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mcnanovna

VNA Calibration

Calibration removes systematic errors from VNA measurements. Without calibration, your readings will include errors from cables, adapters, and the VNA itself.

When to Calibrate

  • First use on a new frequency range
  • After changing cables or adapters
  • After significant temperature changes
  • If measurements look wrong or inconsistent

What You Need

Calibration Standards

StandardPurpose
50Ω LoadReference impedance
OpenOpen circuit (can use bare SMA)
ShortShort circuit
ThroughConnects Port 1 to Port 2

Calibration Procedure

  1. Set the sweep range

    Ask Claude: “Set sweep from 144 to 148 MHz with 101 points”

    Calibration is frequency-specific. Always calibrate at the frequencies you’ll measure.

  2. Connect the LOAD

    Connect the 50Ω load termination to Port 1.

    Ask Claude: “Run cal load”

  3. Connect the OPEN

    Remove the load, leave Port 1 open (or use an open standard).

    Ask Claude: “Run cal open”

  4. Connect the SHORT

    Connect the short standard to Port 1.

    Ask Claude: “Run cal short”

  5. Connect the THROUGH

    Connect Port 1 to Port 2 with a short cable or barrel adapter.

    Ask Claude: “Run cal thru”

  6. Optional: Isolation

    Connect 50Ω loads to both ports.

    Ask Claude: “Run cal isoln”

    This corrects for crosstalk between ports.

  7. Apply calibration

    Ask Claude: “Run cal done”

    This computes and applies the error correction coefficients.

  8. Save calibration

    Ask Claude: “Save calibration to slot 0”

    Saves to NanoVNA flash for later recall.

Verification

After calibration, verify it worked:

  1. Load test: Connect 50Ω load. S11 should be < -40 dB.
  2. Open test: Leave port open. S11 should be ~0 dB.
  3. Through test: Connect through. S21 should be ~0 dB, S11 < -40 dB.

Calibration Slots

The NanoVNA stores calibrations in flash memory:

ModelSlots
NanoVNA-H0-4
NanoVNA-H40-6

Each slot holds one calibration. Common approach:

  • Slot 0: Full range (50 kHz - 900 MHz)
  • Slot 1: HF (1.8 - 30 MHz)
  • Slot 2: VHF (50 - 300 MHz)
  • Slot 3: 2m band (144 - 148 MHz)
  • Slot 4: 70cm band (420 - 450 MHz)

Recalling Calibration

Ask Claude: “Recall calibration from slot 0”

The NanoVNA will use the stored calibration. Note that calibration must match the current sweep settings.

Troubleshooting

High return loss with load

  • Clean connectors with isopropyl alcohol
  • Check for damaged center pin
  • Try a different load

S21 shows high loss through

  • Cable may be damaged
  • Adapters may be loose
  • Recalibrate with the exact cables you’ll use

Calibration doesn’t apply

  • Frequency range must match
  • Try recalibrating
  • Check firmware version