The UHF connector, also called the Amphenolcoaxial connector, is a World War II threaded RF connector design, from an era when UHF referred to frequencies over 30 MHz.Originally intended for use as a video connector in RADAR applications, the connector was later used for RF applications. This connector was developed on basis of a shielded banana plug.
UHF connectors are generally usable through what is now known as the VHF and HF frequenciesand can handle RF power levels over one kilowatt. There is variation between manufacturers with the choice of dielectric, the PTFE types being favored where low loss is desired. The average power handling of the PTFE versions is essentially set by heating of the center pin, and is therefore frequency dependent, as the RF resistance rises as the skin depth falls. At low frequencies the power handling is rather better than that of the similar sized N connector. The UHF connector is the most common connector in amateur radio applications up to 150 MHz. In the US, the silver-plated version with Teflon dielectric is used in UHF applications up to 450 MHz for the 70 cm band.
Despite the name, it is rarely used in commercial applications for UHF frequencies as the non-constant impedance (the impedance drops to 30-40 Ω for a cm or so in the central region of the connector) means they create significant reflections above 300 MHz.The most popular cable plug and chassis-mount socket carry the old Signal Corps nomenclatures PL-259 (plug) and SO-239 (socket). The PL-259 can be used with large diameter coaxial cable, such as RG-8/U and RG-9/U, and the smaller diameter RG-58/U and RG-59/U with the UG-175/U and UG-176/U adapter sleeves. "PL-259" refers to one specific mechanical design, but the term is often used for any compatible UHF cable plug. The thread is 5⁄8 inch 24tpi UNEF standard. Other UHF connectors with a similar, metric, thread have been produced. The center conductor jack on the SO-239 will also accept a 4 mm banana plug.
UHF connectors were replaced in many applications by designs that have a more uniform impedance over the length of the connector, such as the N connector and the BNC connector,but they are still widely used in amateur radio, citizens' band radio, and marine VHF radio where robustness and ease of use are more important than a small mismatch. The reasons for the popularity of the UHF connector is its ease of assembly. While crimp connectors exist, the solderable screw-on connector is more common because no expensive crimping tools are required. The connector is not suitable for outdoor applications by itself but can be made weather resistant with self adhesive silicone C-Tape.
UHF connectors were also used for the input & output of composite video signals for older video equipment (such as VTRs and monitors) dating from the late 1970s and earlier. They were known by BBC engineers as "F & E" connectors, after Films & Equipment, a manufacturer.