Kalibrate-HydraSDR for HydraSDR RFOne

A specialized and optimized port of kalibrate, designed specifically for the HydraSDR RFOne high-performance Software Defined Radio. It scans GSM base stations and uses their broadcast carrier as a highly stable frequency reference. This allows precise measurement and permanent correction of the HydraSDR’s internal TCXO offset (PPM/PPB).

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New HydraSDR Features

1. Hardware-Specific DSP

• Implements a Polyphase Rational Resampler to convert the HydraSDR native sampling rate (2.5 MSPS) to the GSM symbol rate (270.833 kSPS).
• Provides >60 dB aliasing rejection for clean decimation.
• Ensures high-precision timing required for GSM frequency analysis.

2. Direct Flash Calibration

• Can read and write frequency correction values directly from/to the HydraSDR's SPI Flash.
• Automatically resets the device after writing calibration to apply changes immediately.

3. Visualization & Diagnostics

• ASCII Art FFT (-A): Real-time spectrum visualization directly in the console.
• DSP Benchmark (-B): Measures DSP processing throughput on the host CPU.

4. Optimized Scanning

• Adds a fast Power Scan (coarse scan) before fine-frequency detection.
• Improves band scanning performance by approximately 10× compared to earlier versions.

5. Multi-Platform

• Cross-platform build system powered by CMake with support for Windows, Linux, and macOS.

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Calibration Procedure (Step-by-Step)

Follow these steps to permanently calibrate your HydraSDR RFOne TCXO.

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Step 1: Clear Existing Calibration

Reset the calibration value to zero before measuring. This also validates device communication.

kal.exe -W 0

(The device will reset. Wait a few seconds for it to re-enumerate.)

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Step 2: Scan for GSM Base Stations

Scan to find a strong and stable reference signal.

Recommended bands:

• EGSM (900 MHz)
• GSM850
• DCS (1800 MHz) — supported but near hardware limit
• PCS (1900 MHz) — disabled

kal.exe -s EGSM -g 16

Example Output:

kal: Scanning for E-GSM-900 base stations.
E-GSM-900:
 chan:    2 (935.4MHz -36Hz) power:  -33.4 dBFS
 chan:    4 (935.8MHz -134Hz) power:  -52.1 dBFS
 chan:   83 (951.6MHz -147Hz) power:  -49.5 dBFS
 chan:   84 (951.8MHz -315Hz) power:  -50.6 dBFS
 chan:   85 (952.0MHz -180Hz) power:  -57.5 dBFS
 chan:   87 (952.4MHz  29Hz) power:  -50.9 dBFS
 chan:  113 (957.6MHz -16Hz) power:  -33.5 dBFS
 chan:  114 (957.8MHz -140Hz) power:  -42.9 dBFS
 chan:  115 (958.0MHz  117Hz) power:  -54.3 dBFS
 chan:  116 (958.2MHz -83Hz) power:  -54.9 dBFS
 chan:  118 (958.6MHz -54Hz) power:  -24.1 dBFS
...

Select the channel with the highest POWER (for example, 118).

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Step 3: Measure Frequency Error

Tune to the selected channel and measure the frequency offset.

kal.exe -c 118 -g 16

Example Output:

kal: Calculating clock frequency offset.
Using GSM-900 channel 118 (958.6MHz)
Scanning for FCCH bursts ('.' = searching, '+' = found)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

--------------------------------------------------
Results (100 valid bursts out of 100 attempts)
--------------------------------------------------
average         [min, max]      (range, stddev)
-70Hz           [-77, -67]      (10, 2.267751)
overruns: 0
not found: 0

Average Error: -0.073 ppm (-73.379 ppb)

Record the PPB value (in this example: -73).

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Step 4: Write Calibration to Flash

Store the PPB correction value permanently in the device.

kal.exe -W -73

Output:

[-] Erasing flash sector 2 (Calibration area)...
[-] Writing Calibration: -73 ppb (Timestamp: XXXXXXX)...
[+] Calibration written successfully.
[!] Resetting HydraSDR to apply changes...
[+] Device reset command sent.

The device will reboot after writing.

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Step 5: Verify Calibration

Re-measure to confirm the correction is applied.

kal.exe -c 118 -g 16

Expected Result:

• Remaining offset should be within ±0.5 ppm
• Typically around ±250 ppb with a strong signal

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Command Usage

Scan GSM Base Stations

kal.exe -s <band> [options]

Compute Frequency Offset

kal.exe -f <freq> | -c <chan> [options]

Device Maintenance

kal.exe -R               # Read calibration from flash
kal.exe -W <ppb_value>   # Write calibration and reset device

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Command-Line Options

Option	Description
-s	Scan a band (EGSM, GSM900, DCS, GSM850, GSM-R). PCS is disabled.
-f	Absolute frequency of a GSM carrier.
-c	Channel number (ARFCN).
-b	Band indicator (required when using -c).
-g	Gain (0–21 for HydraSDR Linearity Gain).
-R	Read calibration from flash.
-W	Write calibration value (PPB) and reset the device.
-A	Display ASCII FFT spectrum.
-B	Run DSP benchmark and exit.
-v	Verbose output.
-D	Debug messages.
-h	Help text.

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Build & Runtime Notes

1. Runtime Libraries

Ensure the following runtime libraries are present in the same directory as kal.exe under Windows:

• libhydrasdr.dll or hydrasdr.dll
• libusb-1.0.dll
• libwinpthread-1.dll (unless statically linked)
• libfftw3-3.dll (optional if statically linked)

2. Frequency Limitations

• Supported: GSM850, GSM900 / EGSM, GSM-R
• Warning: DCS (1800 MHz) is near the device's hardware limit
• Disabled: PCS (1900 MHz)

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License

This project is licensed under the BSD 2-Clause License.

Based on and heavily refactored from work by:

• Joshua Lackey (2010)
• Steve Markgraf (2012)
• Stan Pitucha

Additional modifications © 2025 Benjamin Vernoux <bvernoux@hydrasdr.com>