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About That UHF Connector
26 June 2023 | by I caused a minor kerfuffle on Twitter recently, when I posted this:
This connector, properly called a PL-259, is the most common RF connector for ham radio use. The female counterpart is called the SO-239 connector. While these connectors are often “UHF” connectors, they actually don’t perform very well at those frequencies (300 to 3000 MHz). So I feel justified in disparaging that name.
The tweet generated a large number of replies, mostly in support of my anti-UHF-naming sentiment. It seems that other highly-educated and thoughtful radio amateurs agree with me. (It seems that the wise hams out there always agree with me.) You should be able to view the thread here: https://twitter.com/K0NR/status/1653575723838492672
Some people pushed back on the anti-UHF sentiment, usually saying that it is the common name for this connecter. A few folks pointed out that Amphenol calls these things “UHF Connectors”, which did surprise me. Who am I to disagree with this manufacturer of high-quality connectors? Of course, Amphenol also says this:
Originally intended for use as a video connector in radar applications, UHF coaxial connectors are general purpose units developed for use in low frequency systems from 0.6 – 300 MHz. Invented for use in the radio industry in the 1930’s, UHF is an acronym for Ultra High Frequency because at the time 300 MHz was considered high frequency. They can be used when impedance mating is not required.
Well, there you have it: the connector was named UHF back when UHF meant up to 300 MHz. (Today, UHF means 300 to 3000 MHz). I particularly like the comment “They can be used when impedance mating is not required.” What? That does not sound good for RF applications. I do agree that these connectors can generally be used to 300 MHz, but these days the ITU calls that VHF (30 to 300 MHz).
Wikipedia provides a more complete explanation, worth reading.
OK, so the name “UHF” is archaic but it has kind of stuck, the way old terminology sometimes does. I am still going to avoid using this term because it really should be deprecated.
And don’t use these connectors above 300 MHz (UHF frequencies). Unless you have to. Which I did last weekend when the only cable available for my 440 MHz antenna had a PL-259 connector on it.
73 Bob K0NR
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6 Responses to “About That UHF Connector”
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I agree with your comments on UHF connectors. I was very disappointed to learn this info over the past few years. Personally I wish BNC were the standard connector instead of UHF PL-259/S0-239. BNC is more convenient to connect and disconnect and are rated up to 3000 MHz. I have to have UHF/BNC adapters all over the place to accommodate my preference of BNC. But, we can’t do much about the default UHF connector on most ham equipment. I hope over time BNC will become more the default.
Other common constant impedance connectors are the TNC “Threaded” and its big brother, the N connector. The BNC “bayonet” is good for quick changes that occur often, such as for test equipment or GOTA/SOTA kits. But a TNC is more secure for connections that are intended to be undisturbed. Harris uses TNCs for commercial mobile equipment.
The one good feature of a PL-259 is that properly installed, it will support the weight of a coax transmission line hanging from a dipole feed point. Unsupported coax in an N connector will tend to have the cable back out of the connector a bit, retracting the center pin, and resulting in an open circuit.
“Properly installed” is the key. Properly soldering the braid on a PL-259 is notoriously difficult, in my opinion. There are compression fit PL-259 connectors which go together similar to an N connector, but they seem to be difficult to find.
I wish we could ditch the “UHF” connector, but I don’t know of another connector that’s as cheap and can withstand the abuse amateurs often inflict on connectors.
The UHF PL-259 along with splice barrel, the PL-258 have a characteristic impedance around 60 Ohms plus or minus. It is easy determined with a micrometer, or an S Parameter test fixture. The most common issues seem to be contamination of the Phenolic insulator and the tendency of the shell to come loose. Plated connectors can be soldered easily by filing off the plating and then soldering to the underlying brass. The use of Nylon for the dielectric is recommended for outdoor installations. The UHF connector has been used for 450 MHz commercial radio equipment since the early 50s and does provide reasonable service in all but critical applications. Due to its internal dimensions it has a higher standoff voltage capability than the smaller connectors. This is important in high VSWR situations. I have used most of the 100 plus “Standard” coax connectors and have found that the PL-259, (83-1SP) works well in most situations below 500 MHz.
I agree with the statement above. Proof…..I use 7/8 hardline for my 1.2 Ghz communications. I took a small piece of house wire and soldered it inside the hollow center conducter of the 7/8 hardline. I have a copper adaptor purchased from the hardware store nected down to the same size as a PL-259. The PL-259 is soldered to the copper adaptor. The house wire which is used as the center conductor was then solder to the tip of the PL-259. The PL-259/copper adaptor combo is hose clamped to the 7/8 hardline . This combination allowed me to have a 1.2 GHz communication 250 miles away. So I agree that the PL-259 will not work on UHF frequencies.
Very interesting, thanks. Andy