Also known as: pigtail, RG316 pigtail, SMA jumper, patch lead
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A coax pigtail is a short, very flexible coaxial jumper — typically thin RG316 — with an SMA connector on one end and whatever your antenna or feedline uses on the other. Where a rigid barrel adapter changes connector type in place, a pigtail changes it over a few inches of bendable cable, so it connects an SDR to a fixed antenna or feedline without hanging the radio’s weight on the jack or forcing an awkward straight-line mate.
What it is
RG316 is a thin PTFE-insulated coax prized for flexibility and temperature tolerance rather than low loss. Over the short span a pigtail spans — inches to a couple of feet — its higher loss per foot is negligible, even at the UHF frequencies trunked systems use, so you get the bend radius and strain relief without paying meaningfully in signal. A pigtail kit usually bundles several jumpers terminated in SMA plus common far-end connectors (BNC, UHF, N, SMA-to-SMA), covering the same mismatches an adapter kit does but as flexible leads.
The practical reason pigtails exist is mechanical. An SDR’s SMA jack is a small solder joint on a circuit board; hanging a heavy antenna, a stack of adapters, or a stiff cable directly off it stresses that joint and can crack it. A short flexible pigtail takes the load and the motion instead, and lets you route the connection around a corner or down to a panel-mounted socket that a straight barrel could never reach.
Relevance to SDR
On the bench, a pigtail is how you get a dongle’s port comfortably away from a crowded USB hub and onto a window-mounted antenna or a length of feedline. It is the flexible complement to the rigid adapter kit: the adapter changes the connector, the pigtail gives you the slack and the strain relief. For an RTL-SDR sat in a USB port with a fixed antenna a foot away, a single pigtail is often the entire cable budget.
What a pigtail is not is a feedline. RG316’s loss climbs steeply with length, so chaining pigtails to reach across a room throws away signal fast. For any real distance, run proper low-loss coax — or, better, keep the RF run short by moving the whole SDR to the antenna on a USB extension and sending data the long way. GopherTrunk decodes whatever the front end captures and has no view of the cable; the pigtail’s only job is to deliver the antenna’s signal to the SDR cleanly and without mechanical stress.
Where to buy
An RG316 SMA pigtail kit (around $15) is the flexible-lead staple — a set of short jumpers in SMA plus the common terminations, so a dongle can reach a fixed antenna or feedline without a rigid barrel taking the strain. It pairs naturally with an SMA adapter kit: the adapters handle the odd in-place transition, the pigtails handle everything that needs to bend.
For a real distance run, step up to low-loss feedline; for the full connector map, see the SDR cables and connectors guide.
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Frequently asked questions
Which coax pigtail should I buy for an SDR?
An RG316 SMA pigtail kit (around $15) is the flexible-lead answer: short jumpers terminated in SMA plus the common far-end connectors, so you can connect a dongle to a fixed antenna or feedline without hanging the SDR’s weight on a rigid barrel adapter. RG316 is thin and very flexible, ideal for tight bends and bench use over the foot or two a pigtail spans.
What is the difference between a pigtail and an adapter?
An adapter is a rigid brass barrel that changes connector type in place; a pigtail is a short flexible cable that changes type over a few inches. Use an adapter when the mating parts can sit directly together; use a pigtail when you need to route around a corner, relieve strain on the dongle’s SMA jack, or reach a panel-mounted antenna without the whole radio dangling from the connector.
Is RG316 lossy?
RG316 has relatively high loss per foot, but a pigtail is only inches to a couple of feet long, so the total loss is negligible even at UHF. Its whole point is flexibility over a short span. For any real distance — across a room or up a mast — switch to lower-loss RG58, RG8X, or LMR-240 feedline rather than extending a thin pigtail.
Can I use a pigtail to move my antenna to the window?
For a short reach, yes — a two-to-three-foot pigtail gets a dongle off a cramped USB port and onto a window-mounted antenna. For a longer reach, do not chain pigtails; either run a proper low-loss feedline or, better, move the whole SDR to the window on a USB extension and keep the RF run short.