NanoVNA Guide for Mesh Antenna Work

The NanoVNA is an affordable vector network analyzer that every serious mesh network operator should own. It measures antenna SWR, impedance, and resonant frequency directly - letting you verify antennas before installation and diagnose field problems.

What a NanoVNA Measures

• SWR (Standing Wave Ratio) - How well your antenna is matched to 50 ohms at each frequency
• S11 (Return Loss) - The logarithmic version of SWR; shows resonance as a dip
• Impedance (R + jX) - The complex impedance of the antenna at each frequency
• Smith Chart - Graphical representation of impedance; useful for matching network design

NanoVNA Selection

For 915 MHz work, any NanoVNA covering 300 kHz to 1.5+ GHz will work:

• NanoVNA-H4 - $55-70, 4-inch screen, covers to 1.5 GHz. Best for comfortable field use.
• NanoVNA-F v2 - $120, covers to 3 GHz, better calibration. Good if you also do 2.4 GHz work.
• Avoid no-name clones below $40 - calibration and accuracy are often poor.

Calibration Procedure

Calibration must be done before every measurement session at the frequency range you're testing:

1. Set frequency range: Start 850 MHz, Stop 980 MHz (bracket the 902-928 MHz band)
2. Connect the OPEN calibration standard to CH0 port; press OPEN
3. Connect the SHORT calibration standard; press SHORT
4. Connect the LOAD (50 ohm) calibration standard; press LOAD
5. Save calibration

Critical: Calibration is performed at the end of your test cable (SMA port that will connect to the antenna). Every adapter or cable change requires recalibration.

Measuring a Mesh Antenna

1. Calibrate NanoVNA at the test port
2. Connect antenna under test to CH0
3. Enable S11 display in SWR mode
4. Set Y-axis to SWR 1-3 range for easy reading
5. Identify the frequency where SWR dips to its minimum - that's the antenna's resonant frequency
6. Read the SWR at 915 MHz specifically

Interpreting Results

Trimming a DIY Antenna

If your DIY antenna resonates slightly off 915 MHz:

• Resonant frequency too high (antenna resonates at 920 MHz instead of 915) - antenna is too short; add length
• Resonant frequency too low (antenna resonates at 910 MHz) - antenna is too long; trim carefully in 2mm increments
• Re-measure after each trim until resonant frequency matches 915 MHz