🔌 Coax loss & ERP
How much of your power actually reaches the antenna through that run of RG-58 - and what your ERP is.
Feedline
At the antenna
- Total loss
- 2.43 dB
- 2.31 dB matched + 0.12 dB from SWR
- Power reaching antenna
- 28.6 W
- 57.1% of what went in
- Lost as heat
- 21.4 W
- EIRP
- 57.0 W
- vs isotropic
- ERP
- 34.8 W
- vs dipole - what the FCC power limits mean
- Per 100 ft
- 4.63 dB
- RG-8X / Mini-8 @ 146 MHz
Rule of thumb: 3 dB is half your power. On 70 cm and 33 cm, cheap RG-58 over a long run can eat more than the difference between a 5 W handheld and a 50 W mobile - spend the money on coax before spending it on watts. Figures are typical datasheet values for new cable; connectors add roughly 0.1-0.2 dB each.