Editing BNC connector (section)

==Types and compatibility==
[[File:BNC 50 75 Ohm.jpg|thumb|right|BNC connectors. From left to right: 75&nbsp;Ω female, 75&nbsp;Ω male, 50&nbsp;Ω female, 50&nbsp;Ω male.]]

===Types===
BNC connectors are most commonly made in 50 and 75 [[ohm]] versions, matched for use with cables of the same [[characteristic impedance]]. The 75 ohm types can sometimes be recognized by the reduced or absent [[dielectric]] in the mating ends but this is by no means reliable. There was a proposal in the early 1970s for the dielectric material to be coloured red in 75 ohm connectors, and while this is occasionally implemented, it did not become standard. The 75 ohm connector has slightly different dimensions from the 50 ohm variant, but the two can nevertheless be made to mate. Note that if a male 50 ohm connector has its pin larger than that of a 75 ohm one  then it can widen the female, causing a faulty connection when a 75 ohm connector is inserted later. The 50 ohm connectors are typically specified for use at frequencies up to 4&nbsp;GHz and the 75 ohm version up to 2&nbsp;GHz.

Video (particularly HD video signals) and [[Digital Signal 3|DS3]] Telco central office applications primarily use 75 ohm BNC connectors, whereas 50 ohm connectors are used for data and RF. Many VHF receivers used 75 ohm [[antenna (radio)|antenna]] inputs, so they often used 75 ohm BNC connectors.

Reverse-polarity BNC (RP-BNC) is a variation of the BNC specification which reverses the polarity of the interface. In a connector of this type, the female contact normally found in a jack is usually in the plug, while the male contact normally found in a plug is in the jack. This ensures that reverse polarity interface connectors do not mate with standard interface connectors.<ref name="amphenol"/>{{failed verification|date=December 2020}} The [[SHV connector]] is a high-voltage BNC variant that uses this reverse polarity configuration.

Smaller versions of the BNC connector, called Mini BNC and High Density BNC (HD BNC), are manufactured by [[Amphenol]]. While retaining the electrical characteristics of the original specification, they have smaller footprints giving a higher packing density on circuit boards and equipment backplanes. These connectors have true 75 ohm impedance making them suitable for HD video applications.

===Compatibility===
The different versions are designed to mate with each other,<ref name="amphenol"/>{{failed verification|date=December 2020}}
and 75&nbsp;ohm and 50&nbsp;ohm BNC connectors that comply with the 2007 IEC standard, IEC 61169-8,<ref name="IEC 61169-8">[https://webstore.iec.ch/publication/4753] Radio-frequency connectors – Part 8: Sectional specification – RF coaxial connectors with inner diameter of outer conductor 6,5 mm (0,256 in) with bayonet lock – Characteristic impedance 50 Ω (type BNC)</ref> will mate non-destructively. At least one manufacturer<ref name="canford-2">[http://www.canford.co.uk/Technical/Article/BNCConnectors Canford]. "In over 15 years and many million BNC connectors we have no first hand experience of incompatibility between 50&nbsp;ohm and 75&nbsp;ohm types, other than extremely rare (and very obvious) manufacturing faults."</ref> claims very high reliability for the connectors' compatibility.

At frequencies below 10&nbsp;MHz the impedance mismatch between a 50&nbsp;ohm connector or cable and a 75&nbsp;ohm one has negligible effects.<ref name="canford-1">[http://www.canford.co.uk/Technical/Article/BNCConnectors BNC Connectors], The Canford Group</ref> BNC connectors were thus originally made only in 50&nbsp;ohm versions, for use with any impedance of cable. Above this frequency, however, the mismatch becomes progressively more significant and can lead to signal reflections.