Feedline Loss Reference
At 915 MHz, cable loss is significant. A long run of cheap coax can negate the benefit of a quality antenna upgrade. This is the canonical loss table for the book; all values are at 915 MHz, sourced from manufacturer datasheets (Times Microwave for LMR types) and expressed per 100 ft of cable.
Loss at 915 MHz per 100 ft
| Cable Type | Loss per 100 ft | Notes |
|---|---|---|
| RG-58 | ~20 dB | Avoid for any outdoor run over about 6 ft (2 m) |
| RG-8X | ~12.6 dB | Acceptable for short indoor runs |
| LMR-200 | ~9.9 dB | Good for runs up to about 30 ft (10 m) |
| LMR-400 | ~3.9 dB | Use for runs over about 30 ft (10 m) |
| LMR-600 | ~2.5 dB | Very long runs; stiff and expensive |
Loss scales linearly with length: divide the per-100 ft figure by 10 for a per-10 ft estimate, or multiply by 0.0328 for a per-metre estimate (for example, LMR-400 at ~3.9 dB/100 ft is ~1.28 dB per 10 m).
Practical guidance
- Rooftop install with a 10-15 ft (3-5 m) run: LMR-200 is ideal
- Runs over about 30 ft (10 m): LMR-400 minimum
- Never use RG-58 for permanent outdoor installs
- Each connector adds loss - a quality N connector adds ~0.1-0.3 dB, while cheaper or worn SMA can reach 0.5-1 dB. Either way, minimize adapters.
The proximity advantage: The best way to minimize cable loss is to mount the radio enclosure close to the antenna. A 0.5 m cable run with any cable type adds negligible loss.
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