Every watt your transceiver produces has to travel through a length of coax before it ever reaches the antenna. Some of that power never arrives — it turns into heat along the way. That's coax loss, and it's one of the most overlooked factors in how well a station actually performs. Understanding roughly how much you're losing, and where, helps you decide whether a cable upgrade will make a real difference or whether your money is better spent elsewhere.
Power Lost Isn't Power You Get Back
Unlike a mismatch that reflects power back toward the radio, loss in the coax itself is gone for good — converted to heat in the center conductor, the shield, and the dielectric insulation. It doesn't show up as a dramatic failure. Your radio still keys up, your SWR meter might even look fine, and you'll still make contacts. The loss is just quietly eating into your signal every single time you transmit, and it also reduces the weak signals you hear coming back in on receive.
What a "Few dB" Actually Costs You
Decibels feel abstract until you tie them to power. A loss of 3 dB means roughly half your transmitter power is gone before it reaches the antenna — if you're running 100 watts, only about 50 watts actually radiates. A loss of 1 dB is a much smaller bite, around 20 percent. These numbers matter most at the margins: a weak DX contact, a marginal net check-in, or a contest exchange buried in noise can hinge on that difference, even though it's invisible on a basic SWR check.
What Actually Drives Coax Loss
Four things determine how much power a given run of coax will waste:
- Cable type — thinner, cheaper coax has more resistive and dielectric loss than thicker, better-engineered cable.
- Frequency — loss increases with frequency, so a cable that performs fine on 80 meters can be noticeably lossy on 10 meters or 2 meters.
- Length — loss is roughly proportional to length, so a 100-foot run loses about twice as much as a 50-foot run of the same cable.
- SWR at the antenna end — a poor match doesn't just reflect power back to the radio, it also increases the effective loss within the cable itself, especially on long runs.
Connectors, moisture intrusion, and sharp bends add smaller amounts of loss too, but cable type, frequency and length are the big three.
Typical Loss Figures by Band
Manufacturers publish attenuation figures for their cable, usually expressed in decibels per 100 feet at specific frequencies. The table above shows commonly published approximate figures for a few popular types. A few patterns are worth remembering even if you forget the exact numbers:
- Loss roughly doubles as you go from the low HF bands up to 10 meters, and roughly doubles again moving from 10 meters up into the 2-meter band.
- Thin, flexible coax like RG-58 is convenient but loses noticeably more than thicker cables like RG-213 or low-loss types such as LMR-400, especially at higher frequencies.
- On 80 or 40 meters, even a long run of modest coax usually loses only a small fraction of your power. The same length run on 6 meters or 2 meters can lose a third or more.
If you operate mostly on the lower HF bands, this is reassuring news — cable choice matters less there. If you're active on 10 meters, 6 meters, or VHF, it matters quite a bit more.
Estimating Your Own Feedline Loss
You don't need test equipment to get a useful estimate. Measure your actual coax run (not line-of-sight distance — include slack, drip loops, and the path it actually takes), find your cable's published loss figure for the band you use most, and scale it to your length. A 150-foot run of cable rated at 2 dB per 100 feet on your band loses about 3 dB — roughly half your power. That simple math, outlined in the steps above, is usually all you need to decide whether to investigate further.
Why High SWR Makes a Bad Cable Worse
Published loss figures assume a well-matched line, usually close to a 1:1 SWR at the antenna. When the antenna presents a poor match, standing waves inside the cable increase the actual loss beyond the datasheet number, and the effect is worse on lossier cable and longer runs. This is one more reason to get your antenna reasonably well matched before worrying about coax quality — fixing the match is often cheaper and more effective than switching cable. For more on what an SWR reading does and doesn't tell you, see our guide on interpreting SWR.
When a Cable Upgrade Is Actually Worth It
Upgrading coax is most worthwhile when any of these apply: your run is long (over roughly 75-100 feet), you operate on 10 meters, 6 meters, or VHF/UHF where loss figures climb fast, you're chasing weak-signal DX or satellite work where every dB counts, or you're running toward the legal power limit and don't want a meaningful chunk of it wasted as heat in the cable. If your run is short and you mostly work the lower HF bands, a modest cable upgrade will usually produce a difference too small to notice in practice. Check current HF propagation conditions before assuming a weak contact was a cable problem — sometimes the band itself is the limiting factor, not your feedline.
Common Mistakes Operators Make
- Judging feedline quality purely by SWR, which says nothing about how much power the cable itself is absorbing.
- Buying the thinnest, most flexible cable for a long run to save on cost, then wondering why signal reports are average.
- Ignoring connector quality — a poorly soldered or corroded PL-259 can add loss and intermittent faults that a loss chart won't predict.
- Coiling excess cable tightly near the radio instead of trimming it to length or routing it sensibly.
- Forgetting that loss figures are for dry, well-terminated cable — water that gets into a damaged jacket or connector will make real-world loss worse than published numbers.
Connectors and Loss Over Time
Coax loss isn't fixed once the cable is installed. Connectors corrode, moisture seals fail, and UV exposure degrades jackets over years outdoors. A cable that measured well when installed can quietly get worse. Periodically inspecting outdoor connections, keeping them properly weatherproofed, and re-seating or replacing a connector that looks chalky or green at the pins is cheap insurance against loss creeping up unnoticed. If you're comparing feedline types for a new antenna project, our comparison of coax and ladder line and our breakdown of common coax types are good starting points.
A Quick Checklist Before You Buy New Coax
- Measure your actual run length, including slack and routing, not just straight-line distance.
- Identify which bands you operate most, since loss varies a lot by frequency.
- Look up the published loss figure for your current cable and do the simple length-scaled math.
- Decide if the estimated loss is large enough to matter for your typical operating (casual local contacts versus weak-signal DX).
- Check your antenna's match first — a lossy cable combined with a poor match compounds the problem.
- Inspect existing connectors for corrosion or water intrusion before blaming the cable itself.
- If you upgrade, choose cable rated for your highest-use band and your actual run length, not just the cheapest option.
Remote Stations Have the Same Math, Just Higher Stakes
If you operate a station remotely using Remote Rig and Station Bridge, the feedline between the radio and antenna hasn't changed — it's still subject to the same loss figures as any home station. The one difference is that you can't walk out and casually inspect a connector between sessions, so getting the feedline right and well-sealed before you leave it unattended matters even more.
The Bottom Line
Coax loss is invisible, gradual, and easy to ignore — which is exactly why it's worth a few minutes of simple math. On the lower HF bands with a short run, it's rarely worth agonizing over. On 10 meters, 6 meters, VHF, or any long cable run, a cheap, thin cable can genuinely be giving away a meaningful fraction of your power before it ever leaves the antenna. Do the estimate, fix the antenna match first, and upgrade the cable when the numbers actually justify it. For quick reference while you're doing that math, the ham radio quick reference page keeps band and mode details handy in one place.
How HamRadioList can help
Before you spend money on a cable upgrade, check the free {{svc:propagation}} page to see whether weak signals or band conditions are really the bottleneck. Once you've logged a few contacts on your new feedline, track the difference in your free {{svc:logbook}}, and if you're shopping for lower-loss coax, browse the {{svc:marketplace}} for what other operators are selling.
- Ham radio marketplace - buy and sell radios, antennas and accessories.
- Live HF propagation - see current band conditions before you call CQ.
- Ham radio quick reference - bands, modes, phonetics and Q-codes on one page.
- Free online ham radio logbook - log every contact, import and export ADIF, sync with QRZ.com and keep your awards organised.
- Remote Rig - operate your own radio from anywhere on Android, iPhone, Windows or Linux, with live push-to-talk audio and CAT control.
New here, or getting back on the air? Create your free HamRadioList account to log contacts, check band conditions and practise for your exam, or browse more guides from the blog. HamRadioList is built by amateur radio operators in Nova Scotia for operators everywhere.