Reader-supported. GopherTrunk is free, open-source software. Some
hardware links on this page go to Amazon with our Associates tag
(gophertrunk-20); if you buy through them we may earn a small
commission at no extra cost to you. It never changes which gear we recommend, and
the software stays free either way. How GopherTrunk is funded →
SDR Cables & Connectors Guide
Your SDR is almost certainly SMA; your antenna might not be — and the cable between them can quietly throw away signal. This is the unglamorous plumbing of an SDR scanner, but getting it right is the difference between a clean control-channel lock and a mysteriously deaf setup. Here is what plugs into what, and which coax to run.
Key takeaways Most SDRs use SMA; antennas often use BNC, UHF (PL-259), N, or F. An adapter kit bridges any mismatch for a few dollars. SMA ≠ RP-SMA — the pins are reversed. Coax loss climbs with frequency — keep runs short, use RG58/RG8X for distance. Every junction costs a little signal — minimize them.
The connectors you will meet
| Connector | Where you see it | Notes |
|---|---|---|
| SMA | Most SDRs, small antennas | The SDR default. Watch for RP-SMA (reversed pin). |
| MCX | Some older/cheaper dongles | Tiny snap-on; adapt to SMA. |
| BNC | Scanners, test gear, some antennas | Quarter-turn bayonet; common on whips. |
| UHF (PL-259 / SO-239) | Scanners, CB, ham, discones | Large screw-on; despite the name, mostly HF/VHF. |
| N | Outdoor / higher-end antennas | Rugged, weatherproof, good to UHF. |
| F | TV-style dongles, cable TV | Push/screw; low quality for RF work. |
SMA and RP-SMA are not interchangeable. They look the same but the center conductor is reversed — RP-SMA (Wi-Fi gear) will not properly mate with the plain SMA on your SDR. When in doubt, buy standard SMA and read the listing.
Adapters and pigtails to keep on hand
16-piece SMA adapter kit
around $13
SMA to/from BNC, UHF, N, and F in both genders. Covers almost any SDR-to-antenna mismatch you will hit — the one thing to buy if unsure.
Adapter kit on Amazon →RTL-SDR Blog RG316 pigtail kit
around $15
Short flexible RG316 pigtails with SMA and common terminations — perfect for connecting a dongle to a fixed antenna or feedline without stress on the jack.
Pigtail kit on Amazon →NooElec SMA connectivity kit
around $18
Eight assorted SMA cables and adapters — extensions, gender changers, and jumpers to reach a window or bench-mounted antenna cleanly.
Cable kit on Amazon →Coax and loss
Cable is not free signal — it is a lossy component, and the loss gets worse as frequency rises. That matters because trunked public-safety systems sit at UHF (700/800 MHz), right where thin cable bleeds the most.
| Coax | Loss | Flexibility | Best for |
|---|---|---|---|
| RG316 | High (per foot) | Very flexible, thin | Short bench pigtails, tight bends |
| RG58 | Medium | Moderate | General jumpers, medium runs |
| RG8X | Lower | Stiffer, thicker | Longer outdoor feedlines |
Rules of thumb that keep signal on the wire:
- Short is better than good. The cheapest way to cut loss is a shorter run. Put the SDR near the antenna and send USB or network the long way, not RF.
- Match the cable to the distance. RG316 for a foot or two; RG58/RG8X for anything across a room or up a mast.
- Fewer junctions. Each adapter adds a little loss and a possible bad contact. One clean adapter is fine; a tower of six is not.
- Long run? Amplify at the antenna. If distance is unavoidable, a mast-mounted LNA recovers feedline loss before it happens — but only if the signal environment is not already strong enough to overload.
Weatherproof outdoor connections. Any junction exposed to weather needs self-amalgamating tape or a proper boot. Water in coax raises loss permanently and corrodes connectors — the slow death of many rooftop antennas.
A typical clean setup
For most people: an SDR with an SMA jack, a short RG316 pigtail or SMA jumper out to a dipole or discone, and — if the antenna terminates in BNC or UHF — one adapter from the kit. That is the whole RF chain. Keep it short, keep it clean, and the dongle will hear everything the antenna does.
Bottom line
Assume your SDR is SMA and your antenna might be anything — so keep a cheap adapter kit on hand and you will never be stuck. Use RG316 for short jumpers and thicker RG58/RG8X for distance, keep every run as short as you can, and minimize junctions. Get the plumbing right and a $35 dongle on a good antenna runs GopherTrunk flawlessly. Next stop: the what-you-need checklist and the hardware setup guide.
Frequently asked questions
What connector does an SDR use?
Most modern SDRs — RTL-SDR Blog, Airspy, HackRF — use an SMA jack. Older or cheaper dongles sometimes use the smaller MCX or the TV-style PAL/F. Many antennas, meanwhile, use BNC, UHF (PL-259/SO-239), or N. An SMA adapter kit bridges almost any mismatch for a few dollars.
What is the difference between SMA and RP-SMA?
They look identical but the pin and socket are reversed. Standard SMA (used by SDRs and most antennas) has a center pin on the male side; RP-SMA (common on Wi-Fi gear) has a center socket. They do not mate properly. Buy plain SMA for SDR work and check listings carefully.
Which coax should I use for an SDR antenna?
For short bench runs, thin RG316 pigtails are fine and flexible. For any real distance, use lower-loss cable — RG58 or RG8X — because loss climbs steeply at the UHF frequencies trunked systems use. Keep every run as short as practical.
Do adapters and cables lose signal?
A little. Each adapter and connector adds a small insertion loss, and cable adds loss per foot that worsens with frequency. One or two quality adapters are negligible; a stack of cheap ones on a long thin cable is not. Minimize the number of junctions and the cable length.
What is a PL-259 / UHF connector?
UHF connectors — the plug is a PL-259, the jack an SO-239 — are the large screw-on connectors common on scanners, CB, and ham gear. Despite the name they are used mostly at HF/VHF. An SMA-to-UHF adapter lets an SDR use an antenna or coax terminated this way.
Do I need a whole connector kit or just one adapter?
If you know both ends, a single adapter is enough. If you are not sure what your antenna terminates in, or you tinker with different gear, a 16-piece SMA adapter kit costs about the price of two single adapters and covers BNC, UHF, N, and F in both directions.