# SWR and Antenna Analyzers

SWR (Standing Wave Ratio) measures how well your antenna is matched to the 50-ohm feedline impedance. A well-matched antenna transfers all power to the air; a mismatched antenna reflects some power back.

## SWR values

<table id="bkmrk-swrreflected-poweras"><thead><tr><th>SWR</th><th>Reflected Power</th><th>Assessment</th></tr></thead><tbody><tr><td>1.0:1</td><td>0%</td><td>Perfect (theoretical)</td></tr><tr><td>1.5:1</td><td>4%</td><td>Excellent</td></tr><tr><td>2.0:1</td><td>11%</td><td>Acceptable</td></tr><tr><td>3.0:1</td><td>25%</td><td>Poor - investigate</td></tr></tbody></table>

## Common causes of high SWR

- Connector not fully tightened (most common)
- Water ingress into connector or cable
- Damaged or kinked coax
- Wrong-band antenna (e.g. 868 MHz antenna on a 915 MHz system)

## NanoVNA for measurement

The NanoVNA (0-80) covers 50 kHz to 3 GHz and is ideal for checking LoRa antenna systems. Connect to the antenna feedpoint, sweep 850-950 MHz, and look for the SWR minimum. A good 915 MHz antenna shows SWR below 1.5:1 across the 902-928 MHz band.

Most commercial LoRa antennas are pre-tuned and work fine out of the box. Measure when troubleshooting performance problems, building DIY antennas, or verifying a new cable run.