The plug that is used for terminating cables between the receiver, transmitter or transceiver and the antenna is generally referred to as the RF connector because it carries the Radio Frequency signal to/from the equipment.
In addition to mating the radio to the antenna via a transmission line (usually a coaxial cable) it may also used on RF test equipment (antenna analyzer, power and SWR meters, spectrum analyzer) and dummy loads. All hams should be familiar with different RF connectors so we’ll give a brief high-level description here.
Good news! There are only four common types of RF connector used in ham radio:
By far the most common RF connector, the PL-259 is used to connect most all modern HF transceivers and VHF/UHF mobile rigs to the antenna. The PL designation stands for plug and the 259 is an old US Signal Corps assignment. It has a male center pin and female thread.
The mating receptacle found on the radios and equipment is known as a SO-239. SO for socket, it features a female center receptacle and has male threads.
The PL-259 and SO-239 combination (details here) is frequently referred to as a “UHF connector” although this designation comes from the 1930s when UHF was considered anything above 30MHz. It has performance limitations above 100MHz so other connector types are more suitable for true UHF use.
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