# 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

<table id="bkmrk-cable-typeloss-per-1"><thead><tr><th>Cable Type</th><th>Loss per 100 ft</th><th>Notes</th></tr></thead><tbody><tr><td>RG-58</td><td>~20 dB</td><td>Avoid for any outdoor run over about 6 ft (2 m)</td></tr><tr><td>RG-8X</td><td>~12.6 dB</td><td>Acceptable for short indoor runs</td></tr><tr><td>LMR-200</td><td>~9.9 dB</td><td>Good for runs up to about 30 ft (10 m)</td></tr><tr><td>LMR-400</td><td>~3.9 dB</td><td>Use for runs over about 30 ft (10 m)</td></tr><tr><td>LMR-600</td><td>~2.5 dB</td><td>Very long runs; stiff and expensive</td></tr></tbody></table>

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.