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.
Navigate to Menu → CAL → CALIBRATE.
Connect the OPEN standard → select OPEN → wait for measurement.
Connect the SHORT standard → select SHORT → wait.
Connect the LOAD (50 Ω) standard → select LOAD → wait.
Save calibration to a slot (0 - 4).
Verify: reconnect LOAD → SWR should read ~1.0, impedance ~50+j0 Ω. This check confirms the calibration math, not absolute accuracy; the supplied standards are adequate for hobby antenna work.
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.