📶 Coaxial Cable Loss Calculator

Understanding Coaxial Cable Loss

Coaxial cable loss increases with frequency and length. At HF (3–30 MHz), even modest cables like RG-58 are usable for short runs. At VHF/UHF (30 MHz+), low-loss cables like LMR-400 become important for anything over 25 feet.

Matched loss is the attenuation when the cable is perfectly terminated (VSWR = 1:1). In real stations, the antenna presents some mismatch, creating additional loss from reflected power bouncing back and forth in the cable. This calculator shows both components separately.

SWR mismatch loss is calculated from the reflection coefficient Γ = (VSWR - 1) / (VSWR + 1). The mismatch loss in dB is -10 × log10(1 - Γ²). For VSWR 1.5:1, this is only about 0.18 dB. For VSWR 3:1, it rises to about 1.25 dB — significant for weak signal work.

Common Cable Types at a Glance

• RG-174: Very thin (2.79mm OD), stranded copper, solid PE dielectric. Loss ~19 dB/100ft at 100 MHz. Internal jumpers and pigtails only, never a main feedline.
• RG-316: Similar thin size to RG-174 (2.92mm OD) but silver-plated copper and PTFE (Teflon) dielectric. Loss ~8 dB/100ft at 100 MHz, noticeably better than RG-174 and tolerates higher temperatures. Common for lab/test jumpers and SDR pigtails.
• LMR-100A: Thin (2.79mm OD) with a copper-clad steel center conductor and solid PE dielectric. Loss ~5.8 dB/100ft at 100 MHz, better than RG-316 despite the small size. Good for short internal runs where RG-58 won't fit.
• RG-58: Small, flexible, cheap (4.95mm OD). Loss ~9.5 dB/100ft at 100 MHz. Good for short HF patch cables. Avoid for VHF runs >25ft.
• RG-8X: Slightly better than RG-58 (6.15mm OD, foam PE). Loss ~6.0 dB/100ft at 100 MHz. A good compromise for mobile installations.
• LMR-240: Similar OD to RG-8X (6.10mm) but foam PE with a higher velocity factor. Loss ~3.2 dB/100ft at 100 MHz, notably better than RG-8X at the same size.
• RG-213: Heavy, low-loss for its era (10.29mm OD, solid PE). Loss ~3.0 dB/100ft at 100 MHz. Still used in HF stations but stiff and heavy.
• LMR-400: Same OD as RG-213 (10.29mm) but modern foam dielectric and copper-clad aluminum center conductor. Loss ~1.5 dB/100ft at 100 MHz, ~2.7 dB at 450 MHz. The go-to upgrade from RG-213 for VHF/UHF stations.
• LMR-600: Even lower loss. Loss ~1.0 dB/100ft at 100 MHz. Expensive but excellent for long runs or weak signal work.
• 9913: Low-loss air dielectric. Similar performance to LMR-400 but more sensitive to moisture if jacket is damaged.

Dimensions and loss figures are drawn from published manufacturer datasheets (Times Microwave LMR series, Belden RG series) and cross-checked against standard amateur radio references such as DX Engineering's technical charts and the KH7O coax loss tables.

FAQ

How much loss is acceptable? For HF, up to 3 dB (50% power loss) is often acceptable. For VHF/UHF weak signal work, aim for under 1 dB. For EME or satellite, every tenth of a dB matters.

Does higher SWR always mean more loss? Yes, but the effect is often overstated. A VSWR of 2:1 adds only about 0.5 dB of mismatch loss. The real problem is stress on the transmitter final amplifier, which may fold back power at high SWR.

Should I use an antenna tuner to reduce SWR? A tuner at the transmitter end does NOT reduce feedline loss. It only makes the transmitter happy. To reduce feedline loss from SWR, use a tuner at the antenna feedpoint, or use open-wire line which has much lower loss at high SWR.