Saving and Recalling Calibration

The NanoVNA can store multiple calibrations in internal flash memory and on SD card. This tutorial explains how to save, recall, and manage your calibration data.

What You Will Learn

• Saving calibration to internal memory slots
• Recalling saved calibrations
• Exporting calibration to SD card
• Managing calibration for different setups

Internal Save Slots

The NanoVNA has multiple internal save slots for calibration data:

Hardware	Save Slots	Slot Numbers
NanoVNA-H (F072)	5 slots	0, 1, 2, 3, 4
NanoVNA-H4 (F303)	7 slots	0, 1, 2, 3, 4, 5, 6

Each slot stores:

• Calibration data (all error terms)
• Frequency range (start, stop)
• Sweep points
• Trace settings
• Marker positions

Note

Slot 0 is automatically loaded at power-on if it contains valid calibration data.

Saving Calibration

1. Complete your calibration

   Perform calibration and touch DONE (see Full Calibration).

2. Open the save menu

   Go to CAL > SAVE

3. Choose a save slot

   Touch the slot number (0-4 or 0-6 depending on hardware).

   The display shows slot status:

   • Empty N - Slot is empty
   • Frequency range - Slot contains calibration with that range

4. Confirm the save

   The calibration is written to internal flash memory.

Tip

Keep a mental or physical note of what each slot contains:

• Slot 0: General purpose (loads at startup)
• Slot 1: HF antennas (1-30 MHz)
• Slot 2: VHF (144-148 MHz)
• Slot 3: UHF (430-440 MHz)
• etc.

Recalling Calibration

1. Open the recall menu

   Touch the screen and navigate to the top-level menu, or use:

   • Short press on encoder to bring up menu
   • Navigate to recall options

2. Select a save slot

   Touch the slot containing your desired calibration.

3. Verify the recall

   The status bar shows the active calibration slot (C0, C1, etc.).

   All settings from that slot are restored:

   • Frequency range
   • Calibration data
   • Trace configuration
   • Marker positions

SD Card Calibration Storage

The NanoVNA can save and load calibration files on a microSD card.

Saving to SD Card

1. Insert a microSD card

   Use a FAT32-formatted card. Maximum recommended size is 32 GB.

2. Complete your calibration

3. Open SD Card menu

   Go to SD CARD > SAVE CALIBRATION

4. Enter a filename

   Use the on-screen keyboard to enter a descriptive name, or use auto-naming.

   Files are saved with .cal extension.

5. Confirm save

   The file is written to the SD card root directory.

Loading from SD Card

1. Insert the SD card

   The SD card must contain previously saved .cal files.

2. Open SD Card menu

   Go to SD CARD > LOAD > LOAD CAL

3. Browse for your file

   Navigate the file browser to find your calibration file.

4. Select the file

   The calibration is loaded and applied immediately.

Note

SD card calibration files are not tied to specific hardware. You can share calibration files between NanoVNA units, but accuracy depends on using identical cables and connectors.

Managing Multiple Calibrations

Strategy: Frequency-Based Slots

Organize slots by frequency range:

Slot	Frequency Range	Purpose
0	50 kHz - 300 MHz	Default, wide range
1	1 - 30 MHz	HF antennas
2	50 - 54 MHz	6m band
3	144 - 148 MHz	2m band
4	430 - 440 MHz	70cm band

Strategy: Cable/Setup-Based Slots

Organize by measurement setup:

Slot	Setup	Notes
0	Direct connection	Short cables for bench work
1	With 1m RG316 cables	Field measurement setup
2	With SMA-to-N adapters	For N-connector antennas
3	With attenuator	High-power device measurement

Strategy: SD Card Archive

Use internal slots for current work and SD card for archive:

1. Save working calibrations to slots 0-2

2. Archive rarely-used calibrations to SD card

   Save with descriptive names: HF_DIPOLE_2024.cal, VHF_YAGI_SETUP.cal

3. Load from SD card when needed

   Copy to an internal slot if you will use it repeatedly.

Calibration Interpolation

When your sweep range differs from the calibration range, the NanoVNA interpolates:

1. Check for interpolation indicator

   The status bar shows D0-D6 instead of C0-C6 when interpolating.

2. Understand the accuracy impact

   • Small frequency differences: Minor accuracy reduction
   • Large differences: Significant accuracy loss
   • Outside calibration range: Extrapolation, poor accuracy

3. Recalibrate if needed

   For best results, recalibrate at your exact frequency range.

Calibration and Power Cycles

With Backup Enabled

If backup mode is enabled (CONFIG > BACKUP > ON):

• Current settings are saved automatically when changed
• At power-on, the last-used calibration slot is recalled
• Frequency range and trace settings are restored

Without Backup

If backup mode is disabled:

• Slot 0 is loaded at power-on (if valid)
• Unsaved changes are lost at power-off
• Manually save important calibrations before powering down

Console Commands for Calibration

For advanced users, the serial console provides calibration commands:

cal                 # Show current calibration status
cal reset           # Clear calibration
cal on              # Enable calibration (apply)
cal off             # Disable calibration (raw data)
save 0              # Save to slot 0
recall 0            # Recall from slot 0

Troubleshooting

Saved calibration shows wrong frequency range

• The calibration was saved with different STIMULUS settings
• Recall will restore the original frequency range
• Adjust frequency after recall if needed (causes interpolation)

Slot shows “Empty” after saving

• Flash write may have failed
• Try saving to a different slot
• Check if internal memory is corrupted (rare)

SD card file won’t load

• Verify file has .cal extension
• Check that SD card is FAT32 formatted
• File may be corrupted; re-save from source

Calibration accuracy degrades over time

• Temperature changes affect calibration
• Connectors may need cleaning
• Recalibrate periodically for best results

Best Practices

1. Always save after calibrating - Unsaved calibrations are lost at power-off

2. Use descriptive organization - Whether by frequency or setup, be consistent

3. Recalibrate when changing cables - Calibration includes cable characteristics

4. Keep Slot 0 for your most common use case - It loads automatically at startup

5. Backup important calibrations to SD card - Internal slots can be overwritten accidentally

Next Steps

• Full Calibration - Complete SOLT procedure
• Enhanced Response Calibration - Quick calibration method
• Your First S11 Measurement - Put calibration to use