NanoVNA Antenna Testing
Overview
A NanoVNA (Vector Network Analyzer) is the essential tool for verifying antenna performance before deployment. It measures SWR (Standing Wave Ratio) and impedance - telling you how well your antenna is matched to the 50 Ω system and whether it is resonant at 915 MHz. A 10-minute NanoVNA check before mounting an antenna can save hours of troubleshooting range problems later.
Models
| Model | Screen | Frequency Range | Price |
|---|---|---|---|
| NanoVNA-H | 2.8″ | 50 kHz - 1.5 GHz | ~$30 - 50 |
| NanoVNA-H4 | 4.0″ | 10 kHz - 1.5 GHz | ~$50 - 70 |
| NanoVNA-F | 4.3″ (metal case) | 10 kHz - 1.5 GHz | ~$50 - 70 |
Frequency note: Common NanoVNA models (H / H4 / F) top out near 1.5 GHz, not 3 GHz - 915 MHz sits comfortably within range. On the basic NanoVNA-H, operation above ~900 MHz uses harmonic mode with reduced dynamic range, so 915 MHz measurements are valid but recalibrate carefully; the H4 and F perform better here. Prices above are approximate as of 2026-06-08 and vary by vendor.
Kit includes: NanoVNA unit, calibration standards (Open/Short/Load), two SMA cables, USB-C charging cable.
Five-Step Testing Procedure
Step 1 - Initial Setup
- Charge the NanoVNA via USB-C before first use.
- Power on.
- Set the frequency range: START = 850 MHz, STOP = 950 MHz.
Step 2 - Calibration (Most Critical)
Calibrate every session or any time you change the frequency range. Calibration compensates for cable and connector losses - skipping it invalidates all measurements.
Recalibrate when: changing frequency range; moving to a significantly different temperature environment; switching to different cables.
Step 3 - Configure Display
- Set Trace 1 to SWR.
- Optionally set Trace 2 to Smith Chart or R+jX for impedance detail.
- Add a marker at 915 MHz.
Step 4 - Connect Antenna
Caution: Disconnect or power down the LoRa radio before connecting a NanoVNA to its antenna line. A NanoVNA is a low-power test source; applying transmit power to a NanoVNA port will damage the instrument.
- Connect antenna cable to CH0 (Port 1).
- Use the shortest possible cable between the NanoVNA and antenna.
- Tighten connectors finger-tight only - do not over-torque SMA.
- Check connector type: LoRa antennas commonly use SMA or RP-SMA. These look identical but are not compatible - verify before connecting.
Step 5 - Interpret Results
SWR Ratings
| SWR | Rating | Action |
|---|---|---|
| 1.0 - 1.5 | Excellent | Deploy with confidence |
| 1.5 - 2.0 | Good - acceptable | Fine for most deployments |
| 2.0 - 3.0 | Marginal - some power loss | Investigate connector quality |
| 3.0+ | Poor - significant loss | Replace antenna or diagnose connector |
Resonant Frequency
The lowest SWR dip on the sweep is the antenna's resonant frequency.
- Dip at 915 MHz - optimal
- Dip below 915 MHz - antenna is slightly long (resonates lower)
- Dip above 915 MHz - antenna is slightly short (resonates higher)
Common Problems & Diagnosis
| Symptom | Likely Cause |
|---|---|
| High SWR across entire 850 - 950 MHz band | Antenna tuned for 868 MHz (European band); damaged or loose connector; missing ground plane on whip antenna |
| SWR varies wildly / unstable reading | Loose connector; damaged cable - wiggle connections while watching display |
| Excellent SWR but poor range | SWR measures impedance match only, not gain. SWR and gain are independent - evaluate both. A 6 dBi antenna with moderate mismatch (2:1, ~0.5 dB loss) still beats a 0 dBi matched antenna at both short and long range; only a severe mismatch (loss exceeding the gain advantage) erases the gain benefit. Evaluate antenna gain separately. |
PC Software: NanoVNA-Saver
NanoVNA-Saver is free, open-source software (Windows/Mac/Linux - search GitHub for "NanoVNA-Saver") that connects to your NanoVNA via USB and provides:
- Larger, higher-resolution graphs
- Data export (CSV)
- Smith chart display
- Touchstone (.s1p) file export for import into antenna modeling software
- Multi-antenna comparison - overlay sweeps from different antennas
Recommended for antenna selection decisions and documentation of deployed infrastructure antennas.
Common Mistakes to Avoid
- Skipping calibration - all measurements are invalid without calibration
- Calibrating at the wrong frequency range - calibration is only valid for the range it was performed at; recalibrate if you change START/STOP
- Testing indoors near metal objects - nearby metal detuning antennas; test in the open or simulate the actual mounting environment
- Using adapters without accounting for electrical length - SMA adapters add a small but measurable electrical length; minimize adapter use
- Confusing SMA and RP-SMA - SMA has center pin on plug; RP-SMA has center pin on jack. Forcing mismatched connectors damages both.