How to calibrate NooElec Nano 2 SDRs from 978MHz to 868MHz?

This tutorial is for European Stratux users who want to recalibrate their NooElec Nano 2 Software Defined Radio (SDR) receivers from 978MHz (US UAT frequency) to 868MHz (European OGN/FLARM frequency).

Background

In the United States, Stratux uses:

• 1090MHz for ADS-B
• 978MHz for UAT (Universal Access Transceiver)

In Europe, we use:

• 1090MHz for ADS-B
• 868MHz for OGN (Open Glider Network) and FLARM

If you purchased a Stratux kit designed for the US market, your second SDR may be calibrated for 978MHz. This guide shows you how to recalibrate it for 868MHz reception.

What You Need

• NooElec Nano 2 SDR (or similar RTL-SDR)
• Linux computer (or Raspberry Pi)
• kalibrate-rtl software
• Antenna suitable for 868MHz

Installing kalibrate-rtl

On your Linux system or Raspberry Pi:

sudo apt-get update
sudo apt-get install kalibrate-rtl

Or build from source:

git clone https://github.com/steve-m/kalibrate-rtl.git
cd kalibrate-rtl
./bootstrap && CXXFLAGS='-W -Wall -O3'
./configure
make
sudo make install

Calibration Process

Step 1: Find GSM Base Stations

First, scan for nearby GSM base stations to use as a frequency reference:

kal -s GSM900

This will list available channels with their frequency offsets.

Step 2: Calculate PPM Offset

Choose a strong channel from the scan results and measure the PPM (parts per million) offset:

kal -c [channel_number]

Note the average PPM value shown.

Step 3: Apply the Calibration

The PPM value you obtained is your SDR's frequency correction factor. You can apply this in Stratux:

1. Connect to Stratux web interface

2. Go to Settings

3. Enter the PPM value in the appropriate field for your 868MHz SDR

Verifying the Calibration

After calibration:

1. Enable the 868MHz OGN option in Stratux settings

2. Go to an area with OGN/FLARM traffic

3. Check if you're receiving traffic on the Traffic page

4. Verify the signal strength is reasonable

Tips for Better Reception

• Use a properly tuned 868MHz antenna
• Position the antenna with clear sky view
• Keep the SDR away from heat sources (they drift with temperature)
• Consider adding a 868MHz bandpass filter for cleaner reception

Troubleshooting

No traffic received:

• Verify the PPM value is correct
• Check antenna connections
• Ensure 868MHz option is enabled in Stratux

Weak signals:

• Try a better antenna
• Add an LNA (Low Noise Amplifier)
• Check for local interference sources

Conclusion

Calibrating your SDR for 868MHz reception opens up OGN and FLARM traffic awareness for European flying. The process is straightforward with kalibrate-rtl, and the improved traffic awareness significantly enhances flight safety.