Also known as: PL-259, SO-239, UHF connector, PL259
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The UHF connector — a threaded pair whose plug is the PL-259 and whose jack is the SO-239 — is a rugged, inexpensive coaxial connector that dominates HF, CB, and lower-VHF amateur gear.1 Its defining electrical quirk is that it is not a constant-impedance connector: the internal geometry does not hold a defined 50 Ω through the joint, so it introduces a reflection that grows with frequency. Despite the “UHF” name — a 1930s marketing label from when 30 MHz counted as ultra-high — it is best used below roughly 300 MHz.
Overview
The UHF connector’s appeal is mechanical and economic. The 5/8-24 threaded shell is large, forgiving, and easy to solder onto thick coax with basic tools, and it handles high transmit power. For HF and the CB/10-metre/2-metre bands, where the frequency is low enough that the impedance discontinuity barely matters, it is a perfectly good, durable connector — which is why generations of amateur and commercial HF/VHF equipment standardised on it.
What it is
Unlike N-type or SMA, which are engineered so the coax’s 50 Ω passes cleanly through the connector body, the PL-259/SO-239 interface changes impedance internally. At HF this reflection is negligible; by the time you reach 300–450 MHz it produces measurable extra SWR and loss. This is why the connector is fine for a 2-metre rig but a poor choice for 70 cm and above, where operators switch to N or BNC. The name is a historical artifact, not a capability claim.
Variants
- PL-259 plug / SO-239 jack is the standard pair (“PL” for plug, “SO” for socket in old military nomenclature).
- Reducers (adapters) let a PL-259 sized for thick RG-8/RG-213 accept thinner RG-58 cable.
- Silver/PTFE versions improve solderability and dielectric quality but do not change the fundamental non-constant-impedance behaviour.
- Right-angle and bulkhead bodies are common for panel mounting.
Relevance to SDR
An SDR listener meets the UHF connector mostly on HF and low-VHF antennas and radios: shortwave receivers, CB and ham HF gear, and many wideband discone bases present an SO-239. Reaching a dongle then means a PL-259/SO-239 to SMA or BNC adapter. Below a few hundred MHz — which covers HF utility, CB, and 2-metre traffic — the connector’s impedance quirk costs almost nothing, so it is a practical, robust interface. For the UHF land-mobile trunking bands (700/800 MHz P25 and DMR), prefer N or SMA and keep the UHF connector out of the path. GopherTrunk is decode software and touches no connectors, but a UHF connector used well above its comfortable range adds reflection and loss that erode the signal-to-noise ratio reaching the receiver.
Where to buy
If you are pulling in an HF, CB, or 2-metre antenna — or a length of scanner/ham coax — that ends in PL-259/SO-239, an SMA-to-UHF adapter kit (8 pieces, all genders, around $12) bridges it to the dongle’s SMA port. For the higher UHF trunking bands (700/800 MHz P25, DMR), skip the UHF connector entirely and run N-terminated feedline instead. If you own a grab-bag of antennas, the broader SMA adapter kit covers UHF, BNC, N, and F in one box.
For the full connector map and coax choices, see the SDR cables and connectors guide.
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Sources
-
UHF connector — Wikipedia, on the PL-259/SO-239 pair, non-constant impedance, high-power HF/VHF use, and the historical “UHF” name. ↩
Frequently asked questions
Which PL-259/SO-239 to SMA adapter should I buy for an SDR?
An SMA-to-UHF adapter kit (8 pieces, all gender combinations, around $12) lets an SDR use a scanner, CB, or ham antenna and coax terminated in PL-259/SO-239. The kit form matters because UHF gear appears as both the PL-259 plug and the SO-239 jack, and the kit carries every SMA-to-UHF combination so you are not caught on the wrong gender.
Can I use a PL-259 antenna at 800 MHz with my SDR?
You can adapt it, but the UHF connector is a poor choice above roughly 300 MHz — it is not a constant-impedance connector, so it adds reflection and loss that grow with frequency. Below a few hundred MHz (HF, CB, 2-metre) the quirk costs almost nothing. For 700/800 MHz P25 or DMR, prefer an antenna and feedline terminated in N or SMA and keep the UHF connector out of the path.
Is a PL-259 the same as an SO-239?
They are the mating pair: the PL-259 is the plug (male), the SO-239 is the jack (socket). The names are old military nomenclature — ‘PL’ for plug, ‘SO’ for socket. An SMA-to-UHF adapter kit includes adapters that mate with each.
Why is it called a UHF connector if it is bad at UHF?
The name is a 1930s marketing label from when 30 MHz counted as ‘ultra-high frequency.’ By modern definitions the connector is really an HF/VHF part; the name is a historical artifact, not a capability claim.