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
| SWR | Reflected Power | Assessment |
|---|---|---|
| 1.0:1 | 0% | Perfect (theoretical) |
| 1.5:1 | 4% | Excellent |
| 2.0:1 | 11% | Acceptable |
| 3.0:1 | 25% | Poor - investigate |
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.
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