What changed
Coax, connectors and chokes — edited Aug 31, 2026 by Unknown editor
This is the first recorded version, so every line is shown as added. Note: Imported from content/wiki
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The companion to [feedline, SWR and tuners](/wiki/station/feedline-and-swr): the physical side —
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what to buy, how to terminate it, and what to do about the current flowing on the outside of the
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braid.
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## Choosing cable
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| Cable | Loss at 14 MHz | Loss at 440 MHz | Use |
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| --- | --- | --- | --- |
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| RG-58 | ~1.0 dB/100 ft | ~6 dB/100 ft | Short jumpers only |
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| RG-8X | ~0.8 dB/100 ft | ~4.7 dB/100 ft | Portable, short HF runs |
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| RG-213 | ~0.6 dB/100 ft | ~3 dB/100 ft | Permanent HF runs |
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| LMR-400 | ~0.4 dB/100 ft | ~2.2 dB/100 ft | Long runs, VHF/UHF |
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| LMR-600 / hardline | ~0.25 dB/100 ft | ~1.3 dB/100 ft | Towers, repeater sites |
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Figures are approximate and worsen with SWR, age and water ingress. Buy from a known supplier —
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copper-clad-aluminum cable sold as RG-213, and cable with a partial braid, are both common.
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## Connectors
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- **PL-259 / SO-239 (UHF)** — the HF standard. Not constant-impedance, and fine to about 150 MHz.
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- **N** — weatherproof and constant-impedance; the right choice above VHF and for outdoor joints.
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- **BNC** — quick-connect, small, common on test gear and portable rigs.
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- **SMA** — handhelds and SDR dongles. Note reverse-polarity SMA on some radios, and that the
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connector on a handheld is easily destroyed by a heavy antenna.
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- Keep a small box of adapters, but minimize them in a permanent run; every joint is a potential
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water path.
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### Installing a PL-259
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Solder-type on RG-213 with a reducer for RG-8X: strip carefully so no braid strands short to the
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center, tin the center pin, and solder the braid through the shell's holes with enough heat to flow
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properly but not so much that the dielectric melts and shifts. Crimp connectors are perfectly good
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and faster if you own the right die. Test every connector with a meter before it goes up the tower.
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## Weatherproofing
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Water in coax is invisible, permanent and the most common reason a station "used to work". Over
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every outdoor joint: electrical tape, then self-amalgamating tape stretched over the whole
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connector, then more electrical tape as a UV cover. Butyl mastic is better still. Drip loops below
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every connector, and never leave a coax end pointing upward.
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## Common-mode current and chokes
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Coax is meant to carry current on the inside of the braid only. Any imbalance at the feedpoint puts
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current on the *outside*, which turns the feedline into part of the antenna. Symptoms: a hot
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microphone, erratic SWR that changes when you touch the radio, computer resets on transmit, and a
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noisy receive.
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Cures:
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- A **1:1 current balun** at the feedpoint of any dipole, OCF or beam.
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- A **choke** of type 31 ferrites on the coax at the antenna, and often a second at the shack
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entrance. Ten to fifteen mix-31 clamp-on beads, or a coil of coax through a large type-31 toroid.
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- Good [grounding and bonding](/wiki/station/grounding-and-lightning) — related, but not a
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substitute. Chokes fix common-mode current; grounds do not.
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## Entering the building
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Bring feedlines to a single grounded entry panel with arrestors, bonded to the house electrical
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ground. This is a lightning and safety requirement as much as a performance one — see
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[grounding and lightning](/wiki/station/grounding-and-lightning).