 volts or less, it&#;s suitable for direct burial or placement in ducts. It&#;s acceptable in wet locations in triplex or quadruplex. Conductors are stranded, compressed aluminum. The neutral conductor has a yellow, triple-extruded stripe.

If you want to learn more, please visit our website Wire to Board Connector Manufacturers.