NanoVNA SOLT Calibration Step by Step

[Pavel]

Short answer: Perform open, short, load and through calibration over the exact frequency span, with the standards connected at the plane where the device under test will attach. Calibration does not remain valid after changing adapters, cables, port extension or the measurement span substantially.

Before you start​

• Check maximum RF input level and DC tolerance before connecting a transmitter, powered line or unknown source to test equipment.
• Warm up the instrument, use known cables and adapters, and calibrate at the connector plane where the device under test will be attached.

Step-by-step method​

1. Step 1: Warm the NanoVNA, inspect connectors and set the final start/stop frequency plus point count before calibration. Attach any adapter or test cable that must be mathematically removed before measuring standards.
2. Step 2: Apply OPEN, SHORT and 50-ohm LOAD to port 1 in the sequence requested, holding the standard without stressing the connector. Confirm each standard before advancing.
3. Step 3: Connect a suitable THROUGH between ports for the two-port step when measuring transmission. Keep the same cables and adapters that will be used for the device under test.
4. Step 4: Save the calibration, verify a known load near 50 ohms and reconnect one standard to check repeatability. If the result is poor, clean and recalibrate rather than smoothing it away.

Concrete example​

For a 100 to 200 MHz filter measurement using two test cables, set that span first and calibrate at the free ends of those cables. Connecting an extra SMA adapter after calibration moves the reference plane and adds its mismatch and loss to the result.

How to judge the result​

Calibration is credible when a known load shows low reflection across the span and reconnection changes are small enough for the intended measurement. Save the span and calibration slot with screenshots.

What to record​

• Save frequency span, calibration state, attenuation, reference level and connector plane with every result.
• Repeat the measurement after reconnecting the device; a large change often points to a poor adapter, cable or calibration.
• Use a VNA for reflection and network measurements, and a spectrum analyzer for signal energy versus frequency.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Calibrating across the instrument's full range and then zooming into a narrow filter can provide poorer resolution and accuracy than calibrating directly over the working span.

Final check​

Reconnect the standards or device under test and repeat the measurement without changing the calibration plane. Save the span, calibration, attenuation and uncertainty with the result.