Reducing noise in radio telescope systems

Reducing noise in a 1420 MHz radio telescope setup (i.e., for detecting the hydrogen line) involves addressing both internal and external sources of interference. Here are the most effective steps you can take:

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📡 Antenna System Optimization

1. Use a High-Gain, Directional Antenna
   • A Yagi-Uda or a large horn antenna will reduce off-axis noise pickup.
   • Ensure correct polarization (usually linear for hydrogen line work).
2. Antenna Location
   • Mount the antenna far from buildings, power lines, Wi-Fi routers, and computers.
   • Use ferrite chokes on coaxial cables where they enter buildings to reduce common-mode noise pickup.

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🧊 Low-Noise Front-End Electronics

3. Install a Low-Noise Amplifier (LNA)
   • Place the LNA as close to the antenna feed point as possible.
   • Look for noise figures under 1 dB if possible.
   • Power the LNA using bias-T to avoid long DC lines.
4. Use Quality Coaxial Cable (Low Loss)
   • LMR-400, RG-223, or similar; avoid RG-58 at these frequencies.
   • Keep cable runs as short as possible.

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🛠️ Receiver and Filtering

5. Use a Narrowband Filter
   • Bandpass filter centered on 1420 MHz (±10–20 MHz) before the receiver to reject out-of-band RFI (e.g., from cell towers or Wi-Fi).
   • High-Q cavity or SAW filters are excellent for this.
6. Shielding
   • Shield the receiver (and computer if nearby) in a grounded metal box.
   • Use shielded cables for all digital connections.

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⚡ Eliminate Local Interference

7. Check for Internal RFI Sources
   • Switch off power supplies, monitors, or network devices near the antenna.
   • Use battery power or linear PSUs if possible for critical electronics.
8. Use a Faraday Cage (Optional but Powerful)
   • Shield your computer and SDR receiver in a fine-mesh grounded enclosure to trap radiated digital noise.

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📊 Data Acquisition Techniques

9. Averaging and Integration
   • Stack multiple scans to increase signal-to-noise ratio (SNR).
   • Use software averaging over time and frequency bins.
10. Use a Clean Power Supply

• Ensure your LNA and receiver get clean, regulated power. Switching noise from cheap PSUs can dominate your baseline.

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🌐 Environmental and Spectral Checks

11. Check Local RFI Spectrum

• Use an SDR to scan from 1–2 GHz and identify any strong RFI sources near 1420 MHz.
• Look for periodic signals (from switching supplies or clocked electronics).

12. Observe at Quiet Times

• Nighttime and early morning often have lower RFI.
• Avoid times when nearby devices like routers or street lights are active.

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