Using digital TV signals for radio meteor scatter

This is very relevant for modern meteor detection, since many traditional continuous-wave (CW) beacons have gone silent while digital TV (DTV) and FM broadcast transmitters now fill the VHF/UHF spectrum.

Here’s a full technical answer:

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⚙️ Overview

Meteor scatter relies on short-lived ionized trails (50–120 km altitude) that can reflect VHF signals for about 0.1 s–2 s.
You can detect these reflections if a transmitter’s signal reaches your receiver only via the meteor trail — i.e., the transmitter is normally over the horizon.

Modern digital TV signals (DVB-T in Europe) are broad, complex, and not CW, but certain parts of their waveform can still be used effectively for meteor scatter analysis.

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📡 Useful Components of a DVB-T Signal

A DVB-T signal is an OFDM (Orthogonal Frequency Division Multiplexing) signal, composed of thousands of narrow carriers (e.g. 1705 in 2K mode, 6817 in 8K mode).

For meteor work, the following components are most useful:

DVB-T Element	Frequency Behaviour	Meteor Scatter Use
Pilot carriers	Fixed-frequency subcarriers that are always present and have known amplitude/pattern.	Excellent for detecting reflections — appear as narrowband spikes you can integrate or cross-correlate.
Transmission header / symbol sync (TPS)	Repeated patterns in the OFDM frame structure.	Can be used for time-domain correlation or for Doppler tracking.
Unmodulated guard interval	Short zero-energy periods (to avoid ISI).	Occasionally useful for timing but not reflection detection.
Overall envelope (broadband noise-like power)	Appears like wideband noise, ~7–8 MHz bandwidth.	Can be monitored by a power detector or FFT as a transient broadband rise when a meteor reflection occurs.

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🔍 Practical Meteor Scatter Techniques Using DTV Signals

1. Passive Forward Scatter Setup:
   • You point your antenna away from the transmitter (so direct path is blocked).
   • The meteor trail acts as a temporary mirror.
   • You detect brief bursts of the DTV carrier energy.
   • Useful for countries where the DTV transmitter is 500–1500 km away.
2. Narrowband Power Detection:
   • Tune an SDR to a known DTV multiplex frequency (e.g. 498 MHz).
   • Use FFT or total power integration to detect sudden signal spikes — these correspond to meteor echoes.
3. Pilot Carrier Locking:
   • Some researchers (e.g., RMOB observers) lock onto a single DVB-T pilot subcarrier (~312 kHz offset in the channel) and detect Doppler shifts using high-resolution FFTs.
   • This allows measurement of meteor velocity and ionospheric drift.
4. Software Correlation / Decoding:
   • Advanced setups use cross-correlation between received DTV signals and a reference signal recorded from the same transmitter (e.g. using a remote SDR or TLE-based modeling).
   • This reveals fine structure in the reflection and enables range estimation.

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🇪🇺 Common DTV Sources for Meteor Scatter in Europe

Country	Typical DTV Band	Example Frequencies	Notes
France	470–698 MHz	e.g. 506, 578 MHz	Strong DVB-T multiplexes useful for scatter (used by FRIPON & amateur observers).
Germany	482–698 MHz	e.g. 522, 650 MHz	Good transmitters for passive meteor scatter.
UK	470–698 MHz	e.g. 490, 530 MHz	Some observers use transmitters at Crystal Palace or Mendip.
Czech Republic / Slovakia	49.739 MHz (analogue legacy) + DTV in 474–858 MHz	The old GRAVES radar (143.050 MHz) is more commonly used, but DTV is viable too.

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📈 Signal Processing Tips

• Use narrow IF bandwidths (~100 kHz) if monitoring pilot carriers.
• Sample at least 100 kS/s, or more for wideband envelope detection.
• Apply short-term FFT (0.1 s windows) to capture transient echoes.
• A log-detector or SDR FFT waterfall easily reveals bursts visually.
• Doppler shifts of several hundred Hz are common during head echoes.

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🧠 Summary

Technique	Signal Part Used	Complexity	Output
Power detection	Whole DTV band	Low	Counts meteors
Pilot tracking	Pilot carriers	Medium	Doppler, direction
Cross-correlation	Known DTV waveform	High	Range, velocity, meteor trail parameters

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