Full Calibration

Calibration is the single most important step for getting accurate measurements from the NanoVNA-F V3. Without it, the instrument’s own internal reflections, cable losses, and connector mismatches corrupt your readings.

A full OSLT calibration uses four known standards — Open, Short, Load, and Through — to mathematically remove systematic errors. After calibration, measurements reflect only the device under test.

What you will need

• SMA OPEN kit — included with the NanoVNA-F V3
• SMA SHORT kit — included
• SMA 50-ohm LOAD kit — included
• SMA-JJ RG405 cable — included (connects PORT1 to the device under test)
• SMA straight-through adapter — optional, for the THROUGH step when not using a cable

Caution

Handle calibration standards by the body, not the connector pin. Fingerprints and debris on the connector interfaces introduce errors. If standards have been exposed to dust, clean the interfaces with isopropyl alcohol and a lint-free wipe before use.

Before you start

1. Set the frequency range first. Navigate to STIMULUS and set START and STOP frequencies to the range you plan to measure. Calibration is most accurate at exactly the frequencies where it was performed.

2. Let the unit warm up. For best accuracy, power on the NanoVNA-F V3 and let it run for 2-3 minutes before calibrating. Temperature changes affect the internal electronics.

3. Decide where the reference plane should be. The calibration reference plane is at the connector where you attach the standards. If you calibrate at the end of a cable, the reference plane is at the cable’s far end. Everything between PORT1 and the reference plane is “calibrated out.”

OSLT calibration procedure

Navigate to CAL on the main menu to begin.

Step 1 OPEN

Connect the SMA OPEN standard to PORT1, or to the far end of the cable attached to PORT1 if you are calibrating at the cable tip. Tap OPEN in the calibration menu. Wait for the confirmation beep (2-3 seconds). The letter 'O' appears in the calibration status area.

Note: The OPEN standard has a specific fringing capacitance that the firmware accounts for. Do not use an unterminated open cable as a substitute -- it will not produce the same result.

Step 2 SHORT

Remove the OPEN standard and connect the SMA SHORT standard in the same location. Tap SHORT. Wait for the beep. The letter 'S' appears in the calibration status.

Note: The SHORT standard should be connected where the OPEN was -- same reference plane.

Step 3 LOAD

Remove the SHORT and connect the SMA 50-ohm LOAD standard. Tap LOAD. Wait for the beep. The letter 'L' appears in the calibration status.

Note: The LOAD is a precision 50-ohm termination. It defines the center of the Smith chart.

Step 4 THROUGH

Remove the LOAD from PORT1. Connect PORT1 directly to PORT2 using the SMA-JJ RG405 cable or a straight-through adapter. Tap THROUGH. Wait for the beep. The letter 'T' appears in the calibration status.

Note: If you only need S11 measurements (single-port), you can skip THROUGH. However, performing all four standards gives the best overall accuracy and is required for S21 measurements.

Step 5 DONE

Tap DONE to apply the calibration. The status area should now show 'OSLT C*' or similar, indicating that correction is active. The asterisk appears if the calibration data is interpolated to the current sweep range.

Saving the calibration

After tapping DONE, the calibration is active but only stored in volatile memory — it will be lost when you power off. To keep it:

1. While still in the CAL menu, tap SAVE.

2. Select a save slot (SAVE 0 through SAVE 12). Slot 0 is loaded automatically at power-on, so it is a good choice for your most-used calibration.

3. The calibration status will update to show the slot number (e.g., “C0”).

See Saving Calibrations for details on managing multiple saved calibrations.

Verifying the calibration

Before measuring anything, verify that the calibration is working correctly. These four checks take less than a minute and can save you from hours of chasing phantom problems.

Check 1: Open on PORT1

Connect the OPEN standard to PORT1 (or cable end).

• S11 LOGMAG should read approximately 0 dB across the entire span.
• S11 Smith chart should show the marker at the far right of the chart (infinite impedance).

Check 2: Short on PORT1

Connect the SHORT standard.

• S11 LOGMAG should read approximately 0 dB.
• S11 Smith chart should show the marker at the far left (zero impedance).

Check 3: 50-ohm Load on PORT1

Connect the LOAD standard.

• S11 LOGMAG should dip well below -30 dB (ideally -40 dB or better). This indicates the calibration sees the load as a near-perfect match.
• S11 Smith chart should show the marker at the center of the chart (50 + j0 ohms).

Tip

If the load check shows only -20 dB instead of -40 dB, the calibration standards may need cleaning, or connectors may be worn. Clean and retry before proceeding.

Check 4: Through between PORT1 and PORT2

Connect PORT1 to PORT2 with the same cable or adapter used during calibration.

• S21 LOGMAG should read approximately 0 dB across the span, confirming no insertion loss on the calibrated through path.

When to recalibrate

Recalibrate whenever:

• You change the frequency range (START or STOP)
• You change or add cables or adapters in the measurement path
• Ambient temperature changes significantly (moving from indoors to outdoors, for instance)
• More than a few hours have passed since the last calibration
• The calibration status shows an asterisk (*), indicating interpolation, and you need the highest accuracy

Note

A quick one-port calibration (OPEN, SHORT, LOAD only) is sufficient when you only need S11 measurements. The THROUGH step adds correction for S21 and improves S11 accuracy at the cost of one extra step.

Troubleshooting calibration

Calibration beep does not sound

• Check that the standard is firmly connected. SMA connectors should be finger-tight plus a fraction of a turn.
• Make sure you tapped the correct button (OPEN, SHORT, LOAD, or THROUGH) in the menu.

Calibration status shows unexpected characters

• If you see lowercase ‘c’ instead of uppercase ‘C’, the calibration is active but with reduced accuracy. This usually means the standards were not applied cleanly.

LOGMAG does not read 0 dB with OPEN or SHORT after calibration

• The most common cause is that the standard was not fully seated during calibration. Redo the affected step.

Next steps

• Saving Calibrations — manage save slots and recall calibrations
• Port Extension — compensate for cable delay when you cannot calibrate at the DUT
• Your First S11 Measurement — apply your calibration to a real measurement