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NanoVNA-H NanoVNA-H Documentation

Crystal Analyzer

The crystal analyzer mode (SERIES XTAL) measures quartz crystal motional parameters including series resonance Fs, parallel resonance Fp, motional inductance Lm, motional capacitance Cm, equivalent series resistance Rm, and holder capacitance C0.

Crystal Equivalent Circuit

Section titled “Crystal Equivalent Circuit”

A quartz crystal can be modeled as:

      Cm       Lm       Rm
  o---||---mmmm---/\/\/---o
  |                       |
  +----------||----------+
             C0 (holder)
  • Fs: Series resonant frequency (Cm, Lm, Rm)
  • Fp: Parallel resonant frequency (when C0 resonates with series arm)
  • Lm: Motional inductance
  • Cm: Motional capacitance
  • Rm: Motional resistance (ESR)
  • C0: Holder/shunt capacitance

Test Setup

Section titled “Test Setup”

Series Connection

Section titled “Series Connection”

Connect the crystal between CH0 and CH1:

CH0 ----[XTAL]---- CH1

Use short leads and proper fixtures for best results.

Required Sweep Range

Section titled “Required Sweep Range”

Set the sweep to span the crystal’s expected frequency:

Crystal FrequencySuggested Span
1-5 MHz+/- 50 kHz
5-20 MHz+/- 20 kHz
20-50 MHz+/- 10 kHz
50+ MHz+/- 5 kHz

Enable Crystal Mode

Section titled “Enable Crystal Mode”
  1. Connect crystal in series between ports
  2. Set frequency range around the crystal’s nominal frequency
  3. Go to DISPLAY > MEASURE
  4. Tap SERIES XTAL
  5. Parameters are displayed on screen

Display Readings

Section titled “Display Readings”
XTAL-SERIES
Fs = 10.000000 MHz
Lm = 10.2 mH  Cm = 24.9 fF  Rm = 8.5 ohm
Q = 75000
Fp = 10.002500 MHz  dF = 2500
Cp = 3.2 pF
  • Fs: Series resonant frequency (maximum transmission)
  • Lm: Motional inductance
  • Cm: Motional capacitance
  • Rm: Motional resistance
  • Q: Quality factor (Fs/bandwidth)
  • Fp: Parallel resonant frequency (minimum transmission)
  • dF: Frequency difference Fp - Fs
  • Cp: Calculated parallel capacitance (C0)

Shell Commands

Section titled “Shell Commands”
Terminal window
# Enable crystal analysis mode
measure xtal


# Disable measurement mode
measure none

Measurement Process

Section titled “Measurement Process”

The firmware automatically:

  1. Finds maximum S21 transmission = series resonance (Fs)
  2. Places marker 0 at Fs
  3. Searches for +45 degree phase point (marker 1)
  4. Searches for -45 degree phase point (marker 2)
  5. Calculates bandwidth from markers 1 and 2
  6. Derives Lm, Cm, Rm from bandwidth and frequency
  7. Finds minimum S21 transmission = parallel resonance (Fp)
  8. Places marker 3 at Fp
  9. Calculates C0 from Fs, Fp, and Cm

Interpreting Results

Section titled “Interpreting Results”

Good Measurements

Section titled “Good Measurements”
  • Clear Fs peak with > 20 dB transmission
  • Distinct Fp minimum near Fs
  • Q > 10000 for AT-cut crystals
  • Rm typically 5-50 ohms

Problem Indicators

Section titled “Problem Indicators”
  • No clear Fs peak: Crystal not oscillating, check connections
  • Fp not found: Widen sweep range
  • Low Q: Damaged crystal or poor connection
  • High Rm: Crystal may be defective

Practical Examples

Section titled “Practical Examples”

Matching Crystals

Section titled “Matching Crystals”
  1. Measure first crystal, note Fs and Cm
  2. Measure second crystal
  3. Compare Fs values (should match within 10 ppm for oscillator use)
  4. Compare Cm values (should be similar for filter use)

Characterizing for Filter Design

Section titled “Characterizing for Filter Design”
  1. Measure Fs, Cm, Lm, Rm
  2. Note C0 (holder capacitance)
  3. Use these values in filter design software
  4. Repeat for all crystals in the filter

Checking Crystal Health

Section titled “Checking Crystal Health”
  1. Measure Rm (should be within datasheet spec)
  2. Check Q factor (should match expected value)
  3. Compare Fs to marked frequency

Tips for Accurate Measurements

Section titled “Tips for Accurate Measurements”

Calculating Load Capacitance Effect

Section titled “Calculating Load Capacitance Effect”

The crystal oscillates at a frequency that depends on the load capacitance CL:

F_load = Fs * (1 + Cm / (2 * (C0 + CL)))

This is why crystals are specified with a particular load capacitance (e.g., “12 pF load”).