Ham Radio Coax Cable Loss Calculator
Calculate signal loss in ham radio coaxial cable by length, frequency, and cable type.
Compare RG-58, RG-8X, LMR-400 loss in dB and watts received.
Coax Cable Loss Calculation
Coax cable attenuation increases with frequency and length. Higher-quality cables (lower loss per 100 ft) are essential for VHF/UHF and HF runs over ~50 ft.
The formula: Total Loss (dB) = (Cable length in feet / 100) × Loss per 100 ft (dB)
Loss per 100 ft (typical, manufacturer specs):
| Cable | 30 MHz | 50 MHz | 144 MHz | 440 MHz | 1.2 GHz |
|---|---|---|---|---|---|
| RG-58 | 1.5 | 2.0 | 4.5 | 8.5 | 16.0 |
| RG-8X (mini-8) | 1.0 | 1.4 | 3.4 | 6.5 | 12.0 |
| RG-213 / LMR-240 | 0.7 | 0.9 | 1.7 | 3.0 | 5.5 |
| LMR-400 | 0.4 | 0.6 | 1.2 | 2.4 | 4.0 |
| LMR-600 | 0.3 | 0.4 | 0.8 | 1.6 | 2.7 |
| Hardline (1/2") | 0.2 | 0.3 | 0.5 | 1.0 | 1.8 |
Power loss in watts: Power received = Transmit power × 10^(−Loss dB / 10)
| Loss (dB) | Power surviving |
|---|---|
| 1 dB | 79% |
| 2 dB | 63% |
| 3 dB | 50% (half!) |
| 6 dB | 25% (quarter) |
| 10 dB | 10% |
| 20 dB | 1% |
Practical implications:
- 3 dB loss = wasting half your power at the antenna
- VHF/UHF: stick to LMR-400 or better for runs over 50 ft
- HF: RG-8X is fine for most home stations under 100 ft
- Adapter and connector loss adds 0.05-0.2 dB each — often negligible but adds up
Cable selection guide:
| Use | Frequency | Length | Recommended |
|---|---|---|---|
| HF mobile | 1-30 MHz | 10-15 ft | RG-58 or RG-8X |
| HF base | 1-30 MHz | 50-100 ft | RG-213 or LMR-400 |
| VHF base | 144 MHz | 30-50 ft | LMR-400 or LMR-600 |
| UHF tower | 440 MHz | 100+ ft | LMR-600 or hardline |
| Microwave | 1.2 GHz+ | any | hardline only |
SWR also matters: A 2:1 SWR typically adds 0.5-1.0 dB on top of the matched loss — not catastrophic, but the antenna mismatch wastes power that gets reflected and dissipated as heat in the cable.