After 60 years, the legacy BNC connector design add new features that provide the highest quality and reliability for future connector applications.
By Wayne Zahlit, Mark Schwartz, and Dale Reed
The intrinsic integrity and continued evolvement of the BNC (Bayonet Neill Concelman) connector have long made it the design of choice for the reliability-driven public service telephone network (PSTN) industry. Recent innovations to the BNC connector, often mistakenly referred to as the British naval connector or confused with the bayonet nut connector, are focused on adapting its legacy design for future applications in the public network, enterprise, and military arenas.
The latest improvements in compliance standards, miniaturization, and quality installation features attest to the BNC connector's rising popularity among network engineers who demand reliability at all costs. The requirement for electronic components to be "faster, smaller, and cheaper" still holds true for connectors. However, because the "faster" is determined by the choice of network transport protocol and "cheaper" has never replaced reliability as the top criteria for connectors in the telephone network, BNC manufacturers have focused on "smaller"—while adding additional reliability testing and new innovative design features (see Connector Specifier, Sept. 2001, p. 13).
The BNC legacy
The BNC connector was developed in the United Kingdom during the 1940s—named for its "bayonet"
coupling mechanism and its two inventors, Paul Neill (who is credited with developing the N-series connector at Bell Labs) and Carl Concelman (an Amphenol engineer and developer of the C-series connector). It is commonly believed that the coupling mechanism was dubbed "bayonet" because it slides straight in and is given a twist, likened to the standard twist-on attachment used to affix the soldier's bayonet to his rifle.
The connector has a center pin connected to the cable conductor and a metal tube connected to the outer cable jacket. A rotating ring outside the tube locks the cable to the female. Although the design is deceptively simple, the result is a solid ground connection that cannot work its way out over time. In other words, once properly connected, the connection is virtually permanent.
The BNC was originally developed as a smaller version of the Type C connector, and was adopted as a common 50-Ω connector for terminating coaxial cable. It is still commonly used on 10Base2 thin Ethernet networks, both on cable interconnections and network cards.
However, the unique position of a telephone monopoly in the Bell System, coupled with a need for best-case attenuation or loss properties in the coaxial signal line, necessitated the creation of a 75-Ω version of the BNC design in the early years. With the lowest attenuation signal, 75-Ω coax is preferred for greater deployment distances, whereas 50-Ω signal lines are best for high current and power levels. Further, a joint decision by Western Electric (now Lucent Technologies) and Bellcore (now Telcordia Technologies) established highly rigorous construction and performance specifications for carrier-grade BNC connectors used in telco operations. These standards continue today and separate standard BNC connectors from those meeting the specifications for "carrier class" reliability.
The legacy of this development resulted in two highly polarized quality classes of connectors—"carrier class" (five 9s reliability standard) and "all others." Telephone companies require the highest quality connectors for routing DS3 lines within the modern central office. Only a few BNC manufacturers meet the challenge of providing connectors with established high performance for these telco applications.
Thus, the BNC market has evolved into a highly polarized landscape of two distinct segments with a corresponding variation in performance and price. While the majority of BNC connectors are produced and marketed for cost-sensitivity, low reliability, and low-frequency applications, telecommunication and data applications require much higher performance attributes for frequency response, mating cycle life, mechanical pull strength, and other service-life characteristics.
Density and standards
In the "faster-smaller-cheaper" world of electronic innovation, the miniaturized "smaller" BNC provides a substantial and valuable decrease in the equipment real estate required in large network termination areas such as the central office. Central office congestion issues are a pain point for the PSTN, and procuring a connection interface that enables substantially higher densities of equipment, without sacrificing quality and reliability, is a critical issue. In response to the problem, the mini-BNC (M-BNC) connector appeared in 2001, increasing densities by as much as 40% (see Fig. 1).
Another important milestone achieved by one leading BNC manufacturer is the completion of Network Equipment Building Systems (NEBS) specification testing for both BNC and M-BNC 75-Ω products. NEBS is the standard baseline for vendor selection and deployment by today's public network carriers in order to gain assurances in product quality, interoperability, and reliability.
Bellcore introduced the NEBS requirements in 1985 as a public document, targeting manufacturers of central office equipment. This introduction extended the original principles from the pre-divestiture-Bell-Labs focus of telephone companies to the growing industry of equipment manufacturers supplying a broad range of telecom equipment.
NEBS testing is extensive, challenging, and an expensive investment for the product manufacturer. For a BNC supplier to be considered by big players such as Verizon, these tests are a requirement today—particularly for equipment in the central office space. NEBS certification involves a barrage of tests from seismic and airborne particulate testing to flame and drop tests.
BNC connectors that pass NEBS testing offer the highest quality and long-term reliability in the field. They also provide sustainability in the face of environmental disasters when the telephone network becomes our society's critical communication link, as it did in the 9/11 World Trade Center disaster.
Common-sense features
Along with miniaturization and successful NEBS testing, dedicated BNC innovators are continually adding new common-sense features to ensure installation and performance quality. The latest feature may not be considered an engineering marvel, but central office technicians are thrilled by it. Envisioned and engineered to improve network installation quality, a simple notch was added at the back of the BNC (or M-BNC) connector to provide a highly visible indication that each connector is fully engaged and secure (see Fig. 2).
Although carriers experience occasional incidents of improper connector termination onto the cable, remedying that problem lies in proper installer training and performance. More common and vexing for carriers is the high incidence of technicians simply not twisting the coupling sleeve completely to lock it in place—and inspecting the connectors is cumbersome and time-consuming within such a tightly-spaced environment, often requiring special tools.
This new, simple visual indicator feature enables technicians, installer, or inspector to visually scan the connector to confirm full engagement (see Fig. 3). It enables rapid, positive identification that the coupling sleeve has been fully rotated—simple, but a huge improvement for the technician and critical for system reliability.
The BNC connector is still a versatile and simplistic device for important coaxial connector applications. Through miniaturization, NEBS testing, and features like the visual indicator, the carrier reaps an indirect cost savings. As central offices gear up for new services, such as fiber-to-the-premise service that delivers triple-play applications, carriers will reap the benefits of reliability and avoid the costly pitfalls of preventable connection problems.
WAYNE ZAHLIT is director of engineering, MARK SCHWARTZ is the quality manager, and DALE REED is vice president of sales and marketing at Trompeter Electronics, a Stratos International company, 31186 La Baya Drive., Westlake Village, CA 91362-4047; Tel: (818) 707-2020; e-mail: dale.reed@trompeter.com.
