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Calibration Menu

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nicsure edited this page Mar 9, 2026 · 21 revisions

Calibration Menu Overview

The Calibration Menu provides tools for calibrating battery measurements and correcting oscillator frequency error.

While this menu is open, the Extra Info field displays live diagnostic values to assist with calibration.

Calibration values can be set via the RMS. See RMS → Calibration

Batt V Cal

Calibrates the displayed battery voltage.

To set this value correctly:

  1. Fully charge the battery
  2. Adjust this value until the battery voltage shown in the Extra Info field reads 8.4 V

This value is typically around 970, but may vary slightly between radios.

Batt Full

Defines the ADC value corresponding to a fully charged battery.

To calibrate:

  1. Fully charge the battery
  2. Note the ADC value shown in the Extra Info field
  3. Set Batt Full to match that ADC value

This value is typically around 1400, but may vary slightly between radios.

Batt Flat

Defines the ADC value at which the battery is considered discharged.

This is typically the point where:

  • The radio still powers on
  • Transmission is no longer possible due to insufficient battery voltage

To calibrate:

  1. Allow the battery to discharge to this flat state
  2. Note the ADC value shown in the Extra Info field
  3. Set Batt Flat to match that ADC value

This value is typically around 1000, but may vary significantly between radios.

Batt Low

Defines the ADC threshold at which the battery is considered low.

This level typically corresponds to the point where:

  • The radio can still transmit
  • However, available battery capacity is nearly exhausted

To calibrate:

  1. Allow the battery to discharge until it reaches the desired low state.
  2. Note the ADC value shown in the Extra Info field.
  3. Set Batt Low to match that ADC value.

This value is typically around 1050, but may vary significantly between radios.

Low Alarm

When enabled, an audible alert will sound every 60 seconds if the battery level is below the threshold defined by Batt Low. If the battery level falls below Batt Flat, the audible alert will sound for twice the normal duration, providing a more urgent warning that the battery is critically low.

  • This alarm also sounds if PTT is pressed while the battery is in a low state, however the PTT alarm sounds regardless of if this setting is enabled or not.

XTAL 671

Compensates for manufacturing tolerances in the radio’s base crystal oscillator.

The reference oscillator should ideally produce 26.000000 MHz, but in practice it will always be slightly high or low. This error is multiplied as operating frequency increases.

Why this matters

Frequency error scales with frequency multiplication. For example:

  • Target frequency: 442 MHz
  • Oscillator frequency: 25.99970 MHz
  • Multiplier: 17
  • Actual tuned frequency: 441.99490 MHz

This results in a 5.1 kHz error.

This is by far the most common cause of “non-bug” reports where:

  • RX CTCSS fails to open squelch
  • RX DCS fails entirely

CTCSS generally requires accuracy within ~1 kHz, and DCS within ~500 Hz, making proper calibration essential.

XTAL 671 Quick Calibration Procedure

Requirements

  • A trusted reference signal:
    • Another radio known to be accurately on frequency, or
    • An external signal generator
    • A known accurate signal, such as from a repeater.
  • The signal must transmit CTCSS or DCS
  • Higher frequencies yield better accuracy

Step-by-Step Calibration

  1. Ensure Main Menu → Advanced → Hunt STones is turned off.

  2. Acquire a trusted signal source, this can be from another radio, a signal generator or a broadcast source such as a repeater. This signal source must be sending a valid CTCSS or DCS.

  3. Configure the VFO:

    • Set RX CTCSS or RX DCS to match the test signal
    • Set Main Menu → VFO → Step to 0.01 kHz
    • Tune to the target frequency
      Example: 450.00000 MHz

  4. Using UP/DOWN, adjust the frequency until squelch opens reliably.

  5. Find the lower limit:

    • Step down until squelch no longer opens
      Example: 450.00020 MHz

  6. Find the upper limit:

    • Step up until squelch no longer opens
      Example: 450.00050 MHz

  7. Calculate the midpoint frequency:

    • (Lower + Upper) / 2
      Example: (450.00020 + 450.00050) / 2 = 450.00035 MHz

  8. Calculate frequency drift:

    • Drift = (Midpoint − Target) × 100,000
      Example: (450.00035 − 450.00000) × 100,000 = 35
      • Note: The resulting value may be negative.

  9. Calculate XTAL 671 value:

    • (Drift × 671) / Target Frequency
      Example: (35 × 671) / 450 = 52.19 → 52

  10. Set XTAL 671 to 52

Notes

  • If the calculated value is negative, enter it as a positive number and press # to flip the sign.

Proper XTAL calibration ensures reliable CTCSS/DCS decoding and accurate frequency display across all bands.

Common Whinges

Q: My radio was on-frequency with the factory firmware, why is it off with nicFW?

A: When these radios are manufactured, each one can be tested on the production line and calibration data written to the radio's stock settings. I cannot do that can I? And I have no idea where this data is stored or what format it is in. So calibration has to be performed by the user, I cannot visit each one of you personally to tune your radios or use a time machine, teleport to China and insert myself into the factory to secretly write my own calibration data to new radios.

Common Questions

Q: Why 671? That seems rather arbitrary.

A: It is anything but arbitrary. The value 671 was chosen for a very specific and practical reason.

To accurately correct oscillator drift, the calibration math requires a reference point. Several factors influenced the choice of this reference:

  • Higher reference frequencies provide better adjustment resolution
  • Values that are easy for processors to work with are preferred, especially powers of two
  • A frequency close to a whole MHz simplifies user-side calculations
  • The value must align cleanly with the radio’s internal frequency representation

Internally, the radio represents frequencies in 10 Hz units.
For example, a frequency of 423.12600 MHz is stored as the integer 42,312,600.

Now consider the frequency 671.08864 MHz.

This value meets all of the design goals:

  • It is reasonably high in frequency
  • It is very close to a round MHz value (671 MHz)
  • Internally it becomes 67,108,864
  • 67,108,864 is a power of two

Perfect.

That is why the calibration constant is 671.

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