UHF Connector

The UHF connector, also sometimes known as the Amphenol coaxial connector was designed in the 1930s by a designer in the Amphenol company for use as an RF connector in the radio industry. The UHF connector was initially intended for use as a video connector for radar equipment, but it later became used in a variety of RF applications.The plug may be referred to as a PL259 coaxial connector, and the socket as an SO239 connector. These are their original military part numbers

... was originally intended for use as a video connector, but was later used as an RF connector....

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UHF connector description

These RF coaxial connectors have a threaded coupling, and this prevents them from being removed accidentally. It also enables them to be tightened sufficiently to enable a good low resistance connection to be made between the two halves. The thread for the UHF connector is a 5/8 inch 24tpi UNEF standard. It is also useful to note that the center conductor jack on the SO-239 will also accept a banana plug. This can be useful for some test applications where access is required.

PL259 RF connectors come in two sizes: for thick and thin coaxial cable. Typically the larger sized version of the PL259 would be used with RG-8/U or RG-9/U while the smaller versions are more suited to cables including RG-58/U. The basic connector remains the same, but the cable entry region is modified for the relevant type of coax cable. Thin coaxial cables are often used for short runs or 'patch' leads but not for long runs as the thinner cables have a higher loss than thicker ones. When a thin coax cable variety is needed, PL259 plugs are commonly used with a "reducer" to fit the large cable entry hole in the plug to the thin cable. It is also interesting to note that the term "PL259" originally referred to one specific mechanical design, although now it is a more generic term referring to a UHF male connector (plug).

UHF connector and reducer

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UHF connector limitations

Although UHF connectors, PL259 and SO239 variants are often used in semi-professional applications they are not widely used in all areas. The drawback of the UHF or Amphenol connector is that it has a non-constant impedance across the length of the cable. This limits their use as an RF connector to frequencies of up to an absolute maximum 300 MHz.

Although the absolute maximum frequency for UHF connectors is 300 MHz, care should be taken when using them. Low cost, and hence low quality versions are often sold, and these use inferior and cheaper materials. These connectors may be sold with CB equipment that is manufactured to a price and their performance will often be suitable to frequencies of 30 MHz maximum.