Mobile/portable lightning receiver for research-grade event capture. Records a full 10 MHz RF segment around ~400 MHz from an antenna array, time‑stamped and triggered by a VLF front‑end. A closely related VLF station RSMS02 shares most subsystems.
RSMS01 is a mobile UHF lightning observation station designed for ground deployments (rooftop platforms on vehicles, or fixed). It complements a VLF receiver (RSMS02) used for robust triggering and coarse detection. Together, both instruments capture long, contiguous, time‑synchronized RF segments of lightning activity for detailed post‑processing (TDoA, interferometry/DOA, correlation to optical/EFM/radiation sensors).
Why UHF + VLF:
- VLF ( 20 kHz to 500 kHz): strong from the main/lightning channel; excellent for reliable triggering and long‑range detection.
- UHF (~370–406 MHz): rich in initial breakdown/leader structure; less contaminated by distant channel energy; ideal for fine‑scale timing/structure.
- 10 MHz contiguous RF capture around ~400 MHz (tunable within local RFI constraints).
- Antenna array (4× QFH elements) enabling future DOA/interferometric processing; current release stores synchronous per‑element I/Q streams.
- Event‑based recording: up to ~1.45 s per trigger with configurable pre/post buffers from a continuous ring‑buffer.
- GNSS‑disciplined timing: PPS‑derived time marks + sample indexes embedded per event for millisecond‑class absolute timing after reconstruction.
- VLF‑driven triggering with adjustable Time‑over‑Threshold (pulse width + level) parameters for noisy environments.
- Stationary or mobile operation: roof‑rack plywood deck or fixed mast mount; active front‑ends in sealed housings.
- Live spectrum/waterfall via fosphor.
Block diagram of the UHF radio receiver used in the experiment. The internals of the active antenna mounted on the car roof are depicted in the blue bubbles on the left part of the schematics.
The station is interconnected with RSMS02 to get a trigger from stronger VLF signals. Therefore, the high-level system schematic looks like the following (the repeated signal strings are omitted).
flowchart LR
subgraph UHF_Antenna_Array [UHF Antenna Array]
Q1[QFH #1]
Q2[QFH #2]
Q3[QFH #3]
Q4[QFH #4]
end
subgraph RF_FrontEnds [Active RF front-ends]
direction LR
BPF1[BPF] --> LNA1[LNA] --> BPF2[BPF] --> LNA2[LNA] --> MIX[Mixer LO] --> LPF[LPF Line-Driver]
end
Q1 & Q2 & Q3 & Q4 --> RF_FrontEnds
RF_FrontEnds -- "I/Q differential over CAT6" --> ADCs[12‑bit ADCs @ 10 MS/s per I/Q]
ADCs --> RBUF[Ring buffer & trigger logic]
RBUF --> STORE[Storage of ~1.45 s per event]
PPS[GNSS PPS time‑mark capture] --> RBUF
subgraph RSMS02 [VLF station RSMS02]
VLFANT[STP loop antenna array] --> VLFADC[ADC] --> VLFTRIG[FPGA trigger threshold + min-width]
end
VLFTRIG -- "Trigger out" --> RBUF
- Filters & gain chain: BPF → LNA (low NF/high OIP3) → BPF → LNA (gain/dynamic range).
- Down‑conversion: high‑linearity UHF mixer with low‑jitter LO distribution.
- Baseband transport: anti‑alias LPF (~5 MHz) and differential line driver; 100 Ω differential over CAT6 to the base unit.
- Shielding/EMI: aluminum housings, differential LVPECL LO distribution, short RF paths.
- QFH (Quadrifilar Helix) elements with inherent quadrature ports → natural I/Q pairing and near‑omnidirectional, circularly‑polarized response across the band. Four elements are arranged in a compact square roof deck.
- Adjustable level and minimum pulse width (typ. starting points: level 10–30 mV, width 5–20 µs) for Time‑over‑Threshold detection.
- Robust to impulsive RFI compared to pure thresholding; suitable for mobile, semi‑urban sites.
- External trigger from VLF arm latches the ring buffer; you get configurable pre‑trigger and post‑trigger blocks.
- Absolute timing: Each event stores sample counters + several last PPS time‑marks → reconstruct UTC for every sample during post‑processing.
- Nominal UHF band: ~370–406 MHz (select center to avoid strong local services; keep 10 MHz window clean). 10 MHz comfortably spans dominant lightning UHF content while keeping data rates manageable and front‑ends practical.
- VLF sensors: shielded STP‑loop antennas; mount orthogonally; keep inverter/SMPS noise away from cabling where possible.
Linux host with recent CUDA/OpenCL drivers recommended for fosphor. Example packages (Debian/Ubuntu). The device uses fosphor for real-time spectral visualization.
sudo apt-get install nvidia-opencl-dev opencl-headers
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Assemble hardware
- Mount 4× QFH elements on a rigid non‑conductive deck (vehicle roof or mast).
- Install active RF front‑ends at the antenna bases; route CAT6 to base unit.
- Mount VLF STP‑loop frame (orthogonal axes), route to RSMS02
- Connect GNSS antenna for PPS to the base unit.
-
Connect & power
- Prefer battery/linear supplies; if an inverter is unavoidable, isolate and test for conducted/ radiated noise before storm operations.
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Run
- Start the VLF UI, set initial level/width; verify trigger with observed lightning.
- Start UHF recorder; confirm ring‑buffer, PPS lock, and per‑element I/Q streams.
- Launch visualization for situational awareness; keep gain conservative to avoid ADC clipping.
Each event contains:
- Per‑element I/Q streams (12‑bit, 10 MS/s, 10 MHz complex BW) for the full capture window (~1.45 s typical).
- Timing metadata: sample indices and recent PPS time‑marks → reconstruct absolute UTC.
- Trigger metadata: VLF detector parameters at trigger time.