Full 2-Port Calibration

A full SOLT (Short-Open-Load-Thru) calibration removes systematic errors from your measurements. This tutorial walks you through the complete process.

What You Will Learn

• When and why to calibrate
• Performing each calibration step
• Understanding calibration status indicators
• Troubleshooting calibration issues

Why Calibrate?

The NanoVNA’s raw measurements include errors from:

• Cable losses and phase shifts
• Connector imperfections
• Internal hardware variations

Calibration measures these errors using known standards, then mathematically removes them from your measurements.

Caution

Calibration is only valid for the frequency range and cables used during calibration. If you change cables or frequency range, recalibrate.

Calibration Standards

A full SOLT calibration uses these standards:

Standard	Description	Connection
OPEN	Open circuit	Nothing connected (cap on connector)
SHORT	Short circuit	Short standard on Port 1
LOAD	50 ohm load	50-ohm terminator on Port 1
THRU	Through connection	Port 1 connected directly to Port 2
ISOLN	Isolation (optional)	Loads on both ports

Tip

Most NanoVNA kits include a calibration kit with SHORT, OPEN, and LOAD standards on a small PCB, plus SMA adapters for THRU.

Before You Start

1. Warm up the NanoVNA

   Let the device run for 5-10 minutes before calibrating. Temperature changes affect calibration accuracy.

2. Connect your measurement cables

   Attach any cables or adapters you will use during measurements. Calibrate with your actual test setup.

3. Set your frequency range

   Go to STIMULUS and set START and STOP frequencies for your measurements.

4. Set sweep points

   More points = more accurate but slower calibration. Default 101 points is usually sufficient.

Full Calibration Procedure

1. Open the calibration menu

   Touch the screen and select CAL > CALIBRATE.

2. Perform OPEN calibration

   • Remove any connector from Port 1 (CH0)
   • If your cal kit has an OPEN standard, connect it; otherwise leave the port open
   • Touch OPEN
   • Wait for the sweep to complete (the button shows a checkmark when done)

3. Perform SHORT calibration

   • Connect the SHORT standard to Port 1
   • Touch SHORT
   • Wait for completion

4. Perform LOAD calibration

   • Connect the 50-ohm LOAD standard to Port 1
   • Touch LOAD
   • Wait for completion

5. Perform THRU calibration

   • Connect Port 1 directly to Port 2 using your measurement cables
   • Touch THRU
   • Wait for completion

6. Perform ISOLN calibration (optional)

   • Connect 50-ohm loads to both Port 1 and Port 2
   • Touch ISOLN
   • Wait for completion

   Note

   ISOLN calibration improves port-to-port isolation measurements. Skip it if you only need basic S11/S21 measurements.

7. Complete the calibration

   Touch DONE to apply the calibration.

   The status bar shows calibration is active (green indicator).

Calibration Status Indicators

After calibration, the screen shows status indicators:

Indicator	Meaning
C0 (green)	Full calibration applied, slot 0
C1-C6	Calibration from save slot 1-6
D0-D6	Calibration applied but from different frequency range (interpolated)
c (lowercase, red)	Calibration disabled or not valid

Caution

If you see D (interpolated), the calibration was done at a different frequency range. For best accuracy, recalibrate at your current frequency range.

Quick Reference: Menu Path

CAL > CALIBRATE > OPEN
CAL > CALIBRATE > SHORT
CAL > CALIBRATE > LOAD
CAL > CALIBRATE > THRU
CAL > CALIBRATE > ISOLN (optional)
CAL > CALIBRATE > DONE

Saving Your Calibration

After completing calibration, save it to a slot for later use:

1. Open the save menu

   Go to CAL > SAVE

2. Choose a save slot

   Select slot 0-6 (NanoVNA-H4 has 7 slots, NanoVNA-H has 5 slots)

3. Confirm save

   The calibration is now stored in flash memory and survives power cycles.

Tip

Use different save slots for different frequency ranges or cable setups. Label them mentally: Slot 0 = HF antennas, Slot 1 = VHF, etc.

Verifying Calibration

After calibration, verify it worked correctly:

1. Check the OPEN standard

   Connect OPEN to Port 1. S11 should show 0 dB return loss (all power reflected).

2. Check the SHORT standard

   Connect SHORT to Port 1. S11 should show 0 dB with 180-degree phase shift.

3. Check the LOAD standard

   Connect LOAD to Port 1. S11 should show very low return loss (better than -40 dB typically).

4. Check the THRU

   Connect Port 1 to Port 2. S21 should show 0 dB (no loss). S11 should show good return loss.

Calibration Range Settings

You can calibrate at one frequency range and use it at another:

1. Check current calibration range

   Go to CAL > RANGE

   This shows the frequency range used for the current calibration data.

2. Understanding interpolation

   If your sweep range differs from the calibration range, the NanoVNA interpolates calibration data. This works reasonably well for small differences but reduces accuracy.

Applying and Disabling Calibration

Apply Calibration

To re-enable calibration after disabling:

Go to CAL > APPLY (shows checkbox when active)

The calibration data is applied to all measurements.

Disable Calibration

To see raw uncalibrated data:

Go to CAL > APPLY and toggle off

This shows what the hardware actually measures before error correction. Useful for troubleshooting.

Reset Calibration

To clear calibration and start fresh:

Go to CAL > RESET

All calibration data is cleared. You must recalibrate before accurate measurements.

Troubleshooting

Calibration fails or gives poor results

• Check that standards are clean and making good contact
• Ensure connectors are tightened properly (finger-tight, do not over-tighten)
• Verify cables are not damaged
• Let the NanoVNA warm up before calibrating

S11 of LOAD is worse than expected

• The included 50-ohm load may have limited accuracy
• For precision work, use a calibrated reference load
• Typical cal kit loads are specified to 1% or better

S21 shows loss even with THRU calibrated

• Check cable quality
• The NanoVNA’s dynamic range is limited; very low loss is hard to measure
• Try reducing the frequency span

Calibration drifts over time

• Temperature changes affect calibration
• Recalibrate if environment temperature changes significantly
• The NanoVNA’s oscillator stability affects high-frequency measurements

Advanced: SOLT Error Terms

The calibration calculates these error terms:

Term	Description
Ed	Directivity error
Es	Source match error
Er	Reflection tracking error
Et	Transmission tracking error
Ex	Crosstalk (isolation) error

You can view calibration status via the serial console with the cal command.

Next Steps

• Saving Calibration - Store calibration to SD card
• Enhanced Response Calibration - Quick single-port calibration
• Your First S11 Measurement - Use your calibration