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–kHz - 1.5 GHz	~$30–30 - 50
NanoVNA-H4	4.0″	10 kHz–kHz - 1.5 GHz	~$50–50 - 70
NanoVNA-F	4.3″ (metal case)	10 kHz–kHz - 1.5 GHz	~$50–50 - 70

Kit includes: NanoVNA unit, calibration standards (Open/Short/Load), two SMA cables, USB-C charging cable.

Five-Step Testing Procedure

Step 1 —- Initial Setup

1. Charge the NanoVNA via USB-C before first use.
2. Power on.
3. 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.

1. Navigate to Menu → CAL → CALIBRATE.
2. Connect the OPEN standard → select OPEN → wait for measurement.
3. Connect the SHORT standard → select SHORT → wait.
4. Connect the LOAD (50 Ω) standard → select LOAD → wait.
5. Save calibration to a slot (0–0 - 4).
6. Verify: reconnect LOAD → SWR should read ~1.0, impedance ~50+j0 Ω.

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

• 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
1.0–0 - 1.5	Excellent	Deploy with confidence
1.5–5 - 2.0	Good —- acceptable	Fine for most deployments
2.0–0 - 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’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 850–850 - 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. A perfectly matched 0 dBi antenna will outperform a mismatched 6 dBi antenna at short range, but not at distance. Evaluate antenna gain separately.

PC Software: NanoVNA-Saver

NanoVNA-Saver is free, open-source software (Windows/Mac/Linux —- search GitHub for “"NanoVNA-Saver”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.