Skip to main content

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

ModelScreenFrequency RangePrice
NanoVNA-H2.8″50 kHz - 1.5 GHz~$30 - 50
NanoVNA-H44.0″10 kHz - 1.5 GHz~$50 - 70
NanoVNA-F4.3″ (metal case)10 kHz - 1.5 GHz~$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 - 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

SWRRatingAction
1.0 - 1.5ExcellentDeploy with confidence
1.5 - 2.0Good - acceptableFine for most deployments
2.0 - 3.0Marginal - some power lossInvestigate connector quality
3.0+Poor - significant lossReplace 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

SymptomLikely Cause
High SWR across entire 850 - 950 MHz bandAntenna tuned for 868 MHz (European band); damaged or loose connector; missing ground plane on whip antenna
SWR varies wildly / unstable readingLoose connector; damaged cable - wiggle connections while watching display
Excellent SWR but poor rangeSWR 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") 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

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.

No comments to display

Back to top