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LRO-H3 1420MHz tuned aerial (Alex Pettit Plate Yagi) not showing difference between sky and ground. Why might this be? Handmade tuned 1420MHz with 13 elements and RTL-SDR Blog V3 software defined radio and Nooelec SAWBird H1 low noise amplifier and filter.

LRO-H3 1420MHz tuned aerial (Alex Pettit Plate Yagi) not showing difference between sky and ground. Why might this be? Handmade tuned 1420MHz with 13 elements and RTL-SDR Blog V3 software defined radio and Nooelec SAWBird H1 low noise amplifier and filter.

If 1420 MHz antenna setup is not showing a difference between sky and ground, it suggests that either the system is not functioning as expected or the signals are too weak to detect. Here are several potential issues and solutions:


1. Signal Sensitivity Issues

The 1420 MHz frequency corresponds to the hydrogen line, which is a very weak natural signal. Small errors in equipment or setup can prevent you from detecting the difference between sky and ground.

Check:

  • LNA Gain: Ensure the Nooelec SAWBird H1 is powered and providing adequate gain. Verify the power supply to the LNA is sufficient (e.g., 5V bias-tee from the RTL-SDR or external power supply).
  • RTL-SDR Gain Settings: Adjust the SDR gain settings in the software. Too low or too high gain can obscure weak signals.
  • RF Noise: Minimize interference from nearby electronics or strong RF sources.

2. Antenna Issues

Handmade 13-element Yagi antenna may not be performing as expected at 1420 MHz.

Check:

  • Tuning Accuracy: Verify that the antenna is precisely tuned to 1420 MHz. A small deviation can result in poor sensitivity.
  • Impedance Matching: Ensure proper matching between the antenna, coaxial cable, and receiver to minimize losses.
  • Beam Direction: Confirm the antenna is pointed correctly at the region of the sky you’re trying to observe.
  • Build Quality: Inspect for construction errors like incorrect element lengths, misalignment, or poor solder joints.

3. Calibration and Setup

Improper calibration of the entire system can result in no noticeable difference between sky and ground.

Check:

  • Signal Detection Test: Use a known signal source (e.g., a signal generator) near 1420 MHz to verify that the system can detect signals.
  • Baseline Measurement: Point the antenna at the ground and observe the noise level, then point it at the sky and compare.
  • Software Configuration: Verify the SDR software (e.g., SDR# or GNU Radio) is set up correctly to detect the narrowband hydrogen line signal.

4. Environmental Factors

External conditions may also affect your ability to detect differences between sky and ground.

Check:

  • Location Noise: Urban environments with high RF noise can drown out weak hydrogen line signals. Try observing in a rural or quiet RF location.
  • Atmospheric Conditions: Poor atmospheric conditions can attenuate the hydrogen line signal.
  • Interference: Ensure there are no strong nearby transmissions near 1420 MHz (e.g., Wi-Fi, microwave ovens, or cell towers).

5. Low Integration Time

The hydrogen line is a very weak signal, and detecting it typically requires a high integration time.

Solution:

  • Integration Software: Use software designed for hydrogen line observations that can integrate signals over minutes or hours.
  • Data Averaging: Averaging multiple readings can help differentiate the sky and ground signals.

Summary of Steps:

  1. Check and tune the antenna for performance at 1420 MHz.
  2. Ensure the LNA and SDR are powered and configured correctly.
  3. Calibrate the system with a known test signal.
  4. Move to a low-noise environment for observation.
  5. Increase integration time and use appropriate software.

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