A Short Guide to Popular RF Connectors

An RF connector is an electrical connector designed to work at radio frequencies in the multi-megahertz range. RF connectors are typically used with coaxial cables and are designed to maintain the shielding that the coaxial design offers. Better models also minimize the change in transmission line impendence at the connection point. Mechanically, they provide a fastening mechanism (i.e., thread, bayonet, braces, or push-pull) and springs for a low-ohm electrical contact while sparing the gold surface. This allows more than 1000 re-connects and also reduces the insertion force.

Some of the most popular types of RF connectors in use today include:

• BNC (Bayonet Niell-Concelman) type (below, left)

• C (Concelman) type, (below, center)

• GR (General Radio) type

• F-type is used for all U.S. domestic cable-television and satellite installations.

• IEC 169-2 type (also called Belling Lee connector) is an EN 60169-2 standardized connector used throughout Europe and other countries for domestic television installations and for FM connector installations.

• Motorola is the standard AM-FM antenna connector used for automotive radios.

• Musa (a 75-ohm connector used in telecommunications and video)

• N (Niell) type (below, right) is a threaded connector invented in the 1940s by Paul Neill of Bell Labs and one of the first connectors capable of carrying microwave-frequency signals.

• NMM (New Motorola Mount), for mobile antennas that features a large, threaded base for durability in the wind.

• TNC (Threaded Niell-Concelman) type

• UHF connector (i.e., PL-259-239)

• 7/16 series (large, versatile 50-ohm impedance connectors with M29 x 1.5 metric threaded coupling) These rugged connectors conform to DIN 47223, and feature good power-handling capability along with VSWR as low as 1.07:1 @ 2 GHz.

Pictured below are C Connectors showing the similarity between 50- and 75-ohm (in red). Note that the 50-ohm plug is bigger and will cause damage if inserted into the 75-ohm mate.
 

Some of the common miniature types of RF connectors in use today include:

• Miniature BNC

• Miniature UHF

• DIN 47223 DIN connectors were originally standardized by Deutsches Institut fÜr Normung (DIN), the German National Standards Organization. DIN standards exist for a large number of different connectors; consequently, the term DIN connector alone does not actually identify any particular type of connector unless the document number of the DIN standard is added next to it. In the context of consumer electronics, the term DIN connector commonly refers to a family of circular connectors that were initially standardized by DIN for analog audio signals. Some of these connectors have been used at a later time in analog video devices and for digital video interfaces, such as MIDI and the IBM PS/2 computer keyboard and mouse cables. The original DIN standards for these connectors are no longer in print and have subsequently been replaced by the equivalent International standard IEC 60130-9

Sub-miniature types include:

• MCX connectors (shown right) were developed in the 1980s, they have the same inner contact and insulator dimensions as the SMB connector but are 30 percent smaller. They employ a snap-on interface and have 50-ohm impedance. They offer broadband capability from DC to 6 GHz

• FME (Fujitsu Microelectronics Europe) connectors are used for mobile antenna applications. It is a miniature screw-coupling type that has 50-ohm impedance and offers excellent electrical performance from DC to 2.0 GHz.

• SMA, SMB, and SMC (Sub-miniature type-A, type-B, and type-C) SMA connectors were developed in the 1960s as a minimal connector interface for coaxial cable with a screw-type coupling mechanism. With 50-ohm impedance, they offer excellent performance from DC to 18 GHz. SMBs are similar but feature a snap-on coupling and are available in either 50-ohm or 75-ohm impedances. They offer excellent electrical performance from DC to 4 GHz. SMCs, on the other hand, use a 10-32 threaded (screw type) interface and are available in either 50- or 75-ohn impedances. They too, offer excellent electrical performance from DC to 10 GHz

• RP-SMA / RSMA (Reverse-polarity SMA) is a proprietary variation of the SMA connector. It is used largely by WiFI device manufacturers such as Linksys, Netgear, and D-Link, and it is deigned to be incompatible with standard SMA connectors in order to comply with the United States FCC regulations that seek to prevent consumers from attaching non-standard antennas to wireless devices. The male RP-SMA connector has the same external housing as a standard male SMA connector; however, the internal prong is replaced by a receptacle. The female RP-SMA connector has the same housing as a standard female SMA connector, however, the prong found on a male SMA connector is on the female RP-SMA connector
   

Precision RF Types
APC-7 (Amphenol Precision Connector-7) is a high-grade genderless, 7mm coaxial connector used for high-frequency applications up to 18GHZ. They are often used in microwave test equipment where the highest possible quality coaxial connection is required. A properly mated pair of APC-7 connectors is virtually lossless and transparent. Their maximum VSWR is 1.04:1. Companies will frequently change the first letter of the acronym to match theirs. For example, MPC-7 would represent an APC-7 type connector from Maury Microwave, or RPC-7 from Rosenberger Micro-Coax. For this reason the acronym GPC-7 was introduced. This is short for General Precision Connector-7.

LPC-7 (Laboratory Precision Connector-7) refers to inner conductors using only air as a means of dielectric. This means that the LPC-7 can only refer to unsupported air conductors. As GPC-7 came into use for lower-grade applications, a catch-all name of PC-7 (Precision Connector-7) is now often used.

Plating Options for RF Connectors
Silver plating has long been standard on RF connectors with brass bodies, but its high cost and low corrosion resistance make it less than ideal in most applications.

Nickel plating is less expensive and more durable than silver, and is standard on many connectors. However, in some applications, nickel plating can introduce unwanted intermodulation distortion, particularly on large size connectors.

For these applications, special optional alloys are available, such as tin/zinc/copper composite. Many of these alloys offer the corrosion resistance of nickel, and the low intermodulation distortion of silver plating. Alloys, such as Albaloy plating, have the same composition and are fully-compatible with other commercial platings designated Sucoplate™, IP-23, white bronze, and tri-alloy.

Gold plating is the best but most expensive option. It is used only in high-reliability applications.