Products & Product Reviews

Guide to Coaxial Connectors: Understanding the Differences Among Coax Connectors

If you’re new to amateur radio, choosing among the various antenna connector types used for radios and antennas may be a bit confusing. They look similar and have cryptic names containing an alphabet soup of letters and numbers. It’s no wonder that some Hams—even experienced ones—sometimes order the wrong ones.

There are four main types of coaxial connectors used in Ham radio you’ll need to know. Below you will find a description of the major antenna connector types and their variations, along with a short history, common uses, and features.

PL-259

The PL-259 is the most common connector used in Ham radio. Also known as a UHF connector, it was designed in the 1930s by the Amphenol company for use as an RF connector in the radio industry when UHF referred to frequencies over 30 MHz—today it’s a bit of a misnomer. This connector is actually based on the banana plug, with a screw-on shield added.

According to their original military part numbers, the male plug is the PL-259 coaxial connector and the matching receptacle is the SO-239 connector. A related barrel connector used to join PL-259 connectors is known as a SO-239 female barrel adapter or double UHF female connector adapter. They’re useful for amateur radio applications to about 150 MHz.

PL-259s are quite versatile when it comes to accommodating a variety of cables with different diameters. When a smaller diameter coax cable variety is used, a PL-259 can be fitted with a reducer to match the large cable entry hole in the connector to the smaller cable.

N/ Type N Connector

The N connector is a threaded RF connector, an improved version of the PL-259. Undoubtedly, the N connector is the best of the bunch in terms of reliability. It also has chassis mount and barrel adapter versions similar to the PL-259.

It was one of the first connectors capable of carrying microwave frequency signals, and was invented in the 1940s by Paul Neill of Bell Labs. Neill is the “N” in the N connector, as well as the “N” in the BNC connector. Originally, the connector was designed to carry signals at frequencies up to 1 GHz in military applications, but today’s common Type N easily handles frequencies up to 11 GHz.

Because of its waterproof and solid mechanical qualities, the Type N connector is often used in base station setups, repeater installs, and anywhere absolute reliability is critical. Also, a growing number of Hams are replacing the UHF connectors on their mobile radios, following the trend of Type N connectors appearing on European mobile radios. The N connector can accommodate various sizes of cable using reducers.

BNC

The BNC (Bayonet Neill-Concelman) coaxial connector is an RF connector used for quick connect/disconnect in RF equipment, test instruments, and radio, television, and video signals. They were once the standard for HT antenna connections and are still found on low-power QRP radios.

BNC connectors contain two bayonet lugs for a twisting interface on the female connector—making them easy to install and remove quickly. They’re best suited for frequencies up to 4 GHz.

A TNC (Threaded Neill-Concelman) is like the BNC, except it has a screw coupling. It has better performance than the BNC connector at microwave frequencies up to 11 GHz and resists loosening from vibration.

SMA

SMA stands for Subminiature Version A. The SMA is a lightweight, all-purpose threaded connector that is particularly good for smaller applications like handhelds. It is usable up to 18 GHz. The SMA was developed around the 1960s in an effort to create a simple connection interface for RF coaxial cable.

The most common place you will use an SMA connector is on recently manufactured handheld/HT radios as the antenna connection or an adapter. Their small size is often more practical than the BNC connector, and the design makes it very difficult to cross-thread. The vast majority of current handheld antennas use SMA connectors.

For the most part, female SMA connectors are used on Chinese radios—brands like Baofeng, Leixen, and Wouxun. The Female SMA is the flipside of the standard SMA, but it’s incompatible with most standard antennas from mainstream brands like Icom, Yaesu, and Kenwood unless you add an adapter.

Which One?

Though they have different names and specs, connectors all share similar features and functions. Your transceiver and antenna will likely determine which you ultimately use. When it comes time to choose these connectors, keep a few things in mind:

Don’t buy cheap. The old adage “you get what you pay for” is very true for connectors. There are many cheap connectors available from many different sources. Buy a good connector from a reputable manufacturer to get the best performance.

Match the connector to your application. Keep in mind the type of coax you plan to use, its power ratings, and connector material—white bronze and silver are good conductors.

Remember to tighten the connector fully. To ensure that the connector is properly mated, it’s essential to make sure that it is fully tightened. Otherwise, there will be resistance between the two adjoining surfaces and losses will occur. Don’t overtighten it, but make sure it is secure.

If the connection is outdoors, be sure it’s moisture- and weather-resistant. My go-to solution is 3M Super 33+ Electrical Tape and Temflex 2155 Rubber Splicing Tape. Wrap with a layer of Temflex, followed by a second layer of Super 33+.

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