The Ham Radio Operator's Complete Guide to Coax Cable

Your transceiver is only as good as the coax connecting it to your antenna. Cheap or incorrectly chosen feedline doesn't just cost you signal — it can waste watts as heat, introduce RF into your shack, and fail completely after a single season outdoors. This guide covers everything a ham operator needs to make smart coax decisions for any band, any power level, and any installation type.

Why Impedance Matching Is the Starting Point

Every piece of ham radio equipment — your transceiver, tuner, antenna, and the coax in between — is designed around a 50-ohm impedance standard. This isn't arbitrary. Fifty ohms is the historical sweet spot between maximum power transfer (which favors lower impedance) and minimum attenuation (which favors higher impedance around 77 ohms for air-dielectric coax). The entire amateur radio ecosystem converged on 50 ohms, and mixing in other impedances — particularly the 75-ohm coax used in cable TV and satellite systems — creates a mismatch that elevates SWR and reduces the power reaching your antenna.

A 75-ohm cable in a 50-ohm system creates an intrinsic SWR of 1.5:1 even with a perfect antenna. That's not catastrophic, but it means you're starting every transmission already at a disadvantage, and your radio's protection circuitry may back off power automatically on some rigs.

Cable Loss at the Frequencies That Matter

Loss is measured in decibels per 100 feet and increases with frequency. A cable that's perfectly adequate for 40-meter HF may be completely unacceptable on 70cm. Here are representative loss figures for the cables commonly used in ham installations:

Every 3 dB of loss cuts your effective power in half. At 440 MHz, a 100-foot run of RG-58 loses 7 dB — that's turning your 100-watt radio into a 20-watt radio before the signal leaves the building. LMR-400 on that same run loses 3.2 dB, delivering about 48 watts to the antenna. The difference is audible on the other end.

HF Setups: When RG-58 Is Fine

For HF operation below 30 MHz, RG-58 is a perfectly reasonable choice for runs under 50 feet. At 10 MHz, 50 feet of RG-58 loses only 0.5 dB — less than half a watt from a 100-watt signal. That's negligible. RG-58 is flexible, inexpensive, and easy to work with connectors. For shack jumpers, connecting a tuner to a transceiver, or short outdoor runs to a wire antenna, it's hard to beat the price-to-performance ratio.

Most HF transceivers use PL-259 (SO-239) connectors, and the standard PL-259-to-PL-259 cable is what you need for radio-to-tuner or transceiver-to-antenna connections:

RG-58 PL-259 to PL-259 Cable

VHF and UHF: Loss Is Critical

On 2 meters (144 MHz) and 70 centimeters (440 MHz), coax loss becomes the dominant factor in your station's performance. A receive-side loss of even 3 dB doubles the noise figure of your entire receive chain — weak signals that were borderline become completely inaudible. On the transmit side, you're simply wasting power as heat in the cable.

LMR-400 is the minimum recommended cable for VHF/UHF runs over 20 feet. It's significantly stiffer than RG-58 (minimum bend radius of 4 inches vs 1.5 inches for RG-58), but the loss figures justify it for any permanent installation. For runs connecting an N-type antenna to a PL-259-ported transceiver, you'll need an N-to-PL-259 cable:

LMR-400 PL-259 to PL-259 Feedline  |  LMR-400 N-Male to PL-259

Tower and Long Runs: LMR-600

When your antenna is on a tower 75 feet or more above the shack, LMR-600 is worth the investment. At 100 feet and 440 MHz, LMR-400 loses 3.2 dB and LMR-600 loses only 2.0 dB. That 1.2 dB difference might not sound like much, but on a receive path it meaningfully improves your noise floor. LMR-600 is 0.59 inches in diameter — thick and heavy — so plan your cable entry and routing accordingly. It requires larger bend radii (minimum 6 inches) and heavier-duty connectors, but for a permanent tower installation it's the professional choice.

LMR-600 PL-259 to PL-259 Ultra Low-Loss Feedline  |  LMR-600 N-Male to PL-259

Connector Types: Matching Connectors to Equipment

PL-259 (SO-239) is on virtually every HF transceiver — Icom, Kenwood, Yaesu, and every classic rig you'll find. It's large, rugged, and solderable. It performs well through HF but its geometry is not controlled above about 300 MHz, so avoid it on VHF/UHF antenna connections if you have a choice.

N-type is the professional outdoor standard for VHF/UHF. It's weatherproof when properly mated, rated to 11 GHz, and handles 500+ watts. Outdoor antennas for 2m/70cm repeaters almost always use N-type. When you have a PL-259 radio and an N-type antenna, you need an adapter cable.

SMA is standard on handheld radios (HTs), SDR dongles, and compact equipment. Its small size limits power handling, but for HT-to-antenna jumpers and SDR connections it's the right connector. Be aware that WiFi gear uses RP-SMA, not standard SMA — the threads look identical but the center pin is reversed and they won't mate.

For a handheld radio antenna jumper going from PL-259 to SMA (connecting an HT with SMA to a mobile antenna with PL-259 base), you need:

RG-58 PL-259 to SMA-Female Cable

Weatherproofing Outdoor Connections

Water ingress is the number one cause of coax failure in outdoor installations. Even a small amount of moisture inside a PL-259 joint dramatically increases loss and SWR. Within a season or two, the center conductor corrodes and the cable becomes effectively useless. All outdoor RF connections need to be weatherproofed.

Use self-amalgamating (self-fusing) tape, not electrical tape. Standard electrical tape dries out, cracks, and loses adhesion after one or two seasons of UV exposure and temperature cycling. Self-amalgamating tape fuses into a solid rubber sleeve that's completely waterproof and UV-resistant. Apply it with 50% overlap, stretched to about half its original width, starting from the cable about 2 inches below the connector and working up toward and over the connector body. Finish with a second layer of UV-resistant vinyl tape over the self-amalgamating tape for additional protection.

The direction matters: start at the cable and work toward the connector so that the tape angles downward and doesn't channel water into the joint. Never start at the top and work down.

Lightning Arrestors: Not Optional

Every outdoor feedline needs a lightning arrestor at the point where it enters the building. This is not just good practice — it's required by the National Electrical Code (NEC 810) for amateur radio installations. A direct lightning strike on or near an outdoor antenna can destroy your entire station and start a fire. Even a nearby strike induces thousands of volts on the feedline.

Gas-discharge arrestors like the PolyPhaser IS-B50LN-C2 are the standard for amateur radio use. They have an N-female-to-N-female pass-through configuration and mount inline on the feedline at the building entry point. The ground lug on the arrestor must be bonded to your building's main ground system — a separate ground rod is not adequate on its own. Mount the arrestor on the outside of the building, not inside, and use a short jumper from the arrestor to your equipment.

Common Mistakes to Avoid

Using 75-ohm cable TV coax. RG-6 and RG-59 are everywhere and they look like 50-ohm coax. But they're 75 ohms, which creates an SWR of 1.5:1 in your 50-ohm system from the start. Your radio's internal protection circuits may reduce power, and the extra reflected power heats the finals. Always verify your coax is marked 50-ohm.

Over-tightening SMA connectors. SMA has a maximum torque of 12 in-lbs. Many people tighten them with pliers because they feel loose — this crushes the PTFE dielectric and permanently distorts the center pin. Finger-tight plus a quarter turn is correct for most applications. If you need a precision connection, use a torque wrench.

Not weatherproofing outdoor connections. A PL-259 connector sitting outdoors without weatherproofing will fail within two seasons. Water wicks into the joint by capillary action, oxidizes the center pin, and the SWR climbs. By the time you notice the degraded performance, the connector may be unsalvageable.

Checking SWR After Installation

Always verify SWR immediately after completing any feedline installation — before you route the cable through walls, staple it to the house, or button up the connector with weatherproofing. An SWR under 1.5:1 is excellent. Under 2:1 is acceptable for most operating. Above 2:1, your radio's protection circuitry will start folding back power on most modern rigs.

High SWR after a new cable installation almost always points to one of four causes: a damaged cable (kinked or crushed during routing), a wrong-impedance cable (75-ohm mixed in), water ingress in a connection (on an old cable), or a bad mechanical connection (connector not fully seated, center pin not soldered, or thread cross-threaded). Check each connector visually, reseat all connections, and re-test before assuming the antenna is the problem.

All cables from CoaxRF are hand-assembled and tested before shipping. If your SWR is off, the cable isn't the issue — start with the antenna and work backward.

Need a custom length? Use the cable configurator to build exactly what you need. Ships next business day.